Tag Archives: Hanadi Sleiman

Disinfectant for backyard pools could be key to new nanomaterials

Research from McGill University (Québec, Canada) focuses on cyanuric acid, one of the chemicals used to disinfect backyard pools. according to a March 1, 2016 McGill University news release (received by email; it can also be found in a March 1, 2016 news item on Nanowerk *and on EurekAlert*),

Cyanuric acid is commonly used to stabilize chlorine in backyard pools; it binds to free chlorine and releases it slowly in the water. But researchers at McGill University have now discovered that this same small, inexpensive molecule can also be used to coax DNA into forming a brand new structure: instead of forming the familiar double helix, DNA’s nucleobases — which normally form rungs in the DNA ladder — associate with cyanuric acid molecules to form a triple helix.

The discovery “demonstrates a fundamentally new way to make DNA assemblies,” says Hanadi Sleiman, Canada Research Chair in DNA Nanoscience at McGill and senior author of the study, published in Nature Chemistry. “This concept may apply to many other molecules, and the resulting DNA assemblies could have applications in a range of technologies.”

The DNA alphabet, composed of the four letters A, T, G and C, is the underlying code that gives rise to the double helix famously discovered by Watson and Crick more than 60 years ago. The letters, or bases, of DNA can also interact in other ways to form a variety of DNA structures used by scientists in nanotechnology applications – quite apart from DNA’s biological role in living cells.

For years, scientists have sought to develop a larger, designer alphabet of DNA bases that would enable the creation of more DNA structures with unique, new properties. For the most part, however, devising these new molecules has involved costly and complex procedures.

The road to the McGill team’s discovery began some eight years ago, when Sleiman mentioned to others in her lab that cyanuric acid might be worth experimenting with because of its properties. The molecule has three faces with the same binding features as thymine (T in the DNA alphabet), the natural complement to adenine (A).  “One of my grad students tried it,” she recalls, “and came back and said he saw fibres” through an atomic force microscope.

The researchers later discovered that these fibres have a unique underlying structure. Cyanuric acid is able to coax strands composed of adenine bases into forming a novel motif in DNA assembly. The adenine and cyanuric acid units associate into flower-like rosettes; these form the cross-section of a triple helix.  The strands then combine to form long fibres.

“The nanofibre material formed in this way is easy to access, abundant and highly structured,” says Nicole Avakyan, a PhD student in Sleiman’s lab and first author of the study. “With further development, we can envisage a variety of applications of this material, from medicinal chemistry to tissue engineering and materials science.”

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

Reprogramming the assembly of unmodified DNA with a small molecule by Nicole Avakyan, Andrea A. Greschner, Faisal Aldaye, Christopher J. Serpell, Violeta Toader,    Anne Petitjean, & Hanadi F. Sleiman. Nature Chemistry (2016) doi:10.1038/nchem.2451 Published online 22 February 2016

This paper is behind a paywall.

*’also on EurekAlert’ added on March 2, 2016.

HIV testing, nano gold, and Uganda; not so obsolete?; new nanotube manufacturing technique from McGill University

There’s a portable blood-testing machine, designed by US-based PointCare, which can give a print-out detailing a patient’s immune status in 10 minutes. The machine was designed for use in third-world or developing world clinics such as the one in Uganda which is described in this BBC story.

One of the problems doctors and medical staff had with equipment for testing HIV patients’ immune system was that the chemicals used as reagents in the testing process were too easily perishable in the high heat common in a lot of countries. PointCare soved the problem this way (from the BBC article):

Dr Hansen [from PointCare] invented a test that uses chemical reagent that can be freeze-dried and stored in temperatures of over 40C.

CD4 screening tests use antibodies – molecular tags that recognise and latch onto a chemical marker on the surface of the cell. By attaching to the cells, they act as flags distinguishing CD4 cells from other white blood cells.

But these antibodies need to be “labelled”, so they can be detected by a machine.

Traditionally, antibodies are labelled using fluorescent markers, but these fluorescent chemicals perish if they are not kept refrigerated. So they’re useless for a medical team operating from a temporary clinic in the heat of an African summer.

Dr Hansen developed a new label. “We use colloidal gold,” explains Dr Krauledat [community physician]. “It’s true nanotechnology – extremely tiny gold particles attached to the anti-CD4 antibody.”

Do go and read the full story because there’s more to it than I’ve included. Meanwhile I had another look at those lithography stories (SFU’s new maskwriting facilities and RAPID) that I was posting about last week. While the new RAPID technique may make the use of ultra-violet light obsolete, they still haven’t approached the nanoscale. The measurement mentioned is “… 2500 times smaller than a human hair” [more here]. The measurement usually mentioned when discussing the nanoscale  is between 1/100,000 ro 1/60,000 (nobody seems to agree on the exact measurement, you can check here) of the width of a human hair equals 1 nanometre.  Weirdly, the Simon Fraser University (SFU) release notes that the new facilities will be able to create structures “… under 20 nanometres about 10,000 times smaller than the diameter of a human hair” [more here]. If I’m doing the math correctly, wouldn’t that be between 1/50,0000 and 1/30,000 of the human hair? I know it’s a little fussy but once a technical writer, always a technical writer and that kind of detail can make a big difference.

Researchers led by Dr. Hanadi Sleiman and Dr. Gonzalo Cosa at McGill University (Montreal, Canada) have developed a new way to manufacture nanotubes using DNA, in short they are DNA nanotubes. The longer story is here and the shorter story is here.