ACS Sens. 2018 Aug 24;3(8):1489-1498. doi: 10.1021/acssensors.8b00267. Epub 2018 Aug 2.
A passive, resonant sensor was developed that can be embedded in closed systems for wireless monitoring of hydrolytic enzyme activity. The resonators are rapidly prototyped from copper coated polyimide substrates that are masked using an indelible marker with an XY plotter and subsequently etched. The resonator's frequency response window is designed by the Archimedean coil length and pitch and is tuned for the 1-100 MHz range for better penetration through soil, water, and tissue. The resonant frequency is measured up to 5 cm stand-off distance by a coplanar, two-loop coil reader antenna attached to a vector network analyzer monitoring the S21 scattering parameter. The resonant frequency is modulated (up to 50 MHz redshift) by changing the relative permittivity of the medium in contact with the resonator (e.g., air to water). The resonant sensors are coated by an enzyme substrate, which, when degraded, causes a change in dielectric and a shift in resonant frequency (up to 7 MHz redshift). The activity (turnover rate, or k) of the enzyme is calculated by fitting the measured data via a custom transport and reaction model which simulates the radial digestion profile. This is used to test purified Subtilisin A and unpurified bacterial protease samples at concentrations of 30 mg/mL to 200 mg/mL with k ranges of 0.003-0.002 and 0.008-0.004 g/ g per second. The sensor response rate can be tuned by substrate composition (e.g., gelatin and glycerol plasticizer weight percentage). Finally, the utility of these sensors is demonstrated by wirelessly measuring the proteolytic activity of farm soil with a measured k of 0.00152 g/( g·s).
一种被动式谐振传感器可用于无线监测水解酶活性，它被嵌入在封闭系统中。该谐振器由铜涂层聚酰亚胺基底快速制成，基底使用可擦除标记和 XY 绘图仪进行掩模处理，然后进行蚀刻。谐振器的频率响应窗口由阿基米德螺旋线圈的长度和间距设计，并针对 1-100MHz 范围进行调谐，以提高在土壤、水和组织中的穿透能力。通过附着在矢量网络分析仪上的共面双环线圈读取器天线，可以在 5cm 间隔距离处测量谐振器的谐振频率，该天线监测 S21 散射参数。通过改变与谐振器接触的介质的相对介电常数（例如，空气到水），可以调制谐振频率（高达 50MHz 的红移）。谐振传感器被酶底物覆盖，当底物被降解时，会导致介电常数发生变化，谐振频率发生偏移（高达 7MHz 的红移）。通过使用定制的传输和反应模型拟合测量数据，可以计算出酶的活性（周转率或 k），该模型模拟了径向消化曲线。该模型用于测试浓度为 30mg/mL 至 200mg/mL 的纯化枯草杆菌蛋白酶 A 和未纯化的细菌蛋白酶样品，k 值范围分别为 0.003-0.002 和 0.008-0.004g/g·s。通过改变底物的组成（例如明胶和甘油增塑剂的重量百分比），可以调整传感器的响应速率。最后，通过无线测量农场土壤的蛋白水解活性，证明了这些传感器的实用性，其测量的 k 值为 0.00152g/（g·s）。
