A scheme for greatly increasing the number of colors that can be produced by arrays of tiny aluminum nanodisks has been demonstrated by A*STAR scientists ("Plasmonic Color Palettes for Photorealistic Printing with Aluminum Nanostructures"). 
Three strategies for producing colors of pixels containing four aluminum nanodisks. Row 1: varying the nanodisk diameter (d) gives 15 colors. Row 2: Varying both the spacing (s) and diameter (d) of the nanodisks gives over 300 colors. Row 3: Varying the diameters (d1 and d2) of the two pairs of diametrically opposite nanodisks gives over 100 colors. (© American Chemical Society) (Also see our Nanowerk Spotlight on this research: "Photorealistic plasmonic printing with aluminum nanostructures") Conventional pigments produce colors by selectively absorbing light of different wavelengths — for example, red ink appears red because it absorbs strongly in the blue and green spectral regions. A similar effect can be realized at a much smaller scale by using arrays of metallic nanostructures, since light of certain wavelengths excites collective oscillations of free electrons, known as plasmon resonances, in such structures. An advantage of using metal nanostructures rather than inks is that it is possible to enhance the resolution of color images by a hundred fold. This enhanced resolution, at the diffraction limit of light, is critical for data storage, digital imaging and security applications. Aluminum — because of its low cost and good stability — is a particularly attractive material to use. Joel Yang and Shawn Tan at the A*STAR Institute of Materials Research and Engineering and co-workers used an electron beam to form arrays of approximately 100-nanometer-tall pillars. They then deposited a thin aluminum layer on top of the pillars and in the gaps between them. In these arrays, each pixel was an 800-nanometer-long square containing four aluminum nanodisks. The plasmon resonance wavelength varies sensitively with the dimensions of the nanostructures. Consequently, by varying the diameter of the four aluminum nanodisks in a pixel (all four nanodisks having the same diameter), the scientists were able to produce about 15 distinct colors — a good start, but hardly enough to faithfully reproduce full-color images. By allowing two pairs of diametrically opposite nanodisks to have different diameters from each other, then varying the two diameters enabled them to increase this number to over 100. Finally, they generated over 300 colors by varying both the nanodisk diameter (but keeping all four diameters within a pixel the same) and the spacing between adjacent nanodisks in a pixel (see image). “This method is analogous to half-toning used in ink-based printing and results in a broad color gamut,” comments Yang. The researchers demonstrated the effectiveness of their extended palette using a Monet painting. They reproduced the image using both a limited and extended palette, with a much better color reproduction from the extended palette. Amazingly, they shrank the image from 80 centimeters to a mere 300 micrometers — a 2,600-fold reduction in size. “The use of a more cost-effective metal has the potential to move this technology closer to adoption,” Tan notes.
Three strategies for producing colors of pixels containing four aluminum nanodisks. Row 1: varying the nanodisk diameter (d) gives 15 colors. Row 2: Varying both the spacing (s) and diameter (d) of the nanodisks gives over 300 colors. Row 3: Varying the diameters (d1 and d2) of the two pairs of diametrically opposite nanodisks gives over 100 colors. (© American Chemical Society) (Also see our Nanowerk Spotlight on this research: "Photorealistic plasmonic printing with aluminum nanostructures") Conventional pigments produce colors by selectively absorbing light of different wavelengths — for example, red ink appears red because it absorbs strongly in the blue and green spectral regions. A similar effect can be realized at a much smaller scale by using arrays of metallic nanostructures, since light of certain wavelengths excites collective oscillations of free electrons, known as plasmon resonances, in such structures. An advantage of using metal nanostructures rather than inks is that it is possible to enhance the resolution of color images by a hundred fold. This enhanced resolution, at the diffraction limit of light, is critical for data storage, digital imaging and security applications. Aluminum — because of its low cost and good stability — is a particularly attractive material to use. Joel Yang and Shawn Tan at the A*STAR Institute of Materials Research and Engineering and co-workers used an electron beam to form arrays of approximately 100-nanometer-tall pillars. They then deposited a thin aluminum layer on top of the pillars and in the gaps between them. In these arrays, each pixel was an 800-nanometer-long square containing four aluminum nanodisks. The plasmon resonance wavelength varies sensitively with the dimensions of the nanostructures. Consequently, by varying the diameter of the four aluminum nanodisks in a pixel (all four nanodisks having the same diameter), the scientists were able to produce about 15 distinct colors — a good start, but hardly enough to faithfully reproduce full-color images. By allowing two pairs of diametrically opposite nanodisks to have different diameters from each other, then varying the two diameters enabled them to increase this number to over 100. Finally, they generated over 300 colors by varying both the nanodisk diameter (but keeping all four diameters within a pixel the same) and the spacing between adjacent nanodisks in a pixel (see image). “This method is analogous to half-toning used in ink-based printing and results in a broad color gamut,” comments Yang. The researchers demonstrated the effectiveness of their extended palette using a Monet painting. They reproduced the image using both a limited and extended palette, with a much better color reproduction from the extended palette. Amazingly, they shrank the image from 80 centimeters to a mere 300 micrometers — a 2,600-fold reduction in size. “The use of a more cost-effective metal has the potential to move this technology closer to adoption,” Tan notes.
