Latchezar Avramov

Bulgarian Academy of Sciences | BAS · Emil Djakov Institute of Electronics

Regretfully, because of her sudden demise, Assoc. Prof. Ekaterina Borisova is no longer amongst us. COVID-19 pulled away a brilliant scientist during the peak of her scientific career (see Fig. 1). All authors would like to express deepest condolences and sincere support to her family, friends, relatives and colleagues! We, therefore, rightfully co...

The present review paper aims to summarize our recent experience in research and development of new phthalocyanine complexes and investigations of the main photophysical, photochemical and photobiological properties which are related to antimicrobial photodynamic therapy (aPDT) as alternative method for inactivation of the resistant pathogens. The...

This paper reports on the production of Ag nanoparticles (AgNPs) in a water solution based on a two-phase pulsed laser procedure in view of therapeutic ophthalmological applications requiring AgNPs size of ≤10 nm with a narrow size distribution. Nanoparticles of this size scale are capable of penetrating the complex ocular barriers, thus ensuring e...

Endogenous fluorescence measurements using UV-VIS excitation wavelengths revealed a variety of natural fluorophores, including the amino acids tyrosine and tryptophan, coenzymes – NADH and flavin, collagen and elastin. Deep minima in the tumor fluorescence signals were observed in the region 540 – 575 nm related to re-absorption of hemoglobin. Such...

The use of polarized light for biomedical diagnostics of skin and mucosa has already a long history. Prior studies have shown a contrast enhancement of the polarimetric values and in images of cancerous and healthy zones tissues. In the present study, reflectance-geometry polarization measurements were made with gastrointestinal tissue (GIT) sample...

Porphyrins used as photosensitizers are accumulated selectively in glioblastoma cells due to the latter heme metabolism disorders and could be used effectively for intraoperative fluorescence staining of the tumor formation and differentiation from normal brain parenchyma. The aim of this work was to investigate the photodynamic properties of 5-ALA...

In the current study, an excitation laser source emitting at 785 nm (100 mW, CW) was used to obtain ex vivo fluorescence of endogenous melanin in pigmented skin with benign, dysplastic and malignant cutaneous lesions. The samples were obtained after surgical removal during standard excision procedure and split for spectral analysis and histological...

The genus Tribulus L. (Zygophyllaceae) includes 12 species, the most important of which is Tribulus terrestris L. This annual herb grows in temperate and tropical climates, and has a rich chemical composition of biologically active substances and chemical elements. Medicinal plants, and the phytopreparations obtained from them, are becoming more an...

Medicinal plants and phytopreparations (herbal medicinal products) obtained from them are successfully used for the treatment of human diseases. The therapeutic effect of the presence in them of a variety of natural compounds and biologically important trace elements, especially in higher concentration concentrates in higher doses. The elemental co...

A newly developed with the participation of the authors device for "optical biopsy" is described. The method involves recording the fluorescent and reflective spectra of human skin for early diagnosis of skin diseases. The diagnosis is based on the different response of diseased and healthy cells to radiation in certain spectral regions. System and...

This work reports on the production of Ag nanoparticles (AgNPs) in water solution based upon two-phase pulsed laser procedure for ophthalmological therapeutic approaches. In this case, the AgNPs should be less then 10 nm and have a narrow size distribution. Nanoparticles of this sized-scale are capable to penetrate the complex ocular barriers, ensu...

Ag- and Cu- doped aluminium oxide coatings were deposited by magnetron sputtering and their structure and composition were analyzed by means of scanning electron microscopy (SEM) and photoelectron spectroscopy (XPS). The coatings’ antimicrobial properties and efficiency against representative bacterial strains of Gram-positive, Gramnegative bacteri...

In this paper, we describe the antibacterial action of Ag-doped Al 2 O 3 nanolayers deposited by RF reactive magnetron sputtering on stainless-steel surgical and microsurgical instruments. Synthesizing Ag/Al 2 O 3 protective coatings is necessary for suppressing the infections caused by pathogenic microorganisms following the application of surgica...

The antibacterial action of Ag-doped Al 2 O 3 nanolayers, deposited by RF reactive magnetron sputtering on hard contact lenses, was established. Synthesis of Ag/Al 2 O 3 protective coatings is necessary for suppressing the infections caused by pathogenic microorganisms following the placement of hard contact lenses. The chemical composition, morpho...

Fluorescence spectroscopy is a sensitive, fast and non-invasive tool for a diagnostics of cancerous gastrointestinal lesions. It could be applied for in situ detection of tumours during primary endoscopic observations or as add-on measurement modality during microscopic observations of tissue histology slides for their initial or retrospective diag...

The effect of Ag-doped aluminium oxide coatings deposited by magnetron sputtering method on the antibacterial efficiency against Gram-positive, Gram-negative bacteria and fungi has been investigated. The structure and composition of coatings were analysed by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), ph...

