A multifunctional probe for optical and electrochemical detection of hydrogen sulfide and real-time selective fungal imaging

This study reports the synthesis of 2-hydroxy-<i>N</i>-(6-nitro-1,3-dioxo-1<i>H</i>-benzo[<i>de</i>]isoquinolin-2(3<i>H</i>)-yl)benzamide (SNN), designed for the selective detection of hydrogen sulfide (H₂S) and real-time imaging of <i>Candida albicans</i>. The probe was synthesized <i>via</i> imidation of 4-nitronaphthalic anhydride with salicyl hydrazide, leveraging the environmentally responsive fluorescence properties of naphthalimide derivatives. SNN demonstrated dual-mode functionality, enabling both optical and electrochemical sensing of H₂S across a range of pH conditions, thereby providing insights into sulfur chemistry. Remarkably, SNN allowed direct wet-mount imaging of <i>C. albicans</i> without the need for prolonged incubation, producing high-contrast fluorescence with minimal background noise <i>via</i> endogenous H₂S activation. It showed selective nuclear localization in <i>C. albicans</i> but did not facilitate fluorescence imaging in <i>Aspergillus niger</i>. Additionally, SNN was used for effective visualization of other fungi associated with bread spoilage, highlighting its promise as a versatile tool for fungal diagnostics and food safety applications. Moreover, the H₂S-specific imaging was validated through incubation studies using 2-(aminooxy)acetic acid hydrochloride, a selective inhibitor of the cystathionine beta-synthase enzyme involved in the production of H₂S and the metabolism of homocysteine.