To compare the effect of microwave irradiation and of conventional heating on the fluorescence of green fluorescent protein (in solution).
An aqueous egg-white solution and a liquid crystal indicator were also used to test temperature measurement.
| 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
|
|
|
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
|
|
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.
| 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 type | CW |
|---|
| 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. |
| 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 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 source |
|
|---|---|
| Additional info | The incident MW power was switched on and off, with the duty cycle decreasing from CW to 10%. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| power | 250 mW | - | - | - | - |
| 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 type | CW |
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| power | 250 mW | - | - | - | - |
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.
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