Chemiluminescence Sensor for miRNA-21 Detection Based on CRISPR-Cas12a and Cation Exchange Reaction

CRISPR for companion diagnostics in low-resource settings

New point-of-care tests (POCTs), which are especially useful in low-resource settings, are needed to expand screening capacity for diseases that cause significant mortality: tuberculosis, multiple cancers, and emerging infectious diseases. Recently, clustered regularly interspaced short palindromic repeats (CRISPR)-based diagnostic (CRISPR-Dx) assays have emerged as powerful and versatile alternatives to traditional nucleic acid tests, revealing a strong potential to meet this need for new POCTs. In this review, we discuss CRISPR-Dx assay techniques that have been or could be applied to develop POCTs, including techniques for sample processing, target amplification, multiplex assay design, and signal readout. This review also describes current and potential applications for POCTs in disease diagnosis and includes future opportunities and challenges for such tests. These tests need to advance beyond initial assay development efforts to broadly meet criteria for use in low-resource settings.

Simultaneous detection of breast cancer biomarkers HER2 and miRNA-21 based on duplex-specific nuclease signal amplification

The detection of a single biomarker is prone to false negative or false positive results. Simultaneous analysis of two biomarkers can greatly improve the accuracy of diagnosis. In this work, we designed a new method for coinstantaneous detection of two breast cancer biomarkers miRNA-21 and HER2 using the properties of duplex-specific nuclease (DSN). Cy5-labeled DNA1 and FAM-labeled DNA2 are used as signal probes to distinguish the two signals. When the sample contains the targets HER2 and miRNA-21, HER2 binds to the HER2 aptamer on the double-stranded DNA2, while miRNA-21 binds to the complementary DNA1. Then, DSN enzyme is added to cut the DNA probes adsorbed on the HER2 aptamer and miRNA-21, releasing the fluorescent groups, which can be readsorbed to the empty sites, thus repeating the cutting of the probes and producing an exponential signal amplification with two distinct fluorescent signals. The detection limits of miRNA-21 and HER2 are 1.12 pM and 0.36 ng mL-1, respectively, with linear ranges of 5 pM to 50 pM and 1 ng mL-1 to 15 ng mL-1. The method was validated in real biological samples, providing a new approach for synchronous analysis of important markers in breast cancer.

CRISPR-Cas-based biosensors for the detection of cancer biomarkers

Along with discovering cancer biomarkers, non-invasive detection methods have played a critical role in early cancer diagnosis and prognostic improvement. Some traditional detection methods have been used for detecting cancer biomarkers, but they are time-consuming and involve materials and human costs. With great flexibility, sensitivity and specificity, the clustered regularly interspaced short palindromic repeats (CRISPR)-associated system provides a wide range of application prospects in this field. Herein, we introduce the background of the CRISPR-Cas (CRISPR-associated) system and comprehensively summarize the diagnosis strategies of cancer mediated by the CRISPR-Cas system, including four kinds of biochemical-based markers: nucleic acid, enzyme, tumor-specific protein and exosome. Furthermore, we discuss the challenges in implementing the CRISPR-Cas system in clinical applications.

Immuno-Rolling Circle Amplification (Immuno-RCA): Biosensing Strategies, Practical Applications, and Future Perspectives

In the rapidly evolving field of life sciences and biomedicine, detecting low-abundance biomolecules, and ultraweak biosignals presents significant challenges. This has spurred a rapid development of analytical techniques aiming for increased sensitivity and specificity. These advancements, including signal amplification strategies and the integration of biorecognition events, mark a transformative era in bioanalytical precision and accuracy. A prominent method among these innovations is immuno-rolling circle amplification (immuno-RCA) technology, which effectively combines immunoassays with signal amplification via RCA. This process starts when a targeted biomolecule, such as a protein or cell, binds to an immobilized antibody or probe on a substrate. The introduction of a circular DNA template triggers RCA, leading to exponential amplification and significantly enhanced signal intensity, thus the target molecule is detectable and quantifiable even at the single-molecule level. This review provides an overview of the biosensing strategy and extensive practical applications of immuno-RCA in detecting biomarkers. Furthermore, it scrutinizes the limitations inherent to these sensors and sets forth expectations for their future trajectory. This review serves as a valuable reference for advancing immuno-RCA in various domains, such as diagnostics, biomarker discovery, and molecular imaging.

