Rapid Colorimetric Detection of Ca(II) Based on Surface Plasmon Resonance Absorbances of 5-PBA@AuNPs Sensor

Calcium ions (Ca²⁺) are essential for a myriad of physiological functions, including excitability, neurotransmitter release, gene transcription, cell proliferation, synaptic plasticity, and hormone secretion. Consequently, the detection of Ca²⁺ concentrations in water is of fundamental and practical significance. In this study, a novel method for the simple, visual, and rapid colorimetric detection of Ca²⁺ is introduced, leveraging the surface plasmon resonance (SPR) absorbances of gold nanoparticles (AuNPs) modified with 5-Pyrimidinylboronic acid (5-PBA). A color change from wine-red to gray-blue was observed with increasing concentrations of Ca²⁺, indicative of the agglomeration of AuNPs. This agglomeration displayed favorable anti-interference properties and selectivity. The limits of detection (LOD) were determined to be 0.08 mM by the unaided eye and 3.29 μM by UV-visible spectroscopy. Moreover, an excellent linear relationship (R²=0.9879) was maintained within the Ca²⁺ concentration range of 0.0 to 0.5 mM. These results suggest that AuNPs modified with 5-PBA are suitable for the quantitative determination of Ca²⁺. Subsequent testing on actual samples confirmed that this new method could be effectively applied to the monitoring of Ca²⁺ in water.