1 mL portions of AgNPs colloidal suspensions and further described aliquots of 0.5 mM solutions of Cys-cabn and Cys-CABN were thermostated at a designated temperature. To initialize the adsorption, 10 µL volume of the first isotopologue solution was added to the AgNPs suspension under continuous stirring. After the designated delay time (0, 1, 10, or 29 minutes), a 10 µL portion of the second isotopologue solution was added to the suspension and the adsorption was continued to the total duration of 30 minutes elapsed since the first aliquot had been introduced. SERS spectrum acquisition was started immediately after this period of time.