SERS and electrochemical dual-mode detection of miRNA-141 by using single Au@Ag nanowire as a new platform

As biomarkers of cancer, the accurate and sensitive detection of microRNAs is of great significance. Therefore, we proposed a surface-enhanced Raman scattering (SERS)/electrochemical (EC) dual-mode nanosensor for sensitively detecting miRNA-141. The nanosensor uses Au@Ag nanowires as a novel SERS/EC sensing platform, which has the advantages of good biocompatibility, fast response, and high sensitivity. The dual-mode nanosensor can not only effectively overcome the problem of insufficient reliability of single signal, but also realize the amplification and stable output of the detection signal, to ensure the reliability and repeatability of miRNA detection. With this sensing strategy, the target miRNA-141 can be detected over a wide linear range (100 fM to 50 nM) (LOD of 18.4 fM for SERS and 16.0 fM for electrochemical methods). In addition, the process shows good selectivity and can distinguish miRNA-141 from other interfering miRNAs. The actual analysis of human serum samples also proves that our strategy has good reliability, repeatability, and has broad application prospects in the field of analysis and detection.

A label-free and rapid fluorometric strategy for microRNA detection using CRISPR-Cas12a coupled with copper nanoparticles

CRISPR-Cas12a with robust trans-cleavage activity were employed to mitigate background fluorescence signal, achieving sensitive detection of miRNA-21. The activation of trans-cleavage activity of Cas12a was achieved by utilizing cDNA as a trigger. Upon the presence of target miRNA-21, cDNA hybridizes with it forming a DNA/RNA double-stranded structure. Exonuclease III (ExoIII) facilitates the degradation of cDNA, releasing the target for subsequent cycles. Due to cDNA degradation, the trans-cleavage activity of Cas12a remains unactivated and does not disrupt the synthesis template of copper nanoparticles. Addition of Cu2+ and AA leads to the formation of highly fluorescent copper nanoparticles. Conversely, in absence of miRNA-21, intact cDNA activates trans-cleavage activity of Cas12a, resulting in degradation of the synthesis template and failure in synthesizing fluorescent copper nanoparticles. This method exhibits excellent selectivity with a low limit of detection (LOD) at 5 pM. Furthermore, we successfully applied this approach to determine miRNA-21 in cell lysates and human serum samples, providing a new approach for sensitive determination of biomarkers in biochemical research and disease diagnosis.

Phosphorothioate-modified G-quadruplex as a signal-on dual-mode reporter for CRISPR/Cas12a-based portable detection of environmental pollutants

BACKGROUND

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a-powered biosensor with a G-quadruplex (G4) reporter offer the benefits of simplicity and sensitivity, making them extensively utilized in detection applications. However, these biosensors used for monitoring pollutants in environmental water samples may face the problem of high background signal and easy interference due to the "signal-off" output. It is obvious that a biosensor based on the CRISPR/Cas12a system and G4 with a "signal on" output mode needs to be designed for detecting environmental pollutants.

RESULTS

By using phosphorothioate-modified G4 as a reporter and catalytic hairpin assembly (CHA) integrated with Cas12a as an amplification strategy, a "signal-on" colorimetric/photothermal biosensor (psG4-CHA/Cas) for portable detection of environmental pollutants was developed. With the help of functional nucleotides, the target pollutant (kanamycin or Pb2+) triggers a CHA reaction to produce numerous double-strand DNA, which can activate Cas12a's trans-cleavage activity. The active Cas12a cleaves locked DNA to release caged psG-rich sequences. Upon binding hemin, the psG-rich sequence forms a psG4/hemin complex, facilitating the oxidation of the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into the blue photothermal agent (oxTMB). The smartphone was employed for portable colorimetric detection of kanamycin and Pb2+. The detection limits were found to be 100 pM for kanamycin and 50 pM for Pb2+. Detection of kanamycin and Pb2+ was also carried out using a portable thermometer with a detection limit of 10 pM for kanamycin and 8 pM for Pb2+.

SIGNIFICANCE

Sensitive, selective, simple and robust detection of kanamycin and Pb2+ in environmental water samples is achieved with the psG4-CHA/Cas system. This system not only provides a new perspective on the development of efficient CRISPR/Cas12a-based "signal-on" designs, but also has a promising application for safeguarding human health and environmental monitoring.

