Construction of Heteroatom-Doped Porous Carbon Architectures for Energy and Sensing Applications

In this chapter, we have concentrated on the main electrocatalytic oxygen processes, oxygen reduction reaction (ORR) and water splitting oxygen evolution reaction (OER), and biosensors based on porous carbon architectures, which are more important areas of research because of the rise in demand for energy management, supply, and disease diagnosis. Heteroatom-doped carbon hollow spheres are very useful because they have a large surface area, mesoporosity, spherical wall thicknesses, edge plane defect sites, catalytic active sites, and fast heterogeneous electron-transfer rates. These properties are very important for making commercial devices. This chapter provides an overview of hollow carbon nanospheres that are doped with single and double heteroatoms, as well as cobalt oxide. These carbon compounds function as dual catalysts for OER and ORR, as well as an effective electrocatalyst for the oxygen reduction process in both acidic and alkaline media. Electrocatalytically, heteroatom-doped carbon sphere-modified electrodes can simultaneously and specifically identify and determine the analytes, while also validating the target species in real samples. N-doped hollow carbon spheres coated-Co3O4 functioned as an efficient dual-function oxygen electrocatalyst for oxygen evolution and oxygen reduction processes and also as a biosensor for highly effective electrochemical sensing of acetaminophen. A symmetric supercapacitor using dual heteroatom-doped and SBA-15 templated porous carbon was also discussed

NANOELECTRONIC DEVICES FOR SENSITIVE DETECTION OF BIOMARKERS IN HEALTHCARE MONITORING

In recent years, biosensors have seen an exponential rise of their applications in a number of fields including the field of health care monitoring, particularly in point-of-care diagnostics. With the contemporary rise of nanotechnology, these biosensors have experienced an ever-growing inclusion of nano scale electronic devices or nanoelectronic devices to exploit the plethora of advantages of nanoelectronics. The performances of these nanoelectronic devices, however, largely depend on the nanomaterials used. Especially, carbon-based nanomaterials such as carbon nanotubes (CNTs) and graphene have proven to be superior candidates compared to others because of their multitude of electronic and mechanical properties suitable for biosensing. In particular, graphene-based FET (GFET) that combines the favorable material properties of graphene as well as the device properties of field-effect transistor have demonstrated its potential in biosensing with high sensitivity and signal-to-noise ratio (SNR). Though GFETs have been applied for sensitive detection of a number of analytes, there are still areas for further development in a number of ways—application of the platform for sensing new biomarkers, developing an integrated microfluidics platform, etc. in order to improve the sensing performances as well as applicability in real-world setting. Therefore, in this seminar, I will discuss the current states and challenges of the GFET-based sensing and present my work to further advance this platform. Moreover, development of a flexible GFET biosensor compatible with wearable platform will also be discussed. To provide the biosensors with the required selectivity, DNA-based aptamers with specific affinity towards the target analyte are used. However, conventional techniques for functionalization of aptamers suffer from several challenges including low throughput, poor control, and long turnaround time. To address these challenges, I will present my efforts on the development of new strategies to address these challenges both on CNT and graphene-based platforms

Fundamental design principles of novel MEMS based Landau switches, sensors, and actuators : Role of electrode geometry and operation regime

Microelectromechanical systems (MEMS) are considered as potential candidates for More-Moore and More-than-Moore applications due to their versatile use as sensors, switches, and actuators. Examples include accelerometers for sensing, RF-MEMS capacitive switches in communication, suspended-gate (SG) FETs in computation, and deformable mirrors in optics. In spite of the wide range of applications of MEMS in diverse fields, one of the major challenges for MEMS is their instability. Instability divides the operation into stable and unstable regimes and poses fundamental challenges for several applications. For example: Tuning range of deformable mirrors is fundamentally limited by pull-in instability, RF-MEMS capacitive switches suffer from the problem of hard landing, and intrinsic hysteresis of SG-FETs puts a lower bound on the minimum power dissipation. ^ In this thesis, we provide solutions to the application specific problems of MEMS and utilize operation in or close to unstable regime for performance enhancement in several novel applications. Specifically, we propose the following: (i) novel device concepts with nanostructured electrodes to address the aforementioned problems of instability, (ii) a switch with hysteresis-free ideal switching characteristics based on the operation in unstable regime, and (iii) a Flexure biosensor that operates at the boundary of the stable and unstable regimes to achieve improved sensitivity and signal-to-noise ratio. In general, we have advocated electrode geometry as a design variable for MEMS, and used MEMS as an illustrative example of Landau systems to advocate operation regime as a new design variabl

