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Semiconductor nanomaterials are often proposed as photocatalysts for wastewater treatment; silica nanomaterials are still largely unexploited because their photocatalytic performances need improvements, especially under visible light. The present study is a proof-of-concept that amorphous silica colloids once submitted to the proper surface modifications change into an efficient photocatalyst even under low-energy illumination source. For this reason, silica-based colloidal nanomaterials, such as bare (SiO2 NPs), aminated (NH2-SiO2 NPs), and Ag NPs-decorated (Ag-SiO2 NPs) silica, are tested as photocatalysts for the degradation of 9-anthracenecarboxylic acid (9ACA), taken as a model aromatic compound. Interestingly, upon irradiation at 313 nm, NH2-SiO2 NPs induce 9ACA degradation, and the effect is even improved when Ag-SiO2 NPs are used. On the other hand, irradiation at 405 nm activates the plasmon of Ag-SiO2 NPs photocatalyst, providing a faster and more efficient photodegradation. The photodegradation experiments are also performed under white light illumination, employing a low-intensity fluorescent lamp, confirming satisfying efficiencies. The catalytic effect of SiO2-based nanoparticles is thought to originate from photo-excitable surface defects and Ag NP plasmons since the catalytic degradation takes place only when the 9ACA is adsorbed on the surface. In addition, the involvement of reactive oxygen species was demonstrated through a scavenger use, obtaining a yield of 17%. In conclusion, this work shows the applicability of silica-based nanoparticles as photocatalysts through the involvement of silica surface defects, confirming that the silica colloids can act as photocatalysts under irradiation with monochromatic and white light. Graphic abstract Silica and Ag-decorated silica colloids photosensitize the formation of Reactive Oxygen Species with 17% efficiencies. ROS are able to oxidase aromatic pollutants chemi-adsorbed on the surface of the colloids. Silica-silver nanocomposites present a photocatalytic activity useful to degrade aromatic compounds.

In this work we report the preparation and characterization of free-standing keratin-based films containing Au/Ag nanorods. The effect of nanorods surface chemistry on the optical and mechanical properties of keratin composite films is fully investigated. Colloid nanorods confer to the keratin films interesting color effects due to plasmonic absorptions of the metal nanostructures. The presence of metal NRs induces also substantial change in the protein fluorescence emission. In particular, the relative contribution of the ordered-protein aggregates emission is enhanced by the presence of cysteine and thus strictly related to the surface chemistry of nanorods. The presence of more packed supramolecular structures in the films containing metal nanorods (in particular cysteine modified ones) is confirmed by ATR measurements. In addition, the films containing nanorods show a higher Young's modulus compared to keratin alone and again the effect is more pronounced for cysteine modified nanorods. Collectively, the reported results indicate the optical and mechanical properties of keratin composites films are related to a common property and can be tuned simultaneously, paving the way to the optimization and improvement of their performances and enhancing the exploitation of keratin composites in highly technological optoelectronic applications.

The modification of amyloid fibrils cytotoxicity through exogenous nanomaterials is crucial to understand the processes controlling the role of protein aggregation in the related diseases. The influence of nanoparticles on amyloid stability yields great interest due to the small size and high surface area-to-volume ratio of nanoparticles. Various physico-chemical parameters play a role in the interaction of proteins and nanoparticles in solution, thus influencing the disaggregation of preformed fibrils. We have examined the influence of two kinds of metallic nanoparticles on lysozyme amyloid fibrils using a multi-technique approach and focalized their impact on cytotoxicity on human neuroblastoma cells (SH-SY5Y). In particular, fluorescence, infrared and circular dichroism spectroscopies, optical and atomic force microscopy experiments have been carried out; the results are analyzed to rationalize the effects of these complexes on neural cell viability. It is remarkable, that the fibrils in the presence of AuNPs, unlike fibrils alone or with AgNPs, do not generate a significant cytotoxic effect even at high concentration and an amyloid degradation effect is visible.

