Colorimetric detection of magnesium (II) ions using tryptophan functionalized gold nanoparticles.

The functional nanoparticles with specific molecular probe appear to be a promising approach for developing colorimetric nanosensor. In this work, we have synthesized tryptophan capped gold nanoparticles (AuNPs) and used to establish colorimetric detection of magnesium (Mg). The colorimetric response of the AuNPs toward Mg was noticed with naked eyes, and spectral changes were monitored by using UV-Vis spectrophotometer. The detection response was rapid (less than 1 min), with a detection limit (LOD) about 0.2 µmol L. The proposed nanoprobe shows characteristic red-shift of the AuNPs at 620 nm and high selectivity for Mg due to the binding affinity of the tryptophan with Mg. The real-time response of the UV-Vis spectrum was monitored at three different concentrations of Mg (0.45, 0.50, and 0.55 µmol L). The AuNPs probe was suitable to provide a molecular platform for selective coordination with Mg over Ca ions, thus it could be facile to establish a practically viable sensing system. Furthermore, experimental results were confirmed to exhibit excellent linear curve for urine and serum samples spiked with Mg. Thus, this nanosensor is practically useful for the detection of Mg, without using expensive instruments, enzymes and/or DNA molecules.