Biomedical subjects

Lanlan Sun

Publications and source records attributed to Lanlan Sun.

6 recordsLinked to original sources

PubMed2007

Effects of bridge ions, DNA species, and developing temperature on flat-lying DNA monolayers.

Recently, we have successfully constructed flat-lying DNA monolayers on a mica surface (J. Phys. Chem. B 2006, 110, 10792-10798). In this work, the effects of various factors including bridge ions, DNA species, and developing temperature on the configuration of DNA monolayers have been investigated by atomic force microscopy (AFM) in detail. AFM results show that the species of bridge ions and developing temperature play a crucial role during the formation process. For example, the divalent cation Zn2+ resulted in many DNA chains stuck side by side in the monolayers due to the strong interactions between it and DNA's bases or the mica surface. Most DNA chain's conglutinations disappeared when the developing temperature was higher than 40 degrees C. Cd2+ and Ca2+ produced more compact DNA monolayers with some obvious aggregations, especially for the DNA monolayers constructed by using Ca2+ as the bridge ion. Co2+ produced well-ordered, flat-lying DNA monolayers similar to that of Mg2+. Furthermore, it was found that the flat-lying DNA monolayers could still form on a mica surface when plasmid DNA pBR 322 and linear DNA pBR 322/Pst I were used as the DNA source. Whereas, it was hard to form DNA monolayers on a (3-aminopropyl)triethoxysilane-mica surface because the strong interactions between DNA and substrate prevented the lateral movement of DNA molecules. These results suggested that the appropriate interactions between divalent cations and DNA or mica surface were important for the formation of flat-lying DNA monolayers. The obtained information is a necessary supplement to our previous studies on the formation kinetics of such monolayers and may be useful for practical application of the monolayers and further theoretical studies.

DNA↗

PubMed2006

A novel strategy to construct a flat-lying DNA monolayer on a mica surface.

Flat-lying, densely packed DNA monolayers in which DNA chains are well organized have been successfully constructed on a mica surface by dropping a droplet of a DNA solution on a freshly cleaved mica surface and subsequently transferring the mica to ultrapure water for developing. The formation kinetics of such monolayers was studied by tapping mode atomic force microscopy (TMAFM) technique. A series of TMAFM images of DNA films obtained at various developing times show that before the sample was immersed into water for developing the DNA chains always seriously aggregated by contacting, crossing, or overlapping and formed large-scale networks on the mica surface. During developing, the fibers of DNA networks gradually dispersed into many smaller fibers up to single DNA chains. At the same time, the fibers or DNA chains also experienced rearrangement to decrease electrostatic repulsion and interfacial Gibbs free energy. Finally, a flat-lying, densely packed DNA monolayer was formed. A formation mechanism of the DNA monolayers was proposed that consists of aggregation, dispersion, and rearrangement. The effects of both DNA and Mg2+ concentration in the formation solution on DNA monolayer formation were also investigated in detail.

Aluminum Silicates↗

PubMed2006

Manipulation, dissection, and lithography using modified tapping mode atomic force microscope.

A modified tapping mode of the atomic force microscope (AFM) was introduced for manipulation, dissection, and lithography. By sufficiently decreasing the amplitude of AFM tip in the normal tapping mode and adjusting the setpoint, the tip-sample interaction can be efficiently controlled. This modified tapping mode has some characteristics of the AFM contact mode and can be used to manipulate nanoparticles, dissect biomolecules, and make lithographs on various surfaces. This method did not need any additional equipment and it can be applied to any AFM system.

Dissection↗

PubMed2005

DNA-network-templated self-assembly of silver nanoparticles and their application in surface-enhanced Raman scattering.

A large-scale lambda-DNA network on a mica surface was successfully fabricated with a simple method. Silver nanoparticles capped with the cationic surfactant cetyltrimethylammonium bromide (CTAB) were self-assembled onto a two-dimensional DNA network template by electrostatic interaction and formed nanoporous silver films, which can be used as active surface-enhanced raman scattering (SERS) substrates. Two probe molecules, Rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP), were studied on these substrates with very low concentrations, and great enhancement factors for R6G (0.21 x 10(10)-4.09 x 10(11)) and 4-ATP (approximately 1.70 x 10(5)) were observed. It was found that the enhancement ability was affected by the DNA concentration and the electrostatic absorption time of the CTAB-stabilized silver nanoparticles on the DNA strands. These SERS substrates formed by the self-assembly of silver nanoparticles on DNA network also show good stability and reproducibility in our experiments.

Aniline Compounds↗

PubMed2005

One-step synthesis of silver nanoparticles, nanorods, and nanowires on the surface of DNA network.

Here, we describe a one-step synthesis of silver nanoparticles, nanorods, and nanowires on DNA network surface in the absence of surfactant. Silver ions were first adsorbed onto the DNA network and then reduced in sodium borohydride solution. Silver nanoparticles, nanorods, and nanowires were formed by controlling the size of pores of the DNA network. The diameter of the silver nanoparticles and the aspect ratio of the silver nanorods and nanowires can be controlled by adjusting the DNA concentration and reduction time.

DNA↗

PubMed2005

Immobilization of DNA on 11-mercaptoundecanoic acid-modified gold (111) surface for atomic force microscopy imaging.

Immobilized DNA on preformed 11-mercaptoundecanoic acids (MUDA) self-assembled monolayers (SAMs) on a gold (111) surface was bound by a divalent cation bridges was imaged by atomic force microscopy (AFM). The DNA immobilization was attributed to the formation of ionic bridges between the carboxylate groups of MUDA and the phosphate groups of DNA. AFM images revealed that DNA molecules could be immobilized strongly enough to permit stable and reproducible imaging. The effect of different bridge cations, such as Mg(2+), Zn(2+) and Cu(2+), and the pH of DNA assembled solution on immobilization and conformation of DNA was studied. Plasmid DNA pBR 322/Pst I molecules were straightened by using a molecular combing technique on the MUDA surface.

DNA↗