Visceral leishmaniasis (L.donovani) is a protozoan infection that attacks mononuclear phagocytes and causes the liver
and spleen damage that can cause death. The investigation presented is a proof of concept development applying a
plasmonic diagnostic platform with simple microfluidic sample delivery and optical readout. An immune-assay method
is applied to the quantification of A2 protein, a highly immunogenic biomarker for the pathogen. Quantification of A2
was performed in the ng/ml range, analysis by ELISA suggested that a limit of 0.1ng/ml of A2 is approximate to 1
pathogen per ml and the sensing system shows the potential to deliver a similar level of quantification. Significant
reduction in assay complexity as further enzyme linked enhancement is not required when applying a plasmonic methodology to an immunoassay. The basic instrumentation required for a portable device and potential dual optical readout where both plasmonic and photoluminescent response are assessed and investigated including consideration of the application of the device to testing where non-literate communication of results is considered and issues of
performance are addressed.
The cost of fabrication and instrumentation presents a significant barrier to uptake of optical mapping as a tool for
genomic investigation. Here a low cost optical instrumentation system to perform optical genomic mapping of DNA
fragment restriction digestion by nanochannel confinement is presented. Specifically, the system is used for the detection
of YOYO-1 labeled DNA within chemically formed nanochannels on a polystyrene chip. The formation of nanochannels
on the polystyrene chip is achieved by solvent swelling of an injection moulded polystyrene substrate. The inverted
microscope based system is compact and of low-cost but offers the sensitivity to detect individual fragments ranging
from 0.56Kb to 9.4Kb of the λ-phage genome within a channels. Conformation of DNA within nanochannels driven by
capillary flow is most consistent with modeled polymer extension in nanoslit.
In previous work, we demonstrate a simple approach to creating a plasmonic polymer. Reflecting upon the need for
greater spot density while still maintaining the objective of low cost analysis, the next generation of device is described
where density up to 24000 sensing spots is achievable. A localized surface plasmon micro-array is described formed by
single or multiple deposition of a nanorod plasmonic polymer by micro-contact printing. The structure of the polymer
can be made micro-porous and thickness can be controlled by a cyclical deposition and rapid heat cure protocol. The
consistency of feature deposition is assessed. The resulting micro-structure provides a large surface area for
immobilization of biomolecules for assay development. Dark-field analysis of the polymer demonstrates complex
microstructure and intense Mie Scattering as expected from gold nanorods. Using fluorescence confocal analysis images
of the polymer demonstrates two independent photo-luminescent emission spectra. The two independent emission
spectra are linked to the positions of the localized surface plasmons of the nanorods, using a pump source of 543nm
excites the transverse plasmon (peak at 550nm)and it's commensurate emission, but doesn't excite the longer emission
around 700nm that is linked to the longitudinal Plasmon around 737nm. The different emissions are demonstrated in the
illumination of different portions of the polymer matrix under each pump source excitation. The potential for multiple
spectroscopic biosensor analysis is discussed.
High throughput plasmonic sensors are a popular research field, standard surface plasmon resonance (SPR)
instruments can achieve high throughput only in imaging configuration. This leads to consideration of pattern
substrates and isolated nanoparticle arrays, both of which have some disadvantages. Spot functionalisation relies
upon mask or pin printing to accomplish density, and this increase the complexity of use and standard operating
procedures. Both patterned and nanoparticle arrays assay platforms are also commonly single use, unlike some SPR
imaging and multi channel angular sensing SPR approaches. The microarray format proposed here is intended for
multiple usages and regenerated, with a simple optical readout method. A plasmonic polymer of exquisite refractive
index sensitivity and incorporate glass-like physical and mechanical stability provides the sensing element to the
platform. Further, the standard sol-gel chemistry is well understood and amenable to easy covalent functionalisation
as well as matrix methods such as nitrocellulose for biomolecule fictionalization. Two forms of polymer templating
have been developed. For spots greater than 700μm a double side tape method can be applied and for sub 700μm
patterned SU-8 and 100nm Aluminum reflective layer allow greater spot resolution. Proof of concept through
refractive index sensing is demonstrated.
