Literature/202404021206 integrated waveguide on electrophoretic separation

• Source: [[@vieillard2007Application of microfluidic chip with integrated optics for electrophoretic separations of proteins]]
• Tags: #electrophoresis #Free-flow-electrophoresis #isotachophoresis

This paper does not give much on the experimental setup, they just relate to a previous paper from the same group [[@mazurczyk2008Low-cost, fast prototyping method of fabrication of the microreactor devices in soda-lime glass]]. The quid is that they fabricate microchannels in soda lime glass and cover them with PDMS. In this way, they can get the negative surface charge of glass and forget about the properties of PDMS.

They also mention that by the method of etching they employ ($Na^+/K^+$ ion exchange), they locally change the refractive index of the substrate, and hence they have a "natural" waveguide. Moreover, it seems that the method gives a waveguide with a circular profile, which matches optical fibers better than waveguides with a rectangular profile.

Some important parameters from the paper:

• Voltages used go from $-1.5kV$ to $1.5kV$ (Labsmith HVS448-3000D)
• At some point, voltages across the channel length are $100V/cm$ (to allow for electrokinetic injection)

The methods on the paper are not based on free flow electrophoresis, but rather on capillary gel electrophoresis, zone exclusion electrophoresis, capillary zone electrophoresis, and electro osmotic flow.

In any case, the addition of a waveguide thanks to refractive index changes on the substrate opens the door to different implementations of these methods.

Sadly the paper does not discuss how the waveguide is used and what kinds of limitations it'll face. Channels are rather big, and evanescent waves will only illuminate a portion. I still believe integrating the channels into a microscope (as the authors did), may be the only way to analyze the samples.