Electrolyte – Gated Organic Field – Effect Transistors (EGOFETs) have attracted considerable interest as electrical transducers due to their low power consumption and strong potential for label – free biosensing. Hydrogels – polymeric networks capable of absorbing and retaining large amounts of water – have emerged as effective solid electrolyte media, enabling the replacement of liquid electrolytes in EGOFETs to form hydrogel-gated OFETs (HYGOFETs). In this work, we demonstrate the use of HYGOFETs for biosensing applications by employing agarose hydrogels functionalized with avidin as the solid electrolyte. The devices were integrated into a lateral flow system, and their electrical response to biotin was systematically investigated under continuous analysis. The bio-recognition event induced a measurable change in device capacitance, allowing the achievement of a very low limit of detection in the fM range. This study highlights the relevance of bio-compatible solid electrolytes for advancing robust, integrated, and physiologically compatible organic bio-sensing platforms.