LSI-based amperometric sensor for real-time monitoring of embryoid bodies

Automated System for Attomolar-Level Detection of MiRNA as a Biomarker for Influenza A Virus

We have developed an automated sensing system for the repeated detection of a specific microRNA (miRNA) of the influenza A (H1N1) virus. In this work, magnetic particles functionalized with DNAs, target miRNAs, and alkaline phosphate (ALP) enzymes formed sandwich structures. These particles were trapped on nickel (Ni) patterns of our sensor chip by an external magnetic field. Then, additional electrical signals from electrochemical markers generated by ALP enzymes were measured using the sensor, enabling the highly sensitive detection of target miRNA. The magnetic particles used on the sensor were easily removed by applying the opposite direction of external magnetic fields, which allowed us to repeat sensing measurements. As a proof of concept, we demonstrated the detection of miRNA-1254, one of the biomarkers for the H1N1 virus, with a high sensitivity down to 1 aM in real time. Moreover, our sensor could selectively detect the target from other miRNA samples. Importantly, our sensor chip showed reliable electrical signals even after six repeated miRNA sensing measurements. Furthermore, we achieved technical advances to utilize our sensor platform as part of an automated sensing system. In this regard, our reusable sensing platform could be utilized for versatile applications in the field of miRNA detection and basic research.

A disposable sensor based on one-pot synthesized tungsten oxide nanostructure-modified screen printed electrodes for selective detection of dopamine and uric acid

Here, screen-printed carbon electrodes (SPCEs) were modified with ultrafine and mainly mono-disperse sea urchin-like tungsten oxide (SUWO3) nanostructures synthesized by a simple one-pot hydrothermal method for non-enzymatic detection of dopamine (DA) and uric acid (UA) in synthetic urine. Sea urchin-like nanostructures were clearly observed in scanning electron microscope images and WO3 composition was confirmed with XRD, Raman, FTIR and UV-Vis spectrophotometer. Modification of SPCEs with SUWO3 nanostructures via the drop-casting method clearly reduced the Rct value of the electrodes, lowered the ∆Ep and enhanced the DA oxidation current due to high electrocatalytic activity. As a result, SUWO3/SPCEs enabled highly sensitive non-enzymatic detection of DA (LOD: 51.4 nM and sensitivity: 127 µA mM-1 cm-2) and UA (LOD: 253 nM and sensitivity: 55.9 µA mM-1 cm-2) at low concentration. Lastly, SUWO3/SPCEs were tested with synthetic urine, in which acceptable recoveries for both molecules (94.02-105.8%) were obtained. Given the high selectivity, the sensor has the potential to be used for highly sensitive simultaneous detection of DA and UA in real biological samples.

Electrochemical Imaging of Endothelial Permeability Using a Large-Scale Integration-Based Device

It is important to clarify the transport of biomolecules and chemicals to tissues. Herein, we present an electrochemical imaging method for evaluating the endothelial permeability. In this method, the diffusion of electrochemical tracers, [Fe(CN)₆]^4-, through a monolayer of human umbilical vein endothelial cells (HUVECs) was monitored using a large-scale integration-based device containing 400 electrodes. In conventional tracer-based assays, tracers that diffuse through an HUVEC monolayer into another channel are detected. In contrast, the present method does not employ separated channels. In detail, a HUVEC monolayer is immersed in a solution containing [Fe(CN)₆]^4- on the device. As [Fe(CN)₆]^4- is oxidized and consumed at the packed electrodes, [Fe(CN)₆]^4- begins to diffuse through the monolayer from the bulk solution to the electrodes and the obtained currents depend on the endothelial permeability. As a proof-of-concept, the effects of histamine on the monolayer were monitored. Also, an HUVEC monolayer was cocultured with cancer spheroids, and the endothelial permeability was monitored to evaluate the metastasis of the cancer spheroids. Unlike conventional methods, the device can provide spatial information, allowing the interaction between the monolayer and the spheroids to be monitored. The developed method is a promising tool for organs-on-a-chip and drug screening in vitro.