Advancing MicroRNA Detection: Enhanced Biotin-Streptavidin Dual-Mode Phase Imaging Surface Plasmon Resonance Aptasensor

MicroRNAs (miRNAs) are novel tumor biomarkers owing to their important physiological functions in cell communication and the progression of multiple diseases. Due to the small molecular weight, short sequence length, and low concentration levels of miRNA, miRNA detection presents substantial challenges, requiring the advancement of more refined and sensitive techniques. There is an urgent demand for the development of a rapid, user-friendly, and sensitive miRNA analysis method. Here, we developed an enhanced biotin-streptavidin dual-mode phase imaging surface plasmon resonance (PI-SPR) aptasensor for sensitive and rapid detection of miRNA. Initially, we evaluated the linear sensing range for miRNA detection across two distinct sensing modalities and investigated the physical factors that influence the sensing signal in the aptamer-miRNA interaction within the PI-SPR aptasensor. Then, an enhanced biotin-streptavidin amplification strategy was introduced in the PI-SPR aptasensor, which effectively reduced the nonspecific adsorption by 20% and improved the limit of detection by 548 times. Furthermore, we have produced three types of tumor marker chips, which utilize the rapid sensing mode (less than 2 min) of PI-SPR aptasensor to achieve simultaneous detection of multiple miRNA markers in the serum from clinical cancer patients. This work not only developed a new approach to detect miRNA in different application scenarios but also provided a new reference for the application of the biotin-streptavidin amplification system in the detection of other small biomolecules.

Ultrasensitive fluorescence microRNA biosensor by coupling hybridization-initiated exonuclease I protection and tyramine signal amplification

Tyramine signal amplification (TSA) has made its mark in immunoassay due to its excellent signal amplification ability and short reaction time, but its application in nucleic acid detection is still very limited. Herein, an ultrasensitive microRNA (miRNA) biosensor by coupling hybridization-initiated exonuclease I (Exo I) protection and TSA strategy was established. Target miRNA is complementarily hybridized to the biotin-modified DNA probe to form a double strand, which protects the DNA probe from Exo I hydrolysis. Subsequently, horseradish peroxidase (HRP) is attached to the duplex via the biotin-streptavidin reaction and catalyzes the deposition of large amounts of biotin-tyramine in the presence of hydrogen peroxide (H2O2), followed by the conjugation of signal molecule streptavidin-phycoerythrin (SA-PE), which generates an intense fluorescence signal upon laser excitation. This method gave broad linearity in the range of 0.1 fM - 10 pM, yielding a detection limit as low as 74 aM. An increase in sensitivity of 4 orders of magnitude was observed compared to the miRNA detection without TSA amplification. This biosensor was successfully applied to the determination of miR-21 in breast cancer cells and human serum. By further design of specific DNA probes and coupling with the Luminex xMAP technology, it could be easily extended to multiplex miRNA assay, which possesses great application potential in 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.

Renewable Electrochemiluminescence Biosensor Based on Eu-MOGs as a Highly Efficient Emitter and a DNAzyme-Mediated Dual-drive DNA Walker as a Signal Amplifier for Ultrasensitive Detection of miRNA-222

Herein, novel europium metal-organic gels (Eu-MOGs) with excellent cathode electrochemiluminescence (ECL) emission are first used to construct biosensors for the ultrasensitive detection of miRNA-222. Impressively, N and O elements of organic ligand 2,2':6,2″-terpyridine 4,4',4″-tricarboxylic acid (H3-tctpy) can perfectly coordinate with Eu3+ to form Eu-MOGs, which not only reduce nonradiative transition caused by the intramolecular free rotation of phenyl rings in other MOGs to enhance the ECL signal with extraordinary ECL efficiency as high as 37.2% (vs the [Ru(bpy)3]2+/S2O82- ECL system) but also reinforce ligand-to-metal charge transfer (LMCT) by the strong affinity between Eu3+ and N and O elements to greatly improve the stability of ECL signals. Besides, an improved nucleic acid cascade amplification reaction is developed to greatly raise the conversion efficiency from target miRNA-222 to a DNAzyme-mediated dual-drive DNA walker as output DNA, which can simultaneously shear the specific recognition sites from two directions. In that way, the proposed biosensor can further enhance the detection sensitivity of miRNA-222 with a linear range of 10 aM-1 nM and a detection limit (LOD) of 8.5 aM, which can also achieve an accurate response in cancer cell lysates of MHCC-97L and HeLa. Additionally, the biosensor can be self-regenerated by the folding/unfolding of related triplets with pH changes to simplify experimental operations and reduce the cost. Hence, this work proposed novel MOGs with stable and intense ECL signals for the construction of a renewable ECL biosensor, supplying a reliable detection method in biomarker analysis and disease diagnosis.

