Stimuli-Responsive Polymer-Based Colorimetric Sensors

• Author / Creator

  Pereira Carvalho, Wildemar Stefanio

• We have witnessed significant progress in the past few decades in the development of stimuli-responsive polymer-based smart materials. A great deal of work has been dedicated to the development of sensors and biosensors that are portable, inexpensive and easy-to-use to be used in resource limited settings where these technologies need to be incredibly robust. The Serpe group discovered colorimetric sensors that are composed of a highly packed pNIPAm-based microgel monolayer “sandwiched” between two thin reflective Au layers, forming an etalon structure. The versatility of the microgels, the ability to easily modify their composition to obtain different responsiveness, and their incorporation into an etalon device makes it possible to develop optical sensors for a numerous of applications. The color of the etalon is a result of light interference within its structure. The group has demonstrated in various publications their potential in detecting a number of analytes in aqueous solution. My Ph.D. research focused on the etalon fabrication process and exploring their ability to be used as portable sensors. Firstly, we developed a painting platform and fabricated highly uniform and reproducible etalon devices using the proposed “doctor blade” technique. We also demonstrated that the quality of the etalon devices is not affected when fabricated by different individuals. Furthermore, we decreased the size of the etalons down to 4 mm2, which allows the fabrication of 1,024 etalons per batch. This is extremely important for larger scale production and commercialization of the technology. Following, a quality control procedure was developed and the etalon’s ability to predict solution pH was evaluated. Here, we characterized their color (RGB values) as a function of pH and studied the effects of variations on temperature, ionic strength and type of ions in solution on their pH measurement accuracy. Moreover, we also demonstrated their potential to be used as portable sensors for quality control. In collaboration with SolarDew International, the etalon devices were used to detect changes in ionic strength of distilled water. Finally, we investigated how the etalon devices respond to different ions belonging to the Hofmeister series and analysed their response kinetics. It was observed that the responses to ions could be predicted based on Hofmeister series and detailed analysis of the response kinetics could provide information of the type of ions in solution.

• Subjects / Keywords

  • Smart polymers
  • pNIPAm microgels
  • colorimetric sensors
  • polymer-based sensors
  • etalon devices

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-f7zw-5v34

• License

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