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.

In this report, we evaluate the present state of the rapidly emerging field of monolayer-protected cluster (MPC) molecules with regard to their synthesis and monolayer functionalization, their core and monolayer structure, their composition, and their properties. Finally, we canvass some of the important remaining research opportunities involving MPCs.

/pdf/monolayer-protected-cluster-molecules-1mpqg67ah9.pdf

Monolayer-Protected Cluster Molecules

Electrogenerated chemiluminescence (also called electrochemiluminescence and abbreviated ECL) is the process whereby species generated at electrodes undergo high-energy electron-transfer reactions to form excited states that emit light. The first detailed ECL studies were described by Hercules and Bard et al. in the mid-1960s, although reports concerning light emission during electrolysis date back to the 1920s by Harvey. After about 40 years study, ECL has now become a very powerful analytical technique and been widely used in the areas of, for example, immunoassay, food and water testing, and biowarfare agent detection. ECL has also been successfully exploited as a detector of flow injection analysis (FIA), high-performance liquid chromatography (HPLC), capillary electrophoresis, and micro total analysis (μTAS). Figure 1 illustrates a time line of various events in the development of ECL. A literature survey using SciFinder Scholar reveals that more than 2000 journal articles, book chapters, and patents on various topics of ECL have been published. The overall number of publications, as shown in Figure 2, has increased exponentially over the past 20 years, of which 40–50% were biorelated. Similar amounts of ECL papers could be also found from the Thomson ISI Web of Science as well as † Telephone (601) 266 4716; fax (601) 266 6075; e-mail wujian.miao@ usm.edu. Wujian Miao received his undergraduate diploma in chemistry from Nantong University (Nantong, China) in 1982, his M.Sc. degree in analytical chemistry from Zhongshan University (Guangzhou, China, with Jinyuan Mo) in 1991, and his Ph.D. degree in electrochemistry from Monash University (Melbourne, Australia, with Alan M. Bond) in 2000. He then served as a Research Scientist in CSIRO (Melbourne, Australia), followed by a postdoctoral fellowship at the University of Texas at Austin with Allen J. Bard in 2001. Since 2004 he has served as an assistant professor of chemistry at the University of Southern Mississippi.

Electrogenerated Chemiluminescence and Its Biorelated Applications

This article provides an up-to-date perspective on the use of anion-exchange membranes in fuel cells, electrolysers, redox flow batteries, reverse electrodialysis cells, and bioelectrochemical systems (e.g. microbial fuel cells). The aim is to highlight key concepts, misconceptions, the current state-of-the-art, technological and scientific limitations, and the future challenges (research priorities) related to the use of anion-exchange membranes in these energy technologies. All the references that the authors deemed relevant, and were available on the web by the manuscript submission date (30th April 2014), are included.

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Anion-exchange membranes in electrochemical energy systems

Anion exchange membranes for alkaline fuel cells: A review

Recent observations of angular distributions of $\ensuremath{\pi}$ mesons in $\overline{p}\ensuremath{-}p$ annihilation indicate a deviation from the predictions of the usual Fermi statistical model. In order to shed light on these phenomena, a modification of the statistical model is studied. We retain the assumption that the transition rate into a given final state is proportional to the probability of finding $N$ free $\ensuremath{\pi}$ mesons in the reaction volume, but express this probability in terms of wave functions symmetrized with respect to particles of like charge. The justification of this assumption is discussed. The model reproduces the experimental results qualitatively, provided the radius of the interaction volume is between one-half and three-fourths of the pion Compton wavelength; the dependence of angular correlation effects on the value of the radius is rather sensitive. Quantitatively, there seems to remain some discrepancy, but we cannot say whether this is due to experimental uncertainties or to some other dynamic effects. In the absence of information on $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ interactions and of a fully satisfactory explanation of the mean pion multiplicity for annihilation, we wish to emphasize the preliminary nature of our results. We consider them, however, as an indication that the symmetrization effects discussed here may well play a major role in the analysis of angular distributions. It is pointed out that in this respect the energy dependence of the angular correlations may provide valuable clues for the validity of our model.

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Influence of Bose-Einstein Statistics on the Antiproton-Proton Annihilation Process

Ru(bpy) 3
 2+
 electrogenerated chemiluminescence (CL) has rapidly gained importance as a sensitive and selective detection method in analytical science. The Ru(bpy) 3
 2+
 ECL is observed when Ru(bpy) 3
 3+
 reacts with Ru(bpy) 3
 +
 and yields an excited state Ru(bpy) 3
 2+*
 . ECL emission can also be obtained when a variety of oxidants and reductants react with the reduced or oxidized forms of Ru(bpy) 3
 2+
 . Either the reductant or the oxidant can be treated as an analyte. The Ru(bpy) 3
 2+
 ECL is used as a detection method for the determination of oxalate and a variety of amine-containing analytes without derivatization in flowing streams such as flow injection and HPLC. When the ECL format is used as a detector for HPLC, unstable post-column reagent addition can often be eliminated and, the problems of both sample dilution and band broadening can be avoided because the Ru(bpy) 3
 3+
 species are generatedin situ in the reaction/observation flow cell. Since NADH is sensitively detected with the Ru(bpy) 3
 2+
 ECL, many clinically important analytes can be detected by coupling them to dehydrogenase enzymes that utilize β-nicotinamide adenine cofactors to convert NAD+ to NADH. Ru(bpy) 3
 2+
 -derivatives are used as CL labels for immunoassay and PCR assay with Ru(bpy) 3
 2+
 /tripropylamine ECL system. The Ru(bpy) 3
 2+
 ECL label can be sensitively determined at subpicomolar concentrations, along with an extremely wide dynamic range of greater than six orders of magnitude. Furthermore, it can eliminate disposal and lifetime problems inherent in radio immunoassays. In this paper, basic principles of the Ru(bpy) 3
 2+
 ECL are discussed. In addition, analytical applications of the Ru(bpy) 3
 2+
 ECL are illustrated with examples.

