Rafael Contreras-Cáceres

Seeded Growth Synthesis of Gold Nanotriangles: Size Control, SAXS Analysis, and SERS Performance

We studied the controlled growth of triangular prismatic Au nanoparticles with different beveled sides for surface-enhanced Raman spectroscopy (SERS) applications. First, in a seedless synthesis using 3-butenoic acid (3BA) and benzyldimethylammonium chloride (BDAC), gold nanotriangles (AuNTs) were synthesized in a mixture with gold nanooctahedra (AuNOCs) and separated by depletion-induced flocculation. Here, the influence of temperature, pH, and reducing agent on the reaction kinetics was initially investigated by UV-vis and correlated to the size and yield of AuNT seeds. In a second step, the AuNT size was increased by seed-mediated overgrowth with Au. We show for the first time that preformed 3BA-synthesized AuNT seeds can be overgrown up to a final edge length of 175 nm and a thickness of 80 nm while maintaining their triangular shape and tip sharpness. The NT morphology, including edge length, thickness, and tip rounding, was precisely characterized in dispersion by small-angle X-ray scattering and in dry state by transmission electron microscopy and field-emission scanning electron microscopy. For sensor purposes, we studied the size-dependent SERS performance of AuNTs yielding analytical enhancement factors between 0.9 × 104 and 5.6 × 104 and nanomolar limit of detection (10-8-10-9 M) for 4-mercaptobenzoic acid and BDAC. These results confirm that the 3BA approach allows the fabrication of AuNTs in a whole range of sizes maintaining the NT morphology. This enables tailoring of localized surface plasmon resonances between 590 and 740 nm, even in the near-infrared window of a biological tissue, for use as colloidal SERS sensing agents or for optoelectronic applications.

Paclitaxel-loaded hollow-poly(4-vinylpyridine) nanoparticles enhance drug chemotherapeutic efficacy in lung and breast cancer cell lines

Paclitaxel (PTX), one of the most effective cytotoxins for the treatment of breast and lung cancer, is limited by its severe side effects and low tumor selectivity. In this work, hollow-poly(4-vinylpyridine) (hollow-p4VP) nanoparticles (NPs) have been used for the first time to generate PTX@p4VP NPs, employing a novel technique in which a gold core in the center of the NP is further oxidized to produce the hollow structure into which PTX molecules can be incorporated. The hollow-p4VP NPs exhibit good physicochemical properties and displayed excellent biocompatibility when tested on blood (no hemolysis) and cell cultures (no cytotoxicity). Interestingly, PTX@p4VP NPs significantly increased PTX cytotoxicity in human lung (A-549) and breast (MCF-7) cancer cells with a significant reduction of PTX IC50 (from 5.9 to 3.6 nM in A-549 and from 13.75 to 4.71 nM in MCF-7). In addition, PTX@p4VP caused a decrease in volume of A-549 and MCF-7 multicellular tumor spheroids (MTS), an in vitro system that mimics in vivo tumors, in comparison to free PTX. This increased antitumoral activity is accompanied by efficient cell internalization and increased apoptosis, especially in lung cancer MTS. Our results offer the first evidence that hollow-p4VP NPs can improve the antitumoral activity of PTX. This system can be used as a new nanoplatform to overcome the limitations of current breast and lung cancer treatments.

Inclusion of silver nanoparticles for improving regenerated cellulose membrane performance and reduction of biofouling

The preparation of silver nanoparticles (AgNPs) and their incorporation into the structure of a regenerated cellulose membrane by dip coating is presented. Morphological characterization of the AgNPs (average diameter of 20±2nm) was carried out by SEM/TEM, while elastic, electrical and antimicrobial properties of the hybrid membrane were also analyzed. The presence of silver nanoparticles in the membrane seems to increases its rigidity and its chemical stability against oxidation, but it only induces small changes in the transport parameters. As expected, AgNPs provide antimicrobial properties to the membrane and consequently the reduction of biofouling without affecting significantly other characteristic parameters, opening the application of the modified membrane to wastewaters treatment.

