Surface Chemistry
< Analytical Chemistry >
Contents
1. Surface Chemistry2. Biosensors3. TEM4. SEM5. AFM
What is the Surface Chemistry?
1. Surface Chemistry
- Surface Science is the study of Physical and Chemical Phe-nomena 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 physico-chemical 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 en-zyme immobilized on the surface which catalyzes a biochemical reac-tion.
CO(NH2)2 + 2H2O + H → 2NH4 + HCO3
NH4 + OH → NH3 + H2O
+ + -
+ -
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 ana-lyte- 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 com-pounds down to ppm and ppb concentration using Radiation in the visi-ble, ultraviolet and near infrared regions by absorbance, Fluores-cence 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 Sen-sors
2. Biosensors
Thermal-Sensitive Sensors - Measuring Heat of Reaction generated by the oxidation of an an-alyte 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 moni-toring with different instrumental parameters and/or different sen-sor 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 spec-imen, 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 Sys-tem
Fig. 7. Composition of TEM.
Principles (2)
3. TEM
• Lens System - Condensor Lens - Objective Lens• Image Recording Sys-tem - 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
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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 sig-nals produced by electron-sample interactions when the inci-dent 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 Disper-sive 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
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4. SEM
- Manufacturer Hitachi Japan - Model No. S-4700 - Year 2001 - Resolution 1.5nm
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4. SEM
- Manufacturer Hitachi Japan - Model No. S-5500 - Year 2006 - Resolution 0.4nm
Principles (1) - It measures the forces acting between a fine tip and a sample. Attractive or Repulsive forces resulting from interac-tions 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 separa-tion. - 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
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5 .AFM
- Manufacturer Veeco - Model No. Nanoscope Ⅳ Multimode AFM - Year 2004 - Resolution Laterally : 400nm Vertically : 400nm
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5 .AFM
- Manufacturer AFM : NT-MDT Raman : Tokyo Instrument - Model No. Nanofinder 30 - Year 2004 - Resolution Laterally : 200nm Vertically : 500nm + obtaining resolution : 50nm
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