Larissa Brentano Capeletti

Tailored Silica-Antibiotic Nanoparticles: Overcoming Bacterial Resistance with Low Cytotoxicity

New and more aggressive antibiotic resistant bacteria arise at an alarming rate and represent an ever-growing challenge to global health care systems. Consequently, the development of new antimicrobial agents is required to overcome the inefficiency of conventional antibiotics and bypass treatment limitations related to these pathologies. In this study, we present a synthesis protocol, which was able to entrap tetracycline antibiotic into silica nanospheres. Bactericidal efficacy of these structures was tested against bacteria that were susceptible and resistant to antibiotics. For nonresistant bacteria, our composite had bactericidal efficiency comparable to that of free-tetracycline. On the other hand, the synthesized composites were able to avoid bacterial growth of resistant bacteria while free-tetracycline has shown no significant bactericidal effect. Finally, we have investigated the cytotoxicity of these nanoparticles against mammalian cells to check any possible poisoning effect. It was found that these nanospheres are not apoptosis-inducers and only a reduction on the cell replication rate was seen when compared to the control without nanoparticles.

Infrared and Raman spectroscopic characterization of some organic substituted hybrid silicas

Nine hybrid silicas bearing the organic substituent groups methyl, octyl, octadecyl, vinyl, phenyl, mercaptopropyl, isocyanatopropyl, chloropropyl and glycidoxypropyl were synthesized by an acid-catalyzed, hydrolytic sol-gel process. The resulting solid materials were characterized by their absorbance and attenuated total reflection (ATR) IR and Raman spectra. The latter technique proved to be particularly useful in the identification of the organic moieties in the hybrid silicas. The effect of the presence of the organic groups on the silica networks was also investigated - there were increases observed in both the SiOSi bond angles and bond lengths. Moreover, deconvolution of the IR-active antisymmetric SiOSi stretching bands permitted detection of the four- and six-membered siloxane rings present in the silicas. There proved to be a greater number of four-membered rings on the surfaces of the particles. Both IR and Raman spectroscopy proved to be invaluable in the characterization of these hybrid materials.

Quantification of indicator content in silica-based pH solid sensors by diffuse reflectance spectroscopy

The amount of alizarin red, brilliant yellow or acridine encapsulated within silica matrixes as colorimetric pH sensors, produced by three sol–gel routes (acid catalyzed, base catalyzed and non-hydrolytic routes), was investigated using diffuse reflectance spectroscopy in the UV-Vis region. Univariate calibration curves using silica (commercial or sol–gel synthesized) as a blank were linear (R2 > 0.99) but did not allow coherent quantification of the pH indicator, likely due to the matrix effect. The standard addition method using the silica blank (produced by the corresponding sol–gel route) to correct background afforded coherent results with standard deviation between 0.017 and 0.59, depending on the sol–gel route and indicator.

Tailored Silica Nanoparticles Surface to Increase Drug Load and Enhance Bactericidal Response

Nanoparticles’ surface properties can be used as triggers to regulate or even enhance biological response and generate tailored structures to substitute conventional antibiotics. Here, silica nanoparticles surface was duly tuned in order to increase the water-insoluble drug load (curcumin) and improve the antibacterial activity. Our main motivation was based on the electrostatic attraction between the positively charged amino groups and the negatively charged curcumin and/or bacteria membrane. In addition, the variation of amino grafting amount on silica nanoparticles indicated that the grafting increase was directly related to the extent of drug entrapped into the nanoparticles as well as to the bactericidal activity. The combination of amino-functionalized silica nanoparticles associated with the presence of curcumin allowed to produce a dual bactericidal system that shows promising perspective for its use in biomedical applications.

Biodiesel water in oil microemulsions: ferrocene as a hydrophobic probe for direct analysis by differential pulse voltammetry at a Pt ultramicroelectrode

Aimed at monitoring biodiesel oxidation stability, a reproducible, simple and rapid procedure for the determination of ferrocene (Fc) as a probe in water in oil microemulsions (W/O MEs) has been successfully developed. Electrochemical measurements have been performed in microemulsions, ME1, containing 10% water, 60% biodiesel (B100) and 30% pseudo-phase, and ME2, containing 9% water, 28% biodiesel and 63% pseudo-phase, in mass, using sodium dodecyl sulphate (SDS) and n-pentanol as surfactant and co-surfactant, respectively. The so prepared MEs have been characterized through viscosity, conductivity and small angle X-ray scattering (SAXS) measurements. Ferrocene oxidation at a Pt ultramicroelectrode (ume), both in ME1 and ME2, has been evidenced either by linear and differential pulse voltammetry (DPV). As compared to ME1, the higher conductivity of ME2 favours carrying electrochemical measurements in this medium. The DPV results indicate a linear relationship between ip and the Fc concentration with a correlation coefficient of 0.999. Thus, the proposed methodology may ultimately be employed for quality control in the biodiesel production line.

Hybrid sol–gel silica adsorbent materials synthesized by molecular imprinting for tannin removal

This study reports the development of a functional adsorbent synthesized by the molecular imprinting method in a sol–gel matrix. The adsorption capacity of the organic-inorganic hybrid adsorbent material was tested on tannin compounds, i.e., phenolic substances that are among the most difficult compounds to remove in industrial wastewater. The specific surface area obtained by nitrogen porosimetry analysis was between 2 and 579 m2 g−1 due to each sol–gel synthetic route used. Small-angle X-ray scattering analysis revealed that the hybrid silicas were arranged in a multi-level structure consisting of three levels of organization and a surface fractal structure. Diffuse reflectance spectroscopy revealed the interactions between the tannins and the silica matrix, and confirmed the partial removal of tannins after ultrasound-assisted extraction. Zeta potential analysis showed that the values ranged between −37.9 and +27.8 mV, where non-functionalized xerogels were anionic and those functionalized with organosilane were cationic. The structural and textural characteristics of the hybrid materials were found to depend on the sol–gel synthetic route, which in turn affected the adsorption capacity. The adsorbent functionalized with (3-Aminopropyl) triethoxysilane was an effective adsorbent for the tannin compounds tested here, with approximately 90% removal in aqueous solutions.Graphical abstract

Optical Sensor Coating Development for Industrial Applications

Optical sensors are important for in situ and ex situ monitoring in industrial processes and environmental control. The development of these tools involves the immobilization of a sensitive element within a matrix. Therefore, the sol-gel process represents a powerful strategy for developing and improving optical sensors, especially those for coating applications. This approach allows the use of several strategies in terms of different synthetic routes and the production of hybrid matrices, which can help to produce highly specific sensors and solve problems such as receptor element leaching. Controlling the textural characteristics allows for tuning of the matrix permeability of analytes to the receptor element without leaching from the network or affecting the receptor identity or functionality. The introduction of organic moieties appears to be a good alternative for providing systems with differentiated characteristics (i.e., performance). Here, recent results describing sol-gel hybrid optical coating sensors are reviewed to demonstrate their state-of-the-art industrial applications for gases, pH, solvents, and ionic species monitoring.