Tag Archives: Ivan P. Parkin

Using quantum dots to detect and identify explosives

This research is courtesy of the University College London (UCL) according to a Dec. 9, 2015 news item on Nanowerk,

A new test for detecting multiple explosives simultaneously has been developed by UCL scientists. The proof-of-concept sensor is designed to quickly identify and quantify five commonly used explosives in solution to help track toxic contamination in waste water and improve the safety of public spaces.

Lead researcher, Dr William Peveler (UCL Chemistry), said: “This is the first time multiple explosives have been detected using a single sensor before, demonstrating proof-of-concept for this approach. Our sensor changes colour within 10 seconds to give information about how much and what explosives are present in a sample. Following further development, we hope it will be used to quickly analyse the nature of threats and inform tailored responses.”

A Dec. 9, 2015 UCL press release (also on EurekAlert), which originated the news item, expands on the theme,

Dr Peveler, added: “We analysed explosives which are commonly used for industrial and military purposes to create a useful tool for environmental and security monitoring. For example, DNT is a breakdown product from landmines, and RDX and PETN have been used in terror plots in recent years as they can be hard to detect using sniffer dogs. Our test can quickly identify these compounds so we see it having a variety of applications from monitoring the waste water of munitions factories and military ranges to finding evidence of illicit activities.”

The sensor is made of quantum dots, which are tiny light-emitting particles or nanomaterials, to which explosive targeting receptors are attached. As each explosive binds to the quantum dot, it quenches the light being emitted to a different degree. The distinct changes in colour are analysed computationally in a variety of conditions to give a unique fingerprint for each compound, allowing multiple explosives to be detected with a single test.

Senior author, Professor Ivan Parkin (UCL Chemistry), said: “Our sensor is a significant step forward for multiple explosives detection. Current methods can be laborious and require expensive equipment but our test is designed to be inexpensive, fast and use a much smaller volume of sample than previously possible. Although all of these factors are important, speed and accuracy are crucial when identifying explosive compounds.”

The team plan to take it from the laboratory into the field by blind testing it with contaminated waste water samples. They also hope to improve the sensitivity of the test by tailoring the surfaces of the quantum dots. Currently, its limit is less than one part per million which the team hope to increase into the part per billion range.

Here’s a link to and a citation for the paper,

Multichannel Detection and Differentiation of Explosives with a Quantum Dot Array by William J. Peveler, Alberto Roldan, Nathan Hollingsworth, Michael J. Porte‡, and Ivan P. Parkin. ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b06433 Publication Date (Web): November 18, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Pretty in violet, a new antimicrobial surface that works in the dark

 Samples of silicone with the various dyes infused. Courtesy: University College of London

Samples of silicone with the various dyes infused. Courtesy: University College of London

A March 25, 2014 news item on Azonano profiles a new antimicrobial surface which works in the dark, as well as, in the light,

Researchers at UCL [University College of London] have developed a new antibacterial material which has potential for cutting hospital acquired infections. The combination of two simple dyes with nanoscopic particles of gold is deadly to bacteria when activated by light – even under modest indoor lighting. And in a first for this type of substance, it also shows impressive antibacterial properties in total darkness.

The UCL March 24, 2014 news release, which originated the news item, describes the current situation with infections in hospitals and the team’s approach to mitigating the problem,

Hospital-acquired infections are a major issue for modern medicine, with pathogens like methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile (C. diff) getting extensive publicity. Although medical establishments have stringent cleaning policies, insist on frequent hand-washing by staff, and have powerful drugs at their disposal, it is difficult to eliminate these infections unless you can make the hospital environment more hostile to microbes. Surfaces, such as door handles, medical equipment, keyboards, pens and so on are an easy route for germs to spread, even onto freshly-cleaned hands.

One possible solution to this is to develop alternative strategies such as antibacterial coatings that make surfaces less accommodating to germs. These surfaces are not like antibacterial fluids that just wash away – the goal is to make a surface which is intrinsically deadly to harmful bacteria.

“There are certain dyes that are known to be harmful to bacteria when subjected to bright light,” explains the study’s corresponding author Ivan Parkin (Head of UCL Chemistry). “The light excites electrons in them, promoting the dye molecules to an excited triplet state and ultimately produces highly reactive oxygen radicals that damage bacteria cell walls. Our project tested new combinations of these dyes along with gold nanoparticles, and simplified ways of treating surfaces which could make the technology easier and cheaper to roll out.”

The UCL news release then goes on to describe the research in some detail,

The team, tested several different combinations of the dyes crystal violet (already used to treat staph infections), methylene blue and nanogold, deposited on the surface of silicone. This flexible rubbery substance is widely used as a sealant, a coating and to build medical apparatus such as tubes, catheters and gaskets, and can also be used as protective casings for things like keyboards and telephones.

While work to create antimicrobial surfaces in the past has often concentrated on complex ways of bonding dyes to the surface, this study took a simpler approach. The researchers used an organic solvent to swell the silicone, allowing the methylene blue and gold nanoparticles to diffuse through the polymer. They then dipped the silicone into a crystal violet solution to form a thin dye layer at the polymer surface.

In their tests, in which infected surfaces were subjected to light levels similar to those measured in hospital buildings, surfaces treated with a combination of crystal violet, methylene blue and nanogold showed the most potent bactericidal effect ever observed in such a surface. Moreover, the treatment did not significantly change the properties of the silicone (for instance, how water repellent it is), and the coating was not affected by rubbing with alcohol wipes, meaning it can stand up to the repeated cleaning that goes on in hospitals, without being worn off.

“Despite contaminating the surface with far more bacteria than you would ever see in a hospital setting, placed under a normal fluorescent light bulb, the entire sample was dead in three to six hours, depending on the type of bacteria,” says the paper’s lead author, Sacha Noimark. “That was an excellent result, but the bigger surprise was the sample which we left in the dark. That sample too showed significant reductions in bacterial load, albeit over longer timescales of about three to eighteen hours. The precise mechanism by which this dark-kill works is not yet clear, though.”

This is the first time a light-activated antimicrobial surface has had any kind of effect in the dark. This, along with its unprecedented performance under hospital lighting conditions, and relatively simple and cost-effective manufacture, means that the technology is extremely promising for future applications.

The team have been granted a patent on the formulation. The work was sponsored through the UCL M3S engineering doctorate centre and co-funded by Ondine Biopharma.

Here’s a link to and a citation for the paper,

Light-activated antimicrobial surfaces with enhanced efficacy induced by a dark-activated mechanism by Sacha Noimark, Elaine Allan, and Ivan P. Parkin. Chem. Sci., 2014, Advance Article DOI: 10.1039/C3SC53186D First published online 05 Mar 2014

This article is behind a paywall. One final note, I believe the difference in publication dates, March 24, 2014 in the news release as opposed to March 5, 2014 as listed on the publication’s website, is due to the probability that the print version was published later.