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Nanoparticles Introduction Diesel engines, among others, emit particles consisting of irregularly shaped solid carbon spherules agglomerated in clusters on which some hydrocarbons, sulphates and water condense. Particles are small existing in a sizes ranging from some nanometres to few micrometers. Exhaust particles have gained the attention of research groups due to environmental and health issues. These particles are believed to be harmfull to humans and animals, to moddify the radiative tranfer of the earth and to damage monuments architectural values.

What is nanoparticle?:

What is nanoparticle? a microscopic particle whose size is measured in nanometers Top-down engineering bulk materials by lithography, micromachining and etching Bottom-up chemical growth of particles on an atom-by-atom or molecule-by-molecule basis Two main routes to form nanoparticle

How do nanoparticles form?:

How do nanoparticles form? Img by deMello, J. & deMello, A. Microscale reactors: nanoscale products. Lab Chip 4, 11N–15N(2004). Chemical reaction takes place Critical concentrantion, nucleation begins Subsequent growth of the nuclei lowers the solute concentration Particles grow and consume all the solute Aggregation happens due to its lowering the free energy Best time to synthesize nanoparticles

Nanoparticles will only be obtained if:

Nanoparticles will only be obtained if Growth stops (e.g. due to the reagent depletion, when the particles are still in the nanometre size range) No subsequent tendency for particle aggregation

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Ideal Properties Of Polymeric Based Nps Are: Natural or synthetic polymer Inexpensive Nontoxic Biodegradable Nonthrombogenic Nonimmunogenic Particle diameter <100nm No platelet aggregation Noninflammatory Prolonged circulation time Types Of Nanoparticles Quantum Dots Nanocrystalline Silicon Photonic Crystals Liposome Gliadin Nanoparticles Polymeric Nanoparticles Solid Lipid Quantum Nanoparticles (SLN) Others-gold,carbon,silver,etc.

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Characterisation of Nanoparticles: Nanoparticle characterization20 is necessary to establish understanding and control of nanoparticle synthesis and applicationsThe primary characterisation of NPs is the size of the newly formed particles. Particles with a very small size (<1000nm), low charge, and a hydrophilic surface are not recognised by the mononuclear phagocytic system(MPS) and, therefore, have a long half life in the blood circulation which is essential for targeting NPs to target brain. Characterization is done by using a variety of different techniques, mainly drawn from materials science. Common techniques are: Electron microscopy [TEM,SEM] Atomic force microscopy [AFM] Dynamic light scattering [DLM] X-ray photoelectron spectroscopy [XPS] Powder x-ray diffractometry [XRD]

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Applications and potential benefits21-23 With nanotechnology, a large set of materials with distinct properties (optical, electrical, or magnetic) can be fabricated. Nanotechnologically improved products rely on a change in the physical properties when the feature sizes are shrunk. Nanoparticles for example take advantage of their dramatically increased surface area to volume ratio. Their optical properties, e.g. fluorescence, become a function of the particle diameter. When brought into a bulk material, nanoparticles can strongly influence the mechanical properties, such as the stiffness or elasticity. Example, traditional polymers can be reinforced by nanoparticles resulting in novel materials e.g. as lightweight replacements for metals. Therefore, an increasing societal benefit of such nanoparticles can be expected. 1. Medicine The biological and medical research communities have exploited the unique properties of nanomaterials for various applications (e.g., contrast agents for cell imaging and therapeutics for treating cancer). Terms such as biomedical nanotechnology, bionanotechnology, and nanomedicine are used to describe this hybrid field.Functionalities can be added to nanomaterials by interfacing them with biological molecules or structures. The size of nanomaterials is similar to that of most biological molecules and structures; therefore, nanomaterials can be useful for both in vivo and in vitro biomedical research and applications.Thus far, the integration of nanomaterials with biology has led to the development of diagnostic devices, contrast agents, analytical tools, physical therapy applications, and drug-delivery vehicles.

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. Diagnostics Nanotechnology-on-a-chip is one more dimension of lab-on-a-chip technology. Biological tests measuring the presence or activity of selected substances become quicker, more sensitive and more flexible when certain nanoscale particles are put to work as tags or labels. Magnetic nanoparticles, bound to a suitable antibody, are used to label specific molecules, structures or microorganisms. Gold nanoparticles, tagged with short segments of DNA can be used for detection of genetic sequence in a sample. Multicolor optical coding for biological assays has been achieved by embedding different-sized quantum dots, into polymeric microbeads. Nanopore technology foranalysis of nucleic acids converts strings of nucleotides directly into electronic signatures. 3. Drug delivery The overall drug consumption and side-effects can be lowered significantly by depositing the active agent in the morbid region only and in no higher dose than needed. This highly selective approach reduces costs and human suffering. An example can be found in dendrimers and nanoporous materials. They could hold small drug molecules transporting them to the desired location. Another vision is based on small electromechanical systems: NEMS are being investigated for the active release of drugs. Some potentially important applications include cancer treatment with iron nanoparticles or gold shells.A targeted or personalized medicine reduces the drug consumption and treatment expenses resulting in an overall societal benefit by reducing the costs to the public health system.

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4. Tissue engineering Nanotechnology can help to reproduce or to repair damaged tissue. This so called “tissue engineering” makes use of artificially stimulated cell proliferation by using suitable nanomaterial-based scaffolds and growth factors. Tissue engineering might replace today’s conventional treatments, e.g. transplantation of organs or artificial implants. On the other hand, tissue engineering is closely related to the ethical debate on human stem cells and its ethical implications. 5. Chemistry and environment Chemical catalysis and filtration techniques are two prominent examples where nanotechnology already plays a role. The synthesis provides novel materials with tailored features and chemical properties e.g. nanoparticles with a distinct chemical surrounding (ligands) or specific optical properties. In this sense, chemistry is indeed a basic nanoscience. In a short-term perspective, chemistry will provide novel “nanomaterials” and in the long run, superior processes such as “self-assembly” will enable energy and time preserving strategies.In a sense, all chemical synthesis can be understood in terms of nanotechnology, because of its ability to manufacture certain molecules. Thus, chemistry forms a base for nanotechnology providing tailor-made molecules, polymers etc. and furthermore clusters and nanoparticles.