Modulated Nanowire Structures for Exploring New Nanoprocessor Architectures and Approaches to Biosensing

For the last decade, semiconducting nanowires synthesized by bottom-up methods have opened up new opportunities, stimulated innovative scientific research, and led to applications in materials science, electronics, optics, and biology at the nanoscale. Notably, nanowire building blocks with precise control of size, structure, morphology, and even composition in one, two, and three dimensions can successfully demonstrate high-performance electrical characteristics of field-effect transistors (FETs) and highly sensitive, selective, label-free, real-time biosensors in the fields of nanoelectronics and nano-biosensing, respectively. This thesis has focused on the design, synthesis, assembly, fabrication and electrical characterization of nanowire heterostructures for a proof-of-concept nanoprocessor and morphology-modulated kinked nanowire molecular nanosensor.Physic

Nanoporous Gold Characterization, Structural Modification and Use as a Solid Support for Biomolecule Immobilization

Nanoporous gold (NPG) has immense technological applications owing to a plethora of properties like large surface area to volume ratio, plasmonic properties, stable gold-thiolate bond formation and a wide range of pore sizes. The surface morphology of nanoporous gold has been altered previously by dealloying and thermal annealing to increase/decrease the pore size and change the surface area. We provide a novel electrochemical annealing technique for post dealloying modification wherein electrochemical sweep cycles in different electrolytes at positive potentials leads to a subsequent increase in pore sizes of nanoporous gold as studied using scanning electron microscopy. Tailoring the surface of nanoporous gold allows us to characterize and study self-assembled monolayers of alkanethiols, including those terminated by carbohydrate moieties. The orientation of these thiols on nanoporous gold is not uniform due to the interconnected framework of pores and ligaments and we try to offer a fair comparison between flat gold and nanoporous gold to determine the surface coverage of these self-assembled monolayers. Carbohydrate-lectin interactions have been studied with the help of dendrimers as linkers. Dendrimers (polyamidoamine generation 4 and 5) have been used as linkers due to their multivalent interactions with carbohydrate moieties and impedance spectroscopy as well as atomic force microscopy techniques have been utilized to study dendrimers attached on nanoporous gold surface using covalent immobilization. This study aims at providing a comprehensive surface property analysis of nanoporous gold

Micro- and nano-devices for electrochemical sensing

Electrode miniaturization has profoundly revolutionized the field of electrochemical sensing, opening up unprecedented opportunities for probing biological events with a high spatial and temporal resolution, integrating electrochemical systems with microfluidics, and designing arrays for multiplexed sensing. Several technological issues posed by the desire for downsizing have been addressed so far, leading to micrometric and nanometric sensing systems with different degrees of maturity. However, there is still an endless margin for researchers to improve current strategies and cope with demanding sensing fields, such as lab-on-a-chip devices and multi-array sensors, brain chemistry, and cell monitoring. In this review, we present current trends in the design of micro-/nano-electrochemical sensors and cutting-edge applications reported in the last 10 years. Micro- and nanosensors are divided into four categories depending on the transduction mechanism, e.g., amperometric, impedimetric, potentiometric, and transistor-based, to best guide the reader through the different detection strategies and highlight major advancements as well as still unaddressed demands in electrochemical sensing

