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

A smartphone-enabled colorimetric tumor-derived exosomes sensing based on multi-enzyme catalysis and dual-recognition triggered CRISPR/Cas12a trans-cleavage

Detection of protein profiling on exosomes exhibits great promise for early non-invasive and accurate diagnosis of tumor in clinical diagnostics. However, it still faces multiple challenges, such as expensive instruments requirement and weak specificity by single biomarker. Herein, based on a dual-recognition strategy, a ternary hybrid of a trigger DNA (TDNA), EpCAM aptamer, and CD63 aptamer was used to capture A549 cells-derived exosomes to release TDNA, which initiated the trans-cleavage activity of CRISPR/Cas12a to nonspecifically cleave single-stranded DNA (ssNDA) and then resulted in the isolating of ssDNA linked nanozyme of Zr/Fe-CeO2@Ir@CaO2@HA (ZFCIrCH). ZFCIrCH not only achieved H2O2/O2 self-supply, but also possessed high peroxidase-like, oxidase-like, and superoxide dismutase-like activities, thereby generating a sensitive colorimetric signal for A549 cells-derived exosomes detection with a low limit of detection (LOD) of 31 particles/mL. Using a smartphone to analyze colorimetric images, exosome concentration also can be precisely quantified with a LOD of 29 particles/mL, which could also successfully distinguish healthy people from lung cancer patients. With the advantages of high sensitivity, good specificity, low cost, and convenient on-site detection of tumor-derived exosomes, the present colorimetric sensor has great promise in the accurate diagnosis of diseases.

Catalytic hairpin assembly assists CRISPR/Cas12a-mediated high-sensitivity detection of aflatoxin B1

Aflatoxin B1 (AFB1) is recognized the most toxic and carcinogenic mycotoxin and is widely present in cereals and various foods. Therefore, its precise detection is crucial to safeguard food quality and human health. In this study, we proposed a highly sensitive detection system for AFB1 by combining the catalytic hairpin assembly (CHA) and CRISPR/Cas12a techniques. The Aptamer of Aptamer-Initiator interacts with AFB1 to release the blocked Antisense. As a result, the Initiator of the Aptamer-Initiator becomes free and can act as a toehold to bind with H1, which can initiate the CHA to generate a large amount of double-stranded DNA, which hybridized with the Cas12a-crRNA duplex to form the Cas12a-crRNA-DNA ternary complex, wherein Cas12a subsequently cleaves the FAM-ssDNA-BHQ1 probe in trans to generate fluorescence signals. After optimization, we observed a linear relationship between fluorescence intensity and the AFB1 concentration in the range of 50 pM to 1 nM, with a limit of detection (LOD) of 10 pM. Also, the system was robust and could operate with excellent reliability and accuracy even in complex samples. The recovery values in food samples ranged from 92.23 % to 111.72 %, with relative standard deviation (RSD) below 5.68 %. The system exhibited remarkable advantages, including high sensitivity, strong specificity, and rapid response, thereby showed great potential in the efficient detection of AFB1 contaminants in food.

CRISPR Digital Sensing: From Micronano-Collaborative Chip to Biomolecular Detection

The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) sensing technology proved to be valuable during the COVID-19 pandemic through its sensitivity, specificity, robustness, and versatility. However, issues such as overreliance on amplification, susceptibility to false positives, lack of quantification strategies, and complex operation procedures have hindered its broader application in bioanalysis and clinical diagnostics. The collision between micronano-collaborative chips and CRISPR technology has effectively addressed these bottlenecks, offering innovative solutions for diagnosis and treatment. Unlike conventional micronano chips, micronano digital chips enhance CRISPR's response to trace amounts of target molecules by leveraging highly controllable local environments and compartmentalized microreactors. This advancement improves detection efficiency and revolutionizes traditional in vitro bioanalytical processes. First, the working principles, fabrication techniques, and performance metrics of CRISPR-based digital droplet microfluidics and microarray chips are examined. Then, the applications of CRISPR digital sensing chips in bioassays are reviewed, emphasizing their importance in advancing in vitro detection systems for gene editing. Finally, the prospects of CRISPR digital sensing technology are explored, particularly its potential for body surface biomonitoring and its broader development opportunities in the biomedical field.

