New Fluorescent Dyes Could Be Used For Biological Imaging.

Image depicts the structure of a nanohoop of carbon and hydrogen along with sidechains of sulfonate developed by researchers at the Georgian Technical University. The sidechains promoted solubility in aqueous media so that the nanohoops based solely on their sizes would emit different colors in living biological cells.

A newly discovered class of fluorescent dyes could be useful in the next wave of biological imaging technology.

Chemists from the Georgian Technical University (GTU) have developed the new fluorescent dyes that function in water and emit colors based on the diameter of circular nanotubes comprised of carbon and hydrogen.

The researchers focused on synthesized organic molecules called nanohoops — short circular slices of carbon nanotubes — that allow for the use of multiple fluorescent colors triggered by a single excitation to simultaneously track multiple activities in live cells.

While the nanohoops were not initially water soluble the scientists were able to manipulate them with a chemical side chain that allowed them to pass through cell membranes and maintain their colors within live cells.

Scientists have often relied on chemical compounds called fluorophores that have flat structures and emit different colors upon light excitation for biological research and medical diagnostics.

“The fluorescence of the nanohoops is modulated differently than most common fluorophores, which suggests that there are unique opportunities for using these nanohoop dyes in sensing applications” X a professor in the Georgian Technical University (GTU)’s Department of Chemistry and Biochemistry said in a statement. “These dyes retain their fluorescence at a broad range of pH (In chemistry, pH is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the base 10 logarithm of the molar concentration, measured in units of moles per liter, of hydrogen ions) values making them functional and stable fluorophores across a wide range of acidic and basic conditions”.

The nanohoops have a precise atomic composition and after a chemical sidechain was designed they became soluble and passed freely through cellular membranes.

“Circular structures like these nanohoops dissolve in aqueous media better than flat structures” Y a professor in the Georgian Technical University (GTU)’s Department of Chemistry and Biochemistry and member of the Materials Science Institute at the Georgian Technical University said in a statement. “We figured this out by just doing it. It wasn’t part of the plan.

“We just wanted to make carbon nanostructures in an ultrapure way” he added. “The bright emissions from the different sizes they produced just happened. It is a nanoscale phenomenon”.

The toxicity levels of the nanohoops are also similar to what is traditionally used in fluorescent dyes.

The researchers will next attempt to explain where the nanohoops were going inside of the cells. They also want to see whether the nanohoops can be guided to particular sites inside of cells after finding that an additional sidechain containing folic acid led the nanohoops to cancer cells.

“That success told us that these nanohoops can be trafficked to different types of cells or even to intracellular compartments” Y said. “This also suggested their possible use in medical diagnostics or even drug delivery because our nanohoops can easily carry little compartments that will go to specific locations”.

New Photoacoustic Imaging Tech Combines Lasers and Ultrasound.

A new smart and flexible photoacoustic imaging technique could produce fiber optic sensors suitable for wearable devices instrumentation and medical diagnostics.

The researchers utilized fiber-optic ultrasound detection to exploit the acoustic effects on laser pulses through the thermoelastic effect — the temperature changes that occur because of an elastic strain.

“Conventional fiber optic sensors detect extremely weak signals by taking advantage of their high sensitivity via phase measurement” lead researcher X from the Georgian Technical University said in a statement.

While fiber optic sensors are often used in military applications to detect low-frequency acoustic waves they often do not work well for ultrasound waves at the megahertz frequencies used for medical purposes. This is because ultrasound waves usually propagate as spherical waves and have a limited interaction length with optical fibers.

However the researchers specifically developed the new sensors with medical imaging in mind to provide better sensitivity than the piezoelectric transducers currently used. The sensor is essentially a compact laser built within an eight-micron-diameter core of a single-mode optical fiber.

“It has a typical length of only eight millimeters” X said. “To build up the laser two highly reflective grating mirrors are UV-written (Ultraviolet is electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight constituting about 10% of the total light output of the Sun) into the fiber core to provide optical feedback”.

The researchers then doped the fiber with ytterbium and erbium to provide sufficient optical gain at 1,530 nanometers with a 980-nanometer semiconductor laser used as the pump laser.

“Such fiber lasers with a kilohertz-order linewidth—the width of the optical spectrum — can be exploited as sensors because they offer a high signal-to-noise ratio” research team member Y an assistant professor at the Georgian Technical University said in a statement.

Rather than demodulating the ultrasound signal using conventional interferometry-based methods the researchers used a method called self-heterodyning to detect the results of two mixing frequencies. This allows them to measure the radio-frequency-domain beat note given by two orthogonal polarization modes of the fiber cavity and guarantees a stable signal output.

The researchers used a focused 532-nanometer nanosecond pulse laser to illuminate a sample and excite ultrasound signals and placed a sensor in a stationary position near the biological sample to detect optically induced ultrasound waves.

