Csóka Balázs, Nagy Géza
MTA-PTE Research Group for Chemical Sensors, Ifjúság útja 6., H-7624 Pécs, Hungary.
J Biochem Biophys Methods. 2004 Oct 29;61(1-2):57-67. doi: 10.1016/j.jbbm.2004.03.001.
Diffusion coefficient of different species in different media is an important property needed in scientific research and practice. A method taking advantage on the special capability of scanning electrochemical microscopy (SECM) is described for the easy and accurate measurement of diffusion coefficient. The method is based on detecting the concentration-time transients with appropriate electrochemical microsensor positioned at the close vicinity of a miniature dose-source device. At a given time (ti), a small dose of the investigated species is introduced. The Deltatmax=(tcmax-ti) value and the distance (d=x+Deltaxn) between the source and the detector microelectrode are used for the calculation of D. While the original set distance (x) cannot be accurately measured in the micrometer scale, the tip travel distance (Deltaxn) of the microscope is well defined. Collecting a few Deltatmax-(x+Deltaxn) data pairs, a reliable value of the diffusion coefficient can be obtained. The procedure is simple, and no exact knowledge of the introduced dose is needed. Two ways of sample dose delivery were used: on the one hand, coulometric generation with current-controlled electric pulse using micro-disc electrode, and on the other one, pressure ejection of a nano-droplet from a glass micropipette. Diffusion coefficient of I2, H2O2, [Ru(NH3)6]Cl3 and K3[Fe(CN)6] were measured in solution and in agarose gel phases of different composition. The effect of polyelectrolyte ion exchangers on the diffusion of the investigated species was checked.
不同物种在不同介质中的扩散系数是科学研究和实践中所需的一项重要性质。本文描述了一种利用扫描电化学显微镜（SECM）的特殊功能来简便、准确测量扩散系数的方法。该方法基于使用合适的电化学微传感器检测位于微型剂量源装置附近的浓度 - 时间瞬变。在给定时间（ti），引入一小剂量的被研究物种。利用Δtmax =（tcmax - ti）值以及源与检测微电极之间的距离（d = x + Δxn）来计算扩散系数D。虽然原始设定距离（x）在微米尺度上无法精确测量，但显微镜的尖端行进距离（Δxn）是明确的。收集几组Δtmax - （x + Δxn）数据对，即可获得可靠的扩散系数值。该过程简单，且无需精确知晓引入的剂量。使用了两种样品剂量输送方式：一方面，使用微盘电极通过电流控制电脉冲进行库仑生成；另一方面，从玻璃微吸管中压力喷射纳米液滴。测量了I2、H2O2、[Ru(NH3)6]Cl3和K3[Fe(CN)6]在不同组成的溶液和琼脂糖凝胶相中的扩散系数。检验了聚电解质离子交换剂对被研究物种扩散的影响。
