Wound state monitoring by multiplexed, electrochemical, real-time, localized, inflammation-tracking nitric oxide sensor (MERLIN)
Nitric oxide (NO) released endogenously by induced nitric oxide synthase (iNOS) in macrophages is a key regulatory biomarker for wound inflammation. Detecting NO directly on the wound bed is challenging due to its short half-life time (6 - 50 s), low physiological concentration (nM - {micro}M) and interferences in the complex wound environment. Existing NO sensors suffer from limitations such as rigid substrates, single point of detection and complex measurement setup. Here we present a compliant, multiplexed, electrochemical, real-time, localized, inflammation-tracking nitric oxide sensor (MERLIN) array for in vivo spatiotemporal measurement of NO, with high sensitivity (15.6 {+/-} 5.0 nA/M for 1.5 mm diameter electrodes), selectivity against nitrites (ca. 27900-fold), ascorbic acid (ca. 3800-fold), and uric acid (ca. 6900-fold), and low limit of detection (8.00 nM). We developed a robust device fabrication protocol, comprehensive and highly reproducible in vitro characterization yielding a consistent device performance deployed for wound healing diagnostics. MERLIN spatiotemporally tracked NO on rat skin wounds for 7 days and results indicated that NO peaks on day 3, in line with previously reported iNOS activity. MERLIN allows spatial mapping of the NO gradient across the wound bed, which can be used to provide diagnostic information to assist wound care.