Universal and Naked-Eye Gene Detection Platform Based on the Clustered Regularly Interspaced Short Palindromic Repeats/Cas12a/13a System

Capillarity-powered and CRISPR/Cas12a-responsive DNA hydrogel distance sensor for highly sensitive visual detection of HPV DNA

The rapid and specific identification and sensitive detection of human papillomavirus (HPV) infection is critical for preventing cervical cancer, particularly in resource-limited regions. In this work, we hope to propose a capillarity-powered and CRISPR/Cas12a-responsive DNA hydrogel distance sensor for point-of-care (POC) DNA testing. Using the thermal reversibility of DNA hydrogel and capillarity, the novel DNA hydrogel distance sensor can be rapidly and simply constructed by loading an ultra-thin CRISPR/Cas12a-responsive DNA-crosslinked hydrogel film at the end of the capillary tube. The target DNA-specific recombinase polymerase reaction (RPA) amplicons activate the trans-cleavage activity of the Cas12a enzyme, cleaving the crosslinked DNA in hydrogel film, and causing an increase of hydrogel's permeability. As a result, a sample solution containing target DNA travels into the capillary tube at a longer distance compared to the negative samples. Reading the solution traveling distance in capillary tubes, the novel sensor realizes target DNA detection without any special equipment. Benefiting from the exponential target amplification of RPA and multiple turnover response of trans-cleavage of CRISPR/Cas12a, the developed sensor can visually and specifically detect as low as 1 aM HPV 16 DNA within 30 min. These outstanding features, including exceptional sensitivity and specificity, simple and portable design, mild measurement conditions, quick turnaround time, and user-friendly read-out, make the novel distance sensor a promising option for POC diagnostic applications.

ddPCR Overcomes the CRISPR-Cas13a-Based Technique for the Detection of the BRAF p.V600E Mutation in Liquid Biopsies

The isolation of circulating tumoral DNA (ctDNA) present in the bloodstream brings about the opportunity to detect genomic aberrations from the tumor of origin. However, the low amounts of ctDNA present in liquid biopsy samples makes the development of highly sensitive techniques necessary to detect targetable mutations for the diagnosis, prognosis, and monitoring of cancer patients. Here, we employ standard genomic DNA (gDNA) and eight liquid biopsy samples from different cancer patients to examine the newly described CRISPR-Cas13a-based technology in the detection of the BRAF p.V600E actionable point mutation and appraise its diagnostic capacity with two PCR-based techniques: quantitative Real-Time PCR (qPCR) and droplet digital PCR (ddPCR). Regardless of its lower specificity compared to the qPCR and ddPCR techniques, the CRISPR-Cas13a-guided complex was able to detect inputs as low as 10 pM. Even though the PCR-based techniques have similar target limits of detection (LoDs), only the ddPCR achieved a 0.1% variant allele frequency (VAF) detection with elevated reproducibility, thus standing out as the most powerful and suitable tool for clinical diagnosis purposes. Our results also demonstrate how the CRISPR-Cas13a can detect low amounts of the target of interest, but its base-pair specificity failed in the detection of actionable point mutations at a low VAF; therefore, the ddPCR is still the most powerful and suitable technique for these purposes.

Recent advances in the CRISPR/Cas system-based visual detection method

Currently, various infectious pathogens and bacterial toxins as well as heavy metal pollution pose severe threats to global environmental health and the socio-economic infrastructure. Therefore, there is a pressing need for rapid, sensitive, and convenient visual molecular detection methods. The rapidly evolving detection approach based on clustered regularly interspaced short palindromic repeats (CRISPR)/associated nucleases (Cas) has opened a new frontier in the field of molecular diagnostics. This paper reviews the development of visual detection methods in recent years based on different Cas and analyzes their advantages and disadvantages as well as the challenges of future research. Firstly, different CRISPR/Cas effectors and their working principles in the diagnosis of various diseases are briefly reviewed. Subsequently, the article focuses on the development of visual readout signals in point-of-care testing using laboratory-based CRISPR/Cas technology, including colorimetric, fluorescence, and lateral flow analysis. Finally, the challenges and prospects of visual detection methods based on CRISPR/Cas technology are discussed.

CRISPR/Cas-mediated "one to more" lighting-up nucleic acid detection using aggregation-induced emission luminogens

CRISPR diagnostics are effective but suffer from low signal transduction efficiency, limited sensitivity, and poor stability due to their reliance on the trans-cleavage of single-stranded nucleic acid fluorescent reporters. Here, we present CrisprAIE, which integrates CRISPR/Cas reactions with "one to more" aggregation-induced emission luminogen (AIEgen) lighting-up fluorescence generated by the trans-cleavage of Cas proteins to AIEgen-incorporated double-stranded DNA labeled with single-stranded nucleic acid linkers and Black Hole Quencher groups at both ends (Q-dsDNA/AIEgens-Q). CrisprAIE demonstrates superior performance in the clinical nucleic acid detection of norovirus and SARS-CoV-2 regardless of amplification. Moreover, the diagnostic potential of CrisprAIE is further enhanced by integrating it with spherical nucleic acid-modified AIEgens (SNA/AIEgens) and a portable cellphone-based readout device. The improved CrisprAIE system, utilizing Q-dsDNA/AIEgen-Q and SNA/AIEgen reporters, exhibits approximately 80- and 270-fold improvements in sensitivity, respectively, compared to conventional CRISPR-based diagnostics. We believe CrisprAIE can be readily extended as a universal signal generation strategy to significantly enhance the detection efficiency of almost all existing CRISPR-based diagnostics.

CRISPR-Cas target recognition for sensing viral and cancer biomarkers

Nucleic acid-based diagnostics is a promising venue for detection of pathogens causing infectious diseases and mutations related to cancer. However, this type of diagnostics still faces certain challenges, and there is a need for more robust, simple and cost-effective methods. Clustered regularly interspaced short palindromic repeats (CRISPRs), the adaptive immune systems present in the prokaryotes, has recently been developed for specific detection of nucleic acids. In this review, structural and functional differences of CRISPR-Cas proteins Cas9, Cas12 and Cas13 are outlined. Thereafter, recent reports about applications of these Cas proteins for detection of viral genomes and cancer biomarkers are discussed. Further, we highlight the challenges associated with using these technologies to replace the current diagnostic approaches and outline the points that need to be considered for designing an ideal Cas-based detection system for nucleic acids.

Advances in plant pathogen detection: integrating recombinase polymerase amplification with CRISPR/Cas systems

Plant pathogens are causing substantial economic losses and thus became a significant threat to global agriculture. Effective and timely detection methods are prerequisite for combating the damages caused by the plant pathogens. In the realm of plant pathogen detection, the isothermal amplification techniques, e.g., recombinase polymerase amplification (RPA) and loop-mediated isothermal amplification (LAMP), have emerged as a fast, precise, and most sensitive alternative to conventional PCR but they often comprise high rates of non-specific amplification and operational complexity. In recent advancements, clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated nuclease Cas systems, particularly Cas12, have emerged as powerful tools for highly sensitive, specific, and rapid pathogen detection. Exploiting the collateral activities of Cas12, which selectively cleaves single-stranded DNA (ssDNA), novel detection platforms have been developed. The mechanism employs the formation of a triple complex molecule comprising guide RNA, Cas12 enzyme, and the substrate target nucleotide sequence. Upon recognition of the target, Cas12 indiscriminately cleaves the DNA strand, leading to the release of fluorescence from the cleaved ssDNA reporter. Integration of isothermal amplification methods with CRISPR/Cas12 enables one-step detection assays, facilitating rapid pathogen identification within 30 min at a single temperature. This integrated RPA-CRISPR/Cas12a approach eliminates the need for RNA extraction and cDNA conversion, allowing direct use of crude plant sap as a template. With an affordable fluorescence visualization system, this portable method achieves 100-fold greater sensitivity than conventional techniques. This review summarizes recent advances in RPA-CRISPR/Cas12a for detecting plant pathogens, covering primer design, field-level portability, and enhanced sensitivity.

