Enhancement of the specificity of an enzyme-based biosensor for L-tryptophan

A new selective amperometric biosensor for reagentless L-tryptophan determination has been developed using immobilized tryptophan-2-monooxygenase (TMO, EC 1.13,12.3). This enzyme-based biosensor provides a rapid-response detection system for concentrations of L-tryptophan between 25 and 1.000 μM in a batch mode system and between 100 and 50,000 μM in a flow-injection mode. The response time was 30 seconds, and the total analysis time was less than 3 minutes. The biosensor retained catalytic activity and fidelity of phenylalanine and tryptophan response for greater than 4 months with repeated usage. The biosensor selectivity to L-tryptophan was dramatically increased relative to phenylalanine when a competitive inhibitor of TMO, indole acetamide (IA), was included. The biosensor was successfully used for L-tryptophan determination in nutrition broth, giving values identical to those determined by HPLC analysis.