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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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