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

A nanoporous interferometric micro-sensor for biomedical detection of volatile sulphur compounds

This work presents the use of nanoporous anodic aluminium oxide [AAO] for reflective interferometric sensing of volatile sulphur compounds and hydrogen sulphide [H2S] gas. Detection is based on changes of the interference signal from AAO porous layer as a result of specific adsorption of gas molecules with sulphur functional groups on a gold-coated surface. A nanoporous AAO sensing platform with optimised pore diameters (30 nm) and length (4 µm) was fabricated using a two-step anodization process in 0.3 M oxalic, followed by coating with a thin gold film (8 nm). The AAO is assembled in a specially designed microfluidic chip supported with a miniature fibre optic system that is able to measure changes of reflective interference signal (Fabry-Perrot fringes). When the sensor is exposed to a small concentration of H2S gas, the interference signal showed a concentration-dependent wavelength shifting of the Fabry-Perot interference fringe spectrum, as a result of the adsorption of H2S molecules on the Au surface and changes in the refractive index of the AAO. A practical biomedical application of reflectometric interference spectroscopy [RIfS] Au-AAO sensor for malodour measurement was successfully shown. The RIfS method based on a nanoporous AAO platform is simple, easy to miniaturise, inexpensive and has great potential for development of gas sensing devices for a range of medical and environmental applications

Iron oxide nanowires from bacteria biofilm as an edfficient visible-light magnetic photocatalyst

Published: July 15, 2016Naturally produced iron oxide nanowires by Mariprofundus ferrooxydans bacteria as biofilm are evaluated for their structural, chemical, and photocatalytic performance under visible-light irradiation. The crystal phase structure of this unique natural material presents a 1-dimensional (1D) nanowire-like geometry, which is transformed from amorphous to crystalline (hematite) by thermal annealing at high temperature without changing their morphology. This study systematically assesses the effect of different annealing temperatures on the photocatalytic activity of iron oxide nanowires produced by Mariprofundus ferrooxydans bacteria. The nanowires processed at 800 °C were the most optimal for photocatalytic applications degrading a model dye (rhodamine B) in less than an hour. These nanowires displayed excellent reusability with no significant loss of activity even after 6 cycles. Kinetic studies by using hydrogen peroxide (radical generator) and isopropyl alcohol (radical scavenger) suggest that OH• is the dominant photooxidant. These nanowires are naturally produced, inexpensive, highly active, stable, and magnetic and have the potential to be used for broad applications including environmental remediation, water disinfection, and industrial catalysis.Luoshan Wang, Tushar Kumeria, Abel Santos, Peter Forward, Martin F. Lambert, and Dusan Losi

Editorial: Engineered Nanoporous Materials for Chemical Sensors and Biosensors

Abstract not availableAbel Santos, Lluis F. Marsal and Tushar Kumeri

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

Advanced biopolymer-coated drug-releasing titania nanotubes (TNTs) implants with simultaneously enhanced osteoblast adhesion and antibacterial properties

Abstract not availableTushar Kumeria, Htwe Mon, Moom Sinn Aw, Karan Gulati, Abel Santos, Hans J. Griesser, Dusan Losi

Porous silicon for drug delivery applications and theranostics: recent advances, critical review and perspectives

Introduction: Porous silicon (pSi) engineered by electrochemical etching has been used as a drug delivery vehicle to address the intrinsic limitations of traditional therapeutics. Biodegradability, biocompatibility, and optoelectronic properties make pSi a unique candidate for developing biomaterials for theranostics and photodynamic therapies. This review presents an updated overview about the recent therapeutic systems based on pSi, with a critical analysis on the problems and opportunities that this technology faces as well as highlighting pSi's growing potential. Areas covered: Recent progress in pSi-based research includes drug delivery systems, including biocompatibility studies, drug delivery, theranostics, and clinical trials with the most relevant examples of pSi-based systems presented here. A critical analysis about the technical advantages and disadvantages of these systems is provided along with an assessment on the challenges that this technology faces, including clinical trials and investors' support. Expert opinion: pSi is an outstanding material that could improve existing drug delivery and photodynamic therapies in different areas, paving the way for developing advanced theranostic nanomedicines and incorporating payloads of therapeutics with imaging capabilities. However, more extensive in-vivo studies are needed to assess the feasibility and reliability of this technology for clinical practice. The technical and commercial challenges that this technology face are still uncertain.Tushar Kumeria, Steven J. P. McInnes, Shaheer Maher and Abel Santo

