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Novel Devices ♦ news digest


quantum dots can be placed very close to the surface of the nanometres raises a huge potential for their use in detecting local electric and magnetic fields. The quantum dots also could be used to charge converters for better light-harvesting, as in the case of photovoltaic cells.


This work is described in detail in the paper, “Self-assembled Quantum Dots in a Nanowire System for Quantum Photonics,” by M. Heiss et al in Nature Materials, (2013). DOI:10.1038/ nmat3557


The team of scientists working on the project came from universities and laboratories in Sweden, Switzerland, Spain, and the United States.


Transforming cell biology


with tiny GaAs QD bioprobes A new quantum dot device composed of gallium arsenide and light-emitting crystal, marks a new age in the study and influence of living cells. The probe could be used for real-time sensing of specific proteins within cells and be adapted to sense biomolecules such as DNA or RNA


Biological research may soon be transformed by a new class of light-emitting probes small enough to be injected into individual cells without harm to the host.


Welcome to biophotonics, a discipline at the confluence of engineering, biology and medicine in which lasers and LEDs) – are opening up new avenues in the study and influence of living cells.


Engineers at Stanford say this was the first study to demonstrate that sophisticated engineered light resonators can be inserted inside cells without damaging the cell. Even with a resonator embedded inside, a cell is able to function, migrate and reproduce as normal.


The researchers call their device a “nanobeam,” because it resembles a steel I-beam with a series of round holes etched through the centre. These beams, however, are not massive, but measure only a few microns in length and just a few hundred nanometres in width and thickness.


It looks a bit like a piece from an erector set of old. The holes through the beams act like a nanoscale hall of mirrors, focusing and amplifying light at the centre of the beam in what are known as photonic cavities. These are the building blocks for nanoscale lasers and LEDs.


A photonic nanobeam inserted in a cell. Clearly visible are the etched holes through the beam as well as the sandwich-like layer structure of the beam itself. The beam structure alternates between layers of GaAs and photonic crystal containing the photon-producing quantum dots


Senior author of a paper describing the work, Jelena Vuckovic, a professor of electrical engineering, says, “Devices like the photonic cavities we have built are quite possibly the most diverse and customisable ingredients in photonics”. “Applications span from fundamental physics to nanolasers and biosensors that could have profound impact on biological research.”


At the cellular level, a nanobeam acts like a needle able to penetrate cell walls without injury. Once inserted, the beam emits light, yielding a remarkable array of research applications and implications.


While other groups have shown that it is possible to insert simple nanotubes and electrical nanowires into cells, nobody had yet realised such complicated optical components inside biological cells.


“We think this is quite a dramatic shift from existing applications and will enable expanded opportunities for understanding and influencing cellular biology,” says the paper’s first author Gary Shambat, a doctoral candidate in electrical engineering.


In this case, the studied cells came from a prostate tumour, indicating possible application for the probe in cancer research. The primary and most immediate use would be in the real-time sensing of specific proteins within the cells, but the probe could be adapted to sense any important biomolecules such as DNA or RNA.


To detect these key molecules, researchers coat the probe with certain organic molecules or antibodies that are known to attract the target proteins, just like iron to a magnet. If the desired proteins are present within the cell, they begin to accumulate on the probe and cause a slight-but-detectable shift in the wavelength of the light being emitted from the device. This shift is a positive indication that the protein is present and in what quantity.


March 2013 www.compoundsemiconductor.net 139


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