2022 Fiscal Year Annual Research Report
Investigation and biosensing application of novel switching function in conductive polymer hydrogels
| Project/Area Number |
22F22729
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| Allocation Type | Single-year Grants |
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| Research Institution | The University of Tokyo |
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Principal Investigator |
坂田 利弥 東京大学, 大学院工学系研究科(工学部), 准教授 (70399400)
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| Co-Investigator(Kenkyū-buntansha) |
TSENG ALEX 東京大学, 工学(系)研究科(研究院), 外国人特別研究員
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| Project Period (FY) |
2022-07-27 – 2024-03-31
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| Keywords | electrochemical sensing / PEDOT |
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| Outline of Annual Research Achievements |
Using UV-Vis-NIR spectroelectrochemistry, we studied the interaction of PEDOT during redox cycling of quinones from bound catechol functional groups in a composite polymer. Whereas PEDOT absorbance band shifts from visible (550 nm) to IR (>900nm) wavelengths during oxidation and reduction, respectively, quinone bands shift from visible (400 nm) to UV (280 nm). Thus, the oxidation state of redox active components and their relative proportions can be followed in-situ. Repeated cycling in physiological buffer conditions found an unexpected accumulation of oxidized PEDOT and reduced catechol, suggesting the formation of a charge-transfer complex between the two species.
Using flexible polyimide substrates, we successfully fabricated devices with suspended channels. Access to electrolyte from top and bottom sides of the hydrogel reduced the effective thickness by half resulting in improved mass transport. Accordingly, the cut-off frequency in the response of a hydrogel transistor amplifier was doubled and the rate of electrocatalyzed oxygen reduction reaction was improved. This new device structure facilitates the use of AC impedance spectroscopy to control the kinetics involved in the evolution of an electrochemical sensing signal.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In FY2022, we planned for two mail goals: first, to incorporate optical absorbance spectroscopy in our experiments; and second, to develop a new device structure using suspended hydrogel channels. Both goals have been achieved.
Using UV-Vis-NIR spectroelectrochemistry, we studied the interaction of PEDOT during redox cycling of quinones from bound catechol functional groups in a composite polymer. Whereas PEDOT absorbance band shifts from visible (550 nm) to IR (>900nm) wavelengths during oxidation and reduction, respectively, quinone bands shift from visible (400 nm) to UV (280 nm). Thus, the oxidation state of redox active components and their relative proportions can be followed in-situ. Repeated cycling in physiological buffer conditions found an unexpected accumulation of oxidized PEDOT and reduced catechol, suggesting the formation of a charge-transfer complex between the two species.
Using flexible polyimide substrates, we successfully fabricated devices with suspended channels. Access to electrolyte from top and bottom sides of the hydrogel reduced the effective thickness by half resulting in improved mass transport. Accordingly, the cut-off frequency in the response of a hydrogel transistor amplifier was doubled and the rate of electrocatalyzed oxygen reduction reaction was improved. This new device structure facilitates the use of AC impedance spectroscopy to control the kinetics involved in the evolution of an electrochemical sensing signal.
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| Strategy for Future Research Activity |
In FY2023, we will proceed to study the effect of monomer composition on the structural, electrochemical, and electro-mechanical properties of the double network hydrogel. Using co-polymers of polyacrylamide, we aim to incorporate functional groups with cationic (e.g., amine), zwitterionic (e.g., sulfobetaine, carboxybetaine), and redox active (e.g., catechol, aminoxyl) properties. Because oxidized PEDOT exists as a complex with anions in aqueous conditions, we expect that altering the electrostatic environment within the hydrogel will mediate charge screening and lead to changes in electronic transport and electro-mechanical behaviour. Additionally, bound redox centers can serve as indicators of electrochemical state, with read-outs by multiple means as previously discussed.
Currently, we are constructing experimental apparatus to support lyophilization (i.e., freeze-drying) of hydrogels. Although this is primarily intended to enable accurate micro-structure characterization of physically cross-linked hydrogels, additional capability for low-temperature processing may enable other techniques such as freeze-casting or pore-size modification to further tune the mechanical and mass transport properties of these materials.
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