Tris (2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence in analytical science

Electrochemical behavior and electrogenerated chemiluminescence (ECL) of tris(2,2‘-bipyridyl)ruthenium(II) (Ru(bpy)32+) immobilized in sol−gel-derived titania (TiO2)−Nafion composite films coated on a glassy carbon electrode have been investigated. The electroactivity of Ru(bpy)32+ ion exchanged into the composite films and its ECL behavior were strongly dependent upon the amount of Nafion incorporated into the TiO2−Nafion composite films. The ECL sensor of Ru(bpy)32+ immobilized in a TiO2−Nafion composite with 50% Nafion content showed the maximum ECL intensities for both tripropylamine (TPA) and sodium oxalate in 0.05 M phosphate buffer solution at pH 7. Detection limits were 0.1 μM for TPA and 1.0 μM for oxalate (S/N = 3) with a linear range of 3 orders of magnitude in concentration. The present ECL sensor showed improved ECL sensitivity and long-term stability, as compared to the ECL sensors based on pure Nafion films. The present Ru(bpy)32+ ECL sensor based on TiO2−Nafion (50%) composite films was ap...

Electrogenerated chemiluminescence from tris(2,2'-bipyridyl)ruthenium(II) immobilized in titania-perfluorosulfonated ionomer composite films

Purpose The aim of this study was to evaluate the outcome of arthroscopic partial repair and margin convergence of irreparable large to massive rotator cuff tears. Methods Between January 2003 and July 2008, 27 patients who met the inclusion criteria underwent arthroscopic partial repair and margin convergence of irreparable large to massive rotator cuff tears. An irreparable tear was defined as a tear with a minimum anterior-to-posterior width of 3 cm or larger, where it was not feasible to completely cover the humeral head with the cuff at the time of surgery. Results The mean preoperative tear size was 42.1 ± 6.2 mm. The mean size of the postoperative residual defect in the repaired tendon along the medial margin of the greater tuberosity was 12.0 ± 5.5 mm. All shoulder scores showed improvement. The Simple Shoulder Test improved from 5.1 ± 1.2 to 8.8 ± 2.1 ( P P P P Conclusions Arthroscopic partial repair and margin convergence showed satisfactory short-term outcomes in irreparable large to massive rotator cuff tears. Thus it is suggested that, even in a large to massive tear that appears irreparable, attempting to repair it as much as possible to possibly convert it into a functional rotator cuff tear by re-creating a balanced forced couple can be helpful in reducing pain, as well as improving functional outcomes. Level of Evidence Level IV, therapeutic case series.

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Arthroscopic partial repair of irreparable large to massive rotator cuff tears.

Three approaches are comparatively evaluated for the use of tris(2,2'-bipyridil)ruthenium(II), Ru(bpy) 3 3+ , as a chemiluminescent reagent in flow streams: (1) external generation of the reactive Ru(bpy) 3 3+ oxidation state followed by contact with the analyte, (2) in situ generation of the Ru(bpy) 3 3+ species from a solution mixture of the analyte and the Ru(bpy) 3 2+ species as it passes through the reaction/observation cell, and (3) in situ generation of the Ru(bpy) 3 3+ species from the Ru(bpy) 3 2+ species immobilized within the observation cell. Oxalate and proline were used as representative analytes for comparison of these three modes with respect to the influence of experimental variables (reagent concentration, flow rate, pH) and resulting analytical performance (detection limit, working range, measurement precision). Additionally, a comparison was made of the relative ECL intensities obtained for a variety of analytes including oxidate, amino acids, aliphatic amines, peptides, and NADH. We find that each approach has its unique set of strengths and weaknesses. The external generation mode yields the most intense emission, especially for simple aliphatic amines, but working curves have poor linearity, and emission intensities have a large dependence on solution flow rate. The in situ immobilized approach results in lower intensities but yields the widest linear dynamic ranges, is most conservative of reagent, and has a particular sensitivity advantage for proline and NADH determinations. The in situ solution mode is superior for the detection of amino acids such as hyptophan, 5-hydroxyhyptophan, and histidine and has time, convenience, and reliability advantages

Won-Yong Lee

Papers

Influence of Bose-Einstein Statistics on the Antiproton-Proton Annihilation Process

Tris (2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence in analytical science

Electrogenerated chemiluminescence from tris(2,2'-bipyridyl)ruthenium(II) immobilized in titania-perfluorosulfonated ionomer composite films

Arthroscopic partial repair of irreparable large to massive rotator cuff tears.

Evaluation of use of tris(2,2'-bipyridyl)ruthenium(III) as a chemiluminescent reagent for quantitation in flowing streams