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In the present study, a modified solvothermal reaction of (hematite) with titanium(IV) butoxide and gold(III) chloride produced ternary Au@TiO2/α-Fe2O3 nanocomposite. The designed Au@TiO2/α-Fe2O3 photocatalyst exhibits nanoring-like structure with high crystallinity indicating the possibility of manufacturing extreme structures and offering a new nanostructure that was not previously studied. Both TiO2 and Au nanoparticles (NPs) were found to be dispersed uniformly on the α-Fe2O3 surface. X-ray diffraction powder technique combined with X-ray photoelectron (XPS) and Raman spectroscopy confirm the formation of the three materials with cubic Au, anatase TiO2 and hematite α-Fe2O3 structures, respectively. The photocatalytic activity proves the performance of this ternary heterojunction to decomposes different pollutants. It was found that, TiO2 absorbs UV-light, α-Fe2O3 absorbs both UV and Visible light and plasmonic gold NPs work as an electron mediator and therefore exhalt the photocatalytic efficiency of the ternary Au@TiO2/α-Fe2O3 photocatalyst. The present work delivers a novel perception to develop a stable photocatalyst based metal oxide/noble-metal hetero-nanostructure for the degradation of different types of pollutants in the industrial zones.

A newly synthesized zinc(II) complex, namely tert-butyl N-(2 mercaptoethyl)carbamatozinc(II) complex [Zn(Boc-S)(2)] (Boc = tert-butyl N-[2-mercaptoethyl]carbamate), has been used as an organozinc precursor for the production of crystalline ZnO and ZnO/TiO2 nanoparticles. The synthesized complex and the obtained nanomaterials were fully characterized using various spectroscopic and surface analysis techniques. Their surface morphology, chemical purity and stoichiometry have been investigated by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) as well as X-ray fluorescence. The synthesized Zn(II) molecular complex, ZnO and ZnO/TiO2 nanomaterials have been tested in alkaline aqueous solution (1.0 MNaOH) for the hydrogen evolution reaction (HER) using various electrochemical techniques. The results revealed high HER catalytic performance of ZnO and ZnO/TiO2 cathode materials, with the latter exhibiting higher catalytic activity recording an exchange current density (j(o)) of 0.3 mA cm(-2). This current value, which approaches that of Pt wire (0.5 mA cm(-2)), cross-sectional area similar to 0.008 cm(2), is about 11 and 100 times greater than those measured for ZnO alone (0.028 mA cm(-2)) and TiO2 alone (0.0032 mA cm(-2)), respectively. Moderate catalytic activity was recorded for the complex catalyst, namely GC-Zn(Boc-S)(2) with j(o) value of (0.01 mA cm(-2)). Tafel slope values of 130 and 122 mV dec(-1) were calculated for ZnO and ZnO/TiO2, respectively. Such Tafel slope values, which are close to that of the Pt wire (120 mV dec(-1)), referred to a Volmer-controlled HER kinetics. Other important electrochemical parameters describing the kinetics of the HER, such as roughness factor (R-f) and turnover frequency (TOF) were also estimated and discussed. The high numerical values of the various HER kinetic parameters recorded for the ZnO/TiO2 catalyst, in addition to its high stability and durability (stable for up to 10 000 continuous cathodic polarization cycles), besides maintaining its morphology and chemical composition after stability test (confirmed from SEM/EDX and XRD examinations), located it in a privileged position among the most efficient HER electrocatalysts reported in the literature.

In this work, PdO/TiO and EuO/TiO nanocomposites (NCs) were synthesized using a new facile, template-free, and one-step solvothermal approach and characterized by several instrumentation techniques. X-ray photoelectron spectroscopy studies revealed the presence of oxidized form of the Pd and Eu nanoparticles within the NC materials (PdO and EuO). The two catalysts exhibited remarkable activity for the hydrogen evaluation reaction (HER) in a strong alkaline solution (4.0 M NaOH) with PdO/TiO catalyst being the best, which recorded an exchange current density (j) of 0.26 mA cm and a Tafel slope (β) of 125 mV dec. Such parameters are not far from those recorded for a commercial Pt/C catalyst (0.71 mA cm and 120 mV dec) performed here under the same operating conditions. EuO/TiO catalyst recorded j and β values of 0.05 mA cm and 135 mV dec. The Tafel slopes 125 and 135 mV dec calculated on the PdO/TiO and EuO/TiO catalysts suggest a HER kinetics controlled by the Volmer step. PdO/TiO catalyzed the HER with a high turnover frequency of 2.3 H/s at 0.2 V versus the reversible hydrogen electrode, while EuO/TiO catalyst only measured a turnover frequency value of 1.25 H/s at the same overpotential. The two catalysts exhibited excellent stability and durability after 10 000 cycles and 72 hours of controlled potential electrolysis at a high cathodic overpotential, reflecting their practical applicability. Scanning electron microscope and X-ray photoelectron spectroscopy examinations revealed that the morphology and chemistry of both catalysts were not altered as a result of the performed long-term stability and durability tests.

This work presents a modified solvothermal process for a facile synthesis of high thermally stable nanocrystalline anatase TiO2 NPs doped with Cu2O NPs. A Z-scheme mechanism was used to account for the enhanced photocatalytic activity exhibited by these materials. Also, the nanocomposite was impregnated in cotton fabric to obtain a modified fiber with high thermal stability, self-cleaning, enhanced UV protection, and antibacterial activity. The as-prepared nanomaterials and the coated fabric were characterized by various physicochemical techniques such as XRD, EDXRF, TGA, TEM, HRTEM, and SEM. The Cu2O/TiO2 molar ratio in the nanocomposite was found to possess a pronounced impact on the crystalline structure, size and morphology of TiO2 NPs. The XRD revealed proper substitutions of the few Ti4+ sites by Cu2+ ions in TiO2 host lattice. Optical measurements showed that the plasmonic peak of the Cu2O/TiO2 nanocomposite was affected by the copper-doping concentration, enhancing self-cleaning of Cu2O/TiO2 under direct sunlight. The TiO2/fiber self-cleaning efficiency (12 h for MB removal) was increased by the in situ growing of Cu2O (5.5 h). Antibacterial activity studies revealed high potential activity of Cu2O/TiO2 against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Kleissella pneumonia, Saccharomyces sp.) bacteria. The promising photocatalytic and biocidal activity of our synthesized Cu2O/TiO2 nanocomposites was ascribed to the reactive oxygen species generated by the Z-scheme mechanism under direct Sunlight.

