Since their initial discovery in 2003, carbon quantum dots (CDs) have attracted significant attention due to their unique optical properties and potential biomedical applications. This review critically examines the past 20 years of research on CDs, with a particular focus on cytotoxicity studies from the last decade. CDs, typically less than 10 nm in size, have been synthesized from various organic and inorganic precursors using multiple methods, including hydrothermal, microwave, and chemical reduction techniques. Their properties can be finely tuned by modifying synthesis parameters and incorporating dopants. The preliminary studies on the biological effects of CDs were published in 2013, highlighting their antibacterial properties and low toxicity in certain contexts. Subsequent research has explored their bioactivity, including their application in drug delivery, bioimaging, and photothermal therapy. However, the cytotoxicity of CDs remains a critical area of investigation. Further studies have demonstrated that surface functional groups, charge, concentration, and size significantly influence their interaction with biological systems. For instance, CDs with positive surface charges exhibit higher cellular uptake and greater cytotoxicity compared to their negatively charged counterparts. In vivo studies utilizing animal models such as zebrafish, mice, and planarians have provided valuable insights into the potential toxicological impacts of CDs. The results indicate that while CDs generally exhibit low toxicity at certain concentrations, high doses can lead to adverse effects, including oxidative stress, organ damage, and disrupted cellular functions. Notably, the route of administration (oral, intravenous, or intraperitoneal) also affects the observed toxicity profiles. The goal of this review is to integrate the results of various studies to provide a balanced perspective on the potential risks and benefits of CDs, guiding future research and applications in nanomedicine. This review underscores the necessity for standardized and comprehensive toxicological evaluations of CDs to fully understand their safety and efficacy for biomedical applications.

Performing ultrafast spectroscopy during nanoparticle synthesis can provide new insights into the kinetics and mechanism of nanoparticle formation. In these experiments, we thoroughly studied the ultrafast decay of the transient absorption signal from reference gold nanoparticles (with well-defined diameters of 5, 20, and 40 nm) and from synthesized gold nanoparticles with 1:1 and 1:4 gold-to-citrate molar ratio. The application of the high repetition rate laser (100 kHz) with short pump pulse duration (10 fs, 470-570 nm) allows the rapid in situ TAS monitoring of the particle growth. Following excitation with femtosecond pulses, the acoustic vibrations of the particles produced periodic oscillations in the transient absorption signal. The decay traces at the selected wavelengths were fitted, and the Fast Fourier Transform (FFT) analysis was used for the determination of the characteristic frequencies of the acoustic vibrations. The frequency of the periodic oscillations decreases with an increasing size. We demonstrate that the formation of monodisperse gold nanoparticles at 75 degrees C can be monitored during the synthesis, providing direct evidence about their quality and particle size in the 12-55 nm particle diameter range. We concluded that the average primary size of the monodisperse gold nanoparticles increased in the 19-23 min synthesis time range as the frequency of the acoustic vibrations decreased for the Au-Cit 1:4 sample and remained constant in the last phase of the synthesis.

A series of three water-soluble methylenetrimethylammonium α-N-heterocyclic thiosemicarbazones (TSCs) was synthesized and characterized, and their proton dissociation and complex formation equilibria with Cu(II), Fe(II), and Fe(III) were studied using UV-visible, NMR, and electron paramagnetic resonance spectroscopic methods. In addition, the structures of one ligand and one Cu(II) complex were determined by single-crystal X-ray diffraction, revealing that the Cu(II) complex adopts coordination of the Schiff base through an (N,N,S) donor set. The interaction of the most active Cu(II) complex with human serum albumin-stabilized gold nanoclusters was also investigated to explore the association of the two systems and the impact of this protein-based matrix on the stability of the complex. The effect of the -CH2-N(CH3)3+ substituent in position 6 of the pyridine ring on the solution chemical properties and cytotoxicity was examined. At physiological pH, the positively charged species dominate for all compounds studied, providing excellent aqueous solubility. The -CH2-N(CH3)3+ moiety resulted in lower stability of the metal complexes compared to their corresponding non-substituted TSC analogues. Complexation with Cu(II) enhanced the activity against human colon adenocarcinoma (Colo205) and lung adenocarcinoma (A549) cell lines, although only moderate cytotoxicity was observed. Association with the protein-stabilized gold nanoclusters induced partial dissociation of the selected Cu(II) complex. Overall, while the methylenetrimethylammonium group in position 6 of the pyridine ring improves aqueous solubility, it adversely affects both metal ion binding capacity and in vitro cytotoxicity against cancer cell lines.