The paper reports on antibacterial and antifungal properties of Ag‐doped Al2O3 nanolayers deposited by RF reactive magnetron sputtering on glass ocular prostheses. The study is provoked by the need of suppressing the infections caused by pathogenic microorganisms following the placement of ocular prostheses. This brings about the idea of forming pr...

This paper presents an experimental approach we have developed to measuring the radial intensity distribution of the cw laser light backscattered from highly scattering media. The experimental results obtained are in good agreement with the theoretical expressions we have obtained formerly describing the peculiarities of this distribution. The appr...

The combination of chitosan (Ch) and hydroxyapatite (HAp) materials for creation of biomimetic matrices suitable for 3D support in tissue engineering is widely used due to its components’ good biocompatibility and non-toxic characteristics. In this paper, we present preliminary experimental results on synthesizing Ch/HAp thin composite films and ir...

The sensitivity of the autofluorescence spectroscopy for morphological and biochemical tissue alterations has been implemented as a “red flag” technique for detection of gastrointestinal tumours. Although this modality has proven beneficial, especially for less experienced physicians, the full capacity of the autofluorescence spectroscopy as diagno...

The detection of early gastric cancer that often develops asymptomatically is crucial for improving patient survival. The photodynamic diagnosis (PDD) of gastric cancer using 5-aminolevulinic acid/protoporphyrin IX (5-ALA/PpIX) has been reported in several studies. However, the selectivity of PDD of gastric tumor is poor with often false-positive r...

The paper presents analysis of hyperspectral images for human skin cancer pathologies diagnostics. Hyperspectral images data contained backscattered spectra of normal skin and tumors. Analysis of hyperspectral images provided information about hemoglobin and melanin content for the differentiation of malignant and benign skin neoplasms based on tis...

The present work reports on the investigation of the possible influence of insulin on the photodynamic effect of the photosensitizer radachlorin on four cell lines: HepG2, HT-29, BJ and BALB/3T3. For a quantitative comparison, the insulin effect on the standard chemotherapy drug methotrexate is also measured. The results show that the EC(Formula pr...

Tissue-like phantoms are important tools in studying light propagation and scattering in biological tissues and in the development, testing and calibration of novel optical diagnostic and therapeutic methods and instruments. This motivates the interest in characterizing the optical properties of tissue-simulating turbid media. In the present work,...

Experimental measurements and theoretical description have been performed of the spatial intensity distribution of the backward radiative response of tissue-like Intralipid-20% dilutions in distilled water irradiated by a collimated near-infrared cw laser beam. The investigations performed are a first step toward a complete estimation of the feasib...

Surface texturing of a thin film of chitosan is carried out for improving its biocompatibility characteristics for diverse tissue engineering applications. The goal of this study is to develop chitosan-based films for cell culture applications by fs laser-assisted modification. Chitosan has the potential to accelerate the reformation of connective...

Optical contrast formation by Ga⁺ ion implantation has been used for focused ion beam (FIB) writing of nano-scale optical patterns in tetrahedral amorphous carbon (ta-C). UV-vis optical spectroscopy results with Ga⁺ broad-beam ion implantation have shown a significant shift of the optical absorption edge to lower photon energies as obtained from op...

In our study we investigate the characteristic differences, with diagnostic meaning, in the synchronous fluorescence spectra (SFS) of cancerous and healthy colorectal tissues, ex vivo. The main observed fluorophores which fluorescence has a diagnostic meaning are tyrosine, tryptophan, NADH, FAD, collagen, elastin, and porphyrines. In the SFS of thr...

We report the development of an improved fluorescence technique for cancer diagnostics in the gastrointestinal tract. We investigate the fluorescence of ex vivo colorectal (cancerous and healthy) tissue samples using excitation-emission matrix (EEM) and synchronous fluorescence spectroscopy (SFS) steady-state approaches. The obtained results are pr...

Electrochemotherapy is an effective method for treatment of skin tumors. To monitor the effects of application of the electrochemotherapy autofluorescence spectra are taken from the lesion and surrounding healthy skin, prior to, immediately after treatment and at the control checkups. Patients are followed up at the first week after treatment and o...

In this study, we analyzed the time-depended scenario of stress response cascade preceding and accompanying brain hemorrhages in newborn rats using an interdisciplinary approach based on: a morphological analysis of brain tissues, coherent-domain optical technologies for visualization of the cerebral blood flow, monitoring of the cerebral oxygenati...

Intensive research in the area of photodynamic therapy (PDT) has been made in recent years revealing it as a promising method for the treatment of tumors and inactivation of pathogenic microorganisms. However, for a broader application of this therapy one major challenge, namely a significant improvement of the targeted drug delivery and uptake, st...

The human skin is a complex, multilayered and inhomogeneous organ with spatially varying optical properties. Analysis of cutaneous fluorescence spectra could be a very complicated task; therefore researchers apply complex mathematical tools for data evaluation, or try to find some specific approaches, that would simplify the spectral analysis. Sync...

