Monitoring the heterogeneity in single cell responses to drugs using electrochemical impedance and electrochemical noise

Impedance Spectroscopy for Bacterial Cell Monitoring, Analysis, and Antibiotic Susceptibility Testing

Conventional approaches for bacterial cell analysis are hindered by lengthy processing times and tedious protocols that rely on gene amplification and cell culture. Impedance spectroscopy has emerged as a promising tool for efficient real-time bacterial monitoring, owing to its simple, label-free nature and cost-effectiveness. However, its limited practical applications in real-world scenarios pose a significant challenge. In this review, we provide a comprehensive study of impedance spectroscopy and its practical utilization in bacterial system measurements. We begin by outlining the fundamentals of impedance theory and modeling, specific to bacterial systems. We then offer insights into various strategies for bacterial cell detection and discuss the role of impedance spectroscopy in antimicrobial susceptibility testing (AST) and single-cell analysis. Additionally, we explore key aspects of impedance system design, including the influence of electrodes, media, and cell enrichment techniques on the sensitivity, specificity, detection speed, concentration accuracy, and cost-effectiveness of current impedance biosensors. By combining different biosensor design parameters, impedance theory, and detection principles, we propose that impedance applications can be expanded to point-of-care diagnostics, enhancing their practical utility. This Perspective focuses exclusively on ideally polarizable (fully capacitive) electrodes, excluding any consideration of charge transfer resulting from Faradaic reactions.

A Transparent Semiconducting Surface for Capturing and Releasing Single Cells from a Complex Cell Mixture

Selective isolation of individual target cells from a heterogeneous population is technically challenging; however, the ability to retrieve single cells can have high significance in various aspects of biological research. Here, we present a new photoelectrochemical surface based on a transparent electrode that is compatible with high-resolution fluorescence microscopy for isolating individual rare cells from complex biological samples. This is underpinned by two important factors: (i) careful design of the electrode by patterning discrete Au disks of micron dimension on amorphous silicon-indium tin oxide films and (ii) orthogonal surface chemistry, which modifies the patterned electrode with self-assembly layers of different functionalities, to selectively capture target cells on the Au disks and resist cell binding to the amorphous silicon surface. The co-stimulation of the surface using light from a microscope and an electric potential triggers the reductive desorption of the alkanethiol monolayer from the Au disks to release the single cells of interest from the illuminated regions only. Using circulating tumor cells as a model, we demonstrate the capture of cancer cells on an antibody-coated surface and selective release of single cancer cells with low expression of epithelial cell adhesion molecules.

Spiers Memorial Lecture. Next generation nanoelectrochemistry: the fundamental advances needed for applications

Nanoelectrochemistry, where electrochemical processes are controlled and investigated with nanoscale resolution, is gaining more and more attention because of the many potential applications in energy and sensing and the fact that there is much to learn about fundamental electrochemical processes when we explore them at the nanoscale. The development of instrumental methods that can explore the heterogeneity of electrochemistry occurring across an electrode surface, monitoring single molecules or many single nanoparticles on a surface simultaneously, have been pivotal in giving us new insights into nanoscale electrochemistry. Equally important has been the ability to synthesise or fabricate nanoscale entities with a high degree of control that allows us to develop nanoscale devices. Central to the latter has been the incredible advances in nanomaterial synthesis where electrode materials with atomic control over electrochemically active sites can be achieved. After introducing nanoelectrochemistry, this paper focuses on recent developments in two major application areas of nanoelectrochemistry; electrocatalysis and using single entities in sensing. Discussion of the developments in these two application fields highlights some of the advances in the fundamental understanding of nanoelectrochemical systems really driving these applications forward. Looking into our nanocrystal ball, this paper then highlights: the need to understand the impact of nanoconfinement on electrochemical processes, the need to measure many single entities, the need to develop more sophisticated ways of treating the potentially large data sets from measuring such many single entities, the need for more new methods for characterising nanoelectrochemical systems as they operate and the need for material synthesis to become more reproducible as well as possess more nanoscale control.