Metal–organic frameworks (MOFs) represent an emerging class of porous crystalline materials with highly customizable periodic structures, offering opportunities for innovation in areas such as sustainable energy and advanced healthcare. Luminescent MOFs are gaining attention as key nanomaterials in photonics due to their tunable optical properties, including controllable emission wavelengths and excellent photostability. Among them, the zirconium-based archetypal UiO-66 stands out for its structural robustness, though its optical properties remain largely unexplored.

In our research, emphasis is placed on understanding the mechanisms underlying its luminescence, especially its photophysical behaviour under thermal treatments and environmental conditions, such as hydration. The optical properties of UiO-66 in powdered form were systematically investigated using steady-state and nanosecond time-resolved photoluminescence (PL) spectroscopy.

For the first time, upon laser excitation at 4.43 eV, the PL spectra of UiO-66 revealed a double-peak emission band comprising two overlapping components, peaking at 2.8 eV and 3.2 eV, with lifetimes of 1.5 ns and 5 ns, respectively. In contrast, UiO-66 in aqueous solution exhibited a single emission peak at 3.1 eV with a lifetime of 5 ns, demonstrating the material’s sensitivity to environmental factors, as water molecules suppress the lower-energy emission transition.
Temperature-dependent effects included a decrease in emission intensity coupled with a notable increase in lifetime as the temperature rose. The radiative rate of the involved transitions was estimated and found to vary with temperature, suggesting possible alterations in the electronic configuration.

Based on these findings, we developed a model to illustrate the photophysical processes occurring within the ligand–metal complex of UiO-66, involving an excitation transfer (ET) from the light-absorbing linker to the zirconium metal node, with ET efficiency strongly affected by external environmental factors.
This study deepens our understanding of the photophysical behaviour of MOFs and paves the way for the tailored design of UiO-66 in advanced optical technologies.

Abstract:

Introduction:
Copper oxide (CuO) nanomaterials have garnered significant attention due to their unique structural, optical, and electrical properties, making them highly suitable for gas sensing applications. As a p-type semiconductor with a narrow band gap, CuO exhibits strong sensitivity and selectivity toward various toxic and combustible gases, including hydrogen sulfide (H₂S), carbon monoxide (CO), and ammonia (NH₃). The present study focuses on the synthesis, characterization, and gas sensing performance of CuO nanomaterials fabricated via a simple and cost-effective route.

Methods:
CuO nanomaterials were synthesized using a sol-gel method followed by calcination at controlled temperatures. Structural and morphological characteristics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). Optical properties were examined through UV–Vis spectroscopy. Gas sensing performance was evaluated in a custom-built chamber using different concentrations of target gases at varying operating temperatures.

Results:
XRD analysis confirmed the formation of monoclinic-phase CuO with high crystallinity. SEM and TEM images revealed the nanostructured nature of the materials, displaying spherical and rod-like morphologies depending on synthesis conditions. UV–Vis spectra indicated strong absorption in the visible region with an estimated band gap of ~1.8 eV. Gas sensing studies demonstrated high sensitivity, rapid response and recovery times, and good selectivity toward H₂S at an optimal operating temperature of 200°C. The sensor also showed stable performance over multiple cycles and good repeatability.

Conclusions:
The synthesized CuO nanomaterials exhibit promising potential as gas sensors due to their favorable structural and sensing properties. These findings underscore the suitability of CuO-based nanostructures for real-time environmental monitoring and industrial safety applications.

