Detection of chemical and biological agents plays a fundamental role in biomedical, forensic and environmental sciences1–4 as well as in anti bioterrorism applications.5–7 The development of highly sensitive, cost effective, miniature sensors is therefore in high demand which requires advanced technology coupled with fundamental knowledge in chemistry, biology and material sciences.8–13

In general, sensors feature two functional components: a recognition element to provide selective/specific binding with the target analytes and a transducer component for signaling the binding event. An efficient sensor relies heavily on these two essential components for the recognition process in terms of response time, signal to noise (S/N) ratio, selectivity and limits of detection (LOD).14,15 Therefore, designing sensors with higher efficacy depends on the development of novel materials to improve both the recognition and transduction processes. Nanomaterials feature unique physicochemical properties that can be of great utility in creating new recognition and transduction processes for chemical and biological sensors15–27 as well as improving the S/N ratio by miniaturization of the sensor elements.28

Gold nanoparticles (AuNPs) possess distinct physical and chemical attributes that make them excellent scaffolds for the fabrication of novel chemical and biological sensors (Figure 1).29–36 First, AuNPs can be synthesized in a straightforward manner and can be made highly stable. Second, they possess unique optoelectronic properties. Third, they provide high surface-to-volume ratio with excellent biocompatibility using appropriate ligands.30 Fourth, these properties of AuNPs can be readily tuned varying their size, shape and the surrounding chemical environment. For example, the binding event between recognition element and the analyte can alter physicochemical properties of transducer AuNPs, such as plasmon resonance absorption, conductivity, redox behavior, etc. that in turn can generate a detectable response signal. Finally, AuNPs offer a suitable platform for multi-functionalization with a wide range of organic or biological ligands for the selective binding and detection of small molecules and biological targets.30–32,36 Each of these attributes of AuNPs has allowed researchers to develop novel sensing strategies with improved sensitivity, stability and selectivity. In the last decade of research, the advent of AuNP as a sensory element provided us a broad spectrum of innovative approaches for the detection of metal ions, small molecules, proteins, nucleic acids, malignant cells, etc. in a rapid and efficient manner.37



Figure 1

Physical properties of AuNPs and schematic illustration of an AuNP-based detection system.



In this current review, we have highlighted the several synthetic routes and properties of AuNPs that make them excellent probes for different sensing strategies. Furthermore, we will discuss various sensing strategies and major advances in the last two decades of research utilizing AuNPs in the detection of variety of target analytes including metal ions, organic molecules, proteins, nucleic acids, and microorganisms.

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Gold nanoparticles in chemical and biological sensing.

▪ Abstract Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several are...

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Proton-Coupled Electron Transfer

Polyoxometalates (POMs) are a subset of metal oxides that represent a diverse range of molecular clusters with an almost unmatched range of physical properties and the ability to form dynamic structures that can range in size from the nano- to the micrometer scale Herein we present the very latest developments from synthesis to structure and function of POMs We discuss the possibilities of creating highly sophisticated functional hierarchical systems with multiple, interdependent, functionalities along with a critical analysis that allows the non-specialist to learn the salient features We propose and present a "periodic table of polyoxometalate building blocks" We also highlight some of the current issues and challenges that need to be addressed to work towards the design of functional systems based upon POM building blocks and look ahead to possible emerging application areas

Polyoxometalates: Building Blocks for Functional Nanoscale Systems

Gold nanoparticle-based electrochemical biosensors

Ordered mesoporous materials prepared by the template route have attracted increasing interest from the electrochemists community due to their plenty of unique properties and functionalities that can be effectively exploited in electrochemical devices. This review will cover the whole field of the intersection between electrochemistry and ordered mesoporous materials. The latter are either electronically insulating (silica and some other metal oxides, as well as silica-based organic–inorganic hybrid materials), semi-conducting (metal oxides), or conducting (metals, carbons). The three main intersection areas are: (1) the development/use of electrochemical methods to characterize the properties of mesoporous materials (i.e., charge and mass transfer processes); (2) the generation of mesostructured solids by electro-assisted deposition using appropriate templates; and (3) the application of these novel materials for electrochemical purposes. The most common devices to date are based on a bulk composite or thin film configuration and the resulting electrodes modified with such mesoporous materials have been successfully applied in various fields, including mainly electrochemical sensing and biosensing as well as energy conversion and storage (620 references).

Mesoporous materials and electrochemistry

Gold nanoparticles-mesoporous silica composite (GNPs-MPS) is developed as a novel enzyme immobilization matrix for biosensor construction The mesoporous silica SBA-15 is chosen and the GNPs-SBA-15 is formed from AuCl4− adsorbed H2N-SBA-15 by NaBH4 reduction The synthesis process of the composite is monitored by UV–vis spectroscopy and the product is characterized by transmission electron microscopy (TEM) measurement An amperometric glucose biosensor is built by immobilizing IO4−-oxidized-glucose oxidase (IO4−-oxidized-GOD) on GNPs-MPS modified Au electrode using 2-aminoethanethiol as a cross-linker Cyclic voltammetry (CV) and amperometry are employed to investigate the catalytic behavior of the biosensor to the oxidation of glucose As a result, the biosensor exhibits an excellent bioelectrocatalytic response to glucose with a fast response time less than 7 s, a broad linear range of 002–14 mM, high sensitivity of 61 μA mM−1 cm−2, as well as good long-term stability and reproducibility These performances could be ascribed to the GNPs-MPS's features, such as excellent conductivity, large surface area and good biocompatibility

