A new (nano) front in hy­giene

The Star Malaysia - Star2 - - SCIENCE -

IMAGINE a hos­pi­tal room, door han­dle or kitchen coun­ter­top that is free from bac­te­ria – and not one drop of dis­in­fec­tant or boil­ing wa­ter or dose of mi­crowaves has been needed to zap the germs.

That is the idea be­hind a star­tling dis­cov­ery made by sci­en­tists in Aus­tralia.

In a study pub­lished last week in the jour­nal Na­ture Com­mu­ni­ca­tions, they de­scribed how a dragon­fly led them to a nano-tech sur­face that phys­i­cally slays bac­te­ria.

The germ-killer is black sil­i­con, a sub­stance dis­cov­ered ac­ci­den­tally in the 1990s and now viewed as a promis­ing semi­con­duc­tor ma­te­rial for so­lar pan­els.

Un­der an elec­tron mi­cro­scope, its sur­face is a for­est of spikes just 500 nanome­tres (500 bil­lionths of a me­tre) high that rip open the cell walls of any bac­terium which comes into con­tact, the sci­en­tists found.

It is the first time that any wa­ter-re­pel­lent sur­face has been found to have this phys­i­cal qual­ity as bac­te­ri­cide.

Last year, the team, led by Elena Ivanova at Swin­burne Univer­sity of Tech­nol­ogy in Mel­bourne, were stunned to find ci­cada wings were po­tent killers of Pseu­domonas aeru­g­in­soa – an op­por­tunist germ that also in­fects hu­mans and is be­com­ing re­sis­tant to an­tibi­otics.

Look­ing closely, they found that the an­swer lay not in any bio­chem­i­cal on the wing, but in reg­u­larly-spaced “nanopil­lars” on which bac­te­ria were sliced to shreds as they set­tled on the sur­face.

They took the dis­cov­ery fur­ther by ex­am­in­ing nanos­truc­tures stud­ding the translu­cent forewings of a red-bod­ied Aus­tralian dragon­fly called the wan­der­ing percher ( Di­pla­codes bipunc­tata).

It has spikes that are some­what smaller than those on the black sil­i­con – they are 240 nanome­tres high. The dragon­fly’s wings and black sil­i­con were put through their paces in a lab, and both were ruth­lessly bac­te­ri­ci­dal.

Smooth to the hu­man touch, the sur­faces de­stroyed two cat­e­gories of bac­te­ria, called Gram-neg­a­tive and Gram­pos­i­tive, as well as spores, the pro­tec­tive shell that coats cer­tain times of dor­mant germs.

The three tar­geted bugs com­prised P. aerug­i­nosa, the no­to­ri­ous Staphy­lo­coc­cus au­reus and the ul­tra-tough spore of Bacil­lus sub­tilis, a wide-rang­ing soil germ that is a cousin of an­thrax.

The killing rate was 450,000 bac­te­rial cells per square cen­time­tre per minute over the first three hours of ex­po­sure.This is 810 times the min­i­mum dose needed to in­fect a per­son with S. au­reus, and a whop­ping 77,400 times that of P. aerug­i­nosa.

If the cost of mak­ing black sil­i­con is an ob­sta­cle, many other op­tions are around for mak­ing nano-scale germ-killing sur­faces, said the sci­en­tists.

“Syn­thetic an­tibac­te­rial nano-ma­te­ri­als that exhibit a sim­i­lar ef­fec­tive­ness... can be read­ily fab­ri­cated over large ar­eas,” they wrote. – AFP

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