CRISPR-Cas12-based detection of SARS-CoV-2

A hairpin reporter-driven feedback CRISPR/Cas signal amplification loop for terminal deoxynucleotidyl transferase activity detection

The CRISPR/Cas12a system has become a powerful tool in biosensing because of its specific target recognition ability and highly efficient trans-cleavage activity. However, a problem faced by the CRISPR/Cas12a system when directly used for trace detection is the linear amplification efficiency of single-cycle digestion. Here, we present a novel hairpin reporter-driven CRISPR/Cas12a (HR-CRISPR) amplification system that establishes a positive feedback loop within the CRISPR/Cas12a platform to finish an exponential and sensitive signal amplification in a one-step reaction. As proof of concept, we applied this strategy to the terminal deoxynucleotidyl transferase (TdT) activity assay without pre-amplification procedure. The polyT strand extended by TdT hybridizes with crRNA, activating Cas12a, which then cleaves the FQ-hairpin reporter. The cleavage products are further elongated by reverse transcriptase using crRNA as a template, reactivating Cas12a and producing exponentially amplified fluorescence signals. This assay offers a simple yet highly sensitive approach for quantifying TdT activity, achieving a low detection limit of 4.55 × 10-6 U. Moreover, it is applicable for inhibitor screening and monitoring TdT activity in human serum samples.

Plasma-based ultrasensitive detection of Mycobacterium tuberculosis ESAT6/CFP10 fusion antigen using a CRISPR-driven aptamer fluorescence testing (CRAFT)

Tuberculosis (TB) screening in clinical diagnosis is challenging due to issues such as sputum dependence, time-consuming procedures, and high costs. In this study, we introduce a CRAFT (CRISPR-Driven Aptamer Fluorescence Testing), an aptamer-based CRISPR/Cas12a assay designed for the rapid and sensitive detection of Mycobacterium tuberculosis (Mtb) antigens from peripheral blood. Aptamer 3 (Ap3) and the aptamer-mediated probe (Aptamer-blocker 3-7) were selected through the Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Ap3 demonstrated a dissociation constant (Kd) of 8.3E-7 M with the ESAT6/CFP10 fusion proteins (EC proteins), which are produced during the replicative phase of Mtb. Upon labeling the EC proteins with Aptamer-blocker 3-7 (Ap-blocker 3-7) probe, single-stranded DNA (ssDNA) blocker 3-7 was released, thereby completing the process for RPA-based CRISPR/Cas12a fluorescence detection. After optimizing multiple parameters, CRAFT achieved a detection limit of 0.1 ag/mL EC proteins (equivalent to 3 protein particles per mL) within 120 min from plasma sample to result. The method was validated with 86 clinical plasma samples confirmed the method's high diagnostic accuracy for Mtb infection (sensitivity: 97.1 %, 95 % confidence interval (CI) [0.849-0.998]); specificity: 98.0 %, 95 % CI [0.897-0.999]), supporting its utility in early therapeutic evaluation of tuberculosis management.

A rapid and ultrasensitive RPA-assisted CRISPR-Cas12a/Cas13a nucleic acid diagnostic platform with a smartphone-based portable device

The spread of infectious diseases can be controlled by early identification of the source of infection and timely diagnosis to stop transmission. Real-time fluorescence quantitative polymerase chain reaction (PCR) is the current gold standard for pathogen diagnosis, with high detection sensitivity and accuracy. However, due to the need for specialized equipment, laboratories, and personnel, it is difficult to achieve rapid and immediate diagnosis during large-scale infectious disease outbreaks. Herein, an optimized CRISPR-based nucleic acid detection method was developed that reduces the CRISPR detection time to 15 min while maintaining high sensitivity. By using nucleic acid extraction-free and lyophilization techniques, the 'sample-in-result-out' detection of the two target genes of SARS-CoV-2, the human internal reference gene, and the negative quality control sample can be completed in 20 min, with a sensitivity of 0.5 copies/μL. Additionally, to facilitate the application, a smartphone-based reverse transcription-recombinase polymerase amplification (RT-RPA)-assisted CRISPR-rapid, portable nucleic acid detection device was developed, integrating functions such as heating, centrifugation, mixing, optical detection and result output. Process control, output, and uploading of detection results were conducted through smartphones. The device is not dependent on a power supply and can perform on-site rapid virus detection in resource-limited settings. Real-time uploading of results helps to rapidly implement epidemic prevention and control measures, providing an innovative means of detection, control, and prevention of virus-based infectious diseases. This important work provides a new and effective tool to manage potential future outbreaks of infectious diseases.

SPECIAL: Phosphorothioate dNTP assisted RPA equipped with CRISPR/Cas12a amplifier enables high-specific nucleic acid testing

Recombinase polymerase amplification (RPA) is one of the most widely used isothermal amplification methods and considered to be a promising tool for point-of-care testing (POCT) molecular diagnosis. However, RPA is prone to have nonspecific amplification occur, due to the poor recognition accuracy of polymerase and recombinase, which severely hindered its clinical application. It is important to improve the specificity of RPA further. Herein, we developed a novel nucleic acid testing method termed phosphorothioate dNTP (dNTPαS) assisted RPA (S-RPA) that employs dNTPαS as substrates to suppress nonspecific amplification effectively. We found that dNTPαS could improve the recognition accuracy of Bsu polymerase and recombinase, thereby enhancing their amplification specificity. Our S-RPA provided much higher specificity (approximately 40 % improvement compared to classical RPA), realizing detection target with single nucleotide mutation. Based on its outstanding performance, we further combined the S-RPA with CRISPR/Cas12a to achieve highly specific and sensitive fluorescence detection, namely S-RPA equipped with CRISPR/Cas12a amplifier (SPECIAL). Our SPECIAL was more sensitive (10-fold higher) than the classical RPA-CRISPR/Cas12a assay, offering 100 % agreement with the qPCR during clinical validation. In summary, a strategy based on dNTPαS was established to enhance the specificity of RPA, thereby improving its practicability and providing a potential POCT tool for molecular diagnosis.

An accurate amplification-free CRISPR/Cas12a-based assay for GES β-lactamase detection

OBJECTIVE

Guiana-Extended-Spectrum (GES) β-lactamases belong to the minor class A β-lactamases and are probably underdiagnosed due to a lack of specific diagnostic tests. There is therefore an urgent need to develop new molecular diagnostic tools that will be able to fill the gap in the detection of rare β-lactamases. Here, we propose an optimized, amplification-free CRISPR/Cas12a-based assay for the accurate detection of GES β-lactamases and we validate its application with clinical isolates (Graphic abstract). Based on the results of examination of 79 standard collection, the proposed assay exhibited 100% sensitivity and specificity, as well as 100% positive and negative predictive values in less than 1.5 hours.

METHODS

We optimized the CRISPR/Cas12a method by harnessing a multiplex crRNA strategy, a highly efficient DNA reporter (TTATT-5C) and the Murine RNase Inhibitor to prevent crRNA degradation.

RESULTS

Our yielded limits of detection of 1 ng/µL and 3 ng/µL in Enterobacterales and Pseudomonas aeruginosa, respectively. The observed difference is due to the location of the blaGES gene. The gene occurs in a chromosomal integron present only in one to three copies in P. aeruginosa, whereas it occurs in plasmids present in multiple copies in Enterobacterales.

CONCLUSIONS

The proposed method could be established as a routine diagnostic tool in clinical microbiology laboratories to fill the gap in availability of commercial diagnostic tests for GES β-lactamases.

ID-CRISPR: A CRISPR/Cas12a platform for label-free and sensitive detection of rare mutant alleles using self-interference DNA hydrogel reporter

Accurate and sensitive detection of single nucleotide variants (SNVs) is paramount for cancer diagnosis and treatment. The CRISPR/Cas12a system shows promise for SNV detection due to its high sensitivity and single-base specificity. However, most CRISPR/Cas12a-based methods rely on F/Q-labeled single-stranded DNA (ssDNA) reporters, which are susceptible to fluorescence fluctuations, thereby reducing accuracy. To address these limitations, researchers have proposed using DNA hydrogels as signal transducers in CRISPR/Cas12a systems. Yet, the encapsulation of indicators into DNA hydrogels introduces additional instability, which could compromise both detection sensitivity and linearity. In this study, we integrated hyperspectral interferometry into a DNA hydrogel-based CRISPR/Cas12a detection platform (ID-CRISPR) to achieve sensitive label-free SNV detection. Using EGFR L858R SNV as a model target, we demonstrated that ID-CRISPR can detect mutant allele frequencies (MAFs) as low as 0.1% with a limit of detection (LOD) of 5 aM, while also showing its potential for quantifying SNV abundance. Its clinical utility was confirmed through analysis of lung tumor samples, with results consistent with sequencing data. Therefore, ID-CRISPR provides a sensitive, label-free, and user-friendly platform for SNV detection, offering new insights into combining optical sensing with DNA hydrogel technology in CRISPR/Cas assays.