Nanostructured materials have attracted a great deal of interest in recent years and their number of proposed applicationshas significantly increased. Their use in biological environments has become a ‘hot’ topic due to the lack of understanding of the complex interplay between nanoparticles distribution and biological exploits. Several
potential applications have in fact been proposed, such as drug delivery, cancer therapy, localized heating, and biological
probes. All these uses are supported by scientific reports and papers that assess nanomaterials' viabilities
and outstanding properties. However, when the bridge from proof of concept to real-world product needs to
be crossed, as human beings are involved, the requirements for material characterization become very stringent.
Without thorough characterization, in fact, it is not possible to check nanoparticles' reproducibility and hence
assess that they will behave in the same way with respect to the desired application, as well as their biocompatibility.
In this talk, we will focus on carbon dots, i.e., carbon-based almost 0-d (the size of a few nm) nanostructures. Carbon
dots can be produced in different ways, in some cases beginning with naturally derived chemicals like citric acid and
urea. After providing a brief description of a few routes that can be used to produce carbon dots, we will focus on their structural composition
in order to establish a strong correlation between their chemical features and physiochemical properties.

The integration of sustainable materials into high-performance energy storage and conversion systems is essential for driving the successful transition to green resource use. In this work, we explore the use of rice husk (RH), an abundant and underutilized agricultural byproduct, as a renewable precursor for synthesizing carbon-based materials suitable for energy storage applications. Two types of materials were derived from RH: carbon aerogels (CAs) and graphene quantum dots (GQDs). The CAs were synthesized through a multi-step process involving two-stage chemical pretreatment to remove lignin, hemicellulose, and silica, followed by gelation, drying, and carbonization. In parallel, GQDs were produced using a simple, solvent-free ball milling method. Both materials were thoroughly characterized using a range of analytical techniques to assess their morphological and structural properties. Their electrochemical performance was then evaluated in lithium-ion batteries and supercapacitors. The GQDs exhibited capacitive behavior with ion intercalation and surface charge accumulation, as demonstrated by cyclic voltammetry and galvanostatic cycling. However, their long-term performance was limited, likely due to poor contact with the electrode matrix and current collector—an issue that may be resolved through optimized formulation strategies. In contrast, the CAs displayed excellent cycling stability, retaining up to 81.2% of their initial capacitance after 10,000 charge–discharge cycles. These findings underscore the potential of rice husk-derived carbon materials as low-cost, sustainable alternatives for the development of efficient and durable energy storage devices.

Advancing electrochemical sensors requires materials that offer both a high surface area and tailored surface properties. In this study, we developed mesoporous gold–silver–copper (AuAgCu) alloy films with a finely tuned composition and internal strain to boost their electrocatalytic activity. These multimetallic films were synthesized using a soft-template approach, in which self-assembled polymer micelles guided the formation of well-defined porous architectures on gold-sputtered glass substrates. By adjusting the relative amounts of gold, silver, and copper during fabrication, we achieved a balanced alloy structure that promotes defect formation and enhances electron transport. Among the compositions tested, the Au₀.₆Ag₀.₂Cu₀.₂ alloy exhibited the most favorable electrochemical performance. Characterization techniques including transmission electron microscopy and X-ray photoelectron spectroscopy confirmed a uniform alloy distribution and the presence of crystal imperfections—such as twin boundaries—that served as additional active sites. Based on follow-up analysis of chronoamperometric data from our ACS Nano-accepted study, the final limit of detection (LOD) for mesoporous AuAgCu films was determined to be 40.1 µM, significantly outperforming mesoporous Au (104 µM) and AuAg (447 µM) under identical, non-enzymatic sensing conditions. Notably, this enhancement was achieved without amplification strategies, photopatterning, or covalent functionalization. These features enabled effective detection of model analytes such as glucose, suggesting strong potential for biosensing and diagnostic applications. In conclusion, this work presents a practical strategy for designing mesoporous multimetallic films with enhanced surface properties and offers valuable insight into atomic-scale tuning of material compositions for improved performance in real-world sensing systems.

The electronic structure of the materials forming nanostructures plays a key role during chemical enhancement. It determines the excitation energy of the non-equilibrium charge carriers (hot electrons and holes) and their interaction with various functional groups of the organic molecules under investigation [1].

