YSI 6 series User Manual page 276

Principles of Operation
Measurement of PE-containing BGA In Vivo
One key characteristic of phycoerythrin-containing BGA is that the cells fluoresce, that is, when irradiated
with light of a particular wavelength, they emit light of a higher wavelength (or lower energy). The ability
of PE to fluoresce while present in whole BGA cells is the basis for all commercial fluorometers capable of
measuring the analyte in vivo. These instruments induce PE to fluoresce by shining a beam of light of the
proper wavelength into the sample, and then measuring the longer wavelength light which is emitted as a
result of the fluorescence process. The YSI 6132 PE Probe uses a green light emitting diode (LED) for the
excitation process. On irradiation with this green light, PE molecules resident in whole cells emit light in
the 565-610 nm region of the spectrum. To quantify the fluorescence, the system detector is usually a
photodiode of high sensitivity that is screened by an optical filter that restricts the detected light. The filter
prevents the green exciting light from being detected when it is backscattered off of particles in the water.
Without the filter, turbid (cloudy) water would appear to contain significant amounts of PE-containing
BGA, even though none were present. The following diagram can be used to better understand the
principles of the YSI system.
Light Source
(Green LED)
The unique YSI 6132 BGA system consists of a probe which is compatible with the optical probe ports of
all YSI 6-series sondes. The output of the sensor is automatically processed via the sonde firmware to
provide readings in either generic fluorescence units (RFU) or cells/mL of PE-containing BGA. Like all
YSI optical probes, the 6132 is equipped with a mechanical wiper to periodically clean the optical face
either by manual or automatic activation. With this feature, the YSI 6132 sensor can be deployed in
environmental water for several weeks without the need for service and is ideal for providing continuous
monitoring of potentially-hazardous PE-containing BGA.
YSI Incorporated Environmental Monitoring Systems Manual
Section 5
Photodetector
Optical Filter
Optical Fiber
5-38