T-Sensors have been demonstrated to allow both absorption- and fluorescence-based detection of analytes directly in complex samples such as whole blood and contaminated environmental samples, without prior separation of blood cells or other soluble and insoluble components. In this paper, we present the implementation of electrochemical detection methods in T-Sensors, as well as their optical validation. Microelectrodes integrated with etched microfluidic flow channels allow traditional electroanalytical techniques to be performed on microliter and smaller volumes and also enable new detection techniques which are based upon the interaction between the microelectrodes and the diffusional mixing that occurs between flow lamina at low Reynolds numbers. Conductivity versus mixing measurements, anodic stripping voltammetry, and isolation of microelectrodes by sheath flow are demonstrated for an experimental device. In a T-Sensor, a sample solution, a receptor solution, and, optionally, a reference solution (a known analyte standard) are introduced in a common channel (T-SensorTM), and laminarly flow next to each other until the exit the structure. Smaller particles such as ions or small proteins diffuse rapidly across the fluid boundaries, whereas larger molecules diffuse more slowly. Large particles show no significant diffusion within the time the two flow streams are in contact. Two interface zones are formed between the fluid layers. The ratio of a property (e.g., fluorescence intensity, stripping voltammetry signal) of the two interface zones is a function of the concentration of the analyte, and is largely free of cross-sensitivities to other sample components and instrument parameters.
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