Hybrid Metallic Nanostructures for Bio and Analytical Applications
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Different hybrid nanoparticles (NPs), including FeM (M=Ni, Au, Pt, Pd) and Fe-biomolecules (biomolecule=glucose oxidase, p53p protein), have been synthesized by a surfactant-free, single-step electrochemical method. FeNi bimetallic NP systems have been chosen as the starting point of the present study. Shape evolution and phase transformation of FeNi NPs obtained by changing their composition is demonstrated. It has been shown that the shape evolution of NPs from concave cube to truncated sphere occurs concurrently with the phase transformation from bcc to fcc. In-situ formation of a very thin Ni-doped FeOOH outer layer and NiFe2O4 intermediate layer on the skin of the NPs is observed, the latter of which passivates the surface and dramatically enhances the air stability. Furthermore, bimetallic FeNi concave nanocubes with high Miller index planes have been obtained through controlled triggering of the different growth modes of Fe and Ni. Taking advantage of the higher activity of the high-index planes, mono-dispersed concave nanocages have been fabricated by introducing a material-independent electroleaching process. With the high-index facets exposed, these concave nanocubes and nanocages are found to be 10 and 100-fold, respectively, more active toward electrochemical detection of 4-aminophenol than cuboctahedrons which provides a label-free sensing approach to monitoring toxins in water and pharmaceutical wastes. In addition, the shape-dependent magnetic properties of a bimetallic system have been studied for FeNi NPs with well-defined concave cubic and octahedron shapes. The alloy composition was chosen to be close to that of Invar FeNi alloys (35% Ni content) but with concurrent presence of both bcc and fcc phases, in order to investigate the role of phase combination in controlling the magnetic properties. The role of the two phases in governing the magnetic properties has also been studied for both bulk and nanoalloys by large-scale density function theory (DFT) calculations using Vienna Ab-initio Simulation Package (VASP, Version 5.2), which provides a new complementary approach to understanding the magnetic properties of alloy materials. To extend the aforementioned method to other hybrid and bimetallic systems, FePt NPs with different compositions (Fe25Pt75, Fe30Pt70, Fe35Pt65) have been synthesized and their chemical sensing investigated for the electro-oxidation of vitamin C. The FePt alloy NPs are found to be superior catalysts for vitamin C electro-oxidation than Pt NPs and are significantly more selective for the detection of vitamin C against other common interference species, including dopamine, citric acid, uric acid, glucose, and NaCl. Enhancement in sensor performance can be attributed to the increase in specific surface area due to reduction of nanocrystallite size and to modification in the Pt electronic structure as a result of nanoalloying. We also synthesize bimetallic FeAu, FePd, and AuPt NPs and investigate their electrochemical properties for As(III) detection. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, Pd) than pristine noble metal NPs (without Fe alloying), with the best performance found for FePt NPs. The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), acting as the most detrimental interfering ion for As detection. The versatility of the method for hybridization of different components is demonstrated by synthesizing size-specific hybrid NPs based on Fe-biomolecules. We have chosen an anticancer peptide (p53p, MW 1.8 kDa) and an common enzyme (glucose oxidase, MW 160 kDa) as model molecules to illustrate the versatility of the method towards different types of molecules over a large size range. We show that the electrostatic interaction for complex formation of metal hydroxide ion with the partially charged side of the biomolecule in the solution is the key to hybridization of metal-biomolecule materials to form complexes as the building blocks. These hybrid NPs with controllable sizes ranging from 30 nm to 3.5 μm are found to exhibit superparamagnetic behavior, which is a big challenge for particles in this size regime. As an example of greatly improved properties and functionality of the new hybrid material, in-vitro toxicity assessment of Fe-glucose oxidase hybrid NPs shows no adverse effect, while the Fe-p53p hybrid NPs are found to selectively bind to cancer cells. The present work therefore definitely demonstrates the general applicability of the hybridization method for synthesis of metallic hybrid NPs with magnetic properties for different applications, including chemical sensing, magnetic resonance imaging contrast agents, and targeted drug delivery carriers.
Cite this work
Nafiseh Moghimi (2015). Hybrid Metallic Nanostructures for Bio and Analytical Applications. UWSpace. http://hdl.handle.net/10012/9128