A stable and selective electrochemical biosensor for the liver enzyme alanine aminotransferase (ALT)

An electrochemical method to determine alanine aminotransferase (ALT) activity over its normal and elevated physiological range was developed based upon detection of l-glutamate at a glutamate oxidase-modified platinum electrode. Measurements were carried out in the presence of ALT co-substrates l-alanine and α-ketoglutarate and current response from either the oxidation of hydrogen peroxide or the re-oxidation of the mediator ferrocene carboxylic acid was employed. The enzyme electrode was tested over a 6-month period and found to retain 79% of its original activity towards ALT detection with >200 measurements performed over this time. Signals associated with interfering electroactive species (ascorbic acid and uric acid) were eliminated using background subtraction at a denatured glutamate oxidase enzyme electrode. The sensitivity of the device was found to be 0.845 nA U−1 L ALT with t90 = 180 s, linear range 10–1000 U L−1 and LOD of 3.29 U L−1 using amperometry at Eapp = 0.4 V vs. Ag/AgCl at 308 K (35 °C).