Paper-based analytical device for point-of-care nucleic acid quantification combining CRISPR/Cas12a and a personal glucose meter

Although CRISPR-based nucleic acid detection has great potential in point-of-care testing due to its simplicity, it has been rarely integrated into paper-based analytical devices (PADs), which are attractive platforms to simplify assays. This work introduces a CRISPR-assisted nucleic acid quantification approach integrated into a PAD with signal readout by a personal glucose meter (PGM). Retention of magnetic beads by filter paper and pre-deposition of all required reagents by freeze-drying stabilized with trehalose enabled the indirect quantification of human papilloma virus (HPV) DNA through a PGM readout without complicated user intervention and complex reagent handling. The calculated limit of detection was 57 pM, which is comparable with other amplification-free CRISPR-based assays detecting nucleic acids. The fully integrated device exhibited good storage stability for up to 4 weeks, suggesting its applicability toward practical point-of-care nucleic acid quantification.

CRISPR/Cas13a-assisted amplification-free miRNA biosensor via dark-field imaging and magnetic gold nanoparticles

MicroRNAs (miRNAs) are short (about 18-24 nucleotides) non-coding RNAs and have emerged as potential biomarkers for various diseases, including cancers. Due to their short lengths, the specificity often becomes an issue in conventional amplification-based methods. Next-generation sequencing techniques could be an alternative, but the long analysis time and expensive costs make them less suitable for routine clinical diagnosis. Therefore, it is essential to develop a rapid, selective, and accurate miRNA detection assay using a simple, affordable system. In this work, we report a CRISPR/Cas13a-based miRNA biosensing using point-of-care dark-field (DF) imaging. We utilized magnetic-gold nanoparticle (MGNPs) complexes as signal probes, which consist of 200 nm-sized magnetic beads and 60 nm-sized gold nanoparticles (AuNPs) linked by DNA hybridization. Once the CRISPR/Cas13a system recognized the target miRNAs (miR-21-5p), the activated Cas13a cleaved the bridge linker containing RNA sequences, releasing 60 nm-AuNPs detected and quantified by a portable DF imaging system. The combination of CRISPR/Cas13a, MGNPs, and DF imaging demonstrated amplification-free detection of miR-21-5p within 30 min at a detection limit of 500 attomoles (25 pM) and with single-base specificity. The CRISPR/Cas13a-assisted MGNP-DF assay achieved rapid, selective, and accurate detection of miRNAs with simple equipment, thus providing a potential application for cancer diagnosis.

CRISPR-Based Gene Editing: a Modern Approach for Study and Treatment of Cancer

The development and emergence of clustered regularly interspaced short palindromic repeats (CRISPR) as a genome-editing technology have created a plethora of opportunities in genetic engineering. The ability of sequence-specific addition or removal of DNA in an efficient and cost-effective manner has revolutionized modern research in the field of life science and healthcare. CRISPR is widely used as a genome engineering tool in clinical studies for observing gene expression and metabolic pathway regulations in detail. Even in the case of transgenic research and personalized gene manipulation studies, CRISPR-based technology is used extensively. To understand and even to correct the underlying genetic problem is of cancer, CRISPR-based technology can be used. Various kinds of work is going on throughout the world which are attempting to target different genes in order to discover novel and effective methodologies for the treatment of cancer. In this review, we provide a brief overview on the application of CRISPR gene editing technology in cancer treatment focusing on the key aspects of cancer screening, modelling and therapy techniques.

Ratiometric nonfluorescent CRISPR assay utilizing Cas12a-induced plasmid supercoil relaxation

Most CRISPR-based biosensors rely on labeled reporter molecules and expensive equipment for signal readout. A recent approach quantifies analyte concentration by sizing λ DNA reporters via gel electrophoresis, providing a simple solution for label-free detection. Here, we report an alternative strategy for label-free CRISPR-Cas12a, which relies on Cas12a trans-nicking induced supercoil relaxation of dsDNA plasmid reporters to generate a robust and ratiometric readout. The ratiometric CRISPR (rCRISPR) measures the relative percentage of supercoiled plasmid DNA to the relaxed circular DNA by gel electrophoresis for more accurate target concentration quantification. This simple method is two orders of magnitude more sensitive than the typical fluorescent reporter. This self-referenced strategy solves the potential application limitations of previously demonstrated DNA sizing-based CRISPR-Dx without compromising the sensitivity. Finally, we demonstrated the applicability of rCRISPR for detecting various model DNA targets such as HPV 16 and real AAV samples, highlighting its feasibility for point-of-care CRISPR-Dx applications.

Sensitive and on-Site Detection of Staphylococcus aureus Based on CRISPR/Cas 13a-Assisted Chemiluminescence Resonance Energy Transfer

Developing a specific, sensitive, rapid, and on-site method for detecting pathogenic bacteria in food samples is critical to ensuring public safety. This article demonstrates a CRISPR/Cas13a system and a chemiluminescence resonance energy transfer (CRET) (CRISPR/Cas 13a-assisted CRET)-based strategy for sensitive and on-site detection of pathogenic bacteria in real samples. Once the hybrid double strand of aptamerS. aureus-cRNA recognizes the target model bacteria of Staphylococcus aureus (S. aureus), the released cRNA would bind with CRISPR/Cas 13a to form a complex of cRNA-CRISPR/Cas 13a, which could cleave the RNA molecule in the detecting probe of horseradish peroxidase (HRP) modified-gold nanoparticles (AuNPs) linked by RNA (AuNPs-RNA-HRP), resulting in an enhanced chemiluminescence signal due to the CRET "OFF" phenomenon after introducing the chemiluminescence substrate of luminol. The CRISPR/Cas 13a-assisted CRET strategy successfully detected S. aureus in drinking water and milk with detection limits of 20 and 30 cfu/mL, respectively, within the recovery of 90.07-105.50%. Furthermore, after integrating with an immunochromatographic test strip (ICTS), the CRISPR/Cas 13a-assisted CRET strategy achieved the on-site detection of as low as 102 cfu/mL of S. aureus in drinking water and milk via a smartphone, which is about 10 times lower than that in the previously reported AuNPs-based colorimetric ICTS, demonstrating a convenient and sensitive detection method for S. aureus in real samples.

