Adsorption of a Carboxylated Silane on Gold: Characterization for its Rational Use in Hybrid Glass/Gold Substrates
Cheng Wei Tony Yang, Isaac Martens, Előd L. Gyenge, Robin F.B. Turner and Dan Bizzotto* *Corresponding Author.
[email protected] SUPPORTING INFORMATION
The Supporting Information below corresponds to the sections of “Results and Discussion” in manuscript.
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Atomic Force Microscopy (AFM)
S1. Topography distributions calculated from AFM contact mode images (scanned using the same tip for all images): cleaned gold substrate before sample scan (red), TMS-EDTA modified gold substrate scan (black), and cleaned gold substrate after sample scan (blue).
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Atomic Force Microscopy (AFM)
S2. Friction distributions calculated from AFM contact mode images (scanned using the same tip for all images): cleaned gold substrate before sample scan (red), TMS-EDTA modified gold substrate scan (black), and cleaned gold substrate after sample scan (blue).
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Atomic Force Microscopy (AFM)
S3. The AFM approach force curves for: TMS-EDTA coated gold (red), 11-MUA coated gold (blue), and bare gold substrate after 11-MUA sample scan (black). The peak signal was defined as the boundary of the gold surface (x = 0 nm). 64 approach curves were obtained for each substrate.
AFM force curves was used to provide a rough estimate of the thickness of TMS-EDTA coated layer, relative to 11-MUA coated Au surface. For the force curves, 64 points in an 8 × 8 grid over the same scan size was sampled. The tip approach speed was 117 nm/s to allow for adequately high resolution sampling at 12.5 kHz. Tip deflections (approach and retraction) were obtained for TMS-EDTA and 11-MUA modified gold surfaces. The force curve data from these two samples were compared for further analysis. Data processing for force curves was conducted in MATLAB. Briefly, the 64 approachonly curves were extracted, processed, and analyzed. First derivatives of cantilever deflection vs piezo movement for the interactions of a silicon nitride tip and TMS-EDTA coated gold (red), 11-MUA coated gold (blue), and cleaned gold substrate (black) are presented. A maximum in the derivative was considered as the position of the gold surface and set to 0 nm. It is observed that the first derivative of deflection of the cantilever for 11-MUA coated Au remained constant at a distance from 3 nm to ~1.6 nm, and started to increase from ~1.6 nm until the boundary of Au surface was reached (x = 0 nm). This result confirmed the thickness of 11-MUA on gold surface and validated this approach for determining the thickness of adsorbed layers. Also evident from the Figure is the fact that TMS-EDTA and 11-MUA interactions with the cantilever tip resulted in similar trends (as contrasted with the bare gold surface). These results indicate that TMS-EDTA and 11-MUA both modify Au substrates with comparable thicknesses (i.e. formation of monolayers).
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Infrared Spectroscopy (PM-IRRAS)
S4. An example of background correction method used for PM-IRRAS data analysis. The spectrum of 10% TMS-EDTA (v/v) modified Au gold slide is shown. Raw PM-IRRAS spectrum (solid line) is plotted with background spectrum determined from spline fitting (dotted line). The asterisks were the manually selected points for creating the spline curve.
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Infrared Spectroscopy (PM-IRRAS)
S5. The background corrected spectrum for 10% TMS-EDTA (v/v) modified Au gold slide is shown. Subsequently, this raw Absorbance spectrum is corrected for sample gain(s) in MATLAB.
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Infrared Spectroscopy (PM-IRRAS)
S6. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) transmission spectra of bulk TMS-EDTA (blue), EDTA (green), and 3-APTMS (red) mixed with KBr powder. The alkyl stretching region (3200-2700 cm-1) is shown. EDTA = ethylenediaminetetraacetic acid.
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Infrared Spectroscopy (PM-IRRAS)
S7. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) transmission spectra of bulk TMS-EDTA (blue), EDTA (green), and 3-APTMS (red) mixed with KBr powder. The fingerprint region (1800-800 cm-1) is shown. EDTA = ethylenediaminetetraacetic acid.
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Infrared Spectroscopy (PM-IRRAS)
S8. Infrared spectra of 3-APTMS: ATR-FTIR transmission spectrum (black) of bulk 3-APTMS mixed with KBr powder, and PM-IRRAS absorption spectrum (red) of 3-APTMS coated planar gold slide. The alkyl stretching region (3200-2700 cm-1) is shown.
