Abstract
Theophylline is commonly used to treat asthma and chronic obstructive pulmonary disease (COPD). It has a narrow therapeutic range (55-110 μM in blood). If levels are too low, the drug is less effective. If too high, it can cause serious side effects like nausea, seizures, irregular heartbeat, low blood pressure, fainting, or even heart attack. Theophylline has a high transfer ratio (70%) from blood to breast milk, which can cause infant health risks. Monitoring theophylline levels in breast milk can help estimate the mother's blood levels and improve breastfeeding safety. However, no point-of-care (PoC) devices are available to measure theophylline at home. To address this, we developed an electrochemical PoC sensor that measures theophylline in breast milk without any sample preparation. The sensor uses laser-induced graphene (LIG) electrodes with no surface modification and is covered by an absorptive glass fiber layer. The device demonstrated a sensitivity of 0.03 μA/μM and a detection limit of 6.5 μM both suitable for therapeutic monitoring in milk. The device is selective against natural changes in milk at different stages of lactation and against other drugs that may also appear in breast milk. The device provided accurate measurements in spiked human milk samples collected at the first, sixth, and 12th months postpartum, with recovery values ranging between 99.2% and 111.0%. This tool adds to the advancement in maternal and infant healthcare and allows mothers on theophylline to manage their dose and protect their newborns while breastfeeding safely.