Calcium Alginate Gel Beads Containing Gold Nanobipyramids for Surface-Enhanced Raman Scattering Detection in Aqueous Samples

The application of surface-enhanced Raman scattering (SERS) in aqueous sample detection is normally limited by the low affinity between analytes and SERS-active nanoparticles. Furthermore, a tendency of uncontrollable aggregation of solute (nanoparticles or analytes) can cause poor reproducibility of the detected SERS signal. Herein, a ready-to-use plasmonic gel bead was developed for rapid and effective detection of aqueous samples with high sensitivity and reproducibility. The SERS gel bead is made of calcium alginate gel beads (CAGBs) that contain gold nanobipyramids (Au NBPs) and an aqueous sample, which can be prepared and detected within only 1 min. Au NBPs/CAGBs can generate an in-depth three-dimensional SERS-active gel network for trapping analytes and offering a uniform hotspot region, which produces a reproducible and uniform signal. Using rhodamine 6G as a model target, the proposed method exhibits excellent reproducibility with a relative standard deviation of 6.57% and a detection limit of 0.4 nM. Then, Au NBPs/CAGBs were applied to quantitatively detect serum uric acid in the range of 10–1000 μM and a limit of detection of 0.18 μM, and the results were strongly consistent with those of the commercial ELISA method. This work offers a low-cost and easy route for the fabrication of a versatile SERS substrate for monitoring disease-related biomarkers and point-of-care testing.