Exploring the Influence of Solvents on Electrochemically Etched Porous Silicon Based on Photoluminescence and Surface Morphology Analysis.

Porous silicon (PSi) has promising applications in optoelectronic devices due to its efficient photoluminescence (PL). This study systematically investigates the effects of various organic solvents and their concentrations during electrochemical etching on the resulting PL and surface morphology of PSi. Ethanol, n-butanol, ethylene glycol (EG) and N,N-dimethylformamide (DMF) were employed as solvents in hydrofluoric acid (HF)-based silicon etching. The PL peak position exhibited progressive blue-shifting with increasing ethanol and EG concentrations, accompanied by reductions in the secondary peak intensity and emission linewidth. Comparatively, changes in n-butanol concentration only slightly impacted the main PL peak position. Additionally, distinct morphological transitions were observed for different solvents, with ethanol and n-butanol facilitating uniform single-layer porous structures at higher concentrations in contrast to the excessive etching caused by EG and DMF resulting in PL quenching. These results highlight the complex interdependencies between solvent parameters such as polarity, volatility and viscosity in modulating PSi properties through their influence on surface wetting, diffusion and etching kinetics. The findings provide meaningful guidelines for selecting suitable solvent conditions to tune PSi characteristics for optimized device performance.

Reduction of Nitroaromatics by Gold Nanoparticles on Porous Silicon Fabricated Using Metal-Assisted Chemical Etching.

In this study, we investigated the use of porous silicon (PSi) fabricated using metal-assisted chemical etching (MACE) as a substrate for the deposition of Au nanoparticles (NPs) for the reduction of nitroaromatic compounds. PSi provides a high surface area for the deposition of Au NPs, and MACE allows for the fabrication of a well-defined porous structure in a single step. We used the reduction of p-nitroaniline as a model reaction to evaluate the catalytic activity of Au NPs on PSi. The results indicate that the Au NPs on the PSi exhibited excellent catalytic activity, which was affected by the etching time. Overall, our results highlighted the potential of PSi fabricated using MACE as a substrate for the deposition of metal NPs for catalytic applications.

Photocatalytic Properties of Graphene/Gold and Graphene Oxide/Gold Nanocomposites Synthesized by Pulsed Laser Induced Photolysis.

Graphene (Gr)/gold (Au) and graphene-oxide (GO)/Au nanocomposites (NCPs) were synthesized by performing pulsed-laser-induced photolysis (PLIP) on hydrogen peroxide and chloroauric acid (HAuCl4) that coexisted with Gr or GO in an aqueous solution. A 3-month-long aqueous solution stability was observed in the NCPs synthesized without using surfactants and additional processing. The synthesized NCPs were characterized using absorption spectroscopy, transmission electron microscopy, Raman spectroscopy, energy dispersive spectroscopy, and X-ray diffraction to prove the existence of hybrid Gr/Au or GO/Au NCPs. The synthesized NCPs were further evaluated using the photocatalytic reaction of methylene blue (MB), a synthetic dye, under UV radiation, visible light (central wavelength of 470 nm), and full spectrum of solar light. Both Gr/Au and GO/Au NCPs exhibited photocatalytic degradation of MB under solar light illumination with removal efficiencies of 92.1% and 94.5%, respectively.

π-Extended Coumarins Derived with Nonhydrolyzable Iminophosphoranes as Two-Photon-Excited Fluorophores.

Novel coumarin-iminophosphorane (IPP) fluorophores that have stable resonance contributions from aza-ylides were formed by using the nonhydrolysis Staudinger reaction. The N═P formation reaction kinetics obey the conventional Staudinger reaction. The absorption and emission profiles of the coumarin-IPP derivatives can be fine-tuned: an electron-donating group at PPh3 enhances absorption and fluorescence, whereas an electron-withdrawing group at C-3 drives absorption and emission peaks toward blue-light wavelengths. Two-photon adsorption, accompanied by anti-Stokes fluorescence, is achieved under near-infrared femtosecond laser excitation.

Targeted photoresponsive carbazole-coumarin and drug conjugates for efficient combination therapy in leukemia cancer cells.

Phototriggered drug delivery systems (PTDDSs) facilitate controlled delivery of drugs loaded on photoactive platform to the target region under light stimulation. The present study investigated the synthesis and efficacy of carbazole-coumarin (CC)-fused heterocycles as a PTDDS platform for the photocontrolled release of a chemotherapeutic agent, chlorambucil, in an in vitro model of human breast and leukemia cancer cells. CC-fused heterocycles were constructed using 4-hydroxycarbazole as the starting material, and further modification of these heterocycles yielded two CC derivatives. CC-7 with an additional - COOH group and CC-8 with the triphenylphosphonium (TPP) group, a mitochondria-targeting ligand introduced in the carbazole ring, dissolved in polar solvents and exhibited emission bands at 360 and 450 nm, respectively. The results indicate that visible light of 405 nm triggers the photolysis of the CC-drug conjugate and efficiently delivers the drug in both in vitro cancer cell models. Cytotoxicity evaluation indicates the suppression of proliferation of both types of cells treated with CC-8 under synergy effect combining drug potency and photosensitization. Further, the lower IC50 of CC-8 toward leukemia cells suggests the efficacy of the TPP ligand in increasing the bioavailability of CC-drug conjugates in leukemia treatment. Studies on mitochondria-targeting drug delivery systems are required for improving the performance of anticancer drugs.