Electrochemiluminescence aptasensing method for ultrasensitive determination of lipopolysaccharide based on CRISPR-Cas12a accessory cleavage activity

In this study, an ultrasensitive electrochemiluminescence (ECL) aptasensing method was developed for lipopolysaccharide (LPS) determination based on CRISPR-Cas12a accessory cleavage activity. Tris (2,2'-bipyridine) dichlororuthenium (II) (Ru(bpy)32+) was adsorbed on the surface of a glassy carbon electrode (GCE) coated with a mixture of gold nanoparticles (AuNPs) and Nafion film via electrostatic interaction. The obtained ECL platform (Ru(bpy)32+/AuNP/Nafion/GCE) exhibited strong ECL emission. Thiol-functionalized single-stranded DNA (ssDNA) was modified with a ferrocenyl (Fc) group and autonomously assembled on the ECL platform of Ru(bpy)32+/AuNP/Nafion/GCE via thiol-gold bonding, resulting in the quenching of ECL emission. After hybridization of the LPS aptamer strand (AS) with its partial complementary strand (CS), the formed double-stranded DNA (dsDNA) could activate CRISPR-Cas12a to indiscriminately cleave ssDNA-Fc on the surface of Ru(bpy)32+/AuNP/Nafion/GCE, resulting in recovery of the ECL intensity of Ru(bpy)32+ due to the increasing distance between Fc and the electrode surface. The combination of LPS and AS suppressed the formation of dsDNA, inhibited the activation of CRISPR-Cas12a, and prevented further cleavage of ssDNA-Fc. This mechanism aided in upholding the integrity of ssDNA-Fc on the surface of the electrode and was combined with ECL quenching induced by the target. The ECL intensity decreased linearly as the concentration of LPS increased from 1 to 50,000 pg/mL and followed a logarithmic relationship. This method exhibited a remarkably low detection limit of 0.24 pg/mL, which meets the requirement for low-concentration detection of LPS in the human body. The proposed method demonstrates the capacity of CRISPR-Cas12a to perform non-specific cutting of single-stranded DNA and transform the resultant cutting substances into changes in the ECL signal. By amalgamating this approach with the distinct identification abilities of LPS and its aptamers, a simple, responsive, and discriminatory LPS assay was established that holds immense significance for clinical diagnosis.

Stimuli-responsive incremental DNA machine auto-catalyzed CRISPR-Cas12a feedback amplification permits ultrasensitive molecular diagnosis of esophageal cancer-related microRNA

Development of new diagnostic methods is essential for disease diagnosis and treatment. In this work, we present a stimuli-responsive incremental DNA machine auto-catalyzed CRISPR-Cas12a (SRI-DNA machine/CRISPR-Cas12a) feedback amplification for ultrasensitive molecular detection of miRNA-21, which is an important biomarker related closely to the initiation and development of cancers, such as esophageal cancer. Strategically, the powerful SRI-DNA machine and efficient trans-cleavage activity of the CRISPR-Cas12a system are ingeniously integrated via a rationally designed probe termed as stem-elongated functional hairpin probe (SEF-HP). The SRI-DNA machine begins with the target miRNA, the trigger of the reaction, binding complementarily to the SEF-HP, followed by autonomously performed mechanical strand replication, cleavage, and displacement circuit at multiple sites. This conversion process led to the amplified generation of numerous DNA activators that are complementary with CRISPR RNA (CrRNA). Once formed the DNA activator/CrRNA heteroduplex, the trans-cleavage activity of the CRISPR-Cas12a was activated to nonspecific cleavage of single-stranded areas of a reporter probe for fluorescence emission. Under optimal conditions, the target miRNA can be detected with a wide linear range and an excellent specificity. As a proof-of-concept, this SRI-DNA machine/CRISPR-Cas12a feedback amplification system is adaptable and scalable to higher-order artificial amplification circuits for biomarkers detection, highlighting its promising potential in early diagnosis and disease treatment.

A MoS2 nanosheet-based CRISPR/Cas12a biosensor for efficient miRNA quantification for acute myocardial infarction

Acute myocardial infarction (AMI) represents the leading cause of cardiovascular death worldwide, and it is thus pivotal to develop effective approaches for the timely detection of AMI markers, especially possessing the characteristics of antibody-free, signal amplification, and manipulation convenience. We herein construct a MoS2 nanosheet-powered CRISPR/Cas12a sensing strategy for sensitive determination of miR-499, a superior AMI biomarker to protein markers. The presence of miR-499 at a trace level is able to induce a significantly enhanced fluorescence signal in a DNA-based molecular engineering platform, which consists of CRISPR/Cas12a enzymatic reactions and MoS2 nanosheet-controllable signal reporting components. The MoS2 nanosheets were characterized by using atomic force microscopy (AFM) and transmission electron microscope (TEM). The detection feasibility was verified by using polyacrylamide gel electrophoresis (PAGE) analysis and fluorescence measurements. The detection limit is determined as 381.78 pM with the linear range from 0.1 ⅹ 10-9 to 13.33 ⅹ 10-9 M in a fast manner (about 30 min). Furthermore, miRNA detection in real human serum is also conducted with desirable recovery rates (89.5 %-97.6 %), which may find potential application for the clinic diagnosis. We describe herein the first example of MoS2 nanosheet-based signal amplified fluorescence sensor for effective detection of AMI-related miRNA.

Enhancing Point-of-Care Diagnosis of African Swine Fever Virus (ASFV) DNA with the CRISPR-Cas12a-Assisted Triplex Amplified Assay

Accurate, ultrasensitive, and point-of-care (POC) diagnosis of the African swine fever virus (ASFV) remains imperative to prevent its spread and limit the losses incurred. Herein, we propose a CRISPR-Cas12a-assisted triplex amplified colorimetric assay for ASFV DNA detection with ultrahigh sensitivity and specificity. The specific recognition of recombinase aided amplification (RAA)-amplified ASFV DNA could activate the Cas12a/crRNA/ASFV DNA complex, leading to the digestion of the linker DNA (bio-L1) on magnetic beads (MBs), thereby preventing its binding of gold nanoparticles (AuNPs) network. After magnetic separation, the release of AuNPs network comprising a substantial quantity of AuNPs could lead to a discernible alteration in color and significantly amplify the plasmonic signal, which could be read by spectrophotometers or smartphones. By combining the RAA, CRISPR/Cas12a-assisted cleavage, and AuNPs network-mediated colorimetric amplification together, the assay could detect as low as 0.1 copies/μL ASFV DNA within 1 h. The assay showed an accuracy of 100% for the detection of ASFV DNA in 16 swine tissue fluid samples, demonstrating its potential for on-site diagnosis of ASFV.

CRISPR/Cas systems combined with DNA nanostructures for biomedical applications

DNA nanostructures are easy to design and construct, have good biocompatibility, and show great potential in biosensing and drug delivery. Numerous distinctive and versatile DNA nanostructures have been developed and explored for biomedical applications. In addition to DNA nanostructures that are completely assembled from DNA, composite DNA nanostructures obtained by combining DNA with other organic or inorganic materials are also widely used in related research. The CRISPR/Cas system has attracted great attention as a powerful gene editing technology and is also widely used in biomedical diagnosis. Many researchers are committed to exploring new possibilities by combining DNA nanostructures with CRISPR/Cas systems. These explorations provide support for the development of new detection methods and cargo delivery pathways, provide inspiration for improving relevant gene editing platforms, and further expand the application scope of DNA nanostructures and CRISPR/Cas systems. This paper mainly reviews the design principles and biomedical applications of CRISPR/Cas combined with DNA nanostructures based on the types of DNA nanostructures. Finally, the application status, challenges and development prospects of CRISPR/Cas combined with DNA nanostructures in detection and delivery are summarized. It is expected that this review will enable researchers to better understand the current state of the field and provide insights into the application of CRISPR/Cas systems and the development of DNA nanostructures.

