High-Density Droplet Microarray of Individually Addressable Electrochemical Cells

Ultradense Array of On-Chip Sensors for High-Throughput Electrochemical Analyses

High-throughput sensors are valuable tools for enabling massive, fast, and accurate diagnostics. To yield this type of electrochemical device in a simple and low-cost way, high-density arrays of vertical gold thin-film microelectrode-based sensors are demonstrated, leading to the rapid and serial interrogation of dozens of samples (10 μL droplets). Based on 16 working ultramicroelectrodes (UMEs) and 3 quasi-reference electrodes (QREs), a total of 48 sensors were engineered in a 3D crossbar arrangement that devised a low number of conductive lines. By exploiting this design, a compact chip (75 × 35 mm) can enable performing 16 sequential analyses without intersensor interferences by dropping one sample per UME finger. In practice, the electrical connection to the sensors was achieved by simply switching the contact among WE adjacent fingers. Importantly, a short analysis time was ensured by interrogating the UMEs with chronoamperometry or square wave voltammetry using a low-cost and hand-held one-channel potentiostat. As a proof of concept, the detection of Staphylococcus aureus in 15 samples was performed within 14 min (20 min incubation and 225 s reading). Additionally, the implementation of peptide-tethered immunosensors in these chips allowed the screening of COVID-19 from patient serum samples with 100% accuracy. Our experiments also revealed that dispensing additional droplets on the array (in certain patterns) results in the overestimation of the faradaic current signals, a phenomenon referred to as crosstalk. To address this interference, a set of analyses was conducted to design a corrective strategy that boosted the testing capacity by allowing using all on-chip sensors to address subsequent analyses (i.e., 48 samples simultaneously dispensed on the chip). This strategy only required grounding the unused rows of QRE and can be broadly adopted to develop high-throughput UME-based sensors. In practice, we could analyze 48 droplets (with [Fe(CN)6]4-) within ∼8 min using amperometry.

One-step construction of multiplexed enzymatic biosensors using light-addressable electrochemistry on a single silicon photoelectrode

The multiplexed detection of metabolites in parallel within a single biosensor plate is sufficiently valuable but also challenging. Herein, we combine the inherent light addressability of silicon with the high selectivity of enzymes, for the construction of multiplexed photoelectrochemical enzymatic biosensors. To conduct a stable electrochemistry and reagentless biosensing on silicon, a new strategy involving the immobilization of both redox mediators and enzymes using an amide bond-based hydrogel membrane was proposed. The membrane characterization results demonstrated a covalent coupling of ferrocene mediator to hydrogel, in which the mediator acted as not only a signal generator but also a renewable sacrifice agent. By adding corresponding enzymes on different spots of hydrogel membrane modified silicon and recording local photocurrents with a moveable light pointer, this biosensor setup was used successfully to detect multiple metabolites, such as lactate, glucose, and sarcosine, with good analytical performances. The limits of detection of glucose, sarcosine and lactate were found to be 179 μM, 16 μM, and 780 μM with the linear ranges of 0.5-2.5 mM, 0.3-1.5 mM, and 1.0-3.0 mM, respectively. We believe this proof-of-concept study provides a simple and rapid one-step immobilization approach for the fabrication of reagentless enzymatic assays with silicon-based light-addressable electrochemistry.

Concentration Enrichment in a Dissolving Microdroplet: Accessing Sub-nanomolar Electroanalysis

Droplet evaporation has previously been used as a concentration enrichment strategy; however, the measurement technique of choice requires quantification in rather large volumes. Electrochemistry has recently emerged as a method to robustly probe volumes even down to the attoliter (10-18 L) level. We present a concentration enrichment strategy based on the dissolution of a microdroplet placed on the surface of a Au ultramicroelectrode (radius ∼ 6.25 μm). By precisely positioning a 1,2-dichloroethane microdroplet onto the ultramicroelectrode with a microinjector, we are able to track the droplet's behavior optically and electrochemically. Because the droplet spontaneously dissolves over time, given the relative solubility of 1,2-dichloroethane in the water continuous phase, the change in volume with time enriches the concentration of the redox probe (Cp2*(Fe)II) in the droplet. We demonstrate robust electrochemical detection down to sub-nM (800 pM) concentrations of Cp2*(Fe)II. For this droplet, 800 pM constitutes only about 106 molecules. We extend the strategy in a single-blind study to determine unknown concentrations, emphasizing the promise of the new methodology. These results take voltammetric quantification easily to the sub-μM regime.

