Conducting Polymer-Reinforced Laser-Irradiated Graphene as a Heterostructured 3D Transducer for Flexible Skin Patch Biosensors

Abstract

Flexible skin patch biosensors are promising for the noninvasive determination of physiological parameters in perspiration for fitness and health monitoring. However, various prerequisites need to be met for the development of such biosensors, including the creation of a flexible conductive platform, bending/contact stability, fast electrochemical kinetics, and immobilization of biomolecules. Here, we describe a conducting polymer-reinforced laser-irradiated graphene (LIG) network as a heterostructured three-dimensional (3D) transducer for flexible skin patch biosensors. LIG with a hierarchically interconnected graphene structure is geometrically patterned on polyimide via localized laser irradiation as a flexible conductive platform, which is then reinforced by poly(3,4-ethylenedioxythiophene) (PEDOT) as a conductive binder (PEDOT/LIG) with improved structural/contact stability and electrochemical kinetics. The interconnected pores of the reinforced PEDOT/LIG function as a 3D host matrix for high loading of "artificial" (Prussian blue, PB) and natural enzymes (lactate oxidase, LOx), forming a compact and heterostructured 3D transducer (LOx/PB-PEDOT/LIG) for lactate biosensing with excellent sensitivity (11.83 μA mM^-1). We demonstrated the fabrication of flexible skin patch biosensors comprising a custom-built integrated three-electrode system achieve amperometric detection of lactate in artificial sweat over a wide physiological linear range of 0-18 mM. The advantage of this facile and versatile transducer is further illustrated by the development of a folded 3D wristband lactate biosensor and a dual channel biosensors for simultaneous monitoring of lactate and glucose. This innovative design concept of a heterostructured transducer for flexible biosensors combined with a versatile fabrication approach could potentially drive the development of new wearable and skin-mountable biosensors for monitoring various physiological parameters in biofluids for noninvasive fitness and health management.

Keywords: conducting polymers; heterostructured 3D transducers; laser-irradiated graphene; skin patch; wearable biosensors.

Scheme 1. Schematic Diagram of the Flexible Skin Patch Biosensor

Figure 1

(a) Sheet resistance and thickness of LIG using different laser powers over the range 30–100%; the inset is the digital image of LIG30–100% strips. (b) Raman spectra of LIG with different laser powers over the range 30–90% and the original polyimide film. (c) Summary of the intensity ratio (I_D/I_G, I_2D/I_G) and FWHM of 2D and G bands. (d) EIS of LIG40–70% in 5 mM Fe(CN)₆^3–/4– in 0.1 M KCl. The top-view (e) and cross-sectional (f) SEM images of LIG50% at different magnifications.

Figure 2

(a) Schematic illustration of patterning PEDOT on LIG; (b) SEM images of PEDOT/LIG and EDS mapping; (c) EIS of PEDOT/LIG and bare LIG50% in 5 mM Fe(CN)₆^3–/4– in 0.1 M KCl; (d) digital image of mounting LIG and PEDOT/LIG onto paper; (e) schematic diagram of the structural stability test; (f) SEM images of LIG (up) and PEDOT/LIG (down) before (left) and after (right) bending; the scale bar is 20 μm and the inset scale bar is 1 μm.

Figure 3

(a) Schematic illustration of PB deposition and LOx loading on porous PEDOT/LIG; (b) SEM images of PB-PEDOT/LIG, and its EDS mapping of key elements C, S, and Fe; (c) SEM images of LOx/PB-PEDOT/LIG; and (d) 3D (left) and orthogonal-section (right) confocal images of FITC-BSA-immobilized PB-PEDOT/LIG.

Figure 4

(a) CVs of PB-PEDOT/LIG to 5 mM H₂O₂ in 0.1 M PBS (pH = 6.4), the scan rate of 50 mV s^–1; (b) current–time curve of PB-PEDOT/LIG to successive addition of H₂O₂ in 0.1 M PBS (pH = 6.4) at 0 V, the inset is the calibration curve, n = 3; (c) schematic of lactate biosensing and signal transduction at LOx/PB-PEDOT/LIG; (d) current–time response curve of LOx/PB-PEDOT/LIG to successive addition of lactate in 0.1 M PBS (pH = 6.4) at 0 V, the inset is the calibration curve, n = 3; and (e) interference study of the LOx/PB-PEDOT/LIG electrode.

Figure 5

(a) Integration of the three-electrode system; (b) amperometric response of the integrated three-electrode system to increasing concentration of lactate in the range of 0–20 mM in artificial sweat; (c) corresponding calibration curve, n = 3; (d) digital image of the 2D patch and the 3D wristband (i), connection with a cable and miniaturized potentiostat (Sensit Smart) (ii), and 3D wristband conformed for wearing (iii); (e) comparison of the 2D patch and the 3D wristband for lactate detection in artificial sweat on the skin model; and (f) integration of the dual-channel electrode system for simultaneous detection of lactate and glucose.