Major Accomplishments of KIST Over Its 40-Year History. Since its foundation over 40 years ago, KIST has remained faithful to its role as a comprehensive research institute supporting Korea's interests and has made active contributions to the growth of the nation's industrial base through advancements in science and technology. A review of its major accomplishments through the years offer a peek into the most significant events in its history.

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Project Name Promptly working antibacterial air filter by coating with silver nanoparticle-decorated silica hybrid particles
Year 2014 Director Kyoungja Woo, Ph.D.
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Promptly working antibacterial air filter by coating with silver nanoparticle-decorated silica hybrid particles


- selected as the front cover paper of an international science journal published by Royal Society of Chemistry


Researchers led by Kyoungja Woo, Ph.D. at Molecular Recognition Research Center of KIST, and Jungho Hwang, Ph.D. at School of Mechanical Engineering of Yonsei University successfully developed a promptly working antibacterial air filter, which is coated with silver nanoparticle-decorated silica hybrid particles and kills germs as soon as they contact by air filtration, thus opening up a new opportunity to remove even the antibiotic-resistant germs such as super-bacteria. 

Conventional air filters have a problem that bacteria tend to proliferate on a filter system when conditions for their survival are satisfied. 

In order to address the aforementioned issue, researches have been conducted to develop air filters coated with antibacterial silver nanoparticles. However, in those cases, antibacterial effect was controversial and a certain period of time was required prior to killing bacteria because of too small size and inhomogeneous coating of silver nanoparticles. 

The silver nanoparticle-decorated silica hybrid particles which were developed by the researchers from KIST and Yonsei Univ. can be used as antibacterial coating material. The average size of silver particles is 30 nanometers, and they have spiked hybrid structures from a silica sphere, so as to kill bacteria immediately. 

In further detail, the silver nanoparticle-decorated silica hybrid particles are basically micron-sized balls. A number of pillars (aminopropyl moieties) are erected on the surface of the balls, and 1~2 nm silver seeds are evenly attached at the end of the pillars, and silver ions are added to sort-out bigger silver seeds and reduced to glue and embed the attached seed-pillar pairs together. That way, 3-dimensional hybrid particles where 30 nm silver particles are tightly bound to the hybrid structures are formed. 

After that, the silver nanoparticle-decorated silica hybrid particles are coated on the surface of an air filter. The silver nanoparticle-decorated silica hybrid particles are tightly glued to the air filter, which ensures a structure reliable enough for commercialization.  

The silver nanoparticle-decorated hybrid silica particles coated on the air filter do not come off even with strong wind at 2 meters per second. (strong wind: A/C 1.5~2 meters per sec., air purifier 1 meter per sec. The researchers tested and confirmed that the hybrid particles did not come off with winds at 2 meters per sec.)

In order to verify the antibacterial effect of the air filter coated with silver nanoparticle-decorated silica hybrid particles, the researchers blew in E. coli and Staphylococcus through the air filter and then observed reactions between the bacteria and the hybrid particles by using an electronic microscope. 

They saw the silver nanoparticles, just like teeth, biting the bacteria, which died as soon as they touched the hybrid particles. 

The research team said “Our research outcome provides a critical evidence to put an end to controversies over the antibacterial effect of silver nanoparticles. Silver nanoparticle-decorated silica hybrid particles can kill bacteria promptly, and even antibiotic-resistant bacteria can be effectively killed. This research finding set the foundation to improve the health and the quality of life for the general public." 

This research was sponsored by the Ministry of Science, ICT and Future Planning, as a Green Nano Technology Development Program, and KIST, as an internal research project. The research article was published as the front cover of Journal of Materials Chemistry B, Vol. 2, No. 39, ) which is an international journal of materials science published by Royal Society of Chemistry (published on-line: Sep. 17, 2014. published off-line: Oct. 21, 2014).

Article title: Prompt and Synergistic Antibacterial Activity of Silver Nanoparticle-Decorated Silica Hybrid Particles on Air Filtration


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Figure 1. Front cover of the journal where the article was published

The air filter (shown in the center of the picture) is coated with silver nanoparticle-decorated silica hybrid particles (yellow). Polluted air flows from the left into the filter and clean air gets out to the right. Bacteria filtered by the antibacterial filtering system immediately cease activity and die as they are bitten by silver nanoparticle-decorated silica hybrid particles.


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Figure 2. Synthesis process of silver nanoparticle-decorated silica hybrid particles  

(a) After surface engineering with aminopropyl moieties, a silica ball has positive charges on the surface and is seeded with silver seeds which have negative charges. 

(b) Big silver seeds are sorted out to make room. 

(c)Remaining silver seeds are grown to make silver nanoparticle-decorated silica hybrid particles.


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Figure 3. Antibacterial effect of silver nanoparticle-decorated silica hybrid particles
;(a, b) Silver nanoparticle-decorated silica hybrid particles coated on the air filter kill bacteria (c, d) Cultivation of mixture solution between silver nanoparticle-decorated silica hybrid particles and bacteria: after 0, 10 mins, 30 mins from the left. (a, c) are E. coli and (b, d) are Staphylococcus in reaction with silver nanoparticle-decorated silica hybrid particles, and the bacteria were killed immediately.
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