CRISPR-Cas12a System for Biosensing and Gene Regulation

Enhanced production of functional CRISPR-AsCas12a protein in Escherichia coli

The CRISPR-Cas12a system is a groundbreaking tool widely used for genome editing and diagnostics in biotechnology and biomedicine research laboratories. Despite its growing application, studies optimizing Cas12a protein production at the laboratory scale using straightforward protocols remains scarce. This study aimed to enhance the lab-scale recombinant production of Acidaminococcus sp Cas12a protein (AsCas12a) in E. coli. Through targeted adjustments of simple parameters, AsCas12a production was significantly increased. The optimized conditions included the use of E. coli BL21(DE3), TB medium supplemented with 1 % glucose, induction with 0.3 mM IPTG for at least 6-9 h, and incubation at 30 °C. Notably, these conditions differ from conventional protocols typically used for Cas12a and related proteins, such as Streptococcus pyogenes Cas9. Upon combining all optimized parameters, AsCas12a production increased approximately 3-fold, from 0.95 mg/mL of bacterial lysate under non-optimized conditions to 3.73 mg/mL under optimized ones. After chromatographic purification, the final protein yield rose approximately 4.5-fold, from 5.2 to 23.4 mg/L of culture volume, without compromising functional activity. The purified AsCas12a retained full activity for programmable in vitro DNA cis-cleavage and collateral trans-cleavage, which was successfully applied to detect the N gene of SARS-CoV-2. This optimized method provide an efficient and high-yield approach for producing functional AsCas12a protein using accessible materials and conditions available to many research laboratories worldwide.

Ultrasensitive RNase H activity detection using the transcription-based hybrid probe and CRISPR/cas12a signal amplifier

Ribonuclease H (RNase H), a critical functional protein in replication and genome stability, is emerging as a crucial therapeutic target for various diseases, including immune disorders. We present a transcription-based hybrid probe, referred to as Hybprobe, and a CRISPR/Cas12a signal amplifier for the rapid, sensitive, and low-cost detection of RNase H activity. In this method, the RNA strand of the Hybprobe is specifically cleaved by RNase H, releasing a single-stranded DNA activator that facilitates recognition and cleavage by the Cas12a/crRNA complex, triggering signal amplification via Cas12a's trans-cleavage activity. The proposed method demonstrates ultra-high sensitivity, capable of detecting RNase H as low as 9.02 × 10-10 U/μL, making it approximately 1,000 times more sensitive than several previously reported methods. Furthermore, we demonstrated the application of this method for RNase H inhibitor evaluation and its practical use across various biological samples, including cell extracts and HIV reverse transcriptase. In summary, the results suggest that this method is a promising tool for the highly sensitive detection of RNase H and the diagnosis of diseases associated with RNase H.

Simple and sensitive SERS platform for Staphylococcus aureus one-pot determination by photoactivated CRISPR/Cas12a cascade system and core-shell DNA tetrahedron@AuNP@Fe3O4 reporter

Staphylococcus aureus (S. aureus) is a widely prevalent Gram-positive bacteria that can cause serious infections and diseases in humans and other organisms. Timely detection and treatment in clinical settings is crucial for patient safety and public health. However, current methods for S. aureus detection still face some limitations, such as time-consuming operation, false positives, and labor-intensive available methodology with low sensitivity. Therefore, it is particularly important to develop a rapid, simple, sensitive, and cost-effective method for detecting S. aureus. We developed a SERS platform based on allosteric aptamer-triggered catalytic hairpin assembly (CHA) and photoactivated CRISPR/Cas12a reactions, combined with a multifunctional core-shell structure as the SERS reporter, enabling highly sensitive one-pot determination of S. aureus. Compared with traditional two-step and one-pot analysis methods, this strategy offers superior sensitivity and can successfully identify real samples contaminated with S. aureus. The platform utilizes light-controlled CHA and CRISPR/Cas12a reactions, effectively preventing interference between different reaction systems. Therefore, the photoactivated one-pot CHA/Cas12a strategy provides a simple, rapid, highly sensitive, specific, and cost-effective method for one-pot determination of S. aureus in clinical samples.

