Biomolecular engineered sensors for diagnostic applications

Electrochemistry is a powerful technique that offers multiple possibilities and which is in constant evolution. Simple modifications of the electrode surface can result in an improvement of the selectivity and sensitivity of the method. However some situations require more complex modifications such as the incorporation of an external agent to the electrode surface, or within the actual electrode. This thesis describes the development and characterization of a range of novel electrochemical sensors for multiple applications covering agri-food, biomedical and environmental contexts. The foundations of the approach rest upon the development of carbon-loaded polycarbonate composite films. Their fabrication is described and the ease with which they can be modified and physically adapted is highlighted and critically evaluated. The response of the resulting sensors have been validated against conventional techniques. An overview of the technologies employing carbon electrodes is presented in Chapter 1 and serves to set the context of the subsequent research. The various methodologies employed are outlined in Chapter 2. Preliminary modifications of the analytical process has evolved from the ex situ functionalisation of the conventional carbon electrodes with copper (Chapter 3) through to the examination of the versatility and complexities of sample pre-treatment (Chapter 4). The pre-treatment of the sample using naphthoquinones as labeling agents has been developed and this work was extended to examine a wholly new derivatisation agent which could have analytical and clinical/veterinary diagnostic merit. A new direction was sought to overcome the limitations of the conventional analytical approach and composite systems were envisaged as providing an accessible yet flexible method of developing electrochemical sensors for discrete probe and flow systems. The basic procedure has been characterization and optimized for a range of analytes such as neurotransmitters (Chapter 5), anti-oxidants (Chapter 6), purine metabolites (Chapter 8) and phosphate (Chapter 9). Each chapter highlights a different aspect and applicability of the composite and go from simple physical surface modification (Chapter 5) to the incorporation of chemical agents (Chapter 6) and more complex systems such as enzymes (Chapters 8 and 9)

Graphene as a flexible electrode: review of fabrication approaches

In recent years, the technological advancement of supercapacitors has been increasing exponentially due to the high demand in electronic consumer products. As so, researchers have found a way to meet that demand by fabricating graphene. As developments are made toward the future, two big advancements to be made are large-scale fabrication of graphene and fabricating graphene as a flexible electrode. This would allow for use in larger products and for manipulation of the unique properties of graphene to accommodate superior design alternatives. While large scale production is still mentioned, this review is specifically focusing on different methods used to fabricate graphene as a flexible electrode. Various fabrication methods, such as Hummers\u27 method, chemical vapor deposition, epitaxial growth, and exfoliation of graphite oxide, used to fabricate graphene in such a way that allows flexibility and utilization of graphene\u27s mechanical and electrical properties are discussed. Additionally, a section on environmentally friendly fabrication approaches is presented and discussed

Polydopamine-Enabled Biomimetic Surface Engineering of Materials:New Insights and Promising Applications

Surface modification is an important approach to modify the properties of materials. Numerous approaches have been adopted to tailor the properties of such materials, which have been proven successful at many scales and parameters. However, most of these techniques are often tedious, poorly adhesive, costly, sometimes hazardous, and surface-specific, hence cannot be extended on a large scale and all kinds of surfaces. These shortcomings have led to the emergence of new dopamine (DA) based green surface modification technique where a thin polydopamine (PDA) layer is deposited on surfaces through a facile polymerization of DA under alkaline conditions to enable the surface for various applications. This surface modification strategy has several advantages over other techniques in deposition processing under mild conditions, cost-effective and straightforward ingredients, and applicability to all kinds of surfaces regardless of their sizes, shapes, and types. Moreover, the PDA layer enhances the surface functionality. Therefore, it can serve as a versatile platform for various secondary reactions for a wide range of applications. Herein, the chemistry of DA is summarized and its polymerized form PDA for the modification of different families of materials’ surfaces with an emphasis on energy, environmental and biological applications.</p

Carbon nanotube based potentiometric aptasensors for protein detection

El diagnóstico rápido de la mayoría de las enfermedades tiene una importancia vital para proporcionar el remedio adecuado y, por lo tanto, el control de problemas de salud. La detección rápida y selectiva de biomoléculas grandes, específicamente proteínas, es uno de los objetivos importantes en este campo. Las técnicas basadas en inmunoensayos son las más comúnmente utilizadas, aunque requieren un marcaje específico. Por lo general, estos métodos también requieren personal altamente capacitado y equipos complejos que se traduce en una metodología relativamente cara y lenta. En la presente tesis aportamos por primera vez un nuevo tipo de aptasensores potenciométricos de estado sólido basados en nanotubos de carbono que pueden detectar analitos grandes, como por ejemplo proteínas, de manera rápida (casi instantánea), selectiva, y sensible sin necesidad de marcaje químico. Los sensores desarrollados responden correctamente a la proteína analito (α-trombina humana) dentro de los niveles fisiológicos en el suero humano.Rapid diagnosis of most illnesses has a vital importance for providing the appropriate cure and hence controlling public health concerns. Fast and accurate detection of large biomolecules, specifically proteins, is one of the major steps regarding the subject. Over recent years, several detection methodologies have been developed. However, almost all of the developed methods either required very complex techniques to be applied, or a long time to obtain the results. The most commonly used techniques were specific label requiring immunoassays. They generally require highly trained staff and complex equipment which results in an expensive and relatively slow methodology. With the present thesis we report a new type of label-free potentiometric solid state carbon nanotube based aptasensors that can detect large analytes, as case example proteins, in a rapid (almost instantaneous), selective and sensitive way, for the first time. The developed sensors successfully responded to analyte protein (human α-thrombin) within physiological human serum levels

