18 September 2015

Made in Russia: graphene oxide biochip

MIPT scientists have created a graphene biosensor that will accelerate the search for drugs for HIV and cancer

Scientists from the Laboratory of nanooptics and plasmonics at MIPT have created an ultra–sensitive biosensor based on graphene oxide, which opens up new opportunities in medicine and pharmaceuticals - it will help in the creation of new drugs and vaccines against dangerous infectious diseases such as HIV, hepatitis, herpes, as well as cancer and many other diseases. The results of the study are published in the journal ACS Applied Materials & Interfaces (Stebunov et al., Highly sensitive and selective sensor chips with graphene-oxide linking layer).

Marker-free biosensors have appeared relatively recently in the laboratories of biochemists and pharmacists, greatly facilitating and simplifying their work. These sensors can detect vanishingly small concentrations of substances and investigate their chemical properties. Unlike other biochemical methods, biosensors do not need to "attach" fluorescent or radioactive markers to the sample molecules, without which the desired substance remained "invisible".

A group from the Laboratory of Nanooptics and Plasmonics, part of the Center for Nanoscale Optoelectronics at MIPT, is developing biosensors based on the use of surface plasmons – electromagnetic waves that occur at the interface of a conductor and a dielectric as a result of resonant interaction between photons and electrons. The parameters of this resonance depend on the properties of the surface so much that even insignificant amounts of "foreign" matter noticeably affect them. Biosensors are able to detect the presence of trillionths of a gram of detectable substance on a square millimeter site.

Such "abilities" make it possible to radically simplify many research procedures in medicine and biology, but the most interesting property of biosensors is that they allow scientists to observe the interaction of molecules in "real time".

"With their help, we can track how a particular chemical reaction is going, we can estimate its speed, which means we can accurately determine how a particular substance acts on a cell, on a pathogenic bacterium. This means that in the near future, preclinical drug trials can be conducted in a fundamentally new way – to accurately predict the effect of the drug, it will be enough to trace the interaction of drugs with living tissue directly on the biosensor. This is a revolution in the creation of new drugs: biosensors will significantly increase the effectiveness of preclinical studies and, perhaps, in the near future will help to defeat incurable diseases," says one of the authors of the study, Yuri Stebunov.

The sensor chips that currently exist – thin plates measuring centimeter by centimeter, where the test samples are deposited – are made mainly of glass coated with a thin layer of gold. Either a layer of thiol molecules or a polymer layer (most often based on carboxymethylated dextran) is created on the chips. Below the chip is a laser that excites plasmon resonance, its characteristics are read from the reflected beam by a photodetector.

The sensitivity of the biosensor depends on the properties of the surface – more precisely, on how many molecules of the substance under study will be able to join the plate. Graphene is considered a promising material for biosensors: it has a large surface area, is cheap to manufacture, and also interacts with a large number of biological molecules.

Stebunov and his colleagues have created and patented a fundamentally new type of chips coated with graphene oxide – a material that promises even greater efficiency than pure graphene. They applied graphene oxide "flakes" to a glass plate coated with a 35-nanometer-thick layer of gold. Then a layer of streptavidin protein was deposited on this surface, which served as a "trap" for molecules. Next, the scientists installed the chip in the BiOptix biosensor and traced how the plasmon resonance parameters react to the presence of complex organic molecules – single-stranded DNA fragments. 

Then similar experiments were carried out with graphene-based biosensors and a commercially available chip based on carboxymethylated dextran. The measurements showed that the graphene oxide sensor is three times more sensitive than the dextran chip and 3.7 times more sensitive than the pure graphene sensor. This means that the new chip requires several times fewer molecules to detect a particular substance. In addition, the "oxide" sensor could be used several more times after a simple regeneration procedure (washing with alkali). It is also important that graphene oxide is cheaper and easier to produce. 

Scientists note that the device they created is actually a prototype, suitable for starting mass production and entering the market.

"Our chip can be used in the development of medicines for infectious, oncological and other types of diseases. Therefore, we expect serious interest from pharmaceutical companies in our development. This sensor can also be used to control the quality of products, in the search for toxins and allergens, in medical diagnostics, which will help reduce the time to perform tests from a day to minutes," says Stebunov.

At the same time, he noted that before the introduction into clinical practice, these sensors need to be simplified and carried out through the testing procedure. According to his estimates, with mass production, a graphene oxide biochip can cost less than $ 10, despite the fact that the biochips that are on the market now cost from $ 80 to $ 200.

The study was supported by the Ministry of Education and Science of the Russian Federation (project part of the state task No. 16.19.2014/K) and the MIPT competitiveness improvement program "5-100". The equipment of the Center for Collective Use of unique scientific equipment in the field of nanotechnology of MIPT was used.

The authors of the study thank BiOptix and its employees Boris Khattatov and Vyacheslav Petropavlovsk for their help, as well as employees of the Department of Technological Entrepreneurship of RUSNANO – MIPT, where this study began.

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