Smart Windows that Self-Illuminate on Rainy Days

– A joint research team from POSTECH and KAIST develops self-powering, color-changing humidity sensors
– Applicable to various fields including smart windows, health care and safety management


Smart windows that automatically change colors depending on the intensity of sunlight are gaining attention as they can reduce energy bills by blocking off sun’s visible rays during summer. But what about windows that change colors depending on the humidity outside during the monsoon season or on hot days of summer? Recently, a Korean research team has developed the source technology for smart windows that change colors according to the amount of moisture, without needing electricity.

The joint research team comprised of Professor Junsuk Rho of departments of mechanical and chemical engineering, Jaehyuck Jang and Aizhan Ismukhanova of Department of Chemical Engineering at POSTECH, and Professor Inkyu Park of KAIST’s Department of Mechanical Engineering. Together, they successfully developed a variable color filter using a metal-hydrogel-metal resonator structure using chitosan-based hydrogel, and combined it with solar cells to make a self-powering humidity sensor. These research findings were published as a cover story in the latest edition of Advanced Optical Materials, a journal specializing in nanoscience and optics.

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Sensors using light are already widely used in our daily lives in measuring the ECG, air quality, or distance. The basic principle is to use light to detect changes in the surroundings and to convert them into digital signals.

Fabri-Pero interference*1 is one of the resonance phenomena that can be applied in optical sensors and can be materialized in the form of multilayer thin films of metal-dielectric-metal. It is known that the resonance wavelength of transmitted light can be controlled according to the thickness and refractive index of the dielectric layer. However, the existing metal-dielectric-metal resonators had a big disadvantage in not being able to control the wavelengths of transmitted light once they are manufactured, making it difficult to use them in variable sensors.

The research team found that when the chitosan hydrogel is made into the metal-hydrogel-metal structure, the resonance wavelength of light transmitted changes in real time depending on the humidity of the environment. This is because the chitosan hydrogel repeats expansion and contraction as the humidity changes around it.


Using this mechanism, the team developed a humidity sensor that can convert light’s energy into electricity by combining a solar battery with a water variable wavelength filter made of metal-hydrogel-metal structured metamterial that changes resonance wavelength depending on the external humidity.

The design principle is to overlap the filter’s resonance wavelength with the wavelength where the absorption of the solar cells changes rapidly. This filter is designed to change the amount of light absorption of solar cells depending on the amount of moisture, and to lead to electric changes that ultimately detect the surrounding humidity.

Unlike the conventional optical humidity sensors, these newly developed ones work regardless of the type of light, whether it be natural, LED or indoor. Also, not only does it function without external power, but it can also predict humidity according to the filter’s color.


Professor Junsuk Rho who led the research commented, “This technology is a sensing technology that can be used in places like nuclear power reactors where people and electricity cannot reach.” He added, “It will create even greater synergy if combined with IoT technology such as humidity sensors that activate or smart windows that change colors according to the level of external humidity.”

The study was supported by the Samsung Research Funding & Incubation Center for Future Technology.

1.Fabry-Perot Interferometer
A device where multiple wavelengths enter a filter, and cause multiple interferences to occur in a particular space to transmit only certain wavelengths and reflect the others to select only the desired data.


Volcanic Eruptions Reduce Global Rainfall

– POSTECH Professor Seung-Ki Min’s joint research team identifies the mechanism behind the reduction in precipitation after volcanic eruptions
– Volcano-induced El Niño amplifies the reduction in precipitation. Safety of geoengineering that mimic volcanoes is not guaranteed.


Climate change is occurring all over the globe as 1°C increase in Earth’s surface temperature has led to the sea level rise, abrupt melting of the Arctic sea ice, and the increase in extreme weather events such as heat waves, droughts, and floods. To accurately predict the anthropogenic climate changes under the increase in greenhouse gases, it is important to understand the effects of natural factors such as solar and volcanic activities. A recent study has shown how global precipitation decreases when volcanoes erupt in the tropics.

Professor Seung-Ki Min and Dr. Seungmok Paik of Division of Environmental Science and Engineering at POSTECH and researchers from the French National Centre for Scientific Research, Swiss Federal Institute of Technology in Zurich, and University of Edinburgh have released new findings that the El Niño induced by volcanic eruptions plays a key role in the decrease in global precipitation. So far, studies have shown that volcanic activity reduces precipitation across the globe, but its specific mechanism had been unclear. These research results were recently published in Science Advances, a sister journal of Science.

During the two to three years following Mount Pinatubo’s eruption in 1991, the average global temperature fell by about 0.2 degrees. This is because the massive dust including sulfur dioxide emitted by the eruption reflected the light from the sun and blocked its heat from reaching the Earth’s surface. Volcanic activities, along with this cooling effect, reduce the global terrestrial precipitation but its amplitude greatly varies depending on climate model simulations. For the first time, the joint research team confirmed that the main factor for the drop in precipitation after volcanic eruptions is the difference in El Niño’s response.


El Niño is a natural climate variability that occurs every three to eight years, with weakened trade winds in the equatorial Pacific Ocean and warmer sea surface temperatures in the equatorial eastern Pacific, causing extreme weather conditions across the globe including drought and heavy rains. Under El Niño’s influence, precipitation reduction occurs especially in the global monsoon regions, including Southeast Asia, India, South Africa, Australia and northern South America.

