An integrated electro-optical biosensor system for rapid, low-cost detection of bacteria

In medical treatment, the detection of pathogens at an early stage of diseases is a key step to set up an appropriate diagnosis. To reach this goal, several techniques have been elaborated for point-of-care diagnostic applications. One of the state-of-the art methods is the application of biosensor devices. Label-free versions of them ensure an appropriate detection of pathogens from fluid samples by their relative sensitivity, rapidity and portability, thus offering a feasible and affordable alternative to the traditional diagnostic techniques. The aim of the present study is to fulfill these requirements with a cheap construction of an electro-optical biosensor, for application as a rapid test in clinical diagnostics. Hence, an integrated microsystem consisting of dielectrophoretic surface-electrodes, a rib waveguide and a microfluidic channel was created for label-free optical detection of bacteria from fluid samples. To model the efficiency of the sensor, we carried out quantitative measurements by observing the light scattered by living Escherichia coli cells located in the vicinity of the waveguide. A significant change in the scattered light pattern was observed even when objectives of moderate magnification (x10, x4.7) were used, implying that such type of sensing of the cells can be achieved by low-cost cameras, as well. The optimal frequency utilized in the process of dielectrophoretic cell-collecting was also established. With this novel system, a detection limit of ca. 102CFU x mL(-1) was achieved, which is relevant to characteristic pathogen concentrations in body fluids, e.g., urine. Our further plan is to utilize this cell-gathering method in other, highly sensitive integrated optical sensor constructions, as well. The working principle of this dielectrophoretically enhanced detection of Escherichia coli cells from their suspensions gives us a low-cost and rapid-sensing alternative to routinely used, but time- and money-consuming other methods. Hence, we expect it to be readily applicable in point-of-care diagnostics as a basis of rapid tests to identify general pathogens from various body fluids.