Fluorescence Optical Detector Board

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Learning from reverse engineering the Illumina Optical Detector Board extracted from a NeoPrep system (discontinued).

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The device electronics is quite straight forward. There is one line of 15 blue LEDs for excitation and two lines of photodiodes. The LEDs are controlled by an LED driver ICs and the photodiodes are read by an photo diode ADC. All comes together by a FPGA (black box). The power pins and input lines to the module are easy accessible on colour coded probe pins (nice).


The optical system for each of the two detector lines, is composed of 3 colour filters, 2 glass lens arrays, one plastic foil lens and 3 coated mirrors. IMG 20200814 133524.jpg IMG 20200814 140343.jpg

The 3 colour filters are:
Filter blue (excitation): 450 - 480 nm
Filter green (emission) : 510 - 550 nm
Filter red (emission) : 600 + nm


There are 3 mirrors in the system.
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Mirror 1: transmission 440 - 510 nm (rest is reflected)
Mirror 2: seems to be a complete mirror
Mirror 3: is actually just a transparent glass

Absorption spectrum from mirror 1.

It is not clear to me as to what the second line of photodiodes is measuring ass all the light seems to be reflected through mirror 2. (Maybe some infrared that I don't see or some very attenuated signal. Or maybe the second line is not used? confused).

Sensor Spectrum

The complete transmission spectrum of the first photo detector line with all the filters and mirrors in place:
540 nm + 5 / - 25 nm



The excitation LED after filtering emits at 470 + 10 /- 15 nm

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Excitation LED without filter.
ExcitationLED withFilter.png
Excitation LED with filter.


Testing the sensor with "R&D Systems ® Luminex ® Bead-Based Assays for Multiplexing" kits.

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There are two light sources used to collect data from samples. The red light source (laser for Luminex® 100/200™ and LED for MAGPIX®) excites the internal dyes in the microspheres so that they can be classified on the bead map. The green light source excites any reporter bound to the surface of the beads (PE-Streptavidin).

In Luminex applications, SA-PE is excited by the 532 nm green laser or 520 nm green LED.
Its emission peak exists at 575 ± 10 nm (orange/yellow).

Systems with two LEDs:
(511 nm) green
(621 nm) red

Excitation: 488 nm blue (azure) (broad excitation, one peak 488 nm, one at 570 nm)
Emission: 575 nm (yellow)

Excitation: 621 nm red ?
Emission: 660 nm (red) and 730 nm (infrared)