Katarina Radulović’s research while affiliated with University of Belgrade – Faculty of Technology and Metallurgy and other places

Adsorption-based plasmonic refractometric biosensors have a great potential for applications in environmental protection, medicine and industry, as they are highly sensitive detectors of a broad range of biological analytes. Their response is determined by the temporal change of the effective refractive index (RI) of the sensing area caused by biomolecules adsorption. Many biomolecules undergo a structural transformation upon a contact with the sensing surface, causing a change in their affinity towards adsorption sites. Different forms of molecules also have different RI, which affects the sensing area effective RI. Adsorption leads to depletion of biomolecules from the sample, affecting the instantaneous rate of change of the number of adsorbed molecules, and thus also the effective RI change. Therefore, it is necessary to investigate the influence of these phenomena on the sensor response. In this work, we derive the first mathematical model that describes the change in the effective RI of the sensing area by taking into account reversible adsorption, structural transformation of adsorbed biomolecules, and sample depletion. We then use that model to analyze influences of these processes on the RI change by studying an exemplary protein adsorption. The results have shown the significant influence of these processes on the sensing area effective RI, and thus on the sensor time response, particularly when extremely low biomolecule concentrations are to be detected. The use of the presented model prevents erroneous interpretation of measurement results in ultrasensitive plasmonic biosensors, which may occur if using models that do not take into account structural transformation and analyte depletion.

This study was carried out at the Danube River and its tributaries during the Joint Danube Survey 4 (JDS4) expedition. Three freshwater benthic species were used to estimate the quantity of microplastics (MPs): Corbicula spp., Limnodrilus hoffmeisteri (Claparede, 1862), and Polypedilum nubeculosum (Meigen, 1804). Following the kick and sweep technique, individuals were sampled using a hand net or dredge. In order to estimate the number of MP particles/individual particles/g wet body mass, the body mass and total length of all specimens were measured. Alkaline (Corbicula spp. and L. hoffmaisteri) and enzymatic (P. nubeculosum) protocols were performed for tissue degradation. All samples were filtered through glass microfiber filters (mesh size 0.5 µm). The particles were photographed, measured, and counted. A total of 1904, 169, and 204 MPs were isolated from Corbicula spp., L. hoffmaisteri, and P. nubeculosum, respectively. To confirm the chemical composition of isolated MPs, a subsample of 46 particles of the fragmented particles from 14 sampling sites was analysed via µ-ATR-FTIR spectroscopy analysis. The particles were characterised as polycarbonate (PC), polyethylene terephthalate (PET), polypropylene–polyethylene copolymer (PP-PE), nylon (polyamide-PA) and cellophane, with the domination of PET.

Laser-induced graphene (LIG) possesses desirable properties for numerous applications. However, LIG formation on biocompatible substrates is needed to further augment the integration of LIG-based technologies into nanobiotechnology. Here, LIG formation on cross-linked sodium alginate is reported. The LIG is systematically investigated, providing a comprehensive understanding of the physicochemical characteristics of the material. Raman spectroscopy, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques confirm the successful generation of oxidized graphene on the surface of cross-linked sodium alginate. The influence of laser parameters and the amount of crosslinker incorporated into the alginate substrate is explored, revealing that lower laser speed, higher resolution, and increased CaCl2 content leads to LIG with lower electrical resistance. These findings could have significant implications for the fabrication of LIG on alginate with tailored conductive properties, but they could also play a guiding role for LIG formation on other biocompatible substrates.

The employment of compounds obtained from natural sources to produce adsorbents and their application in the elimination of antibiotics from industrial effluents have gained significant attention because of their low production cost and sustainability. Herein, chitosan (biopolymer) and smectite (abundant clay mineral) were used for the low-cost and eco-friendly synthesis of a new type of adsorbent. A low-energy-consumption hydrothermal process was applied to the synthesis of the chitosan-derived carbon–smectite nanocomposite with cobalt (H_Co/C-S). The produced nanocomposite was characterized using elemental analysis, ICP-OES, XRPD, low-temperature N2 adsorption–desorption isotherms, FTIR analysis, and point of zero charge. H_Co/C-S (SBET = 0.73 m² g⁻¹, d001 = 1.40 nm, pHPZC = 5.3) was evaluated as a ciprofloxacin adsorbent in aqueous solution. Experimental data were fitted with different kinetic models and interpreted by selected adsorption isotherms. The pseudo-second-order model was found to be the most appropriate, while ciprofloxacin adsorption onto H_Co/C-S was best described by the Redlich–Peterson isotherm (R² = 0.985). The maximum adsorption capacity of H_Co/C-S, according to the Langmuir isotherm (R² = 0.977), was 72.3 mg g⁻¹. Desorption and thermodynamic studies were performed. The obtained results indicated that the new hierarchically designed H_Co/C-S has promising potential to be further tested for application in real wastewater treatment.