Alkyne-based surface-enhanced Raman scattering nanoprobe for ratiometric imaging analysis of caspase 3 in live cells and tissues

Surface-enhanced Raman scattering (SERS) still faces a big challenge in bioanalysis due to the biological background interference and the poor reproducibility of the Raman signal. Accordingly, herein a novel surface-enhanced Raman scattering (SERS) nanoprobe is prepared via the co-assembly of 3-(4-(phenylethynyl)benzylthio) propanoic acid (PEB) tagged-peptides and 4-thiol phenylacetylene (TPA) on gold nanorods, and used for the measurement of caspase 3, as a biomarker. A key advantage of this system is the lack of background alkyne signals throughout the cell. The two alkyne-bearing molecules produce distinct SERS signal but the PEB signal decreases in response to the peptide-cleavage activity of caspase 3, thereby allowing the ratiometric detection of analytes. Under the optimized conditions, the ratiometric peak intensity of I2027/I2218 dynamically increased with increasing caspase 3 concentration in the range from 12.5 to 500 ng/mL, with a detection limit of 1.99 ng/mL based on a signal-to-noise ratio of S/N = 3. The nanoprobe has been successfully applied in a live cell imaging assay of caspase 3 and in an ischemia–reperfusion surgery-treated rat living tissue model. [Display omitted] •A novel SERS strategy for caspase 3 detection has been established.•Alkyne introduced into as the Raman reporter can efficiently reduce the background interference of the cellular components.•The ratiometric signal output strategy could greatly improve the Raman signal reproducibility of the SERS nanosensor.•The prepared SERS nanoprobe was successfully applied for caspase 3 assay in a rat living tissue model.