26 December 2013

The silver light of DNA

St. Petersburg scientists made DNA glow with silver

Alexey Shabelsky, InformnaukaRussian scientists from the Faculty of Physics of St. Petersburg State University managed to stabilize silver clusters in solution using DNA nanoparticles.

This made it possible to create chemically stable biocompatible fluorescent labels with high brightness. Such fluorescent labels are used in biology and medicine to visualize various processes in the cell or various morphological structures.

Scientists chose silver because it is known that silver clusters consisting of several atoms have increased brightness and photostability compared to traditionally used dyes and quantum dots. In addition, which is especially important for biomedical applications, silver clusters are non-toxic.

St. Petersburg scientists for the first time proposed a method for creating such luminescent nanoparticles. It is based on the unique natural ability of the polymer DNA molecule to self-organize. DNA can form compact structures when interacting with short polycations – such as polyamines. As a result, a polymer globule is obtained, the inner layers of which contain silver nanoclusters. Its outer layers protect these clusters from oxidative destruction in solution. At the same time, a large number of silver-DNA clusters can be concentrated inside the globule, which significantly increases the brightness of the particle, and hence the sensitivity of luminescent microscopy methods.

Today, there are about several dozen leading scientific groups abroad engaged in the research of silver clusters and clusters based on other metals stabilized by polymers. Research in this area began less than ten years ago, and many practical and fundamental issues have not yet been resolved. "We joined the solution of these tasks less than two years ago. However, the methods and approaches we have proposed, along with the availability of modern research equipment, allow us to compete with the world's leading teams," says STRF.ru Alexey Kononov, an employee of the Laboratory of Molecular Biophysics.

For the first time, St. Petersburg scientists were able to explain why some metal-DNA clusters can luminesce, while others cannot. The team of authors managed to carry out theoretical calculations and show that only those clusters of DNA with metal that have a filamentous structure, that is, when silver atoms are stretched into a chain, will luminesce. Silver clusters forming planar and spherical structures have luminescent abilities to a much lesser extent.

The calculated structure of a silver cluster of three DNA-stabilized atoms

This observation allows us to develop a further strategy for the purposeful creation of DNA matrices that stabilize the filamentous shape of clusters. Performing calculations for such complex objects requires very significant computing resources and is not available to all scientific groups in the world. Colleagues from the Lomonosov supercomputer complex of Moscow University came to the aid of scientists, whose unique policy allowed them to get completely free access to university facilities. A number of experimental results became possible thanks to access to very expensive equipment of the resource centers of St. Petersburg University, which provide their services to all university employees participating in scientific projects, free of charge.

Luminescent clusters of metals are the basis for the creation of fundamentally new bioassays for medical diagnostics. Their increased photostability also opens up the possibility of their use as emitters in optoelectronics, as well as as an active medium in the creation of lasers. From a fundamental point of view, the study of metal clusters will allow us to formulate the basic principles of cluster physics and build a model that adequately describes the electronic structure and physical properties of these objects, which differ both from atoms and from large metal nanoparticles of the order of tens and hundreds of nanometers in size.

Diagram from an article in The Journal of Physical Chemistry – VM

Further development of techniques for creating metal-DNA nanostructures will significantly advance in the field of medical diagnostics of various diseases at the gene level, i.e. it will be possible to identify the genes responsible for the development of many diseases at the earliest stages of diagnosis. To create so-called site-specific biomarkers, it is possible to use the unique sensitivity of the luminescent properties of metal clusters, both to the chemical structure of the DNA matrix and to its environment. In other words, the metal-DNA structure can be used as a unique fluorescent probe for biodiagnostics.

Sources of information: Volkov et al., Fluorescent Silver Nanoclusters in Condensed DNA ChemPhysChem. Vol. 14, pp. 3543-3550; Ramazanov, Kononov, Excitement Spectra Argument for Threadlike Shape of DNA-Stabilized Silver Fluorescent Clusters, J. Phys. Chem. C, 117 (36), 18681-18687.

Portal "Eternal youth" http://vechnayamolodost.ru26.12.2013

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