(A) SERS spectra of 4-MBA on AgNWs@PTFE after the incubation with 2 μL of PBS solution at different pH values. (B) Calibration curve obtained calculating the area under the bands in the 1400–1425 cm⁻¹ interval relative to vibration of the carboxylate group, normalized for the area of the peak centred at 1592 cm⁻¹ assigned to the benzene ring breathing mode. Calculated data (square symbols) are fitted with a sigmoidal function (black line) and the 95% confidence and prediction bands are reported in dark and light violet, respectively. Three SS solution with different pH values were used in order to test the chip and the obtained results are indicated with red, blue and purple geometrical symbols.