A triple amplification strategy using GR-5 DNAzyme as a signal medium for ultrasensitive detection of trace Pb2+ based on CRISPR/Cas12a empowered electrochemical biosensor

Terminal deoxynucleotidyl transferase-mediated CRISPR sensing platform for simple and point-of-care detection of cobalt pollution

The excessive use of cobalt in various chemical industries and arbitrary discharge of industrial wastewater have led to increased cobalt pollution in soil and water resources, increasing the risk of human exposure to high concentrations of cobalt and necessitating an urgent need for on-site monitoring platform for cobalt pollution. In this study, the terminal deoxynucleotidyl transferase (TdT)-CRISPR platform has been developed. In this platform, cobalt as a cofactor of TdT, can significantly improve the tailing efficiency of TdT-mediated extension. Therefore, when cobalt is present, the detection probe can be extended with poly(T) tails through the TdT-mediated extension, which can be subsequently served as the DNA activator for Cas12a, leading to the cleavage of fluorescence reporter molecules and triggering turn-on fluorescence signals. Consequently, this dual amplification sensing strategy of TdT-CRISPR platform demonstrated exceptional sensitivity (0.83 nM) and high specificity for cobalt over other ions. Furthermore, the method was successfully employed for the detection of cobalt in tap water and river samples. CRISPR-lateral flow assays (CRISPR-LFAs) were evaluated in this study for the simple and point-of-care detection of cobalt pollution. The assays are capable of detecting cobalt concentrations as low as 50 nM, which is significantly lower than the environmental standards of 16.9 μM, through strip analysis with the naked eye. These results commonly suggest that the TdT-CRISPR platform holds significant promise for monitoring cobalt pollution, providing a robust and sensitive solution for on-site detection and contributing to the mitigation of cobalt contamination risks in environmental matrices.

Label-free and ultrasensitive detection of environmental lead ions based on spatially localized DNA nanomachines driven by hyperbranched hybridization chain reaction

A label-free fluorescent sensing strategy for the rapid and highly sensitive detection of Pb2+ was developed by integrating Pb2+ DNAzyme-specific cleavage activity and a tetrahedral DNA nanostructure (TDN)-enhanced hyperbranched hybridization chain reaction (hHCR). This strategy provides accelerated reaction rates because of the highly effective collision probability and enriched local concentrations from the spatial confinement of the TDN, thus showing a higher detection sensitivity and a more rapid detection process. Moreover, a hairpin probe based on a G-triplex instead of a G-quadruplex or chemical modification makes hybridization chain reaction more controlled and flexible, greatly improving signal amplification capacities and eliminating labeled DNA probes. The enhanced reaction rates and improved signal amplification efficiency endowed the biosensors with high sensitivity and a rapid response. The label-free detection of Pb2+ based on G-triplex combined with thioflavin T can be achieved with a detection limit as low as 1.8 pM in 25 min. The proposed Pb2+-sensing platform was also demonstrated to be applicable for Pb2+ detection in tap water, river water, shrimp, rice, and soil samples, thus showing great potential for food safety and environmental monitoring.

CRISPR/Cas12a trans-cleavage mediated photoelectrochemical biosensor based on zeolitic imidazolate framework-67 for ATP determination

An efficient PEC biosensor is proposed for ATP detection based on exciton energy transfer from CdTe quantum dots (CdTe QDs) to Au nanoparticles (AuNPs), integrating CRISPR/Cas12a trans-cleavage activity and specific recognition of ZIF-67 to ATP. Exciton energy transfer between CdTe QDs and AuNPs system is firstly constructed as photoelectrochemical (PEC) sensing substrate. Then, the activator DNAs, used to activate CRISPR/Cas12a, are absorbed on the surface of ZIF-67. In the presence of ATP, the activator DNAs are released due to more efficient adsorption of ZIF-67 to ATP. The released activator DNA activates trans-cleavage activity of CRISPR/Cas12a to degrade ssDNA on the electrode, leading to the recovery of photocurrent due to the interrupted energy transfer. Benefiting from the specific recognition of ZIF-67 to ATP and CRISPR/Cas12a-modulated amplification strategy, the sensor is endowed with excellent specificity and high sensitivity.

CRISPR-powered microfluidic biosensor for preamplification-free detection of ochratoxin A

The CRISPR technology, which does not require complex instruments, expensive reagents or professional operators, has attracted a lot of attention. When utilizing the CRISPR-Cas system for detection, the pre-amplification step is often necessary to enhance sensitivity. However, this approach tends to introduce complexity and prolong the time required. To address this issue, we employed Pd@PCN-222 nanozyme to label single-stranded DNA, referred to as Pd@PCN-222 CRISPR nanozyme, which serves as the reporter of the CRISPR system. Pd@PCN-222 nanozyme possess exceptional catalytic activity for the reduction of H2O2. Compared with traditional electrochemical probe ferrocene and methylene blue without catalytic activity, there is a significant amplification of the electrochemical signal. So the need for pre-amplification was eliminated. In this study, we constructed a CRISPR-Cas system for ochratoxin A, utilizing the Pd@PCN-222 CRISPR nanozyme to amplified signal avoiding pre-amplification with outstanding detection of 1.21 pg/mL. Furthermore, we developed a microfluidic electrochemical chip for the on-site detection of ochratoxin A. This achievement holds significant promise in establishing a practical on-site detection platform for identifying food safety hazards.

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.

Engineered Electrochemiluminescence Biosensors for Monitoring Heavy Metal Ions: Current Status and Prospects

Metal ion contamination has serious impacts on environmental and biological health, so it is crucial to effectively monitor the levels of these metal ions. With the continuous progression of optoelectronic nanotechnology and biometrics, the emerging electrochemiluminescence (ECL) biosensing technology has not only proven its simplicity, but also showcased its utility and remarkable sensitivity in engineered monitoring of residual heavy metal contaminants. This comprehensive review begins by introducing the composition, advantages, and detection principles of ECL biosensors, and delving into the engineered aspects. Furthermore, it explores two signal amplification methods: biometric element-based strategies (e.g., HCR, RCA, EDC, and CRISPR/Cas) and nanomaterial (NM)-based amplification, including quantum dots, metal nanoclusters, carbon-based nanomaterials, and porous nanomaterials. Ultimately, this review envisions future research trends and engineered technological enhancements of ECL biosensors to meet the surging demand for metal ion monitoring.