MicroRNA Sensors Based on CRISPR/Cas12a Technologies: Evolution From Indirect to Direct Detection

MicroRNA (miRNA) has emerged as a promising biomarker for disease diagnosis and a potential therapeutic targets for drug development. The detection of miRNA can serve as a noninvasive tool in diseases diagnosis and predicting diseases prognosis. CRISPR/Cas12a system has great potential in nucleic acid detection due to its high sensitivity and specificity, which has been developed to be a versatile tool for nucleic acid-based detection of targets in various fields. However, conversion from RNA to DNA with or without amplification operation is necessary for miRNA detection based on CRISPR/Cas12a system, because dsDNA containing PAM sequence or ssDNA is traditionally considered as the activator of Cas12a. Until recently, direct detection of miRNA by CRISPR/Cas12a system has been reported. In this review, we provide an overview of the evolution of biosensors based on CRISPR/Cas12a for miRNA detection from indirect to direct, which would be beneficial to the development of CRISPR/Cas12a-based sensors with better performance for direct detection of miRNA.

Mini crRNA-mediated CRISPR/Cas12a system (MCM-CRISPR/Cas12a) and its application in RNA detection

Some non-coding RNAs are abnormally expressed during the occurrence and development of diseases, so it is necessary to develop analytical methods that can specifically and sensitively detect them. In typical CRISPR/Cas12a system, a complete crRNA that can recognize single-stranded or double-stranded DNA is necessary to activate its trans-cleavage activity, which limits its direct application in RNA detection. Here, we prospectively find that slicing the facilitated crRNA in the typical CRISPR/Cas12a system at a fitted site did not affect its trans-cleavage activity, and a mini crRNA-mediated CRISPR/Cas12a system (MCM-CRISPR/Cas12a) was proposed based on this. This system can detect non-coding RNA to pM-level (10 pM for miRNA-21). To expand the application of this system, we combined it with HCR and CHA to establish a detection platform for non-coding RNA. The results show that the proposed method can specifically detect RNA to fM-level (2.5 fM for miRNA-21, 8.98 fM for miR-128-3p, and 81.6 fM for lncRNA PACER). The spiked recovery rates of miRNA-21, miR-128-3p, and lncRNA PACER in normal human serum were in range from 104.7 to 109.4 %, indicating the proposed method owns good applicability. In general, this MCM-CRISPR/Cas12a system further breaks the limitations of the typical CRISPR/Cas12a system that cannot be directly used for non-coding RNA detection. Besides, its combination with HCR and CHA achieves highly sensitive detection of non-coding RNA.

Rolling circle amplification assisted CRISPR/Cas12a dual-cleavage photoelectrochemical biosensor for highly sensitive detection of miRNA-21

BACKGROUND

MicroRNA-21 has been determined to be the only microRNA overexpressed in 11 types of solid tumors, making it an excellent candidate as a biomarker for disease diagnosis and therapy. Photoelectrochemical (PEC) biosensors have been widely used for quantification of microRNA-21. However, most PEC biosensing processes still suffer from some problems, such as the difficulty of avoiding the influence of interferents in complex matrices and the false-positive signals. There is a pressing need for establishing a sensitive and stable PEC method to detect microRNA-21.

RESULTS

Herein, a nicking endonuclease-mediated rolling circle amplification (RCA)-assisted CRISPR/Cas12a PEC biosensor was fabricated for ultrasensitive detection of microRNA-21. The p-p type heterojunction PbS QDs/Co3O4 polyhedra were prepared as the quencher, thus the initial PEC signal attained the "off" state. Furthermore, the target was specifically identified and amplified by the RCA process. Then, its product single-stranded DNA S1 activated the cis- and trans-cleavage abilities of CRISPR/Cas12a, leading to almost all of the PbS QDs/Co3O4 polyhedra to leave the electrode surface, the p-n semiconductor quenching effect to be disrupted, and the signal achieving the "super-on" state. This pattern of PEC signal changed from "off" to "on" eliminated the interference of false-positive signals. The proposed PEC biosensor presented a satisfactory linear relationship ranging from 1 fM to 10 nM with a detection limit of 0.76 fM (3 Sb/N).

