Smartphone-Assisted Colorimetric Detection of Cr3+ using Vitamin B-6 Cofactor Functionalized Gold Nanoparticles and Its Applications in Real Sample Analyses

This communication demonstrates a rapid, reproducible and highly selective colorimetric nanosensor for the detection of Cr3+ ions in aqueous medium using the functionalized gold nanoparticles. The functionalized AuNPs were obtained in three steps: (i) the citrate capped Cit-AuNPs were prepared by standard procedure, (ii) the thiolated Schiff base CAPLP was generated in-situ by reacting vitamin B-6 cofactor pyridoxal 5-phosphate and cysteamine, and then (iii) the CAPLP was decorated over the surface of Cit-AuNPs via ligand exchange method yielding spherical and well dispersed nanoparticles of size similar to 16 +/- 2nm. The wine red color of CAPLP-AuNPs solution turned to purplish blue upon addition of Cr3+ ions along with the SPR band was red-shifted from 525nm to 650nm due to the complexation-induced aggregation of nanoparticles. With a high selectivity and specificity, this nano-assembly shows the detection limit down to 2.34 mu M and finds applicability over a wide range of pH. The developed nanosensor was applied in environmental water samples for Cr3+ ions detection and achieved ideal results. More significantly, the visually detectable color change of CAPLP-AuNPs has been successfully integrated with a smartphone RGBColorValue app to make it useful for on-site fast measurement and real-time online analysis of Cr3+ with the detection limit down to 11 mu M.