Synthesis of Semi-Conducting Nanoparticles within a Protein Template
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E15.3.1
Synthesis of Semi-Conducting Nanoparticles within a Protein Template Kim K. W. Wong and Eric L. Mayes NanoMagnetics Ltd., 108 Longmead Road, Bristol, BS16 7FG, United Kingdom
ABSTRACT
The ability to synthesise and tune photoresponsive and photoredox II-VI semi-conductor nanoparticles by quantum confinement is a continuously and rapidly developing area. Chemical methods are useful in producing dispersions of nanoparticles of uniform size in many organic solvents. Such synthetic methods employ the use of reverse micelles [1,2], phospholipid vesicles[3,4] or capping agents[5,6] to restrict particle size and growth to the nanometre regime. The production of super lattice assemblies, through, for example the use of controlled crystallisation [7], Langmuir monolayers[8], Langmuir Blogget films [9], and self assembled short chain dithiol monolayers[10] on gold substrates has also received attention in the past. This latter approach potentially opens the way for self assembled electro-luminescent devices [11]. The ability to couple organic self assembly and inorganic nano-synthesis could also provide a route toward the chemical synthesis of an organised array of quantum-confined semiconductors. An aspect of this synthesis with construction approach is the possible coupling of biological templating systems to produce biomimetic materials [12,13]. In fact, an example would be the stabilised CdS nanoparticles in yeast binding to phytochelatin peptides which are secreted in response to metal toxicification [14].
INTRODUCTION
Previous work has shown that ferritin, a self assembled iron storage protein with an 8nm poplypeptide cage, can indeed be used for the synthesis and confinement of a range of inorganic materials; such as uranyl oxide [15], manganese oxide [16], and magnetite [17]. In situ sulphidation of the native iron oxide core can also be accomplished or the empty apo-protein can be reconstituted with iron and then the core sulphidated to produce the corresponding sulphide [18]. In each case the nanoparticles are encapsulated and growth is restricted to the internal dimension the protein cavity to give dispersed solutions with potential bio-compatibility and bio-active properties. Work by Pead et al [19] has shown that the apo-protein has the capability of binding other metal ion species enabling the possibility of producing non-native bio-inorganic nanomaterials. This has been demonstrated by the synthesis of a cobalt oxyhydroxide by Douglas et al [20]. The ability of the protein to up-take non native metal ions relies on the accessibility of binding sites via diffusion through molecular channels built into the polypeptide cage. Here, we report on a strategy for the synthesis of semi-conducting nanoparticles focussing on ZnS and ZnSe within the protein. Using an incremental addition methodology and reaction with stoichiometric amounts of Zn(II) with HS and HSe we show that the corresponding compounds can be synthesised and encapsulated within the protein cavity matrix to produce dispersed solutions of ZnS
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