Gold nanoparticle extraction followed by o-phthaldialdehyde derivatization for fluorescence sensing of different forms of homocysteine in plasma

This study reports a selective and sensitive method for fluorescent detection of total, protein-bound, free, and free oxidized homocysteine (HCys) using tris(2-carboxyethyl)phosphine (TCEP) as a reducing agent, fluorosurfactant-capped gold nanoparticles (FSN–AuNP) as a preconcentrating probe, and o-phthaldialdehyde (OPA) as a derivatizing agent. TCEP was used to reduce the disulfide bonds of protein-bound and free oxidized HCys. FSN–AuNPs can extract HCys from a complicated complex because the FSN capping layer stabilizes the AuNPs in a high-salt solution and inhibits non-specific adsorption. HCys was selectively derivatized with OPA in the absence of a nucleophile. By taking advantage of these features, the selectivity of the proposed system is greater than 100-fold for HCys and homocystine (HCys–HCys disulfide; diHCys) compared to any aminothiols. The limits of detection for HCys and diHCys were 4.4 and 4.6 nM, respectively. Different forms of plasma HCys were determined by varying the order of disulfide reduction with TCEP.

► This method provided excellent selectivity toward HCys compared to other sensor.
► This method provided the lowest LOD value for HCys compared to other sensors.
► We determined different forms of HCys in plasma without chromatographic separation.
► Only 30 μL of sample volume is required to determine total and protein-bound HCys.