PEGylation (i.e., attachment of polyethylene-glycol) of carbon nanotubes (CNTs) is one of the most widely used strategies to improve its biocompatibility and aqueous dispersion stability, which are critical for their successful clinical application. However, PEGylation of nanomaterials has recently been associated with production of anti-PEG antibody, low cellular uptake, and degradation. Herein, we explore surface functionalization of CNTs using the bovine-milk-derived protein succinylated β-lactoglobuline (Sblg) as an alternative strategy to PEGylation. The aqueous dispersion stability, in vitro cell uptake and biocompatibility of Sblg-functionalized multiwalled CNTs (Sblg-f-MWCNTs) was compared to PEGylated MWCNTs (PEG-f-MWCNTs). The surface functionalization with Sblg was found to improve the IC50 values of CNTs by ∼5- to 6-fold in comparison with pristine CNTs in various cell lines. Both Sblg-f-MWCNTs and PEG-f-MWCNTs improved the aqueous colloidal stability of CNTs, which remained suspended for a period of one month. Our study concluded that the Sblg provides a cost-effective alternative to the PEG-based CNT functionalization with significant improvement in the biocompatibility and dispersion stability of CNTs.

We present a study on optical and surface chemistry engineering of nanoporous photonic crystals as sensing platforms for detection of ionic copper. The optical sensing system combines glutaraldehyde-crosslinked double-layered polyethyleneimine (PEI-GA-PEI)-functionalized nanoporous anodic alumina gradient-index filters (NAA-GIFs) with reflection spectroscopy for label-free, selective detection of ionic copper in water matrices. The spectral position of the photonic stopband (PSB) of PEI-GA-PEI-functionalized NAA-GIFs is tuned across the visible-NIR spectral region to assess the impact of this optical parameter on the sensing performance of the system. Spectral shifts in the characteristic PSB (ΔλPSB) of PEI-GA-PEI-functionalized NAA-GIFs upon exposure to analytical solutions of ionic copper are used as a sensing parameter. Shifts in ΔλPSB of these photonic crystals are monitored in real-time under dynamic flow conditions. Calibration of the sensing system with analytical solutions of ionic copper from 0.1 to 100 mM shows a dual sensing regime, at low (from 1 to 10 mM) and high (from 10 to 100 mM) concentrations, which is associated with conformational changes of the PEI-GA-PEI functional layer. The binding mechanism of Cu2+ in PEI-GA-PEI-modified NAA-GIFs follows a Freundlich isotherm model. The performance of the PEI-GA-PEI-NAA-GIFs for real-life applications is demonstrated using environmental water. The system shows excellent correlation in both environmental and analytical water solutions. This study provides new opportunities to engineer portable optical sensing systems with tailor-designed features to detect ionic copper for environmental applications.

We report here a facile, template-free and one-step solvothermal approach for the synthesis of high-temperature stable gold/titania nanocomposite (NCs), providing a new, simple, quick and inexpensive wet-chemical route. Our approach is based on the assembly of gold salt and titanium butoxide in dimethyl sulfoxide (DMSO). Also, we present here, for the first time, a cathodically activated Au/TiO2 catalyst with Pt/C activity for the hydrogen evolution reaction (HER) in 0.5 M H2SO4 in the dark. The as-prepared (unactivated) Au/TiO2 NCs exhibits considerable electrocatalytic activity for H2 generation in the dark, with a low onset potential (EHER) of −64 mV vs. RHE, a Tafel slope (-bc) of 60 mV dec−1 and an exchange current density (jo) of 0.12 mA cm−2. Long-term stability and durability tests in 0.5 M H2SO4, employing cyclic voltammetry technique (10,000 of repetitive cycling) and 72 h of chronoamperometry measurements at a high cathodic potential (cathodic activation), reveal that the electrocatalyst activates during such aging processes yielding an activated Au/TiO2 catalyst with Pt/C-like activity for H2 generation (EHER -3 mV, -bc: 35 mV dec−1, and jo: 0.95 mA cm−2). The outstanding HER activity of the activated catalyst is discussed.

A porous photonic crystal is integrated with a plastic medical fixture (IV connector hub) to provide a visual colorimetric sensor to indicate the presence or absence of alcohol used to sterilize the fixture. The photonic crystal is prepared in porous silicon (pSi) by electrochemical anodization of single crystal silicon, and the porosity and the stop band of the material is engineered such that the integrated device visibly changes color (green to red or blue to green) when infiltrated with alcohol. Two types of self-reporting devices are prepared and their performance compared: the first type involves heat-assisted fusion of a freestanding pSi photonic crystal to the connector end of a preformed polycarbonate hub, forming a composite where the unfilled portion of the pSi film acts as the sensor; the second involves generation of an all-polymer replica of the pSi photonic crystal by complete thermal infiltration of the pSi film and subsequent chemical dissolution of the pSi portion. Both types of sensors visibly change color when wetted with alcohol, and the color reverts to the original upon evaporation of the liquid. The sensor performance is verified using E. coli-infected samples.

A porous Si (pSi) microparticle-based delivery system is investigated, and the intrinsic luminescence from the particles is employed as a probe to monitor the release of a model protein payload, bovine serum albumin (BSA). The microparticles consist of a core Si skeleton surrounded by a SiO2 shell. Two types of pSi are tested, one with smaller (10 nm) pores and the other with larger (20 nm) pores. The larger pore material yields a higher mass loading of BSA (3 vs 20%). Two different methods are used to load BSA into these nanostructures: the first involves loading by electrostatic physisorption, and the second involves trapping of BSA in the pSi matrix by local precipitation of magnesium silicate. Protein release from the former system is characterized by a burst release, whereas in the latter system, release is controlled by dissolution of the pSi/magnesium silicate matrix. The protein release characteristics are studied under accelerated (0.1 M aqueous KOH, 21 °C) and physiologically relevant (phosphate-buffered saline, pH 7.4, 37 °C) conditions, and the near-infrared photoluminescence signal from the pSi skeleton is monitored as a function of time and correlated with protein release and silicon dissolution. The thickness of the Si core and the SiO2 shell are systematically varied, and it is found that the luminescence signature can be tuned to provide a signal that either scales with protein elution or that changes rapidly near the end of useful life of the delivery system. Although payload release and particle dissolution are not driven by the same mechanism, the correlations between luminescence and payload elution for the various formulations can be used to define design rules for this self-reporting delivery system.