The key scientific question addressed in this study is whether an agro-industrial biomass precursor and a real electronic-waste-derived rare-earth source can be coupled in a single hydrothermal process to produce carbon quantum dots (CQDs) with preserved carbon-core structure and tunable optical/magnetic properties. A one-step, waste-based hydrothermal synthesis of CQDs directly from cherry-seed biomass and spent fluorescent-lamp phosphor powder is reported, achieving in situ modification with rare-earth elements (REEs). The method simultaneously enables carbonization, nanoparticle formation, and REE coordination without multi-stage post-functionalization Structural and morphological characterization by HR-TEM reveals small graphitic domains (similar to 2-4 nm) preserved upon REE modification. XPS and EDX provide evidence for surface-associated REE species, particularly Dy- and Ho-containing environments, coordinated to oxygen- and nitrogen-containing functional groups. Carbon K-edge XAS analysis indicates that the CQDs preserve a stable sp(2)-dominated carbon framework, with structural features governed primarily by surface-localized oxygen-containing functional groups. FT-IR and UV-Vis spectroscopy indicate changes in the surface ligand environment and the emergence of subtle metal-related electronic states. Photoluminescence studies demonstrate tunable emission: undoped CQDs blue-shift upon dialysis (lambda(em) approximate to 440 nm), whereas REE-doped show red-shifted emission (lambda(em) approximate to 500 nm) and enhanced radiative pathways via metal-ligand charge transfer. Magnetic measurements reveal a three-fold increase in paramagnetic responsiveness in REE-doped CQDs compared to undoped counterparts. These findings establish a sustainable, facile route to multifunctional CQDs with combined optical and magnetic properties, highlighting their potential relevance for future imaging-related applications, provided that cytotoxicity, colloidal stability in biological media, and REE ion-leakage are systematically evaluated.

Bimetallic nanoclusters (NCs) containing gold and silver were prepared by template-assisted synthesis using human serum albumin (HSA) via a newly optimized fabrication route at 25 °C. Additionally, following this procedure, we also reproducibly synthesized further Au/Ag NCs, containing a similar Au:Ag ratio, using bovine serum albumin (BSA), lysozyme (LYZ), transferrin (Tf), and gamma-globulin (γG). The aim was to highlight the importance of experimental conditions of the synthesis (e.g., metal ion: protein molar ratio and metal and protein concentrations, as well as synthesis time, temperature, and pH) for the composition, structure, and optical features of the protein-stabilized ultra-small-sized products. Circular dichroism (CD) spectroscopy revealed that the partial unfolding of the stabilizing proteins is primarily caused by the alkaline synthesis environment rather than the nanocluster formation itself. Furthermore, X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS) successfully confirmed the presence of mainly metallic (Au0) core structures alongside Ag0/Ag+ species, providing the actual metal-to-protein ratios after purification. As a new result, cytotoxicity of these bimetallic NCs was determined by using doxorubicin-sensitive Colo205 and CCD-19Lu human normal fibroblast cell lines, and their antibacterial activity was also evaluated using four different Gram-positive and Gram-negative bacterial strains.

The rational design of mixed micellar systems has emerged as a cornerstone of modern nanomedicine, offering unprecedented control over the solubility and bioavailability of challenging therapeutic agents. This review provides a comprehensive analysis of the physicochemical principles governing the assembly of amphiphilic drugs and surfactants into synergistic nanostructures. By articulating the transition from traditional guest/host solubilization to "drug-as-component" models, we highlight the critical role of molecular interactions in achieving therapeutic precision. It further outlines the experimental methodologies used to investigate these systems and elucidates how they enhance the solubility, stability, and bioavailability of poorly water-soluble drugs. Special emphasis is placed on the practical applications of synergy in reducing systemic toxicity and optimizing drug release kinetics, providing a roadmap for the development of next-generation nano-pharmaceuticals. The functionality of these systems is significantly influenced by the molecular interactions among their constituents; thus, quantitative analysis of these interactions might enhance the formulation of more effective pharmaceuticals. This review outlines the key physicochemical principles of mixed micelle formation, including thermodynamics and synergistic interactions of amphiphiles, while emphasizing their relevance in current research and practical pharmaceutical applications. Various experimental methods, such as surface tension measurement, conductometric and calorimetric tests, and spectroscopic techniques, are compared in terms of their conditions of application and performance in understanding micelle formation and micelle structure. We clearly point out that the interpretation and evaluation of the properties of colloidal systems containing drug molecules solubilized by mixed micelles and an amphiphilic drug incorporated into micelles must be discussed and evaluated separately. Understanding the limitations and characteristics of the physical/chemical principles applied is essential for the rational design of mixed micelle carriers tailored to specific therapeutic needs.