A multiplex self-referencing detection of pathogens using surface enhanced raman scattering nanoprobes with a nano-DEP microfluidic concentrator

In this dissertation, I successfully developed the multiplex self-referencing SERS pathogen (E.coli O157: H7) detection biosensor platform which offers high sensitivity (10^1 CFU/mL) and strain level discrimination by measuring the superimposed SERS signatures with multiple characteristic peaks. To harvest the effective Raman molecular probes, I developed methods to fabricate anisotropic metallic nanoparticles to serve as SERS enhancers, and more importantly, I developed surface modification methodology to add functionality to the SERS enhancers so that they can bind specifically to their pathogen targets for highly accurate and sensitive detection. Gold nanorods (GNRs) and gold/silver nanocages are successfully fabricated with high particle yield. Three highly effective linker molecules (4-Aminothiophenol (4-ATP), 3-Amino-1,2,4-triazole-5-thiol (ATT), and 3-Mercaptopropionic acid (3-MPA)) are identified and designed to conjugate on gold nanostructures, and then different monoclonal antibody molecules are designed to bond to the different linkers through diazo-histine binding (4-ATP and ATT) and EDC/NHS bonding (3-MPA-antibody). In addition, this platform demonstrated excellent separation and concentration capacities by using DEP microfluidic devices and further improves the sensitivity to 10^0 CFU/mL. The integration of microfluidic devices with SERS detection has yielded simple and miniaturized instrumentation that is suitable for the detection and characterization of small volume of chemical and biological analytes with high sensitivity and specificity. For data analysis, various preprocessing methods are used for spectral background removal, baseline correction, smoothing, and normalization. Principle Component Analysis (PCA) is applied to reduce the variable dimensions. A Support Vector Machine (SVM) discriminant analysis model based on statistical multivariate model is being developed for superimposed spectra classification. The validation of spectral classification model (target binding VS no target binding) is evaluated by the accuracy percentage, which is above 95%

Biocomposites

Biocomposites are composite materials consisting of either a polymer matrix or a filler based on biological resources. They have been widely used in numerous applications such as storage devices, photocatalysts, packaging, furniture, biosensors, energy, construction, the automotive industry, and so on due to their great versatility and satisfactory performance. This book focuses on composites made from natural materials (natural fibers and biopolymers) and relates their physical, mechanical, electrical, structural, and biological characteristics as well as their potential applications in biomedicine, pharmaceuticals, and engineering

Engineering of nano-bio interfaces towards the development of portable biosensors

The rapid development in bio-nanotechnology coupled with advancements in microelectronics and computing power has given rise to an enormous potential for the development of point-of-care diagnostic devices and portable biosensors. The application area encompasses human disease detection, analyzing bio-hazardous molecules and toxins and other inorganic materials. Amongst the plethora of receptors in such biosensors, aptamers, which are oligonucleotides with high affinity for target analytes, have demonstrated considerably improved performance over traditional receptors like antibodies. The hallmark of a portable biosensor is high throughput in response to analyte characterized by appreciable signal/noise ratio, dynamic range and low limit of detection. However, these characteristics are difficult to achieve in practical scenarios due to a variety of factors and thus the success is mostly limited to lab based developments. Particularly, the poor commercial success of portable biosensors directed towards human disease detection is noticeable. In this study, effort has been made to address some of the issues like external control over target binding to receptor, low signal/noise ratio and detection in presence of interfering molecules, challenging the practical deployment of a portable aptamer-based biosensor by focusing on engineering of the nano-bio interface of the transducer in such devices. The investigation is carried out in three directions: 1. Electrical actuation of receptor-target complex 2. Impedance characterization of nanoporous transducer 3. Engineering of the receptor arrangement on the transducer The goal of the present research is to provide improved understanding of such processes which can lead to the design and creation of a point-of-care diagnostic device with the ability to detect human disease markers like: (i) Ebola virus protein sGP/GP1-GP2 as a biomarker for Ebola virus infection (ii) NGAL protein related to Acute Kidney Injury Through the research described in this thesis, the following have been understood: (a) The actuation of aptamer-protein complex, where the protein may be dissociated from the aptamer immobilized on the electrode surface due to externally applied electric field depends on the length of the aptamer nucleotide sequence, charge of protein and the surface grafting density of aptamer. (b) Four-electrode electrochemical sensors, utilizing nanoporous alumina membrane with aptamer immobilized on one surface can be used as a biosensor in which membrane impedance depends on target concentration and greater sensitivity is observed with serum albumin in the sample to be tested. Also, there exists an optimal frequency for aptamer-protein complexes which can help in reducing the time of operation of such a biosensor by eliminating the need for long range of frequency scans to get system impedance. (c) Competition mode of sensing, using a receptor weakly attached to the surface via a linker, and having higher propensity to bind with target analyte in the solution compared to remaining surface bound, may be used as a technique to increase signal/noise ratio by increasing sensitivity to low concentration analyte in presence of interfering molecules

Nanocellulose and Nanocarbons Based Hybrid Materials

This highly informative and carefully presented book discusses the preparation, processing, characterization and applications of different types of hybrid nanomaterials based on nanocellulose and/or nanocarbons. It gives an overview of recent advances of outstanding classes of hybrid materials applied in the fields of physics, chemistry, biology, medicine, and materials science, among others. The content of this book is relevant to researchers in academia and industry professionals working on the development of advanced hybrid nanomaterials and their applications