Study of the interactions of gold nanoparticles functionalized with aminolevulinic acid in membrane models

Four-parameter model of thin surface layer contribution to reflectance-absorbance spectroscopy and ellipsometry

The contribution of the surface layer to the reflection coefficients is shown to be determined by four surface integral values, which can be interpreted as real and imaginary parts of two complex permittivity excesses. The reflectance-absorbance spectra are determined by the spectra of these parameters. The spectra of the surface excess integrals cannot be found with the angular measurements of reflection-absorption spectra, which are determined by only three angular dependent terms. To determine these four surface excess integrals, it is necessary to involve the experimental data of spectroscopic ellipsometry or polarization-modulation infrared reflection absorption spectroscopy providing equivalent information about surface. In the case of weakly absorbing bulk medium, the real parts of the excesses can be neglected, permitting calculation of their imaginary parts using the angular dependence of the absorbance. The calculation of these parameters allows to check consistency of the data obtained. Measurements of the angular dependence of the absorbance of p-polarized radiation reflected from the DPPC monolayer upon distilled water were performed. The data obtained turned to be in good agreement with the proposed theoretical analysis.

Unveiling the mechanisms underlying photothermal efficiency of gold shell-isolated nanoparticles (AuSHINs) on ductal mammary carcinoma cells (BT-474)

Gold nanoparticles are valuable photothermal agents owing to their efficient photothermal conversion, photobleaching resistance, and potential surface functionalization. Herein, we combined bioinspired membranes with in vitro assays to elicit the molecular mechanisms of gold shell-isolated nanoparticles (AuSHINs) on ductal mammary carcinoma cells (BT-474). Langmuir and Langmuir-Schaefer (LS) films were handled to build biomembranes from BT-474 lipid extract. AuSHINs incorporation led to surface pressure-area (π-A) isotherms expansion, increasing membrane flexibility. Fourier-transform infrared spectroscopy (FTIR) of LS multilayers revealed electrostatic AuSHINs interaction with head portions of BT-474 lipid extract, causing lipid chain disorganization. Limited AuSHINs insertion into monolayer contributed to hydroperoxidation of the unsaturated lipids upon irradiation, consistently with the surface area increments of ca. 2.0%. In fact, membrane disruption of irradiated BT-474 cells containing AuSHINs was confirmed by confocal microscopy and LDH leakage, with greater damage at 2.2 × 1013 AuSHINs/mL. Furthermore, the decrease in nuclei dimensions indicates cell death through photoinduced damage.

Unsaturation pattern of phosphatidylglycerols modulating the interaction of lysicamine with cells membrane models at the air-water interface

Lysicamine, an alkaloid with tumorigenic activity, was incorporated in cell membrane models made of lipid Langmuir monolayers. Dipalmitoylphosphocholine (DPPC), dioleoylphosphocholine (DOPC), and palmitoyloleoylcholine (POPC) represented non-tumorigenic cell membranes, and dipalmitoylphosphoserine (DPPS), dioleoylphosphoserine (DOPS), and palmitoyloleoylserine (POPS), tumorigenic ones. The monolayers were characterized by tensiometry, infrared spectroscopy, and Brewster Angle Microscopy (BAM). No significant shifts of the isotherms were observed for the saturated lipids (DPPC and DPPS), while for the others (DOPC, POPS, DOPS, and POPS), more significant changes were observed not only in the compression isotherms but also in the surface pressure-time curve for pre-compressed monolayers. The molecular organization, as well as the morphology of the drug-lipid monolayers, could be inferred with infrared spectroscopy and BAM. While the first revealed that the alkyl chain ordering changed upon lysicamine incorporation, the second showed how the drug could distinctly change the state of aggregation of molecular domains at the air-water interface. In conclusion, lysicamine could interact distinctly with each lipid at the air-water interface, showing the dependence not only on the lipid polar groups but also on the level of unsaturation of the alkyl chains.

Organoselenium compounds as functionalizing agents for gold nanoparticles in cancer therapy

Gold nanoparticles (AuNPs) modified with four organoselenium compounds, i.e., 4-selenocyanatoaniline (compound 1), 4,4'-diselanediyldianiline (compound 2), N-(4-selenocyanatophenyl)cinnamamide (compound 3), and N-(3-selenocyanatopropyl)cinnamamide (compound 4), were synthesized following two different approaches: direct conjugation and non-covalent immobilization onto hydrophilic and non-cytotoxic AuNPs functionalized with 3-mercapto-1-propanesulfonate (3MPS). Both free compounds and AuNPs-based systems were characterized via UV-Vis, FTIR NMR, mass spectrometry, and SR-XPS to assess their optical and structural properties. Size and colloidal stability were evaluated by DLS and ζ-potential measurements, whereas morphology at solid-state was evaluated by atomic force (AFM) and scanning electron (FESEM) microscopies. AuNPs synthesized through chemical reduction method in presence of Se-based compounds as functionalizing agents allowed the formation of aggregated NPs with little to no solubility in aqueous media. To improve their hydrophilicity and stability mixed AuNPs-3MPS-1 were synthesized. Besides, Se-loaded AuNPs-3MPS revealed to be the most suitable systems for biological studies in terms of size and colloidal stability. Selenium derivatives and AuNPs were tested in vitro via MTT assay against PC-3 (prostatic adenocarcinoma) and HCT-116 (colorectal carcinoma) cell lines. Compared to free compounds, direct functionalization onto AuNPs with formation of Au-Se covalent bond led to non-cytotoxic systems in the concentration range explored (0-100 μg/mL), whereas immobilization on AuNPs-3MPS improved the cytotoxicity of compounds 1, 3, and 4. Selective anticancer response against HCT-116 cells was obtained by AuNPs-3MPS-1. These results demonstrated that AuNPs can be used as a platform to tune the in vitro biological activity of organoselenium compounds.

