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Graphene method may lead to low-cost diagnostics
CAMBRIDGE, Mass.—A new method of graphene oxide annealing developed at the Massachusetts Institute of Technology (MIT) and National Chiao Tung University may make it possible to capture and analyze individual cells from a small sample of blood. The hope is to use this technology in developing low-cost diagnostic systems that can be used anywhere.
DDNews spoke to Dr. Neelkanth M. Bardhan, a postdoctoral associate at MIT, who says, “The process of mild (low-temperature, at approximately 50° to 80°C) thermal annealing is a one-step process, applied directly on the as-synthesized graphene oxide.” The process is said to be suitable for use on many different forms of graphene oxide, “in the form of aqueous suspension, thin films, foams or [sheets].”
“The process of thermal annealing was proposed based on the results of simulation studies performed on the structure of the graphene oxide material, using a combination of density functional theory (DFT) and molecular dynamics (MD) simulations. Based on these simulations, it was shown that graphene oxide, when it is first synthesized using chemical methods, is a metastable material, with a random distribution of the oxygen functional groups. Given sufficient time, even at room temperature, it is thermodynamically favorable for the structure to phase transform to a more stable state, with the oxygen groups ‘clustered’ into distinct oxidized and graphitic domains while preserving the total oxygen content of the material,” Bardhan continues.
“This process, if left to proceed at room temperature, would take a long time—months, or even years. We hypothesized that by using a low-temperature annealing, we can providing thermal energy, which should speed up the diffusion of the oxygen functional groups, and kinetically accelerate the process of phase transformation resulting in the oxygen clustering. Indeed, this is what we discovered to be the result of the low-temperature annealing process, the details of which are discussed in our previous publication [See Reference: Kumar, P.V. et al., “Scalable enhancement of graphene oxide properties by thermally driven phase transformation,” Nature Chemistry 6, pp. 151-158 (2014)].”
The paper by Bardhan, et. al., titled “Enhanced Cell Capture on Functionalized Graphene Oxide Nanosheets through Oxygen Clustering,” has been published in the journal ACS Nano.
“It’s important to note that graphene oxide is being used as the template material to attach capture agents, which have selectivity to bind to specific kinds of biomolecules such as DNA, proteins, cells or other species of interest. In the present work, the capture agent used was a nanobody against Class II MHC-positive cells,” says Bardhan. “The advantage of using a nanobody is that they can be mass produced at relatively low cost in E. coli bioreactors compared to antibodies, which need to be grown and harvested in living systems. This is one of the key factors which allowed the researchers in the present work to demonstrate a functional cell capture device under $5.”
“Since no other research group was able to improve the structure of graphene oxide at the material level, this is the first known demonstration of such an approach to improve the efficiency of capture of cells and other molecules of interest,” continues Bardhan.
Bardhan says refrigeration is unnecessary for the capture and assessment method. “The whole assay takes only 10 minutes at room temperature (after drawing the blood), with no need for intermediate steps, such as separation of the plasma and other components. Given the rapid speed of the process, it’s possible to do the assay at room temperature and proceed to downstream analysis without loss in cell viability. This makes our approach more suitable for use in emerging markets, and in remote places, or out in the field with lack of access to refrigeration equipment.”
“Through our molecular dynamics simulations, we discovered that when graphene oxide is subjected to the low-temperature annealing treatment, there is a redistribution of the chemical functionality, in that the carbonyl groups are enriched (nearly double) in proportion, at the expense of the epoxy and hydroxyl functional groups,” he explains. “The total oxygen content of the material is unchanged, which is the secret sauce of the low-temperature annealing treatment. This is in stark contrast to all the other methods used in the literature—either chemical or thermal reduction, to improve the properties of graphene oxide, which causes a sharp decrease in the number of oxygen functional groups.”
“We verified that this process actually happens by comparing X-ray photoelectron spectroscopy data of the graphene oxide material, in the original and after the thermal annealing, which showed the appearance of a distinct carbonyl peak after the annealing process. In the subsequent step of the attachment of the capture agent, we are exploiting the increased reactivity of primary amines towards the carbonyl functional group (compared to reactivity towards either the hydroxyl or epoxy functional groups). Since the carbonyl functional group is enriched as a result of the oxygen clustering process, this leads to increased density of functionalization of the nanobodies, and as a result, an enhancement in the efficiency of cell capture (almost doubling, from 54 percent to 92 percent).”
“Efficiency is especially important if you’re trying to detect a rare event,” commented Angela Belcher, the James Mason Crafts Professor in biological engineering and materials science and engineering at MIT and a member of the Koch Institute for Integrative Cancer Research. “The goal of this was to show a high efficiency of capture.”
The team hopes for the next step to be production of a working detector for a specific disease.