Novel HS sensing mechanism derived from the formation of oligomeric sulfide capping the surface of gold nanourchins.

A gold nanourchin (AuNU) probe with a novel sensing mechanism for monitoring HS was developed as a feasible colorimetric sensor. In this study, AuNUs that are selectively responsive to HS were fabricated in the presence of trisodium citrate and 1,4-hydroquinone using a seed-mediated approach. Upon exposure of the AuNU solution to HS, the hydrosulfide ions (HS) in the solution are converted into oligomeric sulfides by 1,4-hydroquinone used as a reducing agent during the synthesis of AuNUs. The oligomeric sulfides formed in the AuNU solution upon the addition of HS were found to coat the surface of the AuNUs, introducing a blue shift in absorption accompanied by a color change in the solution from sky blue to light green. This colorimetric alteration by the capping of oligomeric sulfides on the surface of AuNUs is unique compared to well-known color change mechanisms, such as aggregation, etching, or growth of nanoparticles. The novel HS sensing mechanism of the AuNUs was characterized using UV-Vis spectroscopy, high-resolution transmission microscopy, X-ray photoelectron spectroscopy, surface-enhanced Raman spectroscopy, secondary ion mass spectroscopy, liquid chromatography-tandem mass spectrometry, and atom probe tomography. HS was reliably monitored with two calibration curves comprising two sections with different slopes according to the low (0.3-15 μM) and high (15.0-300 μM) concentration range using the optimized AuNU probe, and a detection limit of 0.29 μM was obtained in tap water.