565 research outputs found
Rationally engineered nanosensors: A novel strategy for the detection of heavy metal ions in the environment
Heavy metal ions (HMIs) have been mainly originated from natural and anthropogenic agents. It has become one of biggest societal issues due to their recognised accumulative and toxic effects in the environment as well as biological media. Key measures are required to reduce the risks posed by toxic metal pollutants existing in the environment. The increased research activities of HMIs detection, and use of technologies based on electrochemical detection that combine with engineered nanomaterials, is a key promising and innovative strategy that can potentially confine heavy metal poisoning. Deep understanding of the characteristics of the physicochemical properties of nanomaterials is highly required. It is also important to interpret the parameters at the nano-bio interface level that merely affect cross-interactions between nanomaterials and HMIs. Therefore, the authors outlined the state-of-the-art techniques that used engineeringly developed nanomaterials to detect HMIs in the environment. The possible novel applications of extensive and relatively low-cost HMIs monitoring and detection are discussed on the basis of these strengths. Finally, it is concluded by providing gist on acquaintance with facts in the present-day scenario along with highlighting areas to explore the strategies to overcome the current limitations for practical applications is useful in further generations of nano-world
Bio-Inspired Materials for Electrochemical Sensors
Electrochemical biosensors are a rapidly growing research area that has greatly improved its specificity, accuracy, and precision in the detection of biomolecules in contemporary literature and industry alike. Typically, these systems exist in a three-electrode conformation with a working electrode functioning as the anode, a counter electrode functioning as the cathode, and a reference electrode allowing for the control of potential in the system. The method by which these sensors work is through the sharing of electrons via redox reactions with the target molecule and the working electrode or modifications on its surface. By exploiting the function of biomaterials that participate in natural substrate-binding redox phenomena, new opportunities for detecting critical molecules in complex situations can be created. In this dissertation, three distinct electrochemical biosensors were created by mimicking natural phenomena and implementing materials that directly or indirectly participate in the corresponding reactions. First, a dopamine sensor was created via a composite of lignin-derived graphene oxide and the marine algae-derived polysaccharide kappa carrageenan. Different ratios of GO, a known electrooxidizing catalyst of dopamine, with kappa carrageenan were used to create a binder-free film for dropcasting on the working electrode. It was designed on the principle of its interactions with the nervous system when injected in rats to induce analgesia, interfering with standard dopamine behavior. The system demonstrated a linear range of 1 - 250 μmol L-1 and a limit of detection of 0.14 μmol L-1 (s/n=3). In the second chapter, a sensor for the human and animal health hazard nitrite was constructed using the transition metal sulfide NiS. Transition metal sulfides are the catalytic center for nitrite oxidation to nitrate in nitrogen fixing bacteria found in the environment. This section utilized a novel electrodeposition method for creating a binderfree layer of NiS on the surface of the glassy carbon electrode. This system demonstrated a linear range of 0.04 – 1 μM, 1 – 5.3 μM and a detection limit of 0.01 μM. For the final chapter, a novel sensor was created for the cryoprotective sugar trehalose, an indicator of bacterial contamination in meat and produce without any electrochemical assay precedent. This system utilized the interactions found between alkali earth metal ions and trehalose in which the two molecules form complexes. Magnesium phthalocyanine, which is a commercially available dye, as well as synthesized magnesium tetraphenylporphyrin and calcium tetraphenylporphyrin were implemented as drop-casted coatings on the working electrode to electrodeposit trehalose on the surface and detect its oxidation via squarewave anodic stripping voltammetry in the complex media Luria-Bertani broth. The system was also used to gauge fluctuations in E. coli in broth by autoclaving the cultures and directly testing the media containing lysed bacteria. The system demonstrated a linear range of 0.25 mM – 100 mM, with magnesium mesotetraphenylporphyrin exhibiting the highest repeatability
Design, development and characterization of nanostructured electrochemical sensors
