Resonant Sensors for Low-Cost, Contact-Free Measurement of Hydrolytic Enzyme Activity in Closed Systems

ACS Sensors
Sadaf CharkhabiNigel F Reuel

Abstract

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 kcat) 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 b...Continue Reading

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