Biomedical subjects

Gang-Yu Liu

Publications and source records attributed to Gang-Yu Liu.

6 recordsLinked to original sources

PubMed2006

High-efficiency stepwise contraction and adsorption nanolithography.

A new miniaturization protocol is demonstrated using stretching and relaxation of an elastomer substrate. A designed microstructure is formed on the stretched substrate and subsequently becomes miniaturized when the substrate relaxes. More importantly, the miniaturized structures can be transferred onto a new substrate for further miniaturization or can be utilized as stamps for nanolithography of designated materials. As an example of this approach, an elastic mold was first cast from a Si mold containing periodic line arrays of 1.5-microm line width. Upon relaxation, line width is reduced to 240 nm. The new elastomer may be used as stamps for micro- and nanofabrication of materials such as proteins. The polymer surface roughness or wrinkling behavior at nanoscale is found to follow classic stability model in solid mechanics. This observation provides means to design and control the surface roughness to meet specific requirements.

Acrylic Resins↗

PubMed2006

Cell mechanics using atomic force microscopy-based single-cell compression.

We report herein the establishment of a single-cell compression method based on force measurements in atomic force microscopy (AFM). The high-resolution bright-field or confocal laser scanning microscopy guides the location of the AFM probe and then monitors the deformation of cell shape, while microsphere-modified AFM probes compress the cell and measure the force. Force and deformation profiles of living cells reveal a cubic relationship at small deformation (<30%), multiple peaks at 30-70% compression, and a rapid increase at over 80% deformation. The initial compression may be described qualitatively and quantitatively using a simple model of a nonpermeable balloon filled with incompressible fluid. Stress peaks reflect cell membrane rupture, followed by the deformation and rupture of intracellular components, beyond which the cell responses become irreversible. The Young's modulus and bending constant of living cell membranes are extracted from the balloon models, with 10-30 MPa and 17-52 kT, respectively. The initial compression of dead and fixed cells is modeled using Hertzian contact theory, assuming that the cell is a homogeneous sphere. Dead cells exhibit a cytoskeleton elasticity of 4-7.5 kPa, while fixation treatment leads to a dramatic increase in the cytoskeletal Young's modulus (150-230 kPa) due to protein cross-linking by imine bonds. These results demonstrate the high sensitivity of the single-cell compression method to the molecular-level structural changes of cells, which suggests a new generic platform for investigating cell mechanics in tissue engineering and cancer research.

Cell Shape↗

PubMed2005

Hybridization with nanostructures of single-stranded DNA.

Nanostructures of single-stranded DNA (ssDNA) were produced within alkanethiol self-assembled monolayers using nanografting, an atomic force microscopy (AFM) based lithography technique. Next, variations of the fabrication parameters, such as the concentration of ssDNA or lines per frame, allowed for the regulation of the density of ssDNA molecules within the nanostructures. The label-free hybridization of nanostructures, monitored using high-resolution AFM imaging, has proven to be highly selective and sensitive; as few as 50 molecules can be detected. The efficiency of the hybridization reaction at the nanometer scale highly depends on the ssDNA packing density within the nanostructures. This investigation provides a fundamental step toward sensitive DNA detection and construction of complex DNA architectures on surfaces.

DNA, Single-Stranded↗

PubMed2004

Molecular-level approach to inhibit degradations of alkanethiol self-assembled monolayers in aqueous media.

A molecular-level approach is developed to prevent or inhibit the degradation processes of alkanethiol self-assembled monolayers (SAMs). Previous studies revealed two degradation pathways: direct desorption and oxidation-desorption. By use of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), in situ and time-dependent imaging reveals and confirms that degradations of alkanethiol SAMs on gold mainly initiate at defect sites, such as domain boundaries and vacancy islands, and then propagate into the ordered domains. Our approach targets at attaching small molecules with preferred adhesion to the defects. The best candidates are aqueous media containing a small amount of amphiphilic surfactant molecules, such as N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO). High-resolution studies demonstrate that DMSO and DMF molecules attach to SAM surfaces and more favorably at defect sites, forming relatively stable adsorbates. This attachment increases the activation energy sufficiently to inhibit both degradation pathways. The robustness of this approach has been investigated as a function of surfactant concentration, solution temperature, and the stirring condition. Molecular-level mechanisms and energetics for degradation inhibition of SAMs are also discussed in detail.

Journal Article↗

PubMed2002

Positioning protein molecules on surfaces: a nanoengineering approach to supramolecular chemistry.

We discuss a nanoengineering approach for supramolecular chemistry and self assembly. The collective properties and biofunctionalities of molecular ensembles depend not only on individual molecular building blocks but also on organization at the molecular or nanoscopic level. Complementary to "bottom-up" approaches, which construct supramolecular ensembles by the design and synthesis of functionalized small molecular units or large molecular motifs, nanofabrication explores whether individual units, such as small molecular ligands, or large molecules, such as proteins, can be positioned with nanometer precision. The separation and local environment can be engineered to control subsequent intermolecular interactions. Feature sizes as small as 2 x 4 nm(2) (32 alkanethiol molecules) are produced. Proteins may be aligned along a 10-nm-wide line or within two-dimensional islands of desired geometry. These high-resolution engineering and imaging studies provide new and molecular-level insight into supramolecular chemistry and self-assembly processes in bioscience that are otherwise unobtainable, e.g., the influence of size, separation, orientation, and local environment of reaction sites. This nanofabrication methodology also offers a new strategy in construction of two- and three-dimensional supramolecular structures for cell, virus, and bacterial adhesion, as well as biomaterial and biodevice engineering.

Animals↗

PubMedDate not supplied

Application of luminescent Eu:Gd2O3 nanoparticles to the visualization of protein micropatterns.

Nanoparticle phosphors made of lanthanide oxides are a promising new class of tags in biochemistry because of their large Stokes shift, sharp emission spectra, long luminescence lifetime, and good photostability. We demonstrate the application of these nanoparticles to the visualization of protein micropatterns. Luminescent europium-doped gadolinium oxide (Eu:Gd2O3) nanoparticles are synthesized by spray pyrolysis. The size distribution is from 5 to 200 nm. The particles are characterized by means of laser-induced fluorescent spectroscopy and transmission electron microscopy (TEM). The main emission peak is at 612 nm. The nanoparticles are coated with avidin through physical adsorption. biotinylated bovine serum albumin (BSA-b) is patterned on a silicon wafer using a microcontact printing technique. The wafer is then incubated in a solution of avidin-coated nanoparticles. Fluorescent microscopic images reveal that the nanoparticles are organized onto designated area, as defined by the microcontact printing process. The luminescent nanoparticles do not suffer photobleaching during the observation, which demonstrates their suitability as luminescent labels for fluorescence microscopy studies. More detailed studies are preformed using atomic-force microscopy (AFM) at a single nanoparticle level. The specific and the nonspecific binding densities of the particles are qualitatively evaluated.

Biosensing Techniques↗