Fig. 4: Experimental demonstration of SERRS and protein sensing.

a Measured SERS spectrum of reference cavity using 0.1 mM and 1 μM cyanine dye concentrations. b Measured SERRS spectrum of TPP cavity using 1 μM, 100 nM, and 10 nM cyanine dye concentrations. Zoomed SERRS spectrum of 100 nM and 10 nM concentrations are shown in the inset of b. All SER(R)S spectra were subtracted from the background (dark) spectra. c Intensity mapping of 943 cm⁻¹ peak from cy7.5 dye, total mapping area is 120 µm × 120 µm. The scale bar is 12 µm. d SERRS spectra of the representative Raman band at 698 cm⁻¹ show an increase in SERRS intensity with an increase in the concentration of cTnI protein. e The maximum number of cTnI molecules (N_max) adsorbed in the illuminated sensor area versus the corresponding Raman intensity shift (ΔI) with respect to a blank sample for different cTnI concentrations. The red curve represents the theoretical fit. Here, ΔI is calculated using 720 cm⁻¹ Raman band, as highlighted in d.