Surface Chemistry

Contents 1. Surface Chemistry 2. Biosensors 3. TEM 4. SEM 5. AFM

 What is the Surface Chemistry? 1. Surface Chemistry - Surface Science is the study of Physical and Chemical Phenomena that occur at the interface of two phases. It includes the fields of Surface Chemistry and Surface Physics. Fig. 1. Research infrastructure at the surface science

 Sensors(1) 2. Biosensors - Designed for the continuous monitoring of the physicochemical or biochemical properties of specific analytes ⇒ To provide Qualitative and/or Qunatitative analytical data. - Composition Fig. 2. Schematic diagram of a chemical or biosensor.

 Sensors(2) 2. Biosensors Biosensor - A thin layer of substance incorporating an immobilized reagent that contains Biorecognition sites (Biorecognition : Especially as part of the Immune system) - Reagents are immobilized by Entrapment or Binding. - Properties of Biosensors ⇒ Robustness, Rapid and Reproducible Response, Appropriate Selectivity/Specificity and Working Range ⇒ Stable Operation

 Electrochemical Sensors 2. Biosensors Potentiometric Sensors - Based on Ion Selective Electrodes, Solid State Redox Electrodes and Field Effect Transistors(FETs). Biosensors ; - Can be made by coating a Glass Electrodes with a layer of an enzyme immobilized on the surface which catalyzes a biochemical reaction. CO(NH 2 ) 2 + 2H 2 O + H → 2NH 4 + HCO 3 NH 4 + OH → NH 3 + H 2 O Urease Fig. 3. Biosensor based on an enzyme-coated ammonium ion-selective electrode.

 Optical Sensors(1) 2. Biosensors - Responding to the absorption or fluorescent emission of electromagnetic radiation by analytes, indicators or analyte- receptor complexes at characteristics wavelengths. - Composition Path of Radiation Optrodes Fig. 4. Optical sensor with Y-configuration cell.

 Optical Sensors(2) 2. Biosensors - To monitor pH, metal ions, dissolved gases and organic compounds down to ppm and ppb concentration using Radiation in the visible, ultraviolet and near infrared regions by absorbance, Fluorescence or reflectance. - Advantages of Optical Sensors → Not requiring an electro system → Providing valuable spectral information over a range of wavelengths - Disadvantages of Optical Sensors → Effecting from ambient light interference(depletion of Immobilized reagents) → Slowing kinetics of the reactions between analytes and reagents

 Themal- and Mass-Sensitive Sensors 2. Biosensors Thermal-Sensitive Sensors - Measuring Heat of Reaction generated by the oxidation of an analyte or its reaction with a reagent - Thermal biosensors incorporating Thermistors measure heats of reaction of enzymes in the detection of urea, glucose, penicillin and cholesterol. Mass-Sensitive Sensors - Based on Piezoelectric Quartz Crystal Resonators covered with a gas-absorbing organic layer. - Absorption of an analyte gas causes a change in Resonance frequency and which is sensitive down to ppb levels.

 Sensor arrays 2. Biosensors - These are groups of sensors that allow simultaneous monitoring with different instrumental parameters and/or different sensor elements. - Being operated at different electrical potentials, frequencies or optical wavelengths. - Being constructed from Three Ion-selective Field Effect Transistors Fig. 5. FET sensor arrays for monitoring pH, sodium and potassium.

 Applications 2. Biosensors Nano-bio Technologies(NBT) · Protein Chip - To determine the presence and/or amount (referred to as relative quantitation) of proteins in biological samples. - Applications of Protein Chip ① Biochip ② Molecular imaging of the Cell → Structural Nano Imaging → Real-time Nano Imaging - Detection Methods ① Fluorescence Detection ② Label-free Detection : AFM, SPR, etc.

 Comparison of Microscopes 3. TEM Fig. 6. Comparison of LM, TEM, SEM.

 Principles (1) - A beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through. An image is formed from the interaction of the electrons transmitted through the specimen. 3. TEM Electron Gun Anode Plate Lens System Image Recording System Fig. 7. Composition of TEM.

