Although it is crucial to monitor the level of biological materials including ascorbic acid, glucose, and uric acid, however it is still challenging to detect them correctly due to their low concentrations in human body fluids. Organic Electrochemical Transistors (OECTs) are often utilized for detecting low-concentration bio-materials because they are affordable to manufacture and adaptable to flexible substrates. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) a kind of conductive polymer used mainly as a channel in OECTs, is useful for detecting ascorbic acid (AA), often known as vitamin-C. In this paper, we offer a simple and inexpensive strategy for fabricating an all-PEDOT:PSS OECTs utilizing laser-induced patterning for the channel and gate electrodes. We optimized the geometrical parameters of the OECTs to achieve the highest sensitivity in a limited total area by adjusting the γ, which is the area ratio between the channel.