Electrochemical Detection and Analysis of Various Current Responses of a Single Ag Nanoparticle Collision in an Alkaline Electrolyte Solution

Abstract

A single silver (Ag) nanoparticle (NP) collision was observed and analyzed in an alkaline solution using the electrocatalytic amplification (EA) method. Previously, the observation of a single Ag NP collision was only possible through limited methods based on a self-oxidation of Ag NPs or a blocking strategy. However, it is difficult to characterize the electrocatalytic activity of Ag NPs at a single NP level using a method based on the self-oxidation of Ag NPs. When using a blocking strategy, size analysis is difficult owing to the edge effect in the current signal. The fast oxidative dissolution of Ag NPs has been a problem for observing the staircase response of a single Ag NP collision signal using the EA method. In alkaline electrolyte conditions, Ag oxides are stable, and the oxidative dissolution of Ag NPs is sluggish. Therefore, in this study, the enhanced magnitude and frequency of the current response for single Ag NP collisions were obtained using the EA method in an alkaline electrolyte solution. The peak height and frequency of single Ag NP collisions were analyzed and compared with the theoretical estimation.

Keywords: alkaline solution; electrocatalytic amplification; electrochemistry; silver (Ag); single nanoparticle; single-molecule studies.

Figure 1

Cyclic voltammograms of Ag UME (red solid) and Cu UME (black dashed) in (a) 50 mM PB or (b) 0.1 M NaOH solution containing 15 mM hydrazine. The current was normalized based on the radius of UMEs (radius: 7.5 μm for Cu and 12.5 μm for Ag). (c) Cyclic voltammograms of Ag NP modified GCE in 0.1 M NaOH with (red solid) and without (black dashed) 15 mM hydrazine. The diameter of GCE is 3 mm. The scan rate was 0.1 V/s.

Figure 2

Chronoamperometric curves for single Ag NP collisions at the Cu UME with different applied potentials from 0 V to 0.7 V in a 0.1 M NaOH solution containing 15 mM hydrazine. Data acquisition time is 50 ms.

Figure 3

(a) Chronoamperometric curves at 0.7 V applied to a Cu UME in a 0.1 M NaOH solution with/without Ag NPs in the absence of hydrazine. (b) Transferred charge distribution of a spike like current response for a single Ag NP collision in the absence of hydrazine. The average transferred charge is 1.8 ± 1.1 pC.

Figure 4

(a) Chronoamperometric curves of single Ag NP collisions obtained when 0.7 V is applied to a Cu UME with different concentrations (0 pM to 1.00 pM) of Ag NP in a 0.1 M NaOH solution containing 15 mM hydrazine. (b) Correlation plot between the collisional frequency and the concentration of the Ag NP.

Figure 5

(a) TEM image of Ag NPs. (b) Size distribution of Ag NPs in TEM image. The average diameter is 50 ± 19 nm. The average surface area of NP is 6.5 × 10⁴ nm³.