Abstract-A Terahertz-Microfluidic Chip with a Few Arrays of Asymmetric Meta-Atoms for the Ultra-Trace Sensing of Solutions

Kazunori Serita,  Hironaru Murakami, Iwao Kawayama, Masayoshi Tonouchi

https://www.mdpi.com/2304-6732/6/1/12/htm

Biosensing with terahertz (THz) waves has received large amounts of attention due to its potential to detect the functional expression of biomolecules in a label-free fashion. However, many practical challenges against the diffraction limit of THz waves and the strong absorption of THz waves into polar solvents still remain in the development of compact biosensors. Here, we present a non-linear, optical, crystal-based THz-microfluidic chip with a few arrays of asymmetric meta-atoms, an elementary unit of metamaterials, for the measurement of trace amounts of solution samples. A near-field THz emission source, that is locally generated in the process of optical rectification at a fs (femtosecond) laser irradiation spot, induces a sharp Fano resonance and modifies the resonance frequency of the meta-atoms when the channel is filled with solution samples of different concentrations. Using this chip, we successfully detected minute changes in the concentration of trace amounts of mineral water and aqueous sugar solutions by monitoring the shift in the resonance frequency. A higher detectable sensitivity of 1.4 fmol of solute in a 128 pL volume of solution was achieved. This was an improvement of one order of magnitude in the sensitivity compared to our previous experiment.

Abstract-Recent advances in the Metamaterial-inspired biosensors

Ahmed Salim, 

Sungjoon Lim

The most recent metamaterial-inspired biosensors have been reviewed by dividing GHz and THz domains.

https://www.sciencedirect.com/science/article/pii/S0956566318304639

Metamaterials (MM)-inspired microwave biosensors are a valuable addition to the field of diagnostic approaches and prognostic tools. The fundamental principle behind these biosensors is unique dielectric signatures corresponding to healthy/diseased tissues. Relying on nonionizing radiation and offering an increased resolution with accuracy comparable to that of ultrasound devices, they are an attractive solution for noninvasive and label-free biosensing applications. High-quality-factor MM-inspired resonators are integrated with microfluidics to accelerate the lab-on-chip and point-of-care diagnostic approaches owing to the small detection volume and overall compact size of these devices. A variety of biomolecular detection, glucose detection and hyperthermia treatment using state-of-the-art MM-inspired biosensors have been discussed. Optical transduction techniques (e.g., surface plasmon resonance) which enhance the sensitivity in terms of limit-of-detection and resolution, have also been outlined. Utilization of microwave biosensors as therapeutic agents is at its initial stages owing to lack of required sensitivity and reliability in recently proposed MM-inspired biosensors

Sensing Method Could Detect Cancer & Diabetes Earlier

https://www.azosensors.com/news.aspx?newsID=12364

By Louise SaulFeb 27 2018

Scientists at Osaka University have developed a new sensing method, which has the potential to detect both cancer and diabetes earlier than ever possible before.

The use of terahertz (THz) waves for biosensing is currently of great interest to scientists and is receiving considerable attention. The team in Osaka have developed a THz microfluidic chip with arrays of meta-atoms that can be used for microanalysis. It is highly sensitive, and label-free, for measurements of biological samples. The new chip can detect trace amounts of known materials and minimal changes in optical constants. The research was published in APL Photonics.

THz radiation lies in between infrared and microwave radiation. The terahertz region provides essential information that clarifies biological reaction dynamics, including the hydrogen bonds and hydrophobic interactions, and it is at comparatively lower energy than that of infrared absorption. They can detect molecular vibrations and rotations, without using labels that can affect the properties of the substances of interest.

Microfluidic devices only need a very low sample volume for measurements, so they are seen as very promising analytical systems. The group from Osaka University have now developed a nonlinear optical crystal (NLOC) chip, combining the THz waves with a microfluidic device, meaning that the proximity of the THz wave source and the solution of interest in a microchannel can be combined.

The early and rapid detection of common diseases is set to be a major application of the technique. There is the potential that cancer, diabetes, and even the influenza virus would be able to be detected with very small volumes of bodily fluid. The sample volume needed allows for the patients to have their pain and discomfort from exploratory procedures reduced. The new technique also has another major benefit of allowing living cells to be analyzed in a non-destructive way.

