Au@Ag@ZIF-8 multifunction probe with internally o-phenylenediamine encoding for the colorimetric, fluorescence, and SERS multi-mode optical detection of reactive sulfur species

Visual, highly selective, and sensitive detection of sulfur dioxide (SO2) and its derivatives (SO32-) in vitro/in vivo is of great significance in maintaining cell homeostasis. A new Au@Ag@ZIF-8 optical sensor with o-phenylenediamine (OPD) internal coding surface-enhanced Raman scattering (SERS) tags based on the free radical reaction was synthesized for multi-mode detection of sulfite. First, Co2+ is oxidized to Co3+. Second, the oxidoreduction between SO32- and Co3+ produces SO4-• and Co2+ to complete the cycle. The resulting SO4-• is further reacted with the chromogenic substrate OPD to form the polymer. Due to the UV–vis absorbance of OPD polymer being stronger than that of OPD, but the fluorescence intensity is lower, and their Raman peaks are obviously different, this sensor can be used for the detection of SO32- through colorimetric, fluorescence, and Raman multi-mode. The main advantages are as follows: (1) high selectivity; (2) achieve fast, visual, and highly sensitive detection of SO32-, and the low limit of detection (LOD) is 1 nM; (3) improve the reliability of detection and expands the detection range (1 nM-800 μM); (4) demonstrate the applicability in recognizing SO32- in HeLa cells to provide accurate information on the dynamic distribution of sulfur in cells.