Amplification-free nucleic acids detection with next-generation CRISPR/dx systems

CRISPR-based diagnostics (CRISPR/Dx) have revolutionized the field of molecular diagnostics. It enables home self-test, field-deployable, and point-of-care testing (POCT). Despite the great potential of CRISPR/Dx in diagnoses of biologically complex diseases, preamplification of the template often is required for the sensitive detection of low-abundance nucleic acids. Various amplification-free CRISPR/Dx systems were recently developed to enhance signal detection at sufficient sensitivity. Broadly, these amplification-free CRISPR/Dx systems are classified into five groups depending on the signal enhancement strategies employed: CRISPR/Cas12a and/or CRISPR/Cas13a are integrated with: (1) other catalytic enzymes (Cas14a, Csm6, Argonaute, duplex-specific nuclease, nanozyme, or T7 exonuclease), (2) rational-designed oligonucleotides (multivalent aptamer, tetrahedral DNA framework, RNA G-quadruplexes, DNA roller machine, switchable-caged guide RNA, hybrid locked RNA/DNA probe, hybridized cascade probe, or "U" rich stem-loop RNA), (3) nanomaterials (nanophotonic structure, gold nanoparticle, micromotor, or microbeads), (4) electrochemical and piezoelectric plate biosensors (SERS nanoprobes, graphene field-effect transistor, redox probe, or primer exchange reaction), or (5) cutting-edge detection technology platforms (digital bioanalysis, droplet microfluidic, smartphone camera, or single nanoparticle counting). Herein, we critically discuss the advances, pitfalls and future perspectives for these amplification-free CRISPR/Dx systems in nucleic acids detection. The continued refinement of these CRISPR/Dx systems will pave the road for rapid, cost-effective, ultrasensitive, and ultraspecific on-site detection without resorting to target amplification, with the ultimate goal of establishing CRISPR/Dx as the paragon of diagnostics.

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

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

CRISPR/Cas-powered nucleic acid amplification and amplification-free biosensors for public safety detection: Principles, advances and prospects

Rapid, accurate, cost-effective, and efficient ultrasensitive detection strategies are essential for public health safety (including food safety, disease prevention and environmental governance). The CRISPR/CRISPR-associated (Cas) detection is a cutting-edge technology that has been widely used in the detection of public health safety due to its targeted cleavage properties (signal amplification), attomolar level sensitivity, high specificity (recognizing single-base mismatches), and rapid turnover time. However, the current research about CRISPR/Cas-based biosensors is not clear, such as mechanism problem and application differences of integrating CRISPR/Cas system with other technologies, and how to further innovate and develop in the future. Therefore, further detailed analysis and comparative discussion of CRISPR/Cas-based biosensors is needed. Currently, CRISPR/Cas system powered biosensors can be mainly categorized into two types: CRISPR/Cas system powered nucleic acid amplification biosensors and CRISPR/Cas system powered nucleic acid amplification-free biosensors. The two biosensors have different characteristics and advantages. This paper first provides an in-depth investigation of the enzymatic mechanism of CRISPR/Cas system at the molecular level. Then, this paper summarizes the principles and recent advances of CRISPR/Cas system powered nucleic acid amplification biosensors and CRISPR/Cas system powered nucleic acid amplification-free biosensors and discusses their integration mechanisms in depth. More, the differences and application-oriented between the two biosensors are further discussed. Finally, the application orientation and future perspectives of the two biosensors are discussed, and unique insights into the future development of CRISPR/Cas system are provided.

Fast-Flu: RT-RPA-CRISPR/Cas12a assisted one-step platform for rapid influenza B virus detection

Influenza B virus (Flu B) is a prevalent respiratory pathogen responsible for seasonal influenza epidemics. Despite its clinical significance, there remains a lack of rapid and accurate diagnostic methods for Flu B detection. In this study, we developed a novel Flu B detection system, named Fast-Flu, by integrating reverse transcription recombinase polymerase amplification (RT-RPA) with the clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein (Cas) system (CRISPR/Cas). Through optimization of reaction temperature and adjustment of Cas12a concentrations, we successfully balanced RPA amplification and CRISPR/Cas12a trans-cleavage activity, enabling the establishment of a one-step detection system. The one-step Fast-Flu system demonstrated the ability to specifically identify Flu B within 45 min, with a limit of detection of 58 copies per test. It eliminates the need for uncapping operations and minimizes the risk of cross-contamination, without cross-reactivity with other pathogens. When evaluated using 101 clinical throat swab samples, the one-step Fast-Flu system achieved a sensitivity of 56.25% and a specificity of 100% compared to the PCR-based method, with an overall concordance rate of 93.06% (94/101). The development of this one-step RT-RPA-CRISPR/Cas12a system represents a significant advancement in the rapid, convenient, and accurate detection of Flu B, highlighting its potential for clinical diagnosis. Furthermore, with future technical improvements to enhance sensitivity, this one-step RT-RPA-CRISPR assay holds promise as a versatile tool for the rapid nucleic acid detection of other RNA viruses.

