Optical Hydrogen Nanothermometry of Plasmonic Nanoparticles under Illumination

The temperature of nanoparticles is a critical parameter in applications that range from biology, to sensors, to photocatalysis. Yet, accurately determining the absolute temperature of nanoparticles is intrinsically difficult because traditional temperature probes likely deliver inaccurate results due to their large thermal mass compared to the nanoparticles. Here we present a hydrogen nanothermometry method that enables a noninvasive and direct measurement of absolute Pd nanoparticle temperature via the temperature dependence of the first-order phase transformation during Pd hydride formation. We apply it to accurately measure light-absorption-induced Pd nanoparticle heating at different irradiated powers with 1 \ub0C resolution and to unravel the impact of nanoparticle density in an array on the obtained temperature. In a wider perspective, this work reports a noninvasive method for accurate temperature measurements at the nanoscale, which we predict will find application in, for example, nano-optics, nanolithography, and plasmon-mediated catalysis to distinguish thermal from electronic effects

Optical properties of refractory metal based thin films

There is a growing interest in refractory metal thin films for a range of emerging nanophotonic applications including high temperature plasmonic structures and infrared superconducting single photon detectors. We present a detailed comparison of optical properties for key representative materials in this class (NbN, NbTiN, TiN and MoSi) with texture varying from crystalline to amorphous. NbN, NbTiN and MoSi have been grown in an ultra-high vacuum sputter deposition system. Two different techniques (sputtering and atomic layer deposition) have been employed to deposit TiN. We have carried out variable angle ellipsometric measurements of optical properties from ultraviolet to mid infrared wavelengths. We compare with high resolution transmission electron microscopy analysis of microstructure. Sputter deposited TiN and MoSi have shown the highest optical absorption in the infrared wavelengths relative to NbN, NbTiN or ALD deposited TiN. We have also modelled the performance of a semi-infinite metal air interface as a plasmonic structure with the above mentioned refractory metal based thin films as the plasmonic components. This study has implications in the design of next generation superconducting nanowire single photon detector or plasmonic nanostructure based devices

Optical fiber sensing using quantum dots

Recent advances in the application of semiconductor nanocrystals, or quantum dots, as biochemical sensors are reviewed. Quantum dots have unique optical properties that make them promising alternatives to traditional dyes in many luminescence based bioanalytical techniques. An overview of the more relevant progresses in the application of quantum dots as biochemical probes is addressed. Special focus will be given to configurations where the sensing dots are incorporated in solid membranes and immobilized in optical fibers or planar waveguide platforms

Antenna near-field wave studies in magnetized plasmas as part of the optimization of auxiliary heating in fusion devicesAntenna near-field wave studies in magnetized plasmas as part of the optimization of auxiliary heating in fusion devices

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Present and future of surface-enhanced Raman scattering

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article

Present and Future of Surface-Enhanced Raman Scattering.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article

Development of Microwave/Droplet-Microfluidics Integrated Heating and Sensing Platforms for Biomedical and Pharmaceutical Lab-on-a-Chip Applications

Interest in Lab-on-a-chip and droplet-based microfluidics has grown recently because of their promise to facilitate a broad range of scientific research and biological/chemical processes such as cell analysis, DNA hybridization, drug screening and diagnostics. Major advantages of droplet-based microfluidics versus traditional bioassays include its capability to provide highly monodispersed, well-isolated environment for reactions with magnitude higher throughput (i.e. kHz) than traditional high throughput systems, as well as its low reagent consumption and elimination of cross contamination. Major functions required for deploying droplet microfluidics include droplet generation, merging, sorting, splitting, trapping, sensing, heating and storing, among which sensing and heating of individual droplets remain great challenges and demand for new technology. This thesis focuses on developing novel microwave technology that can be integrated with droplet-based microfluidic platforms to address these challenges. This thesis is structured to consider both fundamentals and applications of microwave sensing and heating of individual droplets very broadly. It starts with developing a label-free, sensitive, inexpensive and portable microwave system that can be integrated with microfluidic platforms for detection and content sensing of individual droplets for high-throughput applications. This is, indeed, important since most droplet-based microfluidic studies rely on optical imaging, which usually requires expensive and bulky systems, the use of fluorescent dyes and exhaustive post-imaging analysis. Although electrical detection systems can be made inexpensive, label-free and portable, most of them usually work at low frequencies, which limits their applications to fast moving droplets. The developed microwave circuitry is inexpensive due to the use of off-the-shelf components, and is compact and capable of detecting droplet presence at kHz rates and droplet content sensing of biological materials such as penicillin antibiotic, fetal bovine serum solutions and variations in a drug compound concentration (e.g., for Alzheimer’s Disease). Subsequently, a numerical model is developed based on which parametrical analysis is performed in order to understand better the sensing and heating performance of the integrated platform. Specifically, the microwave resonator structure, which operates at GHz frequency affecting sensing performance significantly, and the dielectric properties of the microfluidic chip components that highly influence the internal electromagnetic field and energy dissipation, are studied systematically for their effects on sensing and heating efficiency. The results provide important findings and understanding on the integrated device operation and optimization strategies. Next, driven by the need for on-demand, rapid mixing inside droplets in many applications such as biochemical assays and material synthesis, a microwave-based microfluidic mixer is developed. Rapid mixing in droplets can be achieved within each half of the droplet, but not the entire droplet. Cross-center mixing is still dominated by diffusion. In this project, the microwave mixer, which works essentially as a resonator, accumulates an intensive, nonuniform electromagnetic field into a spiral capacitive gap (around 200 μm) over which a microchannel is aligned. As droplets pass by the gap region, they receive spatially non-uniform energy and thus have non-uniform temperature distribution, which induces non-uniform Marangoni stresses on the interface and thus three-dimensional (3D) chaotic motion inside the droplet. The 3D chaotic motion inside the droplet enables fast mixing within the entire droplet. The mixing efficiency is evaluated by varying the applied power, droplet length and fluid viscosity. In spite of various existing thermometry methods for microfluidic applications, it remains challenging to measure the temperature of individual fast moving droplets because they do not allow sufficient exposure time demanded by both fluorescence based techniques and resistance temperature detectors. A microwave thermometry method is thus developed here, which relies on correlating fluid temperature with the resonance frequency and the reflection coefficient of the microwave sensor, based on the fact that liquid permittivity is a function of temperature. It is demonstrated that the sensor can detect the temperature of individual droplets with ±1.2 °C accuracy. At the final part of the thesis, I extend my platform technology further to applications such as disease diagnosis and drug delivery. First, I develop a microfluidic chip for controlled synthesis of poly (acrylamide-co-sodium acrylate) copolymer hydrogel microparticles whose structure varies with temperature, chemical composition and pH values. This project investigates the effects of monomer compositions and cross-linker concentrations on the swelling ratio. The results are validated through the Fourier transform infrared spectra (FTIR), SEM and swelling test. Second, a preliminary study on DNA hybridization detection through microwave sensors for disease diagnosis is conducted. Gold sensors and biological protocols of DNA hybridization event are explored. The event of DNA hybridization with the immobilized thiol-modified ss-DNA oligos and complimentary DNA (c-DNA) are monitored. The results are promising, and suggests that microwave integrated Lab-on-a-chip platforms can perform disease diagnosis studies