SIGNIFICANCE AND NOVELTY

With innovatively synthesized PbS QDs/Co3O4 polyhedra as the effective quencher for PEC signal, the CRISPR/Cas12a dual-cleavage PEC biosensor possessed excellent selectivity, stability and repeatability. Furthermore, the detection of various miRNAs can be realized by changing the relevant base sequences in the constructed PEC biosensor. It also provides a powerful strategy for early clinical diagnosis and biomedical research.

Pyroelectric-Effect-Assisted Near-Infrared-Driven Photoelectrochemical Biosensor Based on Exponential DNA Amplifier for MicroRNA Detection

Although near-infrared responsive photoelectrochemical (PEC) biosensors have less damage to biological components compared to UV-visible light, they still reveal an inferior response due to the rapid recombination of photogenerated electron-hole. In this study, a near-infrared-driven PEC biosensor is fabricated for microRNA (miRNA) detection via integrating photoelectricity and pyroelectricity. Upon the introduction of target miRNA-21, the exponential DNA amplifier is triggered based on enzyme-assisted strand displacement amplification (SDA), releasing multiple Ag2S reporter probes to hybridize with capture probes immobilized on a CdS-2-mercaptobenzimidazole (2MBI)-modified photoelectrode. As a result, under the stimulation of NIR, the photoelectric conversion of Ag2S NPs generates the photocurrents. In addition, due to the strong hole acceptor ability of MBI, the pyroelectric effect of CdS-2MBI nanocomposites is enhanced, which generates highly pyroelectro-induced charge separation efficiency and induces the pyroelectric current benefited from the spontaneous polarization of CdS-2MBI caused by the temperature variation under the function of Ag2S nanoheaters. Impressively, this PEC biosensor has achieved the sensitive and selective determination of miRNA-21 with a detection limit as low as 54 fM. Overall, this NIR-driven PEC biosensor based on pyroelectric and photoelectric effects opens up a new horizon for bioanalysis and early disease diagnosis.

Cation Exchange Reaction-Mediated Photothermal and Polarity-Switchable Photoelectrochemical Dual-Readout Biosensor

Cation exchange (CE) is a burgeoning method for controlled crystal synthesis; however, its applications in bioanalysis are still in their infancy. Herein, we explored the transformation of ZnIn2S4 in properties after the CE reaction with Cu2+ ions; furthermore, the discrepancy was employed to design a dual-readout detection system of photothermal and polarity-switchable photoelectrochemical (PEC) immunoassays to realize reliable detection of carcinoembryonic antigen (CEA). In the presence of CEA, the CuO nanoparticles (CuO NPs) employed as dual-signal response probes would bond to the microplates and be acidolyzed by HCl to release Cu2+, which could replace Zn2+ and In3+ via the CE reaction. After the CE reaction is completed, the photocurrent would switch from a weak anodic photocurrent to a cathode one by using a 635 nm laser as a signal amplifier, while the photothermal signal would be enhanced with 808 nm laser illumination. On the basis of the polarity-switchable PEC strategy, CEA could be accurately detected from 0.1 to 50 ng mL-1 with a limit of detection (LOD) of 48 pg mL-1 (S/N = 3). Moreover, the photothermal assay for CEA detection possesses a linear range from 0.5 to 100 ng mL-1 with a LOD of 0.21 ng mL-1. In addition, the designed sensing platform only relies on devices with portability that are permitted for point-of-care detection.

Low-Background CRISPR/Cas12a Sensors for Versatile Live-Cell Biosensing

The trans-cleavage activity of CRISPR/Cas12a has been widely used in biosensing. However, many CRISPR/Cas12a-based biosensors, especially those that work in "on-off-on" mode, usually suffer from high background and thus impossible intracellular application. Herein, this problem is efficiently overcome by elaborately designing the activator strand (AS) of CRISPR/Cas12a using the "RESET" effect found by our group. The activation ability of the as-designed AS to CRISPR/Cas12a can be easily inhibited, thus assuring a low background for subsequent biosensing applications, which not only benefits the detection sensitivity improvement of CRISPR/Cas12a-based biosensors but also promotes their applications in live cells as well as makes it possible to design high-performance biosensors with greatly improved flexibility, thus achieving the analysis of a wide range of targets. As examples, by using different strategies such as strand displacement, strand cleavage, and aptamer-substrate interaction to reactivate the inhibited enzyme activity, several CRISPR/Cas12a-based biosensing systems are developed for the sensitive and specific detection of different targets, including nucleic acid (miR-21), biological small molecules (ATP), and enzymes (hOGG1), giving the detection limits of 0.96 pM, 8.6 μM, and 8.3 × 10-5 U/mL, respectively. Thanks to the low background, these biosensors are demonstrated to work well for the accurate imaging analysis of different biomolecules in live cells. Moreover, we also demonstrate that these sensing systems can be easily combined with lateral flow assay (LFA), thus holding great potential in point-of-care testing, especially in poorly equipped or nonlaboratory environments.