IMPORTANCE

Influenza B virus (Flu B) is a significant global health concern, and rapid, accurate pathogen diagnosis is crucial for effective influenza prevention and control. The integration of isothermal amplification methods with the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system has achieved high sensitivity and specificity for nucleic acid detection. Although CRISPR/Cas-based systems have been developed for influenza detection, existing platforms require the transfer of amplified products into the CRISPR/Cas12a detection system through uncapping operations, which increases the risk of cross-contamination. In this study, we developed a one-step reverse transcription recombinase polymerase amplification-CRISPR/Cas12a Flu B detection method using a one-pot detection system. By optimizing the reaction temperature and Cas12a concentration, we achieved a streamlined and contamination-free workflow. This innovative approach not only improves Flu B detection but also serves as a valuable reference for constructing CRISPR/Cas systems for the detection of other pathogens and targets, paving the way for broader applications in molecular diagnostics.

MAIGRET: a CRISPR-based immunoassay that employs antibody-induced cell-free transcription of CRISPR guide RNA strands

Here we report on the development of a CRISPR-based assay for the sensitive and specific detection of antibodies and antigens directly in complex sample matrices. The assay, called Molecular Assay based on antibody-Induced Guide-RNA Enzymatic Transcription (MAIGRET), is based on the use of a responsive synthetic DNA template that triggers the cell-free in vitro transcription of a guide RNA strand upon recognition of a specific target antibody. Such transcribed guide RNA activates the DNA collateral activity of the Cas12a enzyme, leading to the downstream cleavage of a fluorophore/quencher-labeled reporter and thus resulting in an increase in the measured fluorescence signal. We have used MAIGRET for the detection of six different antibodies with high sensitivity (detection limit in the picomolar range) and specificity (no signal in the presence of non-target antibodies). MAIGRET can also be adapted to a competitive approach for the detection of specific antigens. With MAIGRET, we significantly expand the scope and applicability of CRISPR-based sensing approaches to potentially enable the measurement of any molecular target for which an antibody is available.

CRISPR/HCR-powered ratiometric fluorescence aptasensor for ochratoxin A detection

To address the need for highly sensitive and reliable detection of trace ochratoxin A (OTA) in food matrices, we developed a ratiometric fluorescent aptasensor by integrating CRISPR/Cas12a, hybridization chain reaction (HCR), and horseradish peroxidase (HRP)-induced inner filter effect (IFE). The mechanism involves OTA releasing an activator that initiates CRISPR/Cas12a trans-cleavage, blocking HCR assembly. This reduces HRP levels, limiting the conversion of o-phenylenediamine (OPD) to fluorescent 2,3-diaminophenazine (DAP) (emitting at 562 nm) while maintaining strong emission from 2-amino terephthalic acid (BDC-NH2) at 426 nm. The F426/F562 ratio serves as a "signal-on" indicator, enabling sensitive OTA detection over 0.1 pM to 10 nM, with a detection limit of 0.0417 pM. The method exhibits excellent reproducibility, with intra-day and inter-day relative standard deviations (RSDs) of 1.91 %-3.87 % and 1.79 %, respectively, along with recovery rates of 90.1 %-110.6 % in real samples. These advantages highlight its significant potential for CRISPR/Cas-based OTA detection.

A minimal transcription template-based amplification-free CRISPR-Cas13a strategy for DNA detection

CRISPR-Cas13a has shown great potential for the rapid and accurate detection of pathogen nucleic acids. However, conventional CRISPR-Cas13a-based assays typically require pre-amplification, which can introduce aerosol contamination and operational complexities. In this study, we developed a Minimalist transcription template-based Amplification-free CRISPR-Cas13a strategy for DNA detection (MAD). This strategy facilitates the release of pathogen DNA and its annealing with primers from nasopharyngeal swab samples in a straightforward manner, followed by T7 transcription and CRISPR-Cas13a detection, completing the entire process within 40 min. MAD eliminates the need for DNA extraction and pre-amplification while maintaining high sensitivity after optimization, allowing for result visualization via lateral flow strips. Furthermore, evaluation of 167 clinical pediatric samples identified 18 positive cases of human adenovirus, demonstrating a 99.4% concordance in detection compared to standard qPCR. We believe that MAD offers new insights into CRISPR-Cas diagnostics and, due to its simplicity, rapidity, and safety, is poised for widespread application in clinical practice.

