Iatrogenic infections due to contaminated medical devices are significant problem in the field of medicine, and have motivated the search for alternative surface disinfection/sterilization methods and technologies. During the last decade, a strong effort has been made in the field of non-thermal plasmas, including fundamental work from a physical, but also biological point of view. Non-thermal plasmas are used in industry for the modification of surface properties such as to improve wettability and adherence, and also for the deposition of thin films. The present work considers the treatment of surfaces contaminated by either bacteria or proteins with the effluent gas exiting from an atmospheric pressure dielectric barrier discharge. The discharge reactor consisted of a coaxial cylindrical geometry DBD reactor energized by a 30 kHz applied voltage. The effluent gas was used to treat surfaces contaminated with Escherichia coli (strain DH10B) or RNAse A (124 amino acids, 13.7kDa, known to be thermal-resistant). Results show that the decontamination of surfaces by the effluent gas from a humid argon DBD is effective, and that the effectiveness is greater the closer the biological samples are placed to the DBD source. The results also indicate that the mechanism of bacterial inactivation is based on a combination of stable oxidative species such as ozone and hydrogen peroxide as well as shorter lived species such as hydroxyl radical.