In the present work we discuss the interaction of an aqueous solution of tryptophan with thin polycrystalline films made from the intermetallic compounds Ag₃In and AgIn₂. Thin films with the required compositions (Ag/In ratios of 3:1 and 1:2) were prepared by layer-by-layer deposition alternating between very thin films of silver and indium in one vacuum cycle, and the compounds were formed through a self-occurring solid-state reaction. The chemical and phase compositions of the thin films, analyzed by energy-dispersive X-ray microanalysis and X-ray diffraction, confirmed the formation of intermetallic Ag₃In and AgIn₂ compounds.

The electronic states in the Ag-In nanostructures were analyzed by spectroscopic ellipsometry and using density functional theory calculations. The results show that the increased In content in the thin AgIn₂ films led to an increase in the energy for interband transitions from the Ag 4d electronic state to the Fermi level and to a respective increase in the energy and mobility of the generated hot holes. As a result of this, there was a decrease in the intensity of the peak at 1055 cm^-1, corresponding to the NH₂ group, and an enhancement of the peaks caused by the pyrrole and indole rings (situated at 1093, 1229, 1447 and 1490 cm^-1) in the surface enhancement Raman spectra of tryptophan.

These results show that by changing the electronic structure of plasmonic nanostructures, the orientation of the analyzed molecules and the chemical enhancement of the desired functional groups in them can be controlled.

[1]. Todorov, R. and Hristova-Vasileva, T., 2025. ACS Omega 2025, 10, 19, 19243–19255.

[2]. Todorov, R., Hristova-Vasileva, T., Katrova, V. and Atanasova, A., 2023. ACS Omega, 8(16), 14321-14341.

Multidrug-resistant (MDR) bacteria pose a serious threat to global health, requiring new classes of antimicrobial agents. This study presents the development of α-helical antimicrobial peptides (AMPs) as nanoscale molecular tools, designed through a structure-based approach guided by the Main Mechanical Forces (MMFs) method. Amphipathic helical conformations can be predicted and stabilized using MMF-guided design, improving membrane interaction and antimicrobial effectiveness. Starting from the MMF-predicted structure of peptide HT2, amphipathic peptides were designed by aligning hydrophobic and cationic residues on opposite helix faces to target and disrupt bacterial membranes. Three analogues were developed: K1 (Arg1→Lys), K1-4-5 (Arg1/4/5→Lys), and K1-4-5-A, a covalently modified version of K1-4-5 bearing allomaltol as a terminal metal-chelating group. All peptides were synthesized via Fmoc-based solid-phase peptide synthesis, and FT-IR was used to confirm their structural integrity. The structures were also confirmed by ESI+ MS and elemental analysis. The antimicrobial efficacy was assessed against Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae, tested both with the individual peptides and in combination with allomaltol to explore potential synergistic effects. HT2 exhibited strong activity against S. aureus (MIC = 18.75 μM), moderate activity against E. coli (75 μM), and limited efficacy against K. pneumoniae (150 μM). In contrast, K1 was inactive (MIC > 300 μM), highlighting the importance of the Arg1 guanidinium group. K1-4-5 retained partial activity, and its co-administration with allomaltol significantly improved MIC values against S. aureus and E. coli (37.5 μM), suggesting a synergistic effect. Notably, the modified peptide K1-4-5-A restored full activity against S. aureus (MIC = 18.75 μM), comparable to HT2. This work demonstrates how MMF-guided design enables the development of structurally optimized AMPs with dual antimicrobial mechanisms. The combination of membrane-disruptive properties and metal ion chelation offers a promising nanoscale strategy to fight MDR bacteria and develop next-generation nanomaterial-based therapeutics.

Introduction: Ethosomal gels are a novel drug delivery system that combines the benefits of gel with the unique properties of ethosomes for topical administration. Ethosomes are composed of phospholipids, nano vesicles with a high ethanol concentration (20-45%), and water, which enables them to penetrate the stratum corneum more effectively than other conventional formulations. This makes ethosomal gels an ideal platform for delivering a wide range of therapeutics, including both hydrophilic and lipophilic drugs, directly to the site of action on the skin.

