Microfluidic contact lens for continuous monitoring of ocular oxidative stress

Oxidative stress-induced ocular dysfunctions are a significant global health concern. Glutathione (GSH), an abundant antioxidant in tears, can serve as an index for oxidative stress (OS). A coumarin-based fluorescent probe named CCAE was synthesized for GSH monitoring, functioning through structural changes via Michael's addition with GSH and elimination by H₂O₂, which restores the conjugation structure to assess the severity of OS-induced ocular diseases. CCAE demonstrated a high sensitivity with a detection limit (LOD) of 0.12 mM and reversibility for 15 cycles. A wearable contact lens sensor was developed featuring a microfluidic lens patterned with a 365 nm pulsed laser, requiring 6 μL of tears. CCAE was encapsulated in citric acid-crosslinked poly(vinyl alcohol) film and embedded in poly((hydroxyethyl)methacrylate-co-ethylene glycol)/polyvinylpyrrolidone (poly(HEMA-co-EG)/PVP) lenses. A customized smartphone readout device enabled quantitative GSH readings for point-of-care applications. Tested on an ex vivo porcine anterior eye model, the sensor achieved an LOD of 0.204 mM, within a detection range of 0.62-1.17 mM and 0.13-0.73 mM under mild and severe OS conditions respectively. The sensors maintained operational stability for 2 days and storage stability for 1 week. This reversible GSH contact lens sensor offers a unique platform for diagnosing and monitoring OS-related ocular conditions at point-of-care settings.