The surface of a fused silica and oxidized silicon wafer (SiO2/Si(100)) was treated with (4-aminophenyl)trimethoxysilane (1), (3-aminopropyl)triethoxysilane (2), (3-aminopropyl)diethoxymethylsilane (3), and (3-aminopropyl)ethoxydimethylsilane (4) in solution. The thickness of thus formed aminosilane layers was determined with ellipsometry. In most cases silane coupling agents produce monolayers of 6−10 Å thickness, but reagent 2 gives multilayers with variable thickness (6−100 Å) depending upon the dipping time. The aminosilane layers were allowed to react with 4-nitrobenzaldehyde, and formation of the corresponding imines was confirmed by UV−vis spectroscopy. Relative surface density of the amines was calculated from the observed absorbance. In aqueous medium the imines were easily hydrolyzed to regenerate the amine group. The process, the formation, and the subsequent hydrolysis of the imines, can be repeated several times without any noticeable degradation of the absorption characteristics. The ellipsometric data and the measured absorbance show that 3 gives the most uniform molecular layer with the highest surface density of the amine functionality. Meanwhile, 2 provides multilayers lacking uniformity, and the other reagents produce uniform thin layers but with lower surface density of the amine.

The surface of a fused silica and oxidized silicon wafer (SiO2/Si(100)) was treated with (3-aminopropyl)triethoxysilane (1), (3-aminopropyl)diethoxymethylsilane (2), and (3-aminopropyl)ethoxydimethylsilane (3) for 72 h in solution. Thickness of the aminosilylated film out of 1 increases rapidly, and it turns out to be around 100 Å in 72 h. Rather slow increase of the thickness is observed for 2, which produces the layers of 8 and 14 Å in 10 and 72 h, respectively. The reagent 3 produces the monolayers of constant thickness 7−8 Å during the whole span of the reaction. The aminosilane layer was allowed to react with 4-nitrobenzaldehyde to form an imine, and absorbance (A surf) of the imine was recorded by UV−vis spectroscopy. The imine was hydrolyzed in a known volume of water to produce 4-nitrobenzaldehyde, and subsequently its absorbance was measured. Thus observed number of the aldehyde molecules is equivalent to the number of the imine molecules on the surface. With the known surface area of the substrates, the absolute surface density of the imine, that is, the reactive amine group on the surface, was calculated. At an early stage of the aminosilylation with 2, a surface density of 3.9 amine groups per 100 Å2 was measured. A relatively low value was observed for 3. It is also observed that 1 produces a multilayer with rough surface morphology, of which surface density increases sharply by the reaction time. Tilt angle of the imine was estimated from the A surf and the absolute surface density. The angles vary among 23−47° depending on the reaction condition. Second harmonic generation of a laser light of 1064 nm was observed for the imine-formed substrates. X-ray photoelectron spectroscopy utilizing a synchrotron radiation source, in particular for the N(1s) binding energy region, confirmed the chemical transformation. Also, it is observed that the nitro group of the imine is cleaved by X-rays.

Light up my life: Stable, bright, conjugated‐polymer nanoparticles (CPNs) show promise for fluorescence imaging of live cells. The cell‐permeable CPNs are synthesized by a simple solvent exchange, and accumulate exclusively in the cytosol (see picture) without any noticeable inhibition of cell viability.

Fabrication and characterization of 8‐nm‐sized conjugated polymer nanoparticles (CPNs) and two‐photon (2P) imaging of CPN labeled endothelial cells in a collagen‐gel‐based microfluidic device is described. CPNs exhibit super brightness and photostability comparable to quantum dots. The hydrophilicity and non‐toxicity of CPNs enable long‐term monitoring of cells in a tissue model, supporting CPNs' potential in biological and biomedical applications.

BackgroundPost transcriptional gene silencing (PTGS) is a mechanism harnessed by plant biologists to knock down gene expression. siRNAs contribute to PTGS that are synthesized from mRNAs or viral RNAs and function to guide cellular endoribonucleases to target mRNAs for degradation. Plant biologists have employed electroporation to deliver artificial siRNAs to plant protoplasts to study gene expression mechanisms at the single cell level. One drawback of electroporation is the extensive loss of viable protoplasts that occurs as a result of the transfection technology.ResultsWe employed fluorescent conjugated polymer nanoparticles (CPNs) to deliver siRNAs and knockdown a target gene in plant protoplasts. CPNs are non toxic to protoplasts, having little impact on viability over a 72 h period. Microscopy and flow cytometry reveal that CPNs can penetrate protoplasts within 2 h of delivery. Cellular uptake of CPNs/siRNA complexes were easily monitored using epifluorescence microscopy. We also demonstrate that CPNs can deliver siRNAs targeting specific genes in the cellulose biosynthesis pathway (NtCesA-1a and NtCesA-1b).ConclusionsWhile prior work showed that NtCesA-1 is a factor involved in cell wall synthesis in whole plants, we demonstrate that the same gene plays an essential role in cell wall regeneration in isolated protoplasts. Cell wall biosynthesis is central to cell elongation, plant growth and development. The experiments presented here shows that NtCesA is also a factor in cell viability. We show that CPNs are valuable vehicles for delivering siRNAs to plant protoplasts to study vital cellular pathways at the single cell level.

Loosely aggregated conjugated polymer nanoparticles (CPNs) were used as nontoxic and efficient small interfering RNA (siRNA) delivery vehicles with delivery visualization. A significant down regulation (94%) of a target gene was achieved by transfection of HeLa cells with the CPNs/siRNA complexes, supporting CPN as a promising siRNA delivery carrier.

Decarboxylative coupling of sp-sp2 carbons is possible by palladium catalyst. Employing propiolic acid (1) as a difunctional alkyne, and using the consecutive reactions of the Sonogashira reaction and the decarboxylative coupling, unsymmetrically substituted diaryl alkynes were obtained in moderate to good yield.

A synchrotron radiation source was utilized for X-ray photoelectron spectroscopic analysis of a nitrobenzaldimine-formed monolayer. The N(1s) peak intensity for the nitro group becomes reduced upon X-ray irradiation, while C(1s) and O(1s) peaks are invariant. This observation indicates that the nitro group is cleaved selectively, leaving the phenyl ring intact in the layer. The cleavage rate is measured as a function of photon energy and normalized with the photon flux. The cleavage is first-order to the concentration of the nitro group. The rate constant is independent of the incident photon energy, suggesting that the cleavage is not associated with a direct photoexcitation of atomic core electrons. Electrons ejected by the X-ray are proposed as the most viable cause for the bond cleavage. The molecules remaining on the irradiated surface were analyzed with gas chromatography-mass spectrometry coupled with the solid-phase microextraction method after hydrolyzing the imine bond. It is found that the amount of nitrobenzaldehyde is reduced upon the irradiation, but the expected products, benzaldehyde and hydroxybenzaldehyde, are not produced.S0743-7463(98)00349-7 CCC: $15.00