Tushar Kumeria

Label-free reflectometric interference microchip biosensor based on nanoporous alumina for detection of circulating tumour cells

In this report, a label-free reflectometric interference spectroscopy (RIfS) based microchip biosensor for the detection of circulating tumour cells (CTCs) is demonstrated. Highly ordered nanoporous anodic aluminium oxide (AAO) fabricated by electrochemical anodization of aluminium foil was used as the RIfS sensing platform. Biotinylated anti-EpCAM antibody that specifically binds to human cancer cells of epithelial origin such as pancreatic cancer cells (PANC-1) was covalently attached to the AAO surface through multiple surface functionalization steps. Whole blood or phosphate buffer saline spiked with low numbers of pancreatic cancer cells were successfully detected by specially designed microfluidic device incorporating an AAO RIfS sensor, without labour intensive fluorescence labelling and/or pre-enhancement process. Our results show that the developed device is capable of selectively detecting of cancer cells, within a concentrations range of 1000-100,000 cells/mL, with a detection limit of <1000 cells/mL, a response time of <5 min and sample volume of 50 μL of. The presented RIfS method shows considerable promise for translation to a rapid and cost-effective point-of-care diagnostic device for the detection of CTCs in patients with metastatic cancer.

Structural and Optical Nanoengineering of Nanoporous Anodic Alumina Rugate Filters for Real-Time and Label-Free Biosensing Applications

In this study, we report about the structural engineering and optical optimization of nanoporous anodic alumina rugate filters (NAA-RFs) for real-time and label-free biosensing applications. Structurally engineered NAA-RFs are combined with reflection spectroscopy (RfS) in order to develop a biosensing system based on the position shift of the characteristic peak in the reflection spectrum of NAA-RFs (Δλpeak). This system is optimized and assessed by measuring shifts in the characteristic peak position produced by small changes in the effective medium (i.e., refractive index). To this end, NAA-RFs are filled with different solutions of d-glucose, and the Δλpeak is measured in real time by RfS. These results are validated by a theoretical model (i.e., the Looyenga-Landau-Lifshitz model), demonstrating that the control over the nanoporous structure makes it possible to optimize optical signals in RfS for sensing purposes. The linear range of these optical sensors ranges from 0.01 to 1.00 M, with a low detection limit of 0.01 M of d-glucose (i.e., 1.80 ppm), a sensitivity of 4.93 nm M(-1) (i.e., 164 nm per refractive index units), and a linearity of 0.998. This proof-of-concept study demonstrates that the proposed system combining NAA-RFs with RfS has outstanding capabilities to develop ultrasensitive, portable, and cost-competitive optical sensors.

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.

Nanoporous Anodic Alumina: A Versatile Platform for Optical Biosensors

Nanoporous anodic alumina (NAA) has become one of the most promising nanomaterials in optical biosensing as a result of its unique physical and chemical properties. Many studies have demonstrated the outstanding capabilities of NAA for developing optical biosensors in combination with different optical techniques. These results reveal that NAA is a promising alternative to other widely explored nanoporous platforms, such as porous silicon. This review is aimed at reporting on the recent advances and current stage of development of NAA-based optical biosensing devices. The different optical detection techniques, principles and concepts are described in detail along with relevant examples of optical biosensing devices using NAA sensing platforms. Furthermore, we summarise the performance of these devices and provide a future perspective on this promising research field.

Drug-releasing implants: current progress, challenges and perspectives

The need for more efficient drug delivery strategies to treat resilient diseases and the rise of micro and nanotechnology have led to the development of more sophisticated drug-releasing implants with improved capabilities and performances for localised and controlled therapies. In recent years, implantable drug-releasing systems have emerged as an outstanding alternative to conventional clinical therapies. This new breed of implants has shown promising capabilities to overcome the inherent problems of conventional implants and therapies, making clinical treatments more efficient with minimal side effects. Recent clinical trials have demonstrated that this technology can improve the life of patients and increase their life expectancy. Within this context, this review is aimed at highlighting the different types and concepts of drug-releasing implants incorporating new nanomaterials and nanotechnology-based devices. Furthermore, the principles on which these drug-releasing implants are based as well as their advantages and limitations are discussed in detail. Finally, we provide a future perspective in the development of implantable clinical drug-delivery systems based on micro and nanotechnology.