Bipolar Clark-Type Oxygen Electrode Arrays for Imaging and Multiplexed Measurements of the Respiratory Activity of Cells

Various miniature Clark-type oxygen electrodes (COEs), which are typically used to measure dissolved oxygen (DO) concentration in cellular respiration, have been developed since the 1980s. Arrays with individually addressable electrodes that constitute the sensor were used for various applications. However, the large number of leads and contact pads required for connecting the electrodes and the external instrument complicate the electrode layout and make the operation of integrated COE arrays challenging. Here, we fabricated closed bipolar electrochemical systems comprising 6 × 8 and 4 × 4 arrays of COEs for imaging and multiplexed detection. The cathodic compartment was sealed with a hydrophobic oxygen-permeable membrane to separate the internal electrolyte solution from the sample solutions. Using the bipolar Clark-type oxygen electrode (BCOE) arrays and electrochemiluminescence (ECL), we measured the DO concentration at each cathode. The results revealed that the ECL intensity changed linearly with the DO concentration. In addition, we used ECL imaging to investigate the respiratory activity of Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) in suspensions with different cell densities. The ECL images showed that the ECL intensity changed noticeably with the bacterial density. The bacterial respiratory activity was then qualitatively analyzed based on the ECL images acquired successively over a time duration. Further, we measured the antibiotic efficacy of piperacillin, oxacillin, gentamicin, and cefmetazole against E. coli and P. aeruginosa using the BCOE. We found that the ECL intensity increased with the antibiotic concentration, thus indicating the suppression of the bacterial respiratory activity.

Microarray-Based Electrochemical Biosensing

Microarrays are widely utilized in bioanalysis. Electrochemical biosensing techniques are often applied in microarray-based assays because of their simplicity, low cost, and high sensitivity. In such systems, the electrodes and sensing elements are arranged in arrays, and the target analytes are detected electrochemically. These sensors can be utilized for high-throughput bioanalysis and the electrochemical imaging of biosamples, including proteins, oligonucleotides, and cells. In this chapter, we summarize recent progress on these topics. We categorize electrochemical biosensing techniques for array detection into four groups: scanning electrochemical microscopy, electrode arrays, electrochemiluminescence, and bipolar electrodes. For each technique, we summarize the key principles and discuss the advantages, disadvantages, and bioanalysis applications. Finally, we present conclusions and perspectives about future directions in this field.

Emerging open-channel droplet arrays for biosensing

Open-channel droplet arrays have attracted much attention in the fields of biochemical analysis, biofluid monitoring, biomarker recognition and cell interactions, as they have advantages with regard to miniaturization, parallelization, high-throughput, simplicity and accessibility. Such droplet arrays not only improve the sensitivity and accuracy of a biosensor, but also do not require sophisticated equipment or tedious processes, showing great potential in next-generation miniaturized sensing platforms. This review summarizes typical examples of open-channel microdroplet arrays and focuses on diversified biosensing integrated with multiple signal-output approaches (fluorescence, colorimetric, surface-enhanced Raman scattering (SERS), electrochemical, etc.). The limitations and development prospects of open-channel droplet arrays in biosensing are also discussed with regard to the increasing demand for biosensors.

