Thin-film nanostructure-based enzymatic alcohol sensor for wearable sensing and monitoring applications

Fast and accurate detection and monitoring of alcohol consumption have significant importance for safety and clinical applications. The excessive consumption of alcohol causes many health issues, such as colon, rectum, mouth, and throat cancers, liver cirrhosis, stroke, cardiovascular disease, and several psychiatric comorbidities. Alcohol addiction treatments also require close monitoring of the consumption. The correlation of alcohol concentration levels in sweat with the blood alcohol content (BAC) encourages developing a wearable sensing platform for alcohol detection noninvasively, continuously, and in real-time. Moreover, sweat is considered one of the most useful body fluids for biosensing applications since it contains several biomarkers with crucial medical information and is easy to collect. ZnO has exclusive chemical and physical characteristics to enhance chemical stability in physiological environments. Moreover, it has higher catalytic activity, biocompatibility, and a higher isoelectric point (IEP) of 9.5. Such a high IEP of ZnO nanoflakes (NFs) improves any biomolecules' immobilization. Hence, there is no necessity for an additional binding layer between the enzyme and the sensing electrode. A single-step sonochemical approach was developed to synthesize a thin layer of ZnONFs virtually on any substrate. This technique is fast, catalyst-free, less expensive, and ecologically benign, which enables a well-oriented growth on polyethylene terephthalate (PET) over an extensive range. In this study, an electrochemical biosensor was fabricated by immobilization of alcohol oxidase (AOX) on ZnO nanoflakes with a thickness of 20nm, synthesized on Au-coated PET. The results demonstrated a fast response within 5s. The sensor was tested in the range of 1 mg – 400 mg, which covers the entire physiological range, and the sensitivity of the sensor was determined by 3.47 nA/mg/dL/cm2.