In this work, we will explore the possibility of solvent-free functionalization of inner surfaces of (CNTs) with amines of different structure. This method can generate CNTs useful for many applications especially, molecules transport properties of CNT membranes and drug delivery using liberated CNTs. The structural and chemical composition of the functionalized CNTs was analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), which confirm successful and specific inner functionalization of CNTs.

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. Refereed/Peer-reviewed

Optical lenses are among the oldest technological innovations (3000 years ago) and they have enabled a multitude of applications in healthcare and in our daily lives. The primary function of optical lenses has changed little over time; they serve mainly as a light-collection (e.g. reflected, transmitted, diffracted) element, and the wavelength and/or intensity of the collected light is usually manipulated by coupling with various external optical filter elements or coatings. This generally results in losses associated with multiple interfacial reflections, and increases the complexity of design and construction. In this work we introduce a change in this paradigm, by integrating both light-shaping and image magnification into a single lens element using a moldless procedure that takes advantage of the physical and optical properties of mesoporous silicon (PSi) photonic crystal nanostructures. Casting of a liquid poly(dimethyl) siloxane (PDMS) pre-polymer solution onto a PSi film generates a droplet with contact angle that is readily controlled by the silicon nanostructure, and adhesion of the cured polymer to the PSi photonic crystal allows preparation of lightweight (10 mg) freestanding lenses (4.7 mm focal length) with an embedded optical component (e.g. optical rugate filter, resonant cavity, distributed Bragg reflector). Our fabrication process shows excellent reliability (yield 95%) and low cost and we expect our lens to have implications in a wide range of applications. As a proof-of-concept, using a single monolithic lens/filter element we demonstrate: fluorescence imaging of isolated human cancer cells with rejection of the blue excitation light, through a lens that is self-adhered to a commercial smartphone; shaping the emission spectrum of a white light emitting diode (LED) to tune the color from red through blue; and selection of a narrow wavelength band (bandwidth 5 nm) from a fluorescent molecular probe.

pH stimuli responsive drug delivery platforms that can target specific locations along the gastrointestinal tract hold great promise for colorectal cancer therapy. Herein, we present a facile approach to produce microfluidic engineered pH-sensitive magnetic microspherical carriers containing multifunctional therapeutic payloads for synergistic treatment of colorectal cancer. Chemotherapeutics, 5 fluorouracil (5FU) and curcumin (CUR), were chosen due to their synergistic effect for colorectal cancer treatment and prevention. Drugs were loaded onto naturally derived porous silicon nanoparticles (SiNPs) and magnetic bacterial iron oxide nanowires (BacNWs), which acted as drug nanocontainers and magnetic elements, respectively. Drug loaded SiNPs and BacNWs were then encapsulated into polymeric microspheres using droplet-based microfluidics. To ensure controlled drug delivery into the desired site of action (colon and rectum), the microspheres were fabricated using hypromellose acetate succinate polymers, which are insoluble in the acidic medium of the stomach (i.e. pH 1.2) but soluble at basic pH (colon and rectum). Our results confirmed that the microspheres exhibit a narrow size distribution (CV > 5%) with precise size control. Moreover, in vitro dissolution and drug release data confirmed their pH-responsive properties. Motivated by these results, we explored the biocompatibility of microspheres using human RAW 264.7 macrophages. The results revealed the safety of drug free microspheres up to 1000 μg mL-1. Finally, the synergistic action of 5FU and CUR loaded microspheres was investigated on SW480 colon adenocarcinoma cells.

Drug delivery using synthetic nanoparticles including porous silicon has been extensively used to overcome the limitations of chemotherapy. However, their synthesis has many challenges such as lack of scalability, high cost, and the use of toxic materials with concerning environmental impact. Nanoscale materials obtained from natural resources are an attractive option to address some of these disadvantages. In this paper, a new mesoporous biodegradable silicon nanoparticle (SiNP) drug carrier obtained from natural diatom silica mineral available from the mining industry is presented. Diatom silica structures are mechanically fragmented and converted into SiNPs by simple and scalable magnesiothermic reduction process. Results show that SiNPs have many desirable properties including high surface area, high drug loading capacity, strong luminescence, biodegradability, and no cytotoxicity. The in-vitro release results from SiNPs loaded with anticancer drugs (doxorubicin) demonstrate a pH-dependent and sustained drug release with enhanced cytotoxicity against cancer cells. The cells study using doxorubicin loaded SiNPs shows a significantly enhanced cytotoxicity against cancer cells compared with free drug, suggesting their considerable potential as theranostic nanocarriers for chemotherapy. Their low-cost manufacturing using abundant natural materials and outstanding chemotherapeutic performance has made them as a promising alternative to synthetic nanoparticles for drug delivery applications.

Naturally 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.

Luminescent porous silicon nanoparticles (LpSiNPs) display red-orange photoluminescence (PL) that provides large penetration depth for precise deep-tissue imaging and diagnostics. Herein, we describe in detail the fabrication process of porous silicon nanoparticles (pSiNPs), activation of photoluminescence, quantum yield measurement, and PL imaging. LpSiNPs perform as imaging probe for both the continuous wave and time-gated PL imaging.

Hierarchically structured silicon (Si) surfaces with a combination of micro/nano-structures are highly explored for their unique surface and optical properties. In this context, we propose a rapid and facile electroless method to realize hierarchical structures on an entire Si wafer of 3&Prime, diameter. The overall process takes only 65 s to complete, unlike any conventional wet chemical approach that often combines a wet anisotropic etching of (100) Si followed by a metal nanoparticle catalyst etching. Hierarchical surface texturing on Si demonstrates a broadband highly reduced reflectance with average R% ~ 2.7% within 300&ndash, 1400 nm wavelength. The as-fabricated hierarchical structured Si was also templated on a thin transparent layer of Polydimethylsiloxane (PDMS) that further demonstrated prospects for improved solar encapsulation with high optical clarity and low reflectance (90% and 2.8%).