Multiplex detection of respiratory RNA viruses without amplification based on CRISPR-Cas13a immunochromatographic test strips

Acute respiratory infections, caused by RNA viruses like respiratory syncytial virus, influenza, rhinovirus, and coronavirus, are major global health threats. Real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) is the gold standard for detecting these viruses but is time-consuming, complex, and requires specialized equipment. There is a need for rapid, convenient, and multi-target detection methods to improve disease prevention and control. This study developed a multi-target immunochromatographic detection method using LbuCas13a protein and "band elimination" test strips for detecting SARS-CoV-2 and influenza virus. The method's performance was evaluated by testing known 5 positive and 4 negative samples for SARS-CoV-2 and comparing results with fluorescent PCR and colloidal gold methods. Detection sensitivity was quantified using digital PCR and qPCR. The immunochromatographic test strips showed 100% concordance with fluorescent PCR and colloidal gold methods in initial clinical SARS-CoV-2 detection. Subsequently, we used dual-target immunochromatographic test strips to detect 9 SARS-CoV-2 positive samples and 9 H3N2 positive samples. However, false negatives were observed in dual-target detection of SARS-CoV-2 and H3N2 samples, likely due to low sample concentration or sample degradation. The method had a minimum detection limit of 381.75 copies/µL, as determined by digital PCR and qPCR. The developed multi-target immunochromatographic detection method offers a rapid, low-cost, and simple approach for detecting both SARS-CoV-2 and influenza viruses. With high sensitivity, specificity, and reliability, this method holds promise as a practical tool for RNA virus diagnosis and improving public health response to respiratory infections.

Unraveling the Amplification-Free Quantitative Detection of Viral RNA in Nasopharyngeal Swab Samples Using a Compact Electrochemical Rapid Test Device

Providing viral load numbers of infection events aids in the identification of disease severity and in the effective overall patient management. Gold-standard polymerase chain reaction (PCR) techniques make this possible but cannot be applied at the point of need and in low-resource settings. Here, we report on the development of a compact analytical platform that can detect a conserved sequence of the RNA of severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) in 40 min in nasopharyngeal swab samples without the need for any previous purification or gene amplification steps. It combines electrochemical and paper fluidic approaches together with a sandwich hybridization assay performed on magnetic nanoparticles (MNPs) modified with a tailor-designed capture DNA hairpin. The device proves to quantitatively detect viral RNA in a retrospective study carried out with nasopharyngeal swab samples. A sensitivity of 100% and a specificity of 93% were estimated by the receiver operating characteristic (ROC) analysis. However, although molar concentration values of the target RNA sequence are provided, these estimates do not fully correlate with the viral load numbers estimated by RT-qPCR over the whole Ct sample range. Empirical studies have been carried out that have provided clear insights into this hurdle and simple solutions to overcome it, without depriving the device of the features required for potential use in a point-of-care (PoC) environment.

Kinetic analysis and engineering of thermostable Cas12a for nucleic acid detection

Cas12a trans nuclease activity has been leveraged for nucleic acid detection, often coupled with isothermal amplification to increase sensitivity. However, due to the lack of highly efficient thermostable Cas12a orthologs, use of Cas12a in one-pot combination with high temperature (55-65°C) amplification, such as loop-mediated isothermal amplification (LAMP), has remained challenging. Here, we attempt to address this challenge by comparative study of the thermostable, but poorly trans-active YmeCas12a (from Yellowstone metagenome) with the mesophilic, highly trans-active LbaCas12a (from Lachnospiraceae bacterium ND 2006). Kinetic characterizations identified that poor trans substrate affinity (high Km) is the key limiting factor in YmeCas12a trans activity. We engineered YmeCas12a by structure-guided mutagenesis and fusion to DNA-binding domains to increase its affinity to the trans substrate. The most successful combinatorial variant showed 5-50-fold higher catalytic efficiency with the trans substrate depending on the target site. With the improved variant, we demonstrate efficient nucleic acid detection in combination with LAMP in a single reaction workflow, setting the basis for development of point-of-care tests.

From Cas proteins to cutting-edge biosensors: A new era in clinical pathogen diagnostics

Infectious pathogens exert a profound impact on global health and socio-economic stability, positioning them as a critical focus of scientific inquiry. To safeguard public health, propel advancements in medical diagnostics, and ensure food safety, the development of efficient technologies for rapid, onsite detection of pathogens is imperative. In light of recent research breakthroughs, CRISPR/Cas-based technologies for pathogen biosafety and molecular diagnostics have emerged as particularly promising in the realm of infectious disease detection. This review succinctly introduces the working principles of CRISPR/Cas systems and thoroughly discusses the design and development of various CRISPR/Cas-based biosensors. Importantly, this paper explores the robust applications of CRISPR/Cas-assisted biosensing for emerging infectious diseases, highlighting its potential in pathogen diagnostics with features like cost-effectiveness, multiplex detection and POCT applications. Furthermore, challenges and future developments of CRISPR/Cas-based biosensors for rapid and accurate pathogen detection in specialized settings are also summarized, integrating CRISPR detection with portable POCT biosensors, nanomaterials and novel colorimetric materials. As it builds on a lot of foundational work and offers new insights and detailed reference to advance the development and application of CRISPR technologies in clinical pathogen diagnostics, opening new avenues in medical diagnostics and the prevention and control of infectious diseases.

Rapid point-of-need blood fluke detection in Southern Bluefin Tuna samples using recombinase polymerase amplification coupled with lateral flow test (RPA-LF)

Aporocotylid blood flukes Cardicola forsteri and C. orientalis are considered one of the most significant health concerns for Southern Bluefin Tuna (SBT) Thunnus maccoyii ranched in Australia. There is a need for rapid point-of-need diagnostics to detect Cardicola spp. in SBT to allow the industry to make timely management decisions. Recombinase polymerase amplification (RPA) is an isothermal technique which operates at constant low temperature (25-42˚C), and when coupled with a lateral flow (LF) strip, makes an ideal diagnostic tool for rapid, specific, and sensitive identification of pathogens in field applications. RPA-LF assays were designed and validated for detection of C. forsteri and C. orientalis. For each assay, no cross-species amplification was seen and detection as low as 30-50 gene copy equivalents was achieved. Reactions can be completed in 10 minutes. Similar specificity and sensitivity were demonstrated for SBT samples when compared to qPCR analysis, and use of equipment-free incubation using body heat outside of laboratory settings was demonstrated. By developing rapid, ready-to-use diagnostics, the SBT industry can identify risks relating to blood flukes far quicker than is currently possible.

Enhanced the Trans-Cleavage Activity of CRISPR-Cas12a Using Metal-Organic Frameworks as Stimulants for Efficient Electrochemical Sensing of Circulating Tumor DNA

Continued development of clustered regularly interspaced short palindromic repeats (CRISPR)-powered biosensing system on the electrochemical interface is vital for accurate and timely diagnosis in clinical practice. Herein, an electrochemical biosensor based on manganese metal-organic frameworks (MOFs)-enhanced CRISPR (MME-CRISPR) is proposed that enables the efficient detection of circulating tumor DNA (ctDNA). In this design, customized enzyme stimulants (Mn2+) are co-assembled with Cas12a/crRNA to form enzyme-MOF composites, which can be released quickly under mild conditions. The MOFs-induced proximity effect can continuously provide adequate Mn2+ to sufficiently interact with Cas12a/crRNA during the release process, enhancing the trans-cleavage activity of complex available for biosensor construction. The MOFs-based enzyme biocomposites also afford efficient protection against various external stimulus. It is demonstrated that the developed biosensor can achieve ultrasensitive detection of epidermal growth factor receptor L858R mutation in ctDNA with a low detection limit of 0.28 fm without pre-amplification. Furthermore, the engineered mismatch crRNA enables the biosensor based on MME-CRISPR to detect single nucleotide variant with a high signal-to-noise ratio. More importantly, it has been successfully used to detect the targets in clinical practice, requiring low-dose samples and a short time. This strategy is believed to shed new light on the applications of cancer diagnosis, treatment, and surveillance.

