Development of Nanopore Based Label-Free Optical Sensors

Optical sensors play an important role and are employed for more application in today’s lives than ever before. As an example, optical sensing systems have established strong footprints in quality assurance (i.e. ensuring safe levels of controlled substances in drinks and food products) and self-diagnostics (e.g. detection and quantification of glucose in blood or pregnancy assessment test). Conventional optical sensor read-out is based on colour change or signal variation (i.e. absorbance or fluorescence intensity) of the label/tag molecule (i.e. dyes) conjugated to the capture probes. However, requirement of expensive and sophisticated labels/tags and instruments, skilled personnel, and other inherent issues with the dye labels (i.e. short lift-time, concentration dependent quenching etc.) limit their broader application. Therefore, label-free sensors present a great advantage over their label based counterparts. Label-free optical sensors rely on changes in physical properties (e.g. refractive index: n) of the sensing substrate occurring during a binding event. Nanoporous substrates (i.e. porous silicon, nanoporous anodic alumina, and titania nanotubes arrays) prepared by simple and scalable electrochemical anodization process in combination with spectroscopy techniques that can be realized with miniature spectrometer (e.g. reflectometric interference spectroscopy, localized surface plasmon resonance spectroscopy etc.) can potentially overcome the limitations of label-based sensing systems. However, comprehensive and extensive fundamental research must be carried out in this field to make this technology feasible, efficient, reliable, sensitive, selective and inexpensive. In this scenario, this thesis puts forward a novel combination of nanoporous anodic alumina (NAA) and reflectometric interference spectroscopy (RIfS) for developing a highly sensitive detection system for environmental and biomedical sensing application. High surface area, modifiable surface chemistry, and optical activity make NAA a perfect substrate for highly sensitive label-free detection using RIfS platform. Moreover, the geometric features of NAA can be controlled during the fabrication process to generate more complex optical photonic structures. The simplicity and versatility of this combination (i.e. NAA and RIfS) also allows for real-time monitoring of the release of drug for the NAA pores. The most relevant features of this thesis are: 1. NAA Substrate and its Surface Chemistry: Optimization and fabrication of NAA substrate with straight pores using two step electrochemical anodization process. Optimization and modification of NAA surface chemistry with different silanes (e.g. amine terminated or thiol terminated) to impart it selectivity and specificity towards analyte molecules. 2. NAA Photonic Structures: Designing, fabrication, and optimization of NAA pore geometry (i.e. effective medium) to obtain photonic structures (i.e. Rugate filters) that display highly sensitive and selective detection capabilities in combination with RIfS. Comparison of sensing capabilities of NAA straight pores with NAA photonic structures. 3. Flow Cells for Sensing: Designing and fabrication of different types of flow cells including bulk and micro-fluidic flow cell that can accommodate NAA substrates. 4. Sensing of Heavy Metal Ions: Modification of NAA substrate with silane which specifically bind to heavy metal ions such as gold (III) and mercury (II) ions in model solvent (i.e. mili-Q water) and real-life samples (i.e. tap water and water from river Torrens in Adelaide, South Australia). 5. RIfS vs Photoluminescence using NAA Substrate: Sensing properties of NAA studied using RIfS and photoluminescence as the detection techniques, when analytes were introduced into NAA pores under non-specific and specific binding conditions. 6. Real-time Drug Release Monitoring from NAA Pores: NAA pores can act as nanocontainers which can hold substantial amounts of drug molecules that can be released over an extended period of time. NAA loaded with model drug acts as a way of measuring the drug release from its pores in real-time and under dynamic flow conditions using RIfS. The results presented in this thesis are expected to open doors for the development of more innovative and complex NAA photonic structures and surface chemistries aimed to produce highly sensitive and selective miniature, portable, and point-of-care analysis system for various industrial, environmental, and biomedical applications.Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 201

Microwave reflectometric systems and monitoring apparatus for diffused-sensing applications

Most sensing networks rely on punctual/local sensors; they thus lack the ability to spatially resolve the quantity to be monitored (e.g. a temperature or humidity profile) without relying on the deployment of numerous inline sensors. Currently, most quasi-distributed or distributed sensing technologies rely on the use of optical fibre systems. However, these are generally expensive, which limits their large-scale adoption. Recently, elongated sensing elements have been successfully used with time-domain reflectometry (TDR) to implement diffused monitoring solutions. The advantage of TDR is that it is a relatively low-cost technology, with adequate measurement accuracy and the potential to be customised to suit the specific needs of different application contexts in the 4.0 era. Based on these considerations, this paper addresses the design, implementation and experimental validation of a novel generation of elongated sensing element networks, which can be permanently installed in the systems that need to be monitored and used for obtaining the diffused profile of the quantity to be monitored. Three applications are considered as case studies: monitoring the irrigation process in agriculture, leak detection in underground pipes and the monitoring of building structures