This is a publication-based thesis which focuses on the study of electrochemical microbiosensors for glucose detection. It investigates applications of a series of microfabricated gold electrodes based on several nanostructures in electrochemical biosensing technologies, embracing three major methodologies: direct electro-catalytic detection, enzymatic detection and dual-enzyme cascade detection. The study is described over five main chapters with a sixth providing a summary of the material presented and perspectives for the future. Chapter 1 provides an introduction to the field of the electrochemical biosensors with a specific focus on the chosen nanostructures and miniaturized systems, as well as a brief history of the biosensor. Chapter 2 presents results published in ACS Applied Nanomaterials, 2019, 2, 9, 5878-5889. It demonstrates the enzyme free detection of glucose via a direct electro-catalytic reaction. The miniaturized band array electrodes with specific width, length and inter-electrode-distance were integrated with homogeneously distributed copper foam nano dendrites. Such foam deposits presented for the first time at the micro scale were achieved using the in-situ hydrogen bubble template method. The resulting very high electroactive surface area of the porous foam deposits was one of the major advantages in terms of achieving superior performance from each micro band foam electrode towards glucose detection. Moreover, both sensors also showed a strong resistance to the poisoning effects of chloride ions and displayed excellent stability over a period of three months.Chapter 3 presents the first of t wo sets of results for the enzymatic detection of glucose, results published in Elsevier Electrochimica Acta, 2019, 293, 307-317. Chapter 4 then presents the second set of results on this topic which is published in and Elsevier Electrochimica Acta, 2019, 298, 97-105. The aim of these two chapters is to discuss the effect of miniaturization on the enzymatic biosensor performance which was studied in the presence of a carbon quantum dot (CQD) and gold nanoparticle nanohybrid system. CQDs, are a new class of carbon-based materials and have been used here for the first time as a matrix component integrated onto microfabricated gold electrode surfaces for enzyme immobilization and further miniaturization. The biosensors developed were studied by electrochemistry to investigate the analytical performance of each device. By scaling down the surface area of the biosensor, a 13-times increase in sensitivity was achieved towards glucose. Moreover both sensors-planar, micro disk array- exhibited excellent reproducibility, reusability and operational stability in terms of the performance of biosensors. Chapter 5 presents results published in RSC Analyst, 2020 (DOI: 10.1039/C9AN01664C). It demonstrates the operation of a dual-enzyme cascade which was constructed onto a micro band array electrode based on glucose oxidase and horseradish peroxidase enzymes. To achieve a very high surface area, a porous gold-foam was electrodeposited onto surface and then a second electrodeposition layer of chitosan and multi walled carbon nanotube nano-bio-composite. The micro band cascade scheme developed exhibited the highest sensitivity towards glucose detection in comparison to other systems reported in the literature.
Chapter 6 provides an insight into the field of electrochemical biosensing with the support of the achievements presented in this thesis. Thus, by taking advantage of the available system, this chapter discusses the possible future applications of the electrochemical biosensors. The thesis then ends with section 7 which presents some Appendices
Recent Advances in Hybrid Biomimetic Polymer-Based Films: from Assembly to Applications
Biological membranes, in addition to being a cell boundary, can host a variety of proteins that are involved in different biological functions, including selective nutrient transport, signal transduction, inter- and intra-cellular communication, and cell-cell recognition. Due to their extreme complexity, there has been an increasing interest in developing model membrane systems of controlled properties based on combinations of polymers and different biomacromolecules, i.e., polymer-based hybrid films. In this review, we have highlighted recent advances in the development and applications of hybrid biomimetic planar systems based on different polymeric species. We have focused in particular on hybrid films based on (i) polyelectrolytes, (ii) polymer brushes, as well as (iii) tethers and cushions formed from synthetic polymers, and (iv) block copolymers and their combinations with biomacromolecules, such as lipids, proteins, enzymes, biopolymers, and chosen nanoparticles. In this respect, multiple approaches to the synthesis, characterization, and processing of such hybrid films have been presented. The review has further exemplified their bioengineering, biomedical, and environmental applications, in dependence on the composition and properties of the respective hybrids. We believed that this comprehensive review would be of interest to both the specialists in the field of biomimicry as well as persons entering the field
Metallic Nanopores for Single Molecule Biosensing
This thesis describes a novel approach to the fabrication and characterisation of metallic
nanopores and their application for the detection of single DNA molecules. Metallic
nanopores with apparent diameters below 20 nm are produced using electrochemical deposition
and real-time ionic current feedback. Beginning with large nanopores (diameter
100-200 nm) milled into gold silicon nitride membranes using a focused ion beam, platinum
metal is electrodeposited onto the gold surface, thus reducing the effective pore diameter.