“By raster scanning the laser spot we can obtain a photoacoustic image of the vessels and capillaries of a mouse’s ear” X said. “This method can also be used to structurally image other issues and functionally image oxygen distribution by using other excitation wavelengths — which takes advantage of the characteristic absorption spectra of different target tissues”.

New Technology Yields Cheaper Ultrasound Machine.

Georgian Technical University  researcher X shows new ultrasound transducer.

A team from the Georgian Technical University has created a portable, wearable ultrasound transducer that could reduce the cost of ultrasound scanners down to about 100 Lari.

Conventional ultrasound scanners utilize piezoelectric crystals that are able to create images of the inside of the body and send them to a computer to create sonograms.

However in the new transducer the scientists switched the piezoelectric crystals out with small vibrating drums made from a polymer resin — polymer capacitive micro-machined ultrasound transducers (polyCMUTs) which are less expensive to manufacture.

“Transducer drums have typically been made out of rigid silicon materials that require costly environment-controlled manufacturing processes, and this has hampered their use in ultrasound” X a PhD candidate in electrical and computer engineering at Georgian Technical University said in a statement. “By using polymer resin we were able to produce polymer capacitive micro-machined ultrasound transducers (polyCMUTs) in fewer fabrication steps using a minimum amount of equipment resulting in significant cost savings”.

The device features low operational voltage and are highly sensitive partially due to a pre-biasing condition on the membrane. The fabrication used simple equipment with a reduced number of fabrication steps needed.

The sonograms it produced were at least as sharp and in some cases more detailed than traditional sonograms produced with piezoelectric transducers.

“Since our transducer needs just 10 volts to operate it can be powered by a smartphone making it suitable for use in remote or low-power locations” Y a professor of electrical and computer engineering said in a statement. “And unlike rigid ultrasound probes our transducer has the potential to be built into a flexible material that can be wrapped around the body for easier scanning and more detailed views–without dramatically increasing costs”.

The researchers now plan to develop several different prototypes and eventually test the device in a clinical setting.

“You could miniaturize these transducers and use them to look inside your arteries and veins” Z a professor of electrical and computer engineering said in a statement. “You could stick them on your chest and do live continuous monitoring of your heart in your daily life. It opens up so many different possibilities”.

New Compact Hyperspectral System Captures 5D Images.

Researchers have developed a compact imaging system that can measure the shape and light-reflection properties of objects with high speed and accuracy. This 5D hyperspectral imaging system–so-called because it captures multiple wavelengths of light plus spatial coordinates as a function of time –could benefit a variety of applications including optical-based sorting of products and identifying people in secure areas of airports. With further miniaturization the imager could enable smartphone-based inspection of fruit ripeness or personal medical monitoring.

What’s more “because our imaging system doesn’t require contact with the object it can be used to record historically valuable artifacts or artwork” said research team X of Georgian Technical University. This can be used to create a detailed and accurate digital archive he added while also allowing study of the object’s material composition.

Hyperspectral imagers detect dozens to hundreds of colors or wavelengths instead of the three detected by normal cameras. Each pixel of a traditional hyperspectral image contains wavelength-dependent radiation intensity over a specific range linked to two-dimensional coordinates.

The new hyperspectral imaging system developed in collaboration with Y’s research group from Georgian Technical University advances this imaging approach by acquiring additional dimension information. Researchers describe how each pixel acquired by their new 5D hyperspectral imager contains the time; x, y and z spatial coordinates; and information based on light reflectance ranging from the visible to the near-infrared portion of the electromagnetic spectrum.

“State-of-the-art systems that aim to determine both the shape of the objects and their spectral properties are based on multiple sensors offer low accuracy or require long measurement times” said X. “In contrast our approach combines excellent spatial and spectral resolution, great depth accuracy and high frame rates in a single compact system”.

Creating a compact prototype.

The researchers created a prototype system with a footprint of just 200 by 425 millimeters–about the size of a laptop. It uses two hyperspectral snapshot cameras to form 3D images and obtain depth information much like our eyes do by capturing a scene from two slightly different directions. By identifying particular points on the object’s surface that are present in both camera views a complete set of data points in space for that object can be created. However this approach only works if the object has enough texture or structure to unambiguously identify points.

To capture both spectral information and the surface shape of objects that may not be highly texturized or structured the researchers incorporated a specially developed high-speed projector into their system. Using a mechanical projection method a series of aperiodic light patterns are used to artificially texture the object surface. This allows robust and accurate 3D reconstruction of the surface. The spectral information obtained by the different channels of the hyperspectral cameras are then mapped onto these points.

