Biomedical subjects

Zhongdang Xiao

Publications and source records attributed to Zhongdang Xiao.

6 recordsLinked to original sources

PubMed2006

Analysis of fluorescence from algae fossils of the Neoproterozoic Doushantuo formation of China by confocal laser scanning microscope.

Chinese algae fossils can provide unique information about the evolution of the early life. Thin sections of Neoproterozoic algae fossils, from Guizhou, China, were studied by confocal laser scanning microscopy, and algae fossils were fluorescenced at different wavelengths when excited by laser light of 488 nm, 476 nm, and 568 nm wavelength. When illuminated by 488 nm laser light, images of the algae fossils were sharper and better defined than when illuminated by 476 nm and 568 nm laser light. The algae fossils fluoresce at a wide range of emission wavelengths. The three-dimensional images of the fluorescent algae fossils were compared with the transmission images taken by light microscope. We found that the fluorescence image of the confocal laser scanning microscope in a single optical section could pass for the transmission image taken by a light microscope. We collected images at different sample depths and made a three-dimensional reconstruction of the algae fossils. And on the basis of the reconstruction of the three-dimensional fluorescent images, we conclude that the two algae fossils in our present study are red algae.

Cell Wall↗

PubMed2006

Rapid preparation of crystalline colloidal arrays using a strong electric field dialysis.

We present a simple method for rapid preparation of crystalline colloidal arrays (CCAs) by a strong electric field dialysis (SEFD). This method is based on rapid removing of ionic impurities in colloidal suspensions by applying a strong electric field. In a SEFD process, the negatively charged ions in colloidal suspensions are rapidly driven to the anode, the positively charged ones are rapidly driven to the cathode, and the colloidal particles are withheld in the dialysis tube. It was shown that the colloidal particles aggregated on the wall of the dialysis tube could block the SEFD process, which could be overcome by reversing the direction of the electric field. The purified colloidal particles can self-assemble into a crystalline colloidal array, which has an electrostatically stabilized three-dimensional periodic array of colloidal particles with a characteristic lattice spacing that can be varied by dilution. The reflection spectra show distinct peaks due to diffraction from CCAs. Atomic force microscopy (AFM) image illustrates the non-contacted ordering of the colloidal particles in the CCAs embedded in gels. This indicates the formation of high-quality single CCAs. Using a SEFD method, the preparation time of CCAs can be reduced. This new technique will greatly speed up the process of preparing polymerized crystalline colloidal arrays (PCCAs) into real-world application in the analytical field.

Colloids↗

PubMed2005

Attaching single biomolecules selectively to the apex of AFM tips for measuring specific interactions.

We present a general approach for preparing well-defined AFM tips for probing single target molecules. We demonstrated that carboxylic acid groups could be generated by electrochemical oxidation selectively at the apex of an AFM tip that is coated with a monolayer of oligo(ethylene glycol) derivatives for resisting nonspecific interactions. These carboxylic acid groups were used as handles to tether only one ligand molecule, such as biotin, to the tip apex for measurement of specific interactions with biomolecules.

Biocompatible Materials↗

PubMed2005

Atomic force microscopy studies of mesoscopic membranous bubbles on monolayers derived from SiCl3-terminated carbosilane dendrons on mica.

Monolayers of dendrimers were prepared on mica by spin-coating of the second generation carbosilane dendrons with 9 SiCl(3) periphery groups. AFM images of the films showed the presence of soft yet robust, dome-shaped features with a base diameter of 100-2000 nm. The apparent height of the features, ranging from 10 to 200 nm, rapidly reduced under increasing compression force, eventually to the same value ( approximately 2.5 nm) corresponding to a bilayer of the flattened dendrons. The change in shape of the features in response to the compression force from the AFM tip was fully reversible, indicating that the features were robust. The contrast of the features in the tapping mode AFM (TMAFM) phase images flipped at a setpoint ratio of approximately 0.55. In contrast to the reported amplitude vs displacement (A/z) curves for compliant materials, A/z curves of the features showed that the reduction of amplitude was larger than the tip displacement as if the cantilever tip were repelled by the soft features. This result cautions the use of amplitude/phase vs displacement (APD) curves for interpreting TMAFM images and for optimizing conditions for TMAFM imaging of very soft and "sticky" surfaces. On the basis of the AFM studies, we believe that the dome-shaped features are membranous air bubbles. The membranes of the bubbles were probably composed of a bilayer of the dendron molecules bound through the peripheral silanol groups. The bilayer could be formed by self-assembly of the molecules on top of the air bubbles entrapped at the monolayer/solution interface during spin-coating.

Journal Article↗

PubMed2005

Electrical characterization of silicon tips using conducting atomic force microscopy.

The electrical properties of n-doped Si tips have been characterized in conducting atomic force microscopy under various conditions. Si tips with SiO2 layer on them present complex electric properties: which include a larger positive threshold bias, which is different from that of its doped semiconductor material. Silicon tips after removing their SiO2 layer had smaller positive threshold bias; such bias varied with the loading force: smaller loading forces corresponding to larger positive threshold biases, and it remained constant at lower levels for larger loading forces. Humidity of experiments influenced the threshold bias: lower relative humidities (<25%) and larger loading forces were in favor of getting stable threshold bias. The conductance increased remarkably in high relative humidity although it was kept in a narrow range when relative humidity was lower than 40%. Loading force didn't affect the conductance in the examined relative humidity conditions. One advantage of bare silicon tips over commercial conducting ones is that they smaller radius than gold-coated tips; this is in more favor of reaching single molecular electronics.

Electric Conductivity↗

PubMed2003

Modification of silicon AFM cantilever tips with an oligo(ethylene glycol) derivative for resisting proteins and maintaining a small tip size for high-resolution imaging.

We demonstrate that silicon AFM tips can be modified by etching with 2% HF solution followed by reaction with an alpha,omega-oligo(ethylene glycol)alkene. Tips properly modified by this technique maintain a small tip size and effectively reduce the nonspecific interaction with fibrinogen and bovine serum albumin, resulting in greatly improved image resolution and contrast for high-coverage fibrinogen films.

Alkenes↗