We have found that carbon electrodes fabricated by the C-MEMS process to be chemically very inert. Hence, surface modification is necessary for their use as biosensors and electrochemical electrodes. Functionalization of carbon electrodes in an oxygen plasma or by acid treatment has been reported previously. However, there is often a need for selective functionalization only at specific locations on the electrodes, so that they can function as sensor element and also retain pristine surface chemistry in other areas. In this paper, we introduce a novel plasma direct-writing technique for selective functionalization of carbon electrodes with carboxylic groups at room temperature and atmospheric pressure. We demonstrate the plasma direct-writing on two test platforms. On platform one, we draw patterns of carboxylic functional groups on flat glassy carbon electrodes derived from photolithographically patterned photoresist. The second platform is carbon hybrid structure composed of glassy carbon walls and graphitic carbon nanowires suspended in between them by electromechanical spinning. Functionalization was performed only on nanowires by plasma direct-writing technique. The resulting surface chemistry and wettability of the electrodes are investigated by means of water contact angle measurement, Fourier transform infrared spectroscopy and Raman spectroscopy. Carboxylic group functionalization is a first step towards immobilization of DNA or immunoglobulin for carbon based biosensors. Selective surface functionalization is important for better accuracy in biosensing by preventing unwanted immobilization and their interference. The plasma direct-writing technique not only enables controlled writing of functional groups but also enables control of the degree of functionalization in a simple one step procedure.

Acknowledgement

The authors would like to acknowledge Ministry of Science Technology and Innovation (MOSTI) Science Fund (SF-020-2014), Transdisciplinary Research Grant Scheme (TR002A-2014B), and University of Malaya Flagship Grant (FL001-14AET).