The use of plasmonic nanomaterials is a challenging strategy to control radiation and radiation-induced processes at a nanometric scale. The localized surface plasmons of metal nanoparticles have been shown to affect the efficiency of a variety of radiative and non-radiative processes occurring in organic molecules. In this contribution, we present an overview of the results obtained through an original approach based on the hierarchical assembly of plasmonic gold colloids on silica templates, covalently doped with organic dyes. The detailed morphological characterization demonstrates the disposition of gold colloids on silica achieved through the tight control of the synthetic conditions. The studies carried out while gradually increasing the concentration of gold nanoparticles allow the detailed investigation of the effects of the progressive addition of plasmonic particles on the photophysical behaviour of organic molecules. In particular, the fluorescence behaviour of three dyes with different spectral properties, namely fluorescein, rhodamine B and 9-aminoacridine, are investigated in the presence of increasing concentrations of gold nanoparticles. In order to fix the distance between the dye and the gold nanoparticles, the dyes are anchored to silica nanoparticles, and the metal colloids are chemically adsorbed on the silica surface. The steady state and time-resolved data are analysed to evaluate the impact of plasmonic nanoparticles on the radiative and non-radiative processes of the dyes; the data provide evidence that the modulation of the fluorescence intensity (enhancement or quenching) can be achieved by changing the concentration of gold colloids. The plasmonic nanostructures can be employed to favour one deactivation process over the others. For example, we demonstrate that the photoinduced formation of reactive oxygen species (ROS) can be enhanced upon the plasmonic engineering of a photosensitizing agent (Protoporphyrin IX, PpIX). The Vis-excitation of silica-PpIX samples in the presence of gold nanoparticles results in a faster and more efficient photoinduced formation of ROS species either in solution or in a hydrogel. The ROS efficiency data and the fluorescence behaviour of PpIX in the presence of gold colloids suggest that the enhancement of the excitation field occurs through a plasmonic effect. For the application of the assembled hybrid materials, further advantages come from the development of photosensitizer-containing hydrogel films that are able to efficiently produce ROS upon visible excitation. Our preliminary results are herein reported and discussed.

The comprehension and control of the interactions between nanoparticles and proteins at a molecular level are crucial to improve biomedical applications of nanomaterials and to develop nanosystems able to influence and regulate the conformational changes in proteins. In this work, we explore the interactions between Gramicidin A peptide (GramA) and dodecanethiol-stabilized small silver nanoparticles (D-AgNPs), paying particular attention to the effect on GramA conformation in POPC bilayers. D-AgNPs have been prepared to have dimensions (5 nm) and a hydrophobic nature compatible with the POPC lipid bilayer. Fluorescence, Raman and IR spectroscopies have been used to investigate both peptide conformation and its position inside the phospholipid bilayer. Results are discussed in terms of solvent exposure and conformation of GramA peptide.

The immobilization of proteins on inorganic supports is attracting increasing interest since the realization of active surfaces finds application in enzyme-assisted catalysis, environmental sciences, and medical fields. In the present study, cytochrome c (cyt c) is adsorbed on silica nanoparticles (SNPs) and amino-functionalized silica nanoparticles (SNPs-APTES), which are prepared for this purpose and having a diameter of about 50 nm. The peroxidase activity of the protein is investigated under different experimental conditions, to evaluate the impact of differently charged surfaces on the catalytic activity of the biomolecule. The peroxidase activity of cyt c increases upon adsorption on SNPs, and it shows a linear behavior with nanoparticles concentration; on the other hand, the contact with increasing amounts of SNPs-APTES does not affect the catalytic activity of the protein. The kinetic profile of the oxidation reaction is altered for cyt c-SNPs sample, suggesting that upon adsorption, changes in the catalytic process take place. Moreover, we observe that the enhancement of peroxidase activity of cyt c-SNPs is almost completely inhibited in high-ionic-strength buffer: this indicates that the protein establishes electrostatic interactions with SNP. The spectroscopic properties of the adsorbed protein on the two different matrices are investigated by using fluorescence and Raman spectroscopies to account for the enzymatic activity of the hybrid materials. The fluorescence spectra of cyt c-silica bio-composites reveal that the adsorption on silica modifies the microenvironments of the emitting amino acid residues of the protein. Indeed, their fluorescence gains intensity and appears blue-shifted compared to that of the native protein; these modifications are more evident when cyt c is adsorbed on SNPs. Raman spectra suggest that both oxidation and spin state of heme iron change when cyt c is adsorbed on SNPs but not on SNPs-APTES. The spectroscopic data of biocomposite materials are discussed in terms of structural changes to account for the increment of peroxidase activity upon adsorption on the negatively charged surface of SNPs.

