Optimal control-based inverse determination of electrode distribution for electroosmotic micromixer

This paper presents an optimal control-based inverse method used to determine the distribution of the electrodes for the electroosmotic micromixers with external driven flow from the inlet. Based on the optimal control method, one Dirichlet boundary control problem is constructed to inversely find the optimal distribution of the electrodes on the sidewalls of electroosmotic micromixers and achieve the acceptable mixing performance. After solving the boundary control problem, the step-shaped distribution of the external electric potential imposed on the sidewalls can be obtained and the distribution of electrodes can be inversely determined according to the obtained external electric potential. Numerical results are also provided to demonstrate the effectivity of the proposed method

Ionic-complementary Peptide Modified Electrode for Biosensing Application

Self-assembling peptides have emerged as new nanobiomaterials and received considerable attention in the areas of nanoscience and biomedical engineering. One important type is the ionic-complementary peptide, which contains special patterns of positive and negative charge distribution. This thesis explores the application of this special type of peptides for the modification of electrode surfaces. The ionic-complementary peptide modified electrode was then further used to immobilize biologically active molecules, glucose oxidase in the present case, to construct a biosensor. There are two major parts in this thesis. In the first part, an ionic-complementary peptide, EFK16-II, was used to modify a highly ordered pyrolytic graphite (HOPG) electrode surface. The nanofibre structure of the self-assembling peptide on the electrode surface was characterized by atomic force microscopy (AFM). Attenuated total reflection fourier transform infrared sectroscopy (ATR-FTIR) spectra showed that upon addition of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), EFK16-II molecules tend to be cross-linked among themselves. Cross-linking of the peptide diminishes the number of carboxyl groups available for immobilizing a sensing enzyme, i.e., glucose oxidase (GOx). A simple method based on pre-mixing the carbodiimide and GOx was developed; it inhibited peptide cross-linking and significantly improved enzyme immobilization. Biosensors constructed in this way showed increased overall signal intensity and a much higher sensitivity at 4.94mA M-1 cm-2, a six-fold increase compared to the previously-reported peptide-modified electrodes. In the second part, another ionic-complementary peptide, EAK16-II, was used to modify the HOPG electrode. AFM images showed that EAK16-II formed well-ordered nanofibre patterns on the electrode surface. The redox couple Fe(CN)63-/4- was used as a probe to detect the electrochemical properties of the EAK16-II modified electrode. The results showed that the electron transfer at the electrode surface does not change much before and after modification. GOx was immobilized onto the EAK16-II modified HOPG and showed a good response to the concentration change of glucose. Similar to the EFK16-II, inter- or intro-peptide cross-linking also occurs when the solution containing EDC and sulfo-NHS was injected onto EAK16-II modified electrode. The same method as in the first part was applied here to prevent peptide cross-linking. The sensitivity was improved from 0.53mA M-1cm-2 to 2.4mA M-1cm-2. A proposal for constructing a reagentless biosensor by immobilizing both enzyme and mediator onto the electrode was made. However, the results indicated that the mediator, ferrocene carboxylic acid (FCA), was not stable on the surface after being immobilized. A redox protein, cytochrome c (Cyt c), was also immobilized onto an EAK16-II modified electrode. Direct electron transfer (DET) between the redox center of Cyt c and the electrode was observed. However, cyclic voltammetry results indicated that the peptide did not help improve the DET of modified Cyt c. The results presented here demonstrate significant potential for ionic-complementary peptides for constructing electrochemical biosensors

Quantum Anomalous Hall Effect in Graphene Proximity Coupled to an Antiferromagnetic Insulator

We propose realizing the quantum anomalous Hall effect by proximity coupling graphene to an antiferromagnetic insulator that provides both broken time-reversal symmetry and spin-orbit coupling. We illustrate our idea by performing ab initio calculations for graphene adsorbed on the (111) surface of BiFeO3. In this case, we find that the proximity-induced exchange field in graphene is about 70 meV, and that a topologically nontrivial band gap is opened by Rashba spin-orbit coupling. The size of the gap depends on the separation between the graphene and the thin film substrate, which can be tuned experimentally by applying external pressure.Comment: 5pages, 5 figure