Unveiling the detection kinetics and quantitative analysis of colorimetric sensing for sodium salts using...

Rapid, reliable, and sensitive colorimetric detection has been regarded as a highly potential technique for visually monitoring the cation ions. Yet, insight into detection kinetics and quantitative analysis for colorimetric sensing of sodium ions has rarely been revealed. Herein, in-depth kinetic investigations of colorimetric detection using surface-modified Au-nanoparticle (AuNP) probes were performed for interpreting the correlation of salt concentration, reaction duration, and light absorbance. To envision these undisclosed issues, modification of AuNP surfaces with ascorbic acid was found to be highly essential for boosting the detection sensitivity due to adjusting the zeta potential of AuNP colloids towards a slightly positive value. Next, modeling the light absorbance of AuNPs under various aggregation circumstances was employed, which visually elucidated the color change so that it was visible to the naked eye, due to the intense field localization on the edges of aggregated AuNPs. In addition, the involved activation energy of AuNP aggregation was found to follow the first-order Arrhenius formula, with the extracted value of 22.5 kJ mol^-1. Finally, quantitative visualization of colorimetric Na⁺ ion sensing was realized, and the experimental relation was obtained for explicitly determining the unknown concentration of Na⁺ ions in a visual manner.