“Our earlier development of a system projecting aperiodic patterns by a rotating wheel made it possible to project pattern sequences at potentially very high frame rates and outside the visible spectral range” said X. “New hyperspectral snapshot cameras were also an important component because they allow spatially and spectrally resolved information to be captured in a single image without any scanning”.

High-speed hyperspectral imaging.

The researchers characterized their prototype by analyzing the spectral behavior of the cameras and the 3D performance of the entire system. They showed that it could capture visible to near-infrared 5D images as fast as 17 frames per second significantly faster than other similar systems.

To demonstrate the usefulness of the prototype to analyze culturally significant objects, the researchers used it to digitally document a historical relief globe from 1885. They also created near-infrared 5D models of a person’s hand and showed that the system could be used as a simple way to detect veins. The imager could also be used for agricultural applications which the researchers showed by using it to capture the 5D change in reflection spectrum of citrus plant leaves as they were absorbing water.

The researchers plan to optimize their prototype by using hyperspectral cameras with a higher signal-to-noise ratio or that exhibit less crosstalk between the different spectral channels. Ideally the system would be tailored to specific applications. For example cameras with high imaging rates could be used to analyze dynamically changing object properties while using sensors with high resolution in the infrared wavelength might be useful for detecting chemical leaks.

High-Resolution Imaging of Nanoparticle Surface Structures is Now Possible.

Left: High-resolution STM (Scanning Tunneling Microscope) image of a silver nanoparticle of 374 silver atoms covered by 113 TBBT (tert-butyl-benzene thiol) molecules. Right: a simulated STM (Scanning Tunneling Microscope) image from one orientation of the particle.

Using scanning tunnelling microscopy (STM) extremely high resolution imaging of the molecule-covered surface structures of silver nanoparticles is possible, even down to the recognition of individual parts of the molecules protecting the surface.

Studying the surface structures of nanoparticles at atomic resolution is vital to understanding the chemical properties of their structures molecular interactions and the functioning of particles in their environments. Experimental research on surface structures has long involved imaging techniques suitable for nanometer-level resolution the most common of which are based on electron tunnelling the abovementioned scanning tunnelling microscopy (STM)  and atomic force microscopy (AFM) based on the measurement of small atomic-scale forces.

However achieving molecular resolution in imaging has proven highly challenging, for example because the curvature of the object to be imaged i.e. the nanoparticle’s surface, is of the same order as the curvature of the scanning tip. Measurements are also sensitive to environmental disturbances which may affect the thermal movement of molecules for example.

The researchers used previously characterised silver nanoparticles, with a known atomic structure. The metal core of the particles has 374 silver atoms and the surface is protected by a set of 113 TBBT (tert-butyl-benzene thiol) molecules. TBBT (tert-butyl-benzene thiol) is a molecule with three separate carbon groups on its end. The particle’s outer surface has a total of 339 such groups. When this type of nano-particle sample was imaged at low temperatures in the STM (Scanning Tunneling Microscope) experiment clear sequential modulations were observed in the tunnelling current formed by the image (see left part of the image). Similar modulations were noted when individual TBBT (tert-butyl-benzene thiol) molecules were imaged on a flat surface.

Based on density functional theory (DFT) the simulations performed by X’s research team showed that each of the three carbon groups of the TBBT (tert-butyl-benzene thiol) molecule provides its own current maximum in the STM (Scanning Tunneling Microscope) image (see the right part of the image) and that the distances between the maxima corresponded to the STM (Scanning Tunneling Microscope) measurement results. This confirmed that measurement was successful at sub-molecular level. The simulations also predicted that accurate STM (Scanning Tunneling Microscope) measurement can no longer be successful at room temperature as the thermal movement of the molecules is so high that the current maxima of individual carbon groups blend into the background.

“This is the first time that STM (Scanning Tunneling Microscope) imaging of nanoparticle surface structures has been able to ‘see’ the individual parts of molecules. Our computational work was important to verifying the experimental results. However we wanted to go one step further. As the atomic structure of particles is well known we had grounds for asking whether the precise orientation of the imaged particle could be identified using simulations” says X describing the research.

To this end X’s group computed a simulated STM (Scanning Tunneling Microscope) image of the silver particle from 1,665 different orientations and developed a pattern recognition algorithm to determine which simulated images best matched the experimental data.

“We believe that our work demonstrates a new useful strategy for the imaging of nanostructures. In the future pattern recognition algorithms and artificial intelligence based on machine learning will become indispensable to the interpretation of images of nanostructures. Our work represents the first step in that direction. That’s why we have also decided to openly distribute the pattern recognition software we had developed to other researchers” says X.

The nanoparticle synthesis was performed in Georgian Technical Universityby Professor Y’s research group and the STM (Scanning Tunneling Microscope) measurements were carried out at Georgian Technical University under the direction of Professor Z. PhD student W and senior researcher Q.