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This paper is concerned with long-distance interactions between an unbiased metal nanoparticle (NP) and a nanoelectrode employed as a tip in the scanning electrochemical microscope (SECM). A NP immobilized on the inert substrate acts as a bipolar electrode, producing positive SECM feedback. The tip current magnitude depends strongly on the ratio of the particle and tip radii and the heterogeneous charge-transfer kinetics. The onset of electron tunneling was observed at very short separation distances (<2–3 nm) at which the NP behaves as a part of the tip electrode. The rate constant of the electron-transfer (ET) or electrocatalytic reaction at the NP can be extracted from either feedback or tunneling current. The tunneling mode of SECM can be used to investigate heterogeneous reactions occurring at a single NP without making an ohmic contact with it. This technique can also help elucidate nanoparticle/electrode interactions in various electrochemical systems ranging from NPs immobilized on the electrode surface to nanoimpact collision events.
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Electrochemical characterization of the stimuli-response of surface-immobilized elastin-like polymers
Elastin-like polymers (ELPs) are frequently used in a variety of bioengineering applications because of their stimuli-responsive properties. Above their transition temperature, ELPs will adopt different structures that promote intra- and intermolecular hydrophobic contacts to minimize unfavorable interactions with an aqueous environment. We electrochemically characterize the stimuli-responsive behavior of surface-immobilized ELPs corresponding to two proposed states: extended and collapsed. In the extended state the ELPs are more solvated. In the collapsed state, triggered by introducing an environmental stimulus, non-polar intramolecular contacts within ELPs are favored, resulting in quantifiable morphological changes on the surface characterized using electrochemical impedance spectroscopy (EIS). Charge transfer resistance, a component of impedance, was shown to increase after exposing an ELP modified electrode to a high salt concentration environment (3.0 M NaCl). An increase in charge transfer resistance indicates an increase in the insulating layer on the electrode surface consistent with the proposed mechanism of collapse, as the ELPs have undergone morphological changes to hinder the kinetics of the redox couple exchange. Further characterization of the surface-immobilized ELPs showed a reproducible surface modification, as well as reversibility and tunability of the stimuli-response.
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- PAR ID:
- 10124973
- Date Published:
- Journal Name:
- Soft Matter
- ISSN:
- 1744-683X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9SM01681C
