Direct measurement of non-thermal microwave effects on bacterial growth and redox dynamics using a novel high-throughput waveguide applicator

A high-throughput microwave applicator has been designed and characterized to investigate microwave interactions with biological systems. When operated in the TE₁₀ mode, this rectangular waveguide enabled simultaneous exposure of 96 biological samples to a quantifiable electric field (<i>E</i> field) at 2.45 GHz. Optimized electric probe transitions efficiently couple power (up to 50 W) into and out of the waveguide, achieving a voltage transmission coefficient (S₂₁) near unity (0 dB) and a voltage reflection coefficient (S₁₁) below 0.01 ( less than -20 dB). The growth dynamics of <i>Staphylococcus aureus</i> bacteria were analysed after non-thermal, microsecond-pulsed microwave exposure at 25 W r.m.s. of microwave power for 24 h. Post-exposure, <i>S. aureus</i> exhibited significantly higher optical density measurements and growth rates than thermal controls. Fluorescent probes directed towards key redox indicators revealed that microwave exposure altered the cellular redox state. This study provides new insights into the non-thermal effects of pulsed 2.45 GHz microwaves on <i>S. aureus</i> growth dynamics and characterizes a novel high-throughput platform for further exploration of fundamental microwave effects on biological systems.This article is part of the theme discussion meeting issue 'Microwave science in sustainable technologies'.