Chronoampermetric detection of enzymatic glucose sensor based on doped polyindole/MWCNT composites modified onto screen-printed carbon electrode as portable sensing device for diabetes

Abstract

Doped-polyindole (dPIn) mixed with multi-walled carbon nanotubes (MWCNTs) were coated on a screen-printed electrode to improve the electroactive surface area and current response of the chronoamperometric enzymatic glucose sensor. Glucose oxidase mixed with chitosan (CHI-GOx) was immobilized on the electrode. (3-Aminopropyl) triethoxysilane (APTES) was used as a linker between the CHI-GOx and the dPIn. The current response of the glucose sensor increased with increasing glucose concentration according to a power law relation. The sensitivity of the CHI-GOx/APTES/dPIn was 55.7 μA mM^-1 cm^-2 with an LOD (limit of detection) of 0.01 mM, where the detectable glucose concentration range was 0.01-50 mM. The sensitivity of the CHI-GOx/APTES/1.5%MWCNT-dPIn was 182.9 μA mM^-1 cm^-2 with an LOD of 0.01 mM, where the detectable glucose concentration range was 0.01-100 mM. The detectable concentration ranges of glucose well cover the glucose concentrations in urine and blood. The fabricated enzymatic glucose sensors showed high stability during a storage period of four weeks and high selectivity relative to other interferences. Moreover, the sensor was successfully demonstrated as a continuous or step-wise glucose monitoring device. The preparation method employed here was facile and suitable for large quantity production. The glucose sensor fabricated here, consisting of the three-electrode cell of SPCE, were simple to use for glucose detection. Thus, it is promising to use as a prototype for real glucose monitoring for diabetic patients in the future.

Scheme 1. (a) Working electrode modification steps to prepare the CHI-GOx/APTES/1.5%MWCNT-dPIn; and (b) hydrolysis of APTES.

Fig. 1. ATR-FTIR analysis of (A-a) dPIn; (A-b) APTES/dPIn; (A-c) CHI-GOx/APTES/dPIn; (B-a) 1.5%MWCNT-dPIn; (B-b) APTES/1.5%MWCNT-dPIn; (B-c) CHI-GOx/APTES/1.5%MWCNT-dPIn; (A-d) or (B-d) GOx; and (A-e) or (B-e) CHI.

Fig. 2. Surface morphologies at 300 00× of magnification of various modified SPCEs: (a) SPCE; (b) b-SPCE; and the b-SPCE modified with various chemicals; (c) dPIn; (d) CHI-GOx/APTES/dPIn; (e) 1.5%MWCNT-dPIn; (f) CHI-GOx/APTES/1.5%MWCNT-dPIn.

Fig. 3. Electrochemical analysis: (a) cyclic voltammograms; and (b) Nyquist plots of various modified electrodes with the inset. The anodic peaks current vs. the square root of scan rates (ν^0.5) and insets of cyclic voltammograms with different scan rates of: (c) CHI-GOx/APTES/dPIn; and (d) CHI-GOx/APTES/1.5%MWCNT-dPIn. The electrodes were tested in a solution of 5 mM of K₃[Fe(CN₆)]/K₄[Fe(CN₆)] containing 0.1 M PBS solution (pH 7.4) and 0.1 M KCl.

Fig. 4. (a) Cyclic voltammograms in a solution of 5 mM of K3[Fe(CN6)]/K4[Fe(CN6)] containing 0.1 M PBS solution (pH 7.4) and 0.1 M KCl; and (b) current changes (ΔI = Iglc-IPBS) at +0.6 V in 1 mM and 10 mM glucose solutions of the dPIn mixed with various concentrations of MWCNT solutions.

Scheme 2. (a) Components of SPCE; and (b) the possible glucose mechanism of the fabricated glucose sensor.

Fig. 5. Chronoamperometric current responses vs. time at +0.6 V vs. Ag/AgCl and the current change (ΔI = Iglc-IPBS) vs. glucose concentration (C, mM) of: (a), (c) CHI-GOx/APTES/dPIn; and (b), (d) CHI-GOx/APTES/1.5%MWCNT-dPIn. Inset in figures (c) and (d) are logarithmic scale of ΔI vs. C.

Fig. 6. Continuous current response vs. time at +0.6 V vs. Ag/AgCl in various glucose concentrations of: (a) CHI-GOx/APTES/1.5%MWCNT-dPIn; and (b) CHI-GOx/APTES/dPIn.

Fig. 7. Electrochemical characterization by in 1 mM glucose solution: cyclic voltammograms and the anodic and cathodic currents vs. scan rate of (a) and (b) for CHI-GOx/APTES/dPIn; and (c) and (d) for CHI-GOx/APTES/1.5%MWCNT-dPIn.

Fig. 8. (a) Electrode reproducibility; (b) electrode repeatability; (c) electrode stability at different storage times at 4 °C, the electrodes were tested in 1 mM glucose solution; and (d) selectivity in 1 mM of interference chemicals.