A sensitive miRNA detection method based on a split-T7 switch modulating CRISPR/Cas12a system

This study presents a novel method for sensitive miRNA detection based on a split-T7 switch modulating CRISPR/Cas12a system. By integrating the split-T7 promoter-mediated transcription with the CRISPR/Cas12a system, this method can achieve femtomolar detection of the target miRNA within 1 h and successfully analyze miR-21 in samples from various cell lines, demonstrating its potential for clinical applications.

Application and development of CRISPR-Cas12a methods for the molecular diagnosis of cancer: A review

Rapid, sensitive, and specific molecular detection methods are crucial for diagnosing, treating and prognosing cancer patients. With advancements in biotechnology, molecular diagnostic technology has garnered significant attention as a fast and accurate method for cancer diagnosis. CRISPR-Cas12a (Cpf1), an important CRISPR-Cas family member, has revolutionized the field of molecular diagnosis since its introduction. CRISPR-Cas technologies are a new generation of molecular tools that are widely used in the detection of pathogens, cancers, and other diseases. Liquid biopsy methods based on CRISPR-Cas12a have demonstrated remarkable success in cancer diagnosis, encompassing the detection of DNA mutations, DNA methylation, tumor-related viruses, and non-nucleic acid molecule identification. This review systematically discusses the developmental history, key technologies, and principles of CRISPR-Cas12a-based molecular diagnostic techniques and their applications in cancer diagnosis. This review has also discussed the future development directions of CRISPR-Cas12a, aiming for it to become a reliable new technology that can be used in clinical application.

CRISPR technology combined with isothermal amplification methods for the diagnosis of Candida albicans infection

Since Candida albicans, a type of fungus, causes severe infections that pose a significant threat to human health, its rapid detection is critical in clinical antifungal therapy. Traditional fungal diagnostic approaches are largely based on the culture method. This method is time-consuming and laborious, taking about 48-72 h, and cannot identify emerging species, making it unsuitable for critically ill patients with bloodstream infections, sepsis, and so on. Other antigen or nucleic acid amplification-based methods were also found to be unsuitable for Point-of-Care Testing (POCT) diagnosis due to various limitations. Therefore, establishing a new approach for the rapid diagnosis of Candida spp is imperative. Herein, we proposed a novel diagnostic method for invasive fungi detection. Specifically, we created a new CRISPR diagnostic platform for Candida albicans-specific Internal Transcriptional Spacer 2 (ITS2) gene by combining the DNase cleavage activity of Cas12a with Recombinase Polymerase Amplification (RPA). Furthermore, to achieve rapid on-site detection under low-resource conditions, we used a transverse lateral flow strip with a single target to visualize the Cas12a single enzyme digestion product. We designated the platform as a rapid molecular detection tool that integrates RPA and the CRISPR-Cas12a technology. The entire platform can accurately identify Candida albicans within 50 minwhile remaining unaffected by other fungi or bacteria. Furthermore, the detection limit of the platform could reach 102 CFU/ml. Moreover, this approach offers additional benefits, including easy operation, low set-up cost, and broad applicability for Candida albicans detection across medical institutions at all levels, especially in township health centers in resource-poor regions.

Recent development of gold nanochips in biosensing and biodiagnosis sensibilization strategies in vitro based on SPR, SERS and FRET optical properties

Gold nanomaterials have become attractive nanomaterials for biomedical research due to their unique physical and chemical properties, and nanochips are designed to manufacture high-quality substrates for loading gold nanoparticles (GNPs) to achieve specific and selective detection. By utilizing multiple optical properties of different gold nanostructures, the sensitivity, specificity, speed, contrast, resolution, and other performance of biosensing and biological diagnosis can be significantly improved. This paper summarized the sensitivity enhancement strategies of optical biosensing techniques based on the three main optical properties of gold nanomaterials: surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS) and fluorescence resonance energy transfer (FRET). The aim is to comprehensively review the development direction of in vitro diagnostics (IVDs) from two aspects: detection strategies and modification of gold nanomaterials. In addition, some opportunities and challenges that gold-based IVDs may encounter at present or in the future are also mentioned in this paper. In summary, this paper can enlighten readers with feasible strategies for manufacturing potential gold-based nanobiosensors.

