Kang Shin Lee

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.

Disposable thick-film liposome immunosensor for theophylline using immunochromatographic matrix

A novel electrochemical immunosensor based on liposome signal amplification and immunochromatography has been developed for the determination of theoghylline, a therapeutic drug, as a model analyte. The immunosensor is composed of two major parts; a disposable screen-printed electrode and a nitrocellulose strip. The nitrocellulose strip contains a sample loading zone, an immobilized antibody competition zone, and a signal generation zone containing ferrocyanide-loaded liposomes in an ascending sequence. Upon loading a liquid sample to the immunosensor, capillary action causes the theophylline and theophylline-melittin conjugate to migrate through an anti-theophylline antibody zone, where competition occurs. The unbound theophylline-melittin conjugates further migrate into the signal generation zone, where liposomes are disrupted to release the electroactive ferrocyanides which are amperometrically detected by the screen-printed electrode. The current produced is directly proportional to the amount of free theophylline in the sample. The lowest detection limit obtained with this immunosensor is 5 /spl mu/g/ml.