Surface-enhanced Raman scattering (SERS) is a widely used technique for drug detection due to high sensitivity and molecular specificity. The applicability and selectivity of SERS in the detection of specific drug molecules can be improved by gathering information on the specific interactions occurring between the molecule and the metal surface. In this work, multilayer gold-silver bimetallic nanorods (Au@Ag@AuNRs) have been prepared and used as platforms for SERS detection of specific drugs (namely promethazine, piroxicam, furosemide and diclofenac). The analysis of SERS spectra provided accurate information on the molecular location upon binding and gave some insight into molecule-surface interactions and selectivity in drug detection through SERS.

DNA-stabilized silver nanoclusters (DNA-AgNCs) are a class of promising fluorophores for imaging and sensing applications. All aspects of their spectroscopic properties are not yet fully characterized, leaving this field still with a number of fundamental studies to be addressed. In this work, we studied the spectroscopic properties of red-emitting DNA-AgNCs at different pH (5 to 9) and ionic strength μ (0.005 to 0.5). The photophysical properties of high performance liquid chromatography (HPLC) purified DNA-AgNCs proved to be constant over a large range of pH and μ, with absorption, emission and fluorescence decay times only being affected at very high pH and μ values. Non-purified DNA-AgNCs were also unaffected by pH and/or μ variations, but significant differences can be observed between the rotational correlation times of purified and non-purified DNA-AgNCs.

Photodynamic treatments represent a non-invasive tool to intervene in the cell cycle, only when needed, but high excitation power is an important limitation. In this work, protoporphyrin IX (PpIX) is covalently anchored to the surface of silica particles. The hybrid colloids are prepared with different photosensitizer loadings and characterized by TEM, SEM-EDX and spectroscopic methods. The visible excitation of the colloidal samples generates reactive oxygen species, which are quantified by use of a specific chemical scavenger agent (1,3-diphenylisobenzofuran). The determined efficiencies depend on the PpIX loading, being higher in the sample where the aggregation is reduced. To enhance further the photosensitizing performance of silica-PpIX samples, increasing amounts of gold nanoparticles are conjugated to the silica surface in order to exploit the antenna effect of plasmonic nanostructures. The visible excitation of silica-PpIX systems in the presence of gold nanoparticles results in a faster and more efficient photoinduced formation of ROS species reaching a 230 % enhancement of ROS photosensitization when 1013 Au nanoparticles mL−1 (corresponding to circa 75 ppm of gold) are present. The efficiency data are discussed in terms of plasmonic enhancement of the excitation field.

The preparation of tailored nanomaterials able to support cell growth and viability is mandatory for tissue engineering applications. In the present work, silica nanoparticles were prepared by a sol-gel procedure and were then functionalized by condensation of amino groups and by adsorption of silver nanoparticles. Transmission electron microscopy (TEM) imaging was used to establish the morphology and the average dimensions of about 130 nm, which were not affected by the functionalization. The three silica samples were deposited (1 mg/mL) on cover glasses, which were used as a substrate to culture adult human bone marrow-mesenchymal stem cells (hBM-MSCs) and human adipose-derived stem cells (hASCs). The good cell viability over the different silica surfaces was evaluated by monitoring the mitochondrial dehydrogenase activity. The analysis of the morphological parameters (aspect ratio, cell length, and nuclear shape Index) yielded information about the interactions of stem cells with the surface of three different nanoparticles. The data are discussed in terms of chemical properties of the surface of silica nanoparticles.