Applications of MXenes in human-like sensors and actuators

Human beings perceive the world through the senses of sight, hearing, smell, taste, touch, space, and balance. The first five senses are prerequisites for people to live. The sensing organs upload information to the nervous systems, including the brain, for interpreting the surrounding environment. Then, the brain sends commands to muscles reflexively to react to stimuli, including light, gas, chemicals, sound, and pressure. MXene, as an emerging two-dimensional material, has been intensively adopted in the applications of various sensors and actuators. In this review, we update the sensors to mimic five primary senses and actuators for stimulating muscles, which employ MXene-based film, membrane, and composite with other functional materials. First, a brief introduction is delivered for the structure, properties, and synthesis methods of MXenes. Then, we feed the readers the recent reports on the MXene-derived image sensors as artificial retinas, gas sensors, chemical biosensors, acoustic devices, and tactile sensors for electronic skin. Besides, the actuators of MXene-based composite are introduced. Eventually, future opportunities are given to MXene research based on the requirements of artificial intelligence and humanoid robot, which may induce prospects in accompanying healthcare and biomedical engineering applications. [Figure not available: see fulltext.

CARBON NANOMATERIALS AND THEIR ELECTROCHEMICAL APPLICATIONS

Recent years have witnessed the continuously growing interest in the area of nanotechnology. Among the innumerable novel compounds and materials, carbon nanomaterials, especially carbon nanotubes (CNTs) and graphene, are undeniably two of the most glorious shining stars due to their unique structures and promising physical, chemical, and electrical properties. Numerous research projects have been focused on the synthesis, characterization, and functionalization of carbon nanomaterials, as well as their enormous possible applications in energy generation/storage, sensors, electronics, reinforcement of composite materials, and drug delivery. Of particular interest in this dissertation are the functionalization of carbon nanomaterials − either by decorating with Pt nanoparticles (NPs) or by doping with nitrogen atoms − and their electrochemical applications for both fuel cell catalysts (and supports) and electrochemical sensors/biosensors. I have successfully synthesized and characterized hybrid structures of Pt NP-CNTs or Pt NP-graphene, and also a novel carbon nanomaterial − nitrogen doped carbon nanotube cups (NCNCs). The electrochemical properties and applications of these nanomaterials were also investigated. Pt NP decorated CNTs or graphene were studied and compared for their electrochemical sensor performance in order to obtain further understanding on the structure-property relationship between 1-dimensional and 2-dimensional nanomaterials as the sensing platform. Both Pt-CNTs and NCNCs were investigated as fuel cell catalysts with the aim of improving the performance and stability, decreasing the amount of expensive Pt, and most importantly, understanding and optimizing NCNCs as non-precious-metal catalysts to ultimately replace expensive Pt-based catalysts. Pt-CNTs demonstrated extraordinary stability with less material used compared to commercial Pt/C catalysts in long term stability testing. NCNCs also exhibited good catalytic activity towards oxygen reduction reaction (ORR) which makes them promising alternatives to Pt-based catalysts. Further look into the ORR mechanism suggested that the presence of both nitrogen and iron from catalyst of NCNCs synthesis process is crucial for the improved ORR catalytic activity. From the materials point of view, a novel simple sonication method was studied to separate stacked NCNCs into individual nanocups structures, with the long-term objective of drug delivery or nano-reactor applications. Both the separation mechanism and the structure-property relationship of the stacked and separated NCNCs were investigated

Fundamentals and scopes of doped carbon nanotubes towards energy and biosensing applications

Since their first allusion, carbon nanotubes have attracted significant research interest, especially with respect to composite manufacturing as a filler material for enhancing their mechanical and electrical properties. Several methods have been developed for modifying the electrical properties of carbon nanotubes such as CNTs wall's carbon atoms substitution with other appropriate atoms including engineering of their outer surfaces by covalent and noncovalent molecules, such as CNTs channel filling and nano-chemical reactions therein. CNTs with tailored electrical conduction open large perspectives for their applicabilities in advanced technologies. Taking into consideration the innovative advantages of pure and hybrid CNTs, in this article we have comprehensively reviewed the latest state-of-art research developments in the direction of different synthesis strategies, structure-property relationships, and advanced applications towards energy storage, supercapacitors, electrodes, catalytic supports, as well as biosensing