Porous silicon is a potentially useful substrate for fluorescence and scattering enhancement, with a large surface to volume ratio and thermal stability providing a potentially regenerable host matrix for sensor development. A simple process using XeF2 gas phase etching for creating porous silicon is explained. Moreover, how pores diameter can be controlled reproducibly with commensurate effects upon the silicon reflection and pore distribution is discussed. In previous work with this new system, it was clear that control on pore size and morphology was required and a systematic optimization of process conditions was performed to produce greater consistency of the result. The influence of the duration of the pre-etching processing in HF, concentration of the HF in the pre-etching process, and the XeF2 exposure time during the dry etching on surface morphology, pore size, and optical reflectance is explored.
For weak luminescence, quenching of insensitive luminophores by proximity to a gold film improves signal to noise by suppression of background luminescence of Ru(4,7-diphenyl-1,10-anthroline)3Cl2. Initially it was expected that the effects of gold film quenching and nanoparticle enhanced luminescence could be combined to give a summative improvement, but the increase caused by the nanoparticles generates a larger signal to noise ratio and greater sensitivity of those luminophores to the dynamic quenching by gaseous oxygen. Impressive detection limits were achieved on gold coated glass and plain glass, where detection limit was 0.05% and 0.004% and sensitivity 0.02 and 0.05%, respectively.
Porous silicon is a well-known material with interesting properties for a wide variety of applications in electronics,
photonics, medicine, and informatics. We demonstrate fabrication of porous silicon using a dry etching technique. We
demonstrate free standing porous silicon membranes that are only few microns thick. Free standing porous silicon
membranes have the ability to behave as a size-selective permeable membrane by allowing specific sized molecules to
pass through while retaining others. Here, we employ the XeF2 to develop few micrometers thick suspended porous
silicon membranes. The flexibility of XeF2 etching process allows the production of mechanically stable membranes of
different thicknesses. By choosing the appropriate etching parameters and conditions, pore size can be tuned to produce
porous silicon with optically attractive features and desired optical behaviors. The pore size, porosity and thickness of
the various developed ultra-thin free-standing porous silicon membranes were characterized with scanning electron
microscopy and optical transmittance measurements. The fabricated free-standing porous membrane has a typical
transmission spectrum of regular silicon modulated by Fabry-Perot fringes. Porous silicon thin membranes that combine
the properties of a mechanically and chemically stable high surface area matrix with the function of an optical transducer
may find many used in biomedical microdevices.
The field of plasmonics has shown a great promise in the enhancement of luminescence detection. Here, a simple
method to enhance oxygen detection by quenching of Ru[(4,7-diphenyl-1,10-anthroline)3]2+ (or Ru[dpp]2+) in a sol-gel
matrix by localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNP) is presented. In the experiments,
AuNP (10 ± 1.5 nm diameter) were added to a sol that was prepared by hydrolysis of trimethoxysilane,
octyltrimethoxysilane and ethanol in the presence of Ru[dpp]2+ luminophore. The resulting sol of the mixture was
spincoated on glass and allowed to age in the dark for one week to form the sol-gel film. A control sample was also
prepared using the procedure, except that AuNP was not added to the sol. The resulting AuNP embedded sol-gel shows
8.3 times improvement in the baseline (0% O2) intensity (I0) over the control. Moreover, there is a dramatic
improvement in the sensitivity from 0.0011 per % O2 in the control to 0.059 per % O2 with AuNP, for O2 level below
15%. Signal to noise ratio also improved, thus leading to a 100-fold improvement in the detection limit. Using phaseluminometry,
it was determined that there is a reduction in the luminescence lifetime when AuNP is added to the sol-gel
matrix. This reduction in the lifetime can be explained by the near-field interaction between the luminophores and the
AuNP.
