Fig. 8. (a) SERS spectra of Sudan I (incident power was 3.4 mW, data acquisition time was 10 s) at different concentrations; R6G Raman spectra; (b) plot of the peak intensity at 1592 cm⁻¹ as a function of Sudan I concentration (inset represents the linear relationship from 10⁻¹⁰ M to 10⁻⁶ M).