Ing. Markéta Šlapal Bařinková

Life science research has largely benefited from the use of nanoparticles (NPs), yet fundamental issues such as colloidal stability and control over NP size and shape affect NP properties and functions in biomedical applications. Here we show that including capping agents directly into zinc oxide (ZnO) NP synthesis can lead to better control of these properties and their enhanced functionality. A systematic study of the influence capping agents has on the physicochemical and antibacterial properties of ZnO NP synthesized using the microwave (MW)-assisted polyol method is presented. Primary NP size (10–20 nm) was controlled by zinc precursor concentration, and NP shape was influenced by capping agent type. Capping agents enabled control over the surface charge and water interaction properties of ZnO for further investigations involving bacteria. The superior antibacterial effect was observed using positively charged, hydrophilic HMTA-capped ZnO, yet negatively charged hydrophobic OA-capped ZnO still exhibited an antibacterial effect. These observations suggest different underlying mechanisms, and we discuss these differences with particular reference to the specific surface area of ZnO, and how this is key to bacteria-nanoparticle interactions. Appropriate selection of capping agents is crucial for the synthesis of potent ZnO NPs intended for antibacterial applications, specifically for combating resistance.

The combination of nanodiamonds with plasmonic metal particles is being explored for synergic effects that can enhance biosensing and antibacterial treatments, energy harvesting, photocatalysis, and quantum centres. Here we systematically investigate the formation and plasmonic properties of complexes assembled in colloidal mixtures of 20 nm gold or silver nanoparticles with 50 nm HPHT nanodiamonds, the surfaces of which are oxidized or hydrogenated. This approach provides nanocomplexes of well-defined particles with different surface chemistry and electrical conductivity. Nanoscale complexes are formed in each case, as shown by scanning electron microscopy and optical absorption spectra. The stable plasmonic frequency shows that the metal nanoparticles do not become aggregated and keep a few nm gap to nanodiamonds. The concentration dependence study reveals that the plasmonic effect can be significantly increased (up to 124 %) for lower concentrations of metal nanoparticles in the mixtures, whereas their higher concentrations reduce it, regardless of the type of nanodiamond or metal nanoparticle. Based on the experimental results and electromagnetic field-based simulations of the complexes, we discuss a model involving competing charge redistribution and plasmonic interference effects.

The current strategies in the development of Sb2Se3 thin film solar cells involve fabrication and optimization of superstrate and substrate device architectures, with the preferable choice for TiO2 and CdS heterojunction layers. For CdS-based superstrate cells, several studies reported the necessity to apply CdCl2 or other metal halide-based post-deposition treatment (PDT), highlighting improvement of CdS/Sb2Se3 device efficiency. However, the need, effect, and mechanism of such PDT are very often not described. Additionally, the fact that many groups have not succeeded in demonstrating its benefits suggests that this strategy is not straightforward, requiring a deeper understanding towards a more unified concept. The present study proposes an alternative approach to the challenging CdCl2 PDT of CdS in CdS/Sb2Se3 device, involving controllable Cl incorporation in CdS films by systematically varying the concentration of NH4Cl in the CBD precursor solution from 1 to 8 mM. Structural and electrical characterizations are correlated with advanced measurements of Scanning Kelvin Probe, surface photovoltage, and atomic force microscopy to understand the impact of Cl incorporation on the properties of CdS films and CdS/Sb2Se3 devices. The validity of Cl incorporation in the CdS lattice and interdiffusion processes at the CdS-Sb2Se3 interface is confirmed by secondary ion mass spectrometry analysis. It is demonstrated that incorporation of 1 mM of NH4Cl, as a Cl source in CBD CdS, can boost the PCE of CdS/Sb2Se3 by ∼20 %. With this approach, we offer new perspectives on the optimization methodology for Cl-based CdS/Sb2Se3 device processing and complementary understanding of the physiochemistry behind these processes.

Photoactive nanoparticles have recently gained a lot of attention as alternative antimicrobial agents since their antimicrobial properties can be enhanced by illumination. The stable and reproducible application of these conditions is crucial in order to assess the antimicrobial effect of nanoparticles, illumination and the combination of these conditions on cells. Furthermore, the reproducibility of cell growth data is also essential to avoid measurement variability influencing statistical analysis. In this work we designed custom 3D-printed laboratory accessory for a bioreactor that ensured stable illumination of cell suspensions and enabled reproducible growth curves under the same growth conditions. The reproducibility of measurements was tested on Escherichia coli bacteria grown under illumination, with the addition of commercial ZnO nanoparticles, and with the combination of both factors. All tests showed a notable improvement in the reproducibility of bacterial growth curves and standard deviation of the measured data reduced below the documented instrument precision.

The impedance spectroscopy method (AC f = 4–8 MHz at a constant amplitude of 1 V) and Pt-IDE sensors were used to detect and monitor different concentrations (103, 106, and 109 CFU/mL) of both live and dead bacteria cells (Escherichia coli and Staphylococcus aureus). The analysis of the impedance spectra shows the differences in resistance with increasing concentrations for both types of bacteria and the presence of characteristic changes in the frequency range 10–100 kHz. The presence of live bacteria led to a decrease in the impedance value compared to dead cells, and the value of Rs + Rct decreased about two times. © 2023 by the authors. Licensee MDPI, Basel, Switzerland.