Synthesis and Characterization of Core/Shell Nanoparticles

MR. SHAMOON AL ISLAMDEPARTMENT OF PHYSICSUNIVERSITY OF AGRICULTURE FAISALABAD

OUTLINE Nanoparticles Core/Shell nanoparticles Different Shaped Core/Shell Nanoparticles Characterization of Core/Shell nanoparticle Synthesis Role of Nanotechnology in our life Future Prospects References

Nanoparticles are particles between 1 and 100 nanometers in size. In nanotechnology, a particle is defined as a small object that behaves as a whole unit with respect to its transport and properties

Nanomaterials have, one or more dimension in the nanometer scale and subsequently show novel properties from their bulk materials like; Small size High surface area Ease to suspend in liquids Deep access to cells and organelles Improved physical, chemical & biological properties

Nanoparticles:

“To understand the very large, we must understand the very small.”

- Democritus (400 BC)

Core/Shell nanoparticles Emerged at the frontier between materials chemistry and many other fields, such

as electronics, biomedical, pharmaceutical, optics, and catalysis. Core/shell nanoparticles are highly functional materials with modified properties. Because of the shell material coating, the properties of the core particle such as

reactivity decrease or thermal stability can be modified, so that the overall particle stability and dispersibility of the core particle increases.

The purpose of the coating on the core particle are many fold, such as surface modification, the ability to increase the functionality, stability, and dispersibility, controlled release of the core, reduction in consumption of precious materials, and so on.

Nano- and microsized hollow particles are used for different purposes such as microvessels, catalytic supports, adsorbents, lightweight structural materials and thermal and electric insulators.

Different Shaped Nanoparticles Figure: Different core/shell

nanoparticles: i. spherical core/shell nanoparticles; ii. hexagonal core/shell nanoparticles; iii. multiple small core materials coated by

single shell material; iv. nanomatryushka material; v. movable core within hollow shell material.

The properties of nanoparticles are not only size dependent but are also linked with the actual shape.

For example, certain properties of magnetic nanocrystals such as the blocking temperature, magnetic saturation, and permanent magnetization are all dependent on particle size, but the coercivity of the nanocrystals totally depends on the particle shape because of surface anisotropy effects

Other nanoparticle physical and chemical properties such as catalytic activity and selectivity, electrical and optical properties, sensitivity to surface-enhanced Raman scattering (SERS) and the plasmon resonance and melting point are also all highly shape-dependent

Classes of Core/Shell Nanoparticles The core/shell type nanoparticles can be broadly

defined as comprising a core (inner material) and a shell (outer layer material).

These can consist of a wide range of different combinations in close interaction, including inorganic/inorganic, inorganic/organic, organic/inorganic, and organic/organic materials.

The choice of shell material of the core/shell nanoparticle is generally strongly dependent on the end application and use.

Multiple core core/shell particles are formed when a single shell material is coated onto many small core particles together

Inorganic/Inorganic Core/Shell Nanoparticles Inorganic Metallic Shells such as Ni, Co, Pd, Pt and Cu are important for some

specific applications in the field of catalysis, solar energy absorption, permanent magnetic

properties, etc.

Silica coating is the more basic and advantageous as compared with other inorganic (metal or metal oxide) or organic coatings as it reduces the bulk conductivity and increases the suspension stability of the core particles. In addition, silica is the most chemically inert material available; it can block the core surface without interfering in the redox .

Gold coating on any particles enhances many physical properties, such as the chemical stability against redox reactions, the biocompatibility, the bioaffinity through functionalization of amine/thiol terminal groups, and the optical properties (Presaa et al., 2007).

Semiconductor Core/Shell Nanoparticles- particles are used for medical or bioimaging purposes, enhancement of optical properties, light-emitting devices, nonlinear optics, biological labeling, improving the efficiency of either solar cells or the storage capacity of electronics devices, modern electronics field applications, catalysis, etc.

Inorganic/Organic Core/Shell Nanoparticles Inorganic/organic core/shell nanoparticles are made of metal, a metallic compound, metal oxide, or a silica core with a polymer shell or a shell of any other high density organic material. One example is the fact that the oxidation stability of the metal core is increased

when otherwise the surface atoms of the metal core can be oxidized to the metal oxide in a normal environment.

The polymer-coated inorganic materials have a broad spectrum of applications, ranging from catalysis to additives, pigments, paints, cosmetics, and inks.

