We have participated in development of two types of nanostructures with great potential for applications in biomedical imaging and therapy: The first type involves lanthanide-doped fluoride nanocrystals with polymer coatings and feature upconversion fluorescence, the other are derived from animal erythrocytes and contain an infrared absorbing dye indocyanine green.
We have participated in research of nanoparticles which exhibit upconversion fluorescence (UCF; e.g., Yb3+,Tm3+:NaYF4). Such nanoparticles have great potential for diagnostic imaging in medicine and new approaches for cell-specific therapy. We have demonstrated that For one dedicated amphiphilic coating (TPGS) improves UCF performance and at the same time offers very good protection against nanoparticle dissolution in aqueous media, thus sucsessfully preventing acute cytotoxicity. Such properties are critically important with regard to biocompatibility and suitability of such nanostructures for biomedical applications. (Collaboration with Department for Materials Synthesis and Department for Inorganic Chemistry and Technology, IJS, and Medical University of Graz, Austria).
Our three-dimensional model of light transport in spatially heterogeneous optically scattering structures (Monte Carlo) was used for analysis of interaction between intense laser pulses and cutaneous blood vessels containing novel nanostructures with different sizes. These nanostructures were engineered from animal erythrocytes and contained indocyanine green, an FDA approved infrared absorbing dye. Such biocompatible and safe nanoprobes hold great potential for diagnostic imaging in small animals and possibly human patients. (Collaboration with Beckman Laser Institute and Medical Clinic, University of California at Irvine, and University of California at Riverside, USA).
We have continued with development of novel biomedical applications based on pulsed photo-thermal radiometry (i.e., time-resolved measurements of laser-induced infrared emission) and diffuse reflectance spectroscopy. By combining these experimental techniques with inverse analysis utilizing a numerical model of light transport in strongly scattering biological tissues (multi-dimensional optimization) we have developed a unique approach for noninvasive assessment of structure and composition of human skin in vivo. The described methodology was tested by subtle manipulation of healthy human skin, e.g. by using a blood-pressure cuff.
The same approach was applied also to characterization of hemodynamics in human volunteers with incidentally obtained bruises (hematomas). The improved understanding of bruise dynamics (in terms of, e.g., hemoglobin mass diffusion coefficient and biochemical decomposition rate) and derived methodology could enable significantly more accurate determination of the time of injury in forensic investigations. Both studies were supported by equipment loan from Fotona, d.o.o., Ljubljana.
We have performed an experimental study of hyperthermic lipolysis using an Nd:YAG laser (wavelength 1064 nm) and forced air cooling in a porcine model ex vivo. The results show that varying the irradiation power density and duration, as well as the cooling power, enables versatile control over the amplitude and shape of the subsurface temperature distribution. The developed numerical model and improved understanding provide a good basis for further improvement of laser lipolysis treatment.