Revisiting chitosan tripolyphosphate nanogel as a resonance Rayleigh scattering sensor for aluminum ion detection

In this study, the utility of chitosan tripolyphosphate (CS/TPP) nanogel was revisited as a simple, low cost, and biocompatible Resonance Rayleigh Scattering (RRS) sensor for detection of Al³⁺ ions. The RRS intensity varies due to the disruption of CS/TPP electrostatic crosslinks by Al³⁺, which increases the swelling and reduces the RRS intensity. The optimized CS/TPP nanogel sensor exhibits a linear calibration range from 0.25 to 2.5 mM with R² = 0.9853 and a limit of detection (LOD) of 0.077 mM. The chitosan tripolyphosphate nanogel was characterized using various techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), Dynamic light scattering (DLS), Zeta potential analysis, and Fourier transformed infrared spectroscopy (FT-IR). The kinetics of the sensing process were investigated, revealing that the sensing mechanism follows three distinct kinetic phases including alpha, beta, and gamma. This triple phase kinetic behavior consists of Al³⁺ ion diffusion, crosslink disruption, and swelling-driven equilibration, respectively. The selectivity and sensitivity of the sensor were assessed against various cations and anions, with notable interferences from Ag⁺, Hg⁺, and Hg²⁺ ions. The CS/TPP sensor is suitable for screening moderate to high concentrations rather than trace amounts and provide practical, rapid, and low-cost approach for detecting Al³⁺ where ultra-low LOD is not required.