Synthesis, characterization, antimicrobial activity, and toxicity evaluation of aminolevulinic acid-silver and silver-iron nanoparticles for potential applications in agriculture

Aminolevulinic acid (ALA) is considered one of the most critical plants growth regulators and essential precursors for chlorophyll biosynthesis; besides, its photodynamic activity can be used to exterminate larvae and microorganisms in plants and soil. Silver nanoparticles (AgNPs) have unique physicochemical properties and potent antimicrobial, antiviral, and antifungal activities, and in agriculture, their application as nanopesticides has been proposed. In this study, silver and silver–iron nanoparticles capped/stabilized with aminolevulinic acid (ALAAgNPs and ALAAgFeNPs) were synthesized by the photoreduction method and characterized by UV-vis spectroscopy, transmission electron microscopy, and zeta potential analysis. The kinetics of ¹O₂ generation from ALAAgFeNPs were obtained. The ALANP toxicity was evaluated on stalks of E. densa by observing cell morphology changes and measuring chlorophyll content compared with water-treated plants. Antimicrobial activity was tested against E. coli, P. aeruginosa, and Candida albicans. The results suggested that ALANPs (prepared with [AgNO₃] ≤ 0.2 mM and [ALA] ≤ 0.4 mM) could be suitable for applications in the agricultural sector. The presence of ∼0.3 mmol of iron in ALAAgNPs synthesis increased cell uptake and chlorophyll synthesis.

ALA is a natural metabolite in all living cells and possesses low toxicity. ALANPs exhibit high antimicrobial activity, promote plant growth and have the potential to show photodynamic herbicidal properties under solar illumination.

The Past and the Future of Langmuir and Langmuir-Blodgett Films

The Langmuir-Blodgett (LB) technique, through which monolayers are transferred from the air/water interface onto a solid substrate, was the first method to allow for the controlled assembly of organic molecules. With its almost 100 year history, it has been the inspiration for most methods to functionalize surfaces and produce nanocoatings, in addition to serving to explore concepts in molecular electronics and nanoarchitectonics. This paper provides an overview of the history of Langmuir monolayers and LB films, including the potential use in devices and a discussion on why LB films are seldom considered for practical applications today. Emphasis is then given to two areas where these films offer unique opportunities, namely, in mimicking cell membrane models and exploiting nanoarchitectonics concepts to produce sensors, investigate molecular recognitions, and assemble molecular machines. The most promising topics for the short- and long-term prospects of the LB technique are also highlighted.

The efficiency of photothermal action of gold shell-isolated nanoparticles against tumor cells depends on membrane interactions

Photoinduced hyperthermia with nanomaterials has been proven effective in photothermal therapy (PTT) of tumor tissues, but a precise control in PTT requires determination of the molecular-level mechanisms. In this paper, we determined the mechanisms responsible for the action of photoexcited gold shell-isolated nanoparticles (AuSHINs) in reducing the viability of MCF7 (glandular breast cancer) and especially A549 (lung adenocarcinoma) cells in vitro experiments, while the photoinduced damage to healthy cells was much smaller. The photoinduced effects were more significant than using other nanomaterials, and could be explained by the different effects from incorporating AuSHINs on Langmuir monolayers from lipid extracts of tumoral (MCF7 and A549) and healthy cells. The incorporation of AuSHINs caused similar expansion of the Langmuir monolayers, but Fourier-transform infrared spectroscopy (FTIR) data of Langmuir-Schaefer films (LS) indicated distinct levels of penetration into the monolayers. AuSHINs penetrated deeper into the A549 extract monolayers, affecting the vibrational modes of polar groups and carbon chains, while in MCF7 monolayers penetration was limited to the surroundings of the polar groups. Even smaller insertion was observed for monolayers of the healthy cell extract. The photochemical reactions were modulated by AuSHINs penetration, since upon irradiation the surface area of A549 monolayer decreased owing to lipid chain cleavage by oxidative reactions. For MCF7 monolayers, hydroperoxidation under illumination led to a ca. 5% increase in surface area. The monolayers of healthy cell lipid extract were barely affected by irradiation, consistent with the lowest degree of AuSHINs insertion. In summary, efficient photothermal therapy may be devised by producing AuSHINs capable of penetrating the chain region of tumor cell membranes.