Unravelling mechanism for detecting chromium on functionalized gold nanoparticles via a smartphone and spectrophotometric-based systems supported by CIEL*a*b* colour space and molecular dynamics

•Synthesis of citrate stabilized gold nanoparticles and the displacement of citrate ions by DPC on the surface of gold nanoparticles to form DPC-AuNPs.•The use of RGB colour coordinates and CIELa*b* colour system to analyse colour changes upon the addition of Cr (VI) standards in the concentration range of 0.5–50.0 µM.•Molecular dynamics simulation of DPC-AuNPs interaction with Cr (VI), resulting to DPC-Cr (VI) confirming the aggregation of AuNPs.