Selected Papers from the 1st International Electronic Conference on Biosensors (IECB 2020)

The scope of this Special Issue is to collect some of the contributions to the First International Electronic Conference on Biosensors, which was held to bring together well-known experts currently working in biosensor technologies from around the globe, and to provide an online forum for presenting and discussing new results. The world of biosensors is definitively a versatile and universally applicable one, as demonstrated by the wide range of topics which were addressed at the Conference, such as: bioengineered and biomimetic receptors; microfluidics for biosensing; biosensors for emergency situations; nanotechnologies and nanomaterials for biosensors; intra- and extracellular biosensing; and advanced applications in clinical, environmental, food safety, and cultural heritage fields

Nanotechnology enabled microfluidics/Raman spectroscopy systems for bio applications

The vision for this PhD research project was born out of a desire to study the in situ behaviour of suspended nano-materials; specifically, implementing a Raman microscopy system for investigating suspended materials in the microfluidic environment. The author developed a set of innovative research goals to achieve this vision, which include: (1) forming a suitable microfluidic system which can apply controlled forces onto the suspended materials on demand, (2) implementing Raman microscopy to study the behaviour of particles under the influence of such forces while inside the microfluidic system and (3) incorporating the developed microfluidic system for investigating suspended materials of low concentration, including biological cells and surface-enhanced Raman scattering studies. The author implemented the research in three distinct stages such that the work in earlier stages could provide the platform for the future work. In the first stage, the author designed a microfluidic dielectrophoresis platform consisting of curved microelectrodes. This platform was integrated with a Raman microscopy system for creating a novel system capable of detecting suspended particles of various types and spatial concentrations. The system was benchmarked using polystyrene and tungsten trioxide suspended particles, and the outcomes of this novel integrated system showed its strong potential for the determination of suspended particles types and their direct mapping, with several unique advantages over conventional optical systems. In the second stage of this research, the author developed a novel microfluidic-DEP system that could manipulate suspended silver nanoparticles’ spacing in three dimensions. Silver nanoparticles are capable of producing strong surface enhanced Raman scattering (SERS) signals, allowing the Raman system to detect very low concentrations of suspended analytes. DEP provided facile control of the positions and spacings of the suspended silver nanoparticles, and allowed for the creation of SERS hot-spots. The system was studied to determine the optimum DEP and microfluidic flow parameters for generating SERS, and the author was able to demonstrate this as a reversible process. This stage of the research used dipicolinic acid as the target analyte, and the system was demonstrated to have detection limits as small as ~1 ppm concentration levels. In the third stage, the microfluidic-DEP platform was used for trapping and isolating yeast cells. Silver nanoparticles were again used for SERS applications. The trapped cells were interrogated by the Raman system in order to obtain deeper understandings of cells functionalities and their communications under various physical conditions: live vs. dead and isolated vs. grouped. Live vs. dead experiments were conducted as a benchmark, to observe whether SERS is capable of differentiating cells based on the life condition. The research was expanded to study cells that were isolated from one another, and compared those Raman signatures to those from cells in grouped clusters. The author was able to extract unique information from such studies, including the importance of glycine, or proteins with glycine subunits, in the proliferation of yeast cells. The developed system showed great potential as a universal platform for the in situ study of cells, their communications and functionalities

On-chip polarimetry for high-throughput screening of nanoliter and smaller sample volumes

A polarimetry technique for measuring optical activity that is particularly suited for high throughput screening employs a chip or substrate (22) having one or more microfluidic channels (26) formed therein. A polarized laser beam (14) is directed onto optically active samples that are disposed in the channels. The incident laser beam interacts with the optically active molecules in the sample, which slightly alter the polarization of the laser beam as it passes multiple times through the sample. Interference fringe patterns (28) are generated by the interaction of the laser beam with the sample and the channel walls. A photodetector (34) is positioned to receive the interference fringe patterns and generate an output signal that is input to a computer or other analyzer (38) for analyzing the signal and determining the rotation of plane polarized light by optically active material in the channel from polarization rotation calculations