Advances in Portable Visual Detection of Pathogenic Bacteria

Food safety and regulation of consumer welfare are of great concern, so it is necessary to be able to detect pathogenic bacteria quickly and effectively. Although traditional methods of pathogen detection are reliable and widely used, the detection and analysis processes are cumbersome and time-consuming, which is not conducive to fast assays in the field. New detection strategies have emerged in recent years, especially point-of-care testing (POCT) methods, which do not rely on the laboratory and have become an important development direction for pathogen detection. Many visual detection schemes have been developed that integrate portable glucose meters (PGMs), test strips, smartphones, and other portable devices. Importantly, portable and ultrasensitive biosensors have vast promise in detecting pathogens, as they can be suitable tools for clinical diagnosis and the regulation of food safety. This Review focuses on the latest advances in portable device-based methods for visual detection of pathogens, evaluating their advantages and disadvantages.

Highly efficient electrochemical sensing platform for sensitive detection DNA methylation, and methyltransferase activity based on Ag NPs decorated carbon nanocubes

In this paper, we reported a sensitive and selective electrochemical method for quantify DNA methylation, analyzing DNA MTase activity and screening of MTase inhibitor based on silver nanoparticles (Ag NPs) decorated carbon nanocubes (CNCs) as signal tag. The Ag NPs/CNCs was prepared by in situ growth of nanosilver on carboxylated CNCs and used as a tracing tag to label antibody. The sensor was prepared by immobilizing the double DNA helix structure on the surface of gold electrode. When DNA MTase was introduced, the probe was methylated. Successively, anti-5-methylcytosine antibody labeled Ag NPs/CNCs was specifically conjugated on the CpG methylation site. The electrochemical stripping signal of the Ag NPs was used to monitor the activity of MTase. The electrochemical signal has a linear relationship with M.SssI activities ranging from 0.05 to 120U/mL with a detection limit of 0.03U/mL. In addition, we also demonstrated the method could be used for rapid evaluation and screening of the inhibitors of MTase. The newly designed strategy avoid the requirement of deoxygenation for electrochemical assay, and thus provide a promising potential in clinical application.

An electrochemiluminescence assay for sensitive detection of methyltransferase activity in different cancer cells by hybridization chain reaction coupled with a G-quadruplex/hemin DNAzyme biosensing strategy

A sensitive electrochemiluminescence assay coupled HCR with a G-quadruplex/hemin DNAzyme was fabricated for the detection of DNMT1 activity in cancer cells.

Sensitive fluorescent detection of DNA methyltransferase using nicking endonuclease-mediated multiple primers-like rolling circle amplification

Sensitive and reliable detection of DNA methyltransferase (MTase) is of great significance for both early tumor diagnosis and therapy. In this study, a simple, label-free and sensitive DNA MTase-sensing method was developed on the basis of a nicking endonuclease-mediated multiple primers-like rolling circle amplification (RCA) strategy. In this method, a dumbbell RCA template was prepared by blunt-end ligation of two molecules of hairpin DNA. In addition to the primer-binding sequence, the dumbbell template contained another three important parts: 5'-CCGG-3' sequences in double-stranded stems, nicking endonuclease recognition sites and C-rich sequences in single-stranded loops. The introduction of 5'-CCGG-3' sequences allows the dumbbell template to be destroyed by the restriction endonuclease, HpaII, but is not destroyed in the presence of the target MTase-M.SssI MTase. The introduction of nicking endonuclease recognition sites makes the M.SssI MTase-protected dumbbell template-mediated RCA proceed in a multiple primers-like exponential mode, thus providing the RCA with high amplification efficiency. The introduction of C-rich sequences may promote the folding of amplification products into a G-quadruplex structure, which is specifically recognized by the commercially available fluorescent probe thioflavin T. Improved RCA amplification efficiency and specific fluorescent recognition of RCA products provide the M.SssI MTase-sensing platform with high sensitivity. When a dumbbell template containing four nicking endonuclease sites is used, highly specific M.SssI MTase activity detection can be achieved in the range of 0.008-50U/mL with a detection limit as low as 0.0011U/mL. Simple experimental operation and mix-and-detection fluorescent sensing mode ensures that M.SssI MTase quantitation works well in a real-time RCA mode, thus further simplifying the sensing performance and making high throughput detection possible. The proposed MTase-sensing strategy was also demonstrated to be applicable for screening and evaluating the inhibitory activity of MTase inhibitors.

DNA Methyltransferase Activity Assays: Advances and Challenges

DNA methyltransferases (MTases), a family of enzymes that catalyse the methylation of DNA, have a profound effect on gene regulation. A large body of evidence has indicated that DNA MTase is potentially a predictive biomarker closely associated with genetic disorders and genetic diseases like cancer. Given the attention bestowed onto DNA MTases in molecular biology and medicine, highly sensitive detection of DNA MTase activity is essential in determining gene regulation, epigenetic modification, clinical diagnosis and therapeutics. Conventional techniques such as isotope labelling are effective, but they often require laborious sample preparation, isotope labelling, sophisticated equipment and large amounts of DNA, rendering them unsuitable for uses at point-of-care. Simple, portable, highly sensitive and low-cost assays are urgently needed for DNA MTase activity screening. In most recent technological advances, many alternative DNA MTase activity assays such as fluorescent, electrochemical, colorimetric and chemiluminescent assays have been proposed. In addition, many of them are coupled with nanomaterials and/or enzymes to significantly enhance their sensitivity. Herein we review the progress in the development of DNA MTase activity assays with an emphasis on assay mechanism and performance with some discussion on challenges and perspectives. It is hoped that this article will provide a broad coverage of DNA MTase activity assays and their latest developments and open new perspectives toward the development of DNA MTase activity assays with much improved performance for uses in molecular biology and clinical practice.

DNA transducer-triggered signal switch for visual colorimetric bioanalysis

A simple and versatile colorimetric biosensor has been developed for sensitive and specific detection of a wide range of biomolecules, such as oligonucleotides and aptamer-recognized targets. Combining the signal transducer and catalyzed hairpin assembly (CHA)-based signal amplification, the target DNA binds with the hairpin DNA to form a new nucleic acid sequence and creates a toehold in the transducer for initiating the recycle amplification reaction of CHA. The catalyzed assembly process produces a large amount of G-rich DNA. In the presence of hemin, the G-rich DNA forms G-quadruplex/hemin complex and mimic horseradish peroxidase activity, which catalyzes a colorimetric reaction. Under optimal conditions, the calibration curve of synthetic target DNA has good linearity from 50 pM to 200 nM with a detection limit of 32 pM. This strategy has been successfully applied to detect S. pneumoniae as low as 156 CFU mL(-1), and shows a good specificity against closely related streptococci and major pathogenic bacteria. In addition, the developed method enables successful visual analysis of S. pneumoniae in clinical samples by the naked eye. Importantly, this method demonstrates excellent assay versatility for sensitively detecting oligonucleotides or aptamer-recognized targets.