5.1. Detection Formats 475 5.2. Food Quality and Safety Analysis 477 5.2.1. Pathogens 477 5.2.2. Toxins 479 5.2.3. Veterinary Drugs 479 5.2.4. Vitamins 480 5.2.5. Hormones 480 5.2.6. Diagnostic Antibodies 480 5.2.7. Allergens 481 5.2.8. Proteins 481 5.2.9. Chemical Contaminants 481 5.3. Medical Diagnostics 481 5.3.1. Cancer Markers 481 5.3.2. Antibodies against Viral Pathogens 482 5.3.3. Drugs and Drug-Induced Antibodies 483 5.3.4. Hormones 483 5.3.5. Allergy Markers 483 5.3.6. Heart Attack Markers 484 5.3.7. Other Molecular Biomarkers 484 5.4. Environmental Monitoring 484 5.4.1. Pesticides 484 5.4.2. 2,4,6-Trinitrotoluene (TNT) 485 5.4.3. Aromatic Hydrocarbons 485 5.4.4. Heavy Metals 485 5.4.5. Phenols 485 5.4.6. Polychlorinated Biphenyls 487 5.4.7. Dioxins 487 5.5. Summary 488 6. Conclusions 489 7. Abbreviations 489 8. Acknowledgment 489 9. References 489

Surface Plasmon Resonance Sensors for Detection of Chemical and Biological Species

First-generation glucose biosensors relied on the use of the natural oxygen cosubstrate and the production and detection of hydrogen peroxide and were much simpler, especially when miniaturized sensors are concerned. More sophisticated bioelectronic systems for enhancing the electrical response, based on patterned monolayer or multilayer assemblies and organized enzyme networks on solid electrodes, have been developed for contacting GOx with the electrode support. Electrochemical biosensors are well suited for satisfying the needs of personal (home) glucose testing, and the majority of personal blood glucose meters are based on disposable (screen-printed) enzyme electrode test strips, which are mass produced by the thick film (screen-printing) microfabrication technology. In the counter and an additional “baseline” working electrode, various membranes (mesh) are incorporated into the test strips along with surfactants, to provide a uniform sample coverage. Such devices offer considerable promise for obtaining the desired clinical information in a simpler, user-friendly, faster, and cheaper manner compared to traditional assays. Continuous ex-vivo monitoring of blood glucose was proposed in 1974 and the majority of glucose sensors used for in-vivo applications are based on the GOx-catalyzed oxidation of glucose by oxygen. The major factors that play a role in the development of clinically accurate in-vivo glucose sensors include issues related to biocompatibility, miniaturization, long-term stability of the enzyme and transducer, oxygen deficit, short stabilization times, in-vivo calibration, baseline drift, safety, and convenience.

Electrochemical Glucose Biosensors

Carboxyl-modified graphene oxide (GO-COOH) possesses intrinsic peroxidase-like activity that can catalyze the reaction of peroxidase substrate 3,3,5,5-tetramethyl-benzidine (TMB) in the presence of H2O2 to produce a blue color reaction. A simple, cheap, and highly sensitive and selective colorimetric method for glucose detection has been developed and will facilitate the utilization of GO-COOH intrinsic peroxidase activity in medical diagnostics and biotechnology.

Graphene oxide: intrinsic peroxidase catalytic activity and its application to glucose detection.

Conducting polymer hydrogels represent a unique class of materials that synergizes the advantageous features of hydrogels and organic conductors and have been used in many applications such as bioelectronics and energy storage devices. They are often synthesized by polymerizing conductive polymer monomer within a nonconducting hydrogel matrix, resulting in deterioration of their electrical properties. Here, we report a scalable and versatile synthesis of multifunctional polyaniline (PAni) hydrogel with excellent electronic conductivity and electrochemical properties. With high surface area and three-dimensional porous nanostructures, the PAni hydrogels demonstrated potential as high-performance supercapacitor electrodes with high specific capacitance (∼480 F·g-1), unprecedented rate capability, and cycling stability (∼83% capacitance retention after 10,000 cycles). The PAni hydrogels can also function as the active component of glucose oxidase sensors with fast response time (∼0.3 s) and superior sensitivity (∼16.7 μA·mM-1). The scalable synthesis and excellent electrode performance of the PAni hydrogel make it an attractive candidate for bioelectronics and future-generation energy storage electrodes.

/pdf/hierarchical-nanostructured-conducting-polymer-hydrogel-with-4eeyqwdsrk.pdf

Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity

The unique properties of nanoscale materials offer excellent prospects for interfacing biological recognition events with electronic signal transduction and for designing a new generation of bioelectronic devices exhibiting novel functions. In this Highlight I address recent research that has led to powerful nanomaterial-based electrical biosensing devices and examine future prospects and challenges. New nanoparticle-based signal amplification and coding strategies for bioaffinity assays are discussed, along with carbon-nanotube molecular wires for achieving efficient electrical communication with redox enzyme and nanowire-based label-free DNA sensors.

