Test Strip and Optoelectronic Sensors

Nowadays, test strips for the determination of about ten low-molecular weight substances (metabolites, drugs and electrolytes) and eight enzymes are available on the market (Libeer, 1985), one strip usually costing more than US 1. Pocket photometers and computerized photometric and potentiometric devices are being offered as readout instru- 

Optoelectronic biosensors based on immobilized dyes have been developed for the determination of glucose, urea, penicillin, and human serum albumin (Lowe et al., 1983). Other promising approaches use immobilized luciferase or horseradish peroxidase to assay ATP or NADH or, when coupled with oxidases, to measure uric acid or cholesterol. These principles have not yet been generally accepted for use in routine analysis. Most probably, the first commercial optical biosensors will be those for immunological assays. 

Although thermistor devices involving the use of immobilized enzymes or antibodies for a number of clinically relevant substances have been described (Table 22), their practical use is at present limited to a few research laboratories. Thermometric enzyme linked immunosorbent assays are being routinely employed in monitoring the production of monoclonal antibodies. A broad application is restricted by the low sample throughput and the high equipment costs. 

Between 15 and 20 analyzers based on enzyme electrodes are on the market worldwide. They are one-parameter instruments for the measurement of glucose, galactose, uric add, choline, ethanol, lysine, lactate, pesti-ddes, sucrose, lactose, and the activity of a-amylase (Table 23). They provide for a negligible enzyme consumption of less than 1 pg per sample. 

Substance Immobilized biocatalyst Measuring range (mmol/1) or detection limit 

---