Optical imaging of surface chemistry and dynamics in confinement

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Science  25 Aug 2017:
Vol. 357, Issue 6353, pp. 784-788
DOI: 10.1126/science.aal4346
  • Fig. 1 Optical system and microcapillary imaging.

    (A) Schematic of the 3D second harmonic (SH) microscope. SLM, spatial light modulator; PL, polarizer; BS, beam splitter; PSG, polarization state generator; L, achromatic lens; FP, Fourier plane; NA, numerical aperture; SPF, short pass filter; HWP, half-wave plate; PBS, polarizing BS. Left inset: SH spectrum obtained from the capillary interface. Right inset: Intensity distribution depicting the transverse resolution of the system (red) and that of a commercial scanning multiphoton microscope (blue; Leica SP5, NA 1.2). (B) Phase-contrast image of the microcapillary in aqueous solution. (C and D) SH structured image without (C) and with (D) the pattern phase shifted by π/2. (E) Sum of (C) and (D). (F) HiLo image obtained after applying the HiLo algorithm (27) on (C) and (E) (20). The SH intensity is detectable only if the polarization combination is in the XXX direction (i.e., along the surface normal).

  • Fig. 2 Imaging of surface chemistry and potential.

    (A) SH cross-sectional images (2 μm thick) using the XXX polarization combination for different pH values of the electrolyte solution, recorded with an acquisition time of 5 s per image. The color bar indicates both the intensity ISH and the calculated change in the surface potential Φ0. (B) pKa,s values for the deprotonation reaction of the silica/water interface along the wall of a capillary 100 μm wide, obtained by imaging the change in the surface potential while changing the pH under laminar flow from 2 to 12. The pH is determined using a solution of pH indicator dyes in a separate experiment (20). Note that the values are integrated along the X direction. Scale bar, 10 μm. (C) Change in ISH as a function of pH for two different points labeled in (B), pKa,s(A) = 3.8 and pKa,s(B) = 5.9. The extracted surface potential and computed surface charge density values are also displayed (y axes at right). The arrow indicates the direction of the experiment. (D) Histogram of obtained pKa,s values, reflecting the variance in surface reactivity. The red line represents a Gaussian fit.

  • Fig. 3 Dynamic imaging of surface chemical changes.

    (A) Illustration of the experiment. (B) Illustration of the applied field lines (ΔV > 0). (C) Computed ionic charge density in the aqueous solution adjacent to the interface (fig. S7) (20). (D) Electrostatic field and potential drop for ΔV = 10 V and ΔV = –10 V along the symmetry (Y) axis of the capillary. (E) Snapshots of movie S1, recorded with acquisition time of 250 ms for different values of the applied potential (i, 10 V; ii, –10 V; i + ii, composite of five frames each). The ΔV value corresponding to i, ii, iii, and iv is shown in (G). The legend displays the color coding associated with the applied potential, polarization combination, and multiplication factor. The inset at lower right displays the tip region only. All images were normalized with respect to the illuminating beam profile. (F) 3D rendering of the 10 V and –10 V channels (45 stacks per 4° rotation around the Y axis). The inset shows a zoom-in of the tip. (G) ΔV (green), the spatially integrated SH intensity (XXX polarization, red), and the numerical computation (blue) (20).

Supplementary Materials

  • Optical imaging of surface chemistry and dynamics in confinement

    Carlos Macias-Romero, Igor Nahalka, Halil I. Okur, Sylvie Roke

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S12
    • Captions for movies S1 and S2
    • References and Notes

    Images, Video, and Other Media

    Movie S1
    Temporal variations in the SH intensity from the micro-capillary when a sinusoidal external voltage difference is applied
    Movie S2
    A composite 3D rendering of the oriented water at 10 V (red, cyan) and -10 V (green, purple).

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