An optical oxygen sensor system based on the process
of fluorescence quenching is reported. The device detects the fluorescence
quenching of a ruthenium complex, also known as RUDPP by sensing minute
variations of a fluorescent membrane emission intensity.
A dual channel design consisting of a reference
branch and a sensing branch is used. Both branches include modulated light from
a bright blue LED acting as the excitation source coupled through an enclosed
channel to a photo-diode. The sensing branch has the RUDPP fluorescence
quenching membrane sandwiched between the blue LED and the photo-diode, while
the reference branch is void of such membrane. To avoid membrane saturation in
the sensing branch, the excitation source is modulated with a 350 Hz square
wave.
The output signals of the two channels are amplified
separately and subtracted from each other using a difference amplifier.
Adjusting the difference amplifier output to zero effectively ensures
excitation source interference cancellation. The photodiode in the sensing
branch detects the intensity variations as a function of fluorescent quenching
by oxygen. It was possible to isolate the fluorescent signal completely, based
solely on electronic components, without the use of optical filters.
The output signal from the difference amplifier is
further amplified (with an adjustable gain for calibration) and displayed.
Sensor performance was tested and it exhibited both excellent sensitivity and
response time, compared to the recent oxygen sensors reported by others. A
decrease of less than 4 percent oxygen concentration was readily detectable. We
conclude that this design establishes the feasibility of developing an optical
oxygen sensor, relying solely on optoelectronic components for detection.
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