Conjugates of plasmonic nanoparticles with biological macromolecules are important objects of interdisciplinary research. But the greatest potential have the applied research in the field of biomedicine and biotechnologies. The significant interest in the investigation of these objects is due to the fact that they represent a technological platform for designing new generation of nanosized biosensors capable of detecting biomolecular interactions at the level of individual molecules. Biological complexes based on plasmonic nanoparticles are multifunctional and can simultaneously be used for diagnostics and therapy, as well as for medical visualization and monitoring of treating malignant tissues. Moreover, these bioconjugates are low toxicity, which is of special importance in the case of their application for early diagnostics and complex therapy of oncological diseases.
The photodynamic method for tumor treatment based on laser irradiation of affected tissues is a promising approach to solution of these problems. An alternative to the photodynamic method is a method that has been developed in the last decade for the selective thermal action by laser radiation on malignant tumor affected tissues labeled with plasmonic nanoparticles. This method has been named “plasmon-resonant photothermal therapy” (PRPTT).
When using these therapeutic methods, it is of importance to properly select the radiation wavelength that must coincide with both the minimum absorption by hemoglobin, which ensures the deepest penetration of the radiation, and the plasmon absorption band of nanoparticles. When using tumor hyperthermia induced by the local overheating of oncological cells conjugated with nanoparticles, it is of special importance to ensure the selective action of laser radiation on an affected region without involving a healthy tissue. The possibility of the targeted action of radiation on tumor cells alone without damaging healthy tissues is realized by introducing aptamer–nanoparticle bioconjugates into organism. Such bioconjugates, in the form of plasmonic nanoparticles with synthetic oligonucleotides — DNA-aptamers adsorbed on their surface provide functionalization of these complexes and, as a consequence, precisely addressed delivery of the conjugates to a biological target.
So, the research the thermal effects associated with the action of the laser radiation on bioconjugates with plasmonic nanoparticles selective immobilized on the tumors provide important interdisciplinary aim.
We showed computational results for microsecond pulses and lasers with nanosecond pulse duration that are most common and are frequently used in medical practice. The selectivity of the laser hyperthermia of malignant cells with no damage to healthy tissue isprovided by the use of novel gold nanoparticle–DNA aptamer bioconjugates, in which aptamer sizes are specially selected. Therewith, the application of pulsed laser radiation under the conditions of nanoparticle contact with membranes of malignant cells alone via an aptamer makes a fundamental contribution to the localization of the action. Pulses with both micro- and nanosecond durations are optimum from the point of view of the regime of thermal action on a cell membrane, provided that the radiation wavelength coincides with the position of the plasmon absorption band of nanoparticles. Microsecond laser pulses are preferred for use in systems with a larger gap (several tens of nanometers) between a nanoparticle and a membrane. The use of continuous laser radiation results in loss of the localization of the action on a cellular membrane because of the fast temperature relaxation of the region being heated and the formation of a wide uniform temperature field, which covers both malignant and healthy cells. To increase the depth of laser radiation penetration into tissues, one should use biologically inert nanoparticles with plasmon resonance in a range of 600−800 nm, in which hemoglobin is relatively transparent. Extended gold ellipsoids and nanorods, core/shell particles composed of cores with high refractive indices and gold shells are, in particular, among these nanoparticles.