Theophylline is a drug with a narrow therapeutic index, with normal plasma levels ranging from 10 to 20 mg/L. Theophylline overdose can lead to several symptoms, including nausea, vomiting, headaches, pancreatitis, and death. Thus, it is important to monitor theophylline after its consumption. Microneedles (MNs) can be integrated with screen-printed electrodes (SPE) to enable the minimally invasive monitoring of theophylline. In this study, we developed a highly sensitive and accurate electrochemical sensor to detect theophylline based on a gold nanoparticle/boron-doped diamond nanoparticle nanocomposite-modified SPE (AuNP-BDDNP/SPE). In addition, this study aims to determine the feasibility of MN integration with AuNP-BDDNP/SPE for theophylline detection. UV–vis, TEM, and XPS confirmed the successful synthesis of AuNP-BDDNP, whereas FESEM images confirmed the successful modification of …