Diatoms are unicellular photosynthetic algae enclosed in porous 3D nanopatterned silica enclosures called "frustules." The diatom frustules are made from biosilica self-assembled into intricate porous shells that feature unique properties including high specific surface area, biocompatibility, tailorable surface chemistry, thermal stability, and high mechanical and chemical resistance. The ability to cultivate diatoms in artificial environments and their abundant availability of diatom frustules as mineable fossilized mineral deposits (diatomite or diatomaceous earth; DE) make diatom silica a promising natural alternative to synthetic porous silica for a broad range of biomedical, environmental, agricultural, and energy applications. This review article provides a comprehensive and current account of the use of natural DE silica materials in biomedical applications focused mainly on drug delivery with some highlights on biosensing, tissue engineering, and clotting agents. The article also covers some basic physical and chemical aspects of DE material such as purification, surface chemical functionalization, biocompatibility, and cellular uptake that are critical for the development of an efficient drug carrier.

Nanostructuring of Silicon surface has perceived exponential growth over time due to its high demanding properties like superhydrophobicity and high anti-reflection [1]–[3]. Especially hierarchical structures (combination of micro- and nano- structures) on Silicon with significantly increased surface area has demonstrated enhanced optical and surface wettability properties, making it highly suitable for applications like self-cleaning, solar cell, photoluminescence, contamination prevention, etc [3]–[5]. Various techniques like vapour-liquid-solid (VLS), reactive ion etching (RIE), electrochemical etching and wet anisotropic electroless etching have been optimised for micro- and nanostructuring over Silicon surface [5]–[9]. Methods like VLS and RIE are expensive and complicated. Wet electrochemical and electroless etching processes are simpler but electrochemical etching gives a very non-uniform porous structure and electroless etching only gives rise to microstructure and is also dependent on the orientation of Silicon surface. Nanostructuring of Silicon wafers using metal assisted etching has also been reported which is a rapid process [4], [10]. However, this process only results in the formation of nanostructured Silicon. There are reports where wet chemical etching and metal assisted etching process have been combined to realize hierarchical structures on Silicon but it does require longer time and large area uniformity in the formation of hierarchical structures is unpredictable [3], [11]. In this work, for the first time we propose an extremely fast and facile electroless method of fabricating hierarchical structures on Silicon wafer covering a large area. Added major benefits to this proposed method is that complete wafer can be textured within 3 to 8 minutes time span and is not dependent on the orientation or doping concentration of Silicon. The unpolished side of a commercial Silicon wafer having grooved cup shaped microstructures on it was used as the base to deposit silver (Ag) nanoparticles electrolessly. After the Ag nanoparticle deposition for varied time between 30 s to 2 min, the Silicon wafer was etched for different time duration (1 min to 7 min) in dilute mixture of Hydrofluoric acid (HF) and Hydrogen peroxide (H2O2). Eventually the Ag nanoparticles were etched away in dilute Nitric acid leaving behind the hierarchical structures of Silicon unaffected. Pyramidal shaped microstructured Si surface was also used for deposition of Ag nanoparticles followed by a similar processing as mentioned above. Diffused optical reflectance measurement on the hierarchical structured Silicon showed significant reduction by 46% in comparison to plane polished Silicon. Moreover insignificant variation in reflectance was observed over a broad wavelength range of 300 nm to 1400 nm. It is concluded that such facile large area processing of hierarchical anti-reflecting structures on Si can be extremely beneficial for optical applications using Silicon. References: [1] Y. Cao et al., “Fabrication of silicon wafer with ultra low reflectance by chemical etching method,” Appl. Surf. Sci., vol. 257, no. 17, pp. 7411–7414, 2011. [2] Y. Xiu, L. Zhu, D. W. Hess, and C. P. Wong, “Hierarchical silicon etched structures for controlled hydrophobicity/ superhydrophobicity,” Nano Lett., vol. 7, no. 11, pp. 3388–3393, 2007. [3] D. Qi et al., “Simple Approach to Wafer-scale Self-cleaning Antireflective Surfaces,” pp. 1–5. [4] W.-F. Kuan and L.-J. Chen, “The preparation of superhydrophobic surfaces of hierarchical silicon nanowire structures.,” Nanotechnology, vol. 20, no. 3, p. 35605, 2009. [5] Y. Xiu, S. Zhang, V. Yelundur, A. Rohatgi, D. W. Hess, and C. P. Wong, “Superhydrophobic and Low Light Reflectivity Silicon Surfaces Fabricated by Hierarchical Etching,” Langmuir, vol. 24, no. 18, pp. 10421–10426, Sep. 2008. [6] C. R. Tellier and A. Brahim-Bounab, “Anisotropic etching of silicon crystals in KOH solution,” J. Mater. Sci., vol. 29, no. 22, pp. 5953–5971, 1994. [7] G. Barillaro, A. Nannini, and M. Piotto, “Electrochemical etching in HF solution for silicon micromachining,” Sensors Actuators A Phys., vol. 102, no. 1–2, pp. 195–201, Dec. 2002. [8] V. Schmidt, S. Senz, and U. G?sele, “Diameter-Dependent Growth Direction of Epitaxial Silicon Nanowires,” Nano Lett., vol. 5, no. 5, pp. 931–935, May 2005. [9] F. Marty et al., “Advanced etching of silicon based on deep reactive ion etching for silicon high aspect ratio microstructures and three-dimensional micro- and nanostructures,” Microelectronics J., vol. 36, no. 7, pp. 673–677, Jul. 2005. [10] S. Gielis, M. H. vander Veen, S. De Gendt, and P. M. Vereecken, “Silver-assisted Etching of Silicon Nanowires S. Gielis,” ECS Trans., vol. 33, no. 18, pp. 49–58, 2011. [11] D. Z. Dimitrov and C.-H. Du, “Crystalline silicon solar cells with micro/nano texture,” Appl. Surf. Sci., vol. 266, pp. 1–4, 2013.

This work presents the fabrication of carbon nanotube composite membranes with controllable nanotube dimensions (inner diameters and lengths) and surface chemistry and explores their influence on the transport properties and chemical based transport selectivity. These membranes were prepared by growing of vertically aligned multiwalled carbon nanotubes (MWCNTs) inside nanoporous anodic alumina membranes (NAAMs) through a catalyst-free chemical vapour deposition (CVD) approach. The deposition time during CVD process and the length of NAAMs were used to control nanotube dimensions. The thermal annealing and wet and dry oxidation processes were used to control the surface chemistry of inner walls of nanotubes from highly graphitic-hydrophobic to oxygen rich and hydrophilic. The structural features and chemical composition of the prepared membranes are characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The influence of the nanotube dimensions and surface chemistry on molecular transport properties of prepared membranes are assessed by analysing the transport of two models molecules with different hydrophilic–hydrophobic and charge properties. The obtained results reveal that the diffusional flux of model molecules through CNTs-NAAMs can be controlled by nanotube dimensions and surface chemistry of graphitic surface and these parameters can be used to tailor their chemical based molecular separation for specific applications.

