Sequential surface chemical reactions of poly(acrylic acid-co-N-isopropylacrylamide) [poly(AAc-co-NIPAAm)] with AAc contents of 5, 10, and 15 mol %, of which carboxyl groups were previously activated by 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDC), plus poly(vinylamine hydrochloride) through amide linkages produced ultrathin films on a solid substrate. Assembly processes were quantitatively monitored by a quartz crystal microbalance as substrates. Assembled amounts increased with decreasing both AAc and EDC amounts. Subsequent immersion of ultrathin films into aqueous media resulted in the thickness increases, producing ultrathin hydrogels. Swelling ratios were estimated by percent increases in the thickness and increased with increasing AAc and EDC amounts. Swelling ratios were regularly changed by varying the ionic strength and pH of aqueous media. Swelling properties were interpreted on the basis of structural information on ultrathin hydrogels. Cyclic voltammetries using potassium ferricyanide revealed that ions permeated ultrathin hydrogels, and permeabilities were clearly suppressed above a lower critical solution temperature (LCST) of polyNIPAAm. Reversible on−off changes in permeabilities below and above a LCST were potentially observed. Not only structural control but also stimuli responsive functions of ultrathin hydrogels were realized within the present study.

Carbon nanotubes (CNTs) are promising materials for use in amperometric biosensors. The defect sites at their ends, and on their sidewalls, are considered to be edge plane-like defects and show high electrocatalytic activity toward several biological molecules. However, electrocatalytic activity toward H(2)O(2) has not been compared among bamboo-structured CNTs (BCNTs), which have many defect sites; hollow-structured CNTs (HCNTs), which have few defect sites; edge plane pyrolytic graphite (EPG); and traditional glassy carbon (GC). The advantages of using CNTs in electrodes for biosensors are still equivocal. To confirm the utility of CNTs, we analyzed the electrochemical performance of these four carbon electrodes. The slope of the calibration curve for H(2)O(2) at potentials of both +0.6 V and -0.1 V obtained with a BCNT paste electrode (BCNTPE) was more than 10 times greater than the slopes obtained with an HCNT paste electrode and a GC electrode, reflecting the BCNT's larger number of defect sites. Although the slope with the EPG electrode (EPGE) was about 40 times greater than that with BCNTPE at +0.6 V, the slopes with these two carbon electrodes were nearly equivalent at -0.1 V. EPGE demonstrated excessive electrochemical activity, detecting currents on the basis of consumption of oxygen and oxidation of ascorbic acid, even at -0.1 V. In contrast, BCNTPE could dominantly detect a cathodic current for H(2)O(2) at -0.1 V, even when interfering molecules were added. BCNTPE possesses appropriate electrochemical activity and is an effective electrode materials for developing interference-free oxidase-based biosensors operated by the application of an appropriate potential.

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In this report, we describe the finding that bamboo-structured carbon nanotubes (CNT) showed superior electrocatalytic activity toward hydrogen peroxide. The slope of the calibration curve for hydrogen peroxide obtained with the bamboo-structured CNT paste electrode was more than 20 times as large as the slopes obtained with hollow-structured CNT paste and glassy carbon electrodes at an operating potential of 20.1 V, with no interfering reactions. Incorporation of glucose oxidase within the bamboo-structured CNT paste electrode allows the selective detection of glucose in the presence of common interferents without using any permselective membranes. This excellent ability of the bamboo-structured CNT paste electrode toward hydrogen peroxide is applicable to the development of other enzymatic biosensors.