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.

CRISPR/Cas-based colorimetric biosensors: a promising tool for the diagnosis of bacterial foodborne pathogens in food products

Some physical phenomena and various chemical substances newly introduced in nanotechnology have allowed scientists to develop valuable devices in the field of food sciences. Regarding such progress, the identification of foodborne pathogenic microorganisms is an imperative subject nowadays. These bacterial species have been found to cause severe health impacts after food ingestion and can result in high mortality in acute cases. The rapid detection of foodborne bacterial species at low concentrations is in high demand in recent diagnostics. CRISPR/Cas-mediated biosensors possess the potential to overcome several challenges in classical assays such as complex pretreatments, long turnaround time, and insensitivity. Among them, colorimetric nanoprobes based on the CRISPR strategy afford promising devices for POCT (point-of-care testing) since they can be visualized with the naked eye and do not require diagnostic apparatus. In this study, we briefly classify and discuss the working principles of the different CRISPR/Cas protein agents that have been employed in biosensors so far. We assess the current status of the CRISPR system, specifically focusing on colorimetric biosensing platforms. We discuss the utilization of each Cas effector in the detection of foodborne pathogens and examine the restrictions of the existing technology. The challenges and future opportunities are also indicated and addressed.

A label-free and immobilization-free approach for constructing photoelectrochemical nucleic acid sensors utilizing DNA-silver nanoparticle affinity interactions

Efficient and affordable nucleic acid detection methods play a pivotal role in various applications. Herein, we developed an immobilization-free and label-free strategy to construct a photoelectrochemical nucleic acid biosensing platform based on interactions between silver nanoparticles and DNA. First, CRISPR-Cas12a exhibited a trans-cleavage effect on adenine nucleotide sequences upon recognizing the target DNA. The resulting adenine nucleotide sequences of varying lengths then engaged in interactions with silver nanoparticles, leading to a solution characterized by distinct light transmittance. Subsequently, the solution was positioned between the light source and the photoelectrode, strategically impacting the photon absorption step within the photoelectrochemical process. Consequently, the detection of nucleic acid was accomplished through the analysis of the resultant photocurrent signal. The developed platform exhibits a detection limit of 0.06 nM (S/N = 3) with commendable selectivity. The innovative use of adenine nucleotide sequences as cost-effective probes interacting with silver nanoparticles eliminates the need for complex interfacial immobilization processes, significantly simplifying the fabrication of DNA sensors. The outcomes of our research present a promising pathway for advancing the development of economically feasible miniature DNA sensors.

A multiplex RPA-CRISPR/Cas12a-based POCT technique and its application in human papillomavirus (HPV) typing assay

