Organic electrochemical transistors (OECTs) are a promising building block for bioelectronic devices such as sensors and neural interfaces. While the majority of OECTs use simple planar geometry, there is an interest in exploring how these devices operate with much shorter channels on the submicron scale. In this thesis I show a practical route towards minimization of channel length of the transistor using traditional photolithography, enabling a large scale utilization. The fabrication of such transistors using two types of conducting polymers is described here. The first type is a commercial solution-processed spin-coated poly(dioxyethylenethiophene):poly(styrene sulfonate) PEDOT:PSS. The short channel length is exploited to support easy in situ electropolymerization of poly(dioxyethylenethiophene):tetrabutyl-ammonium hexafluorophosphate PEDOT:PF\textsubscript{6} and other counter-ions. I further explore OECT application on a flexible substrate, while also researching conductive polymer based electrochemical sensors. Then, OECT alternatives are discussed, for applications where higher speed is required. A durable electrode material in form of titanium nitride is introduced, together with a chemically stable encapsulation material - aluminium nitride in combination with Parylene-C. Finally, manuscripts dedicated to microfluidics are presented with the aim of directing research and development into the area of lab-on-chip technologies, which implement sensors into microfluidics and thus form an important diagnostic area.