The Role of Experimental Noise in a Hybrid Classical-Molecular Computer to Solve Combinatorial Optimization Problems

Chemical and molecular-based computers may be promising alternatives to modern silicon-based computers. In particular, hybrid systems, where tasks are split between a chemical medium and traditional silicon components, may provide access and demonstration of chemical advantages such as scalability, low power dissipation, and genuine randomness. This work describes the development of a hybrid classical-molecular computer (HCMC) featuring an electrochemical reaction on top of an array of discrete electrodes with a fluorescent readout. The chemical medium, optical readout, and electrode interface combined with a classical computer generate a feedback loop to solve several canonical optimization problems in computer science such as number partitioning and prime factorization. Importantly, the HCMC makes constructive use of experimental noise in the optical readout, a milestone for molecular systems, to solve these optimization problems, as opposed to in silico random number generation. Specifically, we show calculations stranded in local minima can consistently converge on a global minimum in the presence of experimental noise. Scalability of the hybrid computer is demonstrated by expanding the number of variables from 4 to 7, increasing the number of possible solutions by 1 order of magnitude. This work provides a stepping stone to fully molecular approaches to solving complex computational problems using chemistry.

Droplet microarray platforms for high-throughput drug screening

High-throughput screening platforms are fundamental for the rapid and efficient processing of large amounts of experimental data. Parallelization and miniaturization of experiments are important for improving their cost-effectiveness. The development of miniaturized high-throughput screening platforms is essential in the fields of biotechnology, medicine, and pharmacology. Currently, most laboratories use 96- or 384-well microtiter plates for screening; however, they have disadvantages, such as high reagent and cell consumption, low throughput, and inability to avoid cross-contamination, which need to be further optimized. Droplet microarrays, as novel screening platforms, can effectively avoid these shortcomings. Here, the preparation method of the droplet microarray, method of adding compounds in parallel, and means to read the results are briefly described. Next, the latest research on droplet microarray platforms in biomedicine is presented, including their application in high-throughput culture, cell screening, high-throughput nucleic acid screening, drug development, and individualized medicine. Finally, the challenges and future trends in droplet microarray technology are summarized.

Leaf-Inspired Patterned Organohydrogel Surface for Ultrawide Time-Range Open Biosensing

Droplet arrays show great significance in biosensing and biodetection because of low sample consumption and easy operation. However, inevitable water evaporation in open environment severely limits their applications in time-consuming reactions. Herein, inspired by the unique water retention features of leaves, it is demonstrated that an open droplet array on patterned organohydrogel surface with water evaporating replenishment (POWER) for ultrawide time-range biosensing, which integrated hydrophilic hydrogel domains and hydrophobic organogel background. The hydrogel domains on the surface can supply water to the pinned droplets through capillary channels formed in the nether organohydrogel bulk. The organogel background can inhibit water evaporation like the wax coating of leaves. Such a unique bioinspired design enables ultrawide time-range biosensing in open environment from a few minutes to more than five hours involving a variety of analytes such as ions, small molecules, and macromolecules. The POWER provides a feasible and open biosensing platform for ultrawide time-range reactions.

Interfacial design for detection of a few molecules

Major advances in molecular detection are being driven by goals associated with the development of methods that are amenable to miniaturization and automation, and that have high sensitivity and low interference. The new detection methods are confronted by many interfacial issues, which when properly addressed can lead to improved performance. One interfacial property, special wettability, can facilitate precise delivery and local enrichment of molecules to sensing elements. This review summarizes applications of unique features of special wettability in molecular detection including (1) chemical and electrochemical reactions in anchored microdroplets on superwetting surfaces, (2) enrichment of analytes and active materials at low contact areas between droplets and superwetting surfaces, (3) complete opposite affinities of superwetting surfaces toward nonpolar/polar solutes and oil/water phases, and (4) directional droplet transportation on asymmetric superwetting surfaces. The challenges and opportunities that exist in design and applications of special wettability in interfacial delivery and enrichment for detection of a few molecules are also discussed.