Reusable surface amplified nanobiosensor for the sub PFU/mL level detection of airborne virus

We developed a reusable surface-amplified nanobiosensor for monitoring airborne viruses with a sub-PFU/mL level detection limit. Here, sandwich structures consisted of magnetic particles functionalized with antibodies, target viruses, and alkaline phosphatases (ALPs) were formed, and they were magnetically concentrated on Ni patterns near an electrochemical sensor transducer. Then, the electrical signals from electrochemical markers generated by ALPs were measured with the sensor transducer, enabling highly-sensitive virus detection. The sandwich structures in the used sensor chip could be removed by applying an external magnetic field, and we could reuse the sensor transducer chip. As a proof of concepts, the repeated detection of airborne influenza virus using a single sensor chip was demonstrated with a detection limit down to a sub-PFU/mL level. Using a single reusable sensor transducer chip, the hemagglutinin (HA) of influenza A (H1N1) virus with different concentrations were measured down to 10 aM level. Importantly, our sensor chip exhibited reliable sensing signals even after more than 18 times of the repeated HA sensing measurements. Furthermore, airborne influenza viruses collected from the air could be measured down to 0.01 PFU/mL level. Interestingly, the detailed quantitative analysis of the measurement results revealed the degradation of HA proteins on the viruses after the air exposure. Considering the ultrasensitivity and reusability of our sensors, it can provide a powerful tool to help preventing epidemics by airborne pathogens in the future.

Electrochemical Detection and Capillary Electrophoresis: Comparative Studies for Alkaline Phosphatase (ALP) Release from Living Cells

Alkaline phosphatase (ALP) is one of the main biomarkers that is clinically detected in bone and liver disorders using optical assays. The electrochemical principle is important because point-of-care testing is increasing dramatically and absorbance techniques hardly compete with the medical revolution that is occurring. The detection of ALP using electrochemical detection is contributing to the integration systems field, and hence enhancing the detection of biological targets for pharmaceutical research and design systems. Moreover, in vitro electrochemical measurements use cost effective materials and simple techniques. Graphite screen-printed electrodes and linear sweep voltammetry were used to optimize the electrochemistry of the enzymatic product p-aminophenol using the enzyme kinetic assay. ALP release from embryonic and cancer cells was determined from adhesion cell culture. Additionally, capillary electrophoresis and colorimetric methods were applied for comparison assays. The resulting assays showed a dynamic range of ALP ranging from 1.5 to 1500 U/L, and limit of detection of 0.043 U/L. This was achieved by using 70 μL of the sample and an incubation time of 10 min at an optimal substrate concentration of 9.6 mM of p-aminophenol phosphate. A significant difference (p < 0.05) was measured between the absorbance assays. This paper demonstrates the advantages of the electrochemical assay for ALP release from cells, which is in line with recent trends in gene expression systems using microelectrode array technologies and devices for monitoring electrophysiological activity.

Electric and Electrochemical Microfluidic Devices for Cell Analysis

Microfluidic devices are widely used for cell analysis, including applications for single-cell analysis, healthcare, environmental monitoring, and organs-on-a-chip that mimic organs in microfluidics. Moreover, to enable high-throughput cell analysis, real-time monitoring, and non-invasive cell assays, electric and electrochemical systems have been incorporated into microfluidic devices. In this mini-review, we summarize recent advances in these systems, with applications from single cells to three-dimensional cultured cells and organs-on-a-chip. First, we summarize microfluidic devices combined with dielectrophoresis, electrophoresis, and electrowetting-on-a-dielectric for cell manipulation. Next, we review electric and electrochemical assays of cells to determine chemical section activity, and oxygen and glucose consumption activity, among other applications. In addition, we discuss recent devices designed for the electric and electrochemical collection of cell components from cells. Finally, we highlight the future directions of research in this field and their application prospects.

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.

Real-time characterization of uptake kinetics of glioblastoma vs. astrocytes in 2D cell culture using microelectrode array

Extracellular measurement of uptake/release kinetics and associated concentration dependencies provides mechanistic insight into the underlying biochemical processes. Due to the recognized importance of preserving the natural diffusion processes within the local microenvironment, measurement approaches which provide uptake rate and local surface concentration of adherent cells in static media are needed. This paper reports a microelectrode array device and a methodology to measure uptake kinetics as a function of cell surface concentration in adherent 2D cell cultures in static fluids. The microelectrode array simultaneously measures local concentrations at five positions near the cell surface in order to map the time-dependent concentration profile which in turn enables determination of surface concentrations and uptake rates, via extrapolation to the cell plane. Hydrogen peroxide uptake by human astrocytes (normal) and glioblastoma multiforme (GBM43, cancer) was quantified for initial concentrations of 20 to 500 μM over time intervals of 4000 s. For both cell types, the overall uptake rate versus surface concentration relationships exhibited non-linear kinetics, well-described by a combination of linear and Michaelis-Menten mechanisms and in agreement with the literature. The GBM43 cells showed a higher uptake rate over the full range of concentrations, primarily due to a larger linear component. Diffusion-reaction models using the non-linear parameters and standard first-order relationships are compared. In comparison to results from typical volumetric measurements, the ability to extract both uptake rate and surface concentration in static media provides kinetic parameters that are better suited for developing reaction-diffusion models to adequately describe behavior in more complex culture/tissue geometries. The results also highlight the need for characterization of the uptake rate over a wider range of cell surface concentrations in order to evaluate the potential therapeutic role of hydrogen peroxide in cancerous cells.

