Detection of microparticles

The main challenge in the detection of micro scale objects using optical fiber is the stringent light coupling condition with small core fiber as the latter is required to produce micro scale detection region.  The option of laser source allows the OptoReader to produce a light spot in micro scale while maintaining very high brightness.

In this application note, we showcase the detection of 2 µm diameter fluorescent beads using the Optoreader equipped with a laser source. 

The experiments shown in this application note have been realized only with Elveflow’s instruments and accessories. The microfluidic channel is made by soft lithography on PDMS and supported by glass substrate. The width and height of the channel is 50 µm and 60 µm, respectively. For any advice on your research project and experimental needs, do not hesitate to consult our team of specialists.

We can infer the flow rate of the carrier fluid assuming that the beads are carried at the same speed as the liquid. Knowing the particle concentration and the event rate, the flow speed can be determined by the following formula:

where v is the flow speed, f is the event rate, d is the diameter of a bead and s is the solid content. Hence, the flow rate is about 0.44 m/s (80 µl/min) and 2.21 m/s (400 µl/min) in the cases of f = 3 kHz and 15 kHz, respectively.

Furthermore, by varying the applied pressure, one can establish the relation between the flow speed and the applied pressure. The left figure below shows the variation of the event rate with respect to the applied pressure:

Knowing the flow rate, it is possible to perform statistical study about the size of the signal peak associated with the fluorescence. A histogram of the width of the peaks is given in the right-hand figure. The peak width with the most highest occurrence is between 30 µm and 40 µm. This size is close to and could reflect the average width of the illuminated volume as shown in the experimental set-up diagram above.