Shyh-Liang Lou

Flexible thick-film glucose biosensor: Influence of mechanical bending on the performance

The influence of the bending-induced mechanical stress of flexible Nafion/GOx/carbon screen-printed electrodes (SPEs) upon the performance of such glucose biosensors has been examined. Surprisingly, such flexible enzyme/polymer-SPEs operate well following a severe bending-induced mechanical stress (including a 180 degrees pinch), and actually display a substantial sensitivity enhancement following their mechanical bending. The bending-induced sensitivity enhancement is observed only for the amperometric detection of the glucose substrate but not for measurements of hydrogen peroxide, catechol or ferrocyanide at coated or bare SPEs. These (and additional) data indicate that the bending effect is associated primarily with changes in the biocatalytic activity. Such sensitivity enhancement is more pronounced at elevated glucose levels, reflecting the bending-induced changes in the biocatalytic reaction. Factors affecting the bending-induced changes in the performance are examined. While our data clearly indicate that flexible enzyme/polymer-SPEs can tolerate a severe mechanical stress and hold promise as wearable glucose biosensors, delivering the sample to the active sensor surface remains the major challenge for such continuous health monitoring.

A miniaturized glucose biosensor for in vitro and in vivo studies

A miniaturized wireless glucose biosensor has been developed to perform in vitro and in vivo studies. It consists of an external control subsystem and an implant sensing subsystem. The implant subsystem consists of a micro-processor, which coordinates circuitries of radio frequency, power regulator, command demodulator, glucose sensing trigger and signal read-out. Except for a set of sensing electrodes, the micro-processor, the circuitries and a receiving coil were hermetically sealed with polydimethylsiloxane. The electrode set is a substrate of silicon oxide coated with platinum, which includes a working electrode and a reference electrode. Glucose oxidase was immobilized on the surface of the working electrode. The implant subsystem bi-directionally communicates with the external subsystem via radio frequency technologies. The external subsystem wirelessly supplies electricity to power the implant, issues commands to the implant to perform tasks, receives the glucose responses detected by the electrode, and relays the response signals to a computer through a RS-232 connection. Studies of in vitro and in vivo were performed to evaluate the biosensor. The linear response of the biosensor is up to 15 mM of glucose in vitro. The results of in vivo study show significant glucose variations measured from the interstitial tissue fluid of a diabetes rat in fasting and non-fasting periods.

Effects of Electric Potential Treatment of a Chromium Hexacyanoferrate Modified Biosensor Based on PQQ-Dependent Glucose Dehydrogenase

A novel potential treatment technique applied to a glucose biosensor that is based on pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (GDH) and chromium hexacyanoferrate (CrHCF) incorporated into a platinum (Pt) electrode was demonstrated. CrHCF, serving as a mediator, was electrochemically deposited on the Pt electrode as ascertained by CV, SEM, FTIR and XPS measurements. The potential treatment of CrHCF, which converts Fe(II) to Fe(III), enables the glucose detection. The amperometric measurement linearity of the biosensor was up to 20 mM (R = 0.9923), and the detection sensitivity was 199.94 nA/mM per cm2. More importantly, this biosensor remained stable for >270 days.

Using MPTMS as Permselective Membranes of Biosensors

A sol-gel material of (3-mercaptopropyl)trimethoxysilane (MPTMS) is proposed to function as permselective membranes of biosensors. Permselectivity of MPTMS and Nafionreg was compared by studying their anti-interferent ability. Membrane porosity of MPTMS and Nafionreg was first confirmed via voltammetric responses in ferrocynite/ferricynite solution. In the comparison studies, membranes prepared with 20% MPTMS in phosphate buffer solution (PBS) and 1% Nafionreg in 2-propanol (IPA) were used as coating materials on the surface of two platinum (Pt) electrodes. These electrodes were used to electrochemically measure the response currents of ascorbic acid, uric acid, and acetaminophen. The results indicate that the MPTMS-based electrode produced much less response currents from the interference species compared to that of the Nafionreg-based electrode. This denotes that the anti-interferent ability of MPTMS is superior to that of Nafionreg. A platinum working electrode containing glucose oxidase (GOx) immobilized by poly-aniline (PA) and then modified by MPTMS was developed and evaluated. The results show that the optimum applied potential for the glucose biosensor is 0.4 V. This operational potential not only inhibits the response currents from ascorbic acid, uric acid, and acetaminophen but also produces rather high signals for glucose.

Chromium hexacyanoferrate modified biosensor based on PQQ-dependent glucose dehydrogenase

A pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase based platinum electrode was developed to detect glucose. Chromium hexacyanoferrate was modified onto this electrode to serve as an electron transfer mediator between PQQ and the platinum electrode. This biosensor showed the optimal response of glucose measurements at pH 7 and an operation potential of +0.4 V (vs. Ag/AgCl). More importantly the lifespan of the biosensor has been last for 47 days without significant enzyme activity degradation.