Electrochemical Imaging of Cell Activity in Hydrogels Embedded in Grid-shaped Polycaprolactone Scaffolds Using a Large-scale Integration-based Amperometric Device

Tissue engineering requires analytical methods to monitor cell activity in hydrogels. Here, we present a method for the electrochemical imaging of cell activity in hydrogels embedded in printed polycaprolactone (PCL) scaffolds. Because a structure made of only hydrogel is fragile, PCL frameworks are used as a support material. A grid-shaped PCL was fabricated using an excluder printer. Photocured hydrogels containing cells were set at each grid hole, and cell activity was monitored using a large-scale integration-based amperometric device. The electrochemical device contains 400 microelectrodes for biomolecule detection, such as dissolved oxygen and enzymatic products. As proof of the concept, alkaline phosphatase and respiration activities of embryonic stem cells in the hydrogels were electrochemically monitored. The results indicate that the electrochemical imaging is useful for evaluating cells in printed scaffolds.

Electrochemical imaging of cells and tissues

This minireview summarizes the recent achievements of electrochemical imaging platforms to map cellular functions in biological specimens using electrochemical scanning nano/micro-probe microscopy and 2D chips containing microelectrode arrays.

The technological and experimental progress in electrochemical imaging of biological specimens is discussed with a view on potential applications for skin cancer diagnostics, reproductive medicine and microbial testing. The electrochemical analysis of single cell activity inside cell cultures, 3D cellular aggregates and microtissues is based on the selective detection of electroactive species involved in biological functions. Electrochemical imaging strategies, based on nano/micrometric probes scanning over the sample and sensor array chips, respectively, can be made sensitive and selective without being affected by optical interference as many other microscopy techniques. The recent developments in microfabrication, electronics and cell culturing/tissue engineering have evolved in affordable and fast-sampling electrochemical imaging platforms. We believe that the topics discussed herein demonstrate the applicability of electrochemical imaging devices in many areas related to cellular functions.

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.

Electrochemical Motion Tracking of Microorganisms Using a Large-Scale-Integration-Based Amperometric Device

Motion tracking of microorganisms is useful to investigate the effects of chemical or physical stimulation on their biological functions. Herein, we describe a novel electrochemical imaging method for motion tracking of microorganisms using a large-scale integration (LSI)-based amperometric device. The device consists of 400 electrochemical sensors with a pitch of 250 μm. A convection flow caused by the motion of microorganisms supplies redox species to the sensors and increases their electrochemical responses. Thus, the flow is converted to electrochemical signals, enabling the electrochemical motion tracking of the microorganisms. As a proof of concept, capillary vibration was monitored. Finally, the method was applied to monitoring the motion of Daphnia magna. The motions of these microorganisms were clearly tracked based on the electrochemical oxidation of [Fe(CN)₆ ]^4- and reduction of O₂ .

Electrochemical Hydrogel Lithography of Calcium-Alginate Hydrogels for Cell Culture

Here we propose a novel electrochemical lithography methodology for fabricating calcium-alginate hydrogels having controlled shapes. We separated the chambers for Ca²⁺ production and gel formation with alginate with a semipermeable membrane. Ca²⁺ formed in the production chamber permeated through the membrane to fabricate a gel structure on the membrane in the gel formation chamber. When the calcium-alginate hydrogels were modified with collagen, HepG2 cells proliferated on the hydrogels. These results show that electrochemical hydrogel lithography is useful for cell culture.

