Separating very small objects into controllable, easily defined piles seems like an extremely obscure pursuit. However, researchers Christopher Striemer and Philippe Fauchet at UR have recently stumbled upon a revolutionary new way to separate or filter very small objects out of whatever they need to. The consequences of their discovery will be anything but obscure.
The filter in question is actually a porous membrane about 50 atoms thick, capable of resisting up to 15 psi of pressure. Its width is 4,000 times thinner than that of a human hair and is thousands of times smaller than similar filters used today. This makes the filtering membrane astonishingly resistant to abuse and dramatically increases the range of uses it might have.
“It’s amazing, we have a material as thin as some of the molecules it’s sorting and even riddled with holes, but [it] can withstand enough pressure to make real-world nano-filtering a practical reality,” Striemer said. “[The] ultra-thinness means much higher efficiency and lower sample loss, so we can do things that can’t normally be done with current materials.”
Striemer was originally investigating silicon crystallization patterns when he realized that the piece of silicon he was using could be used to separate objects as small as individual proteins with great effectiveness. This was because of its size, which was kept very small to allow examination using an electron microscope. The practical applications of the membrane range from improved dialysis to better fuel cells.
In regards to dialysis, the filter resolves a significant problem with blood separation currently performed by using polymers containing a convoluted tunnel network prone to clogging and other technical difficulties. Manual efforts to try and drill a series of very small holes in a silicon beam proved to be prohibitively expensive.
The UR researchers found that all of these methods could be easily simplified by the nature of silicon crystallization. While being heated, silicon molecules bunch together, forming very small openings that can be used to filter blood with astonishing effectiveness. However, the process is not yet accurate enough to be able to predicate pore size.
“Kidneys do a much better job than dialysis machines of filtering blood proteins and keeping the ones you need, like albumin, and getting rid of toxins, which in some cases are smaller proteins,” Assistant Professor James McGrath said. “They use a type of cellulose or plastic membrane with relatively poor discrimination. We think we can engineer these membranes to provide superior discrimination of proteins, which may make the process of dialysis faster and more effective than it is today.”
Although it cannot currently be done with reliable accuracy, researchers are attempting to develop a way to tightly control the size of holes in the membrane. This development would allow a further refinement of the membranes filtering capabilities.
In addition to improving the quality of dialysis treatment, another attribute of the membrane extends its potential uses to another field. The membrane can be charged so that molecules can now be separated by charge as well as by size. By varying the charge on certain regions of the membrane, researchers hope to apply the discovery to fuel cell research that often requires moving ions of a certain charge from one part of the fuel cell to the other.
Yet another application of the membrane is in air filtering of clean rooms, quarantined hospital zones and any other secure installation.
Finally, and perhaps most importantly, the membrane’s discovery has several important implications for stem cell research. Steve Goldman, Zutes Chair in Biology of the Aging Brain and Professor of Neurology at UR has been in touch with the research team led by Fauchet and admits that he is impressed.
“It’s a spectacularly interesting technology that opens a realm of new possibilities in fields as diverse as organ reconstitution, proteomics and microfluidics,” Goldman said. “Its potential applications to neuroscience, cell biology and medical research may be profound.”
Neurological stem cells grow more efficiently in the presence of certain “helper” cells. After the cells are grown however, separating them from the helper cells becomes problematic. The silicon membrane is only one cell thick, so two groups of cells could potentially be attached to different sides of the membrane and still be able to communicate with each other. This communication, rather than actual cell-on-cell contact, is what drives the successful differentiation of the stem cells. Once the stem cells have matured, they can easily be separated from one side of the membrane.
For the future, the research team plans to refine the process of controlling the perforation size and degree of the membrane by controlling the heating pattern of the silicon. Currently they are subjecting the membrane to durability trials and examining its clogging tendencies.
The team has recently received a contract for $100,000 from Johnson & Johnson to continue their research on the membrane’s applications to dialysis. SeMPore, a company recently founded by the researchers, will commercialize the nano-membranes’ very numerous future manifestations. Intel and AMD have already contacted the company about using the membrane to streamline and filter out the by products of their chip manufacturing processes.Singh is a member of the class of 2008.