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Nanoscale chip system measures light from a single bacterial cell to enable portable chemical detection

05/09/2017

Further development could open door to on-chip biological and chemical sensing applications, e.g. detecting chemicals in real-time continuous flow systems and even in an open-air environment

Researchers at the Hebrew University of Jerusalem have created a nanophotonic chip system using lasers and bacteria to observe fluorescence emitted from a single bacterial cell. To fix the bacteria in place and to route light toward individual bacterial cells, they used V-groove-shaped plasmonic waveguides, tiny aluminum-coated rods only tens of nanometers in diameter. The novel system, described in the journal Nano Letters, paves the way for an efficient and portable on-chip system for diverse cell-based sensing applications, such as detecting chemicals in real-time.

The field of on-chip photonic devices for biological and chemical sensing applications presents many powerful alternatives to conventional analytical techniques for applications ranging from “lab on a chip” to environmental monitoring.  However, these sensing schemes rely mainly on off-chip detection and require a cumbersome apparatus, even when measuring only single cells. 

The Hebrew University team looked for ways to integrate all system components, including light sources and detectors, on-chip at the nanoscale. This would result in a lab-on-chip system that is small, portable and can perform sensing in real-time.

To achieve this, they molecularly engineered live bacteria that emit a fluorescent signal in the presence of target compounds. They paired these on-chip with a nanoscale waveguide, which not only served the purpose of guiding light, but also allowed mechanical trapping of individual bacteria within the V-groove.

In three different illumination conditions, they experimentally demonstrated the interrogation of an individual Escherichia coli bacterial cell using a nanoscale plasmonic V-groove waveguide. First, they measured the light emitted from a bacterium flowing on top of the nanocoupler in a liquid environment by allowing the fluorescence from the bacterium to be coupled directly into the waveguide through the nanocoupler. Next, a bacterium was mechanically trapped within the V groove waveguide and was excited by laser directly either from the top or through the nanocoupler. In all cases, significant fluorescence was collected from the output nano coupler into the detector.

The system worked well both in wet environments, where the bacteria are flowing on top of the waveguide, and in dry conditions, where the bacteria are trapped within the waveguide.

The research was led by Prof. Uriel Levy, Director of The Harvey M. Krueger Family Center for Nanoscience and Nanotechnology at the Hebrew University in collaboration with Prof. Shimshon Belkin, at the Hebrew University’s Alexander Silberman Institute of Life Sciences, who genetically engineered the bacterial sensors, and Prof. Anders Kristensen from the Danish Technical University, who was in charge of fabricating the V-groove waveguides. Prof. Levy is the Eric Samson Chair in Applied Science and Technology, and Prof. Belkin is the Ministry of Labor and Social Welfare Chair in Industrial Hygiene, at the Hebrew University.

Unlike the more traditional plasmonic waveguides consisting of either silver or gold, the choice of aluminum was instrumental for being able to guide the fluorescent light emitted from the bacteria all the way to the output nanocoupler. Furthermore, the waveguide dimensions allow for efficient mechanical trapping of the bacteria and the multimode characteristics may become instrumental in gathering more information, e.g., on the specific position and orientation of the bacteria.

The results provide a clear indication of the feasibility of constructing a hybrid bioplasmonic system using live cells. Future work will include the construction of waveguide network, diversifying the system to incorporate different types of bacterial sensors for the detection of various biological or chemical analytes.

The research is a collaboration between scientists at the Department of Applied Physics, the Rachel and Selim Benin School of Engineering and Computer Science, the Harvey M. Krueger Family Center for Nanoscience and Nanotechnology, and the Alexander Silberman Institute of Life Sciences, at the Hebrew University of Jerusalem, Israel; and the Department of Micro- and Nanotechnology, Technical University of Denmark, Kongens Lyngby, Denmark. Additional researchers include Oren Lotan, Jonathan Bar-David, Cameron L.C. Smith, and Sharon Yagur-Kroll.

Support: The researchers acknowledge financial support from the Danish International Network Programme (grant no. 1370-00124B) with Israel. Work in the Belkin lab was partially supported by the Minerva Center for Bio-Hybrid Complex Systems and by the NATO Science for Peace and Security Programme project 985042.

