Simple SPR-based colorimetric sensor to differentiate Mg2+ and Ca2+ in aqueous solutions

Abstract L-tryptophan functionalized AgNPs were successfully fabricated using a one-pot synthesis method and assessed as a colorimetric probe for rapid and accurate determination of Mg2+ ions. The developed sensor showed a selective response towards Mg2+ with no interference from Ca2+ in the wide concentration range of 1 – 200 µM. The sensor's response was optimized in the pH range of 9 – 10, which can be attributed to the protonation of amine groups and their interaction with Mg2+ ions. The stability and selectivity of the sensor were examined in different salt (NaCl) and other metal ions, respectively. The L-tryptophan-AgNPs sensor detected Mg2+ with the limit of detection of 3 µM, which is way lower than the concentration range of magnesium in human serum (0.75 mM – 1.05 mM). The recovery values of the developed sensor were in the range of 96% – 102% for the determination of Mg2+ in urine samples. The obtained performances proved the potential application of the developed sensor for clinical diagnostic of Mg2+ ions where an accurate and rapid response is needed.