This is a picture of a CNP microcapsule. (Image: QMUL) The researchers constructed tiny microcapsules, just 2 microns in diameter, with individual layers containing CNP that could release the protein slowly and therefore deliver the treatment in the most effective way. In experiments on samples of cartilage taken from animals, they showed that the microcapsules could deliver the anti-inflammatory CNP in a highly effective way. The researchers believe that injections of microcapsules could in the future be used to heal damaged cartilage in people with osteoarthritis. The injections could be delivered easily by a GP. Dr Tina Chowdhury from QMUL's School of Engineering and Materials Science, who leads the research, said: "If this method can be transferred to patients it could drastically slow the progression of osteoarthritis and even begin to repair damaged tissue. "CNP is currently available to treat other conditions such as skeletal diseases and cardiovascular repair. If we could design simple injections using the microcapsules, this means the technology has the potential to be an effective and relatively cheap treatment that could be delivered in the clinic or at home." Dr Stephen Simpson, Director of Research at Arthritis Research UK said: "Current treatment options for osteoarthritis are limited, and therefore developing new ways to treat this painful and debilitating condition is currently a major area of research. The focus is not only about identifying promising new targets, as delivery of a drug to the appropriate site can often be as challenging as developing the treatment itself, and can hinder getting otherwise effective medicines to patients. This work represents a good example of how researchers are developing innovative new approaches to get around this problem."
Nanoplasmonic biosensor for drug allergy diagnosis. The developed biosensor is able to detect the presence of anti-amoxicillin immunoglobulins E (IgE) in patients’ serum, whose concentration increase during an allergic reaction. Short ordered arrays of gold nanodisks are fabricated on glass substrates. Amoxicillin molecules are immobilized over the gold nanodisks by means of a chemical structure (modified dendrimers) that binds both antibiotic and gold. Finally, the serum of the patient flows over the amoxicillin-coated surface of the sensor. The anti-amoxicillin IgEs generated during an allergy outbreak interact with the fixed antibiotic, affecting the properties of the surface. In particular, the binding of the antibody generates a change in the refraction index, which can be monitored. Higher concentration of IgEs will proportionally lead to a higher change in refractive index. With this methodology is therefore possible to quantify the amount IgE in serum, and therefore is possible to diagnose the severity of the allergic reaction. This technique stands out because of its high sensitivity, avoiding the use of labels, being possible to detect small amounts of IgEs directly in serum. The biosensing surfaces are excited by a collimated halogen light source at a particular angle, which allows analysing in real time the evolution and changes of gold’s absorption curve during the interaction events. Another outstanding point of this method is the non-invasive procedure for the patient: just few microliters of serum are needed for the analysis. The ICN2 researchers have devoted a great effort in the optimization of the methodology, in order to obtain a reproducible and accurate calibration of the biosensor, especially to allow direct detection of serum samples (avoiding pre-treatment and dilution). The strategy has been successfully validated with other established methods like ImmunoCAP. Although this current available technique for allergy diagnosis is well stablished and difficult to replace, the use of a compact and portable platform like this one which minimizes time and costs could mean an attractive alternative for allergy diagnosis, and it could be also very useful in other clinical scenarios. At the moment, the biosensor is not available for clinical application as more development is needed to obtain the advanced and quick diagnostic tool they are seeking. However, the aim of the researchers is to design platforms robust and easy to use in order to introduce them in daily clinical practice.