A novel magneto-DNA duplex probe for bacterial DNA detection based on exonuclease III-aided cycling amplification

Development of DNA Biosensors Based on DNAzymes and Nucleases

DNA biosensors play important roles in environmental, medical, industrial and agricultural analysis. Many DNA biosensors have been designed based on the enzyme catalytic reaction. Because of the importance of enzymes in biosensors, we present a review on this topic. In this review, the enzymes were divided into DNAzymes and nucleases according to their chemical nature. Firstly, we introduced the DNAzymes with different function inducing cleavage, metalation, peroxidase, ligation and allosterism. In this section, the G-quadruplex DNAzyme, as a hot topic in recent years, was described in detail. Then, the nucleases-assisted signal amplification method was also reviewed in three categories including exonucleases, endonucleases and other nucleases according to the digestion sites in DNA substrates. In exonucleases section, the Exo I and Exo III were selected as examples. Then, the DNase I, BamH I, nicking endonuclease, S1 nuclease, the duplex specific nuclease (DSN) and RNases were chosen to illustrate the application of endonucleases. In other nucleases section, DNA polymerases and DNA ligases were detailed. Last, the challenges and future perspectives in the field were discussed.

DNA pom-pom nanostructure as a multifunctional platform for pathogenic bacteria determination and inactivation

Pathogenic bacteria levels are significantly related with disease control, clinical diagnosis, and even environmental monitoring. It is becoming highly urgent to achieve ultrasensitive detection of pathogenic bacteria and efficient combat of bacterial infection. Toward this end, we have assembled a DNA Pom-Pom nanostructure (PP-N) based multifunctional platform for pathogenic bacteria determination and inactivation. In particular, one DNA oligonucleotide probe that serve as a trigger was specifically designed for the autonomous cross-opening of metastable DNA hairpin probes and long dsDNA structure formation, achieving a catalytic self-assembly of DNA nanostructure. Numerous DNA strands in this PP-N assembly provide sufficient interaction sites for functional domains and connector, showing high programmability, excellent biostability, as well as selective target recognition. With these properties, the fluorescence dyes modified PP-N platform showed excellent bacteria analysis with both excellent selectivity and ultrasensitive determination limit as low as 2.0 CFU/mL. Furthermore, the aptamer-functionalized and antibiotics loaded PP-N platform demonstrate excellent merits of high antibiotics-loading capacity and negligible cytotoxicity to targets. Therefore, this DNA PP-N assembly based multifunctional platform promise its great application in targeted sensing, combating bacterial infection, and potential clinic therapy.

A label-free fluorescent aptasensor for selective and sensitive detection of streptomycin in milk and blood serum

Sensitive and fast detection of antibiotic residues in animal derived foods and blood serum is of great interest. In this study a fluorescent aptasensor was designed for selective and sensitive detection of streptomycin (STR) based on Exonuclease III (Exo III), SYBR Gold and aptamer complimentary strand. In the absence of STR, the fluorescence intensity is weak. Upon addition of STR, the aptamer binds to its target, leading to release of complementary strand from aptamer and more protection against Exo III function. Following addition of SYBR Gold, a strong fluorescence intensity is obtained. This aptasensor showed a high selectivity toward STR with a limit of detection (LOD) as low as 54.5 nM. The validity of the procedure and applicability of the aptasensor were successfully assessed by detection of STR in a spiked milk and blood serum without interference from the sample matrix.

Lysozyme as a recognition element for monitoring of bacterial population

Bacterial infections remain a significant challenge in biomedicine and environment safety. Increasing worldwide demand for point-of-care techniques and increasing concern on their safe development and use, require a simple and sensitive bioanalysis for pathogen detection. However, this goal is not yet achieved. A design for fluorescein isothiocyanate-labeled lysozyme (FITC-LYZ), which provides quantitative binding information for gram-positive bacteria, Micrococcus luteus, and detects pathogen concentration, is presented. The functional lysozyme is used not only as the pathogenic detection platform, but also as a tracking reagent for microbial population in antibacterial tests. A nonlinear relationship between the system response and the logarithm of the bacterial concentration was observed in the range of 1.2×10(2)-1.2×10(5) cfu mL(-1). The system has a potential for further applications and provides a facile and simple method for detection of pathogenic bacteria. Meanwhile, the fluorescein isothiocyanate -labeled lysozyme is also employed as the tracking agent for antibacterial dynamic assay, which show a similar dynamic curve compared with UV-vis test.