A flow-through amperometric sensor based on dialysis tubing and free enzyme reactors

A generic flow-through amperometric microenzyme sensor is described, which is based on semi-permeable dialysis tubing carrying the sample to be analyz ed. This tubing (300 mum OD) is led through a small cavity, containing the working and reference electrode. By filling this cavity with a few pl of an appropriate enzyme solution, an amperometric enzyme sensor results. As the dialysis tubing is impermeable for large molecular species such as enzymes , this approach does not require any immobilization chemistry, and as a con sequence the enzyme is present in its natural free form. Based on this prin ciple, amperometric sensors for lactate, glucose, and glutamate were formed by filling cavities, precision machined in Perspex (R), with buffered solu tions containing respectively, lactate-, glucose-, and glutamate-oxidase. A ll sensors showed a large linear range (0-35 mM for glucose, 0-3 mM for lac tate, and 0-5 mM for glutamate) covering the complete physiological range. The lower detection limit was in the order of 15-50 muM. Applicability in f low injection analysis systems is demonstrated. (C) 2001 Elsevier Science B .V. All rights reserved.