Accurate to the molecule

DNA and nanotubes were combined to "identify" single proteins

Vladimir Korolev, N+1

Materials scientists from Harvard, the Massachusetts Institute of Technology and the University of California have developed a sensor capable of detecting the release of single protein molecules secreted by microorganisms. It is based on a "forest" of carbon nanotubes connected to DNA aptamers. Scientists hope that the device will help to investigate communication between bacteria – the exchange of signaling molecules, allowing them to coordinate gene expression. The study was published in the journal NatureNanotechnology (Landry et al., Single-molecule detection of protein efflux from microorganisms using fluorescent single-walled carbon nanotube sensor arrays), a press release from MIT New sensors can detect single protein molecules briefly reports about it.

Appearance of the system for qualitative analysis of single proteins
(here and below are the drawings from the article in Nature Nanotechnology).

Proteins in a cell perform a huge number of functions: they accelerate chemical reactions, serve as channels for ions, allow cells to communicate with each other and perform transport functions (for example, hemoglobin in the blood). In this regard, there are a large number of different proteins, and it is quite difficult to single out a specific one among their mixtures. One way is to use protein antibodies that can bind only to the molecules of interest.

However, not only other proteins form strong complexes with proteins. Some short strands of DNA or RNA can bind to the protein under study even more strongly than antibodies. Such particles are called aptamers. In traditional methods of qualitative analysis, protein concentrations of the order of millions of particles per milliliter are required. At the same time, to study protein synthesis in a single organism, it is required to detect particles at the level of single molecules. Similar technologies exist only for labeled proteins.

The authors of the new work proposed the design of a sensor capable of detecting individual molecules of the protein under study, without requiring isotopic or fluorescent labels in its composition. The method is based on the ability of carbon nanotubes to fluorescence. The characteristics of their radiation depend on the environment of the particles.

Fluorescence spectra of carbon nanotubes
with a free aptamer and with an aptamer-protein complex.

The sensor itself consists of an array of carbon nanotubes to which aptamers are attached. At the moment when the desired protein approaches one of these nanotubes, a molecular complex is formed. This predictably shifts the wavelength of the nanotube fluorescence – scientists read the corresponding signal. The sensor itself is placed inside a microfluidic cell, inside which the studied organisms are also located. The fluorescence is read using an infrared microscope.

The main difficulty was that aptamers change their configuration, being tied to nanotubes directly, and lose selectivity to proteins. To avoid this, scientists have developed aptamers with flexible "tails" that allow molecules to attach to carbon nanotubes without distorting the shape. The sensor was tested on several molecules – the signal protein RAP1 and the viral protein HIV1-integrase.

According to scientists, the technique has practically no restrictions on the minimum concentration of detectable particles – the sensor is able to see even single protein molecules. However, the lower the concentration of the detected substance, the longer it takes to detect it. The main application for the sensor may be the study of protein synthesis in organisms. For example, biopharmaceutical companies will be able to monitor in real time the rate of synthesis and quality of proteins produced by genetically modified organisms.

Portal "Eternal youth" http://vechnayamolodost.ru  25.01.2017