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