FRET- based immunoassay using CdTe and AuNPs for the detection of OmpW antigen of Vibrio cholerae

In the past few decades, nanoscales Forster resonance energy transfer (FRET) based techniques have been used to improve the bioanalysis applications. In this study a new FRET immunosensor based on CdTe was developed for detection of Vibrio cholerae outer membrane protein W (OmpW). The assay is based on competitive quantum dot fluorescence quenching by Au nanoparticles (AuNPs). AuNPs with maximum absorption around 517 nm and average size of 14.5 nm was synthesized using the Turkevich method. The Surface of particles was modified with 11-MUA and was conjugated with OmpW via amine coupling method. Formation of Au-OmpW was confirmed by FTIR. Carboxyl functionalized CdTe was conjugated to polyclonal anti-OmpW in the same way. Due to interaction of OmpW with its related antibody, the distance between two particles becomes less than 10 nm and the energy of CdTe transfers to AuNP and cause to decrease of emission intensity. The more the ratio of Au-OmpW, the more quenching of fluorescent emission of CdTe-anti-OmpW via FRET process. By addition of free OmpW, competition between free and conjugated OmpW will cause separation of Au-OmpW from CdTe-anti-OmpW and results in fluorescent recovery. Increase in fluorescence intensity is proportional to the concentration of free OmpW in the analyze solution. The lowest concentration of OmpW that was detected in this study was 2 nM and the linear range of detection was determined to be 2-10 nM. This method is simple, fast and sensitive and also doesn't need any washing step and requires no specific equipment.