Confined active area and aggregation kinetic-based AuNPs@PVP nanosensors for simultaneous colorimetric detection of cysteine and homocysteine as homologues in human urine and serum.

The detection of cysteine (Cys) and homocysteine (Hcy) in biological fluids has great significance for early diagnosis, including Alzheimer's and Parkinson's disease. The simultaneous determination of Cys and Hcy with a single probe is still a huge challenge. To enlarge the differences in space structure (line and ring) and energy (-721.78 and -761.08 Hartree) between Cys and Hcy, and to cause a difference of aggregation kinetics, gold nanoparticles (AuNPs) are capped with hydrophilic and low-toxic polyvinylpyrrolidone (PVP) (named AuNPs@PVP) and some surface-active sites of AuNPs are masked, the active area for the binding between AuNPs and the detection object is confined, meanwhile, the stability of AuNPs is improved. A novel nanosensor based on confined active area and aggregation kinetics of AuNPs@PVP, is designed for the identification and determination of Cys and Hcy in 1 and 3 min, respectively, with sufficiently low detection limit (4.12 and 4.35 μM) and linear range (4.12-100 μM) for health evaluation. This single colorimetric sensor was applied successfully to the determination of urine and serum, evidencing high anti-interference ability.