Ahn Andrew C, Gow Brian J, Martinsen Orjan G, Zhao Min, Grodzinsky Alan J, Baikie Iain D
Martinos Center for Biomedical Imaging, Massachusetts General Hospital, 149 Thirteenth Street, Charlestown, Massachusetts 02129, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Jun;85(6 Pt 1):061901. doi: 10.1103/PhysRevE.85.061901. Epub 2012 Jun 1.
The Kelvin probe measures surface electrical potential without making physical contact with the specimen. It relies on capacitive coupling between an oscillating metal tip that is normal to a specimen's surface. Kelvin probes have been increasingly used to study surface and electrical properties of metals and semiconductors and are capable of detecting material surface potentials with submillivolt resolution at a micrometer spatial scale. Its capability for measuring electrical potential without being confounded by electrode-specimen contact makes extending its use towards biological materials particularly appealing. However, the theoretical basis for applying the Kelvin probe to dielectric or partially conductive materials such as biological tissue has not been evaluated and remains unclear. This study develops the theoretical basis underlying Kelvin probe measurements in five theoretical materials: highly conductive, conductive dielectric with rapid charge relaxation, conductive dielectric with slow charge relaxation, perfect dielectric, and tissue with a bulk serial resistance. These theoretically derived equations are then computationally analyzed using parameters from both theoretical specimens and actual biomaterials-including wet skin, dry skin, cerebrospinal fluid, and tendon. Based on these analyses, a Kelvin probe performs in two distinct ways depending on the charge relaxation rates of the sample: The specimen is treated either as a perfect dielectric or as highly conductive material. Because of their rapid relaxation rate and increased permittivity biomaterials behave similarly to highly conductive materials, such as metal, when evaluated by the Kelvin probe. These results indicate that the Kelvin probe can be readily applied to studying the surface potential of biological tissue.
开尔文探针在不与样品进行物理接触的情况下测量表面电势。它依靠与样品表面垂直的振荡金属尖端之间的电容耦合。开尔文探针越来越多地用于研究金属和半导体的表面及电学性质，并且能够在微米空间尺度上以亚毫伏分辨率检测材料表面电势。其测量电势而不受电极 - 样品接触干扰的能力使得将其应用于生物材料特别有吸引力。然而，将开尔文探针应用于诸如生物组织等介电或部分导电材料的理论基础尚未得到评估，仍然不清楚。本研究建立了在五种理论材料中进行开尔文探针测量的理论基础：高导电性材料、具有快速电荷弛豫的导电介质、具有缓慢电荷弛豫的导电介质、理想电介质以及具有体串联电阻的组织。然后使用来自理论样品和实际生物材料（包括湿皮肤、干皮肤、脑脊液和肌腱）的参数对这些理论推导方程进行计算分析。基于这些分析，根据样品的电荷弛豫速率，开尔文探针以两种不同方式工作：样品要么被视为理想电介质，要么被视为高导电性材料。由于其快速弛豫速率和增加的介电常数，生物材料在用开尔文探针评估时表现得类似于高导电性材料，如金属。这些结果表明开尔文探针可以很容易地应用于研究生物组织的表面电势。
