Au@Ag hollow nanoshells-based SERS integrated microfluidic chip as a sample-to-answer platform for the ultra-sensitive detection of geosmin.

Background: Geosmin (GSM) can compromise the immune systems of aquatic organisms, rendering them more vulnerable to viral and bacterial infections, thereby adversely affecting their growth, reproduction, yield, and quality. Given the relatively low odor thresholds of GSM, there is a critical demand for the development of a highly sensitive and rapid detection method. According to the principle of Surface-enhanced Raman spectroscopy (SERS), localized surface plasmon resonance (LSPR) greatly enhances the Raman signals of adsorbed molecules. To date, no study has reported the application of SERS to detect GSM.

Results: Dual-metal nanomaterials with hollow structures have been proven to provide a large surface area and heightened localized surface plasmon resonance, thereby enhancing the sensitivity of Raman signals. In this study, a sample-to-answer platform was constructed by integrating Au@Ag hollow nanoshells (HNSs)-based SERS and a microfluidic chip for the sensitive, fast, and direct determination of GSM. Under 532 nm excitation, GSM exhibit Raman peaks on the SERS-active Au@Ag HNSs, and there is a relationship between the peak intensity and the concentration of GSM. Owing to the integration of the microfluidic chip, only microliters of reagent are required, and the test results can be achieved within 4 min. The constructed sample-to-answer platform showed a good linear response to GSM in the range of 1 ng/L-1 mg/L, with a detection limit of 0.16 ng/L. An optimal calibration model is established by combining stoichiometric algorithms.

Significance: This work realized the ultra-highly sensitive and fast determination of GSM based on SERS-active Au@Ag HNSs, which provides new insights and is very promising for the on-site monitoring of earthy odors. Our study makes a significant contribution to the literature because the developed SERS-based detection method does not require labels or biomaterials, providing the possibility of highly sensitive and on-site testing of contaminants in food and the environment.