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.

Polydopamine and Its Derivative Materials: Synthesis and Promising Applications in Energy, Environmental, and Biomedical Fields

The Pharmacological Basis of Therapeutics A Textbook of Pharmacology, Toxicology and Therapeutics for Physicians and Medical Students. By Prof. Louis Goodman and Prof. Alfred Gilman. Pp. xiii + 1383. (New York: The Macmillan Company, 1941.) 50s. net.

The Pharmacological Basis of Therapeutics

Lanthanide ions exhibit unique luminescent properties, including the ability to convert near infrared long-wavelength excitation radiation into shorter visible wavelengths through a process known as photon upconversion. In recent years lanthanide-doped upconversion nanocrystals have been developed as a new class of luminescent optical labels that have become promising alternatives to organic fluorophores and quantum dots for applications in biological assays and medical imaging. These techniques offer low autofluorescence background, large anti-Stokes shifts, sharp emission bandwidths, high resistance to photobleaching, and high penetration depth and temporal resolution. Such techniques also show potential for improving the selectivity and sensitivity of conventional methods. They also pave the way for high throughput screening and miniaturization. This tutorial review focuses on the recent development of various synthetic approaches and possibilities for chemical tuning of upconversion properties, as well as giving an overview of biological applications of these luminescent nanocrystals.

Recent advances in the chemistry of lanthanide-doped upconversion nanocrystals

Nanomaterials, such as metal or semiconductor nanoparticles and nanorods, exhibit similar dimensions to those of biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA. The integration of nanoparticles, which exhibit unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and functions. This review describes recent advances in the synthesis of biomolecule-nanoparticle/nanorod hybrid systems and the application of such assemblies in the generation of 2D and 3D ordered structures in solutions and on surfaces. Particular emphasis is directed to the use of biomolecule-nanoparticle (metallic or semiconductive) assemblies for bioanalytical applications and for the fabrication of bioelectronic devices.

Integrated Nanoparticle–Biomolecule Hybrid Systems: Synthesis, Properties, and Applications

Fluorescence resonant energy transfer biosensor based on upconversion-luminescent nanoparticles

To demonstrate their applications in biological and medical fields such as in immunoassays, magnetic separation of cells or proteins, drug or gene delivery, and magnetic resonance imaging, the template-free syntheses of water-soluble and surface functionalized magnetic nanomaterials have become essential and are challenging. Herein, we developed a facile one-pot template-free method for the preparation of amine-functionalized magnetite nanoparticles and hollow nanospheres by using FeCl(3)6 H(2)O as single iron source. These magnetic nanomaterials were characterized by TEM, SEM, XRD, and FTIR technologies. Their magnetic properties were also studied by using a superconducting quantum interference device (SQUID) magnetometer at room temperature. Then the amine-functionalized magnetite nanoparticles were applied to immunoassays and magnetic resonance imaging in live mice.

One-pot synthesis and bioapplication of amine-functionalized magnetite nanoparticles and hollow nanospheres

A well-known gas sensing material SnO2 in combination with reduced graphene oxide was used in heavy metal ions detection for the first time. This work reports the detailed study on the SnO2/reduced graphene oxide nanocomposite modified glass carbon electrode, which could be used for the simultaneous and selective electrochemical detection of ultratrace Cd(II), Pb(II), Cu(II), and Hg(II) in drinking water. The SnO2/reduced graphene oxide nanocomposite electrode was characterized voltammetrically using redox couples (Fe(CN)63–/4–), complemented with electrochemical impedance spectroscopy (EIS). Square wave anodic stripping voltammetry (SWASV) has been used for the detection of Cd(II), Pb(II), Cu(II), and Hg(II). The detection limit (3σ method) of the SnO2/reduced graphene oxide nanocomposite modified GCE toward Cd(II), Pb(II), Cu(II) and Hg(II) is 1.015 × 10–10 M, 1.839 × 10–10 M, 2.269 × 10–10 M, and 2.789 × 10–10 M, respectively, which is very well below the guideline value given by the World Health Organ...

SnO2/Reduced Graphene Oxide Nanocomposite for the Simultaneous Electrochemical Detection of Cadmium(II), Lead(II), Copper(II), and Mercury(II): An Interesting Favorable Mutual Interference

A promising electrochemical sensor was fabricated by electrodeposition of gold nanoparticles on poly(3-methylthiophene) (P3MT)-modified glassy carbon electrode (GCE), forming a nano-Au/P3MT composites-modified GCE (nano-Au/P3MT/GCE). Field emission scanning electron microscope (FE-SEM) and electrochemical techniques were used for the characterization of these composites. It was found that nano-Au/P3MT layer was very uniform, and formed a kind of nanoporous structure. Electrochemical experiments showed that this proposed nano-Au/P3MT composites-modified electrode exhibited excellent electrocatalytic properties for nitrite and iodate. Amperometry revealed that there existed a good linear relationship between peak current with the concentration in the range of 10–1000 μM and the detection limit of 2.3 μM for nitrite and in the range of 5–500 μM and the detection limit of 1.4 μM for iodate. The proposed method has been used as an amperometric detector for analysis of nitrite and iodate in iodized table salt and results were satisfactory. The nano-Au/P3MT composites-modified electrode had good storage stability, reproducibility and anti-interference ability for promising practical application.

Electrochemical determination of nitrite and iodate by use of gold nanoparticles/poly(3-methylthiophene) composites coated glassy carbon electrode

A non-enzymatic amperometric glucose is reported that is based on an glassy carbon electrode modified with a Cu-CuO nanowire (NW) composite. The morphology and the composition of the nanowire were characterized by scanning electron microscopy and X-ray diffraction, respectively. The modified electrode efficiently catalyzes the oxidation of glucose at less-positive potential (0.30 V) in 0.10 M NaOH solution in the absence of any enzymes or redox mediators. The sensor was successfully used for the amperometric sensing of glucose. Linear response was obtained over the concentration range from 0.1 to 12 mM. The common interfering agents ascorbic acid and uric acid do not interfere with the determination of glucose. The modified electrode features high sensitivity, low working potential, excellent stability, and fast amperometric sensing of glucose. Thus it is promising for the future development of non-enzymatic glucose sensors.

Lun Wang

Papers

Fluorescence resonant energy transfer biosensor based on upconversion-luminescent nanoparticles

One-pot synthesis and bioapplication of amine-functionalized magnetite nanoparticles and hollow nanospheres

SnO2/Reduced Graphene Oxide Nanocomposite for the Simultaneous Electrochemical Detection of Cadmium(II), Lead(II), Copper(II), and Mercury(II): An Interesting Favorable Mutual Interference

Electrochemical determination of nitrite and iodate by use of gold nanoparticles/poly(3-methylthiophene) composites coated glassy carbon electrode

Enzyme-free amperometric sensing of glucose using Cu-CuO nanowire composites