Optically Optimized Photoluminescent and Interferometric Biosensors Based on Nanoporous Anodic Alumina: A Comparison

Herein, we present a comparative study about the sensing performance of optical biosensors based on photoluminescence spectroscopy (PLS) and reflectometric interference spectroscopy (RIfS) combined with nanoporous anodic alumina (NAA) platforms when detecting different analytes under distinct adsorption conditions. First, NAA platforms are structurally engineered in order for optimizing the optical signals obtained by PLS and RIfS. Then, the most optimal NAA platforms combined with PLS and RIfS are quantitatively compared by detecting two different analytes: d-glucose and l-cysteine under nonspecific and specific adsorption conditions, respectively. The obtained results demonstrate that such parameters as the analyte nature and adsorption conditions play a direct role in the sensing performance of these platforms. However, as this study demonstrates, PLS-NAA platforms are more sensitive than RIfS-NAA ones. The former shows better linearity (i.e., proportional change in the sensing parameter with analyte concentration), higher sensitivity toward analytes (i.e., sharper change in the sensing parameter with analyte concentration), and lower limit of detection (i.e., minimum detectable concentration of analyte).

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

Here, we report on the development of advanced biopolymer-coated drug-releasing implants based on titanium (Ti) featuring titania nanotubes (TNTs) on its surface. These TNT arrays were fabricated on the Ti surface by electrochemical anodization, followed by the loading and release of a model antibiotic drug, gentamicin. The osteoblastic adhesion and antibacterial properties of these TNT-Ti samples are significantly improved by loading antibacterial payloads inside the nanotubes and modifying their surface with two biopolymer coatings (PLGA and chitosan). The improved osteoblast adhesion and antibacterial properties of these drug-releasing TNT-Ti samples are confirmed by the adhesion and proliferation studies of osteoblasts and model Gram-positive bacteria (Staphylococcus epidermidis). The adhesion of these cells on TNT-Ti samples is monitored by fluorescence and scanning electron microscopies. Results reveal the ability of these biopolymer-coated drug-releasing TNT-Ti substrates to promote osteoblast adhesion and proliferation, while effectively preventing bacterial colonization by impeding their proliferation and biofilm formation. The proposed approach could overcome inherent problems associated with bacterial infections on Ti-based implants, simultaneously enabling the development of orthopedic implants with enhanced and synergistic antibacterial functionalities and bone cell promotion.

Ultrasensitive nanoporous interferometric sensor for label-free detection of gold(III) ions

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.

Nanoporous Anodic Alumina Rugate Filters for Sensing of Ionic Mercury: Toward Environmental Point-of-Analysis Systems

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.

Biomimetic Nanoporous Anodic Alumina Distributed Bragg Reflectors in the Form of Films and Microsized Particles for Sensing Applications

In this study, we produce for the first time biomimetic films and microsized particles based on nanoporous anodic alumina distributed Bragg reflectors (NAA-DBRs) by a rational galvanostatic pulse-anodization approach. These biomimetic photonic structures can feature a broad range of vivid bright colors, which can be tuned across the UV-visible spectrum by engineering their nanoporous structure through different anodization parameters. The effective medium of NAA-DBRs films is systematically assessed as a function of the anodization period, the anodization temperature, and the current density ratio by reflectometric interference spectroscopy (RIfS). This analysis makes it possible to establish the most sensitive structure toward changes in its effective medium. Subsequently, specific detection of vitamin C molecules is demonstrated. The obtained results reveal that NAA-DBRs with optimized structure can achieve a low limit of detection for vitamin C molecules as low as 20 nM, a sensitivity of 227±4 nm μM(-1), and a linearity of 0.9985. Finally, as proof of concept, we developed a new photonic nanomaterial based on NAA-DBR microsized particles, which could provide new opportunities to produce microsized photonic analytical tools.