Photodegradable coumarin-derived amphiphilic dendrons for DNA binding: Self-assembly and phototriggered disassembly in water and air-water interface.

In this article, we demonstrate the self-assembly and photoresponive behavior of a novel coumarin-based amphiphilic dendron in both aqueous solution and air-water interface. The dendritic structure, namely C-IG1, was composed of a lipophilic cholesterol and hydrophilic poly(amido amine) (PAMAM) dendron, and the amphiphilic counterpart is interconnected by a photolabile coumarin carbonate ester, enabling the photoinduced degradation of the amphiphiles in protic solvents via SN1-like mechanism. A Nile red solubilization fluorescence assay suggests a low critical aggregation concentration for the micelle formation of C-IG1 in aqueous solutions (3.9 × 10-5 M); the Langmuir analysis further indicates that C-IG1 possesses significant compressibility in air-water interface, eventually forming homogeneous monolayers with a final molecular area (A0) of 36 Å2. Notably, the micelles and Langmuir monolayer are quite stable until photo-triggered dissociation based on the photocleavage of C-IG1 amphiphile activated by 365-nm incident light. Moreover, the transition in interfacial morphology of the Langmuir monolayer during the assembly and photodegradation processes also can be visually analyzed by incorporating Nile red probes with in situ monitoring through fluorescence microscopy. The thin film deposited on a glass substrate by the Langmuir-Blodgett technique also shows a photoresponsive behavior based on the change in the contact angles of a water droplet on the surface upon light stimulation. The binding affinity of C-IG1 and cyclic DNA determined by the fluorescence quenching analysis of the coumarin reporter suggests a ground-state macromolecular complexation process occurring through polyvalent interactions between the pseudodendrimers and biomacromolecules. The ethidium bromide displacement assay further indicates thus dendriplex formation at low nitrogen-to-phosphorous value (N/P < 1) and confirms that the decomplexation accompanied by DNA release can be achieved through an active phototriggered route under spatiotemporal control.

Near-Infrared-Triggered Photodynamic Therapy toward Breast Cancer Cells Using Dendrimer-Functionalized Upconversion Nanoparticles.

Water-soluble upconversion nanoparticles (UCNPs) that exhibit significant ultraviolet, blue, and red emissions under 980-nm laser excitation were successfully synthesized for performing near infrared (NIR)-triggered photodynamic therapy (PDT). The lanthanide-doped UCNPs bearing oleate ligands were first exchanged by citrates to generate polyanionic surfaces and then sequentially encapsulated with NH2-terminated poly(amido amine) (PAMAM) dendrimers (G4) and chlorine6 (Ce6) using a layer-by-layer (LBL) absorption strategy. Transmission electron microscopy and X-ray diffraction analysis confirm that the hybrid UCNPs possess a polygonal morphology with an average dimension of 16.0 ± 2.1 nm and α-phase crystallinity. A simple calculation derived through thermogravimetric analysis revealed that one polycationic G4 dendrimer could be firmly accommodated by approximately 150 polyanionic citrates through multivalent interactions. Moreover, zeta potential measurements indicated that the LBL fabrication results in the hybrid nanoparticles with positively charged surfaces originated from these dendrimers, which assist the cellular uptake in biological specimens. The cytotoxic singlet oxygen based on the photosensitization of the adsorbed Ce6 through the upconversion emissions can be readily accumulated by increasing the irradiation time of the incident lasers. Compared with that of 660-nm lasers, NIR-laser excitation exhibits optimized in vitro PDT effects toward human breast cancer MCF-7 cells cultured in the tumorspheres, and less than 40% of cells survived under a low Ce6 dosage of 2.5 × 10-7 M. Fluorescence microscopy analysis indicated that the NIR-driven PDT causes more effective destruction of the cells located inside spheres that exhibit significant cancer stem cell or progenitor cell properties. Moreover, an in vivo assessment based on immunohistochemical analysis for a 4T1 tumor-bearing mouse model confirmed the effective inhibition of cancer cell proliferation through cellular DNA damage by the expression of Ki67 and γH2AXser139 protein markers. Thus, the hybrid UCNPs are a promising NIR-triggered PDT module for cancer treatment.

