All of molecular biology can, in a broad sense, be said to be about studying cells. While certain subdivisions may focus on particular parts of cells or certain kinds of cells, it is still all about how cells function and how they are genetically programmed from within to become what they are. Both for the bacterial world and for complex eukaryotic organisms. But studying cells can often be difficult for a variety of reasons, especially on a single cell basis. Beyond just the problems in cultivating the cells themselves, their components are intrinsically tied to their being and can, in most cases, not be considered separate from them.
Techniques On The Very Small
The smallest of levels includes the multitude of proteins and molecular bodies that flit around inside the cellular surface, performing their predetermined tasks. We can largely only look on from outside, hoping to catch a glimpse of how they work in a living cell. And, in many cases, we use destructive techniques that allows us to isolate each piece, but so much knowledge is lost in the process. One also has to worry about working quickly or risk losing the very information that is being sought due to factors that destroy it after death of the cell, such as the role of enzymatic DNases to break down the genome after a cell is no longer viable.
The emergence of so-called “lab-on-a-chip” technologies have allowed for miniaturization of experiments to involve only a single cell thanks to various sorting mechanisms. This sort of research has helped significantly in the fields of cancer studies and for general cell type investigation. Even going so far as being the basis for the next big piece of human research beyond the Human Genome Project, what is being called the Human Cell Atlas that seeks to map out all of the types of cells in the entirety of the human body. It is a major undertaking.
But even these options have their issues. The extraction of a single cell removes it from its natural environment and means that only an instant snapshot of its nature can be taken right at that point in time, as any future results would immediately begin to diverge from how the cell acts as a part of a larger framework. This has led to further tools being made to allow for testing of single cells while allowing them to remain in their natural place. Today’s discussion is about a new one of those tools.
Tweezing Out Cellular Mysteries
Scientists at the Imperial College London have revealed their creation of a set of nanotweezers that can work on the molecular level to extract subcellular components from cells, all while not harming the host cell whatsoever. The making of them involves some complex, yet somehow still simple, pieces of biomedical technology, which will only be described in short herein.
The first step was to make a pair of nanopipettes out of quartz using the process of laser pulling to slowly strip away layers. Then nanoelectrodes were made at the tips of these microscopic pipettes by depositing chemically modified carbon to form a conductive surface. The distance between these two nanoelectrodes is on the order of 10 nanometers. And since human cells are on average the size of tens, hundreds, or even thousands of micrometers, this nanotweezer scale is far below that. When a voltage is expressed across them, the two electrodes create an attractive force, pulling molecules in their direction.
Particles can then be trapped and moved via these tweezers, including being removed entirely from the cell. The force attracting them can be increased either by heightening the voltage or by moving the nanoelectrodes closer together. The former has a limit though, as too high of a voltage can generate heat and also spontaneously cause electrochemical reactions to occur. With this tool in place, it is capable of collecting even DNA around 20-200 base pairs (bp) long, along with other harder to study elements such as transcription factors.
The expertise of the tool was proven through tests that involved collecting DNA 22 bp long and a strand 48,502 bp long, the former single stranded and the latter double stranded. Lastly, a protein on the smaller end of 14.5 kilodaltons was procured. Selective amplification of the DNA through PCR was done to prove that they hadn’t been damaged due to the extraction. Thus, DNA can be sampled directly from the nucleus without harm to it or the cell. A final test for the single molecule level involved the collection of one messenger RNA (mRNA) from the cytoplasm of a cell.
Things can be expanded, however, to also allow for the separation of an entire organelle from inside of a cell. Mitochondria were taken from the axon of a mouse neuron to showcase this feat. These were shown to remain intact during and after extraction thanks to the addition of a fluorescent dye to follow the internal movements while the nanotweezers were in use.
In The Hands Of Molecules
A main and important point of the process, separate from the accomplishments themselves, is that fabrication of the nanotweezers is relatively easy and does not cost expensive materials to produce. So they can easily be utilized by researchers around the world for any number of biological experiments. Its difficult to overstate the areas in which this tool could be included, especially when it comes to genetics, as individual mRNAs can be acquired to visualize active gene expression within a cell.
All this is only with the base tool. The scientists have noted that the nanotweezers may also be modified with different techniques beyond just molecular-level extrication. Scanning and observation components could be attached and inserted into a living cell and produce data on any variety of cellular behavior. The limits of what we can use such a device for are only the limits we choose to restrict ourselves to.
Photo CCs: PNNs at primary somatosensory cortex in mouse brain 02 from Wikimedia Commons