Hg2+-triggered cascade strand displacement assisted CRISPR-Cas12a for Hg2+ quantitative detection using a portable glucose meter

CRISPR-Cas12a is a powerful and programmable tool that has revolutionized the field of biosensing. However, the construction of a CRISPR-Cas12a-mediated portable system for on-site and quantitative detection of mercury ion (Hg2+) has yet to be explored. By integrating a target-triggered cascade toehold-mediated strand displacement reaction (TSDR) and CRISPR-Cas12a, we herein construct a portable on-site biosensor for the quantitative, sensitive, and selective detection of Hg2+ with a glucose meter. The Hg2+ initiates two cascade TSDRs through the T-Hg2+-T interaction to produce multiple double-stranded DNAs that can activate Cas12a's trans-cleavage activity. The Cas12a cleaves the sucrase-modified DNA on the electrode, resulting in the liberation of sucrase into the solution. The freed sucrase can catalyze sucrose to generate glucose, which can be quantitatively monitored by a glucometer. The developed portable biosensor provides a dynamic range of 5 orders of magnitude with a detection limit of 40 fM. This biosensor also displays excellent selectivity and stability for detecting Hg2+. Moreover, environmental water samples are utilized to further verify the robustness and effectiveness of the developed biosensor, highlighting its potential application in environmental monitoring and food safety analysis.

Highly Sensitive, Portable Detection System for Multiplex Chemiluminescence Analysis

Chemiluminescence (CL) has emerged as a critical tool for the sensing and quantification of various bioanalytes in virtually all clinical fields. However, the rapid nature of many CL reactions raises challenges for typical low-cost optical sensors such as cameras to achieve accurate and sensitive detection. Meanwhile, classic sensors such as photomultiplier tubes are highly sensitive but lack spatial multiplexing capabilities and are generally not suited for point-of-care applications outside a standard laboratory setting. To address this issue, in this paper, a miniaturized and versatile silicon-photomultiplier-based fiber-integrated CL device (SFCD) was designed for sensitive multiplex CL detection. The SFCD comprises a silicon photomultiplier array coupled to an array of high numerical aperture plastic optical fibers to achieve 16-plex detection. The optical fibers ensure efficient light collection while allowing the fixed detector to be mated with diverse sample geometries (e.g., circular or grid), simply by adjusting the fiber configuration. In a head-to-head comparison with a lens-based camera system featuring a cooled detector, the SFCD achieved a 14-fold improved limit of detection in both direct and enzyme-mediated CL reactions. The SFCD also features improved compactness and lower cost, as well as faster temporal resolution compared with camera-based systems while preserving spatial multiplexing and good environmental robustness. Thus, the SFCD has excellent potential for point-of-care biosensing applications.

Sensitive and Amplification-Free Electrochemiluminescence Biosensor for HPV-16 Detection Based on CRISPR/Cas12a and DNA Tetrahedron Nanostructures

Rapid and accurate detection of biomarkers was very important for early screening and treatment of diseases. Herein, a sensitive and amplification-free electrochemiluminescence (ECL) biosensor based on CRISPR/Cas12a and DNA tetrahedron nanostructures (TDNs) was constructed. Briefly, 3D TDN was self-assembled on the Au nanoparticle-deposited glassy carbon electrode surface to construct the biosensing interface. The presence of the target would activate the trans-cleavage activity of Cas12a-crRNA duplex to cleave the single-stranded DNA signal probe on the vertex of TDN, causing the Ru(bpy)32+ to fall from the electrode surface and weakened the ECL signal. Thus, the CRISPR/Cas12a system transduced the change of target concentration into an ECL signal enabling the detection of HPV-16. The specific recognition of CRISPR/Cas12a to HPV-16 made the biosensor have good selectivity, while the TDN-modified sensing interface could reduce the cleaving steric resistance and improve the cleaving performance of CRISPR/Cas12a. In addition, the pretreated biosensor could complete sample detection within 100 min with a detection limit of 8.86 fM, indicating that the developed biosensor possesses the potential application prospect for fast and sensitive nucleic acid detection.

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.