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6. Filtration A strong influence of nanochemistry on waste-water treatment, air purification and energy storage devices is to be expected. Mechanical or chemical methods can be used for effective filtration techniques. One class of filtration techniques is based on the use of membranes with suitable hole sizes, whereby the liquid is pressed through the membrane. Nanoporous membranes are suitable for a mechanical filtration with extremely small pores smaller than 10 nm (“nanofiltration”). Nanofiltration is mainly used for the removal of ions or the separation of different fluids. On a larger scale, the membrane filtration technique is named ultrafiltration, which works down to between 10 and 100 nm. One important field of application for ultrafiltration is medical purposes as can be found in renal dialysis. Magnetic nanoparticles offer an effective and reliable method to remove heavy metal contaminants from waste water by making use of magnetic separation techniques. Using nanoscale particles increases the efficiency to absorb the contaminants and is comparatively inexpensive compared to traditional precipitation and filtration methods. 7. Energy The most advanced nanotechnology projects related to energy are: storage, conversion, manufacturing improvements by reducing materials and process rates, energy saving e.g. by better thermal insulation, and enhanced renewable energy sources.

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8. Reduction of energy consumption A reduction of energy consumption can be reached by better insulation systems, by the use of more efficient lighting or combustion systems, and by use of lighter and stronger materials in the transportation sector. Currently used light bulbs only convert approximately 5% of the electrical energy into light. Nanotechnological approaches like light-emitting diodes (LEDs) or quantum caged atoms (QCAs) could lead to a strong reduction of energy consumption for illumination. 9. Recycling of batteries Because of the relatively low energy density of batteries the operating time is limited and a replacement or recharging is needed. The huge number of spent batteries and accumulators represent a disposal problem. The use of batteries with higher energy content or the use of rechargeable batteries or supercapacitors with higher rate of recharging using nanomaterials could be helpful for the battery disposal problem. 10. Information and communication Current high-technology production processes are based on traditional top down strategies, where nanotechnology has already been introduced silently. The critical length scale of integrated circuits is already at the nanoscale (50 nm and below) regarding the gate length of transistors in CPUs or DRAM devices.

Some nanoparticle synthesis examples:

Some nanoparticle synthesis examples Alternating droplet generation in microfluidic device for CdS nanoparticle synthesis Synthesis of silver nanoparticles in a continuous flow tubular microreactor High temperature synthesis of CdSe QDs by a gas-liquid segmented flow reactor

Nanoparticle size:

Nanoparticle size Brus’ equation Where E g =2.58eV, m e =0.19,m h =0.8 427nm corresponding to 2.9eV while 477nm to 2.6eV Then we have: Nanoparticle size ranges from 4.2nm to 8.2 nm Pictures merited by Hung, L.-H. et al. Alternating droplet generation and controlled dynamic droplet fusion in microfluidic device for CdS nanoparticle synthesis. Lab Chip 6, 174–178 (2006). (a) microfluidic droplet fusion (b) direct mixing 427nm 477nm

Synthesis of silver nanoparticles in a continuous flow tubular microreactor:

Synthesis of silver nanoparticles in a continuous flow tubular microreactor Experimental setup of the synthesis of Ag nanoparticles in a tubular microreactor Reactants: silver pentafluoropropionate (98%,Aldrich, 0.08 g) trioctylamine (98%, Aldrich, 386uL) Solvent: isoamyl ether (99%, Aldrich, 6 mL) Ratio between the silver precursor and surfactant: 1:3 Flow rate: 0.08 and 0.7 mL/min Heating temperature: 100-140 ºC Img by Lin, X. Z., Terepka, A. D. & Yang, H. Synthesis of silver nanoparticles in a continuous-flow tubular microreactor. Nano Lett. 4, 2227–2232 (2004). Gauge diameter: 0.84mm

Factors affecting the size of Ag nanoparticle:

Factors affecting the size of Ag nanoparticle Molar ratio Temperature Flow rate Img by Lin, X. Z., Terepka, A. D. & Yang, H. Synthesis of silver nanoparticles in a continuous-flow tubular microreactor. Nano Lett. 4, 2227–2232 (2004).


Conclusion To synthesize nanoparticles by microfluidics: Inhibit the crystal growth when the reaction ends Optimize the parameters (e.g. temperature, flow rate, molar ratio) Shorten the RTD and quicken the mixing rate


Reference deMello, J. & deMello, A. Microscale reactors: nanoscale products. Lab Chip 4, 11N–15N (2004) Hung, L.-H. et al. Alternating droplet generation and controlled dynamic droplet fusion in microfluidic device for CdS nanoparticle synthesis. Lab Chip 6, 174–178 (2006) Lin, X. Z., Terepka, A. D. & Yang, H. Synthesis of silver nanoparticles in a continuous-flow tubular microreactor. Nano Lett. 4, 2227–2232 (2004) Yen, B. K. H., Günther, A., Schmidt, M. A., Jensen, K. F. & Bawendi, M. G. A microfabricated gas–liquid segmented flow reactor for high-temperature synthesis: the case of CdSe quantum dots. Angew. Chem. Int. Edn 44, 5447–5451 (2005)