silicon and azobenzene

The concept of using two-photon excitation in the NIR for the spatiotemporal control of biological processes holds great promise. However, its use for the delivery of nucleic acids has been very scarcely described and the reported procedures are not optimal as they often involve potentially toxic materials and irradiation conditions. This work prepares a simple system made of biocompatible porous silicon nanoparticles (pSiNP) for the safe siRNA photocontrolled delivery and gene silencing in cells upon two-photon excitation. PSiNP are linked to an azobenzene moiety, which possesses a lysine group (pSiNP@ICPES-azo@Lys) to efficiently complex siRNA. Non-linear excitation of the two-photon absorber system (pSiNP) followed by intermolecular energy transfer (FRET) to trans azobenzene moiety, result in the photoisomerization of the azobenzene from trans to cis and in the destabilization of the azobenzene-siRNA complex, thus inducing the delivery of the cargo siRNA to the cytoplasm of cells. Efficient silencing in MCF-7 expressing stable firefly luciferase with siRNAluc against luciferase is observed. Furthermore, siRNA against inhibitory apoptotic protein (IAP) leads to over 70% of MCF-7 cancer cell death. The developed technique using two-photon light allows a unique high spatiotemporally controlled and safe siRNA delivery in cells in few seconds of irradiation.

Topics: Cell Line, Tumor; Humans; Nanoparticles; Neoplasms; Porosity; RNA, Small Interfering; Silicon; Transfection

A novel surface-modification strategy has been developed for the construction of a photocontrolled silicon wafer surface with switchable wettability based on host-guest inclusion complexation. The silicon wafer was first modified by guest molecule azobenzene (Azo) via a silanization reaction. Subsequently, a series of polymers with different polarities were attached to host molecule β-cyclodextrin (β-CD) to prepare β-CD-containing hemitelechelic polymers via click chemistry. Finally, a photocontrolled silicon wafer surface modified with polymers was fabricated by inclusion complexation between β-CD and Azo, and the surface properties of the substrate are dependent on the polymers we used. The elemental composition, surface morphology, and hydrophilic/hydrophobic property of the modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscope, and contact angle measurements, respectively. The antifouling property of the PEG-functionalized surface was evaluated by a protein adsorption assay using bovine serum albumin, which was also characterized by XPS. The results demonstrate that the surface modified with PEG possesses good protein-resistant properties.

Topics: Animals; Azo Compounds; beta-Cyclodextrins; Cattle; Click Chemistry; Particle Size; Photochemical Processes; Serum Albumin, Bovine; Silicon; Surface Properties; Wettability

4-Nitrobenzenediazonium (4-NBD) and 4-bromobenzenediazonium (4-BBD) salts were grafted electrochemically onto H-terminated, p-doped silicon (Si) surfaces. Atomic force microscopy (AFM) and ellipsometry experiments clearly showed layer thicknesses of 2-7 nm, which indicate multilayer formation. Decreasing the diazonium salt concentration and the reaction time resulted in a smaller layer thickness, but did not prevent the formation of multilayers. It was demonstrated, mainly by X-ray photoelectron spectroscopy (XPS), that the diazonium salts not only react with the H-terminated Si surface, but also with electrografted phenyl groups via azo-bond formation. These azo bonds can be electrochemically reduced at Ered = -1.5 V, leading to the corresponding amino groups. This reduction resulted in a modest decrease in layer thickness, and did not yield monolayers. This indicates that other coupling reactions, notably a biphenyl coupling, induced by electrochemically produced phenyl radicals, take place as well. In addition to the azo functionalities, the nitro functionalities in electrografted layers of 4-NBD were independently reduced to amino functionalities at a lower potential (Ered = -2.1 V). The presence of amino functionalities on fully reduced layers, both from 4-NBD- and 4-BBD-modified Si, was shown by the presence of fluorine after reaction with trifluoroacetic anhydride (TFAA). This study shows that the electrochemical reduction of azo bonds generates amino functionalities on layers produced by electrografting of aryldiazonium derivatives. In this way multifunctional layers can be formed by employing functional aryldiazonium salts, which is believed to be very practical in the fabrication of sensor platforms, including those made of multi-array silicon nanowires.

Topics: Azo Compounds; Electrochemical Techniques; Molecular Structure; Oxidation-Reduction; Silicon; Surface Properties

Photoresponsive monolayers of hydrophilically substituted azobenzenes have been prepared by reaction on aminosilane monolayers on silicon surfaces. Grafting densities in the 0.2-1.0 molecule/nm(2) range were determined by X-ray reflectometry. The monolayers exhibit reversible photoisomerization, switching from a more hydrophilic trans state to a less hydrophilic cis state upon UV irradiation, in contrast with the usual behavior of most azobenzene monolayers that switch from a less to a more hydrophilic state. This indicates that the wettability is not dominated by the change in the dipole moment of the azobenzene moiety but originates from variations in the composition of the outer surface of the monolayers resulting from the reorientation of the substituent groups. The light-driven change in the water contact angle correlates linearly with the grafting density but remains small. However, the wettability contrast can be increased by forcing the molecules to stand in an improved vertical orientation, either by densifying the underlying aminosilane monolayer or by filling the voids left at the bottom of the layer of grafted azobenzene molecules.

Topics: Azo Compounds; Membranes, Artificial; Molecular Structure; Photochemistry; Silicon; Surface Properties; Water; Wettability

Topics: Azo Compounds; Microtechnology; Nanotechnology; Optical Phenomena; Polymers; Printing; Silicon

We have synthesized a novel mesogenic azobenzene molecule and studied its monolayer film properties at air-water interface (Langmuir film) and air-solid interface (Langmuir-Blodgett film). The material, H-shaped dimer bis[5-(4'-n-dodecyloxy benzoyloxy)-2-(4''-methylphenylazo)phenyl] adipate (12D1H) exhibits a smectic C phase between 51 and 48 degrees C on cooling. Surface manometry studies showed the formation of a stable monolayer at the air-water interface. Brewster angle microscopy (BAM) showed that liquid domains coexisting with the gas region at large area transformed to a uniform liquid phase with increasing surface density and finally to a collapsed state. We have carried out atomic force microscope (AFM) studies on Langmuir-Blodgett (LB) films transferred onto freshly cleaved hydrophilic mica substrate. The AFM images showed domains of height of about 3.8 nm, which corresponds to the estimated height of the molecule confirming the formation of monomolecular film. On a hydrophobic silicon substrate, the LB transfer yields a bilayer film, which dewets to form uniform nanodroplets of diameter of about 100 nm and height in the range 10-50 nm. Our analysis indicated that the mechanism involved in the formation of nanodroplets can be attributed to spinodal dewetting. The 12D1H molecule containing an azobenzene group undergoes a trans to cis transformation in the presence of ultraviolet light. Our surface manometry studies showed that the monolayer in the presence of ultraviolet light was more stable with a collapse pressure three times that of the monolayer in the dark.

Topics: Adipates; Air; Azo Compounds; Dimerization; Membranes, Artificial; Molecular Structure; Particle Size; Silicon; Surface Properties; Water