Synthesis and comprehensive solid and solution phase characterization of Ru(II)(η6-p-cymene), Os(II)(η6-p-cymene), and Rh(III)(η5-C5Me5) complexes of an indolo[2,3-c]quinoline-derived Schiff base compound (IQPMA) and its simpler analogue (DIPMA), both bearing a bidentate (N,N) chelating motif, are reported. The complexes exhibit enhanced aqueous solubility compared to the free ligands. The structures of five half-sandwich complexes were determined by single-crystal X-ray diffraction. A correlation analysis revealed that, despite the highly similar coordination geometry, conformational variations are primarily governed by steric and electronic interactions between the aromatic ring systems. Complexation of IQPMA and DIPMA with Rh(III)(η5-C5Me5) promoted ligand hydrolysis, while the corresponding Ru(II) and Os(II) organometallic complexes remained stable at physiological pH (7.4). These latter complexes showed very slow aquation kinetics and strong binding to human serum albumin mediated by intermolecular interactions. IQPMA, its complexes, and the DIPMA complexes exhibited weak-to-moderate cytotoxicity, and the Ru(II)(η6-p-cymene) complex of IQPMA was selectively active toward breast adenocarcinoma MCF-7 cells. Metal coordination significantly enhanced antibacterial efficacy against Gram-positive strains and inhibition of biofilm formation. To improve bioavailability, the Ru(II)(η6-p-cymene) complexes were encapsulated into asolectin-derived liposomes (∼200 nm) with high encapsulation efficiency and colloidal stability. Importantly, cytotoxicity assays confirmed that nanoformulation preserved the biological activity of the metal complexes.

Poor stability and low bioavailability often hinder the application of flavonoids, despite their benefits. Integration of nanotechnology and flavonoid research has emerged as a cutting-edge approach to ensure the effective delivery and stabilization of these natural antioxidants. Lipid-based colloidal carriers are widely investigated for improving the solubility and bioavailability of bioactive compounds. In this work, quercetin (Que) and rutin (Rut), two structurally related flavonoids with distinct physicochemical properties, were encapsulated into asolectin (Aso)-based colloids using thin-film hydration, ethanol injection, and microfluidic preparation methods. The influence of formulation routes and drug-to-lipid mass ratios on particle size, ζ-potential, encapsulation efficiency (EE%), and drug loading (DL%) was systematically investigated. Formulations with hydrodynamic diameters below 150 nm and highly negative ζ-potentials were obtained for both flavonoid formulations, however, significant differences were observed in EE% and attainable DL%. Thin-film hydration was proved to be optimal for Que, yielding EE% > 90% and 10-fold increase in water solubility, while microfluidic preparation enabled dominantly higher DL% (~12%) for Rut without precipitation. In vitro release studies demonstrated enhanced dissolution of Que upon formulation, whereas Rut release remained largely diffusion controlled. The results highlight the critical role of unique molecular features and independent preparation methods in determining the performance of lipid-based flavonoid-containing delivery systems.

Photoelectrochemistry provides a direct route to convert sunlight into valuable chemicals. However, high-performance photoelectrode architectures often require complicated synthesis steps and expensive instrumentation. Although physical immobilization (e.g., spray coating) of catalyst particles on semiconductors seems to be a simple and universal approach, it is rarely implemented to prepare photoelectrodes. Here, we highlight challenges associated with such deposition strategies and demonstrate the importance of rational photoelectrode design. Specifically, we introduce metal interlayers (Pd, Au, or Ni) between n-type Si and a spray-coated PdAu catalyst. We show that these interlayers are essential for generating photopotential at the interface, while the PdAu catalyst governs C3 selectivity during glycerol oxidation. We also demonstrate that the interlayer determines key performance metrics (e.g., photopotential, photocurrent density, and stability). With this approach, the best-performing PdAu/Au/Si and PdAu/Ni/Si photoelectrodes can deliver high reaction rates (>100 mA cm-2) with sufficient stability even at higher illumination intensities (50 suns).

