Effervescent sensing tablets for clean handling and shake-free, rapid copper detection in water

Powder-based colorimetric test kits enable rapid reagent dissolution but are prone to spillage, reagent loss, and dispersed waste during field use, whereas conventional compressed tablets provide cleaner handling but often dissolve slowly and require manual shaking. Here, an effervescent 'drop-and-detect' sensing tablet is reported that combines tablet-grade handling robustness with rapid, autonomous reagent release for shake-free copper detection in water. By integrating sensing reagents, stabilizing excipients, and effervescent agents into a single solid-dose platform via powder compression, the system eliminates the need for manual mixing, vortexing, or complex sample handling. The physical properties of the tablets, including weight, hardness, friability, disintegration time, and content uniformity, were evaluated. In addition, dissolution and effervescence kinetics were investigated. Upon contact with water, the autonomous effervescence facilitates complete dissolution and initiates a specific colorimetric reaction. In this mechanism, sodium ascorbate reduces cupric ions (Cu²⁺) to cuprous ions (Cu⁺), which then react with 2,2'-biquinoline-4,4'-dicarboxylic acid (BCA) to form a stable, lavender-colored [Cu(BCA)₂]^3- coordination complex. Compared with a conventional non-effervescent tablet, the effervescent formulation reduced the assay time from 15 min to 2 min while maintaining suitable mechanical integrity for handling and storage. The sensor exhibited a linear response over the 0.3-2.0 mg L^-1 copper range (R² = 0.98) with an LOD of 0.03 mg L^-1 and an LOQ of 0.09 mg L^-1. Good selectivity was observed in the presence of potentially interfering species, and validation using tap, canal, pond, and river water samples supported copper quantification in complex matrices. For Lachine Canal water spiked with 1.0 mg L^-1 Cu, the tablet sensor showed 92.4% agreement with ICP-MS. By bridging the gap between powder reagents and compressed tablets, this effervescent sensing format enables portable, laboratory-free water monitoring while providing a practical route toward solid-dose analytical sensing.