Electrochemical immunosensor based on superwettable microdroplet array for detecting multiple Alzheimer's disease biomarkers

Alzheimer's disease (AD) is a neurodegenerative disease caused by neurons damage in the brain, and it poses a serious threat to human life and health. No efficient treatment is available, but early diagnosis, discovery, and intervention are still crucial, effective strategies. In this study, an electrochemical sensing platform based on a superwettable microdroplet array was developed to detect multiple AD biomarkers containing Aβ40, Aβ42, T-tau, and P-tau181 of blood. The platform integrated a superwettable substrate based on nanoAu-modified vertical graphene (VG@Au) into a working electrode, which was mainly used for droplet sample anchoring and electrochemical signal generation. In addition, an electrochemical micro-workstation was used for signals conditioning. This superwettable electrochemical sensing platform showed high sensitivity and a low detection limit due to its excellent characteristics such as large specific surface, remarkable electrical conductivity, and good biocompatibility. The detection limit for Aβ40, Aβ42, T-tau, and P-tau181 were 0.064, 0.012, 0.039, and 0.041 pg/ml, respectively. This study provides a promising method for the early diagnosis of AD.

Bipolar Electrode Arrays for Chemical Imaging and Multiplexed Sensing

Bipolar electrodes (BPEs) with arrays of cathodic and anodic poles were developed for use in closed bipolar systems. To increase the number of BPEs in the array, the anodic and cathodic poles were connected with each other using thin leads. A further increase in the number of BPEs was achieved by forming the cathodic and anodic poles of the BPEs and the leads in different layers. A device with 9 × 10 arrays of cathodes and anodes was thus realized. When using this device to sense hydrogen peroxide (H₂O₂), the sensitivity and linear range of calibration plots could be adjusted by changing the driving voltage and the area ratio between the cathodic and anodic poles. The devices were used to image H₂O₂ and obtain time-lapse images for the diffusion and dilution of H₂O₂. Furthermore, DNA detection was demonstrated using an electroactive intercalator. The sensitivity could be improved by making the anodic poles smaller with respect to the cathodic pole and concentrating the electrochemiluminescence (ECL) in a small area. The ECL intensity changed according to the target DNA concentration in the solution.

Bioinspired superwettable electrodes towards electrochemical biosensing

Superwettable materials have attracted much attention due to their fascinating properties and great promise in several fields. Recently, superwettable materials have injected new vitality into electrochemical biosensors. Superwettable electrodes exhibit unique advantages, including large electrochemical active areas, electrochemical dynamics acceleration, and optimized management of mass transfer. In this review, the electrochemical reaction process at electrode/electrolyte interfaces and some fundamental understanding of superwettable materials are discussed. Then progress in different electrodes has been summarized, including superhydrophilic, superhydrophobic, superaerophilic, superaerophobic, and superwettable micropatterned electrodes, electrodes with switchable wettabilities, and electrodes with Janus wettabilities. Moreover, we also discussed the development of superwettable materials for wearable electrochemical sensors. Finally, our perspective for future research is presented.

Array of individually addressable two-electrode electrochemical cells sharing a single counter/reference electrode for multiplexed enzyme activity measurements

This work reports on the fabrication and performance of a new on-chip array of gold thin-film electrodes arranged into five individually addressable miniaturized electrochemical cells. Each cell shows a two-electrode configuration comprising a single working electrode and a counter/pseudo-reference electrode that is compartmentalized to be shared among all the cells of the array. Using this configuration, just six contact pads are required, which significantly reduces the chip overall surface area. Electrochemical characterization studies are carried out in solutions containing the two species of reversible redox pairs. The concentration of one redox species can reliably be measured at the working electrode by applying potentiostatic techniques to record the current due to the corresponding electrochemical reaction. The redox counterpart in turn undergoes an electrochemical process at the counter/pseudo-reference electrode, which, under optimized experimental conditions, injects current and keeps the applied potential in the electrochemical cell without limiting the current being recorded at the working electrode. Under these conditions, the electrode array shows an excellent performance in electrochemical detection studies without any chemical or electrical cross-talk between cells. The enzymatic activity of horseradish peroxidase, alkaline phosphatase and myeloperoxidase enzymes is analyzed using different redox mediators. Quasi-simultaneous measurements with the five electrochemical cells of the array are carried out within 1 s time frame. This array layout can be suitable for multiplexed electrochemical immunoassays and immunosensor approaches and implementation in simplified electrochemical ELISA platforms that make use of enzyme labels. Moreover, the array reduced dimensions facilitate the integration into compact fluidic devices.

