Microcavity Array-Based\nDigital SERS Chip for Rapid\nand Accurate Label-free Quantitative Detection of Live Bacteria

In this study, we developed a novel\ndigital surface-enhanced Raman spectroscopy (SERS) chip that integrates\nan inverted pyramid microcavity array, a microchannel cover plate,\nand a multilayer gold nanoparticle (AuNP) SERS substrate. This innovative\ndesign exploits the synergistic effects of the microcavity array and\nthe microchannel to enable rapid and large-scale digital discretization\nof bacterial suspensions. The concentration effect of the picoliter\ncavities, combined with the superior Raman enhancement effect of the\nmultilayer AuNP SERS substrate, allows for the precise identification\nof live bacteria within the microcavities through in situ and label-free\nSERS testing after a short incubation period. By counting the resulting\npositive or negative signals, the concentration of the target analyte\ncan be directly determined via Poisson statistics. Experimental results\ndemonstrate that this method enables the accurate quantification of Escherichia coli (E. coli) BL21 within a 4-h incubation period. Compared with traditional\nanalog SERS detection methods, our proposed digital SERS detection\nstrategy reduces the impact of signal intensity fluctuations, thereby\nsignificantly improving detection efficiency and accuracy. We believe\nthat this digital SERS chip has great application prospects in the\nfields of bacterial detection, antibiotic resistance analysis, and\ncellular dynamics monitoring.