Organic Fluorescent Molecule with High Solid State Lumines- cent Efficiency and Protonation Stimuli-response

A novel organic fluorophor with high solid state luminescent efficiency based on 1,4-bis（2,2-di（pyridin-2-yl）- vinyl）benzene （BDP2VB） was designed and synthesized. It emits faintly in solution, but becomes a strong emitter in the aggregate state, demonstrating its aggregation induced emission （AIE） property. According to the crystal struc- ture analysis, J-type aggregation was formed in the packing mode of the molecule, which was demonstrated to be beneficial to gain high fluorescent quantum efficiency in solid state. Additionally, the emission color of BDP2VB can change dramatically in solid state as well as in solution by the protonation stimuli.

Near-Field Spot for Localized Light-Excitation of a Single Fluorescent Molecule

Zero-mode waveguides have become important tools for the detection of single molecules.There are still,however,serious challenges because large molecules need to be packed into nano-holes.To circumvent this problem,we investigate and numerically simulate a novel planar sub-wavelength 3-dimension(3D)structure,which is named as near-field spot.It enables the detection of a single molecule in highly concentrated solutions.The near-field spot can produce evanescent waves at the dielectric/water interface,which exponentially decay as they travel away from the dielectric/water interface.These evanescent waves are keys for the detection of fluorescently tagged single molecules.A numerical simulation of the proposed device shows that the performance is comparable with a zero-mode waveguide.Additional degrees-of-freedom,however,can potentially supersede its performance.

Appropriate Gate Time for Single Molecular Photon Detection Based on Optimal Signal-to-Noise Ratio Analyses

Signal-to-noise ratio of fluorescence detection from a single molecule ＆ analysed by using time-gated techniques. It is found that the optimal signal-to-noise ratio can be obtained by choosing an appropriate gate time with a certain optical background. The dependences of molecular fluorescence lifetime and the optimal signal-to-noise ratio on the appropriate gate time are respectively discussed with two kinds of background sources~ chaotic state with uniform distribution and coherent state with exponential distribution in time domain. For chaotic state background we find that a certain range for appropriate gate time can be obtained with a definite fluorescence lifetime, larger fluorescence lifetime would lower the value of optimal signal-to-noise ratios. For coherent state background we find that there is also a narrow range of appropriate gate time when lifetime of single molecule is less than that of background photons.

Protein–membrane interactions investigated with surface-induced fluorescence attenuation

Research on protein-membrane interactions has been undeveloped due to the lack of proper techniques to detect the position of proteins at membranes because membranes are usually only about 4-nm thick. We have recently developed a new method named surface-induced fluorescence attenuation （SIFA） to track both vertical and lateral kinetics of a single labelling dye in supported lipid bilayers. It takes advantage of strong interaction between a light-emitting dye and a partially reflecting surface. By applying the technique to membrane proteins being fluorescently labelled at different residues, here we show that SIFA can measure not only the insertion depth of a dye inside a lipid bilayer, but also the position of a dye in solution near the surface. SIFA can therefore be used to study membrane proteins of various types.

Segmental dynamics near the chain end of polystyrene in its ultrathin films:a study by single-molecule fluorescence de-focus microscopy

Rotational motion of fluorophores chemically attached to polystyrene chain-ends in ultra-thin films on solid substrates was studied by single-molecule fluorescence de-focus microscopy.The collective feature of the rotational motion was found and evidenced by the sharp change of the population of fluorophores undergoing rotational motion within a very narrow temperature range(named as the changing temperature,T c).The T c value was found to depend on film thickness and interfacial chemistry and the variation of the T c value is also dependent on the molecular weight of the polymer.The results demonstrate that the spatial confinement effect enhances the segmental mobility near the polymer chain-ends while the interfacial attraction restricts the segmental motion inside the thin film.

Preparation and characterization of sulfonated chitosan-modified gold nanoparticles and their surface electronic payload of charged drugs

Chitosan(CS), a kind of naturally produced polysaccharide with extraordinary biocompatibility and biodegradation, shows much potential to act as reducing and stabilizing agent in the synthesis of gold nanoparticles(AuNPs) for drug delivery. To solve the poor solubility and expand the pharmaceutical applications of CS, various CS derivatives through rational design have been developed and further used to prepare, stabilize, and mediate self-assembling of gold materials. Herein, we chose sulfonic chitosan as a stabilizing reagent for the synthesis of highly stable AuNPs(AuNP/SCSs) with diameters of about 3 nm. For investigating their surface electronic payload of charged drugs, the negatively charged fluorescence isothiocyanate(FITC) and positively charged Rhodamine B(Rb) were used as models to be modified on the surface of the AuNP/SCSs via a layer-by-layer(Lb L) method. With a basis of the fluorescence resonance energy transfer(FRET) principle, via adjusting the distance between AuNPs and fluorescent molecules by tuning the layers of charged polymers, the regulation of the fluorescence intensity of the fluorescent molecules has been achieved. In addition, the drug loading efficiency was investigated.

Voyage inside the cell:Microsystems and nanoengineering for intracellular measurement and manipulation

Properties of organelles and intracellular structures play important roles in regulating cellular functions,such as gene expression,cell motility and metabolism.The ability to directly interrogate intracellular structures inside a single cell for measurement and manipulation has significant implications in the understanding of subcellular and suborganelle activities,diagnosing diseases,and potentially developing new therapeutic approaches.In the past few decades,a number of technologies have been developed to study single-cell properties.However,methods of measuring intracellular properties and manipulating subcellular structures have been largely underexplored.Due to the even smaller size of intracellular targets and lower signal-to-noise ratio than that in wholecell studies,the development of tools for intracellular measurement and manipulation is challenging.This paper reviews emerging microsystems and nanoengineered technologies for sensing and quantitative measurement of intracellular properties and for manipulating structures inside a single cell.Recent progress and limitations of these new technologies as well as new discoveries and prospects are discussed.

Synthesis and characterization of 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles with two-photon fluorescence properties

Four novel 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on“push-core-pull-core-push”molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig-Horner reaction.Their chemical structures were determined to show trans-vinylene character according to infrared(IR)and 1H nuclear magnetic resonance(NMR)spectra.A very effective energy transfer from the excited units to the p-conjugated bridging unit can enhance the two-photon absorption and two-photon fluorescence.

When does a diblock copolymer probe the interfacial rheological effect?

Lateral diffusion of diblock copolymer residing on the interfaces between two immiscible liquids is investigated at single molecular level. Fluorescence correlation spectroscopy was used to study the diffusion of fluorescence-labeled diblock copolymer,polystyrene-b-polyisoprene, at the interface formed between two immiscible liquids. The interfaces are formed between N,N-dimethylformamide(DMF) and a few immiscible liquids, n-alkane and polyisoprene. Interfacial diffusion coefficient of the diblock copolymer probe is found to decrease monotonously with the increase of the molecular length of the interface constituting liquids. The decrease of diffusion coefficient follows the prediction by Einstein relation using the viscosity of the constituting liquids as the variables only for interfaces between DMF and very small n-alkanes. For interfaces formed between DMF and bigger alkanes and especially between DMF and polyisoprene, the diffusion coefficient is much higher than the calculated value,indicating that the probe molecule starts to probe the much less viscous interfacial region because the interfacial width gets larger,whose thickness is comparable to the molecule size of the liquids.