Development of optical microchip sensor for biomolecule detection

Optical sensors play vital roles in many applications in today’s world. Photonic technologies used to design and engineer optical sensing platforms can provide distinctive advantages over conventional detection techniques. For instance, when compared to electronic and magnetic sensing systems, optical sensors require physically smaller equipment and have the capability for delivering more analytical information (e.g. spectroscopic signatures). In addition, demand for low-cost and portable bio-analyte detections is a growing area for applications in healthcare and environmental fields. Among other factors to achieve reliable results in terms of selectivity and sensitivity is key for the detection of bio-analytes with analytical relevance. Commonly used bio-analytical techniques (e. g. high performance liquid chromatography) have been appropriately designed based on qualitative and quantitative analysis. However, the requirement of expensive equipment, and complexity of procedures (e.g. biomolecule labelling, calibrations, etc.) restrict the board applicability and growth of these techniques in the field of biosensing. Optical sensors tackle these problems because they enable selective and sensitive detection of analytes of interest with label-free, real-time, and cost-effective processes. Among them, optical interferometry is increasingly popular due label-free detection, simple optical platforms and low-cost design. An ideal substrate with high surface area as well as biological/chemical stability against degradation can enable the development of advanced analytical tools with broad applicability. Nanoporous anodic alumina has been recently envisaged as a powerful platform to develop label-free optical sensors in combination with different optical techniques. This thesis presents a high sensitive label-free biosensor design combining nanoporous anodic alumina (NAA) photonic structures and reflectometric interference spectroscopy (RIfS) for biomedical, food and agricultural applications. NAA is a suitable optical sensing platform due to its optical properties; a high surface area; its straightforward, scalable, and cost-competitive fabrication process, and its chemical and mechanical stability towards biological environments. Our biosensor enables real-time screening of any absorption and desorption event occurring inside the NAA pores. A proper selection of bio-analytes were able to be detected using this platform which offers unique feature in terms of simplicity and accuracy. The most relevant components of this thesis are categorised as below: 1. Self-ordered NAA fabrication and detection of an enzymatic analyte as a biomarker for cancer diagnosis: Fabrication of NAA photonic films using two step electrochemical anodization and chemical functionalisation. Detection of trace levels of analyte enzyme and its quantification by selective digestion. The NAA photonic film with the enzyme acts as a promising combination for a real-time point-of-care monitoring system for early stages of disease. 2. NAA rugate filters used to establish the binding affinity between blood proteins and drugs: Design, fabrication, and optimisation of NAA anodization parameters using sinusoidal pulse anodization approach (i.e. anodization offset and anodization period) to produce rugate filter photonic crystals that provide two comparative sensing parameters. Establishment of highly sensitive and selective device capable for drug binding assessments linked to treating a wide range of medical conditions. 3. NAA bilayers and food bioactive compound detection: Design, fabrication, and optimisation of NAA anodization parameters (i.e. anodization time and number of anodization steps) to obtain NAA bilayered photonic structures that display the effective response of NAA geometry with different types of nano-pore engineering. The photonic properties of the NAA bilayer were studied at each layer of nano-structure under specific binding of human serum albumin and quercetin as target agent. 4. Single nucleotide polymorphism (SNP) detection: The design and implementation of a Ligation-Rolling Circle Amplification assay to detect a single nucleotide polymorphism associated with insecticide resistance in a pest beetle species, Tribolium castaneum. This proof-of-concept SNP detection assay has the potential to provide a method compatible with a biosensor platform such as NAA. This demonstrates the first step towards the potential development of a genotyping biosensor, and a real-world application of insect insecticide resistance monitoring. The results presented in this thesis are expected to enable innovative developments on NAA sensing technology that could result in highly sensitive and selective detection systems for a broad range of bio-analytes detections.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 201

Combined Punctual and Diffused Monitoring of Concrete Structures Based on Dielectric Measurements

This work presents a microwave reflectometry-based system for monitoring large concretestructures (during the curing process and also while the structure is in use), through the combineduse of punctual and diffused sensing elements. In particular, the adoption of punctual probes ona reference concrete specimen allows the development of an innovative and accurate calibrationprocedure, useful to obtain the value of the water content on a larger structure made of the samematerial. Additionally, a wire-like diffused sensing element can be permanently embedded inbuildings and used to monitor the structure along the entire length of the sensing element. Theadopted diffused sensing element can be used not only to detect dielectric variation during the curingprocess, but also throughout the service life of the structure. The combined use of punctual anddiffused sensing elements represents an important innovation from a procedural point of view, ableto provide detailed and quantitative information on the health status of the structure both duringand after construction

Nanoporous Anodic Alumina Photonic Crystals for Optical Chemo- and Biosensing: Fundamentals, Advances, and Perspectives

