Vertical flow paper-based plasmonic device for cysteine detection

Cystinuria, is an autosomal recessive genetic disorder involving increasingly high levels of poorly soluble cysteine in urine leading to formation of stones. Developing a facile, low-cost, point-of-care and selective sensor for diagnosis of cysteine is imperative. Accordingly, for the detection of cysteine, the present study demonstrates an inexpensive colorimetric, paper-based vertical flow plasmonic micro-well device with a two-minute turn-around time. The method encompasses the use of microbially-synthesized silver nanoparticles (AgNPs) that change from light brown / yellow to dark brown upon binding with Sulphur present in cysteine. This technique allows for visual detection up to 1 × 10^-5 mM cysteine and can be easily offered as a rapid diagnostic test even at setups with minimal resources.