Biosensors based on quantum dots for clinical diagnostics
Unusual fluorophoresMaria Morozova, STRF.ru
At the Institute of Bioorganic Chemistry named after
Academicians M.M. Shemyakin and Yu.A. Ovchinnikov of the Russian Academy of Sciences create biosensors of a new generation using quantum dots. Doctor of Physico-Mathematical Sciences, Professor Vladimir Aleksandrovich Oleinikov, head of the project "Semiconductor nanocrystals, effective fluorophores for biomedical research", tells about the prospects of their application, in particular in clinical diagnostics.
Vladimir Alexandrovich, your research group is engaged in semiconductor nanocrystals. Please tell us about the essence of the research?– In general, semiconductor nanocrystals have a huge potential for use in a variety of areas (electronics, light-emitting devices, energy converters, etc.). We have focused our efforts on creating applications for biology and medicine and are working in two directions: firstly, we are creating sensors based on quantum dots in the form of colloidal nanocrystals; secondly based on them, we develop tools for obtaining information from objects of the nanometer range by near-field microspectroscopy methods, as well as methods and devices for solving clinical diagnostic problems.
How exactly are quantum dots used in the diagnosis of diseases?– A quantum dot is a very small physical object smaller than the radius of the Bohr exciton.
Like other nanoparticles, they easily penetrate the body's protective barriers. And because of such a small size, quantum effects arise in them, for example, strong fluorescence. Using this property, they can be used to visualize pathologies in the body, and the progress of fluorescent quantum dots inside the body can be traced at different levels (the body as a whole, individual organs, cells). They are very bright, even in a conventional microscope you can see individual nanocrystals. This is very important for diagnosis, therapy, and surgery, for example, a cancerous tumor.
One of the advantages of quantum dots is that if they are excited by one radiation source, then depending on their diameter they shine with different light, respectively, they can be used as fluorescent labels. In addition, quantum dots are photostable, that is, they are able to glow for a long time when exposed to high-power density radiation.
Another of their advantages: depending on the material from which they are made, it is possible to obtain fluorescence in the infrared range – where biological tissues are most transparent. At the same time, their fluorescence efficiency is not comparable with any other fluorophores, which allows them to be used to visualize various formations in biological tissues.
In addition to oncological pathologies, what other diseases can detect quantum dots?– In one of our works, we demonstrated the possibilities of quantum dots in clinical proteomics by the example of the diagnosis of the autoimmune disease of systemic sclerosis (scleroderma) by the method of registration of autoimmune antibodies.
In autoimmune diseases, the body's own proteins begin to affect their own biological objects (cell walls, etc.), which causes severe pathology. At the same time, autoimmune antibodies appear in biological fluids. That's what we took advantage of. I must say, there are a number of antibodies to scleroderma. We have demonstrated the diagnostic capabilities of quantum dots using the example of two of them. Antigens to autoantibodies were applied to the surface of polymer microspheres containing quantum dots of a given color (each antigen corresponded to its own microsphere color). The testing mixture, in addition to microspheres, also contained secondary antibodies associated with the signal fluorophore. Next, a sample was added to the mixture, and if it contained the desired autoantibody, a microsphere – autoantibody –signal fluorophore complex was formed in the mixture. In essence, the autoantibody acted as a linker binding a microsphere of a certain color to a signal fluorophore. And then, with the help of flow cytometry, we analyzed these microspheres. The appearance of a simultaneous signal from the microsphere and the signal fluorophore indicated that binding had occurred, and a complex was formed on the surface of the microsphere, including secondary antibodies with the signal fluorophore. At this moment, microsphere crystals and a signal fluorophore, which was associated with a secondary antibody, actually shone. The simultaneous appearance of both signals shows that there is a detectable target in the mixture – an autoantibody, which is a marker of the disease. This is a classic "sandwich" method of registration, when we have two recognizing molecules. We have demonstrated the possibility of simultaneous analysis of several markers, which suggests a high reliability of diagnosis and the possibility of creating drugs to detect the disease at the earliest stage.
What is the advantage of the diagnostic method you have developed using quantum dots over other methods that also use nanoparticles?– The use of even the most accurate methods is limited by any factors.
For example, Luminex devices based on the use of so–called "liquid microchips" - microspheres, spectrally encoded with organic dyes of two colors, are now becoming increasingly widespread. Luminex devices use two lasers, the number of possible codes is about 100. The use of quantum dots for spectral coding allows us to limit ourselves to one laser, and the number of recognized codes can be significantly increased. However, it is very problematic to use quantum dots in existing devices, since they have different properties than those of commonly used organic fluorophores. New devices are needed that will be able to detect a new type of fluorophores (in particular, the conditions of their excitation) and will have special systems for recording and processing the received data, etc. We are currently working on such devices.
How does the scientific community assess your developments on quantum dots?– I can only note that we are developing these areas within the framework of Russian and international projects with the participation of other scientific groups from Moscow and St. Petersburg, as well as scientists from France, Belarus, Germany, Ireland, Spain.
For example, the diagnosis of systemic sclerosis was carried out in a hospital in Reims (France). The diagnostic results were examined at the University of Reims: the reliability of the definition of the disease is close to 100 percent. We are planning to start joint research on cancer diagnostics with the N. N. Blokhin Russian Cancer Research Center of the Russian Academy of Medical Sciences.
What are the future plans of your research group?– One of the priorities of our institute is the development of systems that include quantum dots and biological molecules.
As part of this direction, we are currently working on creating a hybrid system based on bacteriorhodopsin. In particular, under a grant from the Russian Foundation for Basic Research, we are working together with the staff of the Department of Biophysics of Lomonosov Moscow State University on a project called "Nanobiotechnological hybrid materials based on bacteriorhodopsin and quantum dots for biosensory, optoelectronics and energy conversion". Already the first results are very promising.
We are also developing an approach based on the effect of resonant energy transfer, the so-called FRET format. The use of quantum dots in the FRET format can significantly reduce the noise level and, consequently, increase the sensitivity and reliability of detection. We were able to demonstrate this with the example of one diagnostic system.
Our research is carried out in close cooperation with scientists working in other fields, with colleagues from other countries. This makes it possible to dramatically accelerate the receipt of scientific results, solutions, and stimulates the development of new technologies.
Portal "Eternal youth" http://vechnayamolodost.ru02.10.2009