Bio-inspired Superwettable Surface for the Detection of Cancer Biomarker: A Mini Review

Inspired by nature, superwettable material-based biosensors have aroused wide interests due to their potential in cancer biomarker detection. This mini review mainly summarized the superwettable materials as novel biosensing substrates for the development of evaporation-induced enrichment-based signal amplification and visual biosensing method. Biosensing applications based on the superhydrophobic surfaces, superwettable micropatterned surfaces, and slippery lubricant-infused porous surfaces for various cancer biomarker detections were described in detail. Finally, an insight of remaining challenges and perspectives of superwettable biosensor is proposed.

Microfabricated electrochemical sensing devices

Electrochemistry provides possibilities to realize smart microdevices of the next generation with high functionalities. Electrodes, which constitute major components of electrochemical devices, can be formed by various microfabrication techniques, and integration of the same (or different) components for that purpose is not difficult. Merging this technique with microfluidics can further expand the areas of application of the resultant devices. To augment the development of next generation devices, it will be beneficial to review recent technological trends in this field and clarify the directions required for moving forward. Even when limiting the discussion to electrochemical microdevices, a variety of useful techniques should be considered. Therefore, in this review, we attempted to provide an overview of all relevant techniques in this context in the hope that it can provide useful comprehensive information.

Closed Bipolar Electrode Array for On-Chip Analysis of Cellular Respiration by Cell Aggregates

Cell aggregates have attracted much attention owing to their potential applications in tissue engineering and drug screening. To evaluate cellular respiration of individual cell aggregates in these applications, noninvasive and on-chip high-throughput analytical tools are necessary. Electrochemical methods for detecting oxygen concentrations are useful because of their noninvasiveness. However, these conventional methods may be unsuitable for high-throughput detection because it is difficult to prepare many electrodes on a small chip owing to the limitation of area for connecting electrodes. Alternatively, a bipolar electrode (BPE) system offers clear advantages. In this system, electrochemical reactions are induced at both ends of a BPE without complex wiring. In this study, we present a BPE array for detecting the respiratory activity of cell aggregates. Oxygen concentrations near cell aggregates at cathodic poles of BPEs were converted to electrochemiluminescence (ECL) signals of [Ru(bpy)₃]²⁺/tripropylamine at anodic poles of BPEs. To separate ECL chemicals from cell aggregates, we fabricated a closed BPE device containing analytical and reporter chambers. As a proof of concept, 32 BPEs were controlled wirelessly using a pair of driving electrodes, and the respiratory activities of individual MCF-7 cell aggregates as a cancer model were successfully detected by monitoring ECL signals. Compared with conventional electrode arrays for cell analysis, the wiring of the current device was simple because the multiple BPEs functioned with only a single power supply. To the best of our knowledge, this is the first study of on-chip analysis of cellular activity using a BPE system.

Micro-/Nanostructured Interface for Liquid Manipulation and Its Applications

Understanding the relationship between liquid manipulation and micro-/nanostructured interfaces has gained much attention due to the wide potential applications in many fields, such as chemical and biomedical assays, environmental protection, industry, and even daily life. Much work has been done to construct various materials with interfacial liquid manipulation abilities, leading to a range of interesting applications. Herein, different fabrication methods from the top-down approach to the bottom-up approach and subsequent surface modifications of micro-/nanostructured interfaces are first introduced. Then, interactions between the surface and liquid, including liquid wetting, liquid transportation, and a number of corresponding models, together with the definition of hydrophilic/hydrophobic, oleophilic/olephobic, the definition and mechanism of superwetting, including superhydrophobicity, superhydrophilicity, and superoleophobicity, are presented. The micro-/nanostructured interface, with major applications in self-cleaning, antifogging, anti-icing, anticorrosion, drag-reduction, oil-water separation, water collection, droplet (micro)array, and surface-directed liquid transport, is summarized, and the mechanisms underlying each application are discussed. Finally, the remaining challenges and future perspectives in this area are included.

