Interaction of DNA with Globular Proteins of Different Structures in Thin Films on Substrates of Monocrystalline Silicon

The two-component films of mixtures of DNA (from calf thymus) with different proteins: rabbit immunoglobulin (IgG), methemoglobin (MHB) and human serum albumin (HSA) were studied on single-crystal silicon substrates by the method of fluorescence spectroscopy. Registration of fluorescence spectra was performed by λex=260 and 280 nm in the range 340-380 nm. To prepare films the spincoating method was used. Solutions deposited on the substrate contained the small concentrations of proteins 10-9 - 10-15 M at the same quantity of DNA. Shape dependencies of the fluorescence intensity versus concentration differ markedly for each of the used proteins. The decreasing concentration of protein in the film is accompanied by a significant increase of the integrated fluorescence intensity (in comparison with the concentration of 10-9 M) for films of DNA-HSA in 2.5 and 5 times (10-13 and 10-15 M HSA), for films of DNA-IgG in 4.6 and 15.9 times (10-11 and 10-13 M IgG), for films of DNA-MHB in 3.4 times (10-11 M MHB). The single-component films of proteins was studied as control samples whose properties noticeably differ from the properties of DNA-protein systems. The specificity of the fluorescent characteristics of DNA-protein films for proteins of different structure and their different concentrations could be used as the basis for developing biosensor systems.