The technique has been limited previously due to the diffraction limit of THz waves and their strong absorption by water. The new research has shown that THz time-domain spectroscopy (THz-TDS) is a technique that can give new insights into the functional expression and structural change of water, biopolymers, and DNA. When THz methods can be combined with microfluidic devices, it allows for the development of compact THz sensors, as well as new analytical THz devices that have a higher sensitivity.

Using our technique, we have been able to detect solution concentrations of several femtomoles in volumes of less than a nanoliter. Such high-sensitivity detection without the need for labeling moieties has great potential for future low-invasivity clinical techniques.

Professor Masayoshi Tonouchi, Professor of the Tonouchi lab at Osaka University

The sensor chip compared frequency shifts resulting from the presence of ions to those of pure water to analyze mineral concentrations. The chip was tested by using both distilled water and commercial mineral water, and when observing the amount of shift from the resonance frequency of pure water, they found that the solute can be detected with a sensitivity of up to 31.8 femtomoles. The sensitivity of the technique is comparable to standard fluorescence systems, but it can be improved by further optimization of the structure and the arrangement of meta-atoms. Altering the channel depth to reduce the THz absorption into the water can also optimize results.

Achieving high sensitivity without the need for a high-power optical or THz source, near-field probes or prisms opens up a number of possibilities.

Kazunori Serita, Co-Author

Serita explains how their potential findings could lead to rapid detection and compact device designs. He believes the results will lead to an acceleration in the development of THz lab-on-a-chip devices. The new adaptable technology has the potential to have a wide range of uses across many areas, including biochemistry, analytical chemistry, cell biology, and clinical medicine. The low cost of NLOC chips would also allow for disposable and compact sensors, which would be highly beneficial to both fields of medicine and biology.

Thumbnail Image Credit: GiroScience/Shutterstock

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Microanalysis of biological samples for early disease detection

A schematic drawing of solution measurement by using fabricated terahertz microfluidic chip. The chip consists of a local THz radiation point source, a single microchannel and a few arrays of split ring resonators. The THz waves are generated by irradiating laser beam from the backside of the crystal and efficiently interact with the solution flowing inside the microchannel. The optical microscope image of fabricated microfluidic chip is also shown.

Credit: Osaka University

https://www.sciencedaily.com/releases/2018/02/180219103211.htm

The use of terahertz (THz) waves for biosensing is currently receiving considerable attention. THz waves are able to detect molecular vibrations and rotations, without using labels that can affect the properties of the substances of interest.

However, until now, the diffraction limit of THz waves and their strong absorption by water have constrained this technique.

Microfluidic devices are also promising analytical systems because of the low sample volumes needed for sample measurement.

A group of researchers from Osaka University has now developed a nonlinear optical crystal (NLOC) chip, which combines THz waves with a microfluidic device, utilizing the close proximity of the THz wave source and the solution of interest in a microchannel. Their work was published in APL Photonics.

"Using our technique, we have been able to detect solution concentrations of several femtomoles in volumes of less than a nanoliter," corresponding author Masayoshi Tonouchi says. "Such high-sensitivity detection without the need for labelling moieties has great potential for future low-invasivity clinical techniques."

Early and rapid detection of a number of common diseases is expected to be one of the major applications of the technique. Cancer, diabetes, and the influenza virus could potentially be detected with only very small volumes of bodily fluid, reducing the pain and discomfort of numerous exploratory procedures for patients. In addition, the technique allows living cells to be analyzed in a non-destructive way, which has numerous potential benefits in research.

The developed NLOC chip is able to locally generate the THz radiation in close proximity to the single microchannel device, improving efficiency. The sensor chip was used to analyze mineral concentrations by comparing frequency shifts resulting from the presence of ions to those of pure water. Using this technique they determined a sensitivity of 31.8 femtomoles.

"Achieving high sensitivity without the need for a high-power optical or THz source, near-field probes or prisms, opens up a number of possibilities," lead author Kazunori Serita says. "We are very excited about the potential of our findings to lead to rapid detection and compact device design. In particular, we see our results accelerating the development of THz lab-on-a-chip devices."

This highly adaptable technology is likely to ripple out into many areas of analytical and biochemistry, as well as cell biology, and clinical medicine.

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Story Source:

Materials provided by Osaka University. Note: Content may be edited for style and length.