Combination of Double-Mediator System with Large-Scale Integration-Based Amperometric Devices for Detecting NAD(P)H:quinone Oxidoreductase 1 Activity of Cancer Cell Aggregates

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a key enzyme providing cytoprotection from quinone species. In addition, it is expressed at high levels in many human tumors, such as breast cancer. Therefore, it is considered to be a potential target in cancer treatment. In order to detect intracellular NQO1 activity in MCF-7 aggregates as a cancer model, we present, in this study, a double-mediator system combined with large-scale integration (LSI)-based amperometric devices. This LSI device contained 20 × 20 Pt working electrodes with a 250 μm pitch for electrochemical imaging. In the detection system, menadione (MD) and [Fe(CN)₆]^3- were used. Since MD can diffuse into cells due to its hydrophobicity, it is reduced into menadiol by intracellular NQO1. The menadiol diffuses out of the cells and reduces [Fe(CN)₆]^3- of a hydrophilic mediator into [Fe(CN)₆]^4-. The accumulated [Fe(CN)₆]^4- outside the cells is electrochemically detected at 0.5 V in the LSI device. Using this strategy, the intracellular NQO1 activity of MCF-7 aggregates was successfully detected. The effect of rotenone, which is an inhibitor for Complex I, on NQO1 activity was also investigated. In addition, NQO1 and respiration activities were simultaneously imaged using the detection system that was further combined with electrochemicolor imaging. Thus, the double-mediator system was proven to be useful for evaluating intracellular redox activity of cell aggregates.

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.

384-Channel electrochemical sensor array chips based on hybridization-triggered switching for simultaneous oligonucleotide detection

We investigated the feasibility of simultaneous detection of multiple environmentally- and biomedically-relevant RNA biomarker target sequences on a single newly fabricated 384-ch sensor array chip aiming at practical application. The individual sensor is composed of a photolithographically-fabricated Au/Cr-based electrode modified with peptide nucleic acid (PNA) probes. The sensor array chips showed sequence-specific responses upon hybridization of the probes with target sequences complementary to the probes in contrast to mismatch versions. The target oligonucleotides have 15-22 mer sequences from messenger RNAs for estrogen-responsive genes and microRNAs for lung cancer biomarkers. The dependence on target concentrations of sensor responses was observed by using a single chip on which experiments for detection of several target concentrations proceeded simultaneously, with the detection limit of 7.33 × 10^-8 M. As more realistic samples, oligonucleotide samples amplified by PCR from a synthesized template sequence were applied to the chip. They showed sequence-specific responses, revealing the potential for fabricated sensor array chips to be utilized to analyze PCR samples. Unlike complicated and expensive chips that require nanofabrication, our sensor array chips based on glass coated with gold thin films are simple and can be fabricated from inexpensive and readily available materials.

Nanodendritic gold/graphene-based biosensor for tri-mode miRNA sensing

A nanodendritic gold/graphene-based biosensor that can perform fluorescence, SERS and electrochemical tri-modal miRNA detection in a single microdroplet has been developed. The biosensor was used to successfully perform tri-modal quantitative trace miRNA-375 detection, which enormously reduces false positive readings caused by interference and ambiguous signals, and has significant implications for use in precise physiological and pathological diagnosis.

Bioinspired superwettable micropatterns for biosensing

The bioinspired micropatterns exhibit outstanding capacity in controlling and patterning microdroplets, which have offered new functionalities and possibilities towards a wide variety of emerging biological and biomedical applications.

