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Graphene as an Imaging Platform of Charged Molecules.

ABSTRACT: Graphene, a single atom layer of carbon atoms, provides a two-dimensional platform with an extremely high sensitivity to charges due to its unique band structure and high surface-to-volume ratio. Graphene field-effect transistor (G-FET) biosensors have, indeed, demonstrated a detection limit of subnanomolar or even subpicomolar. However, in G-FET, signal is averaged throughout the whole channel, so there remains a need to visualize the spatial distribution of target molecules on a single G-FET, to provide further insight into target molecules and/or biological functions. Here, we made use of graphene as an imaging platform of charged molecules via Raman microscopy. Positively (or negatively) charged microbeads with a diameter of 1 ?m were dispersed in a buffer solution and were attached on graphene. We found out that Raman peaks of graphene, where positively (or negatively) charged beads contacted, were up-shifted (or down-shifted) significantly, indicating that the carrier density in the graphene was locally modulated by the charged beads and the charge state of the beads was represented by the peak-shift direction. From the peak shift, the change in the carrier density was calculated to be +1.4 × 1012 cm-2 (or -1.0 × 1012 cm-2). By taking Raman peak-shift images, we visualized distribution of charged molecules on graphene with a spatial resolution below 1 ?m. The technique described here overcomes the limitation of spatial resolution of G-FET and provides a new route to graphene-based chemical and biosensors.

SUBMITTER: Ushiba S

PROVIDER: S-EPMC6044899 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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Graphene as an Imaging Platform of Charged Molecules.

Ushiba Shota S Ono Takao T Kanai Yasushi Y Inoue Koichi K Kimura Masahiko M Matsumoto Kazuhiko K

ACS omega 20180315 3

Graphene, a single atom layer of carbon atoms, provides a two-dimensional platform with an extremely high sensitivity to charges due to its unique band structure and high surface-to-volume ratio. Graphene field-effect transistor (G-FET) biosensors have, indeed, demonstrated a detection limit of subnanomolar or even subpicomolar. However, in G-FET, signal is averaged throughout the whole channel, so there remains a need to visualize the spatial distribution of target molecules on a single G-FET, ...[more]

PMID: 30023861

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Project description:BackgroundApplications of electric-field-induced permeabilization of cells range from cancer therapy to wastewater treatment. A unified understanding of the underlying mechanisms of membrane electropermeabilization, however, has not been achieved. Protocols are empirical, and models are descriptive rather than predictive, which hampers the optimization and expansion of electroporation-based technologies. A common feature of existing models is the assumption that the permeabilized membrane is passive, and that transport through it is entirely diffusive. To demonstrate the necessity to go beyond that assumption, we present here a quantitative analysis of the post-permeabilization transport of three small molecules commonly used in electroporation research - YO-PRO-1, propidium, and calcein - after exposure of cells to minimally perturbing, 6 ns electric pulses.ResultsInflux of YO-PRO-1 from the external medium into the cell exceeds that of propidium, consistent with many published studies. Both are much greater than the influx of calcein. In contrast, the normalized molar efflux of calcein from pre-loaded cells into the medium after electropermeabilization is roughly equivalent to the influx of YO-PRO-1 and propidium. These relative transport rates are correlated not with molecular size or cross-section, but rather with molecular charge polarity.ConclusionsThis comparison of the kinetics of molecular transport of three small, charged molecules across electropermeabilized cell membranes reveals a component of the mechanism of electroporation that is customarily taken into account only for the time during electric pulse delivery. The large differences between the influx rates of propidium and YO-PRO-1 (cations) and calcein (anion), and between the influx and efflux of calcein, suggest a significant role for the post-pulse transmembrane potential in the migration of ions and charged small molecules across permeabilized cell membranes, which has been largely neglected in models of electroporation.

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Graphene as an Imaging Platform of Charged Molecules.

Publications

Graphene as an Imaging Platform of Charged Molecules.

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