Exploration of CIELAB colour system for the colorimetric detection of Lead ions in environmental water using gold nanoparticles

This study demonstrates the application of gold nanoparticles in a colorimetric CIELAB system to detect lead ion (Pb(II)) in wastewater. The limited capacity of human vision to perceive colour accurately poses a significant challenge in using colorimetric devices. The technique relies on utilising image processing in conjunction with spectrophotometer tools to determine the source of colour changes observed when gold nanoparticles and Pb(II) interact. As the concentration rises, the R values decrease while the G and B values increase. The RGB values are converted to the CIE L*a*b* colour space to determine the colour system coordinates. The concentration of standards experienced an increase, resulting in a shift in R values from red to green. Simultaneously, the L values indicated a shift from darkness to brightness in the standards. A similar trend was noted in curve R and a*, explaining the decrease in a* values as the concentration of Pb(II) increases. This revealed that the standards transitioned from the red zone (+a) to the green zone (−a). The colour variation intensified with the rise in Pb(II) concentration, indicating a clear correlation between the concentration of the analyte being analysed and the observed colour difference. The results were confirmed using spectrophotometric analysis (UV–Visible), which highlighted the emergence of a novel surface Plasmon resonance peak at 680 nm. Notably, the strength of this new surface Plasmon resonance (SPR) peak at 680 nm decreased significantly as the concentration of Pb(II) increased. • Intensity of the red colour diminished with an increase in Pb(II) concentration. • Horseshoe-shaped CIE/Yxy confirmed the clustering of gold nanoparticles. • Findings substantiated the efficacy of the proposed colorimetric sensor.