Towards a targeted Escherichia coli fluorescent biosensor using quantum-dot-decorated geothermal silica nanoparticles

Water quality is assessed based on physical, chemical and biological parameters, including the presence of Escherichia coli (E. coli), a significant pathogen associated with waterborne diseases. In this study, we developed a highly sensitive fluorescent biosensor platform using quantum-dot-modified geothermal-silica-based nanoparticles (SiNP@QD). Amine-CdSe quantum dots (QDs) were incorporated onto the surface as optical transducers and subsequently immobilized with E. coli antibodies to enhance selectivity (SiNP@QD-Ab). The Brunauer-Emmett-Teller (BET) method determined the surface area of the silica nanoparticles to be 137.75 m² g^-1, with the particle size ranging from 40 to 70 nm according to field emission-scanning electron microscope (FESEM) analysis. X-ray diffraction (XRD) analysis confirmed that the nanoparticles were in their amorphous phase. Detection of the bacteria using SiNP@QD-Ab as a biosensor was observed using a fluorescence spectrophotometer with an excitation wavelength of 360 nm, and emission was observed in the range of 400-800 nm. The analytical performance of the biosensor was observed by varying the incubation times and E. coli concentrations, with the optimal incubation time being 15 minutes. The limit of detection (LOD) for SiNP@QD-Ab, at the maximum emission peak of 435 nm, was determined to be 1.6 CFU mL^-1. The SiNP@QD-Ab biosensor offers a swift and accurate method for detecting E. coli, promising significant advancements in public health safety and environmental monitoring.