Development of Ni-ZnO-ACE-2 peptide hybrids as electrochemical devices for SARS-CoV-2 spike protein detection

Owing to fast SARS-CoV-2 mutations, biosensors employing antibodies as biorecognition elements have presented problems with sensitivity and accuracy. To face these challenges, antibodies can be replaced with the human angiotensin converting enzyme 2 (ACE-2), where it has been shown that the affinity between ACE-2 and the receptor binding domain (RBD) increases with the emergence of new variants. Herein, we report on Ni-doped ZnO nanorod electrochemical biosensors employing an ACE-2 peptide (IEEQAKTFLDKFNHEAEDLFYQS-NH2) as a biorecognition element for detecting Spike (S) Wild-Type (WT) protein. The electrode was fully characterized in terms of electrochemical and physical properties. The sensor showed high cross reactivity with Spike protein B.1.1.7 and Spike protein B.1.351. Still, there was no cross reactivity with the Nucleocapsid protein WT, showing that the biosensor can identify ancestral WT S protein and S protein variants of concern. The device exhibited a LOD of 60.13 ng mL-1 across an S protein WT concentration range from 200 ng mL-1 to 1000 ng mL-1 and a LOQ of 182.22 ng mL-1. The calculated sensitivity and specificity were 88.88 and 100 %, respectively. These results proved that the Ni-ZnO sensor has promising prospects for SARS-CoV-2 detection and diagnosis of other viruses, employing peptides as biorecognition elements.

Harnessing bacterial immunity: CRISPR-Cas system as a versatile tool in combating pathogens and revolutionizing medicine

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technology has emerged as an adaptable instrument for several uses. The CRISPR-Cas system employs Cas proteins and programmable RNA molecules to guide the recognition and cleavage of specific DNA regions, permitting accurate genome editing. It is derived from the bacterial immune system and allows for accurate and efficient modification of DNA sequences. This technique provides unparalleled gene editing, control, and precise alteration opportunities. This review aims to offer a comprehensive update of the core concepts of the CRISPR-Cas system and recent progress, while also providing an overview of the significant applications in diverse fields such as microbiology and medicine. The CRISPR-Cas9 gene editing technique has facilitated substantial advancements in comprehending gene function, simulating diseases, and creating innovative therapeutics. CRISPR-based therapeutics present a hopeful prospect for addressing intricate ailments, including genetic disorders, malignancies, and infectious diseases, as they serve as viable substitutes for conventional pharmaceuticals. In microbiology, this method serves as a diagnostic and therapeutic tool that proves highly efficient in eliminating bacteria that have developed resistance to various antibiotics. Despite its significant potential, CRISPR encounters ethical, safety, and regulatory obstacles that necessitate meticulous deliberation. Concerns regarding off-target effects, poor delivery to target tissues, and unwanted side effects emphasize the necessity to thoroughly examine the technology. It is necessary to balance the advantages and difficulties CRISPR presents. Consequently, more rigorous preclinical and clinical experiments are essential before using it in humans.

CRISPR/Cas bioimaging: From whole body biodistribution to single-cell dynamics

This review explores the transformative role of CRISPR/Cas systems in optical bioimaging, emphasizing how advancements in nanoparticle (NP) technologies are revolutionizing the visualization of gene-editing processes both in vitro and in vivo. Optical imaging techniques, such as near-infrared (NIR) and fluorescence imaging, have greatly benefited from the integration of nanoformulated contrast agents, improving resolution, sensitivity, and specificity. CRISPR/Cas systems, originally developed just for gene editing, are now being coupled with these imaging modalities to enable real-time monitoring and quantitative measurements of metabolites, vitamins, proteins, nucleic acids and other entities in specific areas of the body, as well as tracking of CRISPR/Cas delivery, editing efficiency, and potential off-target effects. The development of CRISPR/Cas-loaded NPs allows for enhanced imaging and precise monitoring across multiple scales with multiplexed and multicolor imaging in complex settings, including potential in vivo diagnostics. CRISPR/Cas therapeutics as well as diagnostics are hindered by the lack of efficient and targeted delivery tools. Biomimetic NPs have emerged as promising tools for improving biocompatibility, enhancing targeting capabilities, and overcoming biological barriers, facilitating more efficient delivery and bioimaging of CRISPR/Cas systems in vivo. As the design of these NPs and delivery mechanisms improves, alongside advancements in endolysosomal escape, CRISPR/Cas-based bioimaging will continue to advance, offering unprecedented possibilities in precision medicine and theranostic applications.

Amplification-Free CRISPR/Cas12a-Based Electrochemical Biosensor with Enhanced Sensitivity for Viral Detection

To detect contagious viral nucleic acids, traditional biosensors often require target amplification steps or use fluorescence and Raman probes tagged on nucleic acids, which are time-consuming, complex, and expensive. Recently, the CRISPR/Cas12a has received the attraction for development of nucleic acid biosensors, beyond its conventional role-like gene editing, but the enhancement of the sensitivity of CRISPR/Cas-based biosensors is still required to simplify the biosensing steps. Here, we develop a CRISPR/Cas12a-based electrochemical biosensor for the detection of viral nucleic acids in a simple manner. The novel mismatch Ag probe (MAP), as a sensing probe, and the highly conductive gold electrode on indium tin oxide with a nano array (GELITION) are introduced that enable the amplification-free and ultrasensitive detection of nucleic acids using a CRISPR/Cas12a system. The biosensing ability of the developed biosensor is validated using human papillomavirus type 16 and 18 viral DNAs (HPV16 and HPV18), achieving a limit of detection (LOD) of 1 fM without amplification and complex steps. Our developed biosensor is expected to be applicable in detecting various viruses and could contribute to the early detection of future pandemics.

Metagenome-Derived CRISPR-Cas12a Mining and Characterization

The advent of clustered regularly interspaced short palindromic repeats (CRISPR)-based technologies has revolutionized genome editing, with continued interest in expanding the CRISPR-associated proteins (Cas) toolbox with diverse, efficient, and specific effectors. CRISPR-Cas12a is a potent, programmable RNA-guided dual nickase, broadly used for genome editing. Here, we mined dairy cow microbial metagenomes for CRISPR-Cas systems, unraveling novel Cas12a enzymes. Using in silico pipelines, we characterized and predicted key drivers of CRISPR-Cas12a activity, encompassing guides and protospacer adjacent motifs for five systems. We next assessed their functional potential in cell-free transcription-translation assays with GFP-based fluorescence readouts. Lastly, we determined their genome editing potential in vivo in Escherichia coli by generating 1 kb knockouts. Unexpectedly, we observed natural sequence variation in the bridge-helix domain of the best-performing candidate and used mutagenesis to alter the activity of Cas12a orthologs, resulting in increased gene editing capabilities of a relatively inefficient candidate. This study illustrates the potential of underexplored metagenomic sequence diversity for the development and refinement of genome editing effectors.

Virus Detection by CRISPR-Cas9-Mediated Strand Displacement in a Lateral Flow Assay

In public health emergencies or in resource-constrained settings, laboratory-based diagnostic methods, such as RT-qPCR, need to be complemented with accurate, rapid, and accessible approaches to increase testing capacity, as this will translate into better outcomes in disease prevention and management. Here, we develop an original nucleic acid detection platform by leveraging CRISPR-Cas9 and lateral flow immunochromatography technologies. In combination with an isothermal amplification that runs with a biotinylated primer, the system exploits the interaction between the CRISPR-Cas9 R-loop formed upon targeting a specific nucleic acid and a fluorescein-labeled probe to generate a visual readout on a lateral flow device. Our method enables rapid, sensitive detection of nucleic acids, achieving a limit of 1-10 copies/μL in 1 h at a low temperature. We validated the efficacy of the method by using clinical samples of patients infected with SARS-CoV-2. Compared with other assays, it operates with more accessible molecular elements and showcases a robust signal-to-noise ratio. Moreover, multiplexed detection was demonstrated using primers labeled with biotin and digoxigenin, achieving the simultaneous identification of target genes on lateral flow devices with two test lines. We successfully detected SARS-CoV-2 and Influenza A (H1N1) in spiked samples, highlighting the potential of the method for multiplexed diagnostics of respiratory viruses. All in all, this represents a versatile and manageable platform for point-of-care testing, thereby supporting better patient outcomes and enhanced pandemic preparedness.