Current development of drug microcarriers is mainly based on spherical shapes, which are not biologically favorable geometries for complex interactions with biological systems. Scalable synthesis of drug carriers with nonspherical and anisotropic shapes featuring sustained drug-releasing performances, biocompatibility, degradability, and sensing capabilities is challenging. These challenges are addressed in this work by employing Nature's optimized designs obtained from low-cost diatomaceous earth mineral derived from single-cell algae diatoms. Silica diatoms with unique shapes and 3D microcapsule morphology are converted into silicon diatom replicas with identical structure by a magnesiothermic reduction process. The results reveal that prepared silicon diatoms have a set of unique properties including favorable microcapsule structure with high surface area and micro/mesoporosity providing high drug loading, fast biodegradability, and intrinsic luminescence, which make them highly suitable for low-cost production of advanced drug microcarriers. Their sustained drug release >30 days combined with self-reporting function based on silicon luminescence properties using nonluminescent and luminescent drugs for intravitreal drug therapy is successfully demonstrated. These silicon diatoms offer promising potential toward scalable production of low-cost and advanced microcarriers for broad medical therapies, including theranostics and microrobotic guided drug delivery devices.

Herein, we present a systematic study on the development, optical optimization and sensing applicability of colored photonic coatings based on nanoporous anodic alumina films grown on aluminum substrates. These optical nanostructures, so-called distributed Bragg reflectors (NAA-DBRs), are fabricated by galvanostatic pulse anodization process, in which the current density is altered in a periodic manner in order to engineer the effective medium of the resulting photonic coatings. As-prepared NAA-DBR photonic coatings present brilliant interference colors on the surface of aluminum, which can be tuned at will within the UV-visible spectrum by means of the anodization profile. A broad library of NAA-DBR colors is produced by means of different anodization profiles. Then, the effective medium of these NAA-DBR photonic coatings is systematically assessed in terms of optical sensitivity, low limit of detection and linearity by reflectometric interference spectroscopy (RIfS) in order to optimize their nanoporous structure toward optical sensors with enhanced sensing performance. Finally, we demonstrate the applicability of these photonic nanostructures as optical platforms by selectively detecting gold(iii) ions in aqueous solutions. The obtained results reveal that optimized NAA-DBR photonic coatings can achieve an outstanding sensing performance for gold(iii) ions, with a sensitivity of 22.16 nm μM(-1), a low limit of detection of 0.156 μM (i.e. 30.7 ppb) and excellent linearity within the working range (0.9983).

Electrochemically engineered nanoporous anodized aluminium oxide (AAO) prepared on aluminium (Al) foil by anodization process was employed as a platform for loading different forms of selenium (Se) in order to investigate their release behaviour and potential application for localized drug delivery targeting bone cancer. Several forms of Se including inorganic Se (H2SeO3), organic Se ((C6H5)2Se2), metallic Se, their chitosan composites, electrodeposited (ED) and chemical vapour deposited (CVD) Se were explored and combined with another model drug (indomethacin). Structural, drug-loading and in vitro drug-releasing characteristics of prepared Se-based drug delivery carriers were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and UV-visible spectroscopy (UV-Vis), respectively. Sustained and controlled release of Se was demonstrated through chitosan-composites of inorganic, organic or metallic forms of Se loaded into nanoporous AAO carriers. Cell viability studies showed decreasing toxicity to cancer cells in the order: inorganic Se > ED Se > CVD Se > metallic Se > organic Se. The study suggests new alternatives for localized drug treatment based on low-cost nano-engineered carriers loaded with Se having anti-cancer properties.

Diatomaceous earth or diatom (DE) are naturally available and low cost micro particles with distinct porous structure were used as an adsorbent for the removal of a hazardous dye, Eriochrome Black T (EBT). The surface modification of these DE were performed by sol-gel and hydrothermal methods to obtain a series of adsorbents such as diatom-ceria (DC), diatom-silica xerogel (DX), and diatom-silica xerogel-ceria (DXC). A cauliflower like morphology structure of ceria was observed on DE and DX. The adsorption performance of EBT was conducted by varying various parameters such as pH, adsorbent dosage, initial concentration, contact time and ionic strength. The materials DE, DC, DX and DXC showed the EBT removal efficiencies of 52, 77, 20, and 93%, respectively. The maximum adsorption capacity (qm) of DE, DC, DX and DXC was found to be 13.83, 23.64, 0.2 and 47.02 mgg-1 for the adsorption of EBT, respectively. The selectivity of EBT towards DXC was evaluated by treating a mixture of anionic dyes. The dye removal experiments was performed in presence of inorganic salts, however the presence of these salts did not affect the removal efficiency of DXC. Furthermore, the reusability of DXC was studied by recycling it up to 5 times and even at 5th cycle a removal efficiency of ∼66.8% was found. Thus, these studies demonstrate that the DXC material could be a promising candidate for the removal of EBT via adsorption for real time application in water treatment.

In this study, we demonstrate that an optimal design of the pore geometry and shape of sensing platforms based on nanoporous anodic alumina (NAA) photonic structures is critical to develop optical sensors with improved capabilities. To this end, two types of NAA photonic structures featuring different pore geometries (i.e., pore lengths and diameters) and shapes (i.e., straight and modulated pores) were produced, and their optical characteristics were assessed systematically by reflectometric interference spectroscopy. The geometric features (i.e., pore lengths, diameters, and shapes) were systematically modified in order to establish the optimization paths for the sensitivity, low limit of detection, and linearity of these optical sensing platforms. The obtained results reveal that an optimal design of these nanoporous photonic structures can enhance their sensitivity, achieve a lower limit of detection, and improve their linearity for both nonspecific and specific detection of analytes. Therefore, as th...

A simple frit-free PDMS (polydimethylsiloxane) microfluidic chromatographic device, packed with diatomaceous earth (DE) microparticles as a normal phase stationary material using iron oxide magnetic nanoparticles is described. The separation of two model dyes was successfully demonstrated by integrating on-chip fibre optic detection to create a lab on a chip type of device.

