Microfluidic and Biosensor Chip Technology

The i-STAT System is at the cutting edge of diagnostic technology. With the revolutionary integration of biochemical and silicon chip technologies, the System achieves previously unattainable miniaturization of sophisticated components that provides clinicians a truly portable, nearly instantaneous blood analyzer with no
sacrifice in accuracy and reliability. To meet the needs of the entire hospital, a variety of sensor configurations make it possible to perform a number of critical care assays: electrolytes, general chemistries, blood gases and hematology.

The single use, disposable cartridge contains many of the subassemblies typically found in today's complex laboratory analyzers.

The sensors are micro-fabricated thin film electrodes. The integration of semi-conductor manufacturing process technology with well defined electrochemical principles results in the production of micro-miniaturized sensors with highly reproducible characteristics. Depending on the particular assay, the electrical signals produced are measured by the i-STAT Portable Clinical Analyzer's amperometric, potentiometric or conductometric circuits.

Calibrant solution is contained in the cartridge within a foil pouch. The fluid is a pH buffered aqueous solution of the analytes at known concentrations.

The test cycle is started by placing the cartridge containing the blood sample into the Analyzer. During the test cycle, the analyzer presses the front of the cartridge, causing a barb to puncture the pouch. The calibrant fluid is released to flow over the sensor array for measurement.

When calibration is completed, the analyzer presses the cartridge air bladder which pushes the calibrant solution into the waste reservoir and sends the blood sample over the sensor array for measurement.

All blood and calibrant fluid is contained within the cartridge for safe bio-hazard disposal.

Quality results by design

The i-STAT sensor arrays insure the integrity of the overall analytical process. The solid-state chips contain biosensors configured to perf o rm specific tests with chemically sensitive membranes and films containing reagent chemicals. Sensors perf o rm other functions such as monitoring the quality of the sample being tested. Silicon-type microfabrication utilizing high quality materials that exhibit exceptional stability allows consistent re p roducibility in a high-volume manufacturing environment. This well accepted technology ensures that each cartridge offers a high level of accuracy and reliability.

When blood samples contact the sensors, they are measured electrochemically as follows:

Sodium,Potassium, Chloride, Ionized Calcium, pH and PCO2
are measured by ion-selective electrode potentiometry. Concentrations are calculated from the measured potential through the Nernst equation.

Urea is first hydrolyzed to ammonium ions in a reaction catalyzed by the enzyme urease. The ammonium ions are measured by an ion-selective electrode and concentration is calculated from the measured potential through the Nernst equation.

Glucose is measured amperometrically. Oxidation of glucose, catalyzed by the enzyme glucose oxidase, produces hydrogen peroxide. The liberated hydrogen peroxide is oxidized at an electrode to produce an electric current which is proportional to the glucose concentration.

PO2 is measured amperometrically. The oxygen sensor is similar to a conventional Clark electrode. Oxygen permeates through a gas permerable membrane from the blood sample into an internal electrolyte solution where it is reduced at the cathode. The oxygen reduction current is proportional to the dissolved oxygen concentration.

Hematocrit is determined conductometrically. The measured conductivity, after correction for electrolyte concentration, is related to the hematocrit. A variety of calculated results are available that include HCO3, TCO2, BE, sO2,Anion Gap and Hemoglobin.