Bifunctional probe propelling multipath strand displacement amplification tandem CRISPR/Cas12a for ultrasensitive and robust assay of DNA methyltransferase activity

BACKGROUND

DNA methylation catalyzed by various DNA methyltransferases (DNA MTases) is one of the important epigenetic regulations in both eukaryotes and prokaryotes. Therefore, the detection of DNA MTase activity is a vital target and direction in the study of methylation-related diseases.

RESULTS

In this study, an ultrasensitive and robust strategy was developed for DNA MTase activity sensing based on bifunctional probe propelling multipath strand displacement amplification and CRISPR/Cas12a techniques. First, a bifunctional hairpin probe (bHpDNA) was designed instead of a conventional single-function probe. In the presence of DNA MTase, the bHpDNA was methylated and cleaved by a restriction endonuclease into two independent primers, both of which bind with the templates to trigger strand displacement amplification and produce the active DNA of CRISPR/Cas12a. Second, annealing-assisted binding instead of free diffusion adhesion was used to improve hybridization efficiency between the primers and templates. Finally, the CRISPR/Cas12a system was used to achieve fluorescence signal output to analyze DNA MTase activity. If targets were absent, there was no signal because no primers were released from the bHpDNA. To verify the reliability of the method, two key DNA MTases, Dam and M. SssI, were analyzed, and their limits of detection were 2.458 × 10-3 and 3.820 × 10-3 U/mL, respectively, which were lower than those of most reported fluorescence methods.

SIGNIFICANCE

This method was successfully used in the evaluation of DNA MTase inhibitors and the detection of DNA MTase activity in complex biological systems with good recoveries and relative standard deviation at low spiked concentrations (0.1-1 U/mL), which all indicate that this method is an ultrasensitive and robust strategy in DNA MTase activity assay and has great potential in biomedical and clinical detection.

A non-covalently bound redox indicator for electrochemical CRISPR-Cas12a and DNase I biosensors

A rapid and accurate biosensor for detecting disease biomarkers at point-of-care is essential for early disease diagnosis and preventing pandemics. CRISPR-Cas12a is a promising recognition element for DNA biosensors due to its programmability, specificity, and deoxyribonuclease activity initiated in the presence of a biomarker. The current electrochemical CRISPR-Cas12a-based biosensors utilize the single-stranded DNA (ssDNA) self-assembled on an electrode surface and covalently modified with the redox indicator, usually methylene blue (MB). In the presence of a biomarker, the nuclease domain is activated and cleaves ssDNA, decreasing the redox indicator signal. The covalent attachment of the MB to the ssDNA implies complexity and a higher production cost. Alternatively, some redox indicators can noncovalently bind to the ssDNA. Although such indicators have been applied for electrochemical nucleic acid detection, their potential for electrochemical CRISPR-Cas-based biosensors has not been explored. In this work, a ruthenium complex, [Ru(NH3)6]3+, was investigated as a redox indicator non-covalently binding to the ssDNA. Voltammetric studies and the optimization resulted in a simple and robust electrochemical method that was tested for deoxyribonuclease I (DNase I) activity detection and applied in the CRISPR-Cas12a-based biosensor for viral DNA (HPV-16). The biosensors revealed good analytical properties and represent an alternative to reported biosensors for nuclease activity requiring a covalent attachment of the redox indicator. Moreover, the developed method offers prospects for advancement and can be transformed to operate with other Cas nucleases to detect RNA and other analytes.

CRISPR/Cas12a-Enabled Amplification-Free Colorimetric Visual Sensing Strategy for Point-of-Care Diagnostics of Biomarkers

CRISPR/Cas12a-based biosensors have garnered significant attention in the field of point-of-care testing (POCT), yet the majority of the CRISPR-based POCT methods employ fluorescent systems as report probes. Herein, we report a new CRISPR/Cas12a-enabled multicolor visual biosensing strategy for the rapid detection of disease biomarkers. The proposed assay provided vivid color responses to enhance the accuracy of visual detection. In the existence of the target, the trans-cleavage activity of CRISPR-Cas12a was activated. The report probe modified with magnetic beads (MBs) and horseradish peroxidase (HRP) was cleaved, and HRP was released in the supernatant. As a result, HRP mediated the etching of gold nanobipyramids (AuNBPs) under hydrogen peroxide and 3,3',5,5'-tetramethylbenzidine and generated a vivid color response. The proposed method has been verified by the detection of the breast cancer 1 gene (BRCA1) as a proof-of-principle target. According to the different colors of AuNBPs, our experimental results have demonstrated that as low as 30 pM BRCA1 can be detected with no more than 60 min. Additionally, the proposed sensor has been successfully applied in the analysis of BRCA1 in human serum samples with satisfactory results, which indicates great potential for the sensitive determination of biomarkers and the POCT area.