Gold nanoparticles-mesoporous silica composite used as an enzyme immobilization matrix for amperometric glucose biosensor construction

A novel amperometric sensor of hydrogen peroxide was developed based on the immobilization of myoglobin (Mb) and colloidal gold nanoparticles (CGNs) on a glassy carbon electrode (GCE) by a Nafion film. The immobilized Mb displayed a pair of well-defined and nearly reversible cyclic voltammetric peaks with a formal potential (E°′) of −0.373 V in a 0.1 M phosphate buffer solution (PBS) of pH 6.9. The formal potential of the Mb heme Fe(III)/Fe(II) couple shifted linearly with pH with a slope of −49.6 mV/pH, indicating that the electron transfer is accompanied by single-proton transportation. The immobilized Mb exhibited excellent electrocatalytic response to the reduction of hydrogen peroxide, based on which an unmediated biosensor for hydrogen peroxide was achieved. The linear range for determination of hydrogen peroxide was from 1.5 × 10−6 to 9.0 × 10−5 M with a detection limit of 5.0 × 10−7 M at a signal-to-noise ratio of 3. The stability, repeatability and selectivity of the biosensor were also evaluated.

Hydrogen peroxide biosensor based on myoglobin/colloidal gold nanoparticles immobilized on glassy carbon electrode by a Nafion film

A new amperometric sensor was fabricated based on the immobilization of complex of Na 2 H 6 CoW 11 Co(H 2 O)O 39 ·14H 2 O (CoW 11 Co) and poly(4-vinylpyridine) (PVP) in a TiO 2 sol–gel matrix by vapor deposition method. The preparation process simplified the traditional sol–gel process and prevented the cracking of conventional sol–gel derived glasses. The electrochemical behavior of the new amperometric sensor was studied in detail by cyclic voltammetry, and three reversible two-electron redox waves were observed in acidic aqueous solution in the potential range of −0.1 to −0.7 V. The sensor displays good electrocatalytic activity toward the reduction of bromate, iodate and hydrogen peroxide in acidic aqueous solution and the catalytic mechanisms were also discussed. The catalysis of the sensor towards bromate and iodate was systematically studied by amperometric method. The method gave a linear range from 2.0 × 10 −5 to 4.4 × 10 −3  M and a detection limit of 5.0 × 10 −6  M for BrO 3 − and 2.0 × 10 −6 to 2.8 × 10 −4 and 8.0 × 10 −7  M for IO 3 − , respectively. In addition, the sensor has some distinct advantages over the traditional polyoxometalate sensor, such as simple preparation process, fast response and long-term stability.

A new amperometric sensor for the determination of bromate, iodate and hydrogen peroxide based on titania sol–gel matrix for immobilization of cobalt substituted Keggin-type cobalttungstate anion by vapor deposition method

Structure, photochromic, and electrochemical properties of dioctadecylamine/H3PMo12O40 Langmuir–Blodgett film

A new amperometric sensor for the determination of trichloroacetic acid (TCA) was developed based on the immobilization of myoglobin/colloidal gold nanoparticles in titania sol–gel matrix. The sensor showed a pair of well-defined and nearly reversible cyclic voltammetric peaks for the Mb Fe(III)/Fe(II) with a formal potential (E°′) of −335 mV and a peak-to-peak separation was 61 mV vs. Ag/AgCl (3.0 M KCl) at 100 mV s−1 in 0.1 M pH 7.0 phosphate buffer solutions (PBS). The formal potential of the Mb Fe(III)/Fe(II) couple shifted linearly with the pH with a slope of −51.3 mV/pH, indicating that an electron transfer accompanies single-proton transportation. The sensor displayed a good electrocatalytic response toward the reduction of TCA and the catalytic mechanism was also discussed. The overpotential for the reduction of TCA was lowered by at least 0.8 V compared with that obtained at bare glassy carbon electrode. The linear range spans the concentration of TCA from 2.0×10−6 to1.2×10−5 M and the detection limit was 1.2×10−7 M. In addition, the stability, repeatability and selectivity of the sensor were also evaluated.

Yancai Li

Papers

Gold nanoparticles-mesoporous silica composite used as an enzyme immobilization matrix for amperometric glucose biosensor construction

Hydrogen peroxide biosensor based on myoglobin/colloidal gold nanoparticles immobilized on glassy carbon electrode by a Nafion film

A new amperometric sensor for the determination of bromate, iodate and hydrogen peroxide based on titania sol–gel matrix for immobilization of cobalt substituted Keggin-type cobalttungstate anion by vapor deposition method

Structure, photochromic, and electrochemical properties of dioctadecylamine/H3PMo12O40 Langmuir–Blodgett film

Amperometric Sensor for Trichloroacetic Acid Based on Myoglobin/Colloidal Gold Nanoparticles Immobilized in Titania Sol–Gel Matrix