Carbon quantum dots (CQDs) are inherently photochemically active nanomaterials, exhibiting excitation-dependent emission, proton-responsive surface states, and modifiable redox properties, enabling various sensing applications across fluorescence, electrochemistry, and electrochemiluminescence (ECL) modalities. This comprehensive review elucidates their methodologies, including PET-driven "turn-off/on" fluorescence, ratiometric pH sensing, electrocatalytic currents, and co-reactant-amplified ECL, achieving low detection limits for metal ions, biomolecules, and environmental analytes. Surface-mediated responsiveness is essential to CQD performance, offering exceptional sensitivity while also conferring inherent cross-reactivity. Meta-analysis was conducted using data extracted from previously published studies on CQDs for the detection property, in which the failure ratio was computed as the number of unsuccessful detections divided by the total number of tests reported in each study. Additionally, critical examination reveals inconsistencies in the limit of detection (LOD) metrics and mechanistic uncertainties, as well as strategies for enhancing selectivity through rational doping and molecular recognition hybrids.

Nanoformulation of drugs is a highly important task in medicine to improve their solubility and dissolution. The lipid-based drug delivery systems (LBDDS) facilitate the encapsulation of a broad range of therapeutic agents. Preparation techniques have evolved from simple laboratory "bench" methods to sophisticated, high-throughput technologies. More recently, methods that offer precision, reproducibility, and scalability are in focus as the microfluidics. To the best of our knowledge, we are the first to demonstrate an optimized fabrication protocol of lipid-based colloidal carriers using a low-cost cleaned asolectin (ASO) with a continuously operating basic flow system that offers precise control and high reproducibility. We pointed out how the hydrodynamic diameter, stability, and encapsulation efficiency (EE) can be highly controlled by the initial parameters (flow conditions, pH, storage time, dialysis time, etc.). Tocopherol (TP) and polyvinyl alcohol (PVA) were used as the model drug and stabilizer, respectively. Drug-free carriers having 130-180 nm diameter and 190-300 nm drug-loaded colloids can be fabricated, and it can be confirmed that by nanoformulation the aqueous solubility of TP was increased by 17-20 times. We evaluated the effect of NaCl concentration and pH on the colloids' stability. The application of the PVA stabilizer slightly increases the EE from 68.6% for ASO/TP to 78.4% for ASO/TP/PVA at a dialysis time of 120 min, and it also enables significant drug retention. In addition to diffusion-controlled processes, the presence of the stabilizer increases the role of carrier erosion, according to the fitting of the dissolution data with different kinetic models.

Background: Oral protein delivery is a major challenge in the field of pharmaceutical technology due to poor stability and limited permeability through intestinal barriers. Buccal delivery is a promising alternative with less restricting physiological conditions; however, low protein permeability is still a limiting factor. Multiple nanocarriers have been proposed to improve buccal protein delivery with lipid–polymer hybrid nanoparticles (LPHNs) combining the advantages of both polymeric and lipid-based systems. However, these conventional carriers rely on passive protein protection and lack adaptive release mechanisms. Objectives: This work aimed to develop and systematically optimize an ionic strength-responsive LPHN system that can minimize protein release in buccal ionic conditions while offering a triggered release in plasma after absorption. Methods: LPHNs were prepared by a two-step approach where polymeric cores of Eudragit-L100 were prepared by electrostatic complexation with Lysozyme (LYZ) followed by lipid shell formation by the ethanol injection method. Systematic optimization was performed using two-level factorial and central composite designs. Moreover, the ionic strength responsiveness and in vitro LYZ release were investigated in different ionic strength media. Results: The final optimized formulations, LPHNs and sodium deoxycholate-containing LPHNs (NaDC-LPHNs), exhibited a particle size of 257.2 ± 1.5 nm and 246 ± 5.7 nm, encapsulation efficiency of 69.89 ± 0.22% and 68.14 ± 0.16%, and high drug loading efficiency of 24.11 ± 0.06% and 23.65 ± 0.04%, respectively. Moreover, both formulations showed minimal protein release at low ionic strength (buccal-like) conditions while demonstrating a triggered release at higher ionic strength (plasma-like) conditions. Conclusions: The developed system may provide a promising smart strategy to improve buccal protein delivery by enhancing buccal protection and improving systemic delivery.

