Microfluidic two-dimensional separation of proteins combining temperature gradient focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

A two-dimensional separation system is presented combining scanning temperature gradient focusing (TGF) and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) in a PDMS/glass microfluidic chip. Denatured proteins are first focused and separated in a 15 mm long channel via TGF with a temperature range of 16-47 °C and a pressure scanning rate of -0.5 Pa/s and then further separated via SDS-PAGE in a 25 mm long channel.

Model of separation performance of bilinear gradients in scanning format counter-flow gradient electrofocusing techniques.

Counter-flow gradient electrofocusing allows the simultaneous concentration and separation of analytes by generating a gradient in the total velocity of each analyte that is the sum of its electrophoretic velocity and the bulk counter-flow velocity. In the scanning format, the bulk counter-flow velocity is varying with time so that a number of analytes with large differences in electrophoretic mobility can be sequentially focused and passed by a single detection point. Studies have shown that nonlinear (such as a bilinear) velocity gradients along the separation channel can improve both peak capacity and separation resolution simultaneously, which cannot be realized by using a single linear gradient.

Micellar affinity gradient focusing in a microfluidic chip with integrated bilinear temperature gradients.

Micellar affinity gradient focusing (MAGF) is a microfluidic counterflow gradient focusing technique that combines the favorable features of MEKC and temperature gradient focusing. MAGF separates analytes on the basis of a combination of electrophoretic mobility and partitioning with the micellar phase. A temperature gradient is produced along the separation channel containing an analyte/micellar system to create a gradient in interaction strength (retention factor) between the analytes and micelles.

Bilinear temperature gradient focusing in a hybrid PDMS/glass microfluidic chip integrated with planar heaters for generating temperature gradients.

Temperature gradient focusing (TGF) is a counterflow gradient focusing technique, which utilizes a temperature gradient across a microchannel or capillary to separate analytes. With an appropriate buffer, the temperature gradient creates a gradient in both the electric field and electrophoretic velocity. Combined with a bulk counter flow, ionic species concentrate at a unique point where the total velocity sums to zero and separate from each other.

Fully integrated PDMS/SU-8/quartz microfluidic chip with a novel macroporous poly dimethylsiloxane (PDMS) membrane for isoelectric focusing of proteins using whole-channel imaging detection.

A fully integrated polydimethylsiloxane (PDMS)/modified PDMS membrane/SU-8/quartz hybrid chip was developed for protein separation using isoelectric focusing (IEF) mechanism coupled with whole-channel imaging detection (WCID) method. This microfluidic chip integrates three components into one single chip: (i) modified PDMS membranes for separating electrolytes in the reservoirs from the sample in the microchannel and thus reducing pressure disturbance, (ii) SU-8 optical slit to block UV light (below 300 nm) outside the channel aiming to increase detection sensitivity, and (iii) injection and discharge capillaries for continuous operation. Integration of all these components on a single chip is challenging because it requires fabrication techniques for perfect bonding between different materials and is prone to leakage and blockage.