The team compared several climate model simulations and found that El Niño appeared in the year following a volcanic eruption in most models, with a significant drop in precipitation around the global monsoon region. In particular, the strength of El Niño was different for each simulation, and the stronger the El Niño, the more pronounced the reduction in precipitation occurred. The research team also found that the stronger the volcanic forcing and the greater the warm water volume in the western Pacific Ocean, a stronger El Niño developed, which in turn intensified the reduction in precipitation.


These findings are expected to be used to identify the side effects of geoengineering techniques and to predict the climate of the later years. In particular, it suggests that if geoengineering techniques are used to reduce global warming by spraying sulfur dioxide – the main component of volcanic ash – in the lower stratosphere to imitate artificial volcanoes, they could produce unexpected side effect of changing the precipitation patterns across the globe.

Professor Seung-Ki Min stated, “If geoengineering techniques are applied to mimic volcanoes and block sunlight, drought and water shortages may increase significantly in the monsoon regions – home to two-thirds of the world’s population.”

This research was supported by the Mid-career Researcher Program of the National Research Foundation of Korea.

A ‘15-minute’ quick diagnostic testing for newly emerging viruses introduced.

– Prof. Sung Key Jang of POSTECH developed a quick diagnostic testing for viral infections using aptamers.

– This new technology led to beginning of developing a new COVID-19 diagnostic system and a clinical treatment of the disease.

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The novel coronavirus, named as COVID-19, began in Wuhan, China and is threatening all regions around the globe that the World Health Organization (WHO) has declared this outbreak a pandemic since the swine flu 11 years ago. When such a highly contagious and fatal new disease occurs, it is necessary to quickly identify infected individuals and quarantine them. The most important step in this procedure is to have a quick diagnosis of viral infection.

A research team from POSTECH recently developed a quick diagnostic testing for viral infections that can bring results in 15 minutes by using an aptamer (nucleic acid molecule), a kind of molecular capture. This new test can be applied to diagnosis of all novel viruses and is expected to be used in clinical applications as well.

Prof. Sung Key Jang, Dr. Junyoung Kwon, and Dr. Chandan Narayan of Department of Life Sciences, POSTECH with Aptamer Sciences (Inc.) developed a new method (designated as viro-SELEX) for discovering aptamers against membrane proteins. Using viro-SELEX, they were able to develop aptamers with high sensitivity and specificity for binding to target proteins which led to rapid 15-minute diagnosis of viral infections. Their new discovery is published in the renowned journals, Journal of Biomedical Nanotechnology and Analyst.

There are several ways to test viral infections including molecular assays, immunoassays, and virus cultivation. For COVID-19, molecular assays are used to diagnose, however, the whole diagnosis process is not convenient despite of its high sensitivity. It requires the samples to be sent to professional institutions for analysis, takes more than six hours to analyze, and is highly expensive. Virus cultivation takes even longer time to analyze from two to four weeks and is not appropriate for massive tests. Lastly, immunoassays for COVID-19 has not been developed yet. Unfortunately, there has not been a real-time diagnostic test for COVID-19 developed that can be tested on site where the samples are taken.

An aptamer is a nucleic acid that is composed of DNA or RNA. It is kind of a molecular capture that binds to various targets ranging from a low molecular weight compound to macromolecules such as proteins with high specificity and affinity. DNA aptamers are highly stable and therefore easy to transport and store. When the sequence of aptamer is known, it can be synthesized in mass at economical price. So, it is considered as a substitute for an antibody.

Aptamers are discovered through the process called, SELEX*1. However, it has been challenging to develop aptamers through the conventional SELEX method in cases of virus because its targeted molecules are membrane proteins.


The research team generated recombinant baculoviruses*2 (surrogate viruses) containing target proteins on the viral envelope instead of purifying the membrane proteins. They applied the surrogate viruses in the SELEX process (designated as viro-SELEX.

Based on this new method, they generated new aptamers that bound to viral envelope proteins, HA, of influenza virus. Also, they were able to develop a diagnosis kit that changed a color, indicating the infection of virus like a pregnancy test kit by using a pair of aptamers which bound to different areas of HA. If this kit is used for diagnosis of viral infections, 15 minutes is enough to know the result.

“We can develop aptamers that bind to the spike proteins of COVID-19 with high specificity and affinity by using this newly developed viro-SELEX method. And using the aptamers, we can make a quick diagnosis kit. Moreover, these aptamers may also protect healthy cells from COVID-19 infection through interaction and inactivation of spike proteins. In other words, these aptamers could serve as lead molecules for developing a clinical treatment.” said, Prof. Sung Key Jang.

Meanwhile, the research team began developing a diagnostic test for COVID-19 with Korea Research Institute of Chemical Technology, which has the facility to cultivate COVID-19, and Aptamers Science Inc., which developed a KFDA-approved diagnosis of lung cancer for the first time in the world. Their goal is to establish a platform that can rapidly develop diagnosis and treatment of a novel virus such as COVID-19, MERS, and SARS.

1. SELEX, Systematic Evolution of Ligands by Exponential Enrichment
It is also known as in vitro evolution. It is a method for generating nucleic acids that can bind to targeted molecules with high affinity.

2. Baculoviruses
This virus is pathogenic to insects but not harmful to humans. It is often used for producing proteins in mass.