## 1 Introduction
### MMW Interaction with Water as a Factor for Reduced Cell Growth
Therefore, under conditions of constant frequency, power and exposure duration; the radiation-associated rise in temperature is inversely proportional to the volume of the sample irradiated. Finally, this experiment also confirms the hypothesis that biological cells exhibit high absorbance of MMW irradiation accountable to being constituted of water within a confined volume separated from the environment. The experiment demonstrates that MMW irradiation under the listed parameters raises temperatures to 22 \({}^{\circ}\)C and is therefore not expected to elicit thermal stress on yeast cells, which grow at physiological temperatures of 30 \({}^{\circ}\)C.  
A wave-guide provides a focused beam of irradiation as compared to a horn antenna (see Figure 4) allowing more precise energy delivery. To investigate potential applications of this exposure regime we performed MMW irradiation at 85 GHz and 5 dBm on BY4741 _Saccharomyces cerevisiae_ WT yeast cells using an open-ended waveguide (Figure 5). Single frequency at 85 GHz was used as it provides the maximal threshold powers and affects WT yeast cell growth to the same extent as for all the other examined MMW frequencies (see Figure 1a). The thickness of agar medium and the number of cells were kept the same (50 cells/\(\mu\)L) as those mentioned in the previous experiments. Cells were treated for 3-4 h at the non-thermal exposure power density of 17.17 mW/cm\({}^{2}\) (see Figure 4). Subsequent incubation of these cells under physiological conditions (at 30 \({}^{\circ}\)C for 2 days over a week) did not yield any colony growth. The experiment demonstrates that MMW  
Figure 3: Absorbed power represented as a ratio of incident and reflected power from yeast cells spotted on Synthetic Complete (SC) agar compared to that of plain water and Synthetic Complete (SC) agar without cells respectively. Experiments were performed on a 1 \(\mu\)L spot of 50 cells/\(\mu\)L concentration with a frequency of 85 GHz at an amplitude of 5 dBm over 5 h (corresponding to 1.39 \(\pm\) 0.02 mW/cm\({}^{2}\) surface power density). irradiation using an open-ended waveguide at ~12 times stronger power density than the one involving a horn antenna (see Figures 1 and 4 and Table 1) completely terminates cell growth and division. Figure 4: Comparison of temperature rise during 85 GHz MMW exposure at constant power and treatment duration, involving horn antenna and wave-guide. Indicated volumes of water were irradiated as illustrated. (**A**) Temperature rise of 6500 \(\upmu\)L water during MMW exposure at 1.39 mW/cm\({}^{2}\). (**B**) Temperature rise of 250 \(\upmu\)L water during MMW exposure at 1.39 mW/cm\({}^{2}\). (**C**) Temperature rise of 250 \(\upmu\)L water during MMW exposure at 17.17 mW/cm\({}^{2}\). Frequency, power and duration of exposure were kept constant at the values in the specific experiments as indicated. Figure 5: Block diagram of the experimental setup for irradiation and pictures of the pyramidal horn antenna and waveguide. (**a**) Schematic presentation of irradiating system. (**b**) Picture of a pyramidal antenna. (**c**) Picture of a waveguide.