Nanomaterial-based electrochemical biosensors

This paper presents a glucose sensor using conducting polymer/enzyme nanojunctions and demonstrates that unique features can arise when shrinking a sensor to the nanometer scale. Each nanojunction is formed by bridging a pair of nanoelectrodes separated with a small gap (20−60 nm) with polyaniline/glucose oxidase. The signal transduction mechanism of the sensor is based on the change in the nanojunction conductance as a result of glucose oxidation induced change in the polymer redox state. Due to the small size of the nanojunction sensor, the enzyme is regenerated naturally without the need of redox mediators, which consumes minimal amount of oxygen and at the same time gives very fast response (<200 ms). These features make the nanojunction sensor potentially useful for in vivo detection of glucose.

https://pubs.acs.org/doi/pdf/10.1021/nl048314y

A Conducting Polymer Nanojunction Sensor for Glucose Detection

We have built a high-resolution differential surface plasmon resonance (SPR) sensor for heavy metal ion detection. The sensor surface is divided into a reference and sensing areas, and the differen...

Detection of heavy metal ions in drinking water using a high-resolution differential surface plasmon resonance sensor.

We describe a simple, stable, and high-resolution surface plasmon resonance (SPR) sensor using a quadrant cell photodetector. The sensor focuses a diode laser through a prism onto a gold film that is divided into two areas, one for reference and the other for sensing analyte. The angular shifts of the SPR generated in the two areas are detected with a quadrant cell photodetector. Because signals from the two areas are produced and detected with the same laser, optics, and photodetector, the difference in the SPR angular shifts eliminates errors due to thermal drift, mechanical noise, and laser fluctuations. It also removes the SPR angular shift due to the change in the refractive index of the bulk solution as an analyte solution is introduced into the sample cell each time, and thus gives an accurate detection of the specific adsorption of analyte.

High-performance differential surface plasmon resonance sensor using quadrant cell photodetector

We present a method to assemble Au/polyaniline/Au junctions and demonstrate a chemical sensor application. The building blocks consist of an array of microelectrodes on a silicon chip, microfabricated metallic bars, and a thin polyaniline layer deposited on the microelectrodes or on the bars. The individual bars suspended in solution are placed, with the help of a magnetic field, across the microelectrodes to form the junctions. The polyaniline layer is ∼30 nm thick and modified with glycine-glycine-histidine oligopeptides. Strong binding of Cu2+ to the oligopeptide is converted into a conductance change of the junctions, allowing selective detection of trace amounts of Cu+2 ions.

Magnetic-field-assisted assembly of metal/polymer/metal junction sensors

Rational design of electrocatalysts is important for a sustainable oxygen evolution reaction (OER). It is still a huge challenge to engineer active sites in multi-sizes and multi-components simultaneously. Here, a series of Co x P nanoparticles (NPs) confined in an SiO 2 matrix (SiO 2 /Co x P) is designed and synthesized as OER electrocatalysts. The phosphorization of the hydrolyzed Co-phyllosilicate promotes the formation of ultrasmall and small Co 2 P and CoP. These are firmly confined in the SiO 2 matrix. The coupling of multi-size and multi-component Co x P catalysts can regulate reaction kinetics and electron transfer ability, enrich the active sites, and eventually promote the intrinsic OER activity. The SiO 2 matrix provides abundant porous structure and oxygen vacancies, and these facilitate the exposure of active sites and improve conductivity. Because of the synergy and interplay of multi-sized/component Co x P NPs and the porous SiO 2 matrix, the unique SiO 2 /Co x P heterostructure exhibits low overpotential (293 ​mV@10 ​mA ​cm -2 ), and robust stability (decay 12 ​mV after 5000 CV cycles, 97.4% of initial current after 100 ​h chronoamperometric) for the OER process, exceeding many advanced metal phosphide electrocatalysts. This work provides a novel tactic to design low-cost, simple, and highly efficient OER electrocatalysts. 

Haiqian Zhang

Papers

A Conducting Polymer Nanojunction Sensor for Glucose Detection

Detection of heavy metal ions in drinking water using a high-resolution differential surface plasmon resonance sensor.

High-performance differential surface plasmon resonance sensor using quadrant cell photodetector

Magnetic-field-assisted assembly of metal/polymer/metal junction sensors

Coupling of ultrasmall and small Co P nanoparticles confined in porous SiO2 matrix for a robust oxygen evolution reaction