By simultaneously observing the ion current feedback, the shrinking of the nanopore
can be monitored and terminated at any pre-defined value of the pore conductance in a
precisely controlled and reproducible way.
The ion transport properties of the metallic nanopore system are investigated by characterising
the pore conductance at varying potentials across the nanopore and concentrations
of electrolyte. The results are compared to conventional bare silicon nitride nanopore
systems. Chemical modification at the nanopore surface is also studied using thiolisation
to reduce the capacitive charging effects observed with metallic nanopores. Further to
this, impedance measurements are carried out to study the resistive behaviour exhibited
in these systems. An equivalent circuit model is proposed to validate the results obtained
from the experimental studies.
To evaluate the suitability of these nanopores for applications in single-molecule biosensing,
translocation experiments using λ-DNA are performed. DNA molecules are electrokinetically
driven through the nanopore under an applied electric field, hence as the DNA
translocates through the pore, current blockade events are detected. Each event is the
result of a single molecular interaction of DNA with the nanopore and is characterised
by its dwell time and amplitude. Characterisation studies and noise analysis towards
the applicability of metallic nanopores as single molecule detectors are also studied and
compared to current bare silicon nitride pore systems
Application of Organic-Inorganic Hybrids in Chemical Analysis, Bio- and Environmental Monitoring
Organic-inorganic hybrids (OIH) are considered to be a powerful platform for applications in many research and industrial fields. This review highlights the application of OIH for chemical analysis, biosensors, and environmental monitoring. A methodology toward metrological traceability measurement and standardization of OIH and demonstration of the role of mathematical modeling in biosensor design are also presented. The importance of the development of novel types of OIH for biosensing applications is highlighted. Finally, current trends in nanometrology and nanobiosensors are presented
Application of Biopolymer Doped Polypyrroles in Biomedical Implants and Electrical Stimulation Devices
Organic conductive polymers are emerging new materials for biomedical engineering. They offer surface properties which are attractive for many biomedical applications, such as surface coatings on metallic or biodegradable polymeric implants, tissue engineering scaffolds, implantable electronic tissue stimulation devices and microelectromechanical systems for the manipulation of single living cells in vitro, for example. Owing to the proven compatibility with tissues and cells, conductive polypyrrole (PPy) has been intensively investigated for bone and neural stimulation applications. A salient feature of PPy is its easy modification with bioactive molecules and macromolecules, such as the extracellular matrix (ECM) components of animal tissues. This work assessed the ECM components hyaluronic acid (HA) and chondrointin sulfate (CS) as dopants, which we incorporated into the PPy during the syntheses by electrochemical and oxidative chemical polymerization.Biopolymer doped PPys have been earlier reported to be good substrates for cell cultures. Furthermore, preceding implantation studies have shown promising results. However, considering clinical application and registration of PPy as a biomaterial in commercial cell culturing or tissue engineering products, there are still many practical aspects requiring more attention, such as the establishment of feasible synthetic routes, sterilizability, preservation of the electronic properties during storage and during the incubation in physiological conditions, possible biodegradation mechanisms, stability and biological elimination of the degradation products in vivo, for example. Mass spectroscopy of the hydrolysis products of polylactide (PLA) fibers coated with layer of PPy, suggested that the PPy was biostable in water at neutral pH. Electrical conductivity measurements and Raman spectroscopy showed that the PPy chain was prone to de-doping, and hence the lost its conductivity under biological conditions, but these effects were partly reversible by acid doping and positively biased electrochemical potential. The electrochemical redox activity and electromechanical actuation property of the biopolymer doped PPys was thoroughly studied. It was shown that the biopolymer doped PPy had significant and reversible redox activity, which could be potentially utilized in microelectromechanical stimulation of cells and implantable microscopic actuators.Practical and reproducible polymerization protocols were developed during this work. We took novel approaches and suggested a relatively simple “one-pot” chemical polymerization scheme, avoiding the complications of biological functionalization using potentially toxic click-chemistry. The developed methods were successfully applied in the deposition of electrically conductive, biopolymer doped PPy coatings on polylactide (PLA) nonwoven tissue engineering scaffolds and commercial poly(lactide-co-glycolide)-β-tricalcium