Development of colorimetric biosensors based on the regulation of metal ions reduction

Abstract

Colorimetric sensors, which transform the detection events into color changes, possess a lot of advantages in terms of the naked eye detection, simplicity, no requirement of sophisticated instruments, cost-effectiveness, and easiness of analysis. The development of highly sensitive and selective colorimetric sensors has been a major goal in many fields including disease diagnostics, environmental monitoring, food safety assessment, and forensic science. Nanoparticles of gold and silver have been extensively utilized for the development of colorimetric biosensors owing to their unique optical properties. In this regard, regulation of the metal ions reduction can be utilized to develop new biosensors since it modulates the synthesis of nanoparticles which give a colorimetric signal. By controlling the reduction of novel metal ions, we have developed various colorimetric sensors for the detection of nucleic acids, amino acids, and enzymatic activity. In the first strategy described in chapter 2, a label-free, colorimetric method for ultrasensitive detection of nucleic acids, which is based on photoinduced silver ion (Ag+) reduction by DNA bases, has been developed. In the assay procedure, Ag+ is first allowed to bind to DNA through interactions with its nucleobases. The resulting DNA-Ag+ complex is then photoirradiated with 254 nm UV light, which leads to the reduction of Ag+. This process generates silver nanoparticles (AgNPs) through silver nucleation and deposition around the DNA and gives rise to a visually detectable color change with concomitant formation of an absorption peak at ca. 420 nm. The analytical capability of this simple but very powerful methodology was successfully verified by its use in the direct detection of unamplified genomic DNA from a Salmonella typhimurium pathogen with an ultrahigh sensitivity down to 67 pg/μL. The new assay system greatly simplifies and accelerates the procedure for detecting nucleic acids because it does not require ...