Fig. 3: In vitro performance characterization of the VCMGS.
From: Vertical graphene-coated core-shell microneedle as miniatured sensor for in vivo glucose monitoring
a Representative Raman spectrum of VG. b Transmission electron microscopy image of VG. c Electrochemical stability characterization of the VG-coated MN electrode via CV scanning in PBS over 10 continuous cycles. d CV curves showing the electrochemical performance of VG-coated MN electrode (1) and carbon electrode (2) via K₃[Fe(CN)₆] solution ranging from −0.2 V to 0.6 V. e Graph showing the electrochemical impedance spectroscopy (EIS) of VG electrodes with fitting results via simulation software. The orange dots represented the experimental data while the light orange lines represented the fitted curves. The corresponding equivalent circuit model were showed in the inset, where R₁ represented the solution resistance and C₁ corresponded to the double-layer capacitance. f Frequency-dependent impedance spectra of electrodes with different functional layers. The enlarged impedance profiles of Au-coated MN electrode, VG-coated MN electrode and Pt-coated MN electrode were showed in the inset, respectively. g Comparison of electrochemical impedance values of electrodes with different functional layers measured at 1000 Hz. h Amperometric signals recorded by the VCMGS in glucose concentrations varying from 0 mM to 14 mM. Black arrows indicated the sequential addition of glucose solution. The inset showed the linear calibration plot correlating amperometric response with glucose concentration. i Comparison graph showing the detection sensitivities of VG-based MN electrode versus carbon electrode in glucose concentration measurement. j Selectivity characterization of the VG-based MN sensing electrode. The response of the sensor to glucose concentration fluctuations was examined in the presence of common interfering species including uric acid, cholesterol, and ascorbic acid. k Comparative performance analysis between VG-coated MN electrodes and carbon electrode, including operational stability, charge storage capacity, detection sensitivity, and electrochemical impedance. All parameters were normalized by utilizing the performance of carbon electrode as the baseline. l Fluorescence microscopy image showing the VG-based MN stained with Rhodamine B. m Fluorescence microscopy image showing the cross-section of pig skin stained with Rhodamine B after VCMGS penetration. n Optical microscopy image of the integrated VCMGS. o Stability characterization of the fabricated HMN reference electrode. p Biocompatibility evaluation of the VG electrode. Live cells were stained with Calcein-AM, nuclei with Hoechst, and dead cells with propidium iodide