Flow chemistry allows for more precise control, lower cost, increased safety, improved efficiency, and thus higher reproducibility in chemical reactions. In this paper, the applicability of a commercially available microfluidic device (Syrris Asia Flow system (Syrris Ltd.)) was confirmed for the reproducible fabrication of both drug-free and drug-loaded colloidal particles composed of polycaprolactone (PCl). It was highlighted that tuning of the experimental parameters (e.g., flow rate, polymer concentration, and quality of stabilizers etc.) greatly controls the size, structure, and encapsulation efficiency of the formed colloids. To the best of our knowledge, there is no similar publication in the literature, which would comprehensively characterize the effect of flow conditions and other experimental parameters on the production of these PCl particles. Colloids with a size of 210-300 nm were created in a flow system, and the effect of more than ten different stabilizers like polymers, surfactants, and proteins was evaluated on colloidal stability, encapsulation efficiency and drug release. UV-Vis spectrophotometry and differential scanning calorimetry studies confirm that 50-60 % encapsulation efficiency (EE) and 18-25 % drug loading (DL) can be achieved using Vitamin D3 as a model drug. Dissolution properties of D3 in model gastric juice medium (pH = 1.5) can be greatly controlled by the type of stabilizers in the range of 9-25 %. The release curves were fitted by different kinetic model and the diffusion-controlled feature was obtained in every case.

The determination of neuroactive molecules is an important task in the monitoring of patient health. In this work, a one-step, green preparation protocol has been newly developed to synthesize highly reddish-orangeemitting gold-silver bimetallic nanoclusters reduced and stabilized by transferrin protein (Tf-AuAg NCs). The fabrication route of these bimetallic NCs was optimized first based on different parameters (gold:silver ratio, transferrin and metal concentrations, temperature and synthesis time). The properties of the nanoclusters (NCs) having a controlled gold/silver ratio were thoroughly analyzed using multiple methods, focusing on their optical characteristics. The source and various characteristics (excitation, emission maximum, lifetime) of the emitting species were also determined. Additional quenching studies were performed using iodide, a well-known quencher of tryptophan, to check the effect on different emission peaks. This newly fabricated NCs can play an important role as a sensing agent. Thus, sensing measurements were conducted on tryptophan metabolites (kynurenine and serotonin pathway, a total of 15 molecules) in three different media (phosphate buffered saline (PBS), artificial cerebrospinal fluid (aCSF) and diluted human serum), determining the limit of detection for 3hydroxyanthranilic acid at 0.55 and 0.32 mu M in PBS and aCSF. This molecule is a fluorophore itself whose detection is problematic due to many interfering substances (for example anthranilic acid), while its selective enhancement distinct from other kynurenine pathway molecules can be used for determination at the NCs emission wavelength centered around 610 nm. Additional calorimetric studies were also performed to identify the interaction between the sensed molecule and the Tf-AuAg NCs.

Many studies have shown that gentamicin (GEN) and vancomycin (VAN) are effective in the treatment of musculoskeletal infections, especially when applied locally in the form of sustained-release drug delivery systems. A promising strategy in this area appears to be the impregnation of allogeneic bone grafts with antibiotics loaded poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles (NPs). However, a major problem in formulating such systems is the high water solubility of these antibiotics, which leads to low drug content in NPs and rapid drug release. In this study, hydrophobic ion pairing (HIP) was employed to enhance the antibiotics loading and their prolong release from PLGA NPs. HIP complexes were formed using three anionic surfactants with bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) appearing to be the most effective. A novel potentiometric titration method was used to determine the optimal antibiotic-to-surfactant molar ratio. The VAN-AOT and GEN-AOT complexes were encapsulated into NPs prepared with non-commercial PLGA branched on either polyacrylic acid or tripentaerythritol. The size of the optimized nanoparticle formulations was in the range of 160 to 280 nm with the encapsulation efficiency increased to approximately 24% in the case of VAN-AOT and even to 42% in the case of GEN-AOT. The stability of AOT complexes encapsulated in PLGA NPs in aqueous media was investigated using DLS. Subsequently, the microdilution broth method confirmed the antimicrobial efficacy of the free VAN-AOT and GEN-AOT complexes, as well as PLGA NPs loaded with these complexes. Release studies of allogenic bone grafts impregnated with VAN-AOT formulation revealed a three-day release of VAN, whereas GEN-AOT exhibited an almost linear release pattern of GEN, reaching 33% by day 22. These results indicate that bone grafts impregnated with PLGA NPs loaded with HIP-complexed antibiotics represent a promising approach for localized and sustained antibiotic delivery in the treatment of musculoskeletal infections.