Citation: Oren Lotan, Jonathan Bar-David, Cameron L.C. Smith, Sharon Yagur-Kroll, Shimshon Belkin, Anders Kristensen, and Uriel Levy*. Nanoscale Plasmonic V-Groove Waveguides for the Interrogation of Single Fluorescent Bacterial Cells. Nano Lett., Article ASAP. DOI: 10.1021/acs.nanolett.7b02132. Publication Date (Web): August 3, 2017. http://pubs.acs.org/doi/10.1021/acs.nanolett.7b02132

Videos for Download:

  • http://media.huji.ac.il/new/multimedia/hu170816_nano1.mp4 -A pulsed laser illuminates bacteria which are trapped in a plasmonic waveguide (the waveguide is the dark rectangle seen in the film, bacteria are invisible). The presence of the bacteria causes light coupling into the waveguide. The light then propagates in the waveguide until it is coupled back out by the nano-mirrors and appears as bright pulses on the waveguides' ends.  (Photo credit: Hebrew University)
  • http://media.huji.ac.il/new/multimedia/hu170816_nano2.mp4 - A laser beam excites fluorescent bacteria swimming in a micro-fluidic device. The fluorescent light emitted by these bacteria radiates in all directions, and some of it couples into a plasmonic waveguide and is directed toward the waveguide's end. The direct fluorescence from the bacteria is seen most clearly on the right-hand side, while light which was coupled and propagated in the waveguide appears as a bright spot blinking on the left-hand side. The blinking is a result of the bacteria's changing position, and is correlated to the location of the bacteria relative to the nano-mirror in the waveguide's right side. (Photo credit: Hebrew University)

 

Nanoscale chip system measures light from a single bacterial cell to enable portable chemical detection
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Rapid 3D printing in water using novel hybrid nanoparticles holds promise for old and new industries

01/08/2017

A new type of nano-photoinitiator could lead to advanced biomedical and industrial materials, along with more environmentally friendly printing processes 

Researchers at the Hebrew University of Jerusalem’s Center for Nanoscience and Nanotechnology have developed a new type of photoinitiator for three-dimensional (3D) printing in water. These novel nanoparticles could allow for the creation of bio-friendly 3D printed structures, further the development of biomedical accessories and drive progress in traditional industries such as plastics.

3D printing has become an important tool for fabricating different organic based materials for a variety of industries. However, printing structures in water has always been challenging due to a lack of water soluble molecules known as photoinitiators -- the molecules that induce chemical reactions necessary to form solid printed material by light.

Now, writing in Nano Letters, Prof. Uri Banin and Prof. Shlomo Magdassi at the Hebrew University’s Institute of Chemistry describe an efficient means of 3D printing in water using semiconductor-metal hybrid nanoparticles (HNPs) as the photoinitiators.

3D printing in water opens exciting opportunities in the biomedical arena for tailored fabrication of medical devices and for printing scaffolds for tissue engineering. For example, the researchers envision personalized fabrication of joint replacements, bone plates, heart valves, artificial tendons and ligaments, and other artificial organ replacements.

3D printing in water also offers an environmentally friendly approach to additive manufacturing, which could replace the current technology of printing in organic based inks.

Unlike regular photoinitiators, the novel hybrid nanoparticles developed by Prof. Banin and Prof. Magdassi present tunable properties, wide excitation window in the UV and visible range, high light sensitivity, and function by a unique photocatalytic mechanism that increases printing efficiency while reducing the amount of materials required to create the final product. The whole process can also be used in advanced polymerization modalities, such as two photon printers, which allows it to produce high resolution features.

The research paper was featured in the American Chemical Society (ACS) Editor’s Choice, where ACS offers free public access to new research of importance to the global scientific community, based on recommendations by the scientific editors of ACS journals from around the world. ACS is the leading publisher of peer-reviewed research journals in the chemical and related sciences.

Prof. Magdassi is the Enrique Berman Chair in Solar Energy at the Hebrew University. Prof. Banin is the incumbent of the Alfred & Erica Larisch Memorial Chair at the Institute of Chemistry at the Hebrew University. 

