Sequential detection of dopamine and L-DOPA by a 2,3-dopa-dioxygenase from Streptomyces sclerotialus.

A variety of enzyme-based colorimetric biosensors have been developed for clinical practice; however, these methods will only become cost-effective when they are able to process multiple samples with a high degree of sensitivity. In this study, a novel heat-stable enzyme, 2,3-dopa-dioxygenase from the thermophilic bacterium Streptomyces sclerotialus (SsDDO), was used in the development of a protein- and cell-based biosensor for the detection of L-DOPA for the first time. SsDDO catalyzes the oxidative cleavage of L-DOPA forms linear semialdehyde (AHMS) and cyclizes to a 3-carboxy-3-hydroxyallylidene-3,4-dihydropyrrole-2-carboxylic acid (CHAPCA). We next derivatized CHAPCA by reacting with 3-aminobenzoic acid (MABA) to yield a red-fluorescent pigment. Overall, the detection of L-DOPA via the red fluorescent signal can be completed in only 30 min. We also developed a sequential analysis method to detect the coexistence of dopamine and L-DOPA with a high degree of sensitivity using the dual-fluorescent signals to monitor the therapy of patients with Parkinson's disease treated with L-DOPA. The robustness and applicability of the system were further validated in serum. In addition, paper microfluidics modified with chitosan was applied for fast and cost-effective analysis of dopamine and L-DOPA in the mixed solutions.