Herein, we present an innovative approach to generate a novel type of 3D optical nanostructures based on nanoporous anodic alumina (NAA), the so-called inverted nanoporous anodic alumina funnels (INAAFs). This electrochemical approach takes advantage of the differential dissolution rate of NAA with the annealing temperature, which enables the in-depth engineering of nanopores. The structural engineering of these 3D nanostructures is monitored in situ by reflectometric interference spectroscopy through changes in the effective optical thickness of NAA, making it possible to precisely control the formation of INAAFs in real-time. The resulting INAAFs are optical nanostructures featuring a stratified structure of well-defined cylindrical nanopores with increasing pore diameter from top to bottom. As a result of their geometric characteristics and optical properties, INAAFs are envisaged for replicating novel nanostructures and developing optical and photonic devices.

In this study, we present an ultrasensitive sensor based on nanoporous anodic alumina (NAA) for detection of gold(III) ions (Au(3+) ions) using reflectometric interference spectroscopy (RIfS). Nanoporous anodic alumina, prepared by two-step electrochemical anodization, was functionalized with 3-mercaptopropyl-tirethoxysilane (MPTES) in order to selectively detect Au(3+) ions. Thus prepared, MPTES-NAA sensors were exposed to different concentrations of Au(3+) ions ranging from 0.1 to 750 μM and the changes in the effective optical thickness (ΔEOT) were monitored in real-time. The linear range of these Au(3+) sensors was from 0.1 to 80 μM, with a lower detection limit of 0.1 μM of Au(3+) ions. Furthermore, the specificity of these MPTES-NAA sensors was validated by sequential exposure to 40 μM solutions of Fe(3+,) Mg(2+), Co(2+), Cu(2+), Ni(2+), Ag(+), and Pb(2+), resulting in negligible changes in EOT as compared to the same concentration of Au(3+) ions. Detection of Au(3+) ions in complex and environmentally and biologically relevant solvents such as tap water and phosphate buffer solution (PBS) was also successfully carried out in order to demonstrate the real-life application of these sensors. Finally, the binding isotherm for Au(3+) ions and thiol (SH) group of MPTES-NAA system was determined by fitting the changes in EOT to Freundlich and Langmuir isotherm models.

This study presents a nanotechnological approach to convert commercially available and non-degradable grocery plastic bags into well-organised carbon nanotube membranes with tuneable molecular transport properties. In this nanotechnological process, plastic bags are used as a carbon source while carbon nanotubes (CNTs) are produced by a catalyst/solvent-free chemical vapour deposition (CVD) approach. Furthermore, CNTs are grown inside nanoporous anodic alumina membranes (NAAMs) featuring hexagonally arranged nanopores, which enable the control over the nanotubes’ organisation and geometry. The transport performance of the resulting CNTs–NAAMs is tested by several dye molecules with positive, negative and neutral charge. These results demonstrate the ability of these membranes to selectively tune molecular transport as a function of the interaction between molecules and inner surface of CNTs. This study proves that an environmentally non-degradable wastematerial as commercial plastic bags can be directly used to produce such sophisticated nanodevices as CNTs membranes.

Herein, we present an innovative approach to monitoring in situ drug release under dynamic flow conditions from aluminum implants featuring nanoporous anodic alumina (NAA) covers used as a model of drug-releasing implants. In this method, reflectometric interference spectroscopy (RIfS) is used to monitor in real-time the diffusion of drug from these nanoporous implants. The release process is carried out in a microfluidic device, which makes it possible to analyze drug release under dynamic flow conditions with constant refreshing of eluting medium. This setup mimics the physiological conditions of biological milieu at the implant site inside the host body. The release of a model drug, indomethacin, is established by measuring the optical thickness change with time under four different flow rates (i.e. 0, 10, 30, and 50 μL min(-1)). The obtained data are fitted by a modified Higuchi model, confirming the diffusion-controlled release mechanism. The obtained release rate constants demonstrate that the drug release depends on the flow rate and the faster the flow rate the higher the drug release from the nanoporous covers. In particular, the rate constants increase from 2.23 ± 0.02 to 12.47 ± 0.04 μg min(-1/2) when the flow rate is increased from 10 to 50 μL min(-1), respectively. Therefore, this method provides more reliable and relevant information than conventional in vitro drug release methods performed under static conditions.

We designed and fabricated a smart and stimuli responsive membrane to cater on demand molecular transporting applications. A novel photoswitchable peptide (PSP) was synthesized and attached inside nanoporous anodic alumina membranes (NAAMs) pores. The PSP specifically switched between its cis and trans photostationary states on exposure to 364 nm and 440 nm wavelength lights respectively, which not only provided the ability to control its pore diameter but also the surface chemistry. The switchable molecular transport properties of the PSP-NAAMs have been shown as a function of the light exposure. Most importantly, the molecular transport across PSP-NAAMs could be repeatedly switched between on and off state, which is highly significant for on-demand triggered drug release systems.

This article presents a new method for transferring and enhancing the adhesion of thin nanoporous alumina (NPA) membranes onto non-atomically flat substrates like Fluorine doped Tin Oxide (FTO) coated glass. The study reports use of Glycerol as an additive to reduce the brittleness of the Polystyrene filler that was used to fill the pores of the NPA membrane. Besides, a new refluxing based method is reported here for complete removal of the Polystryrene filler from the porous channels of Alumina. The adhesion between NPA membrane and an underlying electrode was enhanced by electrodepositing a thin (~ 40 nm) intermediate layer of conducting polymer Polyaniline (PANI). The PANI layer acts as an efficient electrostatic adhesive between the NPA and the conducting glass electrode and ensured ultra-strong adhesion of NPA membrane that survived the harsh conditions of CdTe nanowire electrodeposition (60 °C temperature and acidic electrolyte) without delamination for 30 min. The resulting nanowires clearly templated the structure of NPA and displayed free-standing nanowires over a large area with diameter of around 60 nm and length approximately 2.8 µm (aspect ratio ~ 47) and an areal density of 5.9 × 10 nanowires/cm. Total optical absorption measurement on the free-standing CdTe nanowires exhibited an enhancement by 45% over a wavelength range of 350 nm to 1400 nm as compared to CdTe planar thin film of same thickness.