Researchers involved in this study are affiliated with the Center for Nanoscience and Nanotechnology and The Institute of Chemistry at the Hebrew University of Jerusalem, in Israel, and the Institute of Systems Research and Department of Mechanical Engineering at the University of Maryland, in the United States.

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FUNDING: The work was financially supported in part by the Israel Science Foundation and in part by the National Research Foundation of Singapore under the CREATE program.

REFERENCE: Rapid Three-Dimensional Printing in Water Using Semiconductor-Metal Hybrid Nanoparticles as Photoinitiators. Amol Ashok Pawar, Shira Halivni, Nir Waiskopf, Yuval Ben-Shahar, Michal Soreni-Harari, Sarah Bergbreiter, Uri Banin, and Shlomo Magdassi. Nano Letters, June 15, 2017, doi: 10.1021/acs.nanolett.7b01870. Link: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.7b01870

PHOTO: http://media.huji.ac.il/new/photos/hu080117_3d.jpeg - Hybrid nanoparticles as photoinitiators. a. Electron microscope image of hybrid nanocrystal. The inset shows a schematic of semiconductor nanorod with a metal tip. b. Bucky ball structure produced by rapid 3D printing in water using HNPs as photoinitiators. c. Spiral printed with HNPs by two photon printer providing high resolution features. Adapted with permission from Pawar et al., Nano Lett. DOI: 10.1021/acs.nanolett.7b01870. Copyright (2017) American Chemical Society.

Rapid 3D printing in water using novel hybrid nanoparticles holds promise for old and new industries
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First look inside nanoscale catalysts shows ‘defects’ are useful

11/01/2017

Study in leading science journal Nature validates hypothesis that atomic defects are essential to catalytic reactivity

Using one of the world’s brightest light sources to peer inside some of the world’s smallest particles, scientists have confirmed a longstanding hypothesis: that atomic disorder or “defects” at the edges of nanoparticles is what makes them effective as chemical change agents.

The process by which a change agent, or catalyst, accelerates a chemical reaction is key to the creation of many materials essential to daily life, such as plastics, fuels and fertilizers. Known as catalysis, this process is a basic pillar of the chemical industry, making chemical reactions more efficient and less energy-demanding, and reducing or even eliminating the use and generation of hazardous substances.

Although catalysts have been used in industry for more than a century, scientists have yet to observe how their structure impacts their effectiveness as change agents. That’s because catalysts are typically tiny metallic nanoparticles made of precious metals such as Platinum, Palladium or Rhenium. The extreme smallness that makes nanoparticles such effective catalysts also makes it hard to see how they work.

If scientists could peer inside individual nanoparticles’ chemical reactions at a nanoscopic level, they would gather a treasure of useful knowledge for the design of improved catalysts to address the pressing energy needs of the 21st century.

That type of knowledge may now be close at hand, thanks to new research published January 11 in the journal “Nature”. In the new study — led by Dr. Elad Gross from the Institute of Chemistry and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem, and Prof. F. Dean Toste from the College of Chemistry at University of California, Berkeley, and Chemical Science Division at Lawrence Berkeley National Laboratory — researchers directly observed for the first time how metallic nanoparticles, used as catalysts in numerous industrial processes, activate catalytic processes.

Using a light source one million times brighter than the sun, the researchers were able to observe chemical reactivity on single Platinum particles similar to those used as industrial catalysts. What they found is that chemical reactivity primarily occurs on the particles’ periphery or edges, while lower reactivity occurs at the particles’ center.

The different reactivity observed at the center and edges of Platinum particles corresponds to the different properties of the Platinum atoms in the two locations. The atoms are mostly flat at the center, while they’re corrugated and less-ordered at the edges. This disorderly or “defective” structure means that Platinum atoms at the edges are not totally surrounded by other Platinum atoms, and will therefore form stronger interactions with reactant molecules. Stronger interactions can activate the reactant molecules and initiate a chemical reaction that will transform the reactant molecule into a desired product.

The research findings validate a well-known hypothesis in the world of catalysis, which correlates high catalytic reactivity with high density of atomic defects. It also shows, for the first time, that the enhanced reactivity of defected sites can be identified at the single-particle level.