Detection of Parasites in the Field: The Ever-Innovating CRISPR/Cas12a

The rapid and accurate identification of parasites is crucial for prompt therapeutic intervention in parasitosis and effective epidemiological surveillance. For accurate and effective clinical diagnosis, it is imperative to develop a nucleic-acid-based diagnostic tool that combines the sensitivity and specificity of nucleic acid amplification tests (NAATs) with the speed, cost-effectiveness, and convenience of isothermal amplification methods. A new nucleic acid detection method, utilizing the clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) nuclease, holds promise in point-of-care testing (POCT). CRISPR/Cas12a is presently employed for the detection of Plasmodium falciparum, Toxoplasma gondii, Schistosoma haematobium, and other parasites in blood, urine, or feces. Compared to traditional assays, the CRISPR assay has demonstrated notable advantages, including comparable sensitivity and specificity, simple observation of reaction results, easy and stable transportation conditions, and low equipment dependence. However, a common issue arises as both amplification and cis-cleavage compete in one-pot assays, leading to an extended reaction time. The use of suboptimal crRNA, light-activated crRNA, and spatial separation can potentially weaken or entirely eliminate the competition between amplification and cis-cleavage. This could lead to enhanced sensitivity and reduced reaction times in one-pot assays. Nevertheless, higher costs and complex pre-test genome extraction have hindered the popularization of CRISPR/Cas12a in POCT.

Photoactivatable CRISPR/Cas12a Sensors for Biomarkers Imaging and Point-of-Care Diagnostics

In recent years, the CRISPR/Cas12a-based sensing strategy has shown significant potential for specific target detection due to its rapid and sensitive characteristics. However, the "always active" biosensors are often insufficient to manipulate nucleic acid sensing with high spatiotemporal control. It remains crucial to develop nucleic acid sensing devices that can be activated at the desired time and space by a remotely applied stimulus. Here, we integrated photoactivation with the CRISPR/Cas12a system for DNA and RNA detection, aiming to provide high spatiotemporal control for nucleic acid sensing. By rationally designing the target recognition sequence, this photoactivation CRISPR/Cas12a system could recognize HPV16 and survivin, respectively. We combined the lateral flow assay strip test with the CRISPR/Cas12a system to realize the visualization of nucleic acid cleavage signals, displaying potential instant test application capabilities. Additionally, we also successfully realized the temporary control of its fluorescent sensing activity for survivin by photoactivation in vivo, allowing rapid detection of target nucleic acids and avoiding the risk of contamination from premature leaks during storage. Our strategy suggests that the CRISPR/Cas12a platform can be triggered by photoactivation to sense various targets, expanding the technical toolbox for precise biological and medical analysis. This study represents a significant advancement in nucleic acid sensing and has potential applications in disease diagnosis and treatment.

Recent progress on the CRISPR/Cas system in optical biosensors

Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) protein systems are adaptive immune systems unique to archaea and bacteria, with the characteristics of targeted recognition and gene editing to resist the invasion of foreign nucleic acids. Biosensors combined with the CRISPR/Cas system and optical detection technology have attracted much attention in medical diagnoses, food safety, agricultural progress, and environmental monitoring owing to their good sensitivity, high selectivity, and fast detection efficiency. In this review, we introduce the mechanism of CRISPR/Cas systems and developments in this area, followed by summarizing recent progress on CRISPR/Cas system-based optical biosensors combined with colorimetric, fluorescence, electrochemiluminescence and surface-enhanced Raman scattering optical techniques in various fields. Finally, we discuss the challenges and future perspectives of CRISPR/Cas systems in optical biosensors.

CRISPR-Cas12a-mediated dual-enzyme cascade amplification for sensitive colorimetric detection of HPV-16 target and ATP

The establishment of sensitive and facile colorimetric platform based on the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated) system is of great significance for in vitro diagnosis. Herein, we develop a dual-enzyme cascade amplification strategy based on CRISPR-Cas12a and glucose oxidase (GOx) for instrument-free and sensitive detection of target analytes. HPV-16 DNA as the model nucleic acid target directly initiated CRISPR-Cas12a-based signal transduction, resulting in the enzymatic cleavage of ssDNA linker and the release of GOx from magnetic nanoparticles 1 (MNPs1). Following simple magnetic separation, the supernatant containing GOx was taken out and used to catalyze the substrate, resulting in a visually detectable color change. The detection limit (LOD) of HPV-16 DNA was as low as 1 pM, and the entire process could be completed within 70 min without the need for expensive equipment. Notably, the dual-enzyme cascade amplification strategy was successfully applied to the detection of non-nucleic acid targets, such as ATP, via a simple signal transduction process. The visual LOD for ATP detection reaches 2.5 μM. The approach provides a robust, sensitive and reliable point-of-care biosensing platform for the detection of target analytes.

CRISPR/Cas-Powered Amplification-Free Detection of Nucleic Acids: Current State of the Art, Challenges, and Futuristic Perspectives

CRISPR/Cas system is becoming an increasingly influential technology that has been repositioned in nucleic acid detection. A preamplification step is usually required to improve the sensitivity of CRISPR/Cas-based detection. The striking biological features of CRISPR/Cas, including programmability, high sensitivity and sequence specificity, and single-base resolution. More strikingly, the target-activated trans-cleavage could act as a biocatalytic signal transductor and amplifier, thereby empowering it to potentially perform nucleic acid detection without a preamplification step. The reports of such work are on the rise, which is not only scientifically significant but also promising for futuristic end-user applications. This review started with the introduction of the detection methods of nucleic acids and the CRISPR/Cas-based diagnostics (CRISPR-Dx). Next, we objectively discussed the pros and cons of preamplification steps for CRISPR-Dx. We then illustrated and highlighted the recently developed strategies for CRISPR/Cas-powered amplification-free detection that can be realized through the uses of ultralocalized reactors, cascade reactions, ultrasensitive detection systems, or others. Lastly, the challenges and futuristic perspectives were proposed. It can be expected that this work not only makes the researchers better understand the current strategies for this emerging field, but also provides insight for designing novel CRISPR-Dx without a preamplification step to win practicable use in the near future.

Discovery of Diverse CRISPR-Cas Systems and Expansion of the Genome Engineering Toolbox

CRISPR systems mediate adaptive immunity in bacteria and archaea through diverse effector mechanisms and have been repurposed for versatile applications in therapeutics and diagnostics thanks to their facile reprogramming with RNA guides. RNA-guided CRISPR-Cas targeting and interference are mediated by effectors that are either components of multisubunit complexes in class 1 systems or multidomain single-effector proteins in class 2. The compact class 2 CRISPR systems have been broadly adopted for multiple applications, especially genome editing, leading to a transformation of the molecular biology and biotechnology toolkit. The diversity of class 2 effector enzymes, initially limited to the Cas9 nuclease, was substantially expanded via computational genome and metagenome mining to include numerous variants of Cas12 and Cas13, providing substrates for the development of versatile, orthogonal molecular tools. Characterization of these diverse CRISPR effectors uncovered many new features, including distinct protospacer adjacent motifs (PAMs) that expand the targeting space, improved editing specificity, RNA rather than DNA targeting, smaller crRNAs, staggered and blunt end cuts, miniature enzymes, promiscuous RNA and DNA cleavage, etc. These unique properties enabled multiple applications, such as harnessing the promiscuous RNase activity of the type VI effector, Cas13, for supersensitive nucleic acid detection. class 1 CRISPR systems have been adopted for genome editing, as well, despite the challenge of expressing and delivering the multiprotein class 1 effectors. The rich diversity of CRISPR enzymes led to rapid maturation of the genome editing toolbox, with capabilities such as gene knockout, base editing, prime editing, gene insertion, DNA imaging, epigenetic modulation, transcriptional modulation, and RNA editing. Combined with rational design and engineering of the effector proteins and associated RNAs, the natural diversity of CRISPR and related bacterial RNA-guided systems provides a vast resource for expanding the repertoire of tools for molecular biology and biotechnology.

