The precision and depth of our understanding push the chemical measurement is to achieve high sensitive detection of single entities, e.g., single cells, single nanoparticles, single nanobubbles, and single molecules. Electrochemistry stands out as ha direct and effective method for measuring electron transfer processes. High-resolution electrochemical measurements enable precise analysis of redox reactions at micro/nanoscale interfaces, yielding unique electrochemical signals from each entity, and revealing hidden inter-individual differences that are often covered by averaging effects. Various nanostructures, including ultramicroelectrode, nanopipette, nanotip, and nanopore, have been developed to construct electrochemical sensing interfaces that match the size of individual analytes with high spatial resolution and high-sensitivity. Advances in instrumentation enable the high temporal resolution and weak current detection, facilitating the real-time monitoring the dynamic electrochemical processes ranging from sub-milliseconds to microseconds. This capability supports the high-throughput and rapid sensing in solution, enabling identification of rare subpopulations, discovery of reaction intermediates, and mapping of dynamic interaction pathways. For example, nanopore technologies enable single biomolecule sequencing and sensing that can be applied to early and precise diagnosis. Electrochemical measurements at the single-particle level reveal intrinsic heterogeneity of structure-activity relationship for nanomaterials. In-situ electrochemical analysis of individual cells also provide insights into intracellular and inter-cellular biochemical processes while enhancing our understanding of mechanisms related to cell-to-cell communication networks. In recent years, significant advancements have been made in single-entity electrochemical measurements, including developments in nanointerfaces, ultra-sensitive instrumentation, and intelligent data analysis, providing new tools for the studies in micro-/nanomaterials, life sciences, and energy catalysis.

The Single-Entity Electroanalysis special issue (2024, Issues 10 and 11) brings together cutting-edge research from teams with extensive experience in single-entity electroanalysis field, featuring five papers, including two review papers and three research papers. This issue covers a range of innovative work, such as “Single Nanobubble Formation on Au Nanoelectrodes and Au@WS₂ Nanoelectrodes: Voltammetric Analysis and Electrocatalysis”, “Precision Delivery Using Nanopipette for Single-Cell Studies”, “Highly Sensitive Detection of Strontium Ions Using Metal-Organic Frameworks Functionalized Solid-State Nanochannels”, “Platinum Nanoparticle-Based Collision Electrochemistry for Rapid Detection of Breast Cancer MCF-7 Cells”, “Single-entity collisional electrochemistry (SECE) at the micro- and/or nano-interface between two immiscible electrolyte solutions (ITIES)”.

We hope this special collection will provide the knowledge to the readers for conducting in-depth studies in single entity electrochemistry in China. With this preface, we would like to express our heartfelt thanks to all the authors, reviewers and editorial staff for their hard and fruitful work!

Taking advantage of the extremely small size of the gold nanodisk electrode, the single hydrogen nanobubble generated on the surface of the nanoelectrode was studied to evaluate its hydrogen evolution performance. It was found that compared with the bare gold nanodisk electrode, the bubble formation potential of the gold nanodisk electrode modified with tungsten disulfide quantum dots (WS₂ QDs) on the surface was more positive, indicating that its hydrogen evolution activity was higher. Microdynamic model analysis shows that the average standard rate constant of the rate-determining step of the hydrogen evolution reaction of gold nanoelectrodes modified with WS₂ QDs is approximately 12 times larger than that of gold nanoelectrodes. This work based on the formation of nanobubbles provides new ideas for the design and performance evaluation of hydrogen evolution reaction catalysts.

Strontium-90, a highly radioactive isotope, accumulates within the food chain and skeletal structure, posing significant risks to human health. There is a critical need for a sensitive detection strategy for Strontium-90 in complex environmental samples. Here, solid-state nanochannels, modified with metal-organic frameworks (MOF) and specific aptamers, were engineered for highly sensitive detection of strontium ion (Sr²⁺). The synergistic effect between the reduced effective diameter of the nanochannels due to MOF and the specific binding of Sr²⁺ by aptamers amplifies the difference in ionic current signals, enhancing detection sensitivity significantly. The MOF-modified nanochannels exhibit highly sensitive detection of Sr²⁺, with a limit of detection (LOD) being 0.03 nmol·L^-1, whereas the LOD for anodized aluminum oxide (AAO) without the modified MOF nanosheets is only 1000 nmol·L^-1. These findings indicate that the LOD of Sr²⁺ detected by the MOF-modified nanochannels is approximately 33,000 times higher than that by the nanochannels without MOF modification. Additionally, the highly reliable detection of Sr²⁺ in various water samples was achieved, with a recovery rate ranging from 94.00% to 118.70%. This study provides valuable insights into the rapidly advancing field of advanced nanochannel-based sensors and their diverse applications for analyzing complex samples, including environmental contaminant detection, food analysis, medical diagnostics, and more.

Cancer metastasis is the leading cause of death in cancer patients worldwide and one of the major challenges in treating cancer. Circulating tumor cells (CTCs) play a pivotal role in cancer metastasis. However, the content of CTCs in peripheral blood is minimal, so the detection of CTCs in real samples is extremely challenging. Therefore, efficient enrichment and early detection of CTCs are essential to achieve timely diagnosis of diseases. In this work, we constructed an innovative and sensitive single-nanoparticle collision electrochemistry (SNCE) biosensor for the detection of MCF-7 cells (human breast cancer cells) by immunomagnetic separation technique and liposome signal amplification strategy. Liposomes embedded with platinum nanoparticles (Pt NPs) were used as signal probes, and homemade gold ultramicroelectrodes (Au UME) were used as the working electrodes. The effective collision between Pt NPs and UME would produce distinguishable step-type current. MCF-7 cells were accurately quantified according to the relationship between cell concentration and collision frequency (the number of step-type currents generated per unit time), realizing highly sensitive and specific detection of MCF-7 cells. The SNCE biosensor has a linear range of 10 cells·mL^-1 to 10⁵ cells·mL^-1 with a detection limit as low as 5 cells·mL^-1. In addition, the successful detection of MCF-7 cells in complex samples showed that the SNCE biosensors have great potential for patient sample detection.