Biosensors and BioMEMS Lecturer : Dr Nashrul Fazli Mohd Nasir Micropatterning of Substrates Lecturer : Dr Nashrul Fazli Mohd Nasir

Self Assembly Monolayers Overview All types of fabrication, whether on the macro or micro scale, can be divided into two separate methods: „ Top-down: Small sections of a large substance are removed Bottom-up: Designs are created from scratch by assembling together different building blocks The versatility and creativity of the bottom up method has great potential in nanotechnology

Molecular Interactions is the factor which allows self assembly to happen: „ Electrostatic Forces: The columbic interactions between positive and negative charged particles. Hydrogen bonds: Bonding that involves a hydrogen proton donor Dispersion forces (London forces): Weak dipole: Dipole forces that are present in and between all molecules. Hydrophobic effects: Non polar bonding in an aqueous solution.

Characteristics of SAMs „ Few molecules thick Formed by reactions between surface and surface active molecules Give an entire substance the properties of the SAM

Quick Example of SAM: The driving force for the surface aggregation & self-assembly is: a covalent bond formation of the film molecules with the substrate surface via suitable functional groups intermolecular, van der Waals-type interactions between the hydrocarbon chains of the film molecules.

Electrostatic Self Assembly Utilizes the electrostatic interactions between molecules „ Layer by Layer method A surface is first modified so it can bear different charged groups of particles The surface is then dipped into a solution of an oppositely charged solution. Because of electrostatic properties, the solution bonds uniformly onto the entire surface Multiple layers can be added to the surface by alternating the charges on each subsequent layer Photo-switched wettability on an electrostatic self-assembly azobenzene monolayer

Advantages of SAMs Block Copolymer Self Assembly Microphase Separation By manipulating polymers at the molecular level, scientists can modify their behavior to bond, break, or stack in deliberate pattern Microphase Separation When two polymers are forced combine to form a copolymer, they will inherently try to separate from each other. By manipulating intrinsic property scientists can cause block copolymers to form many different shapes and surfaces. Advantages of SAMs Macro surfaces can obtain entirely different properties by only adding nanometer thick surfaces. „ E.g., implants can be coated with surface layers that are biocompatible

Materials Self-Assembly of Integrated Systems It has become feasible to organize and connect organic, inorganic and polymeric chemical components with well-defined functions into integrated electronic, photonic, mechanical, analytical and chemical systems for a future nanotechnology Smaller units are assembled into larger ones, which in turn are organized at a higher dimension. This construction process is continued until the highest level of structural complexity in the hierarchy has been attained Layer-by-layer self-assembled lithium battery PEO: Poly(ethylene oxide) GO: Graphite oxidized by HNO3 and NaClO3 PDDA: Poly(diallyldimethylammonium chloride)

Self assembled monolayers (SAMs) J. C. Love et al., Chem. Rev. 2005, 105, 1103-1169

SAMs can be used to: Modify wetting properties (e.g. water) Selective adhesion „Bio-functionalizing“[1] Prepare functional films Lubricants for hard discs Corrosion protection Photo patterning Electronic devices [1] E. V. Romanova et al., Biomaterials, 2006, Vol. 27, 1665

Self Assembly of Biomolecules on a Substrate Langmuir, Vol. 20, No. 9, 2004, 3495

“Grafting From” Technique How to Graft Molecules/Biomolecules??? “Grafting From” Technique ‘‘Grafting from’’ synthesis of molecular brushes starts with the preparation of a backbone polymer (macroinitiator) with a predetermined number of initiation sites that is subsequently used to initiate polymerization of the side chains. In grafting from via Control Radical Polymerization (CRP) techniques, a low instantaneous concentration of radical species necessarily limits termination events. This is especially important during molecular brush synthesis since intramolecular termination can lead to pendant macrocycles, and more importantly, intermolecular coupling can lead to macroscopic gelation. As such, the grafting from approach enables preparation of long-backbone molecular brushes with a high grafting density and a narrow molecular weight distribution. However, compared to the grafting through approach, grafting from allows less control of side chain length and grafting density.

“Grafting From” monomer macroinitiator ATRP functional group side chain monomer graft polymer

“Grafting Through” Technique How to Graft Molecules/Biomolecules??? Continue… “Grafting Through” Technique The grafting through route involves the polymerization of macromonomers ‘‘through’’ their terminal functionality. Perhaps the most attractive feature of this method is that each repeat unit of the backbone contains a covalently bound side chain. Also, because the macromonomers are prepared separately, the side chains can be characterized prior to polymerization. This allows preparation of brushes with well-defined grafting density and side-chain length. ATRP—Atom Transfer Radical Polymerization ROP—Ring Opening Polymerization Click Chemistry —(find out more at http://en.wikipedia.org/wiki/Azide_alkyne_Huisgen_cycloaddition)

Grafting Through monomer ROP macromonomer side chain monomer ATRP terminal functionality ROP side chain monomer macromonomer ATRP graft polymer 15

Summary of Molecules and Biomolecules Grafting If you are curious? A telechelic polymer is a di-end-functional polymer where both ends possess the same functionality

Polymers: Revision Revision: Polymers are referred as macromolecules due to their giant size The molecules are in the form of long& flexible chains Polymer = many mers Mer originates from meros: parts, thus, polymer means many parts or many mers Monomer refers to stable molecule where the polymer is synthesized

Polymers: Revision Summary of polymer characteristics: In this topic, we can classify polymers into 3 major classes: Fibers, plastics and elastomers Summary of polymer characteristics: Popular polymer under plastic classification: PE,PP, PVC,PSt, fluorocarbons, epoxies, phenolics and polyesters Additives maybe incorporated by the manufacturer to adjust physical, chemical, electrical, thermal and biocompatibility characteristics

Polymers: Revision

Polymers: Revision Other classifications: Natural polymers-silk, rubber, cotton Synthetic polymers-derived from petroleum products Other classifications include response to temperature: Thermal plastic polymers-can be remelted & reshaped repeatedly Thermal setting polymers-permanent shape after melted and once processed Some mechanical properties should be considered: Polymer materials cover wide range of materials each with a different Young’s modulus. As low as several MPa and as high as 4 Gpa. Maximum tensile strengths for polymers are on the order of 100MPa. Lower than metal and semiconductor. Many polymers exhibit viscoelastic behaviors The mechanical properties are influenced by temperature, molecular weight additives, degree of crystallinity and heat treatment history. At this stage polymer electronic devices are not able to compete with semiconductor electronics performances.

Properties of seven polymer materials.

Properties of seven polymer materials.

Deposition of Thin Polymer Films Polymer materials can be deposited using: Spin coating, vapor coating, spray coating and electroplating Polymers can serve as structural layers & provide unique mechanical, electrical, and chemical characteristics not available in semiconductor films Polymer thin films can be removed by dry etching or strong organic solvents including acetone.

Schematic diagram of a method for forming patterned PDMS structures.

Micromachined PDMS O-rings.

Thank You!