Biomedical Engineering Reference
In-Depth Information
surrounding the sample stream [80]. Strategies for optics range from the use of
microscope objectives to polymer waveguides or optical fibers embedded on-
chip [79]. Chip-based solutions employing standard reagents promise cost-effective
solutions for the analysis of drug responses [81], for example, in the application of
SYTO probes for the detection of cell death using automated microfluidic chip-based
cytometry [82].
2.4.2 Compact and New Light Sources
New, convenient, and inexpensive light sources are having an impact upon micro-
scopy and the exploration of efforts to improve signal-to-noise ratios. Flow cytometry
platform design and versatility are also benefiting from the availability of new
lasers [83-85] with the incorporation of diode and DPSS lasers emitting a variety
of wavelengths, for example, in the analysis of time-gated luminescence in a system
employing a UV light emitting diode (LED; 100mW) to excite fluorescence from a
europium chelate immunoconjugate with a long fluorescence lifetime (
m)
with an improvement in the distinction of labeled Giardia cysts in an autofluorescent
background [86]. The integration of
t
>
100
m
time-gated detection of
long-lifetime
m
(1-2000
s) luminescent labels into flow cytometry systems is highly attractive but
has to deal with the need for pulsed operation mode with continuous sample flow. A
particular configuration has been studied using LED excitation to detect europium
dye-labeled targets with the demonstration of the feasibility of detection of europium
calibration beads in a UV LED-excited flow cytometer [87-89].
A recent evaluation of new solid-state laser systems (DPSS 580, 589, and 592 nm
sources), integrated into a cuvette-based flow cytometer (BD LSR II) and a stream-in-
air cell sorter (FACSVantage DiVa), demonstrated the efficient excitation of yellow,
orange, and red excited fluorochromes in comparison to red fluorescent protein
HcRed [90]. The availability of supercontinuum white light lasers [91] also provides
new excitation source for flow cytometry (e.g., 480 nm to the long red (
700 nm)) and
“fine-tuning” of optimal excitation for particular probes without the restriction of
specific laser line emission, as described by Telford et al. [91].
Recent semiconductor microtechnology has greatly reduced laser size down to the
scale of single cells. The integration of ultrasmall lasers with biological systems
makes it possible to create microelectromechanical systems that might revolutionize
cytometry [92]. The integration of biology and photonics will be achieved using
semiconductor optoelectronic crystals. The versatility of semiconductor optoelec-
tronics with its customizable optical and electronic properties makes it an ideal
technology for biophotonics. Unsurprisingly therefore semiconductor laser and
photodiodes have been widely used in biosensing and analysis systems. True
“biophotonic” integration, that is, embedding the living system within the semi-
conductor photonics, is relatively unexplored [92-95]. A format using an intracavity,
vertical geometry biolaser for cell analysis was used to establish a new technique to
rapidly assess the properties of cells flown through a nanolaser semiconductor device
with a detection of biophotonic differences in normal and transformed mouse liver
cells by using intracellular mitochondria as biomarkers for disease [96].
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