Abstract
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.
Highlights
Homogeneous solution without any immobilization, separation and washing steps
A novel colorimetric sensing strategy by combining the signal transducer and CHA is developed for detecting the part of lytA gene of S. pneumoniae[25,26] and the whole cell of Salmonella Typhimurium[27]
The generated abundant G-quadruplex structures are proportional to targets
Summary
Homogeneous solution without any immobilization, separation and washing steps. In this study, colorimetric detection is based on repetitive guanine rich sequence motifs, which can form G-quadruplex/ hemin complex (DNAzyme) in the presence of hemin. A novel colorimetric sensing strategy by combining the signal transducer and CHA is developed for detecting the part of lytA gene of S. pneumoniae[25,26] and the whole cell of Salmonella Typhimurium[27]. The method reveals a great potential to adapt CHA to support even more robust analytical applications, and construct a label-free, enzyme-free, visual, simple, rapid, sensitive and specific platform for the development of low-cost and point-of-care diagnostics. It may be a potential and powerful tool for clinical diagnostics in the future
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