Determination of homocysteine in human plasma with a silver nanopaste-based microfluidic device

Elevated levels of homocysteine (Hcys) in plasma correlate with vascular disease, and accurate detection is crucial to maintaining good health and well-being. However, the specific detection of Hcys without interference from methionine and cysteine remains a challenge. In this study, we present a microfluidic method based on a convex-shaped design and electrochemical detection for the specific determination of Hcys in human plasma using a silver nanopaste-coated paper. The Hcys assays utilize the recombinant enzyme methionine alpha,gamma-lyase (gamma METase), which is applied onto the paper to selectively react with Hcys and generate H2S. This reaction subsequently interacts with the silver nanopaste, forming Ag-S bonds that lead to an increase in the paper's electrical resistance. The paper-based analytical device exhibits a low detection limit of 1.59 x 10-8 M and a wide linear range of 0.1 mu M to 32.5 mu M. It also demonstrates good anti-interference properties, higher stability, and high selectivity compared with other nanoparticle and paper-based sensors. Finally, the biosensor has been successfully applied to the determination of Hcys in human plasma.