Prashant Jain

Nano Letters

Integrated Nanogap Platform for Sub-Volt Dielectrophoretic Trapping and
Real-Time Raman Imaging of Biological Nanoparticles

Introduction

At the University of Minnesota, the lab of Sang-Hyun Oh is working on using nanotechnology and optical methods to advance analytical and sensing method in particular for bio and life science applications. They developed a high-resolution micro Raman spectroscopy system for fast measurements (the researchers talk about a factor 100x advantage in speed over similar systems) where the biological nano particles do not have to be labelled.

The team build microscopic traps for the nanoparticles using an effect called dielectrophoresis on plasmonic nanostructures. The traps capture the bio structures along a small gap that is imaged to a spectrograph so Raman spectra of all captured particles can be collected simultaneously. In addition to this multiplexing advantage gold nanoparticles are used to create a SERS surface enhanced Raman effect to obtain even stronger signals.

for real time monitoring of bio particles in cells. Having such a system will improve capabilities for cell and biological analysis and could lead to development of more capable biosensors.

Guowei Yang, Sun Yat-sen

Science Advances

The optical duality of tellurium nanoparticles for broadband solar energy
harvesting and efficient photothermal conversion

Introduction

The conversion of solar energy is an area of large impact for nanotechnologies. Several spectroscopic techniques are used to probe the properties and applications of nanoparticles. Researchers from China recently published an article about Tellurium nanoparticles for conversion of solar energy. They employ Raman spectroscopy, UV-VIS absorption spectroscopy and dark field scattering spectroscopy to understand the particles properties. The research is featured on Laser Focus World with the article below:

For at least the last decade, “solar thermal” technologies, in which sunlight is used to convert water into steam that runs electric turbines or performs desalination, has been great for the investment community. About six years ago, nanoparticles started to get into the solar-thermal game when Rice University researchers added some nanoparticles to cold water and were able to make steam when they exposed the combination to sunlight.

Since then, a lot of work in what is now termed photothermal conversion has turned to the field of plasmonics, which exploits the wave of electrons that is produced when photons strike a metallic surface. However, producing plasmonic nanostructures is certainly not as straightforward as just adding some nanoparticles to water.

Now, researchers in China have combined the ease of adding nanoparticles to water with plasmonics to create a photothermal conversion process that exceeds all plasmonic or all-dielectric nanoparticles previously reported. Researchers at Sun Yat-sen University (Guangzhou, China) demonstrated in the journal Science Advances what they claim is the first material that simultaneously has both plasmonic-like and all-dielectric properties when exposed to sunlight.

The key to achieving this combination is the use of tellurium (Te) nanoparticles, which have unique optical duality, according to G. W. Yang, professor at Sun Yat-sen University and coauthor of the research.

By dispersing these nanoparticles into water, the water evaporation rate is improved by a factor of three under solar radiation. This makes it possible to increase the water temperature from 29 degrees to 85 degrees Celsius within 100 seconds.

“The Te nanoparticles perform like a plasmonic nanoparticle when it is smaller than 120 nanometers [nm] and then as a high-index all-dielectric nanoparticle when those nanoparticles are larger than 120 nm,” said Yang. The Te nanoparticles are able to achieve this duality because they have a wide size distribution (from 10 to 300 nm). This enhanced absorption can cover the whole solar radiation spectrum.

Another property of the Te nanoparticle is that when it is excited by sunlight, the excitation energy is transferred entirely to the carriers (electrons and holes). This pushes the carriers out of equilibrium and into special states of momentum with higher temperatures.”

Yang explains that as the system evolves toward equilibrium, these carriers relax. As the carriers scatter, it leads to a phenomenon known as Coulomb thermalization, which forms a hot gas of thermalized carriers that couple with phonons and transfer their excess energy to the lattice. This results in the efficient heating of the Te nanoparticles.

For this approach to work for commercial desalination, Yang acknowledges that the current method of producing the Te nanoparticles with nanosecond laser ablation in liquid is limited. “Now, we are trying to prepare the Te nanoparticles by other methods,” he added. But because the Te nanoparticles have a unique optical duality, Yang envisions other applications for the technology. “We want to apply them in sensors or nanoantennas,” he said.