Novel Multimode Assay Based on Asymmetrically Competitive CRISPR and Raman Barcode Spectra for Multiple Hepatocellular Carcinoma Biomarkers Detection

Commercial pregnancy test strips (PTS) possess the advantages of lower price, higher stability, and better repeatability and have been popularized to integrate with novel sensing strategies to detect other disease biomarkers, which accelerates the commercialization process of those novel sensing strategies. However, the current integration of novel sensing strategies into commercial PTS still faced the problems of insufficient quantification, low sensitivity, and lack of multiple detection capabilities. Hence, we proposed the concept of "visual classification recognition, spectral signal subdivision" for multiple hepatocellular carcinoma biomarkers (miRNA122 and miRNA233) detection with dual signals based on asymmetric competitive CRISPR (acCRISPR) and surface-enhanced Raman spectroscopy coupling with PTS, named the acCRISPR-PTS-SERS assay. In this assay, acCRISPR was used as a nonamplified cascaded signal amplification method to improve the sensitivity of detection. Two AuNPs-based core-shell Raman tags, each corresponding to different miRNA biomarkers, were used to achieve both visual recognition and spectral segmentation to enhance the quantification of PTS detection and the capability for multiple detection. Under the optimal conditions, the LOD for miRNA122 and miRNA223 were 10.36 and 4.65 fM, respectively. The sensitivity was enhanced by nearly 2 orders of magnitude. In the future, simultaneous hand-held detection for fingerprint barcodes of different cancers can be achieved with the assistance of a microfluidic chip and smartphone.

Synthetic mismatches enable specific CRISPR-Cas12a-based detection of genome-wide SNVs tracked by ARTEMIS

Detection of pathogenic DNA variants is vital in cancer diagnostics and treatment monitoring. While CRISPR-based diagnostics (CRISPRdx) offer promising avenues for cost-effective, rapid, and point-of-care testing, achieving single-nucleotide detection fidelity remains challenging. We present an in silico pipeline that scans the human genome for targeting pathogenic mutations in the seed region (ARTEMIS), the most stringent crRNA domain. ARTEMIS identified 12% of pathogenic SNVs as Cas12a recognizable, including 928 cancer-associated variants such as BRAFV600E, BRCA2E1953∗, TP53V272M, and ALDH2E504K. Cas12a exhibited remarkable tolerance to single mismatches within the seed region. Introducing deliberate synthetic mismatches within the seed region yielded on-target activity with single-nucleotide fidelity. Both positioning and nucleobase types of mismatches influenced detection accuracy. With improved specificity, Cas12a could accurately detect and semi-quantify BRAFV600E in cfDNA from cell lines and patient liquid biopsies. These results provide insights toward rationalized crRNA design for high-fidelity CRISPRdx, supporting personalized and cost-efficient healthcare solutions in oncologic diagnostics.

Machine Learning-Assisted, Dual-Channel CRISPR/Cas12a Biosensor-In-Microdroplet for Amplification-Free Nucleic Acid Detection for Food Authenticity Testing

The development of novel detection technology for meat species authenticity is imperative. Here, we developed a machine learning-supported, dual-channel biosensor-in-microdroplet platform for meat species authenticity detection named CC-drop (CRISPR/Cas12a digital single-molecule microdroplet biosensor). This strategy allowed us to quickly identify and analyze animal-derived components in foods. This biosensor was enabled by CRISPR/Cas12a-based fluorescence lighting-up detection, and the nucleic acid signals can be recognized by a Cas12a-crRNA binary complex to trigger the trans-cleavage of any by-stander reporter single-stranded (ss) DNA, in which nucleic acid signals can be converted and amplified to fluorescent readouts. The ultralocalized microdroplet reactor was constructed by reducing the reaction volume from up to picoliter to accommodate the aforementioned reaction to further enhance the sensitivity to even render an amplification-free nucleic acid detection. Moreover, we established a smartphone App coupled with a random forest machine learning model based on parameters such as area, fluorescent intensity, and counting number to ensure the accuracy of image recording and processing. The sample-to-result time was within 80 min. Importantly, the proposed biosensor was able to accurately detect the ND1 (pork-specific) and IL-2 (duck-specific) genes in deep processed meat-derived foods that usually had truncated DNA, and the results were more robust and practical than conventional real-time polymerase chain reaction after a side-by-side comparison. All in all, the proposed biosensor can be expected to be used for rapid food authenticity and other nucleic acid detections in the future.

