A Pt layer/Pt disk electrode configuration to evaluate respiration and alkaline phosphatase activities of mouse embryoid bodies

Quality evaluation of cell spheroids for transplantation by monitoring oxygen consumption using an on-chip electrochemical device

Three-dimensional cell spheroids are superior cell-administration form for cell-based therapy which generally exhibit superior functionality and long-term survival after transplantation. Here, we nondestructively measured the oxygen consumption rate of cell spheroids using an on-chip electrochemical device (OECD) and examined whether this rate can be used as a marker to estimate the quality of cell spheroids. Cell spheroids containing NanoLuc luciferase-expressing mouse mesenchymal stem cell line C3H10T1/2 (C3H10T1/2/Nluc) were prepared. Spheroids of high or low quality were prepared by altering the medium change frequency. After transplantation into mice, the high-quality C3H10T1/2/Nluc spheroids exhibited a higher survival rate than the low-quality ones. The oxygen consumption rate of the high-quality C3H10T1/2/Nluc spheroids was maintained at high levels, whereas that of the low-quality spheroids decreased with time. These results indicate that OECD-based measurement of the oxygen consumption rate can be used to estimate the quality of cell spheroids without destructive analysis of the spheroids.

Enhanced resolution of generator-collector studies of enzymatic structures by means of hydrodynamic scanning electrochemical microscopy

In this report, the effects of forced convection on scanning electrochemical microscopy (SECM) studies of enzymes in the context of the generator-collector mode (G/C mode) were investigated. Forced convection was generated via an electrical high precision stirrer integrated into the electrochemical cell. Circular spots of glucose oxidase were immobilized on a gold support serving as model substrate. The diffusion layer of enzymatically generated H₂O₂ was characterized recording probe scan curves (PSCs) in z-direction. Furthermore, the enzyme-modified surfaces were investigated via constant-height SECM imaging in feedback mode and in G/C mode. For methodical comparison all sets of experiments were performed in quiescent solution (conventional approach) and with forced convection, respectively. In contrast to a growing diffusion layer without forced convection by applying forced convection, a constant diffusion layer of produced H₂O₂ was observed. Hence, via hydrodynamic SECM time-independent images within a reasonable time scale of SECM measurements in G/C mode were enabled and their resolution was enhanced.

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.

Electrochemicolor Imaging Using an LSI-Based Device for Multiplexed Cell Assays

Multiplexed bioimaging systems have triggered the development of effective assays, contributing new biological information. Although electrochemical imaging is beneficial for quantitative analysis in real time, monitoring multiple cell functions is difficult. We have developed a novel electrochemical imaging system, herein, using a large-scale integration (LSI)-based amperometric device for detecting multiple biomolecules simultaneously. This system is designated as an electrochemicolor imaging system in which the current signals from two different types of biomolecules are depicted as a multicolor electrochemical image. The mode-selectable function of the 400-electrode device enables the imaging system and two different potentials can be independently applied to the selected electrodes. The imaging system is successfully applied for detecting multiple cell functions of the embryonic stem (ES) cell and the rat pheochromocytoma (PC12) cell aggregates. To the best of our knowledge, this is the first time that a real-time electrochemical mapping technique for multiple electroactive species, simultaneously, has been reported. The imaging system is a promising bioanalytical method for exploring complex biological phenomena.

A local redox cycling-based electrochemical chip device with nanocavities for multi-electrochemical evaluation of embryoid bodies

An electrochemical device, which consists of electrode arrays, nanocavities, and microwells, was developed for multi-electrochemical detection with high sensitivity. A local redox cycling-based electrochemical (LRC-EC) system was used for multi-electrochemical detection and signal amplification. The LRC-EC system consists of n(2) sensors with only 2n bonding pads for external connection. The nanocavities fabricated in the sensor microwells enable significant improvement of the signal amplification compared with the previous devices we have developed. The present device was successfully applied for evaluation of embryoid bodies (EBs) from embryonic stem (ES) cells via electrochemical measurements of alkaline phosphatase (ALP) activity in the EBs. In addition, the EBs were successfully trapped in the sensor microwells of the device using dielectrophoresis (DEP) manipulation, which led to high-throughput cell analysis. This device is considered to be useful for multi-electrochemical detection and imaging for bioassays including cell analysis.

Microstamped Petri dishes for scanning electrochemical microscopy analysis of arrays of microtissues

While scanning electrochemical microscopy (SECM) is a powerful technique for non-invasive analysis of cells, SECM-based assays remain scarce and have been mainly limited so far to single cells, which is mostly due to the absence of suitable platform for experimentation on 3D cellular aggregates or microtissues. Here, we report stamping of a Petri dish with a microwell array for large-scale production of microtissues followed by their in situ analysis using SECM. The platform is realized by hot embossing arrays of microwells (200 μm depth; 400 μm diameter) in commercially available Petri dishes, using a PDMS stamp. Microtissues form spontaneously in the microwells, which is demonstrated here using various cell lines (e.g., HeLa, C2C12, HepG2 and MCF-7). Next, the respiratory activity of live HeLa microtissues is assessed by monitoring the oxygen reduction current in constant height mode and at various distances above the platform surface. Typically, at a 40 μm distance from the microtissue, a 30% decrease in the oxygen reduction current is measured, while above 250 μm, no influence of the presence of the microtissues is detected. After exposure to a model drug (50% ethanol), no such changes in oxygen concentration are found at any height in solution, which reflects that microtissues are not viable anymore. This is furthermore confirmed using conventional live/dead fluorescent stains. This live/dead assay demonstrates the capability of the proposed approach combining SECM and microtissue arrays formed in a stamped Petri dish for conducting cellular assays in a non-invasive way on 3D cellular models.

Alginate gel microwell arrays using electrodeposition for three-dimensional cell culture

In this study, we developed a novel method for fabricating microwell arrays constructed from alginate gels, and the alginate gel microwells were used for three-dimensional (3D) cell culture. The alginate gel microwells were fabricated on a patterned ITO electrode using alginate gel electrodeposition. Embryonic stem (ES) cells or hepatocellular carcinoma cells (HepG2) were cultured in the alginate gel microwells containing 3T3 cells. During the culture, embryoid bodies (EBs) or HepG2 spheroids were successfully fabricated in the alginate gel microwells. The oxygen consumption of the EBs indicated that they were successfully cultured. Liver-specific gene expressions of the HepG2 spheroids apparently increased by performing 3D co-culture in the microwell arrays with 3T3 cells. These results show that the alginate gel microwells are a useful 3D culture system.

Multiparameter analyses of three-dimensionally cultured tumor spheroids based on respiratory activity and comprehensive gene expression profiles

Multicellular spheroids of human breast cancer cells (MCF-7) formed with two different three-dimensional (3D) culture methods were evaluated in detail on the basis of respiratory activity and high-throughput gene expression analysis. The spheroids formed with poly(dimethylsiloxane) (PDMS) microwell arrays indicated significant restriction of the spheroid size, whereas their respiratory activity was 2-fold greater than that formed with the hanging drop culture method. Fluidigm BioMark dynamic array was used for comprehensive and quantitative real-time polymerase chain reaction (qRT-PCR) analysis on the samples whose respiratory activity had been measured. Genes involved in cellular senescence and glucose metabolism indicated significantly higher values for the PDMS microwell culture method than for the hanging drop culture method (P<0.05). Interestingly, samples formed with the PDMS microwell culture method showed stronger responses for glycolysis than those formed with the hanging drop method. These results illustrate the power of multiparameter analysis to characterize multicellular spheroids cultured in different microenvironments even if they have the same morphology.