Smartphone-Coupled Portable Electrocatalytic Interface toward Quantification of Indigo Carmine in Food Matrices via AgNP-Decorated Lamellar LaNi-LDH-Modified GCE.

Indigo carmine (IC) quantification in food matrices requires electrocatalytic interfaces with efficient charge transport. Here, a lanthanum nickel-layered double hydroxide and silver nanoparticle heterostructure (LaNi-LDH/AgNPs) was fabricated by hydrothermal synthesis and sonochemical Ag deposition. Cyclic voltammetry and electrochemical impedance spectroscopy identified LaNi-LDH/AgNPs/GCE at 1:1 as optimal, giving a redox current of 61.61 μA, charge-transfer resistance of 481 Ω, and electroactive surface area of 0.0745 cm2. The composite showed a Tafel slope of 87 mV dec-1 for IC detection. Differential pulse voltammetry afforded a linear range of 0.01-1580 μM, sensitivity of 10.14 μA μM-1 cm-2, and detection limit of 0.00437 μM. The sensor showed reproducibility and repeatability with RSD values of 2.07% and 1.36%, retained 89.16% response after 3 weeks, and achieved 96.71-99.66% recoveries in real food samples using a portable potentiostat, consistent with high-performance liquid chromatography recoveries of 98.10-100.02%.