Biomedical Engineering Reference
In-Depth Information
Oxygen sensors work by quenching fluorescence by molecular oxygen;
measurement requires a fluorescent dye (metal complexes) immobilized and
attached to one end of an optical fiber, and the other end of the fiber is inter-
faced with an excitation light source. The duration and strength of fluorescence
depend on the oxygen concentration in the environment around the dye. The
emitted fluorescence light is collected and transmitted for reading outside of
the bioreactor. These electrodes work better than the traditional platinum probe
electrodes to detect oxygen, working in both liquid and gas phases. Examples of
oxygen sensors include PreSens (
www.presens.de
)
noninvasive oxygen sensors
that measure the partial pressure of both dissolved and gaseous oxygen. These
sensor spots are used for glassware and disposables. The sensor spots are fixed
on the inner surface of the glass or transparent plastic material. The oxygen
concentration can therefore be measured in a noninvasive and nondestructive
manner from outside, through the wall of the vessel. Different coatings for dif-
ferent concentration ranges are available. It offers online monitoring of concen-
tration ranges from 1 ppb up to 45 ppm DO, with dependence on flow velocity
and measuring oxygen in the gas phase as well; these can be autoclaved.
Ocean Optics (
www.oceanoptics.com
) offers the world's first miniature
spectrometer with a wide array of sensors for oxygen, pH, and in the gas
phase.
The pH sensors work by fluorescence or absorption, and for fiber-optic
pH measurements, both fluorescence- and absorbance-based pH indicators
can be applied. For fluorescence, the most common dyes are 8-hydroxy1,3,6-
pyrene trisulfonic acid and fluorescein derivatives, while phenol red and
cresol red are used for absorption-type measurements. Fluorescent dyes
are sensitive to ionic strength limiting their use for broad pH measurement,
more than 3 units.
The new transmissive pH probes from Ocean Optics use a proprietary sol-
gel formulation infused with a colorimetric pH indicator dye. This material
is coated onto the exclusive patches to reflect light back through the central
red fiber or to transmit light through in order to sense the color change of
the patch at a specific wavelength. While typical optical pH sensors are sus-
ceptible to drastic changes in performance in various ionic strength solu-
tions, Ocean Optics' sensory layer has been chemically modified (esterified)
to allow accurate sensing in both high- and low-salinity samples. The trans-
missive pH probes from Ocean Optics can be used with a desktop system as
well as with the Jaz handheld spectrometer suite. The desktop system uses a
module is SpectraSuite software that allows for simplified calibration, conve-
nient pH readings, customizable data logging, and comprehensive exporta-
tion of data and calibration information.
• Proprietary organically modified sol-gel formulation engineered to
maximize immunity to ionic strength sensitivity.