Enhancement and inactivation effect of CRISPR/Cas12a via extending hairpin activators for detection of transcription factors

An enhancement effect for the activation of CRISPR/Cas12a (CRISPR = clustered regularly interspaced short palindromic repeats; Cas = CRISPR-associated) was discovered. That was, a hairpin model with dangling 5' end complementary to crRNA (CRISPR RNA) greatly improved the activity of CRISPR/Cas12a after extention of two random sequences. But, the corresponding intact hairpin without PAM (protospacer adjacent motif) or suboptimal PAM sequences was completely inactive to CRISPR/Cas12a because of the superhigh stability of intact hairpin. According to the finding, a CRISPR/Cas12a-based strategy coupled with a signal reported system was designed for transcription factors detection. By using mono-labeled ssDNA (single-stranded DNA) as reporter and two newly synthesized N-C (nitrogen-doped carbon) nanosheets as scavenger to eliminate the fluorescent background, the strategy realized the detection of NF-ĸB p50 (p50 subunit of nuclear factor kappa-B) with a linear detection range of 0.8 - 2000.0 pM and a LOD of 0.5 pM. The discovery of "enhancement and inactivation effect" not only deepened insight into CRISPR/Cas12a but also broadened the practical application of CRISPR/Cas systems for the molecular detection and disease diagnostics.

Enhancing CRISPR/Cas systems with nanotechnology

CRISPR/Cas systems have revolutionized biology and medicine, and have led to new paradigms in disease diagnostics and therapeutics. However, these complexes suffer from key limitations regarding barriers to cellular entry, stability in biological environments, and off-target effects. Integrating nanotechnology with CRISPR/Cas systems has emerged as a promising strategy to overcome these challenges and has further unlocked structures that accumulate preferentially in tissues of interest, have tunable pharmacological properties, and are activated in response to desired stimuli. Nanomaterials can also enhance CRISPR/Cas-mediated detection platforms by enabling faster, more sensitive, and convenient readouts. We highlight recent advances in this rapidly growing field. We also outline areas that need further development to fully realize the potential of CRISPR technologies.

Development of a separation platform comprising magnetic beads combined with the CRISPR/Cas12a system enabling ultrasensitive and rapid detection of miRNA-21

A separation platform has been developed mediated by a combination of magnetic beads and the CRISPR/Cas12a system to achieve ultrasensitive and rapid detection of miRNA-21 at a low level. In this system, with the assistance of an auxiliary probe, the target miRNA-21 can be specifically combined with three-stranded probes to initiate the SDR reaction. Abundant aptamer A3 was added to the solution that can activate the CRISPR/Cas12a system and initiate the trans-cleavage reaction to recover the fluorescence signal. Using magnetic beads to mediate the separation considerably greatly improves the signal conversion efficiency and detection sensitivity. At the 492 nm excitation wavelength, and 502-650 nm scan range, through analyzing the fluorescence peak intensity at 520 nm, the biosensor's determination range and limit of detection is 8 fM-250 nM and 2.42 fM, respectively, and the RSD is 19.03-37.80. Compared with other biosensors, the biosensor developed exhibited superior performance and the signal recovered excellently in 1% human serum and the LOD is 12.12 fM. This method provides a novel highly sensitive scheme for detecting miRNA .

Progress of CRISPR-based programmable RNA manipulation and detection

Prokaryotic clustered regularly interspaced short palindromic repeats and CRISPR associated (CRISPR-Cas) systems provide adaptive immunity by using RNA-guided endonucleases to recognize and eliminate invading foreign nucleic acids. Type II Cas9, type V Cas12, type VI Cas13, and type III Csm/Cmr complexes have been well characterized and developed as programmable platforms for selectively targeting and manipulating RNA molecules of interest in prokaryotic and eukaryotic cells. These Cas effectors exhibit remarkable diversity of ribonucleoprotein (RNP) composition, target recognition and cleavage mechanisms, and self discrimination mechanisms, which are leveraged for various RNA targeting applications. Here, we summarize the current understanding of mechanistic and functional characteristics of these Cas effectors, give an overview on RNA detection and manipulation toolbox established so far including knockdown, editing, imaging, modification, and mapping RNA-protein interactions, and discuss the future directions for CRISPR-based RNA targeting tools. This article is categorized under: RNA Methods > RNA Analyses in Cells RNA Processing > RNA Editing and Modification RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

Unidirectional trans-cleaving behavior of CRISPR-Cas12a unlocks for an ultrasensitive assay using hybrid DNA reporters containing a 3' toehold

CRISPR-Cas12a can induce nonspecific trans-cleavage of dsDNA substrate, including long and stable λ DNA. However, the mechanism behind this is still largely undetermined. In this study, we observed that while trans-activated Cas12a didn't cleave blunt-end dsDNA within a short reaction time, it could degrade dsDNA reporters with a short overhang. More interestingly, we discovered that the location of the overhang also affected the susceptibility of dsDNA substrate to trans-activated Cas12a. Cas12a trans-cleaved 3' overhang dsDNA substrates at least 3 times faster than 5' overhang substrates. We attributed this unique preference of overhang location to the directional trans-cleavage behavior of Cas12a, which may be governed by RuvC and Nuc domains. Utilizing this new finding, we designed a new hybrid DNA reporter as nonoptical substrate for the CRISPR-Cas12a detection platform, which sensitively detected ssDNA targets at sub picomolar level. This study not only unfolded new insight into the trans-cleavage behavior of Cas12a but also demonstrated a sensitive CRISPR-Cas12a assay by using a hybrid dsDNA reporter molecule.

Bridging the Gap: Can COVID-19 Research Help Combat African Swine Fever?

African swine fever (ASF) is a highly contagious and economically devastating disease affecting domestic pigs and wild boar, caused by African swine fever virus (ASFV). Despite being harmless to humans, ASF poses significant challenges to the swine industry, due to sudden losses and trade restrictions. The ongoing COVID-19 pandemic has spurred an unparalleled global research effort, yielding remarkable advancements across scientific disciplines. In this review, we explore the potential technological spillover from COVID-19 research into ASF. Specifically, we assess the applicability of the diagnostic tools, vaccine development strategies, and biosecurity measures developed for COVID-19 for combating ASF. Additionally, we discuss the lessons learned from the pandemic in terms of surveillance systems and their implications for managing ASF. By bridging the gap between COVID-19 and ASF research, we highlight the potential for interdisciplinary collaboration and technological spillovers in the battle against ASF.

Ultra-sensitive electrochemiluminescent biosensor for miRNA based on CRISPR/Cas13a trans-cleavage-triggered hybridization chain reaction and magnetic-assisted enrichment

The great selectivity and trans-cleavage activity of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas13a had been coupled with high amplification efficiency of hybridization chain reaction (HCR) and magnetic-assisted enrichment, high sensitivity of electrochemiluminescence (ECL) detection to develop an ultra-sensitive biosensor for microRNA-21 (miRNA-21). The CRISPR/Cas13a was used to recognize target RNA with high specificity and performed the trans-cleavage activity. An initiation strand was generated to bind to the probe on the surface of nanomagnetic beads and then trigged HCR to produce long double-strand DNAs (dsDNAs) to realize signal amplification. Ru(phen)32+ can be inserted in the groove of the dsDNAs and acts as the ECL indicator, which can be separated through magnetic enrichment and allowed the platform to reduce the signal background. Under the optimized conditions, there is a good linear correlation between the ECL intensity and the logarithm of miRNA-21 concentration in the range 1 fM-10 nM; the limit of detection (LOD) was 0.53 fM. The proposed system was applied to detect miRNA-21 from the urine of acute kidney injury (AKI) patients with good results.

