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pH Sensing Properties of Flexible, Bias‐Free Graphene Microelectrodes in Complex Fluids: From Phosphate Buffer Solution to Human Serum
Author(s) -
Ping Jinglei,
Blum Jacquelyn E.,
Vishnubhotla Ramya,
Vrudhula Amey,
Naylor Carl H.,
Gao Zhaoli,
Saven Jeffery G.,
Johnson Alan T. Charlie
Publication year - 2017
Publication title -
small
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.785
H-Index - 236
eISSN - 1613-6829
pISSN - 1613-6810
DOI - 10.1002/smll.201700564
Subject(s) - graphene , microelectrode , buffer (optical fiber) , analytical chemistry (journal) , current (fluid) , buffer solution , chemistry , faradaic current , phosphate buffered saline , materials science , chemical physics , nanotechnology , electrode , chromatography , electrochemistry , reference electrode , thermodynamics , computer science , physics , telecommunications
Advances in techniques for monitoring pH in complex fluids can have a significant impact on analytical and biomedical applications. This study develops flexible graphene microelectrodes (GEs) for rapid (<5 s), very‐low‐power (femtowatt) detection of the pH of complex biofluids by measuring real‐time Faradaic charge transfer between the GE and a solution at zero electrical bias. For an idealized sample of phosphate buffer solution (PBS), the Faradaic current is varied monotonically and systematically with the pH, with a resolution of ≈0.2 pH unit. The current–pH dependence is well described by a hybrid analytical–computational model, where the electric double layer derives from an intrinsic, pH‐independent (positive) charge associated with the graphene–water interface and ionizable (negative) charged groups. For ferritin solution, the relative Faradaic current, defined as the difference between the measured current response and a baseline response due to PBS, shows a strong signal associated with ferritin disassembly and the release of ferric ions at pH ≈2.0. For samples of human serum, the Faradaic current shows a reproducible rapid (<20 s) response to pH. By combining the Faradaic current and real‐time current variation, the methodology is potentially suitable for use to detect tumor‐induced changes in extracellular pH.