Chemical sensors based on polymeric materials have been widely investigated since it is easy to amplify the signal and fabricate into practical forms such like solutions, films, and free-standing membranes. These concepts need characteristic interaction between polymers and target molecules such as heavy metal ions, warfare agents, and bio-materials giving a measurable signal in response like fluorescence, color, and structure changes. Among the different types of sensor, Fluorescent polymer sensors have received great deal of attention due to their ability to detect targets at low concentrations and easily measurable optical event. To improve the sensing ability, various functional groups have been introduced into sensor applications and moreover, Self-assembled polymer electrolytes which used can form the specific structures have been used it can lead to the spatial benefits for effective interactions or dynamic changes in structure and signal response.
In this regard, our group reported the new ratiometric pH sensor based on poly(N-phenylmaleimide) (PPMI)-containing block copolymer that emits three different fluorescent colors depending on the pH. The strong solvatochromism and tautomerism of the PPMI derivatives enabled precise pH sensing for almost the entire range of the pH scale. Theoretical calculations have predicted largely dissimilar band gaps for the keto, enol, and enolate tautomers of PPMI owing to lowdimensional conjugation effects. The tunable emission wavelength and intensity of our sensors, as well as the reversible color switching with high-luminescent contrast, were achieved using rational molecular design of PPMI analogues as an innovative platform for accurate H+ detection. The self-assembly of block copolymers on the nanometer length scale was particularly highlighted as a novel prospective means of regulating fluorescence properties while avoiding the self-quenching phenomenon, and this system can be used as a fast responsive pH sensor in versatile device forms.
(Ahn, H. et al. ACS Applied Materials & Interfaces 2015 , 7 , 704-712)
We developed the effective fluorescence sensor using sulfonated block copolymer electrolytes to detect Cu(II) ions in aqueous media. Due to the several benefits from self-assembly and functional groups, this sensor can be considered as a powerful sensor. Research on the development of self-assembled fluorescence sensors is also being performed continuously in our lab and we expect that fluorescence polymer sensors become a promising materials for sensory system to apply into pollutant sensors, medical diagnosis, and real-life applications.
(Ahn, H. et al. ACS Nano 2013 , 7 , 6162-6169)
As the other type of chemical sensors, polymeric humidity sensors which exhibit the change of their physical property depending on humidity have been extensively investigated in past decades. To our knowledge, polymeric humidity sensors usually need a few minutes to change their physical property in response to humidity change. In contrast, a humidity sensor developed by our lab, exhibit extremely fast self-displayed discernible reflective color changes from violet to red, and a few orders of magnitude changes in impedance with exposure to humid air, at the same time. It is due to the fact that nanostructures can help water diffusion through short pathways in nanometer scales and it can be the powerful tools for food industry, medical science, and electronic applications.
(Kim, E. et al. ACS Appl. Mater. Interfaces 2012 , 4 , 5179-5187)