Self-Assembly of Nanogold Triplets on Trimeric Viral Proteins for Infectious Disease Diagnosis

Timely and accurate diagnostics for infectious diseases are essential in preventing their worldwide spread. Though rapid diagnostic tests are favored for their speed, cost-effectiveness, and ease of use, most tests compromise sensitivity, which risks false-negative results. Here, we present the self-assembly of nanogold triplets on trimeric viral surface proteins for a sensitive colorimetric assay to identify viruses. Gold triplets were self-assembled on the viral trimeric surface proteins using ultrasmall gold nanoparticles. We observed a significant wavelength shift of 70 nm, enabling straightforward naked-eye detection through gold triplets that act as catalysts for producing nanoplasmonic viruses. We established the detection limit of 3 × 105 copies/ml using an effective colorimetric assay for detecting SARS-CoV-2. The self-assembly of gold triplets on trimeric viral surface proteins provides a reliable approach to the accurate and sensitive detection of viruses.

Accelerating Cleavage Activity of CRISPR-Cas13 System on a Microfluidic Chip for Rapid Detection of RNA

It is extremely advantageous to detect nucleic acid levels in the early phases of disease management; such early detection facilitates timely treatment, and it can prevent altogether certain cancers and infectious diseases. A simple, rapid, and versatile detection platform without enzymatic amplification for both short and long sequences would be highly desirable in this regard. Our study addresses this need by introducing IMACC, an ICP-based Microfluidic Accelerator Combined with CRISPR, for amplification-free nucleic acid detection. It exploits electrokinetically induced ion concentration polarization (ICP) to concentrate target nucleic acids and CRISPR reagents near the depletion zone boundary within a microfluidic channel. This localized accumulation accelerates the CRISPR-guided promiscuous cleavage of reporter molecules while enhancing their fluorescence signals simultaneously. Simultaneous accumulation of RNA and ribonucleoproteins (RNP) in confined spaces was validated experimentally and numerically, showing overlapping regions. IMACC enabled detection of miRNA-21 (22 bp) down to 10 pM within 2 min of ICP. IMACC ensured CRISPR specificity (single mismatch (N = 1) sensitivity) during ICP, as shown by off-target and mismatch sequence experiments. IMACC was applied to long RNA samples (i.e., SARS-CoV-2), but it statistically remained challenging at this point due to nonlinear intensity trends with copy numbers and large deviations. IMACC enabled rapid detection of short RNAs such as microRNAs using only basic CRISPR reagents in a single microfluidic channel, eliminating the need for extra enzymes or buffer sets, streamlining workflow and reducing turnaround time. IMACC has the potential to advance CRISPR diagnostics and holds promise for improved detection and future prescreening applications.

Advances in portable fiber optic-based aptasensors for on-site detection: design, evolution, and application

The emergence of on-site detection using portable devices has transformed traditional analytical methods, which rely on precise but bulky laboratory instruments, into a promising technique for point-of-care testing. In this case, fiber optic (FO)-based aptasensors, featuring miniaturized devices, high sensitivity, and strong specificity, are candidates to meet the requirement of on-site detection. To enhance the interaction between light and the surrounding environment, numerous FO probes with novel micro/nano-structures have been designed, including tilted fiber Bragg grating (TFBG), long-period grating (LPG), bent, microfiber, D-shaped, and photonic bandgap fibers. Aptamers fold into unique tertiary structure to specifically and sensitively bind with their targets through a direct reaction or a binding-induced structural switch. Benefitting from advancements in FO probes and aptamers, multiple FO-based aptasensors have been constructed for sensitive detection, including evanescent wave-based, fluorescent-, localized surface plasmon resonance (LSPR)-based, and interferometer-based sensors. To date, FO-based aptasensors have been widely applied in clinical diagnosis, environmental monitoring, and food safety. This review focuses on design strategies, evolution, and applications of FO-based aptasensors. The opportunities and challenges of FO-based aptasensors for on-site detection are discussed in depth. This review aims to highlight the significance of FO-based aptasensors for on-site detection and promote their development from laboratory research to practical application.

Cellulose test strips modified with virus-like particles: Advancing viral immunity screening technologies

The COVID-19 pandemic has driven immunity acquisition through infection or vaccination, leading to SARS-CoV-2 antibodies. This study introduces a colorimetric biosensor for COVID-19 immunity screening using Virus-Like Particles (VLPs) with SARS-CoV-2 spike protein motifs on a cellulose carrier. The cellulose was chemically modified with DSS to secure the VLPs, verified via FTIR. Detection utilized the Bradford reagent, with RGB color analysis via ImageJ and smartphone images. The test strips demonstrated high sensitivity (R > 0.998) across a 10-40 µg/mL range in buffer and serum, with 30-minute incubation. They also exhibited selectivity against interferents like albumin, glucose, and urea. Success with undiluted samples highlights clinical potential. This broad-spectrum, REASSURED-compliant method is promising for global testing applications.

A tube-based biosensor for DNA and RNA detection

Affordable, sensitive, and simplified DNA/RNA detection is important for disease diagnosis and enables timely medical intervention measures. Usually, high sensitivity depends on expensive instruments and sophisticated procedures, making sensitivity contradict affordability and simplicity. Here, we proposed an ultra-sensitive single-tube biosensor (USTB) where users can visually detect targets by observing the liquid motion state in a glass tube. The developed instrument-free USTB performed low-cost ($0.1), fast (1 min), and ultra-sensitive detection for both the DNA/RNA fragments (≤1 aM) and the clinical positive samples, which commercial reverse transcription polymerase chain reaction (RT-PCR) and PCR kits could not effectively recognize. Furthermore, USTB is promising to be easily applied to detect other-type biomarkers by the designed smart sensing unit.

Structure-switching G-quadruplex: An efficient CRISPR/Cas12a signal reporter for label-free colorimetric biosensing

G-quadruplex is widely used as a signal reporter for colorimetric biosensor construction. However, the effectiveness of CRISPR/Cas12a in trans-cleaving G-quadruplexes is significantly influenced by their resistance to nuclease, resulting in a weak colorimetric signal response. Herein, a structure-switching G-quadruplex regulated by transducer DNA is used as a signal reporter to construct CRISPR/Cas12a-based biosensors. The transducer DNA lacks a stable secondary structure, enabling efficient cleavage by CRISPR/Cas12a, which subsequently affects the catalytic activity of the G-quadruplex/hemin DNAzyme. We used microRNAs (miRNAs) and ATP as model targets to develop a label-free colorimetric detection platform. By optimizing the DNA sequences and reaction conditions, the biosensors exhibit excellent detection selectivity and sensitivity. The reliability of the proposed method was validated by its consistency with RT-qPCR for miRNAs detection and a commercial chemiluminescence kit for ATP assay, demonstrating its potential in clinical diagnosis and bioanalytical studies. The assay is concise and cost-effective because it does not require DNA labeling, magnetic separation, or enzymatic DNA amplification. Our design strategy avoids the use of G-quadruplex as a cleavage substrate for CRISPR/Cas12a while ensuring an efficient response of the G-quadruplex/hemin DNAzyme to CRISPR/Cas12a system, addressing the issue of G-quadruplex resistance to CRISPR/Cas12a nuclease activity.