Persistent infection with high-risk human papillomavirus (HR-HPV) is the primary and initiating factor for cervical cancer. With over 200 identified HPV types, including 14 high-risk types that integrate into the host cervical epithelial cell DNA, early determination of HPV infection type is crucial for effective risk stratification and management. Presently, on-site immediate testing during the HPV screening stage, known as Point of Care Testing (POCT), remains immature, severely limiting the scope and scenarios of HPV screening. This study, guided by the genomic sequence patterns of HPV, established a multiplex recombinase polymerase amplification (RPA) technology based on the concept of "universal primers." This approach achieved the multiple amplification of RPA, coupled with the CRISPR/Cas12a system serving as a medium for signal amplification and conversion. The study successfully constructed a POCT combined detection system, denoted as H-MRC12a (HPV-Multiple RPA-CRISPR/Cas12a), and applied it to high-risk HPV typing detection. The system accomplished the typing detection of six high-risk HPV types (16, 18, 31, 33, 35, and 45) can be completed within 40 min, and the entire process, from sample loading to result interpretation, can be accomplished within 45 min, with a detection depth reaching 1 copy/μL for each high-risk type. Validation of the H-MRC12a detection system's reproducibility and specificity was further conducted through QPCR on 34 clinical samples. Additionally, this study explored and optimized the multiplex RPA amplification system and CRISPR system at the molecular mechanism level. Furthermore, the primer design strategy developed in this study offers the potential to enhance the throughput of H-MRC12a detection while ensuring sensitivity, providing a novel research avenue for high-throughput detection in Point-of-Care molecular pathogen studies.

Development of a CRISPR-Cas12a based assay for the detection of swine enteric coronaviruses in pig herds in China

Porcine epidemic diarrhea virus (PEDV), Transmissible gastroenteritis virus (TGEV), Porcine deltacoronavirus (PDCoV) and Swine acute diarrhea syndrome coronavirus (SADS-CoV) rank among the most frequently encountered swine enteric coronaviruses (SECoVs), leading to substantial economic losses to the swine industry. The availability of a rapid and highly sensitive detection method proves beneficial for the monitoring and surveillance of SECoVs. Based on the N genes of four distinct SECoVs, a novel detection method was developed in this study by combining recombinant enzyme polymerase isothermal amplification (RPA) with clustered regularly interspaced short palindromic repeats (CRISPR)-associated proteins (Cas) 12a. Results showed that the cut-off value of CRISPR-Cas12a assay for SADS-CoV, PEDV, PDCoV and TGEV was 2.19 × 104 Relative Fluorescence Units (RFU), 1.57 × 104 RFU, 3.07 × 104 RFU and 1.64 × 104 RFU, respectively. The coefficient of variation (CV) of within and between runs by CRISPR-Cas12a assay for 6 clinical diarrhea samples were both less than 10%. The CRISPR-Cas12a assay demonstrated high specificity for TGEV, PEDV, PDCoV, and SADS-CoV with no cross-reactivity to other common swine viruses. This method also exhibited a low limit of detection of 2 copies for each virus. Additionally, the results demonstrated a perfect agreement (100%) between the CRISPR-Cas12a assay and the RT-qPCR assay. Finally, a total of 494 pig samples from the field tested by CRISPR-Cas12a assay showed that positive rate for SADS-CoV, TGEV, PDCoV and PEDV was 0, 0, 1.2% and 48.6%, respectively. The results suggested the great potential of CRISPR-Cas12a assay to detect SECoVs in the field.

CRISPR/Cas12-based electrochemical biosensors for clinical diagnostic and food monitoring

Each organism has a unique sequence of nitrogenous bases in in the form of DNA or RNA which distinguish them from other organisms. This characteristic makes nucleic acid-based detection extremely selective and compare to other molecular techniques. In recent years, several nucleic acid-based detection technology methods have been developed, one of which is the electrochemical biosensor. Electrochemical biosensors are known to have high sensitivity and accuracy. In addition, the ease of miniaturization of this electrochemical technique has garnered interest from many researchers. On the other hand, the CRISPR/Cas12 method has been widely used in detecting nucleic acids due to its highly selective nature. The CRISPR/Cas12 method is also reported to increase the sensitivity of electrochemical biosensors through the utilization of modified electrodes. The electrodes can be modified according to detection needs so that the biosensor's performance can be improved. This review discusses the application of CRISPR/Cas12-based electrochemical biosensors, as well as various electrode modifications that have been successfully used to improve the performance of these biosensors in the clinical and food monitoring fields.

