PubMed Health⌕ Search

Biomedical subjects

Jiyu Fang

Publications and source records attributed to Jiyu Fang.

12 recordsLinked to original sources
PubMed2006

Bending and radial deformation of lipid tubules on self-assembled thiol monolayers.

Lipid tubules represent a hollow, cylindrical supramolecular structure formed by rolled-up lipid bilayers. We find that the lipid tubules of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine can be bent into a loopike shape by the shrinking contact line of droplets on self-assembled monolayers (SAMs) of 1-dodecanethiol. The persistence length of individual lipid tubules is estimated to be approximately 41 microm. The radial deformation of the lipid tubules on SAMs is studied under applied load using atomic force microscope. The stiffness of the tubules in the radial direction is found to increase when the number of the lipid bilayers in the tubule wall increases.

Biomechanical Phenomena↗
PubMed2006

Nanoscale ripples in self-assembled lipid tubules.

Self-assembled cylindrical tubules of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (DC(8,9)PC) have been studied by atomic force microscopy in both the height and amplitude modes. Nanoscale ripple structures in the cylindrical lipid tubules are clearly resolved in amplitude mode images. The periodicity of the ripples is found to be 200 +/- 30 nm for tubules with diameters in the range from 200 to 650 nm. The angle of the ripples with respect to the equator of the tubules shows a bimodal distribution with centers at approximately 28 degrees and approximately 5 degrees.

Journal Article↗
PubMed2006

Positioning and alignment of lipid tubules on patterned Au substrates.

This paper presents a method for positioning and aligning self-assembled tubules of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphochloline (DC(8,9)PC) by withdrawing a patterned Au substrate from tubule solution. The patterned Au substrates with alternating bare Au stripes and thiol monolayer stripes are formed by microcontact printing. We find that the lipid tubules selectively adsorb on the bare Au stripes but show no orientation order. By withdrawing the patterned Au substrates at the direction along the stripes from tubule solution, the lipid tubules are found to be aligned along the direction of the Au stripes. The angular distribution and the density of the aligned lipid tubules depend on the withdrawal rates and the adsorption time, respectively. We conclude that forces causing tubule alignment that originate in the surface tension associated with the moving meniscus dominate alignment forces exerted by the patterned Au substrates.

Journal Article↗
PubMed2005

Liquid-crystal imaging of molecular-tilt ordering in self-assembled lipid tubules.

Self-assembled cylindrical tubules of chiral phospholipids are interesting supramolecular structures. Understanding the molecular-tilt order is a key step in controlling the size and shape of the tubules and designing new functional materials. The current theories based on the chiral interactions, coupled with molecular tilt, have predicted that the tubules could have both uniform and modulated tilt states. Here, we image the molecular-tilt order in the self-assembled tubules of a chiral phospholipid by using liquid crystals as an optical amplification probe. We demonstrate that the organization of the molecular-tilt azimuth in the lipid tubules can induce an azimuthal orientation in the liquid crystals. Both uniform and modulated tilt states of the lipid tubules are observed after liquid-crystal optical amplification.

Diagnostic Imaging↗
PubMed2005

Two-dimensional ordered arrays of aligned lipid tubules on substrates with microfluidic networks.

Microfluidic networks is a powerful tool for aligning one-dimensional materials over a large area on solid substrates. Here we show that lipid nano- and microtubules can be assembled into two-dimensional (2-D) parallel arrays with controlled separations by combining fluidic alignment with dewetting, which occurs within microchannels. We also demonstrate that lipid tubules can be bent into a well-defined shape at the entrance of the channels by the capillary force. Atomic force microscopy is used to study the structure and stability of the aligned lipid tubules on substrates. The deposition experiments with silica colloidal particles show that the 2-D parallel-aligned tubules can be used as a template to synthesize silica films with controlled morphologies and patterns on substrates in a single-step process.

Journal Article↗
PubMed2005

Patterning polymerized lipid vesicles with soft lithography.

The applications of soft lithography in patterning polymerized lipid vesicles of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine on glass substrates are reported. We demonstrate that the polymerized vesicles can be used as a high molecular weight ink to be transferred from a PDMS stamp onto a glass substrate to form two-dimensional stripes with a controlled separation. By combining channel flow with dewetting within microfluidic networks, we assemble the polymerized vesicle into three-dimensional stripes and one-dimension lines on glass substrates. Atomic force microscopy shows that these patterned vesicle structures are stable on glass substrates. The simple, stable, and precise immobilization of lipid vesicles on solid substrates will open up the possibility of integrating them in biosensors and microelectronic devices.

Journal Article↗
PubMed2003

Fluorescence spectral properties of cyanine dye-labeled DNA oligomers on surfaces coated with silver particles.

