Requa M V, Fraikin J-L, Stanton M A, Cleland A N
J Appl Phys. 2009 Oct 1;106(7):74308. doi: 10.1063/1.3243315. Epub 2009 Oct 14.
Impedance sensors perform an important role in a number of biosensing applications, including particle counting, sizing, and velocimetry. Detection of nanoparticles, or changes in, e.g., the interfacial Debye-Hückel layer, can also be performed using nanoscale impedance sensors. One method for monitoring changes in the local impedance is to use radiofrequency reflectometry, which when combined with an impedance-matched sensor can afford very high sensitivity with very large detection bandwidth. Maintaining sensitivity and dynamic range, however, requires continuous tuning of the impedance matching network. Here we demonstrate a dual feedback tuning circuit, which allows us to maintain near-perfect impedance matching, even in the presence of long-term drifts in sensor impedance. We apply this tuning technique to a nanoscale interdigitated impedance sensor, designed to allow the direct detection of nanoparticles or real-time monitoring of molecular surface binding. We demonstrate optimal performance of the nanoscale sensor and tuned impedance network both when modulating the concentration of saline to which the sensor is exposed and when electronically switching between sensors configured in a two-element differential array, achieving a stabilization response time of <20 ms.
阻抗传感器在许多生物传感应用中发挥着重要作用，包括颗粒计数、尺寸测量和测速。使用纳米级阻抗传感器也可以检测纳米颗粒，或者检测例如界面德拜 - 休克尔层的变化。监测局部阻抗变化的一种方法是使用射频反射测量法，当与阻抗匹配传感器结合使用时，它可以在非常大的检测带宽下提供非常高的灵敏度。然而，要保持灵敏度和动态范围，需要对阻抗匹配网络进行连续调谐。在这里，我们展示了一种双反馈调谐电路，即使在传感器阻抗存在长期漂移的情况下，它也能让我们保持近乎完美的阻抗匹配。我们将这种调谐技术应用于纳米级叉指式阻抗传感器，该传感器旨在直接检测纳米颗粒或实时监测分子表面结合。当调节传感器所暴露的盐水浓度时，以及在以二元差分阵列配置的传感器之间进行电子切换时，我们都展示了纳米级传感器和调谐阻抗网络的最佳性能，实现了小于20毫秒的稳定响应时间。