Electrochemical biosensing for E.coli detection based on triple helix DNA inhibition of CRISPR/Cas12a cleavage activity

BACKGROUND

Escherichia coli (E.coli) is both a commensal and a foodborne pathogenic bacterium in the human gastrointestinal tract, posing significant potential risks to human health and food safety. However, one of the major challenges in E.coli detection lies in the preparation and storage of antibodies. In traditional detection methods, antibodies are indispensable, but their instability often leads to experimental complexity and increased false positives. This underscores the need for new technologies and novel sensors. Therefore, the development of a simple and sensitive method for analyzing E.coli would make significant contributions to human health and food safety.

RESULTS

We constructed an electrochemical biosensor based on triple-helical DNA and entropy-driven amplification reaction (EDC) to inhibit the cleavage activity of Cas12a, enabling high-specificity detection of E.coli. Replacing antibodies with nucleic acid aptamers (Apt) as recognition elements, we utilized the triple-helical DNA generated by the binding of DNA2 and DNA5/DNA6 double-helical DNA through the entropy-driven amplification reaction to inhibit the collateral cleavage activity of clustered regularly interspaced short palindromic repeats gene editing system (CRISPR) and its associated proteins (Cas). By converting E.coli into electrical signals and recording signal changes in the form of square wave voltammetry (SWV), rapid detection of E.coli was achieved. Optimization of experimental conditions and data detection under the optimal conditions provided high sensitivity, low detection limits, and high specificity.

SIGNIFICANCE

With a minimal detection limit of 5.02 CFU/mL and a linear range of 1 × 102 - 1 × 107 CFU/mL, the suggested approach was successfully verified to analyze E.coli at various concentrations. Additionally, after examining E.coli samples from pure water and pure milk, the recoveries ranged between 95.76 and 101.20%, demonstrating the method's applicability. Additionally, it provides a feasible research direction for the detection of pathogenic bacteria causing other diseases using the CRISPR/Cas gene editing system.

Highly sensitive detection of Salmonella based on dual-functional HCR-mediated multivalent aptamer and amplification-free CRISPR/Cas12a system

BACKGROUND

Salmonella infection severely threatens human health and causes substantial medical and financial concerns. Sensitive and specific detection of Salmonella in food samples is crucial but remains challenging. While some traditional assays for S. typhimurium are reliable, they suffer from various limitations, such as being time-consuming (culture-based methods), involving intricate nucleic molecular extraction (polymerization chain reaction, PCR), and exhibiting inadequate sensitivity (enzyme-linked immunosorbent assay, ELISA). In this case, it is essential to establish a rapid, simple-operation, and sensitive method for monitoring S. typhimurium to preserve food quality and prevent contamination.

RESULT

Herein, an amplification-free detection method for Salmonella was developed by coupling the aptamer magnetic separation with dual-functional HCR (hybridization chain reaction)-scaffold multivalent aptamer and the activity of CRISPR/Cas12a. In the detection system, the dual-functional HCR-scaffold multivalent aptamer with high binding affinity and specificity was fabricated in advance by assembling numerous Salmonella specific aptamers on the long HCR products. In addition to the enhanced affinity, the HCR-multiApt also contains a massive amount of repeated CRISPR-targetable DNA units in its HCR scaffold, which could trigger the trans-cleavage activity of Cas12a. In the presence of target bacteria, the HCR-scaffold multivalent aptamer could attach on the surface of bacteria effectively and amplified the signal of bacteria into CRISPR/Cas12a based fluorescent readout. The proposed detection system allowed for ultrasensitive detection of Salmonella in a linear range from 100 to 107 cfu mL-1 with a LOD (limit of detection) of 2 cfu mL-1.

SIGNIFICANCE

The novel dual-functional HCR-multiApt presents a simple and powerful strategy for improving the aptamer binding affinity toward Salmonella. Simultaneously, integrating this dual-functional HCR-multiApt with the CRISPR/Cas12a system significantly enhances the sensitivity by cascade signal amplification in a nucleic acids amplification-free way. Finally, leveraging the versatility of the aptamer, this highly sensitive method can be further extended for application in the detection of other bacteria, food safety monitoring, or clinical diagnostics.