Laser-Cut Polymer Tape Templates for Scalable Filtration Fabrication of User-Designed and Carbon-Nanomaterial-Based Electrochemical Sensors

We report here a simple filtration method for the scalable fabrication of user-designed and carbon-nanomaterial-based electrode arrays using laser-cut poly(vinyl chloride) (PVC) tape templates. This method can produce electrode arrays with high uniformity and low resistance from the dilute dispersions of single-walled carbon nanotubes (SWNTs) and graphene nanoplatelets (GNPs). For these two carbon arrays, the SWNT array is demonstrated to possess several interesting properties, e.g., good mechanical properties, excellent flexibility, and favorable electrochemical behavior. Moreover, its porous structure enables the construction of a paperlike solid-state electrochemical sensor using Nafion electrolytes, which is suitable for the on-site monitoring of trace phenol pollutants in electrolyte-free water. Besides, an electrochemically addressable 36-zone sensor was constructed by this method. With the aid of an inexpensive 3D printer, the addressable sensor can achieve the semiautomatic and high-throughput evaluation of antioxidant capacity on a series of vegetables and fruits using a single-channel electrochemical analyzer.

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.

Robust and High Spatial Resolution Light Addressable Electrochemistry Using Hematite (α-Fe2O3) Photoanodes

Light addressable/activated electrochemistry (LAE) has recently attracted attention as it can provide spatially resolved electrochemical information without using pre-patterned electrodes whose sizes and positions are unchangeable. Here, we propose hematite (α-Fe₂O₃) as the photoanode for LAE, which does not require any sort of surface modification for protection or facilitating charge transfer. As experimentally confirmed with various redox species, hematite is stable enough to be used for repetitive electroanalytical measurements. More importantly, it offers exceptionally high spatial resolution so that the "virtual electrode" is exactly as large as the light spot owing to the short diffusion length of the minority carriers. Quantitative analysis of dopamine in this study shows that the hematite-based photoanode is a promising platform for many potential LAE applications including spatially selective detection of oxidizable biomolecules.

An Aqueous Composition for Lubricant-Free, Robust, Slippery, Transparent Coatings on Diverse Substrates

Transparent, durable coating materials that show excellent liquid repellency, both water and oil, have multiple applications in science and technology. In this perspective, herein, a simple aqueous chemical formulation is developed that provides a transparent slippery coating without any lubricating fluids, on various substrates extended over large areas. The coatings repel liquids having a range of polarity (solvents) as well as viscosity (oils and emulsions) and withstand mechanical strains. Exceptional optical transparency of 99% in the range of 350-900 nm along with high stability even after cyclic temperature, frost, exposure to sunlight, and corrosive liquids like aqua regia treatments, makes this material unique and widens its applicability in different fields. Besides, being a liquid, it can be coated on an array of substrates independent of their underlying topography, by various easily available techniques. Aside from these interesting properties, the coating is demonstrated as a potential solution contributing to the remediation of one of the biggest global issues of tomorrow: affordable drinking water. The coated surface can capture 5 L of water per day per m2 at 27 °C when exposed to an atmosphere of 63% relative humidity.

Creation of antifouling microarrays by photopolymerization of zwitterionic compounds for protein assay and cell patterning

Nonspecific binding or adsorption of biomolecules presents as a major obstacle to higher sensitivity, specificity and reproducibility in microarray technology. We report herein a method to fabricate antifouling microarray via photopolymerization of biomimetic betaine compounds. In brief, carboxybetaine methacrylate was polymerized as arrays for protein sensing, while sulfobetaine methacrylate was polymerized as background. With the abundant carboxyl groups on array surfaces and zwitterionic polymers on the entire surfaces, this microarray allows biomolecular immobilization and recognition with low nonspecific interactions due to its antifouling property. Therefore, low concentration of target molecules can be captured and detected by this microarray. It was proved that a concentration of 10ngmL^-1 bovine serum albumin in the sample matrix of bovine serum can be detected by the microarray derivatized with anti-bovine serum albumin. Moreover, with proper hydrophilic-hydrophobic designs, this approach can be applied to fabricate surface-tension droplet arrays, which allows surface-directed cell adhesion and growth. These light controllable approaches constitute a clear improvement in the design of antifouling interfaces, which may lead to greater flexibility in the development of interfacial architectures and wider application in blood contact microdevices.