Plasmonic-based imaging of local square wave voltammetry

Abstract

Square wave voltammetry (SWV) is widely used in electrochemical analysis and sensors because of its high sensitivity and efficient rejection of background current, but SWV by the conventional electrochemical detection method does not provide spatial resolution. We report here a plasmonic method to image local SWV, which opens the door for analyzing heterogeneous electrochemical reactions and for high-throughput detections of microarrays. We describe the basic principle, validate the principle by comparing the plasmonic-based SWV with those obtained with the conventional method, and demonstrate imaging capability for local electrochemical analysis.

Figure 1

(a) Potential waveform for SWV. It consists of square waves superimposed on a linear potential, sweeping from 0 to −0.3 V. (b) Plasmonic response due to the potential waveform shown in (a). (c) Transient current density vs. potential obtained with the conventional electrochemical method. (d) Transient current density vs. potential of the same electrode obtained with the plasmonic-based method. (e) SWV obtained with the plasmonic method. (f) SWV obtained with the conventional electrochemical method. I_f and I_r in (e) and (f) are forward current and reverse current, extracted at the end of each of the forward potential step, and reverse potential step, respectively.

Figure 2

(a) Plasmonic responses in 10 mM Ru(NH₃)₆³⁺ + 0.2 M NaF (red) and in 0.2 M NaF (green). The former contains both the redox reaction current and background current, while the latter contains only the background current. The difference of the two (blue) taken by subtracting the red curve from the blue curve presents background corrected SWV. Note that for clarity the background corrected SWV is shifted up by 30 units. (b) Corresponding plasmonic current densities vs. potential. (c) Zooming-in of current density signals of two potential steps. (d) SWVs with (red) and without correction of the background charging effect (blue).

Figure 3

(a) Surface Plasmon resonance image of a Au surface patterned with thiols (the surface potential was not controlled), the scale bar is 100µm. (b) Local SWVs of the regions marked in (a). (c-f) Snapshots of SWV video of the surface at different potentials (which are pointed out in (b)).

Scheme 1

Experiment setup of SWV imaging. See text for details.