Electrochemistry of CdSe Quantum Dots Studied by Single Molecule Spectroscopy

Abstract

In the last decades, nanoparticles (NPs) have emerged as active materials for various technically relevant processes like photochemistry, electrochemistry, and catalysis. Although numerous studies have been reported on the redox chemistry and electrochemistry of semiconductor NPs (quantum dots, QDs), the dynamics and kinetics of individual QDs at electrode surfaces are still poorly understood to date. In order to obtain more detailed information, the electrochemical reactivity of single CdSe/CdS QDs with negative surface charge has been investigated in this work on a platinum (Pt) microelectrode using fluorescence correlation spectroscopy (FCS). The results show that QDs are irreversibly oxidized in aqueous solution. However, the correlation time and average number of particles retrieved from FCS suggest that the QDs do not lose their emissive properties in a single collision and desorb from the electrode surface without being decomposed significantly.

Single Entity Behavior of CdSe Quantum Dot Aggregates During Photoelectrochemical Detection

“…We have demonstrated photocurrent detection from single entities that form from suspended QDs during the constant irradiation of the solution. The photocurrent displays a stepwise behavior characteristic of entities adsorbing to the surface irreversibly, although some QDs leave the surface, consistent with the observations from single-molecule spectroscopy (Alshalfouh et al, 2019). In suspensions, the QDs behave differently depending on the solvent used to prepare the suspension.…”

“…More recently, Wang et al (2021) studied the electrocatalytic rates (activity) of single MoS 2 quantum dots on a Ag UME towards hydrogen evolution reaction. Alshalfouh et al (2019) studied CdSe quantum dots using impacts and single-molecule spectroscopy in aqueous solutions. They concluded that the QDs are irreversibly oxidized in the aqueous media.…”

Semiconducting Nanoparticles: Single Entity Electrochemistry and Photoelectrochemistry

“…Significantly, it is found that the electro-oxidized QDs are still able to emit light although the emission lifetime decreases. According to this report, different from the widely reported metal NPs in single collision experiment, more collision events are likely required for a small QD to have a complete anodic decomposition (Alshalfouh et al, 2019). According to this report, multiple collision events are required for a QD to have a complete anodic decomposition.…”

“…In addition to the MOS, semiconducting quantum dots (QDs), especially chalcogenide QDs hold unique optical and electrical properties such as narrow emission absorption and high photo-stability, making them increasingly popular in recent years in the applications of optoelectronic devices, catalysis (Barakat et al, 2005), bio-labeling (Lin et al, 2007), lasers (Supran et al, 2013), sensors (Cho et al, 2015), LEDs (Yang et al, 2015) and photovoltaics (Yang et al, 2017). The research on single entity electrochemistry of QDs starts very recently with the report of CdSe/CdS QDs by Alshalfouh et al, 2019. Together with fluorescence correlation spectroscopy (FCS), electrochemical impact measurements was carried out to understand the reactivity as well as dynamics of CdSe/CdS QDs at a Pt microelectrode surface. The latter was around 1 μm in diameter for matching the size of the optical observation volume.…”

“…The motivation for studies of semiconducting (SC) NPs starts from the interest in investigating photoelectrochemical currents for energy conversion in SC nanostructures. Since then, single entity studies on the semiconducting materials such as metal oxides and some quantum dots materials have been performed ( Sardesai et al, 2013 ; Tschulik, et al, 2013 ; Perera et al, 2015 ; Fernando et al, 2015 ; Shimizu et al, 2017 ; Alshalfouh et al, 2019 ; Karunathilake et al, 2020 ; Wang et al, 2021 ). The overarching goal of studying single SC (photo) electrochemistry is to understand the net (photo) electrochemistry catalytic process at single particle level and to establish their instinct activity-structure relationship.…”