The nucleic acid detection using CRISPR/Cas biosensing system with micro-nano modality for point-of-care applications

Nucleic acid detection is considered the golden standard for diagnosing infectious diseases caused by various pathogens, including viruses, bacteria, and parasites. PCR and other amplification-based technologies are highly sensitive and specific, allowing for accurate detection and identification of low-level causative pathogens by targeting and amplifying their unique genetic segment (DNA or RNA). However, it is important to recognize that machinery-dependent diagnostic methods may only sometimes be available or practical in resource-limited settings, where direct implementation can be challenging. CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-based diagnostics offer a promising alternative for nucleic acid detection. These methods provide gene sequence-specific targeting, multiplexing capability, rapid result disclosure, and ease of operation, making them suitable for point-of-care (POC) applications. CRISPR-Cas-based nucleic acid detection leverages the intrinsic gene-editing capabilities of CRISPR systems to detect specific DNA or RNA sequences with high precision, ensuring high specificity in identifying pathogens. When integrated with micro- and nano-technologies, CRISPR-based diagnostics gain additional benefits, including automated microfluidic processes, enhanced multiplexed detection, improved sensitivity through nanoparticle integration, and combined detection strategies. In this review, we analyze the motivations for tailoring the CRISPR-Cas system with microfluidic formats or nanoscale materials for nucleic acid biosensing and detection. We discuss and categorize current achievements in such systems, highlighting their differences, commonalities, and opportunities for addressing challenges, particularly for POC diagnostics. Micro- and nano-technologies can significantly enhance the practical utility of the CRISPR-Cas system, enabling more comprehensive diagnostic and surveillance capabilities. By integrating these technologies, CRISPR-based diagnostics can achieve higher levels of automation, sensitivity, and multiplexing, making them invaluable tools in the global effort to diagnose and control infectious diseases.

Catalytic hairpin assembly-coupled CRISPR/Cas12a biosensor for sensitive detection of melamine in dairy products

We combined catalytic hairpin assembly (CHA) with the Cas12a system for detecting melamine adulteration. This system involved two-step signal conversion and two-level amplification, boosting the sensor's versatility and sensitivity. The sensor showed excellent specificity and applicability for melamine detection in dairy products, and was broadened to viral nucleic acid detection.

Validation of new equipment for SARS-CoV-2 diagnosis in Ecuador: Detection of the virus and antibodies generated by disease and vaccines with one POC device

The COVID-19 pandemic underscored the critical need to enhance screening capabilities and streamline diagnosis. Point-of-care (POC) tests offer a promising solution by decentralizing testing. We aimed to validate the PLUM device (LSK Technologies Inc.), a portable optical reader, to detect SARS-CoV-2 RNA using direct RT-LAMP targeting the ORF1a and E1 genes and patient antibodies by ELISA. The direct RT-LAMP assays employ nasopharyngeal swabs and bypass RNA extraction protocols through a brief chemical and physical lysis step. Test sensitivity and specificity were assessed against gold-standard detection methods in laboratory and field conditions. For samples with Ct values below 25, direct RT-LAMP showed 83% sensitivity and 90% specificity under laboratory conditions and 91% sensitivity and 92% specificity under field conditions. The nucleocapsid antigen antibody assay had 99% positive percent agreement (PPA) and 97% negative percent agreement (NPA), outperforming spike-RBD antigen (98% PPA, 92% NPA) and seroprevalence (98% PPA, 88% NPA) under laboratory conditions. Under field conditions, similar results were found for antibody detection for the nucleocapsid antigen (93% PPA; 100% NPA), spike-RBD (100% PPA; 94% NPA), and seroprevalence (90% PPA; 94% NPA). This study validated the PLUM device as a dual POC tool for direct RT-LAMP-based SARS-CoV-2 and ELISA-based COVID-19 antibody detection.

CRISPR-mediated detection of Pneumocystis transcripts in bronchoalveolar, oropharyngeal, and serum specimens for Pneumocystis pneumonia diagnosis

BACKGROUNDPneumocystis jirovecii pneumonia (PCP) is a leading cause of fungal pneumonia, but its diagnosis primarily relies on invasive bronchoalveolar lavage (BAL) specimens that are difficult to obtain. Oropharyngeal swabs and serum could improve the PCP diagnostic workflow, and we hypothesized that CRISPR could enhance assay sensitivity to allow robust P. jirovecii diagnosis using swabs and serum. Herein, we describe the development of an ultrasensitive RT-PCR-coupled CRISPR assay with high active-infection specificity in infant swabs and adult BAL and serum.METHODSMouse analyses employed an RT-PCR CRISPR assay to analyze P. murina transcripts in WT and Rag2-/- mouse lung RNA, BAL, and serum at 2-, 4-, and 6-weeks after infection. Human studies used an optimized RT-PCR CRISPR assay to detect P. jirovecii transcripts in infant oropharyngeal swab samples, adult serum, and adult BAL specimens from patients who were infected with P. jirovecii and those who were not.RESULTSThe P. murina assays sensitively detected Pneumocystis RNA in the serum of infected mice throughout infection. Oropharyngeal swab CRISPR assay results identified infants infected with P. jirovecii with greater sensitivity (96.3% versus 66.7%) and specificity (100% versus 90.6%) than RT-qPCR compared with mitochondrial large subunit rRNA gene (mtLSU) standard marker, and CRISPR results achieved higher sensitivity than RT-qPCR results (93.3% versus 26.7%) in adult serum specimens.CONCLUSIONSince swabs are routinely collected in pediatric patients with pneumonia and serum is easier to obtain than BAL, this assay approach could improve the accuracy and timing of pediatric and adult Pneumocystis diagnosis by achieving specificity for active infection and potentially avoiding the requirement for BAL specimens.FUNDINGThe work was supported by the NIH (R01AI120033), NHLBI (R35HL139930), the Louisiana Board of Regents Endowed Chairs for Eminent Scholars program, and by research funding provided by National Institute of Allergy and Infectious Diseases (NIAID) (R01AI144168, R01AI175618, R01AI173021). This research was also funded by the NIHR (project 134342) using UK aid from the UK government to support global health research.

Unraveling the future of genomics: CRISPR, single-cell omics, and the applications in cancer and immunology

The CRISPR system has transformed many research areas, including cancer and immunology, by providing a simple yet effective genome editing system. Its simplicity has facilitated large-scale experiments to assess gene functionality across diverse biological contexts, generating extensive datasets that boosted the development of computational methods and machine learning/artificial intelligence applications. Integrating CRISPR with single-cell technologies has further advanced our understanding of genome function and its role in many biological processes, providing unprecedented insights into human biology and disease mechanisms. This powerful combination has accelerated AI-driven analyses, enhancing disease diagnostics, risk prediction, and therapeutic innovations. This review provides a comprehensive overview of CRISPR-based genome editing systems, highlighting their advancements, current progress, challenges, and future opportunities, especially in cancer and immunology.

Establishment of a Rapid Detection Technique Based on RPA-LFD and RPA-CRISPR/Cas12a on Phytophthora pini

Phytophthora pini, a globally dispersed plant pathogen, poses a significant threat to natural ecosystems and cultivated horticultural crops. Early and precise detection of P. pini is essential for effective disease management. This study focused on developing specific, rapid, and sensitive molecular diagnostic techniques to identify the pathogenic oomycete P. pini. We employed recombinase polymerase amplification with lateral flow device (RPA-LFD) and RPA combined with CRISPR/Cas12a. The RPA-LFD method can identify P. pini at concentrations as low as 10 pg/μL in 30 min, while the RPA-CRISPR/Cas12a approach can detect the pathogen at 1 pg/μL in approximately 50 min. These methods are highly effective in identifying disease caused by P. pini and provide a basis for future field detection, which may reduce the economic losses associated with this devastating disease.

