The interface between biomacromolecules and carbon nanotubes (CNTs) is of critical importance in developing effective techniques that provide CNTs with both biomolecular recognition and signal transduction through immobilization. However, the chemical inertness of CNT surfaces poses an obstacle to wider implementation of CNTs in bioanalytical applications. In this paper, we present a review of our recent research activities related to the covalent attachment of biomacromolecules to plasma-patterned and functionalized carbon nanotube films and their application to the fabrication of electrochemical biosensing devices. The SWCNT films were spray-deposited onto a miniaturized three-electrode system on a glass substrate and activated using highly purified atomic oxygen generated in radiofrequency plasma; this introduced oxygen-containing functional groups into the SWCNT surface without fatal loss of the original physicochemical properties of the CNTs. The carboxylated SWCNT electrodes were then selectively modified via amidation or esterification for covalent immobilization of the biomacromolecules. The plasma-treated SWCNT-based sensing electrode had an approximately six times larger effective area than the untreated SWCNT-based electrode, which significantly amplified the amperometric electrochemical signal. Finally, the efficacy of plasma-functionalized SWCNT (pf-SWCNT) as a biointerface was examined by immobilizing glucose oxidase, Legionella pneumophila ( L. pneumophila)-specific antibodies, L. pneumophila-originated DNAs, and thrombin-specific aptamers on the pf-SWCNT-based three-electrode devices. The pf-SWCNT films were found to support direct covalent immobilization of the above-listed biomacromolecules on the films and to thereby overcome the many drawbacks typically associated with simple physisorption. Thus, pf-SWCNT sensing electrodes on which biomacromolecules were covalently immobilized were found to be chemically stable and have a long lifetime.

A fully integrated paper microfluidic electrochemical device equipped with three different cation permeable films is developed to determine blood ions (Cl−, Na+, K+, and Ca2+) at a time. These blood ions that are normally dissolved in the real human blood stream are essential for cell metabolisms and homeostasis in the human body. Abnormal concentration of blood ions causes many serious disorders. The optimized microfluidic device working without any external power source can directly and effectively separate human blood components, and subsequently detect a specific blood ion with minimized interference. The measured sensitivity to Cl−, K+, Na+, and Ca2+ are −47.71, 45.97, 51.06, and 19.46 in mV decade−1, respectively. Potentiometric responses of the microfluidic devices to blood serum samples are in the normal ranges of each cation, and comparable with responses from the commercial blood ion analyzer Abbott i-Stat.

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We present the research results of the use of plasma modification for the fabrication of carbon nanotube-based devices for chemical and biological sensing. The oxygen plasma treatment of multiwalled carbon nanotubes (MWCNTs) effectively grafts oxygen atoms onto the CNT surface. For investigating the impact of plasma modification on the MWCNT-based sensor performance, three different sensors are fabricated: NH3 gas sensors, humidity sensors, and immunosensors. The plasma-modified MWCNTs (p-MWCNTs) exhibit a sensitivity to NH3 that is approximately twice that of the corresponding untreated sensor. The humidity sensor with a p-MWCNT top electrode exhibits a much faster response time compared with the untreated MWCNT electrodes. The p-MWCNT immunosensor exhibits a detection limit almost 1000 times lower than that of the standard ELISA assay, while the untreated MWCNTs exhibit no detectable signal. These results imply that the oxygen-containing functional groups on the CNT surface significantly affect the performance of the CNT-based chemical and biological sensors.

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