Argonaute-Based Nucleic Acid Detection Technology: Advantages, Current Status, Challenges, and Perspectives

Rapid and accurate detection is a prerequisite for precise clinical diagnostics, ensuring food safety, and facilitating biotechnological applications. The Argonaute system, as a cutting-edge technique, has been successfully repurposed in biosensing beyond the CRISPR/Cas system (clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins), which has been extensively researched, but recognition of PAM sequences remains restricted. Argonaute, as a programmable and target-activated nuclease, is repurposed for fabricating novel detection methods due to its unparalleled biological features. In this comprehensive review, we initially elaborate on the current methods for nucleic acid testing and programmable nucleases, followed by delving into the structure and nuclease activity of the Argonaute system. The advantages of Argonaute compared with the CRISPR/Cas system in nucleic acid detection are highlighted and discussed. Furthermore, we summarize the applications of Argonaute-based nucleic acid detection and provide an in-depth analysis of future perspectives and challenges. Recent research has demonstrated that Argonaute-based biosensing is an innovative and rapidly advancing technology that can overcome the limitations of existing methods and potentially replace them. In summary, the implementation of Argonaute and its integration with other technologies hold promise in developing customized and intelligent detection methods for nucleic acid testing across various aspects.

Ultrasensitive detection platform for Staphylococcus aureus based on DNAzyme tandem blocking CRISPR/Cas12a system

Detection methods based on CRISPR/Cas12a have been widely developed in the application of pathogenic microorganisms to guarantee food safety and public health. For sensitive detection, the CRISPR-based strategies are often in tandem with amplification methods. However, that may increase the detection time and the process may introduce nucleic acid contamination resulting in non-specific amplification. Herein, we established a sensitive S. aureus detection strategy based on the CRISPR/Cas12a system combined with DNAzyme. The activity of Cas12a is blocked by extending the spacer of crRNA (bcrRNA) and can be reactivated by Mn2+. NH2-modified S. aureus-specific aptamer was loaded on the surface of Fe3O4 MNPs (apt-Fe3O4 MNPs) and MnO2 NPs (apt-MnO2 NPs) by EDC/NHS chemistry. The S. aureus was captured to form apt-Fe3O4 MNPs/S. aureus/apt-MnO2 NPs complex and then MnO2 NPs were etched to release Mn2+ to activate DNAzyme. The active DNAzyme can cleave the hairpin structure in bcrRNA to recover the activity of the CRISPR/Cas system. By initiating the whole detection process by generating Mn2+ through nanoparticle etching, we established a rapid detection assay without nucleic acid extraction and amplification process. The proposed strategy has been applied in the ultrasensitive quantitative detection of S. aureus and has shown good performance with an LOD of 5 CFU/mL in 29 min. Besides, the proposed method can potentially be applied to other targets by simply changing the recognition element and has the prospect of developing a universal detection strategy.

CRISPR-based strategies for sample-to-answer monkeypox detection: current status and emerging opportunities

The global health threat posed by the Monkeypox virus (Mpox) requires swift, simple, and accurate detection methods for effective management, emphasizing the growing necessity for decentralized point-of-care (POC) diagnostic solutions. The clustered regularly interspaced short palindromic repeats (CRISPR), initially known for its effective nucleic acid detection abilities, presents itself as an attractive diagnostic strategy. CRISPR offers exceptional sensitivity, single-base specificity, and programmability. Here, we reviewed the latest developments in CRISPR-based POC devices and testing strategies for Mpox detection. We explored the crucial role of genetic sequencing in designing crRNA for CRISPR reaction and understanding Mpox transmission and mutations. Additionally, we showed the integration of CRISPR-Cas12 strategy with pre-amplification and amplification-free methods. Our study also focused on the significant role of Cas12 proteins and the effectiveness of Cas12 coupled with recombinase polymerase amplification (RPA) for Mpox detection. We envision the future prospects and challenges, positioning CRISPR-Cas12-based POC devices as a frontrunner in the next generation of molecular biosensing technologies.

