Nanoparticle-assembled capsules

Keywords Hollow spheres Nanoparticles Layer-by-layer assembly Tandem assembly Nanoparticle assembled capsule Interfacial stabilization - Particle stabilized emulsion... 

Another recent development features the in situ formation of liquid colloidal templates. The assembly of NPs at the periphery of these templates is driven by electrostatics, resulting in the formation of robust NP-sheUed hoUow spheres, originally termed nanoparticle-assembled capsules (NACs). This scheme is called tandem assembly , nanoparticle-polymer tandem assembly , or polymer-aggregate tern-plating and presents an alternate, simple and non-destructive route for formation of NP-shelled hollow spheres [6,32-35,40,80,81]. 

Murthy VS, Rana RK, Wong MS (2006) Nanoparticle-assembled capsule synthesis Formation of colloidal polyamine-salt intermediates. J Phys Chem B 110(51) 25619-25627... 

Yu J, Yaseen MA, Anvari B, Wong MS (2007) Synthesis of near-infrared-absoibing nanoparticle-assembled capsules. Chem Mater 19(6) 1277—1284... 

In a very recent publication that appeared after this chapter was reviewed. Woods and Sherry describe a nanoconstruct in which cationic polymers, GdDOTPf and silica nanoparticles are combined to form nanoparticle-assembled capsules (NACs) of 0.2-5.0 pm in diameter. The construct has an interior polymeric region in which GdDOTP ions are dispersed. The corona of the particle is comprised of relatively small (13 nm) silica nanoparticles adsorbed on... 

Xuan J, Jia X-D, Jiang L-P, Abdel-Halim ES, Zhu J-J (2012) Gold nanoparticle-assembled capsules and their application as hydrogen peroxide biosensor based on hemoglobin. Bioelectrochemistry 84 32-37... 

Abstract Nanoparticles (NPs, diameter range of 1-100 nm) can have size-dependent physical and electronic properties that are useful in a variety of applications. Arranging them into hollow shells introduces the additional functionalities of encapsulation, storage, and controlled release that the constituent NPs do not have.This chapter examines recent developments in the synthesis routes and properties of hollow spheres formed out of NPs. Synthesis approaches reviewed here are recent developments in the electrostatics-based tandem assembly and interfacial stabilization routes to the formation of NP-shelled structures. Distinct from the well-established layer-by-layer (LBL) synthesis approach, the former route leads to NP/polymer composite hollow spheres that are potentially useful in medical therapy, catalysis, and encapsulation applications. The latter route is based on interfacial activity and stabilization by NPs with amphiphilic properties, to generate materials like colloidosomes, Pickering emulsions, and foams. The varied types of NP shells can have unique materials properties that are not found in the NP building blocks, or in polymer-based, surfactant-based, or LBL-assembled capsules. 

A new variation of interfacial polymerization was developed by Russell and Emrick in which functionalized nanoparticles or premade oligomers self-assemble at the interface of droplets, stabilizing them against coalescence. The functional groups are then crosslinked, forming permanent capsule shells around the droplets to make water-in-oil (Lin et al. 2003 Skaff et al. 2005) and oil-in-water (Breitenkamp and Emrick 2003 Glogowski et al. 2007) microcapsules with elastic membranes. 

Inorganic nanoparticles themselves can be assembled into mesoscopic structures. Dinsmore et al. proposed an approach for the fabrication of solid capsules from colloidal particles with precise control of size, permeability, mechanical strength, and compatibility (Fig. 2.9).44 This unusual mesoscopic structure is called colloidosome and is prepared through emulsion droplets at a water-oil interface. Following the locking together of the particles to form elastic shells, the emulsion droplets were transferred to a fresh continuous-phase fluid identical to that contained inside the droplets. The resultant structures are hollow, elastic shells whose permeability and elasticity can be precisely controlled. 

Besides the basic interest in the parameters governing particle interfacial assembly, there is also considerable technological potential associated with the structures formed at liquid-liquid interfaces. For example, nanoparticles could serve as building blocks for capsules and membranes with nanoscopic pores for filtering or encapsulation and for delivery purposes. 

This volume provides an overview of a number of extensively used techniques to encapsulate a host of different materials, ranging from confined polymerization to self-assembly. The encapsulation vehicles formed include thin multi-strata films, emulsions, polymersomes, nanoparticle-based hollow spheres and polymer capsules. The potential applications of these systems for encapsulation and their use as microreactors to perform a host of complex reactions are discussed, and examples showing the diversity of properties that can be controlled in these systems are given. 

Where the nanoparticles are reacted directly (rather than being used to catalyze reactions), the achievable sensitivity will depend largely on the quantity of metal attached to each DNA sequence. This has led to the development in label construction illustrated in Fig. 8.1. From the binding of individual particles, researchers have sought techniques to attach assemblies of nanoparticles to a given DNA sequence. As will be described in this chapter, latex colloids provide an ideal base for such assemblies, both as solid supports and as templates for the construction of hollow capsules which can take up nanomaterials. The point of importance is thatthe necessary latex modifications have already been intensively researched for other applications, and so the relevant physical chemistry theory and experimental details are already available. Despite this fact, the use of latex in constructing electrochemical DNA labels is relatively unexplored. 

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