Harald Gießen

ACS

Electrochemistry on Inverse Copper Nanoantennas: Active Plasmonic
Devices with Extraordinarily Large Resonance Shift

Introduction

Prof. Harald Gießen’s group from the University of Stuttgart (Germany) is working on using photonics and nanotechnologies for new applications and devices. The researchers are looking at technologies to create displays operated by controlling plasmonic effects. Plasmonics deals with interactions of light with metallic nanostructures which can be designed to show strong reaction to light at very specific wavelength. For a dynamic, changeable display the position of these resonance wavelengths has to be controlled ideally by applying electrical voltage to the device. The researchers from Germany are creating devices based on thin Cu films with nanostructures etched into them immersed in an electrolyte solution. When applying a voltage, the Cu is electrochemically changed (oxidized or reduced) changing the color of light reflected from the device.

Hideaki Kano

Chemistry Letters

Ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS)
microspectroscopy using a CCD camera with an InGaAs image intensifier

Introduction

Researchers from Japan show the use of ICCD cameras with InGaAs intensifier for coherent anti-Stokes Raman scattering measurements. Unlike detection with conventional CCDs an ICCD is able to restrict signal collection to a single pulse of a high repetition rate excitation system

Tuan Vo-Dinh

Advanced Biomedical and Clinical Diagnostic and
Surgical Guidance Systems XVI

Surface-enhanced patially offset Raman spectroscopy (SESORS) for
biomedical applications

Introduction

A team from Duke University in the US is using Raman spectroscopy for sensing in biological tissue. Raman spectroscopy is being used for several applications in life sciences, the researchers mention cancer detection, inflammation monitoring and measurements of glucose levels as examples.

Yann Camenen

Scientific Reports

Spatially resolved determination of the electronic density and temperature by a visible spectro-tomography diagnostic in a linear magnetized plasma

Introduction

Understanding and controlling the behavior of plasmas has wide applications, from surface treatment and etching in material fabrication to research in propulsion and energy production. Plasmas are states of matter and are comprised of ions and free electrons. The electron temperature and density in a plasma are two important parameters when investigating plasmas.

Although there are electronic methods which measure the electron density and temperature (using so called Langmuir Probes), optical techniques, such as scattering measurements or optical emission spectroscopy, have the advantage of not needing physical probes that could perturb the plasma.

A team of researchers in France and Germany are now showing, via a paper published in Scientific Reports, how to perform optical measurements of a plasma with both spectral and spatial resolution. Their technique is called spectrotomography and uses line of sight emission spectroscopy. For line of sight measurements an optical fiber is positioned in the focus of a small lens so that the emission along the path is detected by the lens.

Tom Vosch

Scientific Reports

Photon Energy Dependent Micro-Raman Spectroscopy with a Continuum
Laser Source

Introduction

Raman spectroscopy typically requires precise, stable and narrow band light sources to produce well defined and sharp spectral features. Therefore, emission lines from gas lasers are often used as excitation sources. However, it can be important to continuously tune the excitation wavelength. For example, some materials like carbon nanotubes, quantum dots or nanowires show resonant Raman features where the scattering intensity is strongly enhanced when exciting at exactly the right wavelength. Also, some Raman features can show energy shifts when the excitation source energy changes like the so-called D band lines in graphene materials.

Jean-Sebastien Lauret

Nature Communications

Single photon emission from graphene quantum dots at room temperature

Introduction

Researchers around Jean-Sebastien Lauret from France are researching new materials like graphene and hybrid perovskites for use in quantum, plasmonics, nanophotonics and magnetometry applications. They have shown that graphene quantum dots can be used as high purity single photon sources. These special light sources are important for quantum research applications and quantum computers.

Arnab Deka

Journal of Applied Physics

Evaluation of beam divergence of a negative hydrogen ion beam using
Doppler shift spectroscopy diagnostics

Introduction