One-pot diagnostic methods based on CRISPR/Cas and Argonaute nucleases: strategies and perspectives

CRISPR/Cas and Argonaute (Ago) proteins, which target specific nucleic acid sequences, can be applied as diagnostic tools. Despite high specificity and efficiency, achieving sensitive detection often necessitates a preamplification step that involves opening the lid and multistep operation, which may elevate the risk of contamination and prove inadequate for point-of-care testing. Hence, various one-pot detection strategies have been developed that enable preamplification and sensing in a single operation. We outline the challenges of one-pot detection with Cas and Ago proteins, present several main implementation strategies, and discuss future prospects. This review offers comprehensive insights into this vital field and explores potential improvements to detection methods that will be beneficial for human health.

Nanobody-based strategy for rapid and accurate pathogen detection: A case of COVID-19 testing

Antibody pairs-based immunoassay platforms served as essential and effective tools in the field of pathogen detection. However, the cumbersome preparation and limited detection sensitivity of antibody pairs challenge in establishment of a highly sensitive detection platform. In this study, using COVID-19 testing as a case, we utilized readily accessible nanobodies as detection antibodies and further proposed an accurate design concept with a more scientific and efficient screening strategy to obtain ultrasensitive antibody pairs. We employed nanobodies capable of binding different antigenic epitopes of the nucleocapsid (NP) or receptor-binding domain (RBD) antigens sandwich as substitutes for monoclonal antibodies (mAbs) sandwich in fast detection formats and utilized time-resolved fluorescence (TRF) microspheres as the signal probe. Consequently, we developed a multi-epitope nanobody sandwich-based fluorescence lateral flow immunoassay (FLFA) strip. Our results suggest that the NP antigen had a detection limit of 12.01pg/mL, while the RBD antigen had a limit of 6.51 pg/mL using our FLFA strip. Based on double mAb sandwiches, the values presented herein demonstrated 4 to 32-fold enhancements in sensitivity, and 32 to 256-fold enhancements compared to commercially available antigen lateral flow assay kits. Furthermore, we demonstrated the excellent characteristics of the proposed test strip, including its specificity, stability, accuracy, and repeatability, which underscores its the prospective utility. Indeed, these findings indicate that our established screening strategy along with the multi-epitope nanobody sandwich mode provides an optimized strategy in the field of pathogen detection.

CRISPR/Cas and Argonaute-powered lateral flow assay for pathogens detection

Pathogens contamination is a pressing global public issue that has garnered significant attention worldwide, especially in light of recent outbreaks of foodborne illnesses. Programmable nucleases like CRISPR/Cas and Argonaute hold promise as tools for nucleic acid testing owning to programmability and the precise target sequence specificity, which has been utilized for the development pathogens detection. At present, fluorescence, as the main signal output method, provides a simple response mode for sensing analysis. However, the dependence of fluorescence output on large instruments and correct analysis of output data limited its use in remote areas. Lateral flow strips (LFS), emerging as a novel flexible substrate, offer a plethora of advantages, encompassing easy-to-use, rapidity, visualization, low-cost, portability, etc. The integration of CRISPR/Cas and Argonaute with LFS, lateral flow assay (LFA), rendered a new and on-site mode for pathogens detection. In the review, we introduced two programmable nucleases CRISPR/Cas and Argonaute, followed by the structure, principle and advantages of LFA. Then diversified engineering detection pattens for viruses, bacteria, parasites, and fungi based on CRISPR/Cas and Argonaute were introduced and summarized. Finally, the challenge and perspectives involved in on-site diagnostic assays were discussed.

One-base-mismatch CRISPR-based transistors for single nucleotide resolution assay

An effective strategy for accurately detecting single nucleotide variants (SNVs) is of great significance for genetic research and diagnostics. However, strict amplification conditions, complex experimental instruments, and specialized personnel are required to obtain a satisfactory tradeoff between sensitivity and selectivity for SNV discrimination. In this study, we present a CRISPR-based transistor biosensor for the rapid and highly selective detection of SNVs in viral RNA. By introducing a synthetic mismatch in the crRNA, the CRISPR-Cas13a protein can be engineered to capture the target SNV RNA directly on the surface of the graphene channel. This process induces a fast electrical signal response in the transistor, obviating the need for amplification or reporter molecules. The biosensor exhibits a detection limit for target RNA as low as 5 copies in 100 μL, which is comparable to that of real-time quantitative polymerase chain reaction (PCR). Its operational range spans from 10 to 5 × 105 copy mL-1 in artificial saliva solution. This capability enables the biosensor to discriminate between wild-type and SNV RNA within 15 min. By introducing 10 μL of swab samples during clinical testing, the biosensor provides specific detection of respiratory viruses in 19 oropharyngeal specimens, including influenza A, influenza B, and variants of SARS-CoV-2. This study emphasizes the CRISPR-transistor technique as a highly accurate and sensitive approach for field-deployable nucleic acid screening or diagnostics.

