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Measuring Electrical Charge and Molecular Interaction at Solid/Liquid Interface from Integrated Transient Induced Molecular Electronic Signal (i-TIMES)


To determine the surface charge density near the electrode surface plays an important role in the studies related to biomedical device and bio-related surface reaction. This dissertation presents a technique, Integrated Transient Induced Molecular Electronic Signal (i-TIMES) method, which is an extended technique from our previous system to study surface charge density and biomolecular interaction on the electrode surface.

i-TIMES method is consisted of a microfluidic device with two platinum electrodes embedded in it which are connected to the differential inputs of a transimpedance amplifier (TIA). Based on i-TIMES method and the designed experimental process, we are able to quantify the amount of the surface charge within the electrical double layer at the liquid/solid interface for different buffer strengths, buffer types and pH values. Most uniquely, since i-TIMES signal is generated by the mobile ion or molecule which is not permanently adhered to the electrode surface, the surface molecular coverage can be obtained by comparing the surface charge density on the electrode surface before and after modification. We have measured the surface coverage for thiol-modified single-strand deoxyribonucleic acid (ssDNA) as anchored probe and 6-Mercapto-1-hexanol (MCH) as blocking agent on the platinum surface to prove the concept.

In addition, by introducing the biomolecule into the system, we can further demonstrate the effect on surface charge density with different type of biomolecules. The effect of molecular concentration on the surface charge density has been demonstrated based on various biomolecules including protein (lysozyme and bovine pancreatic ribonuclease A), ligand (N,N’,N″-triacetylchitotriose (TriNAG), p-aminobenzamidine (pABA) and uridine-3'-phosphate(3’-UMP)) and aptamer. Furthermore, the biomolecular interaction can also be determined by analyzing the change of the surface charge density based on our own developed i-TIMES physical model.

Overall, our results indicate that the i-TIMES technique is highly sensitive to the physical and chemical properties of large and small molecules and each type of molecule can produce a unique footprint in its i-TIMES signal. Through these experiments, we have demonstrated that i-TIMES method not only can offer a simple and accurate technique to quantify surface charge density on a metal surface but also can be an enabling tool for studies of biomolecular interaction and surface functionalization for biochemical sensing and reactions. Technologically, i-TIMES provides an accurate and convenient tool for quantitative study of surface charge density and molecular interactions without molecular labeling or immobilization. The technique can be attractive to many applications including drug discovery.

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