Label-Free Imaging of Mesenchymal Stem Cell Spheroid Differentiation with Flexible-Probe SECM and a Microfluidic Device

Mesenchymal stem cells (MSCs) have emerged as an indispensable source for stem cell research and preclinical studies due to their capacity for in vitro proliferation and their potential to differentiate into mesodermal lineages, particularly into osteoblasts. This capability has propelled their application in the fields of bone regeneration and osteochondral repair. Traditional methodologies for assessing the differentiation status of MSCs necessitate invasive procedures such as cell lysis or fixation. In this study, we introduce a nondestructive technique that utilizes an integrated label-free approach to evaluate the osteogenic maturation of MSC spheroid aggregates. This method employs scanning electrochemical microscopy (SECM) with a flexible probe in conjunction with a top-removable microfluidic device designed for easy SECM access. By tracking the production rate of p-aminophenol (PAP) in the generation/collection mode and assessing morphological changes via the negative feedback mode using [Ru(NH3)6]Cl3 (Ruhex), we can discern variations in the alkaline phosphatase (ALP) activity indicative of osteogenic differentiation. This innovative strategy enables the direct evaluation of osteogenic differentiation in MSC spheroids cultured within microwell arrays without necessitating any labeling procedures. The utilization of a flexible microelectrode as the probe that scans in contact mode (with probe-substrate distances potentially as minimal as 0 μm) affords enhanced resolution compared to the traditional stiff-probe technique. Furthermore, this method is compatible with subsequent molecular biology assays, including gene expression analysis and immunofluorescence, thereby confirming the electrochemical findings and establishing the validity of this integrative approach.

Electrochemical Detection of Tumor-Derived Extracellular Vesicles on Nanointerdigitated Electrodes

Tumor-derived extracellular vesicles (tdEVs) are attracting much attention due to their essential function in intercellular communication and their potential as cancer biomarkers. Although tdEVs are significantly more abundant in blood than other cancer biomarkers, their concentration compared to other blood components remains relatively low. Moreover, the presence of particles in blood with a similar size as that of tdEVs makes their selective and sensitive detection further challenging. Therefore, highly sensitive and specific biosensors are required for unambiguous tdEV detection in complex biological environments, especially for decentralized point-of-care analysis. Here, we report an electrochemical sensing scheme for tdEV detection, with two-level selectivity provided by a sandwich immunoassay and two-level amplification through the combination of an enzymatic assay and redox cycling on nanointerdigitated electrodes to respectively enhance the specificity and sensitivity of the assay. Analysis of prostate cancer cell line tdEV samples at various concentrations revealed an estimated limit of detection for our assay as low as 5 tdEVs/μL, as well as an excellent linear sensor response spreading over 6 orders of magnitude (10-106 tdEVs/μL), which importantly covers the clinically relevant range for tdEV detection in blood. This novel nanosensor and associated sensing scheme opens new opportunities to detect tdEVs at clinically relevant concentrations from a single blood finger prick.

Micro/nanoelectrochemical probe and chip devices for evaluation of three-dimensional cultured cells

Herein, we present an overview of recent research progress in the development of micro/nanoelectrochemical probe and chip devices for the evaluation of three-dimensional (3D) cultured cells. First, we discuss probe devices: a general outline, evaluation of O₂ consumption, enzyme-modified electrodes, evaluation of endogenous enzyme activity, and the collection of cell components from cell aggregates are discussed. The next section is focused on integrated chip devices: a general outline, electrode array devices, smart electrode array devices, droplet detection of 3D cultured cells, cell manipulation using dielectrophoresis (DEP), and electrodeposited hydrogels used for fabrication of 3D cultured cells on chip devices are discussed. Finally, we provide a summary and discussion of future directions of research in this field.