Mesoporous materials, such as porous silicon and porous polymer gratings (Bragg structures), offer an attractive platform for the encapsulation of chemical and biological recognition elements. These materials include the advantages of high surface to volume ratio, biocompatibility, functionality with various recognition elements, and the ability to modify the material surface/volume properties and porosity. Two porous structures were used for chemical and biological sensing: porous silicon and porous polymer photonic bandgap structures. Specifically, a new dry etching manufacturing technique employing xenon difluoride (XeF2) based etching was used to produce porous silicon Porous silicon continues to be extensively researched for various optical and electronic devices and applications in chemical and biological sensing are abundant. The dry etching technique to manufacture porous silicon offers a simple and efficient alternative to the traditional wet electrochemical etching using hydrofluoric acid. This new porous silicon material was characterized for its pore size and morphology using top and cross-sectional views from scanning electron microscopy. Its optical properties were determined by angular dependence of reflectance measurements. A new class of holographically ordered porous polymer gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. As an alternative structure and fabrication process, porous polymer gratings that include a volatile solvent as the phase separation fluid was fabricated. Porous silicon and porous polymer materials were used as substrates to encapsulate gaseous oxygen (O2) responsive luminophores in their nanostructured pores. These substrate materials behave as optical interference filters that allow efficient and selective detection of the wavelengths of interest in optical sensors.
Porous silicon is an attractive platform for the encapsulation of chemical and biological recognition elements. We
demonstrate fabrication of porous silicon using a dry etching technique. The Xenon Difluoride etching technique allows
selective formation of porous silicon with a standard photoresist layer as mask. We demonstrate free standing 5μm thick
porous silicon films for biological sample filtering. Further, we employ the porous silicon as a substrate for the
immobilization of xerogel thin films that encapsulate specific analyte responsive luminophores in their pores. The porous
silicon behaves as an optical interference filter which allows selective enhancement of the wavelengths of interest.
Time-resolved photoluminescence (TRPL) across the full spectrum of a 240 layer ZnTe/ZnSe super-lattice structure has been performed using a femtosecond Ti-Sapphire laser and a streak camera system for detection. A significant change of the PL lifetime is observed across the emission spectrum decreasing smoothly from ~ 100 ns at 2.35 eV, to less than a few nanoseconds at 2.8 eV. The increase of the PL lifetime in the low energy region of the emission spectrum is strong
evidence to support the formation of type-II quantum dots (QDs) from excitons bound to clusters of Te-atoms. In such QDs the confined holes and the free electrons are spatially separated, thus increasing the radiative lifetime. This result is consistent with recent photoluminescence (PL) measurements in which evidence of the combined contribution of excitons bound isoelectronically to Te-atoms, and type-II QDs was observed.
Relatively intense deep-green/yellow photoluminescence emission at ~600 nm is observed for InGaN/GaN multi quantum well (MQW) structures grown on bulk AlN substrates, demonstrating the potential to extend commercial III-Nitride LED technology to longer wavelengths. Optical spectroscopy has been performed on InGaN MQWs with an estimated In concentration of greater than 50% grown by metalorganic chemical vapor phase epitaxy at 750oC. Temperature- and power-dependence, time-resolved photoluminescence as well as spatially resolved cathodoluminescence measurements and transmission electron microscopy have been applied to understand and elucidate the nature of the mechanism responsible for radiative recombination at 600nm as well as higher energy emission band observed in the samples. A comparison between samples grown on bulk AlN and sapphire substrates indicate a lower degree of compositional and/or thickness fluctuation in the latter case. Our results indicate the presence of alloy compositional fluctuation in the active region despite the lower strain expected in the structure contrary to that of low In composition active regions deposited on bulk GaN substrates. Transient photoluminescence measurements signify a stretched exponential followed by a power decay to best fit the luminescence decay indicative of carrier hopping in the active region. Our results point to the fact that at such high In composition (>30%) InGaN compositional fluctuation is still a dominant effect despite lower strain at the substrate-epi interface.
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