Recently, the rapid developments of sensing methodology, instrumentations, and data analysis methods jointly spurred the growing interests of electrochemistry at a confined space (Figure 1). To present the latest advances in this field, in this review, we mainly cover up-to-date research in electrochemical confinement during the last two years. To provide a full view of this topic for readers, we also selectively cite several representative research before 2017 as well. Herein, we first illustrate typical electrochemically confined spaces, including nano/microelectrode, nanopore, nanopipet, and confined space in other structures. Followed by the discussion of summarized preparation processes and sensing mechanisms of these confined structures, we then highlight the most recent achievements of electrochemically confined space in single entity measurement, from single molecules, single particles, to single cells. Furthermore, we explore the exciting combination of multitechniques at a confined space. Finally, we reach a perspective by presenting the unique requirement of the promising sensors and data mining with brand new capabilities to advance the field of electrochemical sensing at a confined space.Analytical Chemistry pubs.acs.org/ac Review

We have employed glass nanopore as a single molecule technique for direct sensing amyloidosis process of Aβ1–42 peptide, which of great significance in Alzheimer's disease.

CsPbX3 NCs with different photoluminescence properties were synthesized by anion exchange. A mechanism was supposed by exploring luminescence evolution.

The potential distribution at the electrode interface is a core factor in electrochemistry, and it is usually treated by the classic Gouy–Chapman–Stern (G–C–S) model. Yet the G–C–S model is not applicable to nanosized particles collision electrochemistry as it describes steady-state electrode potential distribution. Additionally, the effect of single nanoparticles (NPs) on potential should not be neglected because the size of a NP is comparable to that of an electrode. Herein, a theoretical model termed as Metal-Solution-Metal Nanoparticle (M-S-MNP) is proposed to reveal the dynamic electrode potential distribution at the single-nanoparticle level. An explicit equation is provided to describe the size/distance-dependent potential distribution in single NPs stochastic collision electrochemistry, showing the potential distribution is influenced by the NPs. Agreement between experiments and simulations indicates the potential roles of the M-S-MNP model in understanding the charge transfer process at the nanoscale.

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Single-entity electrochemistry (SEE) provides powerful means to measure single cells, single particles, and even single molecules at the nanoscale by diverse well-defined interfaces. The nanoconfined electrode interface has significantly enhanced structural, electrical, and compositional characteristics that have great effects on the assay limitation and selectivity of single-entity measurement. In this Perspective, after introducing the dynamic chemistry interactions of the target and electrode interface, we present a fundamental understanding of how these dynamic interactions control the features of the electrode interface and thus the stochastic and discrete electrochemical responses of single entities under nanoconfinement. Both stochastic single-entity collision electrochemistry and nanopore electrochemistry as examples in this Perspective explore how these interactions alter the transient charge transfer and mass transport. Finally, we discuss the further challenges and opportunities in SEE, from the design of sensing interfaces to hybrid spectro-electrochemical methods, theoretical models, and advanced data processing.

The nanoparticle‐based electrocatalysts’ performance is directly related to their working conditions. In general, a number of nanoparticles are uncontrollably fixed on a millimetre‐sized electrode for electrochemical measurements. However, it is hard to reveal the maximum electrocatalytic activity owing to the aggregation and detachment of nanoparticles on the electrode surface. To solve this problem, here, we take the hydrogen evolution reaction (HER) catalyzed by palladium nanoparticles (Pd NPs) as a model system to track the electrocatalytic activity of single Pd NPs by stochastic collision electrochemistry and ensemble electrochemistry, respectively. Compared with the nanoparticle fixed working condition, Pd NPs in the nanoparticle diffused working condition results in a 2–5 orders magnitude enhancement of electrocatalytic activity for HER at various bias potential. Stochastic collision electrochemistry with high temporal resolution gives further insights into the accurate study of NPs’ electrocatalytic performance, enabling to dramatically enhance electrocatalytic efficiency.

Hydrogen evolution reaction (HER) catalyzed by molybdenum sulfide quantum dots (MoS2 QDs) has attracted extensive attention in the energy field. Monitoring HER catalyzed by MoS2 QDs based on a glass nanopore with an electrochemically confined effect was proposed for the first time. MoS2 QDs inside the glass nanopore is driven toward the orifice of the nanopore and bonded with the Ag nanoparticles (Ag NPs) to form a single nanocomposite. When enough voltage is applied across the orifice, the single Ag NP acts as a single nanoparticle electrode to conduct the electrochemically bipolar reaction on its two extremities. In the process, HER is catalyzed by MoS2 QDs, and Ag NPs are oxidized at the same time. The appearance of blockages on the elevated ionic current is attributed to the generation of a H2 bubble. Furthermore, by analyzing the modulations in the ionic current oscillation, the frequency of hydrogen bubble generation that is related to the catalytic efficiency of MoS2 QDs could be estimated. The results reveal the capability of the glass nanopore for the real-time monitoring electrocatalytic behavior, which makes the glass nanopore an ideal candidate to further reveal the heterogeneity of catalytic capability at the single particle level.