Chemical Information Conversion System by Using Hydrogel-Modified Ultramicroelectrodes

水凝胶，如聚（n -异丙基丙烯酰胺）和聚丙烯酰胺，已经成功地修饰在铂超微电极表面。通过在电极表面引入乙烯基，然后在电极表面合成凝胶，建立了化学改性的方法。这些凝胶修饰的电极，在膨胀状态下凝胶的形状是半球形的，浸入含有氧化还原分子的水溶液中，并进行电化学测量。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。利用电化学方法，在平衡状态和反溶胀状态下，实现了凝胶内氧化还原分子浓度和扩散系数的独立测定。这为研究水凝胶的微环境和动力学提供了一种新的方法，同时也为将水凝胶的大膨胀变化（包括体积-相转变）转化为电信号提供了一种新的方法。在达到平衡膨胀状态的聚n -异丙基丙烯酰胺（PNIPAAm）凝胶中，氧化还原分子[Ru(NH_3)_6]Cl_3的浓度和扩散率表明，凝胶在膨胀状态下与外部溶液的浓度和扩散率没有太大差异，而在收缩凝胶中发现了明显的缩合和抑制络合物的扩散率。对于聚丙烯酰胺（PAAm）凝胶，用N-二茂铁甲基-N， N， N-三甲基六氟磷酸铵（Fc）作为氧化还原分子，不仅测量了平衡态，还测量了膨胀态的瞬态。将凝胶从水中浸入丙酮中，在收缩过程中测量的瞬态电解电流与时间（i-t）曲线揭示了以下事实：1)i-t曲线在某一时刻出现峰值，而不是简单的下降。2)粒径较小的凝胶比粒径较大的凝胶出现峰的时间早，且峰时间与凝胶在水中半径的平方成正比。3)峰值电流随凝胶在水中半径的减小而增大。考虑到凝胶在收缩过程中的动力学和空间不均匀性，分析了产生这些结果的机理。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