Gold nanostar@graphene quantum dot as a new colorimetric sensing platform for detection of cysteine

We here report on a facile method for preparation of gold nanostar-graphene quantum dot (AuNS@GQD) composite, which produces highly active surfactant-free AuNSs. The etching reaction of this composite with Na2SO3 was studied and used as a new sensing strategy for colorimetric detection of nM levels of cysteine. In the presence of Na2SO3, the shape of AuNSs changes to sphere-like nanoparticles, leading to a distinct color change of solution from light green to indigo. This phenomenon results from the redox reaction of Au atoms at the apexes and sharp corners of the NSs with oxygen which leads to the formation of [Au(SO3)(2)](3-). Our studies indicated that the stars with larger sizes show greater activity in etching reaction since they have more branches and sharper tips. Due to the strong coordination between Au and thiols, pre-added cysteine can protect the AuNSs from SO32-etching and so the shape and the color of AuNSs remain unaltered. This anti-etching effect was used for the detection of cysteine with the detection limit as low as 0.35 nM. The developed colorimetric sensor was validated by HPLC method and applied for analysis of human plasma samples. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

A facile method for preparing a gold nanostar-graphene quantum dot composite was reported, which resulted in highly active surfactant-free gold nanostars. The composite was used in a new sensing strategy for colorimetric detection of cysteine by studying its etching reaction with Na2SO3. Larger gold nanostars showed greater activity in the etching reaction, and pre-added cysteine protected the nanostars from etching, allowing for sensitive detection of cysteine with a detection limit of 0.35 nM.