Min-Chol Shin

Microfabricated conductometric urea biosensor based on sol-gel immobilized urease

A conductometric biosensor was constructed with a sol-gel immobilized urease on a microfabricated interdigitated array (IDA) gold electrode. Tetramethoxysilane (TMOS) was used as a sol-gel precursor for the immobilization of the urease and the performance of the resulting urea biosensor was controlled through the water content in the acid-catalyzed hydrolysis of the sol-gel stock solution. The sol-gel-derived urea biosensor showed relatively wide dynamic range of 0.2–50 mM in 5 mM imidazole-HC1 buffer at pH 7.5. Furthermore, the urea biosensor exhibited good sensor-to-sensor reproducibility (6.5 %) and storage stability (50 % of its original activity retained after 3 weeks) when stored in 5 mM imidazole-HC1 buffer at 4 °C. The urea biosensor was successfully applied for the urea determination in urine sample by employing the differential measurement format consisting of an active IDA conductometric sensor containing sol-gel-immobilized urease and a reference IDA conductometric sensor containing bovine serum albumin layer instead of the urease.

Electrochemical adsorption of glucose oxidase onto polypyrrole film for the construction of a glucose biosensor

Abstract By electrochemical adsorption of glucose oxidase (GOD) on a polypyrrole (PPy) layer, a heterobilayer glucose electrode with the configuration Pt/PPy/GOD has been constructed. The PPy film is grown on the platinum surface by galvanostatic electropolymerization, and its thickness is optimized to act as an anti-interference layer against electro-oxidizable interfering compounds such as ascorbate. The optimal conditions for the fabrication of the Pt/PPy/GOD electrode and the characteristics of the resulting electrode are investigated. The diffusion of glucose through the PPy film is analysed electrochemically by comparison of the level of current coming from the Pt/PPy/GOD and Pt/ PPy/GOD/PPy electrodes, respectively.

Effects of Enzyme Concentration and Film Thickness on the Analytical Performance of a Polypyrrole/Glucose Oxidase Biosensor

Abstract We describe the effect of preparation conditions during electropolymerization such as enzyme concentration in the deposition solution and film thickness on the analytical performance of the resulting polypyrrole / glucose oxidase (PPy/GOD) film. The responses of the resulting PPy/GOD biosensor to glucose and ascorbate were characterized and optimized. It was found that the enzyme concentration and the film thickness have the equivalent effects on the response of the resulting biosensor and that several optimal sets of the two parameters exist. The investigations regarding the response characteristic and the suppression of interference clearly indicate that the performance of biosensor could be significantly improved by making the film thick at low enzyme concentration.

A Field-Portable Toxicity Tester using Bacterial Bioluminescence

This paper describes a simple, inexpensive and easily constructed toxicity biosensor that uses freeze-dried bioluminescent bacteria, photobacterium phosphoreum IFO 13896. To compensate for bacterial activity, we apply a differential photometer circuit to measure bioluminescence. Instead of a photomultiplier tube, dual photodiodes were used to reduce the cost of the sensor system. The concentrations of toxic compounds causing 50% light loss (50% effective concentrations, EC50) were determined immediately and 30 min after rehydration of the bacteria from a freeze-dried state. The EC50 values at dual mode operation with differential amplification are nearly constant for the temperature range between 10 and 25degC, whereas the EC50 values at single mode operation increase with temperature, resulting in low sensitivity. The performance of the portable biosensor as a tool for determining p-nitrophenol, mercury, cadmium, and lead toxicity is demonstrated.