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(2+)). The colorimetric response of the AuNPs toward Mg(2+) 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(-1). The proposed nanoprobe shows characteristic red-shift of the AuNPs at 620 nm and high selectivity for Mg(2+) due to the binding affinity of the tryptophan with Mg(2+). The real-time response of the UV-Vis spectrum was monitored at three different concentrations of Mg(2+) (0.45, 0.50, and 0.55 µmol L(-1)). The AuNPs probe was suitable to provide a molecular platform for selective coordination with Mg(2+) over Ca(2+) 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(2+). Thus, this nanosensor is practically useful for the detection of Mg(2+), without using expensive instruments, enzymes and/or DNA molecules.