Objectives: The incorporation of ethosomes into gel matrices enhances stability andcontrolled release while also providing ease of application and improved skin retention. Ethosomal gels have demonstrated great promise in the treatment of dermatological conditions such as psoriasis, fungal infections, and localized pain management.

Methods: Ethosomes were prepared using different concentrations of phospholipid PLH90, alcohol, propylene glycol, and carbopol and characterized by particle size, zeta potential, and entrapment efficiency. Furthermore, in vitro, in vivo, ex vivo, and pharmacokinetic studies were conducted.

Conclusion: The combination of ethosomal technology with gel systems can offer improved therapeutic efficacy, patient compliance, and enhanced skin bioavailability, making it a promising approach for topical drug delivery. It is advantageous to address the issue of frequent dosing caused by the shorter half-life of medications.

Quasi-two-dimensional (quasi-2D) perovskites are promising candidates for circularly polarized luminescence (CPL) materials and spin light-emitting diodes (LEDs), owing to their strong spin–orbit coupling (SOC), tunable chiral-inducing structures, and compatibility with device fabrication processes. However, achieving high dissymmetry factors and efficient spin-LED performance remains challenging because single chiral cation systems of quasi-2D perovskites suffer from limited chiral induction and poor phase tunability. In this work, we introduced a mixed-cation strategy by incorporating an achiral organic spacer, 2-phenoxyethanamine (POEA⁺), into quasi-2D perovskites based on a single chiral cation. The incorporation of POEA⁺ not only passivated defects and improved the optical properties of the perovskite films, but also enhanced chirality-induced spin selectivity (CISS) by promoting the formation of intermediate phases and facilitating a more efficient energy transfer process. As a result, the mixed-cation perovskite film exhibited a significantly enhanced CPL signal at 702 nm, with a maximum photoluminescence dissymmetry factor (g_lum) of 4 × 10⁻³ at room temperature. Furthermore, LEDs based on the optimized film demonstrated a high external quantum efficiency (EQE) of 4.22%. This work proposes an effective strategy to simultaneously enhance the chiroptical properties of quasi-2D perovskite and improve the quality of the films, which shows the great potential for future applications in chiroptoelectronics and spintronics.

Metal halide perovskite light-emitting diodes (PeLEDs) have emerged as promising emitters for visible light communication (VLC) applications owing to their excellent optoelectronic properties and cost-effective fabrication. While various strategies have been proposed to enhance PeLEDs’ modulation performance, their practical application in VLC systems remains at an early, demonstrative stage. A key challenge lies in imbalanced charge injection and interfacial defects, which severely limit the modulation bandwidth and VLC performance. Specifically, the potential of interfacial engineering in solving these issues remains underexplored. Herein, we propose a multifunctional interfacial modification strategy by employing zwitterionic betaine citrate (BC) to simultaneously passivate defects and achieve balanced charge injection. The BC molecules effectively coordinate with undercoordinated Pb²⁺ ions, reducing the trap state density, while their ionic interaction with PEDOT:PSS decreases the hole injection barrier. Additionally, the employed methanol solvent selectively removes insulating PSS, improving interfacial conductivity and morphology. The synergistic effects of improved charge injection, defect passivation and optimized interface morphology lead to reduced non-radiative losses and a significantly lower resistance–capacitance (RC) time constant, both of which are critical for enhancing VLC performance. Consequently, optimized devices achieve a modulation bandwidth of 4.9 MHz and a data rate of 55.56 Mbps, far exceeding those of control devices and representing the best performance reported to date for devices with comparable active areas. This work systematically investigates the role of interfacial engineering in VLC performance and offers a viable pathway toward high-speed PeLED-based VLC systems.