Kaige Wang

Studying Properties of Composite Nano-PAA-Au Array for the Optimal SERS Sensitivity

The composite structure of nano-porous anodic alumina (nano-PAA) coated with noble metal layer has been demonstrated to be one kind of high-sensitive surface-enhanced Raman scattering (SERS)-active substrate. However, the experimental investigations on influences of parameters were restricted by correlation between variables. And in relevant simulation studies, nano-tips at intersections of unit edges on the surface and the metal attaching to inside walls of nano-holes which are crucial for the enhancement of electric field were commonly idealized. To obtain the optimal structure of nano-PAA-Au array for SERS applications, numerical evaluations of the electric field distributions and intensities at hotspots were carried out on a proposed precise model. The influence of structure and excitation parameters which determined the electromagnetic enhancement have been systematically investigated. The numerical data shows that the intensity and distribution of surface electric field is evidently affected by both the characteristics of nano-tips and the metal attaching to the inside wall of holes. In addition, the designed substrate was synthesized accordingly and demonstrated to be higher sensitive with an achieved enhancement factor of 1.04xa0×xa0107. The study would be helpful in designing high-sensitive SERS-active substrates.

Studying compaction-decompaction of DNA molecules induced by surfactants

The mechanism and detailed processes of DNA compaction and decompaction are essential for the life activities, as well as for the researches in the molecular biology, genetics and biomedicine. The compaction of two kinds of DNA molecules caused by Cetyltrimethyl Ammonium Bromide (CTAB) and their decompaction induced with sodium dodecyl sulfate (SDS) or excessive amount of CTAB have been investigated with multiple perspectives such as the UV-VIS spectrophotometry, dynamic light scattering, and zeta potential. The compaction phenomenon of DNA can easily be observed when the CTAB combines with the DNA, not just when the molar ratio QCTAB/QDNA is approximately equal to 1 as the conventional recognition, but also when QCTAB/QDNA <1,DNA can be compacted; Molecular state of DNA is only changed in the conformational structure, but not in the chemical structure. Finally, a model is suggested to help catch on the biophysical mechanism of DNA chain conformational change.

Influence of concentration on distribution properties of stretched-DNA in the MEC studied with fluorescence imaging and drop shape analyzing

Stretching and manipulating DNA efficiently is significant for exploring the properties and applications of single DNA molecules. Here, the influence of concentrations of buffer and DNA on properties of stretched DNA molecules in the molecular evaporation combing (MEC) is investigated systematically with the single molecule fluorescence imaging microscopy and the high-precision drop shape analyzing technology. The stretched degree and uniformity of combed DNA molecules decrease as the buffer concentration are increased from 7 to 20mM. When the buffer concentration changes from 12 to 15mM, the stretched DNA molecules are apt to form a ringlike pattern. During the MEC process, there exist two kinds of evaporation modes, i.e., the constant contact angle mode and the constant contact radius mode. The former only takes effect in the lower concentration of buffer and DNA, enabling the uniform stretching. While the latter plays the leading role in the higher concentration, promoting the formation of the ringlike pattern of DNA molecules.

Nanopores for the study of single biomolecules

Nanoscale containers and devices fabrication and application are recently attracted much attention. The surface profiles of nanoscale patterns are very important for nanotechnology and nano-devices integration. Nanopits and nanopores arrays are fabricated with focused ion beam tool. The morphologies of these small containers were explored by atomic force microscopy. The topography of every nanopattern looks like a volcano; and each nanopit has a V-shaped cross section with a pronounced ring-shaped structure that surrounds the crater. The main reason of this protruded ring structure is the swelling of the substrate due to amorphization and it is the inherent shape obtained by single-pass FIB milling. In this fabricating case, the redeposition effect is minor. The atomic force microscopy results of the nanopits rim morphologies are helpful to the micro- and nanoscale devices integration.