Optimization of SERS scattering by Ag-NPs-coated filter paper for quantification of nicotinamide in a cosmetic formulation

•A SERS analytical method was developed for nicotinamide quantification.•Ag-NPs-coated filter paper synthesis was optimized to improve SERS signal.•The optimal condition presented an improvement of 70,000 times in the signal.•Unlike the Raman spectrum of the sample, the SERS was selective for the analyte.•The SERS method is shown to be faster, greener and cheaper than the HPLC method.

Supported silver nanoparticles on filter paper were synthesized using Tollens' reagent. Experimental designs were performed to obtain the highest SERS enhancement factor by study of the influence of the parameters: filter paper pretreatment, type of filter paper, reactants concentration, reaction time and temperature. To this end, fractional factorial and central composite designs were used in order to optimize the synthesis for quantification of nicotinamide in the presence of excipients in a commercial sample of cosmetic. The values achieved for the optimal condition were 150 mM of ammonium hydroxide, 50 mM of silver nitrate, 500 mM of glucose, 8 min for the reaction time, 45 °C temperature, pretreatment with ammonium hydroxide and quantitative filter paper (1–2 µm). Despite the variation of SERS intensity, it was possible to use an adapted method of internal standard to obtain a calibration curve with good precision. The coefficient of determination of the linear fit was 0.97. The method proposed in this work was capable of quantifying nicotinamide on a commercial cosmetic gel, at low concentration levels, with a relative error of 1.06% compared to the HPLC. SERS spectroscopy presents faster analyses than HPLC, also complex sample preparation and large amount of reactants are not necessary.

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