Study type: Medical/biological study (experimental study)

Evidence for a specific microwave radiation effect on the green fluorescent protein. med./bio.

Published in: Biophys J 2006; 91 (4): 1413-1423

Aim of study (acc. to author)

To compare the effect of microwave irradiation and of conventional heating on the fluorescence of green fluorescent protein (in solution).

Background/further details

An aqueous egg-white solution and a liquid crystal indicator were also used to test temperature measurement.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 8.53 GHz
Modulation type: CW
Exposure duration: intermittent, about 200 s on/off, at each of 6 decreasing power levels, for a total of 3200 s
  • power: 250 mW maximum (250, 200, 160, 100, 50, 20, and 250 mW)
  • SAR: 4,000 W/kg maximum (at 250 mW)
Exposure 2: 8.53 GHz
Modulation type: pulsed
Exposure duration: intermittent, about 200 s on/off, at CW and each of 3 decreasing duty cycles, for a total of 1600 s
Exposure 3: 250 MHz–20 GHz
Modulation type: CW
Exposure duration: continuous, with increasing frequencies, 10 s at each step, for a total of 4000 s

General information

The EGFP fluorescence was excited by a 488-nm Argon laser with its beam directed across a transparent 2-mm diameter glass pipette (with 150-µm walls) containing the sample. The temperature dependence of the EGFP fluorescence was measured by a thermocouple in close vicinity of the laser beam. In the absence of MW radiation, the sample was heated between 22 and 43°C using a water bath or a thermal resistor.

Exposure 1

Main characteristics
Frequency 8.53 GHz
Type
Charakteristic
Exposure duration intermittent, about 200 s on/off, at each of 6 decreasing power levels, for a total of 3200 s
Modulation
Modulation type CW
Exposure setup
Exposure source
Distance between exposed object and exposure source 0.25 mm
Chamber The MW applicator was brought to a distance of 100 µm above the glass pipette in such a way that the probe's apex aimed directly at the laser illuminated region.
Setup For narrowband measurements, a special 8.5 GHz applicator was used, based on a narrow rectangular aperture microfabricated on the convex surface of the sapphire dielectric resonator. The operating frequency of the probe was 8.53 GHz, and the bandwidth with the sample present was typically 0.3 GHz.
Additional info The incident MW power was switched on and off, decreasing from 250 mW to 20 mW, and finally returning to 250 mW. In a different experiment, the MW power was varied in steps of 0.1 dBm with a dwell time of 2 s.
Parameters
Measurand Value Type Method Mass Remarks
power 250 mW maximum - - 250, 200, 160, 100, 50, 20, and 250 mW
SAR 4,000 W/kg maximum calculated - at 250 mW

Exposure 2

Main characteristics
Frequency 8.53 GHz
Type
Charakteristic
Exposure duration intermittent, about 200 s on/off, at CW and each of 3 decreasing duty cycles, for a total of 1600 s
Modulation
Modulation type pulsed
Pulse width 1 µs
Additional info

pulse periods of 2, 5 and 10 µs, resulting in duty cycles of 50, 20, and 10%

Exposure setup
Exposure source
Additional info The incident MW power was switched on and off, with the duty cycle decreasing from CW to 10%.
Parameters
Measurand Value Type Method Mass Remarks
power 250 mW - - - -

Exposure 3

Main characteristics
Frequency 250 MHz–20 GHz
Type
Charakteristic
Exposure duration continuous, with increasing frequencies, 10 s at each step, for a total of 4000 s
Modulation
Modulation type CW
Exposure setup
Exposure source
Distance between exposed object and exposure source 0.25 mm
Additional info The frequency was varied from 250 MHz to 20 GHz in steps of 50 MHz with a dwell time of 10 s at each step.
Parameters
Measurand Value Type Method Mass Remarks
power 250 mW - - - -

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

A specific microwave effect on the fluorescence of the green fluorescent protein molecule which is distinguishable from conventional heating is found. In both cases the fluorescence intensity decreased, but the effect of microwave exposure on the fluorescence is stronger than expected from thermal physics considerations. Although the microwave irradiation heated the solution, the microwave-induced changes in fluorescence cannot be explained by heating alone.

Study character:

Study funded by

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