Demanded by modern medical diagnosis, advances in microfabrication technology have led to the development of fast, sensitive and selective electrochemical sensors for clinic analysis. This review addresses the principles behind electrochemical sensor design and fabrication, and introduces recent progress in the application of electrochemical sensors to analysis of clinical chemicals such as blood gases, electrolytes, metabolites, DNA and antibodies, including basic and applied research. Miniaturized commercial electrochemical biosensors will form the basis of inexpensive and easy to use devices for acquiring chemical information to bring sophisticated analytical capabilities to the non-specialist and general public alike in the future.

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Electrochemical Sensors for Clinic Analysis.

Cofactor regeneration for sustainable enzymatic biosynthesis

Recent advances in nanotechnology have provided various nanoscale materials that can be used as support for enzyme immobilization. Nanobiocatalysis integrating the biocatalyst and nanoscale materials is drawing great attention as innovative technology. Nanobiocatalysis could achieve not only a much higher enzyme loading capacity and a significantly enhanced mass transfer efficiency, but also unbelievable stabilization. In this review, we will present and discuss the recent progress in nanobiocatalysis and its applications in the fields of bioelectronics, bioconversion, and proteomics.

Recent progress in nanobiocatalysis for enzyme immobilization and its application

This paper describes the design and fabrication of a "pop-up" electrochemical paper-based analytical device (pop-up-EPAD) to measure beta-hydroxybutyrate (BHB)-a biomarker for diabetic ketoacidosis-using a commercial combination BHB/glucometer. Pop-up-EPADs are inspired by pop-up greeting cards and children's books. They are made from a single sheet of paper folded into a three-dimensional (3D) device that changes shape, and fluidic and electrical connectivity, by simply folding and unfolding the structure. The reconfigurable 3D structure makes it possible to change the fluidic path and to control timing; it also provides mechanical support for the folded and unfolded structures that enables good registration and repeatability on folding. A pop-up-EPAD designed to detect BHB shows performance comparable to commercially available plastic test strips over the clinically relevant range of BHB in blood when used with a commercial glucometer that integrates the ability to measure glucose and BHB (combination BHB/glucometer). With simple modifications of the electrode and the design of the fluidic path, the pop-up-EPAD also detects BHB in buffer using a simple glucometer-a device that is more available than the combination BHB/glucometer. Strategies that use a "3D pop-up"-that is, large-scale changes in 3D structure and fluidic paths-by folding/unfolding add functionality to EPADs (e.g., controlled timing, fluidic handling and path programming, control over complex sequences of steps, and alterations in electrical connectivity) and should enable the development of new classes of paper-based diagnostic devices.

A Paper-Based "Pop-up" Electrochemical Device for Analysis of Beta-Hydroxybutyrate.

Biofouling on surfaces can deleteriously affect the function of electrochemical sensor used in a biological fluid. The demand is thus to develop a sensor operatable in complex matrices. Herein, we concisely review the technologies developed to date to minimize fouling of electrochemical interfaces by blood-based fluids with an emphasis on affinity biosensing. The methods toward this sensor fabrication that are discussed here include approaches where; chemically modified surfaces with antifouling layers such as ethylene oxides, zwitterionics and some alternative antifouling agents; physical forces such as fluidic systems; electrode surface topography, prevent biofouling, as well as recent approaches where biofouling does not interfere with the response (aptasensors). Furthermore, the important emerging field of implantable biosensors, originated from such fabrication procedures is discussed.

Approaches Toward Allowing Electroanalytical Devices to be Used in Biological Fluids

In this work, Rb-doped hierarchical flower-like In2O3 microspheres were synthesized via a facile one-step solvothermal method along with the subsequent thermal treatment. The morphology and structure of the as-synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Gas sensors based on the pure and Rb-doped In2O3 were fabricated and their gas sensing properties were systematically investigated. The sensors based on 1 mol% Rb-doped In2O3 exhibited ultrahigh response (Rg/Ra = 1502) to 5 ppm NO2 at 75 °C, which was over 2 times higher than that of pure In2O3. Moreover, the sensors showed good response towards NO2 down to ppb level (Rg/Ra = 10.2–100 ppb), a very low theoretical detection limit of 3.5 ppb, high selectivity and reliable repeatability. The excellent and enhanced NO2 gas sensing properties were mainly owing to its high specific surface area, novel hierarchical structure and increased surface chemisorbed oxygen species induced by Rb doping.

