Development of an enhanced visual signal amplification assay for GSH detection with DNA-cleaving DNAzyme as a trigger

One-step construction of bioinspired multi-enzyme mimicking nanozyme as a universal platform for multi-mode sensing and catalytic degradation

Nanozymes, a category of nanomaterials with exceptional enzyme-like activity, exhibit the significant promise to overcome the inherent limitations of natural enzymes. Inspired by the active site structure of natural laccase, a biomimetic MA-Cu nanozyme with three-dimensional network structure was constructed in water system through one-step complexation based on the specific coordination between nitrogen-rich triazine heterocyclic melamine and Cu2+, in a facile, green and economical manner. Compared to natural laccase, MA-Cu possesses superior multi-enzyme mimicking activity, stability and cost-effectiveness. Through comprehensive characterizations, activity tests and theoretical calculations, the catalytic mechanism and the ligand-tunability of enzyme-like activity have been thoroughly investigated. Based on its multi-enzyme-like activities, a multifunctional monitoring platform for sulfide in food, epinephrine in preparations and glutathione in cells was successfully constructed, respectively. Notably, a green degradation and discrimination platform based on MA-Cu for various pollutants was developed, exhibiting distinguished substrate universality and detoxication capacity. As a stable, easily scalable and commercially applicable nanozyme, MA-Cu is expected to become a compelling candidate for replacing natural enzyme, showing excellent prospects in environmental remediation and biosensing.

Naked-eye detection of plant viral disease using polymerase chain reaction amplification and DNAzyme

Plant viral diseases can seriously affect the yield and quality of crops. In this work, a convenient and highly sensitive biosensor for the visual detection of plant viral disease is proposed by the PCR-induced generation of DNAzyme. In the absence of nucleic acid for a target plant virus, the primers prohibited the production of G-quadruplex by forming a hairpin structure. However, PCR amplification occurred and generated a number of specific PCR products with free G-quadruplex sequences at both ends in the presence of the target cDNA. A catalytically active G-quadruplex DNAzyme was formed with the help of K+ and hemin, resulting in the formation of colored products visible to the naked eye and a strong absorbance by the addition of ABTS2- and H2O2. The absorbance and the logarithm of target cDNA concentrations showed a good linear relationship in the range of 10 fM-1.0 nM, with a linear regression equation of A = 0.1402 lg c + 0.3761 (c: fM) and a detection limit of 0.19 fM. This method was successfully applied to the analysis of emerging tobacco mosaic virus (TMV) infections in tobacco leaf samples collected in the field due to its flexibility and convenience, indicating a potential application for the early detection of plant viral disease.

Visual isothermal amplification detection of ASFV based on trimeric G-quadruplex cis-cleavage activity of Cas-12a

African swine fever virus (ASFV) is a kind of DNA virus and can infect both domestic pigs and wild boars with fatality up to 100%. The contaminated meat products mainly led to the worldwide transmission of ASFV. The outbreak of ASF greatly affects the supply stability of meat products as well as the development of the global pig industry. In this study, a visual isothermal amplification detection assay for ASFV based on trimeric G-quadruplex cis-cleavage activity of Cas12a was developed. The introduction of Cas12a could discriminate the specific amplification from the non-specific amplification and improve the sensitivity. The detection limit was as low as 0.23 copies/μL. This assay had good potential in the detection of ASFV and would be helpful for the stability of meat production and supply.

A CRISPR/Cas12a-assisted array for Helicobacter pylori DNA analysis in saliva

Helicobacter pylori infection has become a threat to the world populations. This leads to an urgent need of an efficient and convenient approach to accurately diagnose H. pylori infection. Saliva-based diagnoses are particularly welcomed for their efficiency and convenience. Aiming at saliva sample analysis, we proposed a CRISPR/Cas12a-assisted array, which had integrated H. pylori concentration detection and genotype screening functions. Single-nucleotide variations (SNVs) could be distinguished using the screening array with different probes, and an isothermal cycling strategy was combined with the trans-cleavage activity of Cas12a for signal amplification to improve accuracy of the diagnosis. As a demonstration, the SNV screening array was fabricated by utilizing the hybridization efficiency difference caused by mismatched bases. The array was able to successfully distinguish between ten H. pylori genotypes, and combined with the successful SDA biosensing, it had a LOD of as low as 60 fM. It was also able to diagnose H. pylori infection in saliva samples from infected patients. Together, the developed array has a potential in large-scale clinical screening and is a promising tool for the diagnosis and prevention of H. pylori infection-related diseases.