Plasma polymerization is nowadays considered as a promising and versatile technique for polymer films deposition with functional properties, without affecting the intrinsic properties of the substrates. Among various atmospheric pressure plasma technologies the so-called “Atmospheric Pressure Plasma Dielectric Barrier Discharges” (APDBD)  has recently received a lot of attention due to the easy ignition of a stable discharge and its scalability.The present work aims at designing plasma polymer films for bio-applications such as, (i) drug delivery system (application 1) thanks to their high surface-to-volume ratios allowing to retain and release specific molecules, (ii) Biosensor (application 2) due to the ability of the coating to absorb enzymes.In this frame different plasma polymers obtained from methacrylic acid were prepared by applying the so called Yasuda  parameter corresponding to the ratio between the energy applied and the precursor mass unit, in order to obtain hydrophilic coatings with a tunable volume density of carboxylic functions. The impact of the process parameters on the physical and chemical properties of plasma polymerized methacrylic acid was evaluated by studying the carboxylic group concentration, as well as the chemical structure and morphology of the deposit. In application 1, the entrapped target molecule, acetaminophen, could be release from the plasma polymer coating by simply dipping the film in the methanol solution.In application 2, the alkaline phosphatase diffused in the whole plasma polymer film and can be detected by dipping the coating into p-nitrophenyl phosphate solutions for the evaluation of the activity. The enzymatic activity was well preserved even after several days and MALDI-TOF analyses show the chemical structure preservation of the acetaminophen entrapped in the plasma polymer film.