Available strategies for improving the biosynthesis of surfactin: a review

Surfactin is an excellent biosurfactant with a wide range of application prospects in many industrial fields. However, its low productivity and high cost have largely limited its commercial applications. In this review, the pathways for surfactin synthesis in Bacillus strains are summarized and discussed. Further, the latest strategies for improving surfactin production, including: medium optimization, genome engineering methods (rational genetic engineering, genome reduction, and genome shuffling), heterologous synthesis, and the use of synthetic biology combined with metabolic engineering approaches to construct high-quality artificial cells for surfactin production using xylose, are described. Finally, the prospects for improving surfactin synthesis are discussed in detail.

Unamplified system for sensitive and typing detection of ASFV by the cascade platform that CRISPR-Cas12a combined with graphene field-effect transistor

At present, the 100% case fatality and the cross-infection of virus strains make the ASFV 's harm to society continue to expand. The absence of an effective commercial vaccine poses early detection remains the most effective means of curbing ASFV infection. Here, we report a cascaded detection platform based on the CRISPR-Cas12a system combined with graphene field-effect transistor sensors. The cascade platform could detect ASFV as low as 0.5 aM within 30 min and achieve typing of wild and vaccine strains of ASFV in a single detection system. The evaluation of 16 clinical samples proved that, compared with the gold standard Real-time PCR method, this platform has outstanding advantages in sensitivity, specificity and typing. Combining CRISPR-Cas12a's high specificity with the bipolar electric field effect of graphene field-effect transistor, the cascade platform is expected to achieve clinical application in the field of DNA disease detection, and provides a new direction for multi-strain disease typing.

A universal and sensitive gene mutation detection method based on CRISPR-Cas12a

Single nucleotide mutations are highly related to the occurrence and development of cancer. The development of simple single nucleotide mutation detection methods with high sensitivity and specificity has great clinical significance for the prevention, diagnosis, treatment and prognosis evaluation of cancer. In recent years, CRISPR/Cas12a has been developed as a highly sensitive, simple and fast tool for nucleic acid detection. However, the specificity and universality of current detection methods based on it are still insufficient, so their clinical applications are limited. Herein, we developed a simple and rapid single nucleotide mutation detection method based on CRISPR/Cas12a system. This method not only solves the problem of PAM sequence restriction of CRISPR/Cas12a, but also significantly improves the specificity of CRISPR/Cas12a for single nucleotide mutation and greatly improves the sensitivity. We detected three clinically significant mutations, PTEN R130Q, BRAF V600E, and TP53 R248W, with a detection limit of 0.1%. Finally, we further verified the clinical practicability of this method. We selected TP53 R248W mutation site for testing. The accuracy of testing results for 10 clinical samples was as high as 100%. In conclusion, the detection method of specific PCR combined with CRISPR/Cas12a is simple, rapid, universal and highly sensitive. We believe that this method has promising application prospects in clinical diagnosis of cancer.

Advancements in CRISPR-Based Biosensing for Next-Gen Point of Care Diagnostic Application

With the move of molecular tests from diagnostic labs to on-site testing becoming more common, there is a sudden rise in demand for nucleic acid-based diagnostic tools that are selective, sensitive, flexible to terrain changes, and cost-effective to assist in point-of-care systems for large-scale screening and to be used in remote locations in cases of outbreaks and pandemics. CRISPR-based biosensors comprise a promising new approach to nucleic acid detection, which uses Cas effector proteins (Cas9, Cas12, and Cas13) as extremely specialized identification components that may be used in conjunction with a variety of readout approaches (such as fluorescence, colorimetry, potentiometry, lateral flow assay, etc.) for onsite analysis. In this review, we cover some technical aspects of integrating the CRISPR Cas system with traditional biosensing readout methods and amplification technologies such as polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), and recombinase polymerase amplification (RPA) and continue to elaborate on the prospects of the developed biosensor in the detection of some major viral and bacterial diseases. Within the scope of this article, we also discuss the recent COVID pandemic and the numerous CRISPR biosensors that have undergone development since its advent. Finally, we discuss some challenges and future prospects of CRISPR Cas systems in point-of-care testing.