Synthesis of photoresponsive hybrid alginate hydrogel with photo-controlled release behavior.

A photoresponsive hybrid alginate hydrogel was successfully prepared by Ca(2+)-mediated crosslinking reaction with a mixture of ß-cyclodextrin-grafted alginate (ß-CD-Alg) and diazobenzene-modified poly(ethylene glycol) (Az2-PEG). The water-soluble Az2-PEG exhibits efficient trans-to-cis isomerization of the terminal azobenzene moieties under UV-light irradiation and readily switched back to the initial trans state under visible light. Because of low affinity between ß-CD and cis-Az, the host-guest inclusion complex formed by ß-CD and trans-Az gradually dissociates under UV-light exposure. Accordingly, the bulk gel exhibits substantial photo-induced transformation in gel morphology by the appearance of significant comb-like cavities. This photosensitive behavior accompanied by the structural degradation enables the rapid release of entrapped dye molecules under UV light stimulus. Moreover, an incident light with higher power and mild acidic environment are capable of accelerating the photo-triggered release, thus allowing the potential applications toward acute wound healing.

Optothermal Switching of Cholesteric Liquid Crystals: A Study of Azobenzene Derivatives and Laser Wavelengths.

The laser-initiated thermal (optothermal) switching of cholesteric liquid crystals (CLCs) is characterized by using different azobenzene (Azo) derivatives and laser wavelengths. Under 405-nm laser irradiation, Azo-doped CLCs undergo phase transition from cholesteric to isotropic. No cis-to-trans photoisomerization occurs when the 405-nm laser irradiation is blocked because only a single laser is used. The fast response of Azo-doped CLCs under the on-off switching of the 405-nm laser occurs because of the optothermal effect of the system. The 660-nm laser, which cannot be used as irradiation to generate the trans-cis photoisomerization of Azo, is used in Anthraquinone (AQ)-Azo-doped CLCs to examine the optothermal effect of doped Azo. The results show that the LC-like Azo derivative bearing two methyl groups ortho to the Azo moiety (A4) can greatly lower the clearing temperature and generate large amount of heat in AQ-A4-doped CLCs.

Self-aggregation of amphiphilic [60]fullerenyl focal point functionalized PAMAM dendrons into pseudodendrimers: DNA binding involving dendriplex formation.

In this research, we successfully performed a "click" synthesis of amphiphilic poly(amido amine) dendron-bearing fullerenyl conjugate (C60 G1 ) using a copper(I)-catalyzed azide-alkyne cycloaddition reaction. The strong hydrophobicity of the C60 moiety induces self-assembly of C60 G1 into core-shell-like "pseudodendrimers" with a uniform size distribution and positively charged peripherals. The pseudodendrimers were well-characterized by atomic force microscopy (AFM), transmission electron microscopy, and dynamic light scattering. On the basis of electrostatic interactions, the polycationic C60 G1 assembly can serve as a nonviral gene vector. An ethidium bromide displacement assay and agarose gel electrophoresis both indicated that C60 G1 assembly forms stable complexes with the cyclic reporter gene (pEGFP-C1) at low nitrogen-to-phosphorous (N/P) ratios. AFM analysis revealed a dynamic complex-formation process, and confirmed the synthesis of C60 G1 /pEGFP-C1 hybrids with a particle dimensions less than 200 nm. Fluorescence microscopy and flow cytometry revealed that 51% of HeLa and 43% of MCF-7 cells are positive to the YOYO-1-labeled hybrids at an N/P ratio of 2, being comparable to TurboFect-mediated delivery.

trans/cis-Isomerization of fluorene-bridged azo chromophore with significant two-photon absorbability at near-infrared wavelength.

Azo-containing materials have been proven to possess second-order nonlinear optical (NLO) properties, but their third-order NLO properties, which involves two-photon absorption (2PA), has rarely been reported. In this study, we demonstrate a significant 2PA behavior of the novel azo chromophore incorporated with bilateral diphenylaminofluorenes (DPAFs) as a π framework. The electron-donating DPAF moieties cause a redshifted π-π* absorption band centered at 470 nm, thus allowing efficient blue-light-induced trans-to-cis photoisomerization with a rate constant of 2.04 × 10(-1) min(-1) at the photostationary state (PSS). The open-aperture Z-scan technique that adopted a femtosecond (fs) pulse laser as excitation source shows an appreciably higher 2PA cross-section for the fluorene-derived azo chromophore than that for common azobenzene dyes at near-infrared wavelength (λex =800 nm). Furthermore, the fs 2PA response is quite uniform regardless of the molecular geometry. On the basis of the computational modeling, the intramolecular charge-transfer (ICT) process from peripheral diphenylamines to the central azo group through a fluorene π bridge is crucial to this remarkable 2PA behavior.

Direct formation of platinum nanoparticles by internally isopropanol-modified dendritic poly(amido amine).

