Architecting BiVO4 on halloysite nanotubes: A high-performance electrode for theophylline detection with elucidated oxidation pathway

A composite of bismuth vanadate (BiVO 4 ) with halloysite nanotubes (Hly) deposited on glassy carbon electrodes (BiVO 4 /Hly@GCE) allows for the fast determination of theophylline using differential pulse voltammetry. Under optimized conditions in 0.1 M phosphate buffer (pH 7.0), the method delivers a wide linear range of 0.2–933 μM with a limit of detection of 0.0023 μM (3σ/m) and a limit of quantification of 0.0077 μM (10σ/m). Precision is high, with intra-day RSD = 2.4% ( n = 10, 50 μM) and inter-day RSD = 3.1% ( n = 5 days), and electrode-to-electrode reproducibility shows RSD = 3.8% (n = 5). Electrodes show operational stability by retaining at least 92% of the initial response after 20 cycles. Analysis of common beverage constituents have shown this system is operationally selective as they did not produce a signal bias response. A linear regression analysis was used to obtain 95–104% recoveries as well as a low standard deviation for the coffee, milk tea, and green tea samples after dilution, which indicates the loss of a reagent due to the absence of an analysis procedure The straightforward composite fabrication and robust analytical performance support routine, cost-effective screening of theophylline in complex matrices.