Novel H2S sensing mechanism derived from the formation of oligomeric sulfide capping the surface of gold nanourchins

Abstract

A gold nanourchin (AuNU) probe with a novel sensing mechanism for monitoring H₂S was developed as a feasible colorimetric sensor. In this study, AuNUs that are selectively responsive to H₂S were fabricated in the presence of trisodium citrate and 1,4-hydroquinone using a seed-mediated approach. Upon exposure of the AuNU solution to H₂S, 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 H₂S 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 H₂S 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. H₂S 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.