We examined the fluorescence spectral properties of DNA oligomers, labeled with Cy3 or Cy5, when bound to quartz surfaces coated with metallic silver particles. Prior to binding of labeled DNA the surfaces were treated with polylysine or 3-aminopropyl triethoxysilane or were coated with avidin for binding of biotinylated oligomers. The fluorescence intensities were increased an average of 8-fold on these surfaces. Despite the increased emission intensity, the photostability of the labeled DNA was the same or higher on the silver-coated surfaces than on the uncoated slides. The time-integrated intensities, that is the area under the intensity plots with continuous illumination, increased an average of 6-fold. In all cases the lifetimes were dramatically shortened on the silver particles, indicating an over 100-fold increase in the radiative decay rates. These results suggest the use of substrates containing silver particles for increased sensitivity of DNA detection on DNA arrays.

Avidin↗
PubMed2003

Increased resonance energy transfer between fluorophores bound to DNA in proximity to metallic silver particles.

We examined the effects of metallic silver particles on resonance energy transfer (RET) between fluorophores covalently bound to DNA. A coumarin donor and a Cy3 acceptor were positioned at opposite ends of a 23-bp double helical DNA oligomer. In the absence of silver particles the extent of RET is near 9%, consistent with a Forster distance R(0) near 50 A and a donor to acceptor distance near 75 A. The transfer efficiency increased when the solution of AMCA-DNA-Cy3 was placed between two quartz plates coated with silver island films to near 64%, as determined by both steady-state and time-resolved measurements. The apparent R(0) in the presence of silver island films increases to about 110 A. These values of the transfer efficiency and R(0) represent weighted averages for donor-acceptor pairs near and distant from the metallic surfaces, so that the values at an optimal distance are likely to be larger. The increased energy transfer is observed only between two sandwiched silvered slides. When we replaced one silvered slide with a quartz plate the effect vanished. Also, the increased energy transfer was not observed for silvered slides separated more than a few micrometers. These results suggest the use of metal-enhanced RET in PCR, hybridization, and other DNA assays, and the possibility of controlling energy transfer by the distance between silver surfaces.

Base Sequence↗
PubMed2003

Fluorescence spectral properties of cyanine dye labeled DNA near metallic silver particles.

Recent studies have demonstrated that silver metallic particles can increase the quantum yield and decrease the lifetimes of nearby fluorophores. These studies are extended to double stranded DNA oligomers labeled with N,N'-(dipropyl)-tetramethylindocarbocyanine (Cy3) or N,N-(dipropyl)-tetramethylindodicarbocyanine (Cy5). The proximity to silver particles increases the apparent quantum yields and decreases the lifetimes of the double helical DNA 23-mer labeled individually with Cy3 or Cy5. The decreased lifetimes are accompanied by apparently increased photostability of the labeled oligomers near silver particles. Because of spatial averaging across the sample these results are likely to significantly underestimate the effects of silver particles on labeled DNA localized at an optimal distance from the metallic surface. These results suggest that DNA arrays fabricated on substrates with silver particles can display increased sensitivity and photostability in the analysis of gene expression.

Base Sequence↗
PubMed2002

Radiative decay engineering. 2. Effects of Silver Island films on fluorescence intensity, lifetimes, and resonance energy transfer.

Metallic surfaces can have unusual effects on fluorophores such as increasing or decreasing the rates of radiative decay and the rates of resonance energy transfer (RET). In the present article we describe the effects of metallic silver island films on the emission spectra, lifetimes, and energy transfer for several fluorophores. The fluorophores are not covalently coupled to the silver islands so that there are a range of fluorophore-to-metal distances. We show that proximity of fluorophores to the silver islands results in increased fluorescence intensity, with the largest enhancement for the lowest-quantum-yield fluorophores. Importantly, the metal-induced increases in intensity are accompanied by decreased lifetimes and increased photostability. These effects demonstrate that the silver islands have increased the radiative decay rates of the fluorophore. For solvent-sensitive fluorophores the emission spectra shifted to shorted wavelengths in the presence of the silver islands, which is consistent with a decrease of the apparent lifetime for fluorophores near the metal islands. We also observed an increased intensity and blue spectral shift for the protein human glyoxalase, which displays a low quantum yield for its intrinsic tryptophan emission. In this case the blue shift is thought to be due to increased emission from a buried low-quantum-yield tryptophan residue. Increased intensities were also observed for the intrinsic emission of the nucleic acid bases adenine and thymine and for single-stranded 15-mers poly(T) and poly(C). And finally, we observed increased RET for donors and acceptors in solution and when bound to double-helical DNA. These results demonstrate that metallic particles can be used to modify the emission from intrinsic and extrinsic fluorophores in biochemical systems.

Adenine↗