CRISPR/Cas-Based Diagnostics in Agricultural Applications

Pests and disease-causing pathogens frequently impede agricultural production. An early and efficient diagnostic tool is crucial for effective disease management. Clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR-associated protein (Cas) have recently been harnessed to develop diagnostic tools. The CRISPR/Cas system, composed of the Cas endonuclease and guide RNA, enables precise identification and cleavage of the target nucleic acids. The inherent sensitivity, high specificity, and rapid assay time of the CRISPR/Cas system make it an effective alternative for diagnosing plant pathogens and identifying genetically modified crops. Furthermore, its potential for multiplexing and suitability for point-of-care testing at the field level provide advantages over traditional diagnostic systems such as RT-PCR, LAMP, and NGS. In this review, we discuss the recent developments in CRISPR/Cas based diagnostics and their implications in various agricultural applications. We have also emphasized the major challenges with possible solutions and provided insights into future perspectives and potential applications of the CRISPR/Cas system in agriculture.

A cathodic photoelectrochemical biosensor based on CRISPR/Cas12a trans-cleavage mediated p-n heterojunction quenching mode for microRNA determination

In this study, a cathodic photoelectrochemical (PEC) bioanalysis for sensitive determination of microRNA (miRNA) has been constructed based on CRISPR/Cas12a trans-cleavage mediated [(C6)₂Ir(dcbpy)]⁺PF₆^- (C6 represents coumarin-6 and dcbpy represents 4,4'-dicarboxyl-2,2'-bipyridine)-sensitized NiO photocathode and p-n heterojunction quenching mode. The [(C6)₂Ir(dcbpy)]⁺PF₆^--sensitized NiO photocathode exhibits a stable and dramatically improved photocurrent signal due to highly effective photosensitization of [(C6)₂Ir(dcbpy)]⁺ PF₆^-. Then Bi₂S₃ quantum dots (Bi₂S₃ QDs) is captured on the photocathode, resulting in markedly quenching of the photocurrent. When target miRNA is specifically recognized by the hairpin DNA to stimulate the trans-cleavage activity of CRISPR/Cas12a, leading to the leave of the Bi₂S₃ QDs. The photocurrent is gradually recovered with the increasing target concentration. Thus, the quantitative signal response to target is achieved. Benefiting from excellent performance of NiO photocathode, intense quenching effect of p-n heterojunction and accurate recognition ability of CRISPR/Cas12a, the cathodic PEC biosensor shows a wider linear range over 0.1 fM-10 nM, with a low detection limit of 36 aM. Also, the biosensor exhibits satisfying stability and selectivity.

Advances in Point-of-Care Testing of microRNAs Based on Portable Instruments and Visual Detection

MicroRNAs (miRNAs) are a class of small noncoding RNAs that are approximately 22 nt in length and regulate gene expression post-transcriptionally. miRNAs play a vital role in both physiological and pathological processes and are regarded as promising biomarkers for cancer, cardiovascular diseases, neurodegenerative diseases, and so on. Accurate detection of miRNA expression level in clinical samples is important for miRNA-guided diagnostics. However, the common miRNA detection approaches like RNA sequencing, qRT-PCR, and miRNA microarray are performed in a professional laboratory with complex intermediate steps and are time-consuming and costly, challenging the miRNA-guided diagnostics. Hence, sensitive, highly specific, rapid, and easy-to-use detection of miRNAs is crucial for clinical diagnosis based on miRNAs. With the advantages of being specific, sensitive, efficient, cost-saving, and easy to operate, point-of-care testing (POCT) has been widely used in the detection of miRNAs. For the first time, we mainly focus on summarizing the research progress in POCT of miRNAs based on portable instruments and visual readout methods. As widely available pocket-size portable instruments and visual detection play important roles in POCT, we provide an all-sided discussion of the principles of these methods and their main limitations and challenges, in order to provide a guide for the development of more accurate, specific, and sensitive POCT methods for miRNA detection.

Dual-amplification system based on CRISPR-Cas12a and horseradish peroxidase-tethered magnetic microspheres for colorimetric detection of microcystin-LR

A novel dual-amplification system based on CRISPR-Cas12a and horseradish peroxidase (HRP) was developed for colorimetric determination of MC-LR. This dual-amplification was accomplished by combining the nuclease activity of CRISPR-Cas12a with the redox activity of HRP. HRP linked to magnetic beads through an ssDNA (MB-ssDNA-HRP) was used to induce a color change of the 3,3',5,5'-tetramethylbenzidine (TMB)-H₂O₂ chromogenic substrate solution. Specific binding of MC-LR with its aptamer initiated the release of a complementary DNA (cDNA), which was designed to activate the trans-cleavage activity of CRISPR-Cas12a. Upon activation, Cas12a cut the ssDNA linker in MB-ssDNA-HRP, causing a reduction of HRP on the magnetic beads. Consequently, the UV-Vis absorbance of the HRP-catalyzed reaction was decreased. The dual-signal amplification facilitated by CRISPR-Cas12a and HRP enabled the colorimetric detection of MC-LR in the range 0.01 to 50 ng·mL^-1 with a limit of detection (LOD) of 4.53 pg·mL^-1. The practicability of the developed colorimetric method was demonstrated by detecting different levels of MC-LR in spiked real water samples. The recoveries ranged from 86.2 to 118.5% and the relative standard deviation (RSD) was 8.4 to 17.6%. This work provides new inspiration for the construction of effective signal amplification platforms and demonstrates a simple and user-friendly colorimetric method for determination of trace MC-LR.

CRISPR Assays for Disease Diagnosis: Progress to and Barriers Remaining for Clinical Applications

Numerous groups have employed the special properties of CRISPR/Cas systems to develop platforms that have broad potential applications for sensitive and specific detection of nucleic acid (NA) targets. However, few of these approaches have progressed to commercial or clinical applications. This review summarizes the properties of known CRISPR/Cas systems and their applications, challenges associated with the development of such assays, and opportunities to improve their performance or address unmet assay needs using nano-/micro-technology platforms. These include rapid and efficient sample preparation, integrated single-tube, amplification-free, quantifiable, multiplex, and non-NA assays. Finally, this review discusses the current outlook for such assays, including remaining barriers for clinical or point-of-care applications and their commercial development.

CRISPR-Based Biosensing Strategies: Technical Development and Application Prospects

Biosensing based on CRISPR-Cas systems is a young but rapidly evolving technology. The unprecedented properties of the CRISPR-Cas system provide an innovative tool for developing new-generation biosensing strategies. To date, a series of nucleic acid and non-nucleic acid detection methods have been developed based on the CRISPR platform. In this review, we first introduce the core biochemical properties underpinning the development of CRISPR bioassays, such as diverse reaction temperatures, programmability in design, high reaction efficiency, and recognition specificity, and highlight recent efforts to improve these parameters. We then introduce the technical developments, including how to improve sensitivity and quantification capabilities, develop multiplex assays, achieve convenient one-pot assays, create advanced sensors, and extend the applications of detection. Finally, we analyze obstacles to the commercial application of CRISPR detection technology and explore development opportunities and directions.

