High sensitivity colorimetric determination of L-cysteine using gold nanoparticles functionalized graphene oxide prepared by photochemical reduction method

• AuNps and AuNps@ GO were prepared by photochemical reduction method. • The colorimetric detection of L-cysteine was demonstrated in a nanomolar order concentration. • 4-Hydroxybenzophenone was used as photoreducing agent for Au ions. • AuNps and AuNps@ GO acted as simple and sensitive nano-sensors for L-cysteine. This study aimed for the development of a cost effective and efficient method for L-cysteine detection, without employing expensive instrumentation within a short analysis time. The proposed method has been involved in the photochemical preparation of gold nanoparticles and gold nanoparticles on graphene oxide nanostructures. The gold nanoparticles and gold nanoparticles on graphene oxide acted as simple and sensitive nano-sensors for L-cysteine, due to the molecular structure of the L-cysteine presented –NH 2 and –SH, which is very attractive for coordination to gold nanoparticles and crosslink gold nanoparticles causing aggregation and color change. By using the gold nanoparticles on graphene oxide as a probe, the colorimetric detection of L-cysteine in a nanomolar order concentration was demonstrated.