Effects of down-regulation of ackA expression by CRISPR-dCpf1 on succinic acid production in Actinobacillus succinogenes

Succinic acid (SA), a key intermediate in the cellular tricarboxylic acid cycle (TCA), is a 4-carbon dicarboxylic acid of great industrial value. Actinobacillus succinogenes can ferment various carbon sources and accumulate relatively high concentrations of SA, but few reliable genetic engineering tools exist for A. succinogenes and this has hindered strain improvement to increase SA production for industrial application. Two different repressors, endonuclease-deactivated Cas9 (dCas9) from Streptococcus pyogenes and Cpf1 (dCpf1) from Francisella tularensis, were applied to construct a CRISPRi system in A. succinogenes. Codon-optimized Cas9 and native Cpf1 were successfully expressed in A. succinogenes, and the corresponding sgRNA and crRNA expression elements, promoted by the fumarate reductase promoter, frd, were introduced into the CRISPRi plasmid. The highest repression of the ackA gene (encoding acetate kinase) and thereby acetic acid production (~ eightfold) was achieved by the dCpf1-based CRISPRi system, in which the mutation site, E1006A acted at the start of the coding region of ackA, the gene which regulates acetic acid biosynthesis. Compared with the ackA gene knockout mutant, cell growth was moderately improved and SA production increased by 6.3%. Further, the SA titer and productivity in a 3 L fermenter reached 57.06 g/L and 1.87 g/L/h, and there was less acetic acid production. A dCpf1-based CRISPRi-mediated gene repression system was successfully established for the first time, providing a simple and effective tool for studying functional genomics in A. succinogenes and optimizing SA production.

Detection of Cancer Marker Flap Endonuclease 1 Using One-Pot Transcription-Powered Clustered Regularly Interspaced Short Palindromic Repeat/Cas12a Signal Expansion

As a critical functional protein in DNA replication and genome stability, flap endonuclease 1 (FEN1) has been considered a promising biomarker and druggable target for multiple cancers. We report here a transcription-powered clustered regularly interspaced short palindromic repeat (CRISPR)/Cas12a signal expansion platform for rapid and sensitive detection of FEN1. In this method, the probe cleavage by FEN1 generated a free 5' flap single-stranded DNA which could hybridize with the single-stranded T7 promoter-bearing template and trigger the extension. Then, the CRISPR guide RNA (crRNA) transcribed from the extended template activated the collateral DNase activity of Cas12a, releasing the fluorophore from the quenched DNA signal probe to report the FEN1 detection result. The high specificity for FEN1 was validated by comparing with other repair-relevant proteins. The limit of detection (LOD) could be as low as 0.03 mU, which is sensitive enough to detect the FEN1 activity in biological samples. In addition, the inhibition assay of FEN1 was also successfully achieved with this platform, proving its potential in inhibitor screening. In summary, this study provides a novel biosensor for FEN1 activity analysis and provides new insights into the development of CRISPR-based biosensors for non-nucleic acid targets.

Dual-amplified CRISPR-Cas12a bioassay for HIV-related nucleic acids

Nucleic acid amplification strategies have successfully dominated ultrasensitive bioassays, but they sometimes bring high time-consumption, multi-step operation, increased contamination risk, and mismatch-related inaccuracy. We proposed a nucleic acid amplification-free method called the AuNPs-tagging based CRISPR-Cas12a bioassay platform. The signal amplification was realized by integrating the self-amplification effect of CRISPR-Cas12a with the enhancement effect of the large number of detectable atoms inside each gold nanoparticle. The proposed method achieved a low LOD of 1.05 amol in 40 min for HIV-related DNA.