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Journal Reference:

1. Kazunori Serita, Eiki Matsuda, Kosuke Okada, Hironaru Murakami, Iwao Kawayama, Masayoshi Tonouchi. Invited Article: Terahertz microfluidic chips sensitivity-enhanced with a few arrays of meta-atoms. APL Photonics, 2018; 3 (5): 051603 DOI: 10.1063/1.5007681

Thin, flat meta-lenses with tunable features developed

Korean-UK group makes “credit card-thick” metasurface lenses from graphene and gold, to focus terahertz beams.  

http://optics.org/news/8/11/44?webSyncID=776b28d9-cc7c-7cae-388c-544e71035da4&sessionGUID=1ccd516a-90a0-0b40-8604-5dc1a6e754b4&_ga=2.190507624.2107229762.1512083484-178576186.1505831485

                                                                                      

Thinner, flatter: Conventional lens and metalens.

Credit card-thick, flat lenses with tunable features based on graphene and gold have been developed by a partnership of Korean- and UK-based researchers. They say that such optical devices “could become optical components for advanced applications, such as amplitude-tunable lenses, lasers (so-called vortex phase plates), and dynamic holography.”

The scientists work at the Center for Integrated Nanostructure Physics, in the Institute for Basic Science, the Korea Advanced Institute of Science and  Technology and the University of Birmingham. The work has been published in Advanced Optical Materials.

The paper describes the properties of a newly-developed metasurface (a 2D material that can control the electric and magnetic components of light and direct them as wanted) which works as a convex lens. It is made of a gold sheet pierced with micrometer-sized U-shaped holes and covered with graphene.

Conventional solid convex lenses concentrate light on a spot. Similarly with this metasurface, the pattern of apertures of the metalenses focusing the incoming beam. In addition, the microholes can also change light polarization. For example, the metalens can convert the left-circular polarization wave to right-circular polarization (clockwise).

Graphene advantages

The researchers have achieved a conversion rate of 35%. They comment that converting circular polarization could be useful in a number of fields, for example biosensing and telecommunications. To be able to control a range of optical properties, the scientists took advantage of graphene’s unique electronic features and used them to tune the output beam’s intensity or amplitude. The scientists liken graphene’s function to the exposure operation of a camera.                                                                                                                   

        Metalenses’ features.

In the case of the camera, a mechanical control allows a certain shutter’s opening time and size to determine the amount of light entering the instrument. The metalens instead regulates exposure via an electric tension applied to the graphene sheet, without the need for bulky components. When voltage is applied to the graphene layer, the output beam becomes weaker.

'Very sensitive'

“Using metalenses, you can make microscopes, cameras, and tools used in very sensitive optical measurements, much more compact,” clarifies Teun-Teun Kim, lead author of the study.

The metalenses were designed specifically for terahertz radiation. This radiation can pass through some materials such as fabrics and plastics, but at a shorter depth than microwave radiation. For this reason it is employed for surveillance and security screening.

Kim added, “While conventional optical lenses have a thickness of several centimeters to several millimeters, this metalens is just a few tens of micrometers thick. The intensity of the focused light can be effectively controlled and it could find useful applications in ultra-small optical instruments.”

Abstract-Electrical 2π phase control of infrared light in a 350-nm footprint using graphene plasmons

• Achim Woessner,
• Yuanda Gao,
• Iacopo Torre,
• Mark B. Lundeberg,
• Cheng Tan,
• Kenji Watanabe,
• Takashi Taniguchi,
• Rainer Hillenbrand,
• James Hone,
• Marco Polini
• & Frank H. L. Koppens
• 
  

http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2017.98.html

Modulating the amplitude and phase of light is at the heart of many applications such as wavefront shaping, transformation optics, phased arrays, modulators and sensors. Performing this task with high efficiency and small footprint is a formidable challenge. Metasurfaces and plasmonics are promising, but metals exhibit weak electro-optic effects. Two-dimensional materials, such as graphene, have shown great performance as modulators with small drive voltages. Here, we show a graphene plasmonic phase modulator that is capable of tuning the phase between 0 and 2π in situ. The device length of 350 nm is more than 30 times shorter than the 10.6 μm free-space wavelength. The modulation is achieved by spatially controlling the plasmon phase velocity in a device where the spatial carrier density profile is tunable. We provide a scattering theory for plasmons propagating through spatial density profiles. This work constitutes a first step towards two-dimensional transformation optics for ultracompact modulators and biosensing.