In many applications, the particles are coated to stabilize them in the suspension media, and the stability of such a colloidal suspension depends mainly on the attractive and repulsive forces between the particles (Bao et al., 2007).

Organic/Inorganic Core/Shell Nanoparticles The core of this particular class of core/shell nanoparticles is made of a polymer,

and different copolymers. The shell can also be made from different materials, such as metals, metal oxides

or silica. The inorganic material, especially a metal oxide coating on an organic material, is

beneficial in several respects, such as increased strength of the overall material, resistance to oxidation, thermal and colloidal stability, and abrasion resistance.

At the same time, these particles also show polymeric properties such as excellent optical properties, flexibility, and toughness, and in addition they can improve the brittleness of the inorganic particles (Ammar et al., 2007).

Organic/Organic Core/Shell Nanoparticles In this category, both the core and shell particles are made of a polymer or another organic material. These classes of particles are known as “smart particles” and have a wide range

of applications in different fields, such as drug delivery, biosensing, chemical separation, biomaterials, and catalysis.

The advantages of having a polymer coating on another polymer is to modify the physical properties of the overall material, such as toughness or the glass transition temperature.

Polymer/polymer core/shell particles are also extensively used for controlled drug release applications in in vivo systems because of their good biodegradable and drug encapsulation property (Kayal and Ramanujan, 2010).

Approaches for Core/Shell Nanoparticle SynthesisApproaches for nanomaterial synthesis can be broadly divided into two categories: The “top-down” approach often uses traditional workshop or microfabrication

methods where externally controlled tools are used to cut, mill, and shape materials into the desired shape and order. The most common techniques are lithographic techniques (e.g., UV, electron or ion beam),laser-beam processing, and

mechanical techniques (e.g., machining, grinding, and polishing). “Bottom-up” approaches, on the other hand, exploit the chemical properties of the molecules to cause them to self- assemble into some useful conformation. The most common bottom -up approaches are chemical synthesis, chemical vapor deposition, film deposition and growth etc.

However, the bottom-up approach can produce much smaller sized particles and has the potential to be more cost-effective in the future because of the advantages of absolute precision, complete control over the process, and minimum energy loss compared with that of a topdown approach.

TECHNIQUES, CLASSIFICATION, AND MECHANISM OF CORE/SHELL NANOPARTICLE SYNTHESIS

In general, core/shell nanoparticles are synthesized using a two-step process, first synthesis of core and second the synthesis of the shell.

The synthesis techniques of core/shell nanoparticles can be classified into two types depending on the availability of core particles: the core particles are synthesized and separately incorporated into the system with proper

surface modification for coating the shell material; the core particles are synthesized in situ, and this is followed by coating of the shell material.

The basic advantage of external core synthesis is the fact that core particles are available in pure form and hence there is less possibility of impurities on the core surface.

Whereas, in in situ synthesis, the main problem is that some impurity from the reaction media may be trapped between the core and shell layer.

The most important step during synthesis of core/shell particles is to maintain uniform coating and to control the shell thickness.

Some of the various synthetic methods for core/ shell particles used by different research groups are precipitation, polymerization, microemulsion, sol-gel condensation, layer by layer adsorption techniques etc.

Core/Shell Nanoparticles Synthesis Schematic

ROLE OF NANOTECHNOLOGY IN OUR LIFE:Nanotechnology has applications in all convincible areas, and scientists / researchers are finding newer applications of the nano materials and nano fabricated materials.

Currently nanotechnology is most widely used in Cosmetics, Medicines/ Drugs, Defense, Fabrics, Energy and Water purification, but in few years all other domains will also be using nanotechnology as potential tool (Szostko et al., 2013).

Nanotechnology in Drugs(Cancer) Provide new options for drug delivery and drug therapies. Enable drugs to be delivered to precisely the right location in the body and

release drug doses on a predetermined schedule for optimal treatment. Attach the drug to a nanosized carrier. They become localized at the disease site, i.e cancer tumour. Then they release medicine that kills the tumour Current treatment is through radiotherapy or chemotherapy. Nanobots can clear the blockage in arteries.

Nanotechnology in Fabrics The properties of familiar materials are being changed by

manufacturers who are adding nano-sized components to conventional materials to improve performance.

For example, some clothing manufacturers are making water and stain repellent clothing using nano-sized whiskers in the fabric that cause water to bead up on the surface.