 Principles (2) 3. TEM Lens System - Condensor Lens - Objective Lens Image Recording System - Projection Lens Fig. 8. Lens system of TEM.

 Properties 3. TEM High Resolution : 0.4nm Variable Analysis - BF(Bright Field), DF(Dark Field), etc. → By Electron Diffraction Structural Analysis of Solid Sample Analysis in air Complex Sample Pre-treatment Slow Analysis

 KBSI in Jeonju 3. TEM Charteristics - Accelerated electrons : : 200keV - Resolution : 0.1nm

 Principles (1) - Accelerated electrons in an SEM carry significant amounts of kinetic energy, and this energy is dissipated as a variety of signals produced by electron-sample interactions when the incident electrons are decelerated in the solid sample. 4. SEM Electron Gun - Thermionic Electron Gun - Field Emission Electron Gun Anode Plate Lens system Scanning Coils Detector TV Scanner Fig. 9. Composition of SEM.

 Principles (2) 4. SEM Magnetic Lens - Condenser Lens - Objective Lens Aperature Scanning coil, Stigmator Fig. 10. Lens system of SEM.

 Principles (3) 4. SEM Detection - Topography, Morphology ⇒ SE (Secondary Electron) - Topography, Crystallography, Composition ⇒ BSE (Backscattered Electron), EBSD (Electron Backscattered Diffraction) - Composition ⇒ X-ray (EDS : Energy Dispersive Spectrometer), WDS : Wave Dispersive Spectrometer), CL (Cathode Luminescence) Fig. 11. Scattering of electrons

 Properties 4. SEM High Resolution (SEM : 3~5 nm, FE-SEM : 0.5~2 nm) Various Range of Magnification Deep Depth of Field High Vacuum Working (under 10 Torr) Sample - Coated by Au or Pt ⇒ “Charge-up Effect” - Representative Sample - Physical & Chemical Stability - Clean Surface - Roughness -5

 KBSI in Jeonju 4. SEM - Manufacturer Hitachi Japan - Model No. S Year Resolution 1.5nm

 KBSI in Jeonju 4. SEM - Manufacturer Hitachi Japan - Model No. S Year Resolution 0.4nm

 Principles (1) - It measures the forces acting between a fine tip and a sample. Attractive or Repulsive forces resulting from interactions between the tip and surface will cause a positive or negative bending of the cantilever. 5. AFM Fig. 12. Principle of AFM and the scanned cantilever/tip system.

 Principles (2) Force-distance Curve 5. AFM Fig. 13. Scheme of force-distance curve

 Modes(1) 5. AFM Fig. 14. Modes of AFM

 Modes(2) 5. AFM 1. Contact mode · Advantages - High scan speeds - “Atomic resolution” is possible - Easier scanning of rough samples with extreme changes in vertical topography · Disadvantages - Lateral forces can distort the image - Capillary forces from a fluid layer can cause large forces normal to the tip-sample interaction. - Combination of these forces reduces spatial resolution and can cause damage to soft samples.

 Modes(3) 5.AFM 2. Non-contact mode · Advantages - Low force is exerted on the sample surface and no damage is caused to soft samples. · Disadvantages - Lower lateral resolution, limited by tip-sample separation. - Slower scan speed to avoid contact with fluid layer.

 Modes(4) 5.AFM 3. Tapping mode · Advantages - Higher lateral resolution (1nm to 5nm) - Lower forces and less damage to soft samples in air · Disadvantages - Slower scan speed than in contact mode

 KBSI in Jeonju 5.AFM - Manufacturer Veeco - Model No. Nanoscope Ⅳ Multimode AFM - Year Resolution Laterally : 400nm Vertically : 400nm

 KBSI in Jeonju 5.AFM - Manufacturer AFM : NT-MDT Raman : Tokyo Instrument - Model No. Nanofinder 30 - Year Resolution Laterally : 200nm Vertically : 500nm + obtaining resolution : 50nm