PMOD-2000 uses a noninvasive optical method for detecting the
concentration of O2 in tissue. The operating principle for the unit is
based on the quenching of phosphorescence by oxygen in phosphors
that have been injected into the blood. To determine the concentration
of O2 in the area of tissue being measured, phosphorescence
lifetime measurements are taken using a sinusoidally modulated light
source for excitation and frequency lock for phosphorescence detection.
The PMOD operates over a frequency range from 200 to 20,000
Hz, allowing measurements of phosphorescence lifetimes from <15
microseconds to 1.5 milliseconds. Measurements can be carried out
either at constant frequency or constant phase shift. This technique
differs from other methods of O2 detection in that this method is totally
noninvasive, with the fiber optic bundle outside of the tissue in
which the O2 is being measured. The PMOD-2000 has a very high
accuracy throughout the physiological range and provides real time
measurements with high temporal resolution (~1 sec/measurement).
The phosphors that are used with this system have absolute
calibration and follow Stern-Volmer behavior. Once a phosphor is
calibrated for a given temperature and solvent conditions these values
are stable, eliminating the possibility of measurement drift and
the requirement for re-calibration at the time of the measurement.
The system has two channels (sources) of excitation light. The standard
system comes with one wavelength set to 524 nm (suitable for the
porphyrin based phosphors) and 635 nm (suitable for the tetrabenzoporphyrin
based phosphors). Other combinations of excitation wavelengths
are available. Please call our technical sales department for further
information.
Phosphorescence emission is in the range of 660 to 760 nm (porphyrins)
or 760 to 900 nm (tetrabenzoporphyrins). Since bright ambient
light can saturate the detector, it is recommended that the work
area be lighted with DC powered monochromatic light sources.
The ‘Cool Colors’ LED lamps are specifically designed for this purpose.
When an appropriate lamp is used, this light does not interfere
with the phosphorescence measurements.
Types of Phosphors and Phosphor Kits Available
Pd-meso-tetra (4-carboxyphenyl) porphyrin
This phosphor (Oxyphor RO) is dissolved in the presence of 0.5% or
greater of bovine serum albumin. It provides excellent oxygen sensitivity
and has been accurately calibrated (see Lo et al., 1996). This
phosphor has an absorption band near 524 nm and emission near
690 nm and can be used for surface O2 measurements in tissues.
Lyophilized Porphyrin Kit*
1.2 g. approx. amount needed for approx. 30 rat (rats weighing
300 g each) and 10 cat (cats weighing 3 kg each) experiments using
the PMOD instrument. Lyophilized porphyrin contains (approx.):
9% Pd-meso-tetra (4-carboxyphenyl) porphine which is bound to
80% BSA (clinical grade, low fatty acid), 8% NaCl, and 3% TRISMA
buffer. Accessories include one (1) 10 cc syringe, three (3) syringe
filters (25 x .22 micron), and three (3) 4.0 mL amber glass vials with
foil caps.