phosphate (PLGA-β-TCP) bone fixation screws.The physical properties and cell response of HA and CS doped PPys (PPyHA and PPyCS) electrode coatings were investigated by atomic force microscopy (AFM) and electrochemical methods. Drastically different behaviour of adipose stem cells (hASC) was found on the different electrode coatings, highlighting the sensitity of the hASCs on the nanoscopic and microscopic surface properties of the PPy substrate, such as surface roughness, elasticity and surface potential distribution, factors which could be engineered during the synthesis and affected by external stimuli during incubation in cell culture medium.In conclusion, the resuls of this thesis supported the use of PPy coatings in bone tissue engineering. The electropolymerized films and also the chemically polymerized PPyHA and PPyCS coatings on bioabsorbable polymer were highly compatible with hASCs, supported cell adhesion and could be utilized in delivering direct electrical stimulation in vitro. There is also future potential in designing permanently implantable scaffolds and microstimulation devices, but still further insight into the biodegradation mechanism and biological elimination of PPy in vivo is needed
NATURE-INSPIRED MATERIAL STRATEGIES TOWARDS FUNCTIONAL DEVICES
Naturally sourced, renewable biomaterials possess outstanding advantages for a multitude of biomedical applications owing to their biodegradability, biocompatibility, and excellent mechanical properties. Of interest in this dissertation are silk (protein) and chitin (polysaccharide) biopolymers for the fabrication of functional biodevices. One of the major challenges restricting these materials beyond their traditional usage as passive substrate materials is the ability to combine them with high-resolution fabrication techniques. Initial research work is directed towards the fabrication of micropatterned, flexible 2D substrates of silk fibroin and chitin using bench-top photolithographic techniques. Research is focused on imparting electrochemical properties to silk proteins using conducting polymers (PEDOT: PSS and PANI) and a naturally occurring semiconductor, eumelanin. The utility of conducting biomimetic composites in device applications was demonstrated by the fabrication of fully organic silk based flexible electrochemical biosensors. The biosensors display excellent detection of dopamine and ascorbic acid with high sensitivity. A flexible silk-PEDOT: PSS based temperature sensor is also demonstrated for the accurate monitoring of skin surface temperature. Finally, the challenge of conformability at the biological interface is addressed using structure-based design strategies. Inspiration from the Japanese art of paper cutting was taken for the formation of patterned cuts on silk fibroin films using photolithography. Micropatterned cuts can increase the conformability of films to soft biological interfaces by enhancing their strain tolerance. By doping with polyaniline (PANI), flexible, intrinsically conductive silk kirigami sheets could be fabricated. Such systems have potential in personalized healthcare monitoring devices, improving efficient disease detection and diagnosis
3D printed neuromorphic sensing systems
Thanks to the high energy efficiency, neuromorphic devices are spotlighted recently by mimicking the calculation principle of the human brain through the parallel computation and the memory function. Various bio-inspired \u27in-memory computing\u27 (IMC) devices were developed during the past decades, such as synaptic transistors for artificial synapses. By integrating with specific sensors, neuromorphic sensing systems are achievable with the bio-inspired signal perception function. A signal perception process is possible by a combination of stimuli sensing, signal conversion/transmission, and signal processing. However, most neuromorphic sensing systems were demonstrated without signal conversion/transmission functions. Therefore, those cannot fully mimic the function provides by the sensory neuron in the biological system. This thesis aims to design a neuromorphic sensing system with a complete function as biological sensory neurons. To reach such a target, 3D printed sensors, electrical oscillators, and synaptic transistors were developed as functions of artificial receptors, artificial neurons, and artificial synapses, respectively. Moreover, since the 3D printing technology has demonstrated a facile process due to fast prototyping, the proposed 3D neuromorphic sensing system was designed as a 3D integrated structure and fabricated by 3D printing technologies. A novel multi-axis robot 3D printing system was also utilized to increase the fabrication efficiency with the capability of printing on vertical and tilted surfaces seamlessly. Furthermore, the developed 3D neuromorphic system was easily adapted to the application of tactile sensing. A portable neuromorphic system was integrated with a tactile sensing system for the intelligent tactile sensing application of the humanoid robot. Finally, the bio-inspired reflex arc for the unconscious response was also demonstrated by training the neuromorphic tactile sensing system
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