Medical Design Briefs - April 2022 - 45

Sample
Illumination Optics
Detection Optics
Ultra-Miniature - High Reliability
Quartz Crystals, Oscillators
and Sensors
Emission Filter
LED Light
Source
Detector
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Fig. 3 - Two common illumination architectures are used in qPCR instruments. Figure 1 shows the
illumination and excitation paths separated with a dichroic beam splitter. This figure illustrates the
architecture preferred for applications that require multiple target detection channels (i.e., up to 4-
6 channels), since this type of system layout is not dependent on dichroic filters.
Input Power
Wavelengths/Emission Lines
Out Light Divergence
Emitting Area
Intensity
Warm-Up Time
Lifetime (hours)
Price ($)
Hg (HBO) Lamps Xe (XBO) Lamps Lasers
100 W
75 W
Multiple
discrete peaks
High
Large
High
Long
200
Low
Decay in Brightness (With Time) Yes
Safety Considerations
Yes
Broadband
High
Large
High
Long
400
Low
Yes
Yes
LEDs
10s to 100 mW 5 W
Many discrete
laser lines
Low
Small
Highest
Short
>50,000
Highest
No
Yes
Multiple
narrowband
peaks
High
Smaller
Lower
Short
Up to 40,000
Low
No
No
Table 1. A comparison of the pros and cons of the three commonly used illumination sources in
fluorescence imaging.
path to minimize signal crosstalk between
detection channels.
n Illumination Source Selection
When starting a PCR instrument design,
a team chooses a test assay fluorescent dye
based on several biological factors, and
then the next step is to select the optimal
illumination source. Two factors that drive
the illumination source selection are its
peak emission wavelength and the output
power. These two factors should overlap
with the peak absorption wavelength of
the fluorophore and the amount of energy
required to excite it efficiently, creating
a high number of fluorescence emission
photons for detection. Therefore, to
achieve optimal fluorescence and subsequently
SNR, it is best to choose a light
source with an emission wavelength that
matches the peak absorption wavelength
of the fluorophore or is close to it.
Medical Design Briefs, April 2022
Cov
The second consideration for source
selection is the intensity required to
excite the fluorophore. The source
should have high coupling efficiency to
the delivery optics to deliver the optimum
irradiance to the sample. Careful
consideration is required to optimize the
illumination optics for high light collection
and direction to the sample, typically
a microfluidic cartridge or plastic vial.
Table 1 compares the pros and cons of
the three commonly used illumination
sources in fluorescence imaging. From
the data presented in Table 1, it is possible
to conclude that LEDs and lasers
have few advantages over arc lamps.
LEDs as
illumination
sources
for
qPCR diagnostics are a great choice.
They are available over a wide range of
wavelengths and are readily available at
absorption wavelengths of commonly
used fluorophores. In addition, LEDs
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Medical Grade Crystals,
Oscillators and Sensors
* High stability and precision
* Used in implantable devices
* Excellent long term aging
* Low power consumption
STATEK CORPORATION
ISO 9001
AS9100
512 N. Main St., Orange, CA 92868
Tel. 714-639-7810
Fax 714-997-1256
www.STATEK.com
Free Info at http://info.hotims.com/82320-815

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Medical Design Briefs - April 2022

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