Surface-Enhanced Raman Spectroscopy Monitoring of Enzymatic Domino Reactions on Ag Nanoshells for Sensitive Metabolite Detection

The reliable monitoring of metabolites in biofluids plays a pivotal role in the diagnosis, treatment, and long-term management of various diseases. Surface-enhanced Raman spectroscopy (SERS) is considered a promising tool for metabolite detection because of its unique advantages for detecting trace amounts of chemical and biological molecules without requiring extensive sample preprocessing. In this study, a SERS sensor is proposed, utilizing silver nanoshells in cooperation with enzymes and 4-mercaptobenzoic acid (4-MBA) as a bifunctional molecule, to monitor two distinct biological metabolites, lactate and cholesterol, at their respective levels. In our method, the enzymatic reactions between oxidases and their specific metabolites initiate a domino reaction, resulting in significant changes in the SERS signal of 4-MBA. Through systematic sensor optimization, the quantification of lactate (1.0 × 10 –1 to 1.0 × 10 –7 M) and cholesterol (1.0 × 10 –2 to 1.0 × 10 –6 M) in a buffer solution was successfully achieved using the SERS intensity as an indicator. The limits of detection for lactate and cholesterol were estimated to be 2.7 × 10 –7 and 1.0 × 10 –8 M, respectively. Our proposed SERS sensor precisely detected lactate concentrations in serum samples, with a high accuracy of over 91%, demonstrating high selectivity for compounds with similar structures and serum constituents. Our SERS sensor platform can be utilized as an efficient and versatile tool for measuring lactate concentrations in serum samples and is expected to have the potential to advance personalized healthcare solutions through rapid point-of-care testing.