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Title: Development of a colorimetric nanosensor and nano-biosorbents from amyloid fibrils of hen lysozyme for rapid detection of chromium(VI) and removal of dye and chromium(VI) pollutants
Authors: Leung, Wai Hong
Degree: Ph.D.
Issue Date: 2017
Abstract: Amyloid fibrils are the hallmarks of amyloid diseases in which proteins or peptide fragments aggregate into water-insoluble materials under physiologically relevant conditions. Notorious examples include Alzheimer's and Parkinson's diseases. Amyloid fibrils accumulate in large quantities in human bodies can cause serious damage to organs and tissues (e.g. the liver, the kidneys and the brain). Amyloid fibrils are formed through the formation of intermolecular hydrogen bonds between the polypeptide chains of proteins/peptide fragments, giving rise to the common structural characteristic of cross-β sheet structure. Because proteins contain polypeptide chains, the formation of amyloid fibrils is generally thought to be a generic property of all proteins, including those that are not relevant to amyloid diseases. Despite their disease-related property, amyloid fibrils possess characteristic structural properties that render themselves promising nano-biomaterials for various applications in environmental protection. (1) Amyloid fibrils can be prepared under green and mild aqueous conditions in just one step. (2) Many amyloid fibrils have nano-sized and robust structures, and possess both net +/- charges and hydrophobic regions along their fibrillar structures, thus enabling themselves to adsorb ionic analytes/charged molecules rapidly and efficiently. (3) Amyloid fibrils have large room to be further developed into tailor-made and "super-functional" nanofibers for specific applications through protein engineering or chemical modifications at their reactive amino acid residues (e.g. Lys, Cys, Glu and Asp). These unique properties provide an opportunity for chemosensing of heavy metals and harmful chemical removals in wastewater/natural water. We have successfully developed a rapid, sensitive and cost-effective colorimetric nanosensor from amyloid fibrils of hen lysozyme for detecting Cr(VI), a carcinogenic metal ion existing as negatively charged chromate in dilute aqueous solution. Hen lysozyme is positively charged in aqueous solution and can therefore form nanofibers with high positive charges upon formation of fibrils. These positively charged nanofibers act as strong binders to Cr(VI) and "concentrate" Cr(VI) (existing at trace levels) onto their structures. Upon addition of Cr(VI)-specific colorimetric agent DPC, the adsorbed Cr(VI) will be reduced to Cr(III) and form a distinctive pink complex on lysozyme nanofibers. This nanosensor can rapidly detect Cr(VI) down to 30 ppb level within 10 min on a naked-eye format. Moreover, the nanosensor can distinguish toxic Cr(VI) from less toxic Cr(III) and other metal ions. With its ability to provide rapid, sensitive and cost-effective Cr(VI) detection on an instrument-free format, the nanosensor may facilitate on-site Cr(VI) monitoring in wastewater/natural water and particularly benefit poor regions/countries lacking sufficient laboratory resources and well-trained personnel for extensive water monitoring.
We further studied the ability of lysozyme nanofibers to act as nano-biosorbents for removing dye pollutants, which are common chemical pollutants in water pollution. Our zeta-potential and ANS fluorescence studies have shown that lysozyme nanofibers carry both positive charges (in the pH range of 3.0-9.0) and hydrophobic regions along their fibrillar structures. With these special structural properties, we reasoned that lysozyme nanofibers can adsorb dye molecules with both charged groups and aromatic scaffolds through electrostatic attraction and hydrophobic interaction. Lysozyme nanofibers can adsorb the anionic dyes Reactive Black 5 and Acid Blue 29 and the cationic dye Victoria Blue B rapidly and efficiently; the adsorption equilibrium for these dyes can be reached in 1-13 min, and the maximum adsorption capacity for these dyes lies in the range of 100-159 mg g-1. Moreover, lysozyme nanofibers can maintain over 60% dye removal efficiency in industrial wastewater. Lysozyme nanofibers are also compatible with magnetite nanoparticles to form magnetic nanofibers which can provide rapid and convenient dye removals through the application of an external magnetic field and maintain high dye removal efficiency (92-99%) after undergoing 20 cycles of desorption. We then explored the possibility of surface chemical modification of amyloid fibrils as to enhance the adsorption performance on Cr(VI). The carboxyl groups on lysozyme nanofibers surface were modified with ethylenediamine through an EDC-NHS reaction, which provided extra free amino groups for Cr(VI) adsorption. Mass spectral analysis has verified that ethylenediamine was successfully linked to the surface of lysozyme nanofibers. Based on such characterization, we envisaged that more Cr(VI) ions could be adsorbed by the modified lysozyme nanofibers. Comparative study on the effects of different parameters like pH, contact time, the dose of adsorbent and initial metal concentration on Cr(VI) adsorption by unmodified and modified lysozyme nanofibers was investigated. A consistent result has shown that modified lysozyme nanofibers exhibit a better Cr(VI) adsorption performance than unmodified lysozyme nanofibers. The adsorption capacity of Cr(VI) on modified lysozyme nanofibers was enhanced by 38% at pH 7.0 when comparing with the adsorption capacity on unmodified lysozyme nanofibers. Furthermore, modified lysozyme nanofibers preserve their unique structural and functional properties for rapid and efficient adsorption on Cr(VI) with a fast adsorption equilibrium (1 min). The success of surface chemical modification of amyloid fibrils with the enhanced performance for Cr(VI) removal demonstrates a latent capability for development of multifunctional lysozyme nanofibers for different applications.
Subjects: Hong Kong Polytechnic University -- Dissertations
Chromium -- Toxicology
Water -- Purification
Pages: xv, 248 pages : color illustrations
Appears in Collections:Thesis

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