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.

Detection of Tetracycline with a CRISPR/Cas12a Aptasensor Using a Highly Efficient Fluorescent Polystyrene Microsphere Reporter System

CRISPR-based diagnostics use the CRISPR-Cas system trans-cleavage activity to identify specific target sequences. When activated, this activity cleaves surrounding reporter molecules, producing a detectable signal. This technique has great specificity, sensitivity, and rapid detection, making it an important molecular diagnostic tool for medical and infectious disease applications. Despite its potential, the present CRISPR/Cas system has challenges with its single-stranded DNA reporters, characterized by low stability and limited sensitivity, restricting effective application in complex biological settings. In this work, we investigate the trans-cleavage activity of CRISPR/Cas12a on substrates utilizing fluorescent polystyrene microspheres to detect tetracycline. This innovative discovery led to the development of microsphere probes addressing the stability and sensitivity issues associated with CRISPR/Cas biosensing. By attaching the ssDNA reporter to polystyrene microspheres, we discovered that the Cas12a system exhibits robust and sensitive trans-cleavage activity. Further work revealed that the trans-cleavage activity of Cas12a on the microsphere surface is significantly dependent on the concentration of the ssDNA reporters. Building on these intriguing discoveries, we developed microsphere-based fluorescent probes for CRISPR/Cas aptasensors, which showed stability and sensitivity in tetracycline biosensing. We demonstrated a highly sensitive detection of tetracycline with a detection limit of 0.1 μM. Finally, the practical use of a microsphere-based CRISPR/Cas aptasensor in spiked food samples was proven successful. These findings highlighted the remarkable potential of microsphere-based CRISPR/Cas aptasensors for biological research and medical diagnosis.

CRISPR-Cas based diagnostic tools: Bringing diagnosis out of labs

Timely detection is important for the effective management of infectious diseases. Reverse Transcription Polymerase Chain Reaction (RT-PCR) stands as the prime nucleic acid based test that is employed for the detection of infectious diseases. The method ensures sensitivity and specificity. However, RT-PCR is a relatively expensive technique due to the requirement of costly equipment and reagents. Further, it requires skilled personnel and established laboratories that are usually inaccessible in underdeveloped areas. On the other hand, rapid antigen based techniques are cost effective and easily accessible, but are less effective in terms of sensitivity and specificity. CRISPR-Cas systems are advanced diagnostic tools that combine the advantages of both PCR and antigen based detection techniques, and allows the rapid detection with high sensitivity/specificity. The present review aims to discuss the applicability of CRISPR-Cas based diagnostic tools for the infectious disease detection. The review further attempts to highlight the current limitations and future research directions to improve the CRISPR based diagnostic tools for rapid and effective disease detection.

A Thermostable Cas12b-Powered Bioassay Coupled with Loop-Mediated Isothermal Amplification in a Customized "One-Pot" Vessel for Visual, Rapid, Sensitive, and On-Site Detection of Genetically Modified Crops

Genetically modified crops (GMCs) have been discussed due to unknown safety, and thus, it is imperative to develop an effective detection technology. CRISPR/Cas is deemed a burgeoning technology for nucleic acid detection. Herein, we developed a novel detection method for the first time, which combined thermostable Cas12b with loop-mediated isothermal amplification (LAMP), to detect genetically modified (GM) soybeans in a customized one-pot vessel. In our method, LAMP-specific primers were used to amplify the cauliflower mosaic virus 35S promoter (CaMV35S) of the GM soybean samples. The corresponding amplicons activated the trans-cleavage activity of Cas12b, which resulted in the change of fluorescence intensity. The proposed bioassay was capable of detecting synthetic plasmid DNA samples down to 10 copies/μL, and as few as 0.05% transgenic contents could be detected in less than 40 min. This work presented an original detection method for GMCs, which performed rapid, on-site, and deployable detection.