Methods, systems, and devices are disclosed for providing test strip electrochemical sensors for rapid quantitative analysis of analytes in physiological fluids. In one aspect, an electrochemical sensor includes a substrate; an electrode contingent including a first electrode having a coating of carbon nanotubes (CNTs) and a second electrode on the substrate; and an entrapment layer formed on the first electrode to attach an enzymatic substance capable of causing a redox reaction in the presence of a target analyte of a fluid sample which produces a redox-active product, in which the entrapment layer is structured to include a conductive polymer film that is reversibly dopable to conduct charge carriers across the entrapment layer and at the first electrode. For example, the electrochemical sensor can be provided on a disposable test strip to quantify L-DOPA levels in whole blood, plasma, or serum samples.