“Our findings provide insights about the ways by which the atomic structure of catalysts controls their reactivity. This knowledge can direct the design of improved catalysts that will make chemical process greener, by decreasing the amount of energy that is consumed in the process and preventing the formation of unwanted, potentially hazardous, products,” said Dr. Elad Gross, from the Institute of Chemistry and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem.

To peer into individual nanoparticles, researchers focused a bright infrared beam generated in a synchrotron source (Advanced Light Source, Lawrence Berkeley National Laboratory) into a thin probe with an apex diameter of 20 nanometers. The probe acts as an antenna, localizes the infra-red light in a specific range, and by that provides the capabilities to identify molecules which reside on the surface of the catalytic nanoparticles. By scanning the particles with the nanometric probe while it is being radiated by the infrared light, the researchers were able to identify the locations and conditions in which chemical reaction occurs on the surface of single particle.

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

PHOTO: http://media.huji.ac.il/new/photos/hu170110_nano.tif - Chemical reactivity was identified on the surface of single Platinum nanoparticles, which are similar to the particles which are used as catalysts in various industrial processes. The chemical reactivity was measured by focusing a bright infrared beam into the apex of a thin tip with a diameter of 20 nm that monitored the chemical reactivity on the particle’s surface. (Credit: Hebrew University of Jerusalem)

CITATION: Chung-Yeh Wu, William J. Wolf, Yehonatan Levartovsky, Hans A. Bechtel, Michael C. Martin, F. Dean Toste, & Elad Gross. High-spatial-resolution mapping of catalytic reactions on single particles. Nature, Advance Online Publication (AOP) on January 11, 2017. doi:10.1038/nature20795. Paper will be online at http://dx.doi.org/10.1038/nature20795.

- Dov Smith

First look inside nanoscale catalysts shows ‘defects’ are useful
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Ultra-precise chip-scale sensor detects unprecedentedly small changes in environmental conditions at the nanoscale

18/01/2017

Chip scale high precision measurements of physical quantities such as temperature, pressure and refractive index have become common with nanophotonics and nanoplasmonics resonance cavities. As excellent transducers to convert small variations in the local refractive index into measurable spectral shifts, resonance cavities are being used extensively in a variety of disciplines ranging from bio-sensing and pressure gauges to atomic and molecular spectroscopy. Chip-scale microring and microdisk resonators (MRRs) are widely used for these purposes owing to their miniaturized size, relative ease of design and fabrication, high quality factor, and versatility in the optimization of their transfer function.

The principle of operation of such resonative sensors is based on monitoring the spectrum dependence of the resonator subject to minute variation in its surrounding (e.g., different types of atoms and molecules, gases, pressure, temperature).  Yet despite several important accomplishments, such optical sensors are still limited in their performances, and their miniaturization is highly challenging.

Now, a team from the Hebrew University of Jerusalem has demonstrated an on-chip sensor capable of detecting unprecedentedly small frequency changes. The approach consists of two cascaded microring resonators, with one serving as the sensing device and the other playing the role of a reference -- thus eliminating environmental and system fluctuations such as temperature and laser frequency.

"Here we demonstrate a record-high sensing precision on a device with a small footprint that can be integrated with standard CMOS technology, paving the way for even more exciting measurements such as single particle detection and high precision chip scale thermometry," said Prof. Uriel Levy, Director of the Harvey M. Krueger Family Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem, and a faculty member at the Department of Applied Physics in the Rachel and Selim Benin School of Computer Science and Engineering.

Among the innovations that made this development possible are chip scale integration of reference measurement, and a servo-loop locking scheme that translates the measured effects from the optical domain to the radio frequency domain. These enabled the researchers to quantify their system capabilities using well-established RF technologies, such as frequency counters, spectrum analyzers, and atomic standards.

The research appears in the peer-reviewed journal Optica, published by The Optical Society. The MRRs were fabricated at the Hebrew University's Center for Nanoscience and Nanotechnology.

CITATION: Liron Stern, Alex Naiman, Gal Keinan, Noa Mazurski, Meir Grajower, and Uriel Levy, "Ultra-precise optical to radio frequency based chip-scale refractive index and temperature sensor," Optica 4, 1-7 (2017). Link: https://doi.org/10.1364/OPTICA.4.000001.

