Introduction

Electrochemistry offers considerable promise for on-chip immunoassays and for designing self-contained and disposable chips for medical diagnosis. The attractive features of electrochemical technologies include its high sensitivity, inherent miniaturization, low cost, low power requirements, and high compatibility with advanced micromachining, can be applied for the construction of biosensors and bacteria inactivation systems.

Biosensor with ferrocene labeled antibody

Ferrocene derivatives are fast and reversible redox mediators and are common compounds in bio-sensors. A flow-immunoassay system for the detection of hemoglobin A1c (HbA1c) was developed using ferrocene-conjugated antibody and boronate affinity chromatography. An on-chip type boronate affinity chromatography was constructed for the separation of HbA1c and a ferrocene labeled anti-human hemoglobin (Hb) antibody was used for the electrochemical detection of HbA1c. The assay procedure includes immunoreactions with ferrocene conjugated to anti Hb antibody (Fc-antibody) and HbA1c, the separation of immunocomplexes with Fc-antibody and HbA1c, and the electrochemical detection of the immunocomplexes. A linear correlation between the increase of current and HbA1c concentration was obtained. The flow immunoassay of HbA1c was successfully achieved using blood cell lysates.



Automated water toxicity biosensor.

Automated water toxicity biosensor for monitoring cyanides

An on-line biosensor consisting of immobilized Thiobacillus ferrooxidans and an oxygen electrode was developed for automated monitoring of acute toxicity in water samples. T. ferrooxidans is an obligatory acidophilic, autotrophic bacterium and derives its energy by the oxidation of ferrous ion, elemental sulfur, and reduced sulfur compounds including metal sulfides. The assay is based on the monitoring of a current increase by addition of toxicoids, which is caused by the inhibition of bacterial respiration and decrease in oxygen consumption. A linear relationship was obtained at KCN concentration in the range of 0.5-3.0 M in a flow-type monitoring system. The sensor response was within an error of 10% for 30 membranes. This flow-type monitoring sensor was operated continuously for 5 months. In addition, T. ferrooxidans immobilized membrane can also be stored for one month at 4 degrees C.

Electrochemical Bacteria Inactivation System

The inactivation of microbial cells attached at the initial layer should be an effective approach to inhibit biofouling. In marine environments, the formation of biofilms are important for subsequent attachment and development of invertebrate larvae. The microbially generated biofilms are known to affect settlement and metamorphosis of oyster larvae and mussels. For these reason, inactivation of microbial cell attached to substratum during initial stage is important.

In our laboratory, we have been developing methods to prevent the accumulation of biofouling organisms using an electrically conductive plastic electrode, which is made out of graphite and silicon. Carbon-chloroprene and carbon-urethane sheet electrodes are known for their capability to coat large surfaces. We then utilized this material for the electrochemical prevention of biofouling in seawater cooling pipes where we discovered that it was possible to inactivate microbial cells without generating toxic substances. In search for a better electrode system, TiN electrodes and conductive paints were selected and used. The results were promising as marine bacteria were killed electrochemically by applying electricity using the conductive paint and the TiN film electrode respectively.