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

Abstract 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.