Collision (or impact) of single palladium nanoparticles (Pd NPs) on gold (Au), copper (Cu), nickel (Ni), and platinum (Pt) ultramicroelectrodes (UMEs) were investigated via electrocatalytic amplification method. Unlike the blip responses of previous Pd NP collision studies, the staircase current response was obtained with the Au UME. The current response, including collision frequency and peak magnitude, was analyzed depending on the material of the UME and the applied potential. Adsorption factors implying the interaction between the Pd NP and the UMEs are suggested based on the experimental results.

The concentration of human immunoglobulin E (IgE) in blood is an indicator for diagnosing an allergy. For detecting human IgE by an electrochemical immunosensor, redox mediator molecules were modified on a gold electrode using thiolated organic molecules, which can form self-assembled monolayers on the electrode surface. Ferrocene was used as a redox mediator, and the current signal was amplified via redox cycling using 4-aminophenol. Measurements were obtained after the immobilization of the target-captured antibody, target human IgE, biotin-conjugated secondary antibody, and avidin alkaline phosphatase in a sandwich-type immunosensor configuration. The prepared immunosensor exhibited a limit of detection of 1 IU/mL and dynamic range of 3-30 IU/mL. K E Y W O R D S electrocatalytic reaction, electrochemical biosensor, ferrocene, gold (Au) electrode, human immunoglobulin E

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.