Optical sensors are a class of devices that enable the identification and/or quantification of analyte molecules across multiple fields and disciplines such as environmental protection, medical diagnosis, security, food technology, biotechnology, and animal welfare. Nanoporous photonic crystal (PC) structures provide excellent platforms to develop such systems for a plethora of applications since these engineered materials enable precise and versatile control of light–matter interactions at the nanoscale. Nanoporous PCs provide both high sensitivity to monitor in real-time molecular binding events and a nanoporous matrix for selective immobilization of molecules of interest over increased surface areas. Nanoporous anodic alumina (NAA), a nanomaterial long envisaged as a PC, is an outstanding platform material to develop optical sensing systems in combination with multiple photonic technologies. Nanoporous anodic alumina photonic crystals (NAA-PCs) provide a versatile nanoporous structure that can be engineered in a multidimensional fashion to create unique PC sensing platforms such as Fabry–Pérot interferometers, distributed Bragg reflectors, gradient-index filters, optical microcavities, and others. The effective medium of NAA-PCs undergoes changes upon interactions with analyte molecules. These changes modify the NAA-PCs’ spectral fingerprints, which can be readily quantified to develop different sensing systems. This review introduces the fundamental development of NAA-PCs, compiling the most significant advances in the use of these optical materials for chemo- and biosensing applications, with a final prospective outlook about this exciting and dynamic field

Inkjet printed LED based pH chemical sensor for gas sensing

Predictable behaviour is a critical factor when developing a sensor for potential deployment within a wireless sensor network (WSN). The work presented here details the fabrication and performance of an optical chemical sensor for gaseous acetic acid analysis, which was constructed using inkjet printed deposition of a colorimetric chemical sensor. The chemical sensor comprised a pH indicator dye (bromophenol blue), phase transfer salt tetrahexylammonium bromide and polymer ethyl cellulose dissolved in 1-butanol. A paired emitter-detector diode (PEDD) optical detector was employed to monitor responses of the colorimetric chemical sensor as it exhibits good sensitivity, low power consumption, is low cost, accurate and has excellent signal to noise ratios. The chemical sensor formulation was printed directly onto the surface the emitter LED, and the resulting chemical sensors characterised with respect to their layer thickness, response time and recovery time. The fabrication reproducibility of inkjet printed chemical sensors in comparison to drop casted chemical sensors was investigated. Colorimetric chemical sensors produced by inkjet printing, exhibited an improved reproducibility for the detection of gaseous acetic acid with a relative standard deviation of 5.5 % in comparison to 68.0 % calculated for drop casted sensors (n = 10). The stability of the chemical sensor was also investigated through both intra and inter-day studies

Dielectric Spectroscopy in Biomaterials: Agrophysics

Being dependent on temperature and frequency, dielectric properties are related to various types of food. Predicting multiple physical characteristics of agri-food products has been the main objective of non-destructive assessment possibilities executed in many studies on horticultural products and food materials. This review manipulates the basic fundamentals of dielectric properties with their concepts and principles. The different factors affecting the behavior of dielectric properties have been dissected, and applications executed on different products seeking the characterization of a diversity of chemical and physical properties are all pointed out and referenced with their conclusions. Throughout the review, a detailed description of the various adopted measurement techniques and the mostly popular equipment are presented. This compiled review serves in coming out with an updated reference for the dielectric properties of spectroscopy that are applied in the agrophysics fiel

Nanoporous anodic alumina platforms: engineered surface chemistry and structure for optical sensing applications

Electrochemical anodization of pure aluminum enables the growth of highly ordered nanoporous anodic alumina (NAA) structures. This has made NAA one of the most popular nanomaterials with applications including molecular separation, catalysis, photonics, optoelectronics, sensing, drug delivery, and template synthesis. Over the past decades, the ability to engineer the structure and surface chemistry of NAA and its optical properties has led to the establishment of distinctive photonic structures that can be explored for developing low-cost, portable, rapid-response and highly sensitive sensing devices in combination with surface plasmon resonance (SPR) and reflective interference spectroscopy (RIfS) techniques. This review article highlights the recent advances on fabrication, surface modification and structural engineering of NAA and its application and performance as a platform for SPR- and RIfS-based sensing and biosensing devices.Tushar Kumeria, Abel Santos and Dusan Losi

Microwave Reflectometry Sensing System for Low-Cost in-vivo Skin Cancer Diagnostics

Skin cancer is one of the most commonly diffused cancers in the world and its incidence rates have constantly increased in recent years. At the current state of the art, there is a lack of objective, quick and non-invasive methods for diagnosing this condition; this, combined with hospital crowding, may lead to late diagnosis. Starting from these considerations, this paper addresses the implementation of a microwave reflectometry based-system that can be used as a non-invasive method for the in-vivo diagnosis and early detection of biological abnormalities, such as skin cancer. This system relies on the dielectric contrasts existing between normal and anomalous skin tissues at microwave frequencies (in a frequency range up to 3 GHz). In particular, a truncated open-ended coaxial probe was designed, manufactured and tested to sense (in combination with a miniaturized Vector Network Analyzer) the variations of skin dielectric properties in a group of volunteer patients. The specific data processing demonstrated the suitability of the system for discriminating malignant and benign lesions from healthy skin, ensuring simultaneously effectiveness, low cost, compactness, comfortability, and high sensitivity