HaloTag-Modified, Ferrocene Labeled Self-Assembled Monolayers for Protein Sensing
Ferrocene (Fc)-based disulfide molecules of various lengths with amino acid scaffolds and alkane or oligo(phenylene-ethynylene) (OPE) bridges are used in a mixed SAM with a di-(ethylene oxide) terminal mercaptoundecanol diluent (PEG<sub>2</sub>). The relative height of the Fc redox reporter in the SAM is compared to determine if there are protective effects like antifouling and specific detection. The HaloTag-binding motif is used as a proof-of-concept to investigate the electrochemical response to the HaloTag protein due to its known covalent and fast linkage. When the Fc-SAMs are exposed to the HaloTag protein, there are an antifouling nature and more specific detection for the engulfed Fc-based molecules (<b>C</b><sub><b>6</b></sub><b>tBu/Halo</b>). The further out the Fc is from the SAM layer, the more nonspecific adsorption is detected. The double layer capacitance (CD<sub>L</sub>) has the smallest change for the <b>C</b><sub><b>6</b></sub><b>tBu</b> control (ΔCD<sub>L</sub> = -0.1 μF cm<sup>-2</sup>) showing antifouling properties and produces a large change (ΔCD<sub>L</sub> = 0.9 μF cm<sup>-2</sup>) as well as a shift in oxidation potential when the active <b>C</b><sub><b>6</b></sub><b>Halo</b> is exposed to the HaloTag protein (Δ<i>E</i><sub>1/2</sub> = 50 ± 10 mV). The remaining Fc molecules are partially in or outside the PEG<sub>2</sub> layer, allowing more ion penetration/mobility even when the HaloTag protein is bound. Generally, a more disordered environment was observed for the Fc-based molecules when adding the HaloTag ligand, which is evident from a larger <i>E</i><sub>fwhm</sub> and higher CD<sub>L</sub>. Desorption of the SAMs with sodium iodide (NaI) showed retention of the HaloTag protein bound with the corresponding ligand, whereas negative controls did not. Self-assembled monolayers for MALDI mass spectrometry (SAMDI-MS) were used as an orthogonal detection technique to show the qualitative binding of the HaloTag protein to the electrode. Together, these results provide insight into the antifouling and detection methods of engulfing the redox molecules in the SAM diluent.
Authors
- Xudong Ji (ORCID: https://orcid.org/0000-0003-3068-3650)
- Andrew R. Brotherton (ORCID: https://orcid.org/0000-0002-7260-2006)
- Eric J. Berns (ORCID: https://orcid.org/0000-0002-2203-0847)
- Matthew D. Bailey (ORCID: https://orcid.org/0000-0002-7870-234X)
- Milan Mrksich (ORCID: https://orcid.org/0000-0002-4964-796X)
- Kyle T. Sullivan (ORCID: https://orcid.org/0000-0002-1779-2919)
- Jonathan Rivnay (ORCID: https://orcid.org/0000-0002-0602-6485)
- Guru Prakash Neupane (ORCID: https://orcid.org/0000-0002-8947-1428)
- Thomas J. Meade (ORCID: https://orcid.org/0000-0001-6202-1155)
Institutions
- Evanston Hospital (US)
Publication Details
- Journal
- Langmuir
- Published
- 2024-10-16
- DOI
- https://doi.org/10.1021/acs.langmuir.4c02941
- Primary Topic
- Molecular Junctions and Nanostructures
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- National Science Foundation
- U.S. Department of the Interior
- Northwestern University
- Defense Advanced Research Projects Agency
- Advanced Research Projects Agency
- Materials Research Science and Engineering Center, Harvard University
- Interior Business Center
- International Institute for Nanotechnology, Northwestern University
- National Institute of Biomedical Imaging and Bioengineering
- Division of Materials Research
- Division of Electrical, Communications and Cyber Systems