On-demand quantitative SERS bioassays facilitated by surface-tethered ratiometric probes.

Reliable and user-friendly sensing of target analytes in complex biofluids is of fundamental importance to biological science and medicine. Surface-enhanced Raman spectroscopy (SERS) has proven to be capable of detecting molecules with high sensitivity, but achieving robust quantitative detection remains a challenge mainly because of the severe signal fluctuation at electromagnetic hot spots. Here, we describe an on-demand and quantitative SERS strategy for metabolite profiling based on a chip-based sensing device that adopts stable and surface-tethered small-molecule probes as Raman reporters. These probes with a ratiometric response allow for sensitive and reproducible SERS detection by offering an internal calibration to correct the signal fluctuation caused by the spatiotemporal variation of assay conditions. Meanwhile, the chip-based sensing scheme makes time-separated on-demand detection possible. Ultimately, due to the flexibility in choosing diverse ratiometric Raman probes, we expect the proposed quantitative SERS sensing concept to be useful for studies in the fields of cell biology and clinical diagnosis.