Automatic Assay of Blood Cholinesterase in the Field

"A unique minimally invasive system for painless blood testing, now being commercialized for diabetic blood glucose monitoring, can be adapted to measure blood cholinesterase activity. The consumable, the key novel system component, consists of a hollowsilicon microneedle comparable in cross-section to a human hair integrated with lab-on-a-chip microfluidics. This device is made by silicon microfabrication technology developed for the manufacture of electronic integrated circuits, and can be produced inhigh volume at low unit cost. In use, the microneedle punctures the skin and draws a 10 to 60 nanoliter blood sample into the chip, where the assay is performed automatically. On-chip microfluidics under microprocessor control mix the blood sample with abuffered solution of a selected cholinesterase substrate, and an integrated electrochemical biosensor measures the rate of choline (or thiocholine) production. The strength of this new approach lies in the combination of biosensors and our unique siliconmicroneedles, which possess high strength, flexibility, and fracture toughness resulting from extensive MEMS (microelectromechanical systems) R&D in the proposer's laboratory. By rendering use easy and painless and sharply reducing cost, disposable chipsfor field measurement of the activities of specific enzymes in blood, such as the cholinesterases, become practical. Assay methods for true and pseudo cholinesterases, and for genet