Variety Differentiation: Development of a CRISPR DETECTR Method for the Detection of Single Nucleotide Polymorphisms (SNPs) in Cacao (Theobroma cacao) and Almonds (Prunus dulcis)

To prevent food fraud, products can be monitored by various chemical-analytical techniques. In this study, we present a CRISPR-Cpf1 DETECTR-based assay for the differentiation of plant ingredients in sweet confectionary like fine and bulk-cocoa, or bitter and sweet almonds. To enable rapid in-field analysis, the trans-cleavage activity of the Cpf1 enzyme was used to develop a DETECTR (DNA endonuclease-targeted CRISPR trans reporter) assay for simple, highly specific fluorometric detection of single nucleotide polymorphisms (SNPs). The endonuclease Cpf1 requires the protospacer adjacent motif (PAM) 5'-TTTV-3' for activation, but the recognition sequence is freely programmable. The SNPs were selected to alter the Cpf1 specific PAM sequence. As a result, sequences that do not carry the canonical PAM sequence are not detected and thus not cut. The optimized system was used for both raw material and processed products such as cocoa masses or marzipan with a limit of detection of 3 ng template DNA. In addition, we were able to implement the system in the context of an LFA (lateral flow assay) to serve as a basis for the development of rapid test systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12161-023-02500-w.

Probe-based quantitative PCR and RPA-Cas12a molecular diagnostics for detection of the tomato pest Phthorimaea absoluta (Lepidoptera: Gelechiidae)

The tomato pest Phthorimaea absoluta Meyrick is highly invasive but has not yet invaded North America. However, several morphologically similar species are already present, making detection of P. absoluta presence and invasion challenging. We designed a quantitative PCR molecular diagnostic to differentiate P. absoluta, P. operculella (Zeller), or Keiferia lycopersicella (Walsingham) (Lepidoptera: Gelechiidae) DNA. Additionally, we developed an RPA-Cas12a molecular diagnostic that allows for the isothermal detection of P. absoluta DNA, eliminating the need for a thermocycler. The results of the RPA-Cas12a diagnostic can be visualized simply using a UV light source and cell phone camera. We expect these diagnostics to improve quarantine and prevention measures against this serious agricultural threat.

Gold Nanomaterials-Implemented CRISPR-Cas Systems for Biosensing

Due to their superiority in the simple design and precise targeting, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas systems have attracted significant interest for biosensing. On the one hand, CRISPR-Cas systems have the capacity to precisely recognize and cleave specific DNA and RNA sequences. On the other hand, CRISPR-Cas systems such as orthologs of Cas9, Cas12, and Cas13 exhibit cis-cleavage or trans-cleavage activities after recognizing the target sequence. Owing to the cleavage activities, CRISPR-Cas systems can be designed for biosensing by degrading tagged nucleic acids to produce detectable signals. To meet the requirements of point-of-care detection and versatile signal readouts, gold nanomaterials with excellent properties such as high extinction coefficients, easy surface functionalization, and biocompatibility are implemented in CRISPR-Cas-based biosensors. In combination with gold nanomaterials such as gold nanoparticles, gold nanorods, and gold nanostars, great efforts are devoted to fabricating CRISPR-Cas-based biosensors for the detection of diverse targets. This review focuses on the current advances in gold nanomaterials-implemented CRISPR-Cas-based biosensors, particularly the working mechanism and the performance of these biosensors. CRISPR-Cas systems, including CRISPR-Cas9, CRISPR-Cas12a, and CRISPR-Cas13a are discussed and highlighted. Meanwhile, prospects and challenges are also discussed in the design of biosensing strategies based on gold nanomaterials and CRISPR-Cas systems.

A Cas12a ortholog with distinct TTNA PAM enables sensitive detection of HPV16/18

CRISPR-associated (Cas) nucleases are multifunctional tools for gene editing. Cas12a possesses several advantages, including the requirement of a single guide RNA and high fidelity of gene editing. Here, we tested three Cas12a orthologs from human gut samples and identified a LtCas12a that utilizes a TTNA protospacer adjacent motif (PAM) distinct from the canonical TTTV PAM but with equivalent cleavage ability and specificity. These features significantly broadened the targeting scope of Cas12a family. Furthermore, we developed a sensitive, accurate, and rapid human papillomavirus (HPV) 16/18 gene detection platform based on LtCas12a DNA endonuclease-targeted CRISPR trans reporter (DETECTR) and lateral flow assay (LFA). LtCas12a showed comparable sensitivity to quantitative polymerase chain reaction (qPCR) and no cross-reaction with 13 other high-risk HPV genotypes in detecting the HPV16/18 L1 gene. Taken together, LtCas12a can broaden the applications of the CRISPR-Cas12a family and serve as a promising next-generation tool for therapeutic application and molecular diagnosis.

CRISPR-cas technology: A key approach for SARS-CoV-2 detection

The CRISPR (Clustered Regularly Spaced Short Palindromic Repeats) system was first discovered in prokaryotes as a unique immune mechanism to clear foreign nucleic acids. It has been rapidly and extensively used in basic and applied research owing to its strong ability of gene editing, regulation and detection in eukaryotes. Hererin in this article, we reviewed the biology, mechanisms and relevance of CRISPR-Cas technology and its applications in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) diagnosis. CRISPR-Cas nucleic acid detection tools include CRISPR-Cas9, CRISPR-Cas12, CRISPR-Cas13, CRISPR-Cas14, CRISPR nucleic acid amplification detection technology, and CRISPR colorimetric readout detection system. The above CRISPR technologies have been applied to the nucleic acid detection, including SARS-CoV-2 detection. Common nucleic acid detection based on CRISPR derivation technology include SHERLOCK, DETECTR, and STOPCovid. CRISPR-Cas biosensing technology has been widely applied to point-of-care testing (POCT) by targeting recognition of both DNA molecules and RNA Molecules.

RNA-Dependent RNA Targeting by CRISPR-Cas Systems: Characterizations and Applications

Genome editing technologies that are currently available and described have a fundamental impact on the development of molecular biology and medicine, industrial and agricultural biotechnology and other fields. However, genome editing based on detection and manipulation of the targeted RNA is a promising alternative to control the gene expression at the spatiotemporal transcriptomic level without complete elimination. The innovative CRISPR-Cas RNA-targeting systems changed the conception of biosensing systems and also allowed the RNA effectors to be used in various applications; for example, genomic editing, effective virus diagnostic tools, biomarkers, transcription regulations. In this review, we discussed the current state-of-the-art of specific CRISPR-Cas systems known to bind and cleave RNA substrates and summarized potential applications of the versatile RNA-targeting systems.

CRISPR/Cas12a-powered evanescent wave fluorescence nanobiosensing platform for nucleic acid amplification-free detection of Staphylococcus aureus with multiple signal enhancements

Although CRISPR-based biosensors for pathogenic detection are highly specific, they not sensitive enough and nucleic acid amplification is generally required to improve their sensitivity. However, this allows only binary operations and significantly limits practical applications. Here, a CRISPR/Cas12a-powered Evanescent wAve fluorescence nanobiosensing plaTform (CREAT) was developed for ultrasensitive nucleic acid amplification-free quantitative detection of pathogens with multiple signal enhancements. In addition to collateral cleavage amplification of the CRISPR/Cas12a system, we constructed nanophotonic structure-based evanescent wave fluorescence enhancement, Mg²⁺ or DNA-mediated fluorescence enhancement, and air-displacement fluorescence enhancement strategies for ultrasensitive detection of Staphylococcus aureus (S. aureus). Especially, the fluorescence signal detected by CREAT can be significantly enhanced by adding a simple air displacement step, thus improving detection sensitivity. This nanobiosensor detected real samples containing S. aureus, with a detection limit of 592 CFU/mL and 13.2 CFU/mL in 45 min and 90 min, respectively, which are comparable to those of RT-qPCR. This paves a new way for simple, rapid, sensitive, robust, and flexible on-site detection of S. aureus as well as other pathogens.