Combining CRISPR-Cas12a with Microsphere Array-Enhanced Fluorescence for Portable Pathogen Nucleic Acid Detection

The detection of food contamination in a swift and sensitive manner is essential for safeguarding public health. Clustered regularly interspaced short palindromic repeats (CRISPR)-based assays for nucleic acid detection are renowned for their high specificity and convenient, related studies have focused on refining the Cas protein and optimizing the CRISPR (cr)RNAs design within CRISPR-based assays for enhancing the sensitivity of nucleic acid detection. Our research offers innovative insights into enhancing the fluorescence signal output intensity from a physical standpoint, thereby presenting a practical and cost-effective strategy to lower the detection thresholds in CRISPR-based assays. By a layer of microsphere arrays was spread onto the bottom of the microfluidic chip to enhance the fluorescence signal of the sample via self-assembly of the microspheres. Recombinase polymerase amplification (RPA) was used to amplify target sequences, followed by crRNA binding to activate Cas enzyme, cleaving fluorescein amidite (FAM)-labeled reporters and emitting a fluorescent signal. The method successfully identified SARS-CoV-2 positive samples (10 clinical samples and 8 environmental contamination samples) and distinguished them from negative samples. Meanwhile, it successfully detected 4 food contamination Shigella samples and 5 clinical Shigella samples. In this study, the developed method exhibited a detection limit (LoD) of 75 fM for SARS-CoV-2 (POCT with USB camera: 50 fM) and 100 fM for Shigella (POCT with USB camera: 75 fM). It also demonstrated promising sensitivity (100%) and specificity (100%) in a small-sample validation. Combined portable and automated detection was achieved using a smartphone to receive and process the fluorescent signals obtained from the samples. The detection platform developed in this study is not only applicable for the detection of pathogens in cold-chain food products, but also extends to pathogen detection in community hospitals and resource-limited areas, providing an efficient solution for rapid pathogen screening in different settings. Moreover, different nucleic acid samples can be detected by changing the RPA primer and CRISPR crRNA. This method provides a paradigm for studying enhanced fluorescence signaling and holds significant potential to advance the commercialization and practical use of CRISPR fluorescence sensors.

Porous GNPs assisted LAMP-CRISPR/Cas12a amperometric biosensor as a potential point of care testing system for SARS-CoV-2

A simple and ultrasensitive amperometric biosensor is introduced which has the potential to be applied as a point of care test for SARS-CoV-2 monitoring. It was prepared by integrating the reverse transcription loop-mediated isothermal amplification (RT‑LAMP) and CRISPR/Cas12a nuclease activity on a modified gold screen-printed electrode (GSPE). The GSPE is modified with double-end thiolated oligonucleotide reporters conjugated to porous gold nanoparticles (PGNPs) and inserted into a homemade poly-methyl methacrylate cartridge. This biosensor was integrated with a low-cost electronic kit to make a platform with the potential to be applied as a point-of-care testing system. The PGNPs on the reporters create a dense, negatively charged barrier that repels the redox couple of [Fe(CN)6]3-/4- from the GSPE surface. Upon the addition of a real sample, followed by LAMP amplification and Cas12a nuclease activity on disposable GSPE, in the presence of SARS-CoV-2, the single-guide RNA binds to the target sequence and activates Cas12a. The activated Cas12a then cleaves the reporters, releasing the PGNPs. This removal of electrostatic hindrance allows the redox couple of [Fe(CN)6]3-/4- to approach the positively charged GSPE, enhancing the amperometric signal. This biosensor offers an outstanding detection limit of 143 zM (~ 86 copies/mL) and a linear response from 4.7 to 7062 aM for SARS-CoV-2 real samples. By using double-end thiolated reporters and porous GNPs, this novel testing system makes it possible to minimize the required sample volume and reagent costs.

Rapid molecular detection of Senecavirus A based on reverse transcription loop-mediated isothermal amplification (RT-LAMP) and CRISPR/Cas12a

Introduction

Senecavirus A (SVA), an emerging vesicular pathogen, is responsible for porcine idiopathic vesicular disease (PIVD). This disease is closely associated with porcine vesicular disease and acute neonatal piglet mortality, presenting a substantial threat to the global swine industry. At present, the absence of effective drugs or vaccines for treating the disease makes accurate diagnosis of SVA of paramount importance for the effective prevention and control of the disease.

Methods

In this study, we combined reverse transcription loop-mediated isothermal amplification (RT-LAMP) and Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated protein12a (CRISPR/Cas12a) using a dual-labelled fluorescence quencher or fluorescent biotin single-stranded DNA reporter molecule to develop two rapid, reliable, and portable visual SVA assays: RT-LAMP-Cas12a-FQ and RT-LAMP-Cas12a-FB.

Results

The two methods exhibited comparable detection limits, with 9.6 copies/μL achieved in 40 and 45 minutes, respectively. They did not cross-react with non-target nucleic acids extracted from other related viruses and showed high specificity for SVA RNA detection. Furthermore, the methods demonstrated satisfactory performance in detecting 69 porcine adventitious samples, with no significant differences from that of quantitative reverse transcription polymerase chain reaction (RT-qPCR).

Discussion

In summary, the RT-LAMP-Cas12a-FQ and RT-LAMP-Cas12a-FB methods developed are promising for early detection and routine surveillance of porcine SVA in resource-poor areas.

Rapid and visual detection of transmissible gastroenteritis virus using a CRISPR/Cas12a system combined with loop-mediated isothermal amplification

BACKGROUND

Transmissible gastroenteritis (TGE) is a highly contagious intestinal disease caused by transmissible gastroenteritis virus (TGEV). The primary techniques for identifying TGEV involve enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and fluorescent quantitative PCR (qPCR). However, these approaches are complex, demanding specialized tools and significant time. Therefore, a precise, swift, and effective differential diagnosis method is crucial for TGEV prevention. In recent years, clustered regularly interspaced short palindromic repeats (CRISPR) and Cas-associated proteins have become popular for their high specificity, unique cleavage activity, and ease of detection. CRISPR-Cas12a, a novel RNA-guided nucleic acid endonuclease, is emerging as a powerful molecular scissor.

RESULTS

In this study, we designed three pairs of crRNA targeting the N gene of TGEV. Following the selection of the most appropriate crRNA, we established the loop-mediated isothermal (LAMP) amplification method with a sensitivity of 102 copies/µL. And based on this, we established the CRISPR-Cas12a fluorescence assay with a sensitivity of 100 copies/µL. Furthermore, we established a CRISPR/Cas12a lateral-flow dipstick assay with a sensitivity of 102 copies/µL. Importantly, none of these methods exhibited cross-reactivity with other related viruses, enabling quicker and more straightforward observation of experimental results.

CONCLUSIONS

We have successfully developed a CRISPR-Cas12a fluorescence assay and a CRISPR/Cas12a lateral-flow dipstick assay for clinical TGEV detection. Overall, we created a portable, quick, and sensitive TGEV assay with strong specificity utilizing the CRISPR-Cas12a system.

RNA aptamer-based CRISPR-Cas12a system for enhanced small molecule detection and point-of-care testing

The CRISPR-Cas12a system has emerged as a robust platform for small molecule detection. However, existing methodologies primarily emphasize DNA aptamer-based strategies. This study introduces an RNA aptamer-based CRISPR-Cas12a approach due to the fact that the majority of small molecules lack corresponding DNA aptamers. The approach employs theophylline RNA aptamer (TA) to regulate Cas12a activity through competitive inhibition of crRNA. The results demonstrate that this system effectively detects theophylline (TP) in various food, beverage, and human serum samples, exhibiting excellent selectivity and sensitivity. Additionally, a visual paper-based detection system showcases its applicability for real-time analysis in food matrices and human serum. The RNA aptamer-based CRISPR-Cas12a strategy holds significant potential for diverse biomedical applications, offering a versatile tool for future sensing applications through customized RNA aptamer designs for small molecules.

Trans-nuclease activity of Cas9 activated by DNA or RNA target binding

Type V and type VI CRISPR-Cas systems have been shown to cleave nonspecific single-stranded DNA (ssDNA) or single-stranded RNA (ssRNA) in trans, but this has not been observed in type II CRISPR-Cas systems using single guide RNA. We show here that the type II CRISPR-Cas9 systems directed by CRISPR RNA and trans-activating CRISPR RNA dual RNAs show RuvC domain-dependent trans-cleavage activity for both ssDNA and ssRNA substrates. Cas9 possesses sequence preferences for trans-cleavage substrates, preferring to cleave T- or C-rich ssDNA substrates. We find that the trans-cleavage activity of Cas9 can be activated by target ssDNA, double-stranded DNA and ssRNA. The crystal structure of Cas9 in complex with guide RNA and target RNA provides a structural basis for the binding of target RNA to activate Cas9. Based on the trans-cleavage activity of Cas9 and nucleic acid amplification technology, we develop the nucleic acid detection platforms DNA-activated Cas9 detection and RNA-activated Cas9 detection, which are capable of detecting DNA and RNA samples with high sensitivity and specificity.

