Keiko Oka

An automated ELISA system using a pipette tip as a solid phase and a pH-sensitive field effect transistor as a detector

A fully automated ELISA system was constructed using a pipette tip as a solid phase, urease as a detecting enzyme, and a pH-FET as a detector of urease activity. The inner wall of the end part of a pipette tip was used as a solid phase, and the urease activity of the conjugate, captured after a two-step immunoreaction, was measured by coupling the pipette tip with the pH-FET in a pH-measuring cell. Full automation of the ELISA system was achieved by using a disposable reagent cartridge and three pipetters for all mechanical operations, including sample dilution and B/F separation. This system can treat 60 samples per hour with an assay time of 21 min for all assay configurations. The system was applied to two-step sandwich assays for AFP, CEA, HBsAg, and HBsAb, a two-step competition assay for HBcAb, and a second antibody assay for HTLV-I Ab.

Diagnostic System for Helicobacter pylori Urease Based on a pHsensitive Field Effect Transistor

A rapid diagnostic system for Helicobacter pylori (H. pylori) was developed based on an urease analyser using a pH‐sensitive field effect transistor (pH‐FET). The system is composed of a solid‐phase capillary‐tube and a pH‐measuring cell. The solid‐phase tube, with an inner diameter 0.55 mm and coated with a monoclonal antibody against H. pyloris urease, was used to selectively capture the urease in endoscopically collected gastric mucus. The urease activity on the inner surface of the solid‐phase tube was measured by coupling it with ph‐FET in a pH measuring cell containing urea solution. Before immuno reaction in the solid‐phase, gastric mucus was diluted with a phosphate buffered saline containing 1% n‐octylglucoside, which was effective for accelerating the release of active urease from H. pyloris cells suspended in the sample solution. As a result of preliminary evaluations, it was found that the clinical sensitivity and specificity were 100 and 86%, respectively, using a bacteriological test as a reference.

Endoscopic Urease Sensor System for Detecting Helicobacter pylori on Gastric Wall Using a pH-sensitive Field Effect Transistor

An endoscopic tube‐tip type urease sensor was developed for the purpose of on‐site detection of Helicobacter pylori (H. pylori) using a pH‐sensitive field effect transistor (pH‐FET). The sensor is composed of an endoscopic‐tube connected to a feed pump with a urea solution and a pH‐FET attached to a sensor holder at the open end of the tube. The urease activity on the gastric wall can be measured by bringing the sensor into contact with the gastric wall just after replacing gastric juice with the urea solution. The presence of H. pylori causes a pH change in the urea solution inside the sensor holder in 20 seconds due to the strong urease activity of this bacterial species. After measurement, the sensor is detached from the wall, and washed with urea solution by turning on the urea pump. A measurement at one site is completed within 30 seconds. Repetition of the procedure makes multi‐site measurements possible. In preliminary evaluations, it was found that clinical sensitivity and specificity were 89% and 86%, respectively, using standard bacteriological testing results as a reference.