This study is the first realisation of true optical rugate filters (RFs) based on nanoporous anodic alumina (NAA) by sinusoidal waves. An innovative and rationally designed sinusoidal pulse anodisation (SPA) approach in galvanostatic mode is used with the aim of engineering the effective medium of NAA in a sinusoidal fashion. A precise control over the different anodisation parameters (i.e. anodisation period, anodisation amplitude, anodisation offset, number of pulses, anodisation temperature and pore widening time) makes it possible to engineer the characteristic reflection peaks and interferometric colours of NAA-RFs, which can be finely tuned across the UV-visible-NIR spectrum. The effect of the aforementioned anodisation parameters on the photonic properties of NAA-RFs (i.e. characteristic reflection peaks and interferometric colours) is systematically assessed in order to establish for the first time a comprehensive rationale towards NAA-RFs with fully controllable photonic properties. The experimental results are correlated with a theoretical model (Looyenga–Landau–Lifshitz – LLL), demonstrating that the effective medium of these photonic nanostructures can be precisely described by the effective medium approximation. NAA-RFs are also demonstrated as chemically selective photonic platforms combined with reflectometric interference spectroscopy (RIfS). The resulting optical sensing system is used to assess the reversible binding affinity between a model drug (i.e. indomethacin) and human serum albumin (HSA) in real-time. Our results demonstrate that this system can be used to determine the overall pharmacokinetic profile of drugs, which is a critical aspect to be considered for the implementation of efficient medical therapies.

Structural engineering of porous anodic aluminum oxide (AAO) nanostructures by anodization has been extensively studied in the past two decades. However, the transition of this technique into the fabrication of AAO-based one-dimensional photonic crystal is still challenging. Herein, we report for the first time on the fabrication of AAO optical microcavities by a rationally designed anodization approach. In our study, two feasible methods are used to fabricate microcavities with tunable resonance peak across the visible and near-infrared spectra. Distributed Bragg reflector (DBR) nanostructures are first fabricated by pulse anodization approach, in which the anodization voltage was periodically manipulated to achieve pseudosinusoidal modulation of the effective refractive index gradient along the depth of the AAO nanostructures. Microcavities were created by creating a nanoporous layer of constant porosity between two AAO-DBR nanostructures, and by introducing a shift of the phase of the porosity gradient along the depth of AAO. The position of the resonance peak in these microcavities can be linearly tuned by means of the duration of the high voltage anodization. These optical nanostructures are sensitive to alterations of the effective media inside the nanopores. The AAO microcavity shows a central wavelength shift of 2.58 ± 0.37 nm when exposed to water vapor. Our research highlights the feasibility of anodization technique to fabricate AAO-based photonic nanostructures for advanced sensing applications.

Herein, we present a systematic study on the development, optimisation and applicability of interferometrically coloured distributed Bragg reflectors based on nanoporous anodic alumina (NAA-DBRs) in the form of films and nanoporous microparticles as visual/colorimetric analytical tools. Firstly, we synthesise a complete palette of NAA-DBRs by galvanostatic pulse anodisation approach, in which the current density is altered in a periodic fashion in order to engineer the effective medium of the resulting photonic films in depth. NAA-DBR photonic films feature vivid colours that can be tuned across the UV-visible-NIR spectrum by structural engineering. Secondly, the effective medium of the resulting photonic films is assessed systematically by visual analysis and reflectometric interference spectroscopy (RIfS) in order to establish the most optimal nanoporous platforms to develop visual/colorimetric tools. Then, we demonstrate the applicability of NAA-DBR photonic films as a chemically selective sensing platform for visual detection of mercury(II) ions. Finally, we generate a new nanomaterial, so-called photonic dust, by breaking down NAA-DBRs films into nanoporous microparticles. The resulting microparticles (μP-NAA-DBRs) display vivid colours and are sensitive towards changes in their effective medium, opening new opportunities for developing advanced photonic nanotools for a broad range of applications.

Oriented composite nanofibers consisting of porous silicon nanoparticles (pSiNPs) embedded in a polycaprolactone or poly(lactide-co-glycolide) matrix are prepared by spray nebulization from chloroform solutions using an airbrush. The nanofibers can be oriented by an appropriate positioning of the airbrush nozzle, and they can direct growth of neurites from rat dorsal root ganglion neurons. When loaded with the model protein lysozyme, the pSiNPs allow the generation of nanofiber scaffolds that carry and deliver the protein under physiologic conditions (phosphate-buffered saline (PBS), at 37 °C) for up to 60 d, retaining 75% of the enzymatic activity over this time period. The mass loading of protein in the pSiNPs is 36%, and in the resulting polymer/pSiNP scaffolds it is 3.6%. The use of pSiNPs that display intrinsic photoluminescence (from the quantum-confined Si nanostructure) allows the polymer/pSiNP composites to be definitively identified and tracked by time-gated photoluminescence imaging. The remarkable ability of the pSiNPs to protect the protein payload from denaturation, both during processing and for the duration of the long-term aqueous release study, establishes a model for the generation of biodegradable nanofiber scaffolds that can load and deliver sensitive biologics.

A smart and reversibly photoswitchable membrane based on an azobenzene photo-switch containing peptides attached inside the pores of nanoporous anodic alumina membranes (NAAMs) is presented. The transport of molecules of interest across the photoswitchable peptide (PSP) functionalized NAAMs can be effectively controlled and manipulated as a function of the photostationary state of the azobenzene group in a PSP.

Nanoporous membrane based molecular separation and transporting have gained huge attention in recent years due to an immediate need for simple, cost-competitive, and miniature ultrafiltration, chromatography and desalination devices. Nanoporous anodic alumina membranes (NAAMs) are one of the most popular materials of choice for the aforementioned applications due to its outstanding and unique set of chemical, physical, and structural properties. This chapter provides details of fabrication of NAAMs and surface modification techniques employed for enabling NAAMs for chromatography and molecular transporting applications. Next, fundamentals of chromatography and recent studies on nanopore-chromatographic systems based on nanoporous anodic alumina are summarized. Also, fundamentals of molecular transporting across NAAMs and recent examples are compiled in this chapter. The objective of this chapter is to provide a simple yet detailed overview of fabrication of NAAMs based chromatographic and molecular transporting devices with an emphasis on their performance.

Porous silicon produced by electrochemical etching of silicon has become one of the most popular materials used in many scientific disciplines as a result of its outstanding and unique set of chemical and physical properties and cost-competitive fabrication processes. To understand the electrochemical mechanisms taking place in the course of the etching of silicon is a key factor to control and modify the structure of this versatile porous material. This makes it possible to produce a broad range of structures, which can range from a porous matrix to arrays of nanowires. These structures are unique and bring new opportunities for multiple research fields and applications such as biotechnology, medicine, optoelectronics, chemistry and so forth. This chapter is aimed at compiling and summarising the fundamental aspects behind the production of porous silicon structures by electrochemical and metal-assisted etching of silicon wafers. Our objective is to provide a simple but detailed overview about the fabrication process of porous silicon, with special emphasis on the different fabrication conditions and geometric and morphological features of the resulting silicon nanostructures.