Advancing Precision Medicine: Recent Innovations in Gene Editing Technologies

The advent of gene editing has significantly advanced the field of medicine, opening new frontiers in the treatment of genetic disorders, cancer, and infectious diseases. Gene editing technology remains a dynamic and promising area of research and development. Recent advancements in protein and RNA engineering within this field have addressed critical issues such as imprecise edits, poor editing efficiency, and off-target effects. Advancements in delivery methods have allowed the achievement of therapeutic or even selection-free gene editing efficiency with reduced toxicity in primary cells, thereby enhancing the safety and efficacy of gene manipulation. This progress paves the way for transformative changes in molecular biology, medicine, and other fields. This review provides a comprehensive overview of the advancements in gene editing techniques, focusing on prime editor proteins and their engineered variants. It also explores alternative systems that expand the toolkit for precise genomic modifications and highlights the potential of these innovations in treating hematological disorders, while also discussing the limitations and challenges that remain.

Innovative strategies for enhancing AuNP-based point-of-care diagnostics: Focus on coronavirus detection

Highly pathogenic coronaviruses have consistently threatened humanity, encompassing SARS-CoV, MERS-CoV, SARS-CoV-2 and others. Swift detection and accurate diagnosis play a crucial role in promptly identifying high-risk populations, enabling timely intervention, and effectively breaking the transmission chain to reduce casualties. However, the diagnostic "gold standard" reverse transcription-polymerase chain reaction (RT-PCR) failed to meet the overwhelming demand during the pandemic due to insufficient equipment and trained personnel, impeding the effective control of viral spread. Undoubtedly, there is an urgent need for the development of convenient, rapid, and sensitive point-of-care (POC) diagnostic technology. Gold nanoparticles (AuNPs) satisfy the substantial market demand for biosensors owing to their exceptional optical properties and stability. In this comprehensive review, we summarize the potential advantages of AuNPs in visual solution colorimetry and lateral flow assays (LFAs) for the diagnosis of COVID-19. We delve into the techniques for enhancing LFA signals, with the goal of increasing both detection sensitivity and specificity. Furthermore, we include the application of smartphones for unbiased and objective interpretation of results. The examples presented in this review are anticipated to inspire researchers in designing AuNPs biosensors to address current and potential outbreaks of infectious diseases in the future.

Ultrasensitive, Real-Time Detection of Viral Antigens and RNA Enabled by Scalable Graphene-Based FET Sensors for Pathogen Detection: A Case Study on COVID-19

Herein, a novel and simple electrospray (ES) printing technique was developed for the fabrication of ultrathin graphene layers with precisely controlled nanometer-scale thickness, where graphene oxide (GO) was electrosprayed on wafers and subsequently chemically reduced into reduced GO (rGO). Utilizing that technique, we prepared ultrathin rGO in-plane graphene field-effect transistor (GFET)-based biosensors coupled with a portable prototype measuring system for point-of-care detection of pathogens. We illustrate the use of such prepared GFETs to detect COVID-19, using the SARS-CoV-2 nucleocapsid protein antigen (N-protein) and genomic viral RNA as detection targets. The electrosprayed and chemically reduced rGO films enhance the molecular detection in GFET sensors through significant local gating effects. The device detects the N-protein from the SARS-CoV-2 Omicron variant in a culture medium with an LOD of 1.44 PFU/mL and in clinical oropharyngeal samples with an LOD of 45 genome copies/mL in 5 min. It also successfully detects viral RNA in oropharyngeal swabs within 10 min. The GFET sensor responses were further analyzed using our proprietary wireless, miniaturized, and portable FET analyzer, coupled with a smartphone detecting app. Altogether, we present low-cost and mass-producible GFETs with high-quality graphene channels, enabling a portable, efficient, and accurate solution for point-of-care pathogen detection and in clinical testing. This technology has the potential to become a crucial tool in preventing future global epidemic outbreaks.

Nanophotonic biosensors for COVID-19 detection: advances in mechanisms, methods, and design

The growing societal impact of coronavirus disease 2019 (COVID-19) has underscored the urgent need for innovative strategies to address the ongoing challenges posed by the pandemic. While rapid therapeutic interventions remain critical for short-term mitigation, equally vital is the development of accessible and efficient diagnostic tools to curb viral transmission. In this context, optical sensing technologies have emerged as foundational tools for detection and diagnosis, owing to their rapid response, user-friendliness, and adaptability. These attributes strengthen their indispensable role in identifying severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19. This review systematically outlines the structural components of SARS-CoV-2 virions and their respective biological functions, classifies optical biosensors according to their underlying principles and evaluates the advantages and limitations of each methodology in real-world diagnostic applications. By addressing current detection challenges, these optical platforms not only enhance our capacity to manage SARS-CoV-2 but also establish a framework for deploying optical sensing technologies in future pandemic scenarios.

Highly parallel profiling of the activities and specificities of Cas12a variants in human cells

Several Cas12a variants have been developed to broaden its targeting range, improve the gene editing specificity or the efficiency. However, selecting the appropriate Cas12a among the many orthologs for a given target sequence remains difficult. Here, we perform high-throughput analyses to evaluate the activity and compatibility with specific PAMs of 24 Cas12a variants and develop deep learning models for these Cas12a variants to predict gene editing activities at target sequences of interest. Furthermore, we reveal and enhance the truncation in the integrated tag sequence that may hinder off-targeting detection for Cas12a by GUIDE-seq. This enhanced system, which we term enGUIDE-seq, is used to evaluate and compare the off-targeting and translocations of these Cas12a variants.

CRISPR/Cas-Based Prenatal Screening for Aneuploidy: Challenges and Opportunities for Early Diagnosis

Aneuploidy is increasingly recognized globally as a common cause of miscarriage among expectant mothers. The existing prenatal screening techniques for detecting aneuploidy have several limitations. The ability to diagnose aneuploidy early in a non-invasive manner is not feasible with the current screening methods, as they may produce false positive or false negative results. Recently, the widely used gene editing tool CRISPR/Cas has shown great promise in diagnostics. This review summarizes the prenatal screening tests used in the first trimester to assess aneuploidy conditions. Additionally, we discuss the advantages and disadvantages of molecular diagnostic tests, including the benefits and challenges of CRISPR/Cas-based trisomy detection. Thus, the proposed prenatal screening using CRISPR/Cas could provide significant benefits to expectant mothers by potentially enabling the early diagnosis of trisomy, helping to prevent miscarriage and birth defects. Furthermore, it opens new avenues for research, allowing clinicians and researchers to develop, optimize, and implement CRISPR/Cas-based prenatal screening assays in the future.

Recombinase-Controlled Multiphase Condensates Accelerate Nucleic Acid Amplification and CRISPR-Based Diagnostics

Isothermal techniques for amplifying nucleic acids have found extensive applications in genotyping and diagnostic tests. These methods can be integrated with sequence-specific detection strategies, such as CRISPR-based detection, for optimal diagnostic accuracy. In particular, recombinase-based amplification uses proteins from the Escherichia virus T4 recombination system and operates effectively at moderate temperatures in field and point-of-care settings. Here, we discover that recombinase polymerase amplification (RPA) is controlled by liquid-liquid phase separation, where the condensate formation enhances the nucleic acid amplification process. While two protein components of RPA could act as scaffold proteins for condensate formation, we identify T4 UvsX recombinase as the key regulator orchestrating distinct core-shell arrangements of proteins within multiphase condensates, with the intrinsically disordered C-terminus of UvsX being crucial for phase separation. We develop volumetric imaging assays to visualize RPA condensates and the reaction progression in whole volumes, and begin to dissect how macroscopic properties such as size distribution and droplet count could contribute to the overall reaction efficiency. Spatial organization of proteins in condensates may create optimal conditions for amplification, and disruption of such structures may diminish the amplification efficiency, as we demonstrate for the case of reverse transcription-RPA. The insight that RPA functions as a multiphase condensate leads us to identify the UvsXD274A mutant, which has a distinct phase-separation propensity compared to the wild-type enzyme and can enhance RNA detection via RPA-coupled CRISPR-based diagnostics.