Recent progress in nucleic acid detection with CRISPR

Recent advances in CRISPR-based biotechnologies have greatly expanded our capabilities to repurpose CRISPR for the development of molecular diagnostic systems. The key attribute that allows CRISPR to be widely utilized is its programmable and highly specific nature. In this review, we first illustrate the principle of the class 2 CRISPR nucleases for molecular diagnostics which originates from their immunologic defence systems. Next, we present the CRISPR-based schemes in the application of diagnostics with amplification-assisted or amplification-free strategies. By highlighting some of the recent advances we interpret how general bioengineering methodologies can be integrated with CRISPR. Finally, we discuss the challenges and exciting prospects for future CRISPR-based biosensing development. We hope that this review will guide the reader to systematically learn the start-of-the-art development of CRISPR-mediated nucleic acid detection and understand how to apply the CRISPR nucleases with different design concepts to more general applications in diagnostics and beyond.

Portable rapid detection of maize chlorotic mottle virus using RT-RAA/CRISPR-Cas12a based lateral flow assay

INTRODUCTION

Maize lethal necrosis seriously threatens maize production worldwide, which was caused by coinfection by maize chlorotic mottle virus (MCMV) and a potyvirid. To effectively control maize lethal necrosis, it is vital to develop a rapid, sensitive, and specific detection method for the early diagnosis of MCMV in host plant tissues.

METHODS

We established a rapid detection procedure by combining the one-step reverse-transcription recombinase-aided amplification (one-step RT-RAA) and CRISPR/Cas12a-based lateral flow assay in one tube (one-tube one-step RT-RAA/CRISPR-Cas12a), which can be implemented on a portable metal incubator at 37~42°C. Furthermore, the crude extract of total RNA from plant materials using alkaline-PEG buffer can be directly used as the template for one-step RT-RAA.

RESULTS

The developed one-tube one-step RT-RAA/CRISPR-Cas12a lateral flow assay can detect as low as 2.5 copies of the coat protein (CP) gene of MCMV and 0.96 pg of the total RNA extracted from MCMV infected maize leaves. Furthermore, the MCMV infected maize leaves at 5 dpi having no obvious symptoms was detected as weak positive.

DISCUSSION

The crude extraction method of total RNA from plant materials required no complicated device, and all the procedures could be implemented at room temperature and on a portable metal incubator, costing a total time of about 1h. The one-step RT-RAA reagents and CRISPR/Cas12a reagents can be lyophilized for easy storage and transportation of reagents, which makes this method more feasible for the filed detection. This method presents rapidness, robustness and on-site features in detecting viral RNA, and is a promising tool for the field application in minimally equipped laboratories.

CRISPR-Cas system manipulating nanoparticles signal transduction for cancer diagnosis

Early diagnosis of cancer is important to improve the survival rate and relieve patient pain. Sensitive detection of cancer related biomarkers in body fluids is a critical approach for the early diagnosis of cancer. The clustered regularly interspaced short palindromic repeat-associated protein (CRISPR-Cas) system has emerged as a molecular manipulation technology because of its simple detection procedure, high base resolution, and isothermal signal amplification. Recently, various nanomaterials with unique optical and electrical characteristics have been introduced as the novel signal transducers to enhance the detection performance of CRISPR-Cas-based nanosensors. This review summarizes the working mechanisms of the CRISPR-Cas system for biosensing. It also enumerates the strategies of CRISPR-manipulated nanosensors based on various signal models for cancer diagnosis, including colorimetric, fluorescence, electrochemical, electrochemiluminescence, pressure, and other signals. Finally, the prospects and challenges of CRISPR-Cas-based nanosensors for cancer diagnostic are also discussed. This article is categorized under: Diagnostic Tools > Biosensing.

CRISPR-Cas12a coupled with universal gold nanoparticle strand-displacement probe for rapid and sensitive visual SARS-CoV-2 detection

Point of care (POC) diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are particularly significant for preventing transmission of coronavirus disease 2019 (COVID-19) by any user at any given time and place. CRISPR/Cas-assisted SARS-CoV-2 assays are viewed as supplemental to RT-PCR due to simple operation, convenient use and low cost. However, most current CRISPR molecular diagnostics based on fluorescence measurement increased the difficulty of POC test with need of the additional light sources. Some instrument-free visual detection with the naked eye has limitations in probe universality. Herein, we developed a universal, rapid, sensitive and specific SARS-CoV-2 POC test that combines the outstanding DNase activity of Cas12a with universal AuNPs strand-displacement probe. The oligo trigger, which is the switch the AuNPs of the strand-displacement probe, is declined as a result of Cas12a recognition and digestion. The amount of released AuNPs produced color change which can be visual with the naked eye and assessed by UV-Vis spectrometer for quantitative detection. Furthermore, a low-cost hand warmer is used as an incubator for the visual assay, enabling an instrument-free, visual SARS-CoV-2 detection within 20 min. A real coronavirus GX/P2V instead of SARS-CoV-2 were chosen for practical application validation. After rapid virus RNA extraction and RT-PCR amplification, a minimum of 2.7 × 102 copies/mL was obtained successfully. The modular design can be applied to many nucleic acid detection applications, such as viruses, bacteria, species, etc., by simply modifying the crRNA, showing great potential in POC diagnosis.

Towards Point of Care CRISPR-Based Diagnostics: From Method to Device

Rapid, accurate, and portable on-site detection is critical in the face of public health emergencies. Infectious disease control and public health emergency policymaking can both be aided by effective and trustworthy point of care tests (POCT). A very promising POCT method appears to be the clustered regularly interspaced short palindromic repeats and associated protein (CRISPR/Cas)-based molecular diagnosis. For on-site detection, CRISPR/Cas-based detection can be combined with multiple signal sensing methods and integrated into smart devices. In this review, sensing methods for CRISPR/Cas-based diagnostics are introduced and the advanced strategies and recent advances in CRISPR/Cas-based POCT are reviewed. Finally, the future perspectives of CRISPR and POCT are summarized and prospected.

Review of CRISPR/Cas Systems on Detection of Nucleotide Sequences

Nowadays, with the rapid development of biotechnology, the CRISPR/Cas technology in particular has produced many new traits and products. Therefore, rapid and high-resolution detection methods for biotechnology products are urgently needed, which is extremely important for safety regulation. Recently, in addition to being gene editing tools, CRISPR/Cas systems have also been used in detection of various targets. CRISPR/Cas systems can be successfully used to detect nucleic acids, proteins, metal ions and others in combination with a variety of technologies, with great application prospects in the future. However, there are still some challenges need to be addressed. In this review, we will list some detection methods of genetically modified (GM) crops, gene-edited crops and single-nucleotide polymorphisms (SNPs) based on CRISPR/Cas systems, hoping to bring some inspiration or ideas to readers.