Transfection, or introducing foreign genetic substances such as nucleic acids into cells, is often needed for gene research and therapy. Now a cell is very small — about 10-thousandth of a millimeter. How do you ship stuff inside them, past the wall (membrane)?

Well, it can be done. Though several techniques have emerged in the recent past, transfection is an evolving science. Now, a team of researchers from IIT-Madras, in collaboration with scientists from the UK and Taiwan, have achieved a signal breakthrough.

Broadly, there are three ways of doing transfection. First, biological, in which the desired genetic material is introduced into a virus; the virus is then used as a truck to take the material inside the cell. Easy method, but there are undesirable side-effects — it could trigger an immuno-response from the body or set off harmful genetic mutations.

Second, the chemical method — you attach your shipment to the positive ions of certain chemicals (cationic polymer, cationic amino acids) and they get attracted to the negatively charged cell membrane. This is tough, because you have to match the chemicals to the type of cell, or else the ‘transfection efficiency’ will be low.

The third method, physical, is gaining ground. Here again, there are different techniques, such as micro-injection, biolistics and electroporation. Micro-injection is straightforward injection but demands high skill and is laborious. ‘Biolistics’, or biological ballistics, is expensive as it needs equipment for mixing the shipment material with gold and shooting it into the cell using a gene-gun.

Electroporation, a more fancied technique, involves applying an electric field to the cell, so that its permeability increases — the holes in its walls get bigger, so that our shipment passes through. For this, of course, you would need extremely small electrodes (at least one-thousandth of an mm).

Researchers often need to work with a single cell because bulk transfection techniques, involving millions of cells together, provide only average data. In contrast, single-cell transfection techniques (SCTT) provide a better understanding of the interactions between molecules and organelles, which can help in the development of therapeutics and diagnostic tools.

Professors Tuhin Subhra Santra of IIT-Madras, Srabani Kar of the University of Cambridge, and Fan-Gang Tseng and Hwan-You Chang of the Hua University of Taiwan have jointly developed a device for electroporation that uses nano-, rather than micro-, electrodes.

Now, that is extremely small. A nano is one-thousandth of micro. The researchers fabricated a very precise array of nano-electrodes with the help of advanced micro/nanofabrication techniques. The gap between two nano-electrodes was 70 nanometers and the interspace between an array of nano-electrodes was 5 micrometers. The electric pulse creates temporary hydrophilic (water-loving) pores, through which the desired cargo could be slipped in. In the experiment, the researchers used their device to deliver into a cell material such as cell-impermeable dyes, quantum dots (nano crystals that can ferry electrons) and plasmids (a kind of DNA).

But why bother with nano-electrodes and what is wrong with micro-electrodes? With nano-electrodes, the voltage applied is small (4V to 6V) and, because of this, the cell lives longer (3 to 4 days). With micro-electrodes, the voltage needed is large enough to kill the cell within minutes after the cargo gets in. Due to the smaller nano-electrode surface area, the electrolysis effect was almost negligible, which enhanced cell viability, Santra told Quantum.

Also, with nano-electrodes it is possible to choose where to puncture holes in the cell membrane. This brings in two advantages. One, you deny the entry of other unwanted materials into the cell. Two, you can do parallel transfection of multiple drugs and see how they interact. “This nanodevice provides a spatial and temporal dosage control technique, offering high transfection efficiency and cell viability,” Santra said.

As such, this technology is a significant breakthrough in transfection techniques, which can aid drug research.



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