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Infrared Spectroscopy (PM-IRRAS)
S9. Infrared spectra of 3-APTMS: ATR-FTIR transmission spectrum (black) of bulk 3-APTMS mixed with KBr powder, and PM-IRRAS absorption spectrum (red) of 3-APTMS coated planar gold slide. The fingerprint region (1800-800 cm-1) is shown.
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Infrared Spectroscopy (PM-IRRAS)
S10. Infrared spectra of TMS-EDTA: ATR-FTIR transmission spectra (black) of bulk TMS-EDTA mixed with KBr powder, and PM-IRRAS absorption spectra (red) of TMS-EDTA coated planar gold slide. The alkyl stretching region (3200-2700 cm-1) is shown. The ATR-FTIR spectrum of TMS-EDTA was background subtracted to obtain a flat baseline.
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Infrared Spectroscopy (PM-IRRAS)
S11. Infrared spectra of TMS-EDTA: ATR-FTIR transmission spectra (black) of bulk TMS-EDTA mixed with KBr powder, and PM-IRRAS absorption spectra (red) of TMS-EDTA coated planar gold slide. The fingerprint region (1800-800 cm-1) is shown.
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Electrochemical Differential Capacitance Measurements
The area of the Au bead electrode was estimated using the following procedure: 1. Capacitance curves of 50 mM Perchlorate Buffer (pH 12) and DiffCap Buffer (pH 12) were obtained. 2. The raw capacitance value of Perchlorate Buffer at -0.9V was determined to be ~4.26µF. 3. The capacitance value from Step 2) was divided by by 17µF/cm2 (a value proposed by Shepherd et al. to be constant for the negative potentials of Perchlorate Buffer) to obtain an estimate of the area of the gold bead electrode. 4. An electrode area of ~0.25 cm2 was determined. 5. Subsequently, the correction factor (for taking into account the area of the Au bead electrode) for all differential capacitance curves was determined by dividing the capacitance of DiffCap Buffer at -0.9V (~4.11µF) by the area estimated from Step 4), and a value of 16.4µF/cm2 was determined.
S12. The area of the Au bead electrode was estimated by dividing the capacitance of Perchlorate Buffer pH 12 at -0.9V (~4.26µF) by 17µF/cm2. An electrode area of ~0.25 cm2 was determined. Subsequently, the capacitance at -0.9V for DiffCap Buffer pH 12 (~4.11µF) was divided by the estimated area, and the correction factor of 16.4µF/cm2 was determined.
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Electrochemical Differential Capacitance Measurements
S13. The Open Circuit Potentials (OCP) of cleaned bare Au bead electrode immersed in 10% TMSEDTA (v/v) solution with (dotted curve) and without (solid curve) oxygen were determined.
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Electrochemical Differential Capacitance Measurements
S14. Averaged and normalized electrochemical differential capacitance data at equilibrium (360 s with stirring) for individual DiffCap buffer components: 1) 100 mM phosphate (circle), 2) 100 mM phosphate and 65 mM KOH (square), and 3) DiffCap Buffer (triangle) – 100 mM phosphate, 65 mM KOH, and 500 mM KCl.
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Electrochemical Differential Capacitance Measurements
S15. Raw capacitance data for DiffCap Buffer measurements from four independent experiments (from four different days).
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Electrochemical Differential Capacitance Measurements
S16. Averaged raw DiffCap Buffer data and its corresponding standard deviation obtained from taking the average of the four curves in previous figure. These standard deviation values were used to estimate the errors in Frumkin fittings (to obtain the free energies of adsorption and the lateral interaction parameters).
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Electrochemical Differential Capacitance Measurements
S17. Raw capacitance data for three independent measurements (from three different days) of 20µM TMS-EDTA in DiffCap buffer. Small differences in the shape of the curves were observed, indicating high reproducibility of the experimental procedure.
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Electrochemical Differential Capacitance Measurements
S18. The stability of freshly cleaned bare Au bead electrode (circle) and TMS-EDTA modified Au bead electrode (square) in DiffCap buffer.
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Electrochemical Differential Capacitance Measurements
S19. The calculated surface coverage curves for all potentials. Pseudo-capacitance features are clearly visible for potentials less than -0.5V. As a result, only surface coverage values for potentials between -0.5 V and 0.2 V were analyzed.
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Electrochemical Differential Capacitance Measurements
S20. Titration curve for adding 1M HCl to 10% TMS-EDTA (v/v) solution.
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