MEMS-based microfluidic resonator biosensor with calix[4]arene functionalized AuNPs for Ca ²⁺ detection: experimental and simulation study

Abstract Calcium ion (Ca 2+ ) levels in drinking water are crucial for human health, influencing bone strength, muscle function, and nerve signaling. This study aimed to detect Ca 2+ using a MEMS-based microfluidic resonator with Calix[4] arene methoxy ester functionalized gold nanoparticles (Calix1-AuNPs). The binding of Ca 2+ with Calix1 was assessed by the measurements of the resonator’s resonance frequency ( f ), full width at half maximum (FWHM), and quality factor ( Q ). FWHM increased by 34.34 Hz, while f and Q dropped by 6.88 Hz and 1.33, respectively, for 10 −6 M CaSO 4 . Finite element analysis revealed that the cantilever operated in coupled torsional and flexural modes, and that geometric parameters and flow velocity governed its eigenfrequencies and quality factor. The density functional theory (DFT) calculations confirmed strong Ca 2+ binding to a single Au4-Calix1 molecule with Δ E int = −164.66 and Gibbs free energy of −108.66 kJ mol −1 at the B3LYP/LAN2DZ level of theory in the water solvent system.