Nanozyme based colorimetric detection of biogenic gaseous H₂S using Ag@Au core/shell nanoplates with peroxidase-like activity

A highly sensitive and facile colorimetric assay is introduced for detecting biogenic gaseous H₂S using peroxidase (POD)-like catalytic activity of silver core/gold shell nanoplates (Ag@Au NPls). H₂S can react with Ag@Au NPls to form Ag₂S or Au₂S on their surface, which can reduce POD-like activity of Ag@Au NPls and consequently decrease the absorbance at 650 nm due to oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂). For in situ and multiple detection of H₂S, we utilized a microplate cover with 24 polydimethylsiloxane inner wells where Ag@Au NPls reacted with H₂S gas followed by treatment with TMB/H₂O₂. As a result, the change in absorbance at 650 nm showed a linear relationship with the H₂S concentration in the range 0.33 to 2.96 μM (0.36 absorbance/μM H₂S in PBS, R² = 0.994) with a limit of detection of 263 nM and a relative standard deviation of 4.4%. Finally, this assay could detect H₂S released from Eikenella corrodens, used as a model bacterium, in a short time (20 min) or at a low number of bacteria (1 × 10⁴ colony forming units/mL). Therefore, this assay is expected to be applied for the study of H₂S signaling in bacterial physiology, as well as measure H₂S production released from other oral bacteria that cause halitosis and oral diseases, leading to the subsequent diagnosis.