Targeted Nanoparticles Combine Imaging Attack: Cancer + Other Conditions

Nanosystems that are ‘theranostic’—they combine both therapeutic and diagnostic functions—present an exciting new opportunity for delivering drugs to specific cells and identifying sites of disease.

Bin Liu of the A*STAR Institute of Materials Research and Engineering, and colleagues at the National University of Singapore, have created nanoparticles with two distinct anticancer functions and an imaging function, all stimulated on demand by a single light source. The nanoparticles also include the cell-targeting property essential for treating and imaging in the correct locations.

The system is built around a polyethylene-glycol-based polymer that carries a small peptide component that allows it to bind preferentially to specific cell types. The polymer itself serves as a photosensitizer that can be stimulated by light to release reactive oxygen species (ROS). It also carries the chemotherapy drug doxorubicin in a prodrug form.

 

Surface peptides (purple arrows) allow fluorescent nanoparticles to bind to a protein (green) on the target cells and be taken up into the cells. Light exposure prompts the nanoparticles to generate reactive oxygen species (ROS), kills the cells, and also liberates the drug doxorubicin (orange), which can then enter the cell nucleus. Credit: WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The natural fluorescence of the polymer assists with diagnosis and monitoring of therapy as it shows where nanoparticles have accumulated. The ROS generated by light stimulation have a direct ‘photodynamic’ therapeutic activity, which destroys the targeted cells. The ROS additionally break the link between the polymer and the doxorubicin. Thus, cancer cells can be subjected to a two-pronged attack from the ROS therapy and the chemotherapy drug that is released within them (see image).

“This is the first nanoplatform that can offer on-demand and imaging-guided photodynamic therapy and chemotherapy with triggered drug release through one light switch,” explains Liu, emphasizing the significance of the system.

The researchers demonstrated the power of their platform by applying it to a mixture of cultured cancer cells, some of which overexpressed a surface protein that could bind to the targeting peptide on the nanoparticles. Fluorescence imaging indicated that the nanoparticles were taken up by the target cells and that ROS and doxorubicin were released within these cells—all at significantly higher levels than in cells used as controls. The doxorubicin that was released in the cell cytoplasm readily entered the nucleus—its site of activity. Crucially, the combined therapy had a greater cytotoxic effect than any one therapy alone.

“The white light used in this work does not penetrate tissue sufficiently for in vivo applications,” Liu explains, “but we are now attempting to use near-infrared laser light to improve the tissue penetration and move toward on-demand cancer therapy.” She also suggests that with a few modifications, the system may be suitable for the diagnosis and treatment of other pathological processes including inflammation and HIV infection.

Explore further: Introducing the multi-tasking nanoparticle

 

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SUBCOMMITTE EXAMINES BREAKTHROUGH NANOTECHNOLOGY OPPORTUNITIES FOR AMERICA

Chairman Terry: “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development.”

WASHINGTON, DC – The Subcommittee on Commerce, Manufacturing, and Trade, chaired by Rep. Lee Terry (R-NE), today held a hearing on:

“Nanotechnology: Understanding How Small Solutions Drive Big Innovation.”

 

 

“Great Things from Small Things!” … We Couldn’t Agree More!

 

Dye-sensitized solar cell absorbs a broad range of visible and infrared wavelengths: Increases Efficiencies

 

Dye-sensitized solar cells (DSSCs) rely on dyes that absorb light to mobilize a current of electrons and are a promising source of clean energy. Jishan Wu at the A*STAR Institute of Materials Research and Engineering and colleagues in Singapore have now developed zinc porphyrin dyes that harvest light in both the visible and near-infrared parts of the spectrum1. Their research suggests that chemical modification of these dyes could enhance the energy output of DSSCs.

DSSCs are easier and cheaper to manufacture than conventional silicon solar cells, but they currently have a lower efficiency. Ruthenium-based dyes have been traditionally used in DSSCs, but in 2011 researchers developed a more efficient dye based on a zinc atom surrounded by a ring-shaped molecule called a porphyrin. Solar cells using this new dye, called YD2-o-C8, convert visible light into electricity with an efficiency of up to 12.3 per cent. Wu’s team aimed to improve that efficiency by developing a zinc porphyrin dye that can also absorb infrared light.

The most successful dyes developed by Wu’s team, WW-5 and WW-6, unite a zinc porphyrin core with a system of fused carbon rings bridged by a nitrogen atom, known as an N-annulated perylene group. Solar cells containing these dyes absorbed more infrared light than YD2-o-C8 and had efficiencies of up to 10.5 per cent, matching the performance of an YD2-o-C8 cell under the same testing conditions (see image).

Zinc porphyrin dyes were used to create solar cells that can absorb both visible and near-infrared light. Credit: A*STAR Institute of Materials Research and Engineering 

Theoretical calculations indicate that connecting the porphyrin and perylene sections of these dyes by a carbon–carbon triple bond, which acts as an electron-rich linker, improved the flow of electrons between them. This bond also reduced the light energy needed to excite electrons in the molecule, boosting the dye’s ability to harvest infrared light.

Adding bulky chemical groups to the dyes also improved their solubility and prevented them from aggregating—something that tends to reduce the efficiency of DSSCs.