In manufacturing bullet proof jackets Making spill & dirt resistant, antimicrobial, antibacterial

fabrics.

Nanotechnology in Mobile Morph, a nanotechnology concept device developed by Nokia Research Center (NRC) and the University of Cambridge (UK). The Morph will be super hydrophobic making it extremely dirt repellent. It will be able to charge itself from available light sources

using photovoltaic nanowire grass covering it's surface. Nanoscale electronics also allow stretching. Nokia

envisage that a nanoscale mesh of fibers will allow our mobile devices to be bent, stretched and folded into any number of conceivable shapes.

Nanobots Close to the scale of 10-9. Largely in R&d phase . Nanobots of 1.5 nanometers across, capable

of counting specific molecules in a chemical sample. Since nanorobots would be microscopic in size, it would

probably be necessary for very large numbers of them to work together to perform microscopic and macroscopic tasks.

Capable of replication using environmental resources . Application:

Detection of toxic components in environment.

In drug delivery. Biomedical instrumention.

Nanotechnology in Electronics Electrodes made from nanowires enable flat panel displays

to be flexible as well as thinner than current flat panel displays. Nanolithography is used for fabrication of chips. The transistors are made of nanowires, that are

assembled on glass or thin films of flexible plastic. E-paper, displays on sunglasses and

map on car windshields.

Nanotechnology in computers The silicon transistors in your computer may be replaced by

transistors based on carbon nanotubes. A carbon nanotube is a molecule in form of a hollow cylinder

with a diameter of around a nanometer which consists of pure carbon.

Nanorods is a upcoming technology in the displays techniques due to less consumption of electricity and less heat emission.

Size of the microprocessors are reduced to greater extend.  Researchers at North Carolina State University says that

growing arrays of magnetic nanoparticles, called nanodots.

Other uses Cutting tools made of nanocrystalline materials, such as tungsten carbide, tantalum

carbide and titanium carbide, are more wear and erosion-resistant, and last longer than their conventional counterparts.

Silver nanocrystals have been embedded in bandages to kill bacteria and prevent infection.

Nanoparticulate-based synthetic bone Formed by manipulating calcium and phosphate at the molecular level.

Aerogels lightest known solid due to good insulating properties is used in space suits and are proposed to use in space craft.

Future Prospects

The future generations of core/shell nanoparticles will exhibit many new properties that will surely result in new applications with improved performance.

Generally core/shell nanoparticles are well-known for better stability, for being able to protect the core material from the surrounding environment, for improved physical and chemical properties, for improved semiconductor properties, for easy biofunctionalization, etc.

Most of the recent exciting discoveries show that there is tremendous scope in biomedical applications such as controlled drug delivery and release, targeted drug delivery, bioimaging, cell leveling, biosensors, diagnostics, immunoassays, and many more.

In the near future, the development of new materials has the potential for improving the treatment of cancer and many other life threatening diseases.

Also, the future of nanotechnology could very well include the use of nanorobotics. These nanorobots have the potential to take on human tasks as well as tasks that humans could never complete. The rebuilding of the depleted ozone layer could potentially be able to be performed.

References:1. Bao, Y., H. Calderon and K.M. Krishnan. 2007. Synthesis and characterization of magnetic-Optical Co−Au

core−shell nanoparticles. J. Phys. Chem. C. 111:1941-1944.

2. Kayal, S. and R.V. Ramanujan. 2010. Anti-cancer drug loaded Iron–Gold core–shell nanoparticles (Fe@Au) for magnetic drug targeting. Journal of Nanoscience and Nanotechnology. 10:1-13.

3. Szostko, B.K., U. Wykowska, A. Basa and K.Szymański. 2013. Chemical preparation of core-shell nanoparticles. NUKLEONIKA. 58:35-38.

4. Presaa, P.D.L., M. Multignera, M.P. Moralesb, T. Ruedaa, E. Fernández-Pinela and A. Hernandoa. 2007. Synthesis and characterization of FePt/Au core-shell nanoparticles. Proceedings of the Joint European Magnetic Symposia. 209:8-39.

5. Ammar, M., F. Mazaleyrat, J.P. Bonnet, P. Audebert, A. Brosseau, G. Wang and Y. Champion. 2007. Synthesis and characterization of core–shell structure silica-coated Fe29.5Ni70.5 nanoparticles. Nanotechnology. 18:28.