FUNDING: Funding for this research was received from the European Research Council (ERC-LIVIN 648575).

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

Ultra-precise chip-scale sensor detects unprecedentedly small changes in environmental conditions at the nanoscale
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Quantum Leap: Scientists Demonstrate a Compact, Efficient Single Photon Source That Can Operate at Ambient Temperatures On a Chip

04/05/2016

Highly directional single photon source concept is expected to lead to a significant progress in producing compact, cheap, and efficient sources of quantum information bits for future applications

Quantum information science and technology has emerged as a new paradigm for dramatically faster computation and secure communication in the 21st century. At the heart of any quantum system is the most basic building block, the quantum bit or qbit, which carries the quantum information that can be transferred and processed (this is the quantum analogue of the bit used in current information systems). The most promising carrier qbit for ultimately fast, long distance quantum information transfer is the photon, the quantum unit of light.

The challenge facing scientists is to produce artificial sources of photons for various quantum information tasks. One of the biggest challenges is the development of efficient, scalable photon sources that can be mounted on a chip and operate at room temperature. Most sources used in labs today have to be very cold (at the temperature of liquid Helium, about -270C), which requires large and expensive refrigerators. Many sources also emit photons in undefined directions, making efficient collection a hard problem.

Now, a team of scientists from the Hebrew University of Jerusalem has demonstrated an efficient and compact single photon source that can operate on a chip at ambient temperatures. Using tiny nanocrystals made of semiconducting materials, the scientists developed a method in which a single nanocrystal can be accurately positioned on top of a specially designed and carefully fabricated nano-antenna.

In the same way large antennas on rooftops direct emission of classical radio waves for cellular and satellite transmissions, the nano-antenna efficiently directed the single photons emitted from the nanocrystals into a well-defined direction in space. This combined nanocrystals-nanoantenna device was able to produce a highly directional stream of single photons all flying to the same direction with a record low divergence angle. These photons were then collected with a very simple optical setup, and sent to be detected and analyzed using single photon detectors.

The team demonstrated that this hybrid device enhances the collection efficiency of single photons by more than a factor of 10 compared to a single nanocrystal without the antenna, without the need for complex and bulky optical collection systems used in many other experiments. Experimental results show that almost 40% of the photons are easily collected with a very simple optical apparatus, and over 20% of the photons are emitted into a very low numerical aperture, a 20-fold improvement over a freestanding quantum dot, and with a probability of more than 70% for a single photon emission. The single photon purity is limited only by emission from the metal, an obstacle that can be bypassed with careful design and fabrication.

The antennas were fabricated using simple metallic and dielectric layers using methods that are compatible with current industrial fabrication technologies, and many such devices can be fabricated densely on one small chip. The team is now working on a new generation of improved devices that will allow deterministic production of single photons straight from the chip into optical fibers, without any additional optical components, with a near unity efficiency. 

"This research paves a promising route for a high purity, high efficiency, on-chip single photon source operating at room temperature, a concept that can be extended to many types of quantum emitters. A highly directional single photon source could lead to a significant progress in producing compact, cheap, and efficient sources of quantum information bits for future quantum technological applications", said Prof. Ronen Rapaport, of the Racah Institute of Physics, The Department of Applied Physics, and the Center of Nanoscience and Nanotechnology at the Hebrew University of Jerusalem.

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

FUNDING: The research was supported in parts by the Einstein Foundation Berlin; the U.S. Department of Energy: Office of Basic Energy Sciences, Division of Materials Sciences and Engineering; the European Cooperation in Science and Technology through COST Action MP1302 Nanospectroscopy;  and by the Ministry of Science and Technology, Israel.

REFERENCE: Highly Directional Room-Temperature Single Photon Device. Nitzan LivnehMoshe G. HaratsDaniel IstratiHagai S. Eisenberg, and Ronen Rapaport. Nano Lett., 2016, 16 (4), pp 2527–2532. DOI: 10.1021/acs.nanolett.6b00082. Link: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b00082

Quantum Leap: Scientists Demonstrate a Compact, Efficient Single Photon Source That Can Operate at Ambient Temperatures On a Chip
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