Two novel, simple and fast methods were developed for spectrophotometric micro-determination of methionine
(MET, the analyte) using amino acids stabilized-silver nanoparticles (AgNPs). These methods were based on
controlled preparation of AgNPs using NaBH4 as reducing agent, and subsequently stabilized using two different
amino acids, i.e., alanine for sol 23 and leucine for sol 26. The thus stabilized-AgNPs and their binding with MET
were confirmed and investigated using different tools as UV/Vis spectrum, TEM, FT-IR and cyclic voltammetry.
All experimental conditions such as the effects of pH, time, temperature and the ionic strength were investigated
and optimized. After that, a calibration curves were constructed based on the decrease in the surface Plasmon
resonance, (SPR) peak with a characteristic pale yellow color, at about 390 nm after MET addition to sol 23 and
sol 26 due to the binding between MET and stabilized-AgNPs and in turn color changed to a pale gray. The
dynamic range for MET quantification was 1.5–15.0 μg/mL for both sols with good correlation coefficients and
high precision. With respectable recovery percentages, the established procedures were successfully used to
determine MET in pharmaceutical capsules and in some spiked human blood samples.