Some creatures in nature, such as chameleons, turkeys, etc., change their color to adapt to changes in the environment. These adaptive colors are achieved by changing the volume or thickness of the soft layer of cells or proteins in response to environmental stimuli (e.g., temperature, humidity, etc.). Today, in a modern society with multiple pollutants, visual adaptation is also required to intuitively sensing humidity, light, temperature, specific molecular concentrations, etc., so as to achieve visual responses such as weather forecasting and air quality detection. Thus, environmentally sensitive discoloration materials can be monitors that transcend human perception. As research progresses, structural shading schemes based on photonic crystals open up unprecedented possibilities in colorimetric sensor applications. However, the current study has the problem of slow response and single color selection, which is difficult to meet the needs of rapid response and selective color response in practical applications.
Young Min Song of Gwangju Institute of Science and Technology in South Korea, Jin-Woo Oh of Pusan University, et al. proposed a colorimetric sensor based on a dynamically responding virus (M-13 phage) with a highly depleted resonance promoter (HLRP). The ultra-thin M-13 phage layer responds quickly to external stimuli, exhibits reliable color-changing behavior, and adjusts color from the corresponding palette without modifying the dynamic response layer. During a real-world demonstration, a colorimetric sensor that is insensitive to external stimuli can intuitively sense environmental changes by hiding/showing patterns. In addition, the colorimetric sensor is tested for monitorability in harsh environments by exposure to a variety of volatile organic chemicals. The study was published in Advanced Science as a paper titled "Large-Area Virus Coated Ultrathin Colorimetric Sensors with a Highly Lossy Resonant Promoter for Enhanced Chromaticity."
【Preparation and Characterization of Colorimetric Sensor】
Figure 1a shows a colorimetric sensor coated with virus. The M-13 viral layer used as a dynamic response layer expands/dissolves due to external changes, resulting in colorimetric behavior of HLRP. This phage is a bacterial virus consisting of single-stranded DNA wrapped around various primary and secondary shell proteins (Figure 1b). Thus, a colorimetric sensor with a hydrophilic phage layer can show a noticeable color change for changes in humidity (Figure 1d). This noticeable color change in the HLRP bacteriophage layer compared to other substrates is achieved by strong resonance absorption at specific wavelengths (Figure 1e). To confirm the resonance enhancement effect of HLRP with the phage layer, the authors calculated the dynamic variation reflection spectra of HLRP and other substrates (Figure 1g), and the results showed that the sensor was sensitive to the spectral response of color in the wavelength range of 500-600 nm. In order to improve the practicality of this scheme, the authors prepared a uniform large-area ultra-thin bacteriophage layer by spin coating method. This method uses an electron beam evaporator, deposited on wafer-level HLRp through the cornea, resulting in a uniformly covered large area of ultra-thin bacteriophage layer (Figure 1h).
Figure 1 Preparation and characterization of colorimetric sensors
【Selective color response of the sensor】
To optimize the design of the HLRP, Figure 2a shows an contour plot of the calculated reflectance versus a specific refractive index wavelength (λc = 500 nm), as well as a schematic diagram of the composition of each separated HLRP layer. These reflective regions with the wide wavelength of HLRP move within the visible light range, resulting in colorimetric behavior (Figure 2c). To confirm the correlation between the chromaticity response and dynamic changes, Figure 2d shows the RGB color set, where the thickness of each coating is 60 nm, i.e., the initial thickness of the spin-coated viral layer is 100 nm. By adjusting the design of the HLRP, the authors achieve significant color changes in the dynamic response layer, and the chromaticity values change widely or locally with dynamic changes within the RGB gamut. Figure 2g shows a color set with a variety of color selectivity in various material combinations, which provides a selective color response of the colorimetric sensor, thereby enabling a color design that is sensitive/insensitive to external stimuli.
Figure 2 Diversity of selective color responses
Figure 3 Optimization of the manufacturing process of the sensor
【Volatile Organic Compound Detection】
Figure 4a shows wild-type (WT) phage detection by three genetically engineered types (3A, 4E, and 3W) phages and shows a range of sensing processes for colorimetric sensors. Due to the sensitivity of HLRP to color, each pixel coated with four different bacteriophages can show a noticeable color change. To analyze these color responses, the RGB value of the sensor is detected under a series of volatile organic compounds at varying concentrations. Each genetically engineered phage responds selectively to different substances through the interaction properties of each receptor. Using these built-in responses of genetically engineered bacteriophages, each combination of RGB values corresponding to the concentration and type of organic compound forms a dataset. For the selectivity of the sensor to various substances, Figure 4b depicts a pattern that combines the selective color development response of each genetically engineered bacteriophage to different substances. These patterns show the specific shape of each substance and also have different color patterns corresponding to each chemical at ppb concentrations (Figure 4c).
Figure 4 Selective color response to different substances
Summary: The author proposes a fast, dynamic-response color-changing material with simple structure and high color selectivity, allowing the design of a colorimetric sensor that can intuitively detect environmental changes. The ultra-thin M-13 phage layers, which are rotated on HLRP, exhibit sensitive colorimetric behavior while having strong resonance changes for rapid dynamic response. In addition, the method enables the detection of hazardous chemicals and is suitable for large-area manufacturing, laying the foundation for future use in everyday and industrial environments.
Original link:
https://onlinelibrary.wiley.com/doi/10.1002/advs.202000978
Source: Frontiers of Polymer Science
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