| RESEARCH HIGHLIGHTS |


The team created the material using


positively charged molecules linked together in a chain to attract negatively charged bacteria cells. It has a unique structure with one ‘tail’ at each end of the chain, and they found that, once the bacterium is ‘caught’, these tails act


like drills that penetrate and destroy the bacte- rial cell membranes. When the cell membranes are ruptured, the bacteria die instantly. Crucially, Zhang’s team also found


that the oligomer is self-gelling in alcohol. This property will make the material easy


to use in products such as hand wash and surface spray.


1. Riduan, S. N., Yuan, Y., Zhou, F., Leong, J., Su, H. et al. Ultrafast killing and self-gelling antimicrobial imidazolium oligomers. Small 12, 1928–1934 (2016).


Photoacoustic imaging: BOOSTING THE CONTRAST


THE CONTRAST OF PHOTOACOUSTIC IMAGES MAY BENEFIT FROM A PROMISING COMPOUND WITH LOW TOXICITY AND HIGH STABILITY


When injected into a mouse, osmium carbonyl clusters (below) enhance the contrast of photoacoustic images, which are obtained by using near-infrared laser light (red) to excite acoustic waves (purple and yellow).


Near-IR light Now, Malini Olivo at the A*STAR


Singapore Bioimaging Consortium and co-workers have discovered a way to shift the optical absorption of metal carbonyl clusters to longer wavelengths. They found that using metal cores that have high nuclearity pushes the optical contrast into the near-infrared range (680 to 1,000 nanometers), which is so important for photoacoustic imaging. When they injected osmium carbonyl


[Os10 (µ6-C)(CO)24]2- Acoustic waves


A compound for enhancing the contrast of photoacoustic imaging — an emerging imaging modality that involves ‘listening’ to the sound generated by laser light — has been developed by A*STAR researchers1. Photoacoustic imaging is an intriguing way


to capture a picture of biological tissue in the body. Researchers shine ultrashort pulses of near-infrared laser light onto the region to be imaged. Tissue absorbs the light, causing it to heat up and expand and the expansion generates sound waves that are picked up by an ultrasound detector and used to generate an image. Since it does not use ionizing radi- ation, photoacoustic imaging is safer


32 A*STAR RESEARCH


than X-ray imaging and combines the advantages of optical imaging (good contrast) with those of ultrasound imaging (high spatial resolution and tissue penetration). Currently, it is mainly used in research laboratories, but it has several potential clinical applications. Compounds known as contrast agents are


used to boost the contrast of photoacoustic images. While metal carbonyl clusters — molecules with metal atoms at their centers and limbs of carbon monoxide — have high photoacoustic contrasts, the contrast peaks at wavelengths that are too low to be useful for photoacoustic imaging.


clusters into the bloodstream of mice, they observed up to a four-fold enhancement in the photoacoustic signal from certain tissues, compared to that obtained with metal carbonyl clusters that have a low nuclearity. “We demonstrated the potential of


high-nuclearity carbonyl clusters of ruthe- nium and osmium as photoacoustic contrast agents in whole-body preclinical imaging,” says Olivo. “The clusters exhibit low toxicity, high stability and superior photoacoustic stability compared to the clinically approved near-infrared dye indocyanine green.” More broadly, the study emphasizes a


neglected class of compounds. “This work highlights the potential biological applications of organometallic complexes, which have not been well explored,” says Olivo. “Metal-based therapeutic and imaging agents are becoming increasingly important.


ISSUE 5 | OCTOBER – DECEMBER 2016


Adapted from Ref. 1 with permission of The Royal Society of Chemistry


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