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.

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.

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.

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.

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.