Millimeter wave absorption spectra of biological samples

Area of Science:

• Electromagnetism
• Biophysics
• Spectroscopy

Background:

• Previous research suggested specific microwave absorption resonances in biological specimens.
• Understanding these resonances is crucial for applications in biology and medicine.

Purpose of the Study:

• To investigate microwave absorption spectra of various biological samples.
• To verify or refute the existence of previously reported absorption resonances.

Main Methods:

• Utilized a computer-controlled system for swept-frequency absorption measurements (26.5–90.0 GHz).
• Examined aqueous solutions (DNA, RNA) and cell suspensions (BHK-21/C13, Candida albicans, Escherichia coli).
• Tested frozen cell samples at cryogenic temperatures.

Main Results:

• Observed no sharp spectral peaks; absorbance was dominated by water's properties.
• Adjustments in power, modulation, and temperature did not reveal unique sample-specific resonances.
• Frozen samples showed reduced insertion loss but no reproducible absorption peaks.

Conclusions:

• The strong absorbance of water significantly masks any potential biological resonances in the studied frequency range.
• Concludes that previously reported special resonances are likely erroneous.
• Highlights the dominant role of water in microwave absorption of biological materials.