We report a reducing agent-free method for preparing platinum (Pt) nanoparticles by internally isopropanol (IPA)-modified dendritic poly(amido amine) (PAMAM). The internally modified dendritic PAMAM were synthesized via divergent strategy using 1,3-diaminopropanol as a linking spacer, and NMR analyses confirm the embedded IPA moieties within the dendrimers by the appearance of characteristic proton and carbon resonances at 3.81 and 67.9 ppm, respectively. The in situ formation of stable Pt colloids was carried out by thermal treatment in the presence of internally modified dendritic PAMAM bearing either ester or alcohol peripherals, suggesting that the internal IPA functionalities dominate the reduction of Pt4+ ions. Moreover, the overall reducing rate was accelerated with increasing pH values. This result agreed with a reaction feature for preparing metal nanocomposites through polyol process in which basic environment facilitates the thermal-promoted reduction of metal ions accompanied with the oxidation of internal hydroxyl groups. The morphology of the dendrimer/Pt composite monitored by a transmission electron microscope (TEM) exhibited narrowly dispersed and roughly spherical shaped nanoparticles with a mean diameter of 5.4 nm.

Intrinsically fluorescent PAMAM dendrimer as gene carrier and nanoprobe for nucleic acids delivery: bioimaging and transfection study.

This study successfully evaluated gene delivery and transfection toward rat C6 glioma cell lines mediated by intrinsic blue fluorescent poly(amido amine) (PAMAM) dendrimer. We used three antisense oligonucleotides, (AS-ODN) p75, NGF1, and NGF2 for knocking down specific protein expressions. The three oligonucleotides were electrostatically associated with the photoluminescent amino-terminated PAMAM dendrimer to yield fluorescent complexes at various nitrogen-to-phosphorus (N/P) ratios. Compared with pristine PAMAM dendrimer and hyperbranched polyethylenimine (PEI), the fluorescent PAMAM dendrimer revealed lower in vitro cytotoxicity toward C6 cells, allowing us to transfect the cells with the AS-ODN complexes under a higher N/P ratio. Due to the intrinsic fluorescence, cellular uptake behavior could be directly analyzed by fluorescence microscopy and flow cytometry, without additional fluorescence labeling. As expected, the result clearly suggested that the uptake efficiency increased as the N/P value increased. Furthermore, the quantified data obtained from flow cytometry indicated relatively higher uptake efficiency for the p75 complex, which is mainly due to different association patterns between the fluorescent dendrimer and AS-ODNs. At N/P = 20, atomic force microscopic analysis confirmed that the p75 complex formed well-condensed, spherical particles with dimensions less than 200 nm, but that NGF2 AS-ODN associated poorly with the dendrimer. Finally, Western blot analysis indicated that these complexes were capable of knocking down the specific protein expression to a certain level, being comparable to the hyperbranched PEI-mediated gene transfection. Our preliminary results clearly indicated that intrinsic fluorescent PAMAM dendrimers show promise as gene vehicles that can achieve delivery, transfection, and bioimaging at the same time.

Immobilization of amphiphilic dendron on silica particles toward the application to ultrahigh pressure liquid chromatography.

Amphiphilic poly(amido amine) (PAMAM) dendrons were immobilized on the surface of silica particles, following the solid phase strategy. PAMAM dendrons were constructed by the repetitive feeding of methyl acrylate and ethylenediamine as the monomers. The peripheral functionalization of amine to long alkyl ends generated the amphiphilic PAMAM dendron on the silica surface. These amphiphilic dendron-modified silica particles were applicable as new packing materials for ultrahigh pressure liquid chromatography.

Surface functionalization of carbon micro coils and their selective immobilization on surface-modified silicon substrates.

Surface functionalization of carbon micro coils (CMCs) was performed by acid treatment at different times. Nitric acid oxidation produced CMC with acidic functional groups, although morphology of CMCs was modified after the oxidation. The selective immobilization of as-prepared CMC from an aqueous dispersion was examined on differently surface-modified silicon substrates. It was confirmed that the acid-treated CMC was selectively immobilized on a silicon substrate by chemical bonding with amine-terminated self-assembled monolayers on a silicon substrate, while the pristine CMC was not.

Fluorescence Investigations of Oxygen-Doped Simple Amine Compared with Fluorescent PAMAM Dendrimer.

Blue emission of oxygen-doped tertiary amine (triethylamine), a key unit of fluorescent poly(amido amine) dendrimer, was demonstrated. It was found that the fluorescence intensity could be further enhanced if the tertiary amines locate densely in the dendrimer interior as the branching sites. Moreover, a solvatochromic phenol blue, instead of oxygen, is able to induce the blue fluorescence of the tertiary amino-branching sites based on a guaranteed host-guest complexation of phenol blue molecules and dendrimer interior.