Personalised medicine and diagnostics is a rapidly growing field of research and general interest. Important tools for individual patient care are so called point-of-care devices. These typically simple and inexpensive instruments allow the untrained user to perform simple diagnostic analyses without the need for a specialised laboratory. Other fields of application are for example health care projects in developing countries where access to modern high-throughput facilities is often impossible or sectors not related to the medical field, like environmental monitoring or food safety. The aim of this PhD project was to develop a modular platform based on electrochemical impedimetric sensing. This device can easily be modified by changing the biological receptors and therefore offers a broad range of possible applications. To keep the costs and the environmental footprint low the entire biosensor was designed in plastic; featuring a microfluidic channel and an electrode system fabricated from conductive polymers. Aptamers were used as recognition elements providing a more stable alternative to antibodies for easier handling and a longer shelf life. Moreover, aptamers have a much wider range of possible target molecules than antibodies. The biosensor platform was successfully adapted to different tasks and tested against three very different analytes: DNA, antibiotics and virus particles. Throughout the experiments the sensors showed high sensitivity and were able to detect very low analyte concentrations in both buffered solutions, milk and saliva samples.