<![CDATA[Drug theophylline is a bronchodilator used to treat asthma and chronic obstructive pulmonary disease (COPD), but precise monitoring is required to avoid side effects. Therefore, this study aimed to develop a screen-printed electrode (SPE) modified with a composite of green-synthesized silver nanoparticles and boron-doped diamond nanoparticles using tea polyphenols (Ag-BDDTP/SPE) for detecting theophylline. Formation of AgNPs was confirmed by UV-Vis spectroscopy, which showed a localized surface plasmon resonance peak at ~450 nm. Transmission electron microscopy revealed polydisperse nanoparticles with an average diameter of 39.94 nm. During the electrochemical detection of theophylline, square-wave voltammetry (SWV) was employed to evaluate signal-to-background (S/B) ratio, linearity, detection limits, selectivity, reproducibility, and recovery. The Ag-BDDTP/SPE electrode had an S/B value of 2.93, higher than BDDTP/SPE (1.65) and bare SPE (1.54). The detection and quantification limits were 1.043 and 3.478 μM, respectively, with a linear range of 30–100 μM. Selectivity tests confirmed tolerance against potential interferents, including D-glucose, ammonium sulfate, and urea. Precision analysis yielded a %RSD value of 0.92%. Accuracy testing with artificial urine showed good recovery values of 101.65% for Ag-BDDTP/SPE and 90.36% for BDDTP/SPE. In conclusion, the Ag-BDDTP/SPE electrode demonstrated greater sensitivity and accuracy than unmodified electrodes, highlighting its potential for reliable theophylline monitoring in clinical applications.]]>
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