Synthesis of catalytically active gold clusters on the surface of Fe3O4@SiO2 nanoparticles

This work proposes a novel method to obtain catalytically active gold clusters by using the water-soluble 5,10,15,20-Tetrakis(4-trimethyl-ammonio-phenyl)porphyrin under mild conditions instead of using strong reducing agents. Uniform gold clusters were obtained with a diameter comprised between 1 and 2 nm and long-term stability. Furthermore, the water-soluble porphyrin was immobilized on the SiO2 shell of a core@shell Fe3O4@SiO2 nanoparticles to directly synthesize gold clusters onto the surface of Fe3O4@SiO2 nanoparticles featuring their magnetic recovery. Fe3O4@SiO2@Au nanoparticles were found to be catalytically active for the reduction of 4-nitrophenol to 4-aminophenol using NaBH4 and giving very high pseudo-first-order rate constant comprised between 0.7 and 2.7 min−1. Our results demonstrate that Fe3O4@SiO2@Au nanoparticles are stable catalysts and do not degrade during the catalytic process under the reaction conditions enabling their magnetic recuperation.

DMABI tripod structures with sensing capabilities: synthesis, characterization and fluorescence analysis

We present herein the synthesis, and the structural and spectroscopic analysis of a non-planar tripod-shaped p-(N,N′-dimethylamino)benzyliden-1,3-indandione (DMABI) chromophore. This novel molecule is composed of a Si core with three incorporated arms, each of them contains a 1,3-indandione derivative with an electron donating (−NMe2) group, thus providing fluorescence capabilities. We prepared a DMABI arm by coupling a p-(N,N′-dimethylamino)benzaldehyde (DMAB) tripod substituted molecule with 1,3-indandione via aldol condensation. The structures of DMAB-tripods were confirmed by spectroscopic data and studied by quantum chemical calculations. Fluorescence spectroscopy was used for optical characterization. Quantum yields and the corresponding lifetimes reveal typical characteristics of conjugated derivatives. Finally, we monitored the enhancement in fluorescence intensity of compound 1 in the presence of 4-chloro-2,6-dinitroaniline (4CDNA) in the range between 0 and 20 mg L−1. We justify this enhancement by calculated energies and the distribution of the HOMO and the LUMO for DMABI-tripod and 4CDNA.

Thermo-responsive microgels based on encapsulated carbon quantum dots

In this work carbon quantum dot (CQD) nanoparticles are synthesized from D-lactose using a hydrothermal method and then they are coated with polyethylene glycol (CQDs@PEG). These particles exhibit a monodisperse spherical morphology with an average particle size of ∼4 nm. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy showed the presence of the hydroxyl groups from the ethylene glycol molecules grafted onto the CQDs’ surfaces, which confirms that PEG was covalently attached to the nanoparticles’ surfaces. Fluorescence analysis demonstrates a shift in the emission at 495 nm after PEG coating. Modified carbon dots were introduced into thermo-responsive pNIPAM microgels. The resultant pNIPAM–CQDs@PEG hybrid system exhibits interesting fluorescence properties. Transmission electron microscopy (TEM), fluorescence microscopy, and energy-dispersive X-ray (EDX) spectroscopy confirm the incorporation of CQD particles into the microgels. Finally, dynamic light scattering (DLS) analysis confirms that further hybrid microgels based on pNIPAM are thermo-responsive, with a transition temperature similar to that of a system with an ionic component.

Tripalmitin nanoparticle formulations significantly enhance paclitaxel antitumor activity against breast and lung cancer cells in vitro

Paclitaxel (PTX) is one of the drugs of choice in the treatment of breast and lung cancer. However, its severe side effects, including mielosuppression, cardiotoxicity and neurotoxicity, frequently cause treatment to be discontinued. Solid lipid nanoparticles (NPs) of glyceril tripalmitate (tripalmitin) loaded with PTX (Tripalm-NPs-PTX) including modifications by the addition of hexa(ethylene glycol), β-cyclodextrin and macelignan were developed. All NPs-PTX formulations displayed excellent hemocompatibility and significantly enhanced PTX antitumor activity in human breast (MCF7, MDAMB231, SKBR3 and T47D) and lung (A549, NCI-H520 and NCI-H460) cancer cells. Tripalm-NPs-PTX decreased PTX IC50 by as much as 40.5-fold in breast and 38.8-fold in lung cancer cells and Tripalm-NPs-PTX macelignan inhibited P-glycoprotein in resistant tumor cells. In addition, Tripalm-NPs-PTX significantly decreased the volume of breast and lung multicellular tumor spheroids that mimics in vivo tumor mass. Finally, Tripalm-NPs-PTX decreased the PTX IC50 of cancer stem cells (CSCs) derived from both lung and breast cancer cells (6.7- and 14.9-fold for MCF7 and A549 CSCs, respectively). These results offer a new PTX nanoformulation based on the use of tripalmitin which improves the antitumor activity of PTX and that may serve as an alternative PTX delivery system in breast and lung cancer treatment.