Enhanced NO2 gas sensing properties based on Rb-doped hierarchical flower-like In2O3 microspheres at low temperature

A disposable amperometric biosensor for monitoring the blood ketones has been developed. It can be used to determine the concentration of β-hydroxybutyrate without pretreatment of blood samples. Enzymes are immobilized on screen-printed carbon electrodes. For immobilizing the enzymes, first a layer of hydrophilic gel CMC was printed on the screen-printed carbon electrodes. β-Hydroxybutyrate dehydrogenase, cofactor NAD and electron transfer mediator, potassium ferricyanide are immobilized on the electrode surface by adsorption. Experimentally the compositions of β-hydroxybutyrate dehydrogenase, potassium ferricyanide, NAD and other components are optimized. Amperometry performed by a handheld meter is used for the determination of β-hydroxybutyrate concentration. Two microliters of whole blood or serum is needed for one test, and the response time of the sensor is 50 s. Experimental results show that the responses of the sensors have relevant good linearity in the range 1.5–550 mg L−1. The testing results by the biosensors and the routine hospital blood analyzer are agreed closely.

A new handheld biosensor for monitoring blood ketones

One-step solvothermal synthesis of hierarchical WO3 hollow microspheres with excellent NO gas sensing properties

The chemical industrial park is an important source of volatile organic compounds (VOCs) emissions which is difficult to monitor due to its diversity and low concentration. In this work, a hybrid sensor array consisting of six gas sensors (four semiconductor sensors, one electrochemical sensor, and one photo ionization detector) was constructed to measure VOCs. Three most frequently detected VOCs in a Chinese fine chemical industrial park, namely toluene, dichloromethane, ethyl acetate, and their mixtures, were tested all below 5 ppm (even below 1 ppm in many cases). Support vector machine (SVM) and back-propagation artificial neural network (BP-ANN) based on different input features, including steady-state responses (SS), the first four components preprocessed by principal component analysis (PCA) and linear discriminant analysis (LDA), were trained and evaluated. The 10-fold cross validation results indicate that SS-SVM and SS-ANN are two best models with accuracy and $\text{R}^{{2}}$ of about 94% and 0.95 for the validation set, respectively. Compared with LDA, PCA is more suitable for dimension reduction in this study, since the performance of models with the first 4 PCs are closer to that of models with SS. The results demonstrate that the proposed hybrid sensor array system with SVM and ANN models is able to identify and quantify low-concentration VOCs mixtures. This method is promising to be used for low-cost and online monitoring of VOCs emissions in chemical industrial parks.

Hybrid Gas Sensor Array to Identify and Quantify Low-Concentration VOCs Mixtures Commonly Found in Chemical Industrial Parks

The invention relates to a high-sensitivity ammonia gas sensor and a preparation method thereof The high-sensitivity ammonia gas sensor comprises a gold interdigital electrode substrate and a gas sensitive material layer, wherein the gold interdigital electrode substrate is composed of an aluminum oxide ceramic substrate on the lower layer and a gold interdigital electrode fixed to the surface ofthe aluminum oxide ceramic substrate, and the surface of the gold interdigital electrode is coated with the gas sensitive material layer; and the main component of the gas sensitive material layer isprecious metal ruthenium modified tungsten oxide, sodium tungstate is adopted as a tungsten source, and ruthenium chloride is adopted as a precious metal source According to the high-sensitivity ammonia gas sensor and the preparation method thereof, the gas sensitive material is deposited on the gold interdigital electrode by using a 3D printing method, the gas sensitive film with controllable thickness and shape can be conveniently and quickly obtained, and the preparation method is simple, low in manufacturing cost and suitable for large-scale production; and the modification of the precious metal ruthenium enhances the surface activity of the gas-sensitive material, and promotes the reaction between a gas to be detected and the gas-sensitive material, thereby further enhancing the gas-sensitive property

Yongguang Wang

Papers

Enhanced NO2 gas sensing properties based on Rb-doped hierarchical flower-like In2O3 microspheres at low temperature

A new handheld biosensor for monitoring blood ketones

One-step solvothermal synthesis of hierarchical WO3 hollow microspheres with excellent NO gas sensing properties

Hybrid Gas Sensor Array to Identify and Quantify Low-Concentration VOCs Mixtures Commonly Found in Chemical Industrial Parks

High-sensitivity ammonia gas sensor and preparation method thereof