We studied the level of blood oxygen saturation (SpO2) in the brain in newborn rats in the pre- and post-stroke periods, as well as the changes in cerebral blood flow and beta-arrestin-1 as a marker of hypoxic stress. Our results show that mild hypoxia precedes the stroke development and is associated with venous relaxation and decrease blood outfl...

In vivo and ex vivo point-by-point measurements of excitation-emission matrices (EEM) from skin tumours using linear polarizer and analyzer for excitation and emission light were carried out. The fluorescence spectra obtained reveal differences in spectral intensity, related to general attenuation, due to filtering effects of used polarizer/analyze...

The suggested technique is a subsequent stage for data obtaining from diffuse reflectance spectra and images of diseased tissue with a final aim of skin cancer diagnostics. Our previous work allows us to extract patterns for some types of skin cancer, as a ratio between spectra, obtained from healthy and diseased tissue in the range of 380 – 780 nm...

Excitation-emission matrices were used for detection of the autofluorescence properties of surgically excised normal and cancerous mucosa of lower gastrointestinal tract tissues (colon and rectum carcinoma). Linear polarization of the excitation and emission fluorescence light was additionally applied to evaluate the influence of anisotropic fluoro...

In this work, extended investigations are performed of the extinction coefficient of Intralipid-20% dilutions in distilled water depending on the Intralipid concentration, for laser radiation wavelengths in the red and near-infrared regions covering the so-called tissue optical window. The extinction is measured by using an approach we have develop...

The experimental investigations on different aspects of optical tomography require the knowledge of the optical parameters of tissues and tissue-like phantoms in order to unambiguously interpret the experimental data and specify characteristic inhomogeneities in tissue diagnostics. The main optical parameters of interest are the absorption coeffici...

Wine and brandies are multicomponent systems and conventional fluorescence techniques, relying on recording of single emission or excitation spectra, are often insufficient. In such cases synchronous fluorescence spectra can be used for revealing the potential of the fluorescence techniques. The technique is based on simultaneously scanning of the...

Autofluorescence has been proven to be a very sensitive, accurate, noninvasive method for detection of early pathological changes in tissues. This optical method has the potential to provide a real-time diagnosis of different benign, dysplastic and malignant tissue pathologies. We obtain tissue samples after surgical excision of preliminary clinica...

In this report we will present our recent investigations of the fluorescence properties of lower part gastrointestinal tissues using excitation-emission matrix and synchronous fluorescence spectroscopy measurement modalities. The spectral peculiarities observed will be discussed and the endogenous sources of the fluorescence signal will be addresse...

Synchronous autofluorescence spectroscopy (SFS) using excitation in the range of 280-440 nm and varying delta lambda from 10 to 200 nm were applied on lower GIT tumours obtained after surgical excision. Due to the improved efficiency of SFS for the signals, where the delta lambda is optimal, we could obtain higher spectral resolution for the detect...

For the DRS measurements of skin benign, dysplastic and malignant lesions in vivo we applied halogen lamp (LS-1, OceanOptics Inc, Dunedin, Fl, USA) as a continuous light source in the region of 400-900 nm, optical probe (6+1 fibers) for the delivery of illumination and diffuse reflected light from the skin investigated and microspectrometer USB4000...

We present fluorescence data obtained from normal and cancerous gastrointestinal tissues - oesophageal and colon lesions, taken up to two hours after surgical removal with and without exogenous fluorescent markers applied. The major goal was to acquire information on the differences between the fluorescent spectra of normal and pathological tissues...

The possibility is studied to develop a straightforward analytical approach to the determination of the optical properties of liquid turbid media having forward-peaked scattering indicatrices. The approach is based on investigating the in-depth behavior of the radius and the axial intensity of a laser radiation beam propagating through the turbid m...

We investigated more than 500 clinical cases to receive the spectral properties of basal cell (136 patients) and squamous cell carcinoma (28), malignant melanoma (41) and different cutaneous dysplastic and benign cutaneous lesions. Excitation at 365, 385 and 405 nm using LEDs sources is applied to obtain autofluorescence spectra, and broad-band ill...

Used polarized light for fluorescence excitation one could obtain response related to the anisotropy features of extracellular matrix. The fluorophore anisotropy is attenuated during lesions' growth and level of such decrease could be correlated with the stage of tumor development. Our preliminary investigations are based on in vivo point-by-point...

The Gram-negative Actinobacillus actinomycetemcomitans and Fusobacterium nucleatum are major causative agents of aggressive periodontal disease. Due to increase in the number of antibiotic-resistant bacteria, antimicrobial Photodynamic therapy (aPDT) seems to be a plausible alternative. In the present work, photosensitization was performed on Gram-...

The limitations of standard endoscopy for detection and evaluation of cancerous changes in the gastrointestinal tract (GIT) are significant challenges and initiate development of new diagnostic modalities. Therefore many spectral and optical techniques are applied recently into the clinical practice for obtaining qualitatively and quantitatively ne...