Abstract
Introduction
Accurate real-time health monitoring with fabric-based biomedical devices is coming to the foreground with improvements in efficiency [1,2]. Cotton fabric-based wearable sensors are a soft and breathable substrate that provides comfort to patients. Flexibility, robustness and easy integration with skin or garments provide real-time updates of health issues [3]. Fast response time and low cost make the textile-based wearable sensors eye-catcher of the clinical market. Wearable sensors are used in various important clinical applications and the real status of a chronic wound is one of the critical issues. Wearable sensors for monitoring various wound parameters are reported using gauze [4,5]. These reported sensors suffered from mechanical and chemical stability with poor wireless connectivity [6,7]. In this study we have fabricated a textile woven, conformal, and conductive gauze based sensor that enables quantitative sensing of uric acid in chronic wound fluid.
Sensor Design
Cotton gauze was cleaned via acetone solution and kept for drying in the oven for 2 hrs. The cotton gauze surface was modified with graphene nano-platelet via dipping the treated gauze in graphene solution for 15 minutes followed by drying at room temperature. Graphene reducing agent basic L-cysteine solution was used to reduce oxidized graphene nano-platelets into neutral graphene-modified conductive gauze. Obtained conductive gauze is a flexible substrate. Screen printing technique is used for printing WE, RE and CE with silver ink (Fig. 1 A). The electrochemical response of uric acid on fabricated conductive gauze was evaluated via a multichannel electrochemical station (CHI-230B Potentiostat).
Electrochemical Measurement
Cyclic voltammetry was performed to evaluate the response of uric acid in a phosphate buffer saline solution (pH 7.4) over the fabricated conductive gauze. The well-defined redox peak at -0.38 V and 0.08 V in cyclic voltammogram confirms the selective and sensitive sensing of uric acid (Fig. 1 B). The linear response of scan rates and obtained current signal of uric acid confirms the diffusion-limited kinetics on conductive gauze. The diffusion-limited kinetics supports the mass transport mechanism on gauze (Fig. 1 C). This facilitates the ppm level selective sensing of uric acid and confirms the feasibility of fabricated gauze as a wound dressing. The uric acid response was evaluated for the same concentration (100 m M) on two conductive gauzes. Both gauzes were showing excellent reproducibility with RSD 1.2%. Furthermore, to evaluate the diffusion coefficient of uric acid on conductive gauze chonoamperometry measurements using different uric acid concentrations (50, 75, 100, 125 mM) in phosphate buffer saline (pH 7.4) were performed (Fig. 1 D). The mean diffusion coefficient of uric acid as per the Cottrell equation is 4.15×10−7 cm2 s-1. The result obtained from both electrochemical techniques, cyclic voltammetry and chronoamperometry confirm diffusion-limited kinetics on conductive gauze based flexible sensors.
Conclusions
The excellent electrochemical response of uric acid on metallic printed conductive gauze and reproducibility could open a new approach and flexible material for wound dressing. The mechanical stability in a thorough washing and flexibility test is under progress. Cheap, easily available, skin comfortable, disposable features and with the obtained electronic signal of fabricated conductive gauze, encourage us to design novel wound dressing, which can be integrated with human skin or garments and could serve as an assistant to monitor the status of chronic wounds.
References
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Figure 1