Substrate integrated waveguide resonant cavity sensor

Abstract

A current area of active research is the development of biosensors. Biosensors have been constructed to examine a large range of target analytes such as enzymes, antibodies, DNA, and cells. The majority of currently developed biosensors require the use of labels which attach to an analyte to enhance the sensitivity of the sensor to a significant level. Labeling targets introduces many drawbacks: added complexity to the detection process, increased preparation time, and most importantly, the possible modification of analyte properties due to the attachment of the label. For these reasons, there has been much attention on electronic means of label-free biological agent detection. One such electronic biosensing method is the use of a resonant circuit operating at microwave frequencies for impedance and dielectric spectroscopy. In these spectroscopic measurements, changes in the resonant frequency of the circuit are detected and correlated to the presence of a specific analyte. Various resonator circuits have been utilized in dielectric spectroscopy and biomolecule detection; however, these biosensors, although label-free, possess their own idiosyncratic complications such as imprecise and convoluted test sample deposition schemes. To address some of the challenges associated with existing biosensors, a device is presented demonstrating the potential to be used for label-free biosensing and promises a convenient sample deposition procedure. The instrument is based on the construction of a substrate integrated waveguide analog of an enclosed section of rectangular waveguide. Classical microwave engineering principles were used to give an outline of key electrical characteristics and dimensions, and full-wave finite element analysis software was utilized to further refine and optimize the device. A fabricated prototype was tested through measurement of scattering parameters using a network analyzer. The archetypal resonant circuit discussed herein can be used to extract the complex permittivity from test materials. Discussions of the cardinal design parameters, sensitivity analysis, and permittivity extraction techniques are provided. Suggestions for continued development are presented based on experience gained from the design of the prototype sensor. Proposed future work includes a scaled-down version of the substrate integrated waveguide resonator and testing with biological agents such as biofilms and single cells.