Engineered CRISPR/Cas Ribonucleoproteins for Enhanced Biosensing and Bioimaging

CRISPR-Cas systems represent a highly programmable and precise nucleic acid-targeting platform, which has been strategically engineered as a versatile toolkit for biosensing and bioimaging applications. Nevertheless, their analytical performance is constrained by inherent functional and activity limitations of natural CRISPR/Cas systems, underscoring the critical role of molecular engineering in enhancing their capabilities. This review comprehensively examines recent advancements in engineering CRISPR/Cas ribonucleoproteins (RNPs) to enhance their functional capabilities for advanced molecular detection and cellular imaging. We explore innovative strategies for developing enhanced CRISPR/Cas RNPs, including Cas protein engineering through protein mutagenesis and fusion techniques, and guide RNA engineering via chemical and structural modifications. Furthermore, we evaluate these engineered RNPs' applications in sensitive biomarker detection and live-cell genomic DNA and RNA monitoring, while analyzing the current challenges and prospective developments in CRISPR-Cas RNP engineering for advanced biosensing and bioimaging.

Dithiothreitol Facilitates LbCas12a with Expanded PAM Preference for Ultrasensitive Nucleic Acid Detection

Clustered regularly interspaced short palindromic repeats-associated (CRISPR/Cas) proteins have been used for a growing class of in vitro molecular diagnostics due to their modularity and high specificity in targeting nucleic acid. However, the requirement of a protospacer adjacent motif (PAM) for Cas protein-catalyzed trans-cleavage poses a challenge for random nucleic acid detection. Here, we demonstrate that dithiothreitol (DTT) enables LbCas12a to adopt a relaxed preference for PAM base pairing, thereby expanding the target sequence space. Accordingly, we propose a DTT-mediated CRISPR/Cas12a toolbox (DTT-deCRISPR) that exhibits relaxed PAM specificity and is readily compatible with nucleic acid amplification techniques including recombinase polymerase amplification (RPA) and polymerase chain reaction (PCR). As a proof of concept, we integrate DTT-deCRISPR with frequently used PCR for sensitively and selectively detecting high-risk human papillomavirus (HPV) 16 and 18. The platform demonstrates the ability to detect synthesized HPV 16 and 18 plasmids down to 1 aM within 60 min. Based on the receiver operating characteristic curve analysis, the clinical sensitivities of the developed method for detecting HPV 16 and 18 are 93.75% and 80.00%, respectively. We further incorporate it into a lateral flow assay (LFA) for point-of-care detection, and the HPV 16 and HPV 18 abundances determined by LFA for clinical samples are consistent with the fluorescence analysis results. Together, this work uncovers an unexpected connection between DTT and PAM preferences of LbCas12a, promoting the universality and flexibility of CRISPR technology in molecular diagnostics.

Accurate Molecular Sensing based on a Modular and Customizable CRISPR/Cas-Assisted Nanopore Operational Nexus (CANON)

Solid-state nanopore is a promising single molecular detection technique, but is largely limited by relatively low resolution to small-size targets and laborious design of signaling probes. Here we establish a universal, CRISPR/Cas-Assisted Nanopore Operational Nexus (CANON), which can accurately transduce different targeting sources/species into different DNA structural probes via a "Signal-ON" mode. Target recognition activates the cleavage activity of a Cas12a/crRNA system and then completely digest the blocker of an initiator. The unblocked initiator then triggers downstream DNA assembly reaction and generate a large-size structure easy for nanopore detection. Such integration of Cas12a/crRNA with DNA assembly establishes an accurate correspondence among the input targets, output DNA structures, and the ultimate nanopore signals. We demonstrated dsDNA, long RNA (i.e., Flu virus gene), short microRNA (i.e., let-7d) and non-nucleic acids (i.e., Pb2+) as input paradigms. Various structural assembly reactions, such as hybridization chain reaction (HCR), G-HCR and duplex polymerization strategy (DPS), are adapted as outputs for nanopore signaling. Simultaneous assay is also verified via transferring FluA and FluB genes into HCR and G-HCR, respectively. CANON is thus a modular sensing platform holding multiple advantages such as high accuracy, high resolution and high universality, which can be easily customized into various application scenes.

Advances in Virus Biorecognition and Detection Techniques for the Surveillance and Prevention of Infectious Diseases

Viral infectious diseases pose a serious threat to global public health due to their high transmissibility, rapid mutation rates, and limited treatment options. Recent outbreaks of diseases such as plague, monkeypox, avian influenza, and coronavirus disease 2019 (COVID-19) have underscored the urgent need for efficient diagnostic and surveillance technologies. Focusing on viral infectious diseases that seriously threaten human health, this review summarizes and analyzes detection techniques from the perspective of combining viral surveillance and prevention advice, and discusses applications in improving diagnostic sensitivity and specificity. One of the major innovations of this review is the systematic integration of advanced biorecognition and detection technologies, such as bionanosensors, rapid detection test strips, and microfluidic platforms, along with the exploration of artificial intelligence in virus detection. These technologies address the limitations of traditional methods and enable the real-time monitoring and early warning of viral outbreaks. By analyzing the application of these technologies in the detection of pathogens, new insights are provided for the development of next-generation diagnostic tools to address emerging and re-emerging viral threats. In addition, we analyze the current progress of developed vaccines, combining virus surveillance with vaccine research to provide new ideas for future viral disease prevention and control and vaccine development, and call for global attention and the development of new disease prevention and detection technologies.

An RPA-CRISPR/Cas12a based platform for rapid, sensitive, and visual detection of Apis mellifera filamentous virus

Apis mellifera filamentous virus (AmFV) is an emerging DNA virus significantly affecting honey bee health. AmFV infections weaken bee resistance to other pathogens, and can cause tissue lysis and death. Early, accurate detection of AmFV is crucial for timely intervention and preventing large-scale outbreaks. Current AmFV detection relies largely on polymerase chain reaction (PCR)-based methods. To enable rapid field detection of AmFV, we developed a rapid and ultrasensitive detection platform using recombinase polymerase amplification (RPA) combined with clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated nuclease 12a (Cas12a) technology. A CRISPR RNA (crRNA1) specifically targeting the AmFV Bro gene was designed, ensuring no cross-reactivity with other insect DNA viruses or uninfected honey bees. After optimization of the reaction time, the platform generated results within 35 min: 20 min for the RPA reaction and 15 min for CRISPR-mediated cleavage. Two visualization approaches, fluorescence-based and lateral flow dipstick, were used to display the detection results. The detection sensitivity of both approaches was as few as 10 copies of the AmFV genome. Validation with field-collected honey bee samples demonstrated consistency with conventional PCR, revealing widespread latent AmFV infections in the field. Taken together, we successfully developed an RPA-CRISPR/Cas12 platform for rapid, specific, and sensitive detection of AmFV in Apis mellifera and Apis cerana. This platform holds promise as a simple, accurate, and cost-effective tool for point-of-care AmFV diagnosis in the field.

Amplification-free, OR-gated CRISPR-Cascade reaction for pathogen detection in blood samples

Rapid and accurate detection of DNA from disease-causing pathogens is essential for controlling the spread of infections and administering timely treatments. While traditional molecular diagnostics techniques like PCR are highly sensitive, they include nucleic acid amplification and many need to be performed in centralized laboratories, limiting their utility in point-of-care settings. Recent advances in CRISPR-based diagnostics (CRISPR-Dx) have demonstrated the potential for highly specific molecular detection, but the sensitivity is often constrained by the slow trans-cleavage activity of Cas enzymes, necessitating preamplification of target nucleic acids. In this study, we present a CRISPR-Cascade assay that overcomes these limitations by integrating a positive feedback loop that enables nucleic acid amplification-free detection of pathogenic DNA at atto-molar levels and achieves a signal-to-noise ratio greater than 1.3 within just 10 min. The versatility of the assay is demonstrated through the detection of bloodstream infection pathogens, including Methicillin-Sensitive Staphylococcus aureus (MSSA), Methicillin-Resistant Staphylococcus aureus (MRSA), Escherichia coli, and Hepatitis B Virus (HBV) spiked in whole blood samples. Additionally, we introduce a multiplexing OR-function logic gate, further enhancing the potential of the CRISPR-Cascade assay for rapid and accurate diagnostics in clinical settings. Our findings highlight the ability of the CRISPR-Cascade assay to provide highly sensitive and specific molecular detection, paving the way for advanced applications in point-of-care diagnostics and beyond.