Chemical Information Conversion System by Using Hydrogel-Modified Ultramicroelectrodes

聚N-异丙基丙烯酰胺和聚丙烯酰胺等水凝胶已成功地修饰到铂超微电极表面。化学修饰是通过在电极表面引入乙烯基团，然后在电极表面合成凝胶来实现的。将这些凝胶修饰电极浸泡在含有氧化还原分子的水溶液中，并进行了电化学测量。电极表面凝胶的化学修饰允许在凝胶的膨胀和收缩状态下进行电化学测量，并进一步在膨胀的过渡状态下进行电化学测量，即从膨胀到收缩状态，反之亦然。通过在平衡和反式…中利用电化学方法，实现了对凝胶内氧化还原分子浓度和扩散系数的独立测定更近的肿胀状态。在聚N-异丙基丙烯酰胺(PNIPAAm)凝胶中，氧化还原分子[Ru(NH_3)_6]Cl_3的浓度和扩散系数达到平衡溶胀时，[Ru(NH_3)_6]Cl_3的浓度和扩散系数与外部溶液在膨胀状态下的浓度和扩散系数没有太大差别，而在收缩的凝胶中，络合物的扩散系数有相当大的缩合和抑制。对于聚丙烯酰胺(PAAM)凝胶，以N-二茂铁甲基-N，N，N-三甲基六氟磷酸铵(FC)为氧化还原分子，进行了平衡状态和瞬时溶胀状态下的测定。将凝胶浸入水中丙酮的收缩过程中测得的瞬时电流-时间(i-t)曲线表明：1)凝胶的i-t曲线在某一时刻出现峰值，而不是简单地下降；2)较小尺寸的凝胶比较大尺寸的凝胶更早出现峰值，峰值时间与凝胶在水中半径的平方成正比；3)峰值电流随着凝胶在水中半径的减小而增加。考虑到凝胶在收缩过程中的动力学和空间不均匀性，分析了这些结果的机理。较少

Hydrogels, such as poly(N-isopropyl acrylamide) and polyacrylamide, have been successfully moified onto the surface of Pt ultramicroelectrodes. The chemical modification has been established by the introduction of vinyl group onto the electrode surface, followed by the synthesis of the gels on the electrode surface. These gel-modified electrodes, where the shape of the gel is hemispherical in the swollen state, were immersed in aqueous solutions containing redox molecules, and electrochemical measurements were conducted. The chemical modification of the gels on the electrode surface allowed to conduct electrochemical measurements both in the swollen and shrunken states of the gels, and further in the transition states of swelling, i.e., from the swollen to shrunken states and vice versa. Independent determination of of the concentration and diffusion coefficient of the redox molecules inside the gels has been achieved by exploiting electrochemical methods both in equilibrated and trans … More ient state of swelling. This provides a new methodology to study micro-environment and dynamics of hydrogels, and at the same time, to convert large swelling change of hydrogels, including the volume-phase transition, to electric signal.In poly(N-isopropyl acrylamide)(PNIPAAm) gels, reaching equilibrated swelling, the concentration and diffusivity of redox molecule, [Ru(NH_3)_6]Cl_3, indide the gels were not so different from those of the outside solution in the swollen state, whereas considerable condensation and suppression in the diffusivity of the complex were found in the shrunken gels.For polyacrylamide(PAAm) gels, the measurements not only in the equilibrated state but also in the transient state of swelling were conducted by using N-ferrocenylmethyl-N, N, N-trimethylammonium hexafluorophosphate (Fc) as a redox molecule. The transient electrolytic current vs time(i-t) curves measured in the shrinking process, where the gel was immersed into acetone from water, revealed the following facts :1) The i-t curve showed a peak at a certain time, instead of simple decreasing.2) A smaller size gel showed the peak at earlier time than a larger size gel, and the peak time was directly proportional to the square of the radius of the gel in water.3) The peak current increased with decreasing the radius of the gel in water.Mechanism for these results has been analyzed, taking into consideration the dynamics and spatial inhomogeneity of the gels in the shrinking process. Less