Microfluidic platform for measuring mechanical and electrical properties of single cells

Undoubtedly, microfluidics has opened many new windows of opportunities for single-cell analysis. Droplet microfluidics, for example, has shown great promises for encapsulation, manipulation, and incubation of single-cells within nL-pL droplets at very high throughputs. As the field grows more and more methods get developed providing researchers with ever-increasing microfluidic tools for single-cell analysis. The field has now been one more step expanded by the development of an integrated optical stretching and electroporation microfluidic chip for biophysical analysis of single cells.

A research team led by Wenhui Wang of Tsinghua University is working on making a microfluidic platform for the multiparameter characterization of single cells. The results of the study which is published in Nature Microsystems and Nanoengineering journal describes a microfluidic device utilizing optical fibers and electrodes for simultaneous measurement of mechanical and electrical properties of different cell types. They tested five different cell types as a proof of concept and demonstrated the potential of their microfluidic device for studying how cancer changes cell properties.

“We provided proof of concept by testing five types of cells (HeLa, A549, HepaRG, MCF7 and MCF10A) and determined five biophysical parameters, namely, shear modulus, steady-state viscosity, and relaxation time from the stretching deformation and area-specific membrane capacitance and cytoplasm conductivity from the rotation spectra.”

The microfluidic chip was aimed at the simultaneous measurement of both mechanical and electrical properties of the cells. Mechanical properties are physical and intrinsic markers of the cells that can affect cell adhesion, polarization, etc. Electrical properties relate to the chemical composition and structure of the cells and can relate to cell identity, viability, and growth. Mechanical and chemical properties require different techniques for measurement and combining these different techniques in one microchip can be challenging. Rather than using serial microfluidic devices for sequential measurements, they took an innovative approach to combine the two in a single microfluidic device.

The proposed microfluidic device consists of an indium tin oxide (ITO) patterned glass slide which is walled by a carbon-PDMS (cPDMS) electrodes. Two optical fibers were aligned and placed orthogonal to the microchannel on either side of the cPDMS. These fibers formed an optical tweezer that was used for trapping and stretching single cells. The four electrodes were connected to an AC signal to generate an electrical field for rotating the trapped cell. The device operates in a capture–trap–stretch–relax–rotate–release manner. The rotational speed of the cell in relation to the AC signal and the stretching rate of the cell can be recorded to extract the electrical and mechanical properties of the cell, respectively. 

The combination of optical trapping and electroporation proved to be helpful in the simultaneous measurement of multiple biophysical properties of single cells. This technique is envisioned to be useful in the cancer-related analysis of cells.

Read the original article: On-chip integrated optical stretching and electrorotation enabling single-cell biophysical analysis