A Mycoplasma Genomic DNA Probe using Gated Nanoporous Anodic Alumina

[EN] A nanoporous anodic alumina (NAA)-based sensor system for the detection of Mycoplasma was developed through the implementation of "molecular gates" selective to the presence of this bacterium. The capped support showed a negligible cargo release, while presence of Mycoplasma genomic DNA resulted in the release of rhodamine B fluorescent dye. This sensor system presents a limit of detection of 20 genomic DNA copies mu L-1 and was applied to the detection of Mycoplasma bacteria in competitive environments, such as culture cell media.We thank the Spanish Government (projects MAT2015-64139-C41-R, AGL2015-70235-C2-2-R, and TEC2015-71324-R (MINECO/FEDER, UE)), the Generalitat Valenciana (project PROMETEOII/2014/047), the Catalan authority (project AGAUR 2014SGR1344), and ICREA under the 2014 ICREA Academia Award for support. L.P. thanks to PROMETEOII/2014/047 for his contract. We thank the Electron Microscopy Service at the UPV for support.Pla, L.; Xifre Perez, E.; Ribes, À.; Aznar, E.; Marcos Martínez, MD.; Marsal, L.; Martínez-Máñez, R.... (2017). A Mycoplasma Genomic DNA Probe using Gated Nanoporous Anodic Alumina. ChemPlusChem. 82(3):337-341. https://doi.org/10.1002/cplu.201600651S33734182

One-pot synthesis of pH-responsive Eudragit-mesoporous silica nanocomposites enable colonic delivery of glucocorticoids for the treatment of inflammatory bowel disease

Oral glucocorticoids are backbones for the acute management of inflammatory bowel disease (IBD). However, the clinical effectiveness of conventional oral dosage forms of glucocorticoids is hindered by their low delivery efficiency and systemic side effects. To overcome this problem, a smart drug delivery system with high loading capacity and colonic release by coating functionalized mesoporous silica nanoparticles (MSNs) with a pH‐responsive polymer Eudragit S100 is proposed. In vitro dissolution tests show that Eudragit‐coated MSNs can limit the burst release of loaded prednisolone and budesonide in the gastric environment with more than 60% of the drugs released only at colonic pH (i.e., pH ≥ 7). In vivo therapeutic efficacy of budesonide‐loaded nanoparticles is tested in a murine model of dextran sodium sulfate‐induced colitis. An oral budesonide dose of 0.2 mg kg−1 nanoparticles with Eudragit coating improves the disease activity index compared to other groups. Interestingly, both coated and uncoated nanoparticles show pathological improvements demonstrated by similar levels of histological colitis score. However, coated nanoparticles significantly decrease mRNA expression of the cytokines (Il‐1β, Il‐17, and Il‐10) particularly in proximal colon, indicating colonic delivery. Overall, this study demonstrates the effectiveness of a simple method to fabricate targeted nanomedicine for the treatment of IBD.Peer reviewe

Rationally designed dendritic silica nanoparticles for oral delivery of exenatide

Type 2 diabetes makes up approximately 85% of all diabetic cases and it is linked to approximately one-third of all hospitalisations. Newer therapies with long-acting biologics such as glucagon-like peptide-1 (GLP-1) analogues have been promising in managing the disease, but they cannot reverse the pathology of the disease. Additionally, their parenteral administration is often associated with high healthcare costs, risk of infections, and poor patient adherence associated with phobia of needles. Oral delivery of these compounds would significantly improve patient compliance; however, poor enzymatic stability and low permeability across the gastrointestinal tract makes this task challenging. In the present work, large pore dendritic silica nanoparticles (DSNPs) with a pore size of ~10 nm were prepared, functionalized, and optimized in order to achieve high peptide loading and improve intestinal permeation of exenatide, a GLP-1 analogue. Compared to the loading capacity of the most popular, Mobil Composition of Matter No. 41 (MCM-41) with small pores, DSNPs showed significantly high loading owing to their large and dendritic pore structure. Among the tested DSNPs, pristine and phosphonate-modified DSNPs (PDSNPs) displayed remarkable loading of 40 and 35% w/w, respectively. Furthermore, particles successfully coated with positively charged chitosan reduced the burst release of exenatide at both pH 1.2 and 6.8. Compared with free exenatide, both chitosan-coated and uncoated PDSNPs enhanced exenatide transport through the Caco-2 monolayer by 1.7 fold. Interestingly, when a triple co-culture model of intestinal permeation was used, chitosan-coated PDSNPs performed better compared to both PDSNPs and free exenatide, which corroborated our hypothesis behind using chitosan to interact with mucus and improve permeation. These results indicate the emerging role of large pore silica nanoparticles as promising platforms for oral delivery of biologics such as exenatide.We thank the National Health and Medical Research Council’s Project Grant GNT1107836 and Early Career Fellowship and Career Development Fellowship to A.P. We also thank NHMRC for EC Fellowship to T.K. We would also like to thank the Centre of Microscopy and Microanalysis at The University of Queensland for providing facilities to conduct TEM. This article was, in part, a result of the project NORTE-01-0145-FEDER-000012, supported by the Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). This work was financed by FEDER—Fundo Europeu de Desenvolvimento Regional funds—through the COMPETE 2020–Operational Programme for Competitiveness and Internationalization (POCI), Portugal 2020, and by Portuguese funds through FCT—Fundação para a Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior in the framework of the project “Institute for Research and Innovation in Health Sciences” (POCI-01-0145-FEDER-007274)