Characterizing aMetal-Dielectric Interface for MicrowaveBioprocessing

Extraction, digestion, and microbial inactivation are all common steps in laboratory assays and bioprocessing. To this end, many different techniques and devices have been developed to reduce the time and cost requirements for these, including one termed microwave lysing triangles (MLTs), which consist of a thin metal film deposited on a glass substrate in the shape of two triangles separated by a 2 mm gap to form a metal-dielectric interface. When irradiated at microwave frequencies (2.45 GHz), this interface produces rapid heating and generates reactive oxygen species (ROS) and microbial inactivation within biological samples. In this work, we have further characterized this interface and the role of the metal films in processing samples using several assays, including enzyme activity, protein denaturation, and microbial inactivation. Our results show that while the metal-dielectric interface is necessary to process samples, but direct contact between the sample with the metal films is not required if irradiation time and power are sufficiently high. Additionally, we demonstrate that the minimum power and time requirements are dependent on the physical size of the analyte in question, with large proteins needing greater irradiation times or powers than small proteins and bacteria needing even more irradiation time or power. Beyond the implications for microwave sample processing, our findings may have utility for material designs and applications in the microwave frequency range due to similar interfaces being present in many of them.