Electrochemical camera chip for simultaneous imaging of multiple metabolites in biofilms

Monitoring spatial distribution of metabolites in multicellular structures can enhance understanding of the biochemical processes and regulation involved in cellular community development. Here we report on an electrochemical camera chip capable of simultaneous spatial imaging of multiple redox-active phenazine metabolites produced by Pseudomonas aeruginosa PA14 colony biofilms. The chip features an 8 mm × 8 mm array of 1,824 electrodes multiplexed to 38 parallel output channels. Using this chip, we demonstrate potential-sweep-based electrochemical imaging of whole-biofilms at measurement rates in excess of 0.2 s per electrode. Analysis of mutants with various capacities for phenazine production reveals distribution of phenazine-1-carboxylic acid (PCA) throughout the colony, with 5-methylphenazine-1-carboxylic acid (5-MCA) and pyocyanin (PYO) localized to the colony edge. Anaerobic growth on nitrate confirms the O2-dependence of PYO production and indicates an effect of O2 availability on 5-MCA synthesis. This integrated-circuit-based technique promises wide applicability in detecting redox-active species from diverse biological samples.

Spatiotemporal norepinephrine mapping using a high-density CMOS microelectrode array

A high-density amperometric electrode array containing 8192 individually addressable platinum working electrodes with an integrated potentiostat fabricated using Complementary Metal Oxide Semiconductor (CMOS) processes is reported. The array was designed to enable electrochemical imaging of chemical gradients with high spatiotemporal resolution. Electrodes are arranged over a 2 mm × 2 mm surface area into 64 subarrays consisting of 128 individual Pt working electrodes as well as Pt pseudo-reference and auxiliary electrodes. Amperometric measurements of norepinephrine in tissue culture media were used to demonstrate the ability of the array to measure concentration gradients in complex media. Poly(dimethylsiloxane) microfluidics were incorporated to control the chemical concentrations in time and space, and the electrochemical response at each electrode was monitored to generate electrochemical heat maps, demonstrating the array's imaging capabilities. A temporal resolution of 10 ms can be achieved by simultaneously monitoring a single subarray of 128 electrodes. The entire 2 mm × 2 mm area can be electrochemically imaged in 64 seconds by cycling through all subarrays at a rate of 1 Hz per subarray. Monitoring diffusional transport of norepinephrine is used to demonstrate the spatiotemporal resolution capabilities of the system.

Advanced LSI-based amperometric sensor array with light-shielding structure for effective removal of photocurrent and mode selectable function for individual operation of 400 electrodes

We have developed a large-scale integrated (LSI) complementary metal-oxide semiconductor (CMOS)-based amperometric sensor array system called "Bio-LSI" as a platform for electrochemical bio-imaging and multi-point biosensing with 400 measurement points. In this study, we newly developed a Bio-LSI chip with a light-shield structure and a mode-selectable function with the aim of extending the application range of Bio-LSI. The light shield created by the top metal layer of the LSI chip significantly reduces the noise generated by the photocurrent, whose value is less than 1% of the previous Bio-LSI without the light shield. The mode-selectable function enables the individual operation of 400 electrodes in off, electrometer, V1, and V2 mode. The off-mode cuts the electrode from the electric circuit. The electrometer-mode reads out the electrode potential. The V1-mode and the V2-mode set the selected sensor electrode at two different independent voltages and read out the current. We demonstrated the usefulness of the mode-selectable function. First, we displayed a dot picture based on the redox reactions of 2.0 mM ferrocenemethanol at 400 electrodes by applying two different independent voltages using the V1 and V2 modes. Second, we carried out a simultaneous detection of O2 and H2O2 using the V1 and V2 modes. Third, we used the off and V1 modes for the modification of the osmium-polyvinylpyridine gel polymer containing horseradish peroxidase (Os-HRP) at the selected electrodes, which act as sensors for H2O2. These results confirm that the advanced version of Bio-LSI is a promising tool that can be applied to a wide range of analytical fields.

Fully integrated CMOS microsystem for electrochemical measurements on 32 × 32 working electrodes at 90 frames per second

Microelectrode arrays offer the potential to electrochemically monitor concentrations of molecules at high spatial resolution. However, current systems are limited in the number of sensor sites, signal resolution, and throughput. Here, we present a fully integrated complementary metal oxide semiconductor (CMOS) system with an array of 32 × 32 working electrodes to perform electrochemical measurements like amperometry and voltammetry. The array consists of platinum electrodes with a center-to-center distance of 100 μm and electrode diameters of 5 to 50 μm. Currents in the range from 10 μA down to pA can be measured. The current is digitized by sigma-delta converters at a maximum resolution of 13.3 bits. The integrated noise is 220 fA for a bandwidth of 100 Hz, allowing for detection of pA currents. Currents can be continuously acquired at up to 1 kHz bandwidth, or the whole array can be read out rapidly at a frame rate of up to 90 Hz. The results of the electrical characterization meet the requirements of a wide range of electrochemical methods including cyclic voltammograms and amperometric images of high spatial and temporal resolution.