Modification of Surfaces for Biological Applications

• Main Author: Milkani, Eftim
• Other Authors: Stephen Lambert, Committee Member
• Format: Others
• Published: Digital WPI 2010
• Subjects: Surface modification; biological applications
• Online Access: https://digitalcommons.wpi.edu/etd-dissertations/216; https://digitalcommons.wpi.edu/cgi/viewcontent.cgi?article=1215&context=etd-dissertations

Understanding and controlling the nature of interactions at interfaces between various materials and systems has always been of interest, but with the fast development and need of new technologies it has become crucial to employ these interactions for various applications that range from biosensing of analytes in bodily fluids and the environment, to the development of bio-compatibatible and bio-mimicking surfaces that can be used to successfully couple biological systems to artificial materials and also build models for understanding biological systems better. Self-assembled monolayers (SAMs) are organized molecular assemblies that are formed by spontaneous adsorption of a compound in solution to a surface. They can change the surface properties without the need of changing the physical properties of the bulk material. Formation of SAMs on different substrates was investigated and performed in the work described in the thesis to be used in the detection of nucleic acids and enzyme inhibitors, development of surfaces with anti-adhesive and anti-microbial properties, development of surfaces for directed and patterned cell adhesion, and the construction of artificial membranes that can be used for studying the interaction of membrane proteins and the discovery of new pharmaceuticals. The surface of gold substrates was modified with alkanethiol compounds in order to attach biomolecules such as nucleic acids and proteins which allowed the modified surface to be used as a biosensor. Binding interactions were detected by electrochemical impedance spectroscopy and surface plasmon resonance. A surface resonance sensor provided a platform for the detection of DNA and RNA oligonucleotide sequences and also the detection of one-nucleotide mismatches from the hybridization these oligonucleotides. The same sensor platform, but with a different surface modification, was used to covalently attach an enzyme whose inhibitors are used as therapeutic drugs and also as pesticides and nerve agents. The sensor was able to detect two of these inhibitors, which are used in the treatments of Alzheimer's disease, at a range of concentrations. This allowed the determination of binding affinity constants for the two inhibitors. The surface of gold was modified with functional groups in order to obtain inert surfaces with anti-adhesive properties with regard to the attachment of proteins. These surfaces are of interest in generating bio-compatible medical implants that can resist rejection from the host's immune system andor the formation of bacterial biofilms. The inert property was combined with anti bacterial properties by attaching an antibiotic which is known to kill bacteria by binding to the cell membrane. Following characterization of gold surfaces by contact angle measurements, ellipsometry, grazing angle FT-IR, cyclic voltammetry and electrochemical impedance spectroscopy, the surface of glass substrates was modified with similar functional groups, by switching to a different coupling ligand for the substrate. Alkoxysilanes were used to modify the surface of glass, which can also be used to modify other materials, such as polymers and stainless steel. Gold and glass surfaces were also modified with antibodies, other proteins, and other functional groups which favored or prevented cell adhesion. This led to the ability for patterned and directed adhesion, and differentiation of several cell lines. Preparation and chemical modification of magnetic beads and the ability to modify the bead surface created the possibility to grow and trap cells in a flow-through magnetic bioreactor, which will be used for the continuous production of metabolites and growth of tissue in a three-dimensional construct. Modification of gold substrates also led to the construction of artificial phospholipid membranes, whose composition can be controlled and most importantly can be used for the insertion and characterization of membrane proteins on a two-dimensional platform. This will allow for characterization of ligand-protein and protein-protein interactions with surface characterization techniques such as surface plasmon resonance and electrochemical impedance spectroscopy. The various surface modifications and applications described in this work underscore a general theme that the surface of many different materials can be modified by using the correct functional groups for the formation of the self-assembled monolayer on the substrate surface, thus obtaining the same surface properties without the need to change the physical and chemical properties of the bulk material.