Polyelectrolyte complexes (PECs) are polymeric nanostructures created by the self-assembly of oppositely charged macromolecules. PEC-based novel biomaterials are currently being researched as controlled drug delivery vehicles due to their unique combination of beneficial properties. In this work, the formation of a new colloid system composed of human apo-transferrin (Tr) protein and high-molecular-weight hyaluronic acid (HyA) polysaccharide was studied from numerous perspectives because, to the best of our knowledge, no information is available regarding this PEC-based Tr-HyA formula. For detailed characterization, the experimental results of several physicochemical and colloid chemistry techniques, such as light scattering, rheology, titration microcalorimetry, and electron microscopy, were analyzed. It was emphasized that the pH and mass ratio of the macromolecules greatly influence the self-assembly process. Particles with enhanced stability were prepared at a Tr/HyA = 2:1 mass ratio. The applicability of these colloid particles with a diameter of 240-260 nm as drug delivery vehicles was evaluated by encapsulating several practically water-insoluble molecules to increase their solubility in water. We highlighted that the nanoformulation revealed ca. 3 times better solubility and enhanced release for vitamins D3 and K1 compared to the unformulated ones.

Ternary cesium-copper halide pseudo-perovskites are an emerging class of semiconductors in the field of optoelectronics. Similarly to metal-halide perovskites, by controlling the halide-composition, their emission properties can be fine-tuned. Here, a post-synthetic halide exchange method was employed to alter the halide-composition and thus the emission properties of polycrystalline Cs3Cu2Br5 layers.

The development of Rh(III)(η5-C5Me5) and Ru(II)(η6-p-cymene) complexes of 4,7-dichloro-1,10-phenanthroline (DCP) and bathophenanthroline (BP) aims to increase aqueous solubility and potential bioavailability of the lipophilic ligands while also enabling selective activity against multidrug-resistant (MDR) cancer cells. Complexes [M(η6-arene/η5-arenyl)(DCP/BP)Cl]Cl were prepared and characterized by means of nuclear magnetic resonance, infrared, electrospray ionization mass spectrometry, and single crystal X-ray diffraction for [Rh(III)(η5-C5Me5)(DCP)Cl]PF6 and [Ru(II)(η6-p-cymene)(BP)Cl]PF6. The complexes are highly stable in a wide pH range with increased hydrophilicity, and the Rh complexes showed fast and significant binding to human serum albumin (HSA). Cytotoxicity tests were conducted in various breast cancer cells and in cocultured cell lines of the uterine sarcoma parental MES-SA and its MDR counterparts. Both the ligands and their organorhodium complexes displayed a higher cytotoxicity against the MDR MES-SA/Dx5 cells than against the parental cells. As the complex [Rh(III)(η5-C5Me5)(BP)Cl]Cl showed the most promising results (IC50 = 0.23 μM (MES-SA/Dx5) with selectivity ratio 6.7), it was selected for nanoformulation using HSA and also combined with d-α-tocopheryl polyethylene glycol 1000 succinate and poly(lactic-co-glycolic acid). Both composites showed a good encapsulation efficiency and colloidal stability. Based on the in vitro cytotoxicity assays, the use of HSA as a carrier is a promising strategy to enhance the pharmacological properties of the MDR-selective Rh(III)(η5-C5Me5) complexes of 1,10-phenanthroline derivatives.

Gold nanoclusters suspension were effectively synthesized under alkaline conditions in a chemical reduction process involving gold(III) chloride trihydrate and lysozyme (LYZ) molecules. Their size determined by high-resolution transmission electron microscopy (HR-TEM) was equal to 1.9 +/- 0.5 nm. The nanoclusters, referred to as LYZ-Au NCs, were stable at pH below 4 and above 8, exhibiting a hydrodynamic diameter between 8 and 11 nm. The isoelectric point of LYZ-Au NCs appeared at pH 5.0. The suspension showed a pronounced fluorescence characterized by the red-emitting band at 668 nm. The deposition kinetics and stability of LYZ-Au NCs on bare and poly(diallyldimethylammonium chloride) (PDADMAC)-modified silica sensors were studied using quartz crystal microbalance (QCM). The influence of ionic strength, pH, and suspension concentration on the kinetics of LYZ-Au NCs deposition was determined. The significant increase in the maximum coverage of LYZ-Au NCs with ionic strength was attributed to the decreasing range of electrostatic interactions between deposited clusters. Atomic force microscopy (AFM) confirmed the formation of homogeneous layers of LYZ-Au NCs with controlled coverage on bare silica at pH 3.5 and PDADMAC-modified silica. It was shown by confocal microscopy investigations, that these layers also exhibited pronounced fluorescent properties.