Evaluation of AgFON-based SERS combined with various headspace methods for the detection of thiol compounds in wine.

The thiol compounds present in wine 4-mercapto-4-methyl-2-pentanone (4MMP), 3-mercapto-1-hexanol (3MH), and 3-mercaptohexyl acetate (3MHA) are key components contributing to the aromatic characteristics of wines such as Sauvignon Blanc, giving muscat and blackcurrant notes. This study evaluated the effectiveness of surface-enhanced Raman spectroscopy (SERS) using silver-film over nanosphere (AgFON) substrate combined with immersion, static headspace, and dynamic headspace methods. The immersion method was found unsuitable for detection of target molecules in low concentrations due to interference from wine-derived components. In contrast, detection was difficult in the gas-phase conditions with the static headspace method, whereas the introduction of an acceptor phase under liquid-phase conditions facilitated spectral observation of the target compounds. Furthermore, the headspace method with dynamic control of the acceptor demonstrated the detectability of 4MMP, with characteristic spectral features observable at 10 nM under the examined experimental conditions. For 3MH and 3MHA, peaks overlapping with other wine components remained an issue. Principal component analysis (PCA) was applied as an exploratory tool to visualize spectral variance, and the results showed partial cluster overlap under certain conditions, while revealing trends that differentiate thiol-containing samples from wine-derived backgrounds. These results indicate that the headspace SERS approach using AgFON combined with an acceptor phase has potential for the detection of thiol compounds in wine, particularly for 4MMP.