Diboronic-Acid-Based Electrochemical Sensor for Enzyme-Free Selective and Sensitive Glucose Detection

Abstract

A diboronic acid anthracene-based fluorescent system for detecting blood glucose could be used for 180 days. However, there has not yet been a boronic acid immobilized electrode to selectively detect glucose in a signal-increased way. Considering malfunctions of sensors at high sugar levels, the electrochemical signal should be increased proportionally to the glucose concentration. Therefore, we synthesized a new diboronic acid derivative and fabricated the derivative-immobilized electrodes for the selective detection of glucose. We performed cyclic voltammetry and electrochemical impedance spectroscopy with an Fe(CN)₆^3-/4- redox pair for detecting glucose in the range of 0-500 mg/dL. The analysis revealed increased electron-transfer kinetics such as increased peak current and decreased semicircle radius of Nyquist plots as the glucose concentration increased. The cyclic voltammetry and impedance spectroscopy showed that the linear detection range of glucose was 40 to 500 mg/dL with limits of detection of 31.2 mg/dL and 21.5 mg/dL, respectively. We applied the fabricated electrode to detect glucose in artificial sweat and obtained 90% of the performance of the electrodes in PBS. Cyclic voltammetry measurements of other sugars such as galactose, fructose, and mannitol also showed linear increased peak currents proportional to the concentrations of the tested sugars. However, the slopes of the sugars were lower than that of glucose, indicating selectivity for glucose. These results proved the newly synthesized diboronic acid is a promising synthetic receptor for developing a long-term usable electrochemical sensor system.

Keywords: boronic acid; diabetes; electrochemical sensor; glucose monitoring; self-assembly.

Scheme 1

Seven steps required for synthesizing diboronic anthracene with two primary amines for electrochemically detecting glucose.

Figure 1

Cyclic voltammograms of electrodes cleaned by (a) rinsing with EtOH and (b) electrochemical cycling in diluted H₂SO₄. A total of 50 µL of 0.1 × PBS (pH 7.4) containing 10 mM Fe(CN)₆^3−/4− and 0.1 M KCl was applied to the electrodes and CV measurements were carried out.

Scheme 2

Schematics illustrating two steps required for fabricating DA-immobilized electrodes.

Figure 2

Electrochemical analysis for MBA- and DA-immobilized electrodes. (a) Cyclic voltammograms and (b) Nyquist plots obtained for surface-modified electrodes by applying 50 µL of 0.1 × PBS (pH 7.4) containing 10 mM Fe(CN)₆^3−/4− and 0.1 M KCl to the electrodes. Inset shows the enlarged image of the Nyquist plots of the bare electrode and EDC/NHS treated electrode.

Figure 3

Electrochemical detection of glucose using DA-modified electrode. (a) CVs and (b) peak currents obtained after applying 50 µL of 0.1 × PBS (pH 7.4) containing 10 mM Fe(CN)₆^3−/4−, 0.1 M KCl, and glucose in the range of 0–500 mg/dL to the electrodes.

Figure 4

(a) Nyquist plots and (b) electron transfer resistances obtained applying 50 µL of 0.1 × PBS (pH 7.4) containing 10 mM Fe(CN)₆^3−/4−, 0.1 M KCl, and glucose in the range of 0–500 mg/dL to the DA-modified electrode. Inset in (a,b) is the equivalent circuit model and the relative electron transfer resistance respectively. R_cto represents the electron transfer resistance without glucose.

Figure 5

Simplified illustration to depict space occupied by moving phenyl rings depending on interacting with saccharide molecules. The gray area indicates space generated by rotating or vibrating phenyl rings. Freely moving phenyl rings should occupy more space than saccharide-linked ones.

Figure 6

Cyclic voltammograms obtained by applying 20 µL of 0.1 × PBS (pH 7.4) to the asymmetric-membrane-attached electrodes depending on added amount of the redox pair.

Figure 7

Electrochemical detection of glucose in artificial sweat using DA-modified electrode with asymmetric membrane. (a) Cyclic voltammograms and (b) peak currents obtained using glucose in the range of 0–500 mg/dL. 20 µL of artificial sweat containing glucose was applied to the electrodes and CV measurements were carried out.

Figure 8

Electrochemical selectivity of DA-immobilized electrode for detecting saccharides. in the range of 0–500 mg/dL. 50 µL of 0.1 × PBS (pH 7.4) congaing 10 mM Fe(CN)₆^3−/4−, 0.1 M KCl, was applied to the electrodes and CV measurements were carried out (a,c,e) Cyclic voltammograms and (b,d,f) corresponding peak currents obtained using fructose, mannitol, and galactose, respectively.