However, both WW-5 and WW-6 are slightly less efficient than YD2-o-C8 at converting visible light into electricity, and they also produce a lower voltage. “We are now trying to solve this problem through modifications based on the chemical structure of WW-5 and WW-6,” says Wu.

Comparing the results from more perylene–porphyrin dyes should indicate ways to overcome these hurdles, and may even extend light absorption further into the infrared. “The top priority is to improve the power conversion efficiency,” says Wu. “Our target is to push the efficiency to more than 13 per cent in the near future.”

Explore further: A new way to make microstructured surfaces

More information: Luo, J., Xu, M., Li, R., Huang, K.-W., Jiang, C. et al. N-annulated perylene as an efficient electron donor for porphyrin-based dyes: Enhanced light-harvesting ability and high-efficiency Co(II/III)-based dye-sensitized solar cells. Journal of the American Chemical Society 136, 265–272 (2014). DOI: 10.1021/ja409291g

Low Cost Laser Technique Improves Electrical & Photo Conductivity in Nanomaterials

NUS scientists use low cost technique to improve properties and functions of nanomaterials: By ‘drawing’ micropatterns on nanomaterials using a focused laser beam, scientists could modify properties of nanomaterials for effective applications in photonic and optoelectric applications

Singapore | Posted on July 22nd, 2014

Through the use of a simple, efficient and low cost technique involving a focused laser beam, two NUS research teams, led by Professor Sow Chorng Haur from the Department of Physics at the NUS Faculty of Science, demonstrated that the properties of two different types of materials can be controlled and modified, and consequently, their functionalities can be enhanced.

Said Prof Sow, “In our childhood, most of us are likely to have the experience of bringing a magnifying glass outdoors on a sunny day and tried to focus sunlight onto a piece of paper to burn the paper. Such a simple approach turns out to be a very versatile tool in research. Instead of focusing sunlight, we can focus laser beam onto a wide variety of nanomaterials and study effects of the focused laser beam has on these materials.”

Mesoporous silicon nanowires were scanned by a focused laser beam in two different patterns, imaged by bright-field optical microscope, as depicted by (a) and (c), as well as fluorescence microscopy, as depicted by (b) and (d). Evidently, the images hidden in boxes shown in (a) and (c) are clearly revealed under fluorescence microscopy.

Micropatterns ‘drawn’ on MoS2 films could enhance electrical conductivity and photo conductivity

Molybdenum disulfide (MoS2), a class of transition metal dichalcogenide compound, has attracted great attention as an emerging two-dimensional (2D) material due to wide recognition of its potential in and optoelectronics. One of the many fascinating properties of 2D MoS2 film is that its properties depend on the thickness of the film. In addition, its properties can be modified once the film is modified chemically. Hence one of the challenges in this field is the ability to create microdevices out of the MoS2 film comprising components with different thickness or chemical nature.

To address this technological challenge, Prof Sow, Dr Lu Junpeng, a postdoctoral candidate from the Department of Physics at the NUS Faculty of Science, as well as their team members, utilised an optical microscope-focused laser beam setup to ‘draw’ micropatterns directly onto large area MoS2 films as well as to thin the films.

With this simple and low cost approach, the scientists were able to use the focused laser beam to selectively ‘draw’ patterns onto any region of the film to modify properties of the desired area, unlike other current methods where the entire film is modified.

Interestingly, they also found that the electrical conductivity and photoconductivity of the modified material had increased by more than 10 times and about five times respectively. The research team fabricated a photodetector using laser modified MoS2 film and demonstrated the superior performance of MoS2 for such application.

This innovation was first published online in the journal ACS Nano on 24 May 2014.

Hidden images ‘drawn’ by focused laser beam on silicon nanowires could improve optical functionalities

In a related study published in the journal Scientific Reports on 13 May 2014, Prof Sow led another team of researchers from the NUS Faculty of Science, in collaboration with scientists from Hong Kong Baptist University, to investigate how ‘drawing’ micropatterns on mesoporous silicon nanowires could change the properties of nanowires and advance their applications.

The team scanned a focused laser beam rapidly onto an array of mesoporous silicon nanowires, which are closely packed like the tightly woven threads of a carpet. They found that the focused laser beam could modify the optical properties of the nanowires, causing them to emit greenish-blue fluorescence light. This is the first observation of such a laser-modified behaviour from the mesoporous silicon nanowires to be reported.

The researchers systematically studied the laser-induced modification to gain insights into establishing control over the optical properties of the mesoporous silicon nanowires. Their understanding enabled them to ‘draw’ a wide variety of micropatterns with different optical functionalities using the focused laser beam.

To put their findings to the test, the researchers engineered the functional components of the nanowires with interesting applications. The research team demonstrated that the micropatterns created at a low laser power are invisible under bright-field optical microscope, but become apparent under fluorescence microscope, indicating the feasibility of hidden images.

Further research

The fast growing field of electronics and optoelectronics demands precise material deposition with application-specific optical, electrical, chemical, and mechanical properties.

To develop materials with properties that can cater to the industry’s demands, Prof Sow, together with his team of researchers, will extend the versatile focused laser beam technique to more nanomaterials. In addition, they will look into further improving the properties of MoS2 and mesoporous silicon with different techniques.

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