MOHAMMAD REZA NAJAF TOMARAEI

Bactericidal Nanoparticles

http://extension.missouri.edu/NewsAdmin/Photos/2011/Cicada%2003.jpghttp://www.clicktop10.com/wp-content/uploads/2013/07/Exploding-Bacteria.jpg

A team of international scientists from Spain and Australia has discovered the first known instance of a biomaterial that can kill bacteria on contact, only due to its physical properties.

Nanoscale sized pillars were found to be existing in the wings of a species of insects called “Clanger Cicada”.

These natural nano-pillars trap and slowly kill bacteria by pulling their cells apart.

Clanger Cicada -- their wings consist of an antibacterial nano-scaled structures.[1]

Top figures: The nano-pillars as imaged by an SEM.[2]

Bottom figure: Surface topography of Circada’s wings.[3]

When a bacteria lands on these approximately 240 nm high “blunted spikes”, they don’t pop.

Instead, the bacteria sticks and slowly tears apart as its cell skin descends down to the wing surface between the spikes.

3D representation of the discovered natural nano-pillars.[4]

In order to verify the process, scientists cooked some bacteria in microwave to cause different degrees of elasticity in their skin.

Those bacteria with more elastic skin were torn apart while the more rigid ones weren’t.

Microscopic image of the bacteria getting destroyed by the needle-like surface structures on Cicada’s wings. [4]

A synthetic alternative to these nano-pillars is black silicon.

Accidentally discovered in the 1990s, black silicon has a surface that is modified with nanoscale spike structures which give the material very low reflectivity (that’s why it’s called black silicon).

There are two methods by which black silicon can be synthesized:

1. Reactive-ion etching (dry etch) – A micro-fabrication process which uses chemically reactive plasma to remove material deposited on wafers.[5]

SEM micrograph of black silicon formed by Reactive-ion etching technique. [5]

2- Mazur’s method (optical hyperdoping developed at Harvard University) – Focusing a train of femtosecond (one tenth of a second) laser pulses on silicon wafers in presence of heavy chalcogen elements (group 16 elements such as selenium (Se), and tellurium (Te).) [6]

Black silicon made with optical hyperdoping.

Both the natural nano-pillars and the synthesized black silicon were tested and showed extreme bactericidal properties.

It’s worthy to note that these surfaces are smooth to human touch, but can destroy Gram-negative and Gram-positive bacteria, as well as spores.

The test results also showed: A killing rate of 450,000

bacterial cells per square centimeter per minute over the first three hours of exposure.

The concentration of bacteria used was more than several hundred times the amount needed to infect a person.

Applications and future plans: This anti-bacterial substance

can be used in hospital rooms, door handles, kitchen countertops, etc.

Producing black silicon might be a bit expensive, so research can be done to find cheaper methods for mass production.

However… Many viruses have a

protecting capsule so these nano-pillars won’t kill them.

If this method is used, there is a high probability that bacteria with thick/rigid walls survive and develop a resistant strain.

Resources1. www.brisbaneinsects.com/brisbane_cicadas/Clanger.ht

m2. http://

www.intechopen.com/books/optical-devices-in-communication-and-computation/bio-inspired-photonic-structures-prototypes-fabrications-and-devices

3. http://phys.org/news/2013-03-cicada-wing-bacteria-contact-video.html

4. http://phys.org/news/2013-11-germ-killing-nanosurface-front-hygiene.html

5. http://en.wikipedia.org/wiki/Black_silicon 6. http://

mazur.harvard.edu/research/detailspage.php?rowid=1