MSU scientists discovered a new way for sensing the levels of an important amino acid

February 15, 2018

A team from the Faculty of Chemistry of MSU together with its colleagues suggested a new method for determining the levels of cysteine - a substance used in many chemical drugs - with the help of gold nanoparticles. Unlike current methods, this one does not require complex reactions or expensive equipment. An article with the results of the study was published in Sensors and Actuators B journal.

Cysteine is an amino acid found in keratins (proteins contained in nails, hair, and feathers). It deactivates toxins, acts as an antioxidant, protects against X-rays and radiation, and is used in medicinal drugs and food additives. Moreover, its presence in blood may be an indication of certain conditions, such as Alzheimer's disease or cardiovascular, liver, or skin disorders. Therefore, determining the level of cysteine in biological liquids can be considered a diagnostic tool, and in drugs - a quality control method.

As a rule, the content of cysteine in a solution is detected using the luminescence method, but it requires expensive equipment, additional procedures, and qualified personnel. Therefore, a simpler and cheaper procedure is required.

The authors of the study suggested using gold nanoparticles that are 20 nanometers in diameter and require a simple production method. In a solution they form a stable colloid system, i.e. don't sink down to the bottom of the vessel.

"It is very easy to obtain such particles, especially the non-modified ones. One just has to take a gold compound, say, chloroaudic acid, and sodium citrate (a salt of citric acid), mix them and heat up - that's all the synthesis that is required. The process is simple and can be carried out in almost any lab," commented Vladimir Apyari, a co-author of the work, senior research assistant of the Faculty of Chemistry, MSU, and doctor of chemistry.

The scientists noticed gold nanoparticles due to their ability to quickly change color (from ruby red to blue) upon aggregation into bigger formations. Because of this property they are used to detect ions of different metals, anions, and organic compounds. When nanoparticles react with cysteine, they are aggregated, and the solution's spectral characteristics and colour change. These changes can be measured with a spectrophotometer or even seen with a naked eye. The reaction takes a couple of minutes.

Cysteine detection in a solution has certain disadvantages. For example, no spectrophotometer analysis can be carried out in a muddy or coloured environment, and cleansing is required. To avoid it, nanoparticles may be placed on the surface of a solid material, such as polyurethane foam. The particles are completely consumed by polyurethane foam in 15-20 minutes.

According to the authors, in the future their study may help to develop new detection methodologies. In some of them more complicated nanoparticles with added analytical groups (chemical structures that bind with the analyzed substance) may be used. Therefore, the method may be adapted to detect and determine the levels of other compositions.

The study was carried out in collaboration with scientists from the National Research Center "Kurchatov Institute".
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Lomonosov Moscow State University

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