Nanoporous anodic alumina (NAA) is fabricated by a simple yet cost-effective self-ordering anodization process of aluminium foils, which yields highly ordered and columnar nanopores. These ordered pores impart NAA with unique optical and electrochemical properties, which have been intensively researched to develop smart, efficient, cost-competitive and portable yet complex sensing and biosensing systems. This chapter provides detailed fundamentals of sensing techniques and recent advances in development of NAA based sensing and biosensing technologies.

As a result of its physical and chemical properties, nanoporous anodic alumina (NAA) has been envisaged as a promising nanomaterials for developing optical biosensing system with outstanding capabilities and performances. Recent studies have demonstrated that the combination of NAA with different optical techniques can yield a variety of innovative optical sensing systems for a broad range of analytes and applications. In this context, this chapter aims to report on the recent advances and developments of NAA-based optical biosensing systems. The different optical detection techniques, principles and concepts of NAA-based optical biosensing systems will be described in detail. Our objective is to provide a simple but detailed overview about the different NAA-based optical biosensing systems, with especial emphasis on the performance and capabilities of these devices. Finally, we will provide a future perspective on challenges and developments for this promising research field.

Herein, we present an ultrasensitive, cost-competitive, and portable optical sensing system for detecting ionic mercury in environmental water. This analytical system combines structurally engineered and chemically modified nanoporous anodic alumina rugate filters (NAA-RFs) with reflection spectroscopy (RfS). The sensing performance of the proposed system is assessed through several tests, establishing its sensing performance (i.e., linear working range from 1 to 100 μM of Hg(2+), low limit of detection 1 μM of Hg(2+) ions (i.e., 200 ppb), and sensitivity of 0.072 nm μM(-1)), chemical selectivity (i.e., exposure to different metal ions Co(2+), Mg(2+), Ni(2+), Cu(2+), Pb(2+), Fe(3+), Ca(2+), Cr(6+), and Ag(+)) and metal ions binding mechanism (i.e., fitting to Langmuir and Freundlich isotherm models). Furthermore, the detection of Hg(2+) ions in tap and environmental water (River Torrens) is successfully carried out, demonstrating the suitability of this system for developing environmental point-of-analysis systems.

A study of reflective interference spectroscopy [RIfS] properties of nanoporous anodic aluminium oxide [AAO] with the aim to develop a reliable substrate for label-free optical biosensing is presented. The influence of structural parameters of AAO including pore diameters, inter-pore distance, pore length, and surface modification by deposition of Au, Ag, Cr, Pt, Ni, and TiO2 on the RIfS signal (Fabry-Perot fringe) was explored. AAO with controlled pore dimensions was prepared by electrochemical anodization of aluminium using 0.3 M oxalic acid at different voltages (30 to 70 V) and anodization times (10 to 60 min). Results show the strong influence of pore structures and surface modifications on the interference signal and indicate the importance of optimisation of AAO pore structures for RIfS sensing. The pore length/pore diameter aspect ratio of AAO was identified as a suitable parameter to tune interferometric properties of AAO. Finally, the application of AAO with optimised pore structures for sensing of a surface binding reaction of alkanethiols (mercaptoundecanoic acid) on gold surface is demonstrated. Refereed/Peer-reviewed

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.

The concept of a microfluidic biosensing device based on reflective interferometric spectroscopy (RIfS) is presented in this article. The key element of the sensor is a highly ordered nanoporous structure of anodic aluminium oxide (AAO) integrated into a microfluidic chip combined with an optical fiber spectrophotometer. AAO was prepared by electrochemical anodization of aluminium using 0.3 M oxalic acid. The structural and geometrical features of the AAO porous structures were controlled to provide optimal RIfS sensing characteristics and there sensing capabilities were explored using two different strategies; i) detection based on the response generated by pefusion of analyte ions inside the pores and ii) detection based on specific adsorption of analyte molecules on surface of AAO pores. The second strategy is based on chemical modification of the AAO surface to target molecules based on specific surface binding reactions. In this work two cases are presented, including the binding of small thiol molecules on gold-modified AAO (Au-AAO) and binding of larger targets such as circulating tumour cells (CTC) on antibody-modified AAO. Our preliminary results show an excellent capability of our system in the detection of different analytes using both strategies, and confirm good potential for the development and application of interferometric label-free biosensing devices in a wide range of biomedical applications. Refereed/Peer-reviewed

The design of a microfluidic nanoporous reflective interferometric (RIfS) sensor is presented. The key element of the sensor is a highly ordered nanoporous structure of anodic aluminium oxide (AAO) integrated into a microfluidic chip and combined with an optical fibre spectrophotometer and notebook computer. AAO with controlled pore dimensions was prepared by electrochemical anodization of aluminium using 0.3 M oxalic acid at 50V for 40 minutes. The performance of the microfluidic RIfS for sensing of surface binding reaction of alkanethiols (mercapto undecanoic acid) on gold is evaluated showing excellent sensitivity. The results show potential for development and application of interferometric label-free biosensing elements for a wide range of biomedical applications. Keywords: Reflective interferometric spectroscopy, Fabry-Perot fringes, microchip interference sensor, nanoporous alumina. Refereed/Peer-reviewed

This Letter reports the use of nanoporous anodic aluminium oxide (AAO) for reflective interferometric gas sensing. Gas detection is based on changes of the interference signal from AAO porous layer as a result of the specific adsorption of gas molecules on a metal coated surface. Two different metal coatings – gold (Au) and platinum (Pt) – were used and their application for the detection of hydrogen sulphide (H2S) and hydrogen (H2) is shown. The practical application of a microchip Au-AAO sensor for measurement of H2S concentration and monitoring of malodour is also presented. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optimisation of reflective interferometric properties of nanoporous aluminium oxide (AAO) fabricated by electrochemical anodization using different conditions is presented. The influence of structural modification of pores includeing the changing of pore diameters and pore depth on interference pattern was investigated. Chemical modification of pore surface such as metal deposition and nanoparticle immobilisation was additionally used to further optimise interference properties of AAO. The results of this study will be used for development of the label-free interferometric biosensor or chemosensors with increased sensitivity Refereed/Peer-reviewed