Optical particle analyser with illumination at an oblique angle onto a non-transparent microfluidic chip

1 . An optical particle analyser, comprising:

a microfluidic chip having a flow channel for carrying particles arranged between a transparent window and a non-transparent substrate, at least a portion of the flow channel having a rectangular cross section; and

a light source configured to emit an illumination beam towards the flow channel,

wherein the microfluidic chip and the light source are arranged such that, in use, an angle of incidence of the illumination beam impinges the transparent window at an oblique angle;

a particle focusing mechanism configured to concentrate the particles within the flow channel;

wherein the particle focusing mechanism is configured to produce two particle foci;

wherein each particle foci are aligned with respect to a plane of the microfluidic chip; and

wherein the light source is further configured such that the illumination beam uniformly illuminates the particles in the flow channel.

2 . The optical particle analyser of claim 1 , wherein the illumination beam is linearly polarized before it impinges the transparent window, and the angle of incidence is equal to a Brewster angle of the transparent window.

3 . The optical particle analyser of claim 1 , wherein the illumination beam is a stigmatic Gaussian illumination beam, or a top-hat beam.

4 . The optical particle analyser of claim 1 , further comprising an FSC detector arranged in a path of the illumination beam after it has been specularly reflected from the microfluidic chip;

wherein the FSC detector is configured to measure forward scatter of the illumination beam.

5 . The optical particle analyser of claim 4 , further comprising:

a beam stop or spatial filter arranged between the microfluidic chip and the FSC detector,

wherein the beam stop is configured to absorb specular reflections of the illumination beam, and

wherein the spatial filter is configured to pass the specular reflections of the illumination beam and block light scattered by the particles in the flow channel.

6 . The optical particle analyser of claim 5 , further comprising a forward collection lens arranged between the microfluidic chip and the FSC detector.

7 . The optical particle analyser of claim 1 , further comprising an SSC detector configured to measure side scatter of the illumination beam.

8 . The optical particle analyser of claim 1 , further comprising a fluorescence detector configured to measure fluorescence from the microfluidic chip at one or more wavelengths.

9 . The optical particle analyser of claim 1 , further comprising a side collection lens arranged between the microfluidic chip and a side detection module, wherein the side detection module comprises an SSC detector and/or a fluorescence detector.

10 . The optical particle analyser of claim 1 , wherein the particle focusing mechanism is an inertial focuser.

11 . The optical particle analyser of claim 1 , wherein the particle focusing mechanism is a 2D sheath flow configured to concentrate the particles within a narrow range of the flow channel with respect to a width of the flow channel.

12 . The optical particle analyser of claim 1 , wherein the particle focusing mechanism is a 3D sheath flow configured to concentrate the particles within a narrow range of the flow channel with respect to a width and height of the flow channel.

13 . The optical particle analyser of claim 1 , wherein the non-transparent substrate comprises a reflective coating.