Electronic Supplementary Material
Glucose biosensor based on glucose oxidase immobilized on unhybridized titanium dioxide nanotube arrays
Wei Wanga, b, Yibing Xiea, b *, Yong Wanga, Hongxiu Dua,b, Chi Xiaa,b, Fang Tiana
a School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China
b Suzhou Research Institute of Southeast University, Suzhou 215123, China
*Corresponding author: E-mail address: (Y. Xie)
Effect of pH on cyclic voltammetry
The pH value of the supporting electrolyte has an influence not only on the current of the redox peak [1] but also the activity of GOx [2]. So the proper pH is beneficial to achieve a high performance of biosensors. The cyclic voltammetry of the bare TiO2 nanotube arrays electrode was investigated over the pH values from 5.8 to 7.8 in the phosphate buffer solution containing 0.5 mM H2O2 (Fig. S2A). Fig. S2B showed the effect of pH on the reduction peak currents response. When the pH of the phosphate buffer solution is very low or very high, the electrode all exhibits low response current to H2O2. An optimum response current can be found at pH 6.8. This result is also consistent with other research work that the pH values from 6.0 to 7.5 reflects the optimum conditions for enzymatic mediated electrochemical reactions [3]. Hence, the optimal pH of 6.8 was chosen in the further study.
Impedance measurement of the electrodes
The electrochemical impedance spectroscopy is a sensitive and nondestructive method to macroscopically reflect the state of the interface and the electron transfer process [4]. So it has been widely used in recent decades. The electrochemical impedance spectroscopy of TiO2 nanotube arrays electrode before and after GOx immobilization were monitored in phosphate buffer solution (0.2 M, pH 6.8) containing 1 mM [Fe(CN)6]3-/4- redox probe. The electrochemical impedance data were recorded at open circuit potential of -0.5 V in the frequency range from 100 kHz to 0.01 Hz with perturbation amplitude of 5 mV. The Nyquist plot of bare TiO2 nanotube arrays electrode displays two distinct regions, dependent of the frequency range (Fig. S3A). In the high frequency region (5 Hz-100 kHz), a short straight line with an angular coefficient close to 45° is the characteristic of ion diffusion into the porous structure of the electrode. While in the low frequency region (10 mHz-10 Hz), a second straight line observed with the phase angle close to 90°, thereby tends to become purely capacitive, characteristic of a diffusion-limited process [5], and also characteristic of a porous conducting film [6]. Then, another similar Nyquist plot was found for the enzyme electrode (Fig. S3B). The result indicates that the immobilization of glucose oxidase onto the TiO2 nanotube arrays electrode does not increase the internal resistance of the electrode. It still keeps the fast electron transfer capability.
The effect of scan rate on the electrochemical response of the electrodes
The effect of scan rate on the electrochemical response of the bare TiO2 nanotube arrays electrode was displayed in Fig. S4. Cyclic voltammetry was run in 0.2 M phosphate buffer solution (pH 6.8) containing 0.5 mM H2O2, at different scan rates of 10, 20, 40, 60, 80, 100, 150 and 200 mV s-1, respectively (Fig. S4A). It is obvious that the reduction peak currents are dependent on scan rate. Fig. S4B displayed the reduction peak currents are proportional to the square root of scan rate value when the scan rate increases from 10 to 200 mV s-1. The correlation coefficient, R2 is 0.9976. It indicates that the redox reaction on the bare TiO2 nanotube arrays electrode is diffusion-controlled electrochemical process [7].
Table S1. Sensitivities characteristics of our unhybridized and other hybridized TiO2 based sensors for glucose detection. (CNT=carbon nanotubes, GR=Graphene, TNTs=TiO2 nanotubes).
(mM) / Low detection limit (μM) / Stability
(current %) / Sensitivity
(µA mM-1 cm-2) / Reference
Ti/TiO2/Au/PB/GOx / 0.015-4.0 / 5 / 90 (21 days) / 36 / [3]
TiO2/CNT/Pt/GOx / 0.006-1.5 / 5.7 / - / 0.24 / [8]
TiO2/GR/GOx / 0-8 / - / 94.4 (100 cycles) / 6.2 / [9]
CNT/TiO2/Nafion/GOx / 0.05-5 / 20 / 80 (30 days) / 154 / [10]
Pt-DENs/TNTs/GOx / 0.01-12 / 1 / 90 (21 days) / 43.6 / [11]
ITO/TiO2(IO)/GOx / 0.05-2.5 / 0.02 / 90 (10 days) / 151 / [12]
meso-HAP/meso-TiO2/MWCNT/GOx / 0.01-15.2 / 2 / 86 (30 days) / 57.0 / [13]
Our biosensor / 0.05-0.65 / 3.8 / 86 (6 days) / 199.61 / This work
Table S2. Determination of glucose in real samples using the unhybridized TiO2 nanotube arrays glucose biosensor under an applied potential of -0.5 V (vs. SCE).
Sample / Added (mM ) / Found (mM) / Recovery (%)1 / 0.1 / 0.104 / 104
2 / 0.2 / 0.189 / 94.5
3 / 0.3 / 0.287 / 95. 7
4 / 0.4 / 0.409 / 102.3
5 / 0.5 / 0.488 / 97.6
Fig. S1. XRD patterns for the TiO2 nanotube arrays and the standard data of JCPDS card No. 21-1272.
Fig. S2. (A) Cyclic voltammograms of 0.5 mM H2O2 at different pH values at a scan rate: 100 mV s-1. (B) Effect of pH on the reduction peak currents response of bare TiO2 nanotube arrays electrode.
Fig. S3. Nyquist plots of the bare TiO2 nanotube arrays (A) and enzyme (B) electrodes. Inset: high frequency region of Nyquist plots of bare TiO2 nanotube arrays electrode (a) and enzyme electrode (b).
Fig. S4. (A) Cyclic voltammograms of bare TiO2 nanotube arrays electrode at different scan rates (10, 20, 40, 60, 80, 100, 150 and 200 mV s-1) in 0.2 M phosphate buffer solution (pH 6.8) containing 0.5 mM H2O2; (B) The plot of reduction current of (A) with square root of the scan rate value.
Fig. S5. Current-time responses of the three electrodes after a successive addition of 0.1 mM hydrogen peroxide in 0.2 M phosphate buffer solution (pH 6.8) under an applied potential of -0.5 V (vs. SCE), (A) The current-time response of bare Ti sheet electrode; (B) The current-time response of bare TiO2 film electrode; (C) The current-time response of bare TiO2 nanotube arrays electrode.
Fig. S6. Calibration curves for the amperometric response of three types of electrodes to electro-reduction of H2O2, (A) The calibration curves of bare Ti sheet electrode; (B) The calibration curves of bare TiO2 film electrode; (C) The calibration curves of bare TiO2 nanotube arrays electrode.
Fig. S7. Calibration curves for the amperometric response of the three electrodes for successive addition of 50 µM glucose: (A) Calibration curve of Ti sheet enzyme electrode as a function of glucose concentration; (B) TiO2 film enzyme electrode as a function of glucose concentration; (C) TiO2 nanotube arrays enzyme electrode as a function of glucose concentration.
Fig. S8. Stability analyses of the electrode. (A) Influence of electroactive interferences of ascorbic acid, sucrose, L-cysteine, L-histidine and L-glycine on the biosensor response, under an applied potential of -0.5 V (vs. SCE). (B) Long-term stability of the unhybridized TiO2 nanotube arrays glucose biosensor stored in dry condition at 4 °C.
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