Nanotechnology

Expanded color gamut with fast-response colorimetric sensor for real-time monitoring

The proposed sensor design incorporates a porous germanium layer (Pr-Ge) that significantly improves the color representation and a nanohole array that increases the responsiveness of the sensor. Credit: Busan University Associate Professor Gil Ju Lee

Colorimetric sensors detect changes in the environment by intuitively changing colors, easily visible to the naked eye without the need for additional equipment. Moreover, it operates with zero power consumption. By producing a visual change in color without the need for additional equipment, these sensors could play a key role in applications such as food packaging and preservation of ancient artifacts, where optimal humidity is critical for quality control. There is a gender.

To accurately detect humidity, a colorimetric sensor must cover a wide range of colors, exhibit a linear correlation between color and humidity, respond quickly, and maintain long-term stability. In general, sensors that achieve color development through structural changes have an advantage over sensors based on chemical reactions.

Among these, Fabry-Perot resonance-based metal-hydrogel-metal (MHM) structures stand out due to their simplicity and the production of diverse colors, which are often used to create cavities in hydrogels using swelling materials such as chitosan. Because changes in thickness result in different colors. However, traditional designs still suffer from limited color representation and slow response times.

To address these issues, a Korean research team led by Associate Professor Gil Ju Lee from Busan National University’s School of Electrical and Electronic Engineering has developed an innovative two-dimensional (2D) nanostructured Fano resonant colorimetric sensor (nFRCS). did.

Dr. Lee said, “Our design introduces a nanohole array that utilizes Fano resonance and plasmonic resonance, which significantly improves the color gamut by controlling the reflectance spectrum from subtractive to additive color mixture. Furthermore, these nanohole channels also have improved responsiveness. The results of this study are published in the journal Optica.

nFRCS consists of a silver-chitosan-silver MHM structure with a thin top layer and a thick bottom layer. The MHM also has a thin porous germanium (Pr-Ge) coating. This coating is an important addition that transforms the MHM from a Fabry-Perot cavity to a Fano cavity, which significantly improves the color representation.

Furthermore, nFRCS incorporates a 2D nanohole array (NHA) into the MHM layer, establishing a direct route for water vapor in the surrounding environment to reach and interact with the chitosan layer. Due to the hydrophilic nature of chitosan, under high humidity conditions, chitosan absorbs water molecules and swells, and under dry conditions, it releases water molecules and shrinks in volume, resulting in a color change depending on the humidity level. .

These NHAs also improve the responsiveness of the sensor, and their ordered pattern promotes additional light-matter interactions such as surface plasmon resonance (SPP) and localized surface plasmon resonance (LSPR), further improving performance.

The researchers fabricated the nFRCS sensor using roll-to-plate nanoimprint lithography (NIL). NIL uses a stamping-like method to transfer nanoscale patterns to the MHM layer. Compared with traditional expensive nanostructure fabrication techniques, this method saves both time and cost.

In experiments, the fabricated nFRCS exhibited a wide color gamut exceeding standard RGB (sRGB), with sRGB coverage of 141% and Adobe RGB coverage of 105%, outperforming previous studies. Furthermore, it showed excellent responsiveness with a response time of 287 ms and a recovery time of 87 ms.

Highlighting the sensor’s wide range of applications, Dr. Lee said, “Beyond humidity sensing, nFRCS can also act as a health monitoring device, intelligent display, and interior material, reacting to external stimuli by producing distinct color shifts. This design could work as a framework for other types of colorimetric sensors to detect various environmental changes other than humidity. ”

Overall, this innovative sensor represents a major advance for zero-power, real-time environmental monitoring.

More information: Hee Jun Nam et al, Ultrafast, Fano resonant colorimetric sensor with high chromaticity beyond standard RGB, Optica (2024). DOI: 10.1364/OPTICA.532433

Provided by Busan University

Source: Fast-response colorimetric sensor expands color gamut for real-time monitoring (October 18, 2024) from https://phys.org/news/2024-10-fast-colorimetric-sensor-real-gamut 2024 Retrieved October 20, 2015.html

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