Preparation, characterization, and protein-resistance of films derived from a series of α-oligo(ethylene glycol)-ω-alkenes on H–Si(111) surfaces

A series of oligo(ethylene glycol) (OEG)-terminated monolayers were prepared by photo-activated grafting of OEG-alkenes with the general formula CH2CH(CH2)m(OCH2CH2)nOCH3 (abbreviated as Cm+2EGn, m = 8, 9; n = 3–7) on hydrogen-terminated silicon (111) surfaces using different deposition conditions. The films were characterized by contact-angle goniometry, ellipsometry, X-ray photoelectron spectroscopy (XPS) and tested for protein resistance. Films prepared under a higher vacuum showed a higher thickness and exhibited better protein resistance with increasing ethylene glycol (EG) units. Remarkably, the films prepared from C10EGn were generally thicker than those from their corresponding homologues C11EGn, and displayed better resistance to protein adsorption, which were probably due to the odd–even effect from the alkyl chain. Prepared under high vacuum conditions (∼10−5 mbar), the C10EG7 films with a thickness of 40 A adsorbed <0.8% (the detection limit of N 1s XPS) monolayer of fibrinogen in a standard assay. The films remained protein-resistant (adsorbed <3% monolayer of fibrinogen) even after 28 days in phosphate buffered saline (PBS) at 37 °C or 17 days in MC3T3-E1 cell culture with 10% fetal bovine serum at 37 °C. Therefore, the C10EG7 films prepared under high vacuum conditions represent the most protein-resistant and stable films on non-oxidized silicon substrates.

Covalent immobilization of dysprosium-based metal–organic chains on silicon-based polymer brush surfaces

We report on a process for immobilizing metal–organic chains constructed of dysprosium and sodium ions based on 5-aminopyridine-2-carboxylic acid, onto silicon-based surfaces coated with poly(acrylic acid) (PAA) polymer brushes. Atomic force microscopy (AFM) and fluorescence microscopy were used to study the film morphology before and after the deposition of the 1D metallo-organic polymer. The covalent linkage of the dysprosium complex is also confirmed using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (SEM-EDS) analysis. Using magnetic force microscopy (MFM) we particularly addressed the magnetic properties of the grafted metal–organic structure. These results suggest a simple and effective method for incorporation of such molecules onto nanometric surfaces.

Au@p4VP core@shell pH-Sensitive Nanocomposites Suitable for Drug Entrapment

We synthesize and characterize pH-responsive hybrid nanocomposites with SERS and drug loading applications. This colloidal system is structured by spherical 50 nm Au cores individually coated by a pH-sensitive shell of poly4-vinylpyridine (Au@p4VP). The synthesis of these hybrid nanocomposites is performed in two steps, a first one involves the fabrication of vinyl-functionalized Au nanoparticles, and a second one includes the controlled overgrowth of a p4VP shell by free radical polymerization. As a result, Au@p4VP hybrid systems with a mean diameter ranging from 150 to 57 nm are obtained upon varying the monomer concentration at synthesis. Au@p4VP nanocomposite exhibits pH-response capabilities, confirmed by cryo-TEM analysis, Small Angle X-ray Scattering (SAXS) and Zeta Potential (ZP) measurements at different pH conditions. The Au@p4VP particles also display a controllable swelling response, which depends on the cross-linker density within the polymer. This swelling capability is analyzed by Dynamic Light Scattering (DLS), and UV-vis spectroscopy at different pHs. The pH-responsive capability is here exploited for the chemical entrapment of doxorubicin hydrochloride (Dox) into the polymer network. The presence of this molecule is resolved by Surface Enhanced Raman Spectroscopy (SERS) measurements. The entrapment efficiency of Dox by the Au@p4VP system is determined via NMR spectroscopy of the supernatants.