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.

/pdf/gold-nanoparticles-in-chemical-and-biological-sensing-5e2qojkdzn.pdf

Gold nanoparticles in chemical and biological sensing.

An Introduction to MultiAgent Systems.

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

Microneedles for drug and vaccine delivery.

A macroporous silicon micromonolith containing ca. 40,000 regular channels of 3.3 μm in diameter per square millimeter has been successfully functionalized with an Au/TiO2 catalyst for CO preferential oxidation (CO-PrOx) in the presence of hydrogen. The functionalization of the silicon microchannels has been accomplished by growing a SiO2 layer on the channel walls, followed by exchange with a titanium alkoxyde precursor and decomposition into TiO2 and, finally, by anchoring carbosilanethiol dendron protected pre-formed Au nanoparticles. Catalytically active centers at the Au-TiO2 interface have been obtained by thermal activation. With this method, an excellent homogeneity and adherence of the catalytic layer over the microchannels of the macroporous silicon micromonolith has been obtained, which has been tested for CO-PrOx at 363-433 K and λ=2 under H2/CO=0-20 (molar). The macroporous silicon micromonolith converts ca. 3 NmL of CO per minute and mL of micro reactor at 433 K under H2/CO=20, suggesting that it could be particularly effective for hydrogen purification in low-temperature microfuel cells for portable applications.

Macroporous silicon microreactor for the preferential oxidation of CO

We study the photonic band gap formation in 2D photonic crystals comprising rods covered with a thin interfacial layer. The dielectric constant of the interfacial layer is different from that of the rods and background material. The rod together with the surrounding interfacial layer can therefore be treated as a single rod having a core and cladding regions. We study how the thickness and the dielectric constant of the cladding material affect the properties of photonic gaps in 2D photonic lattices. Specifically, we consider triangular and honeycomb lattices consisting of air rods drilled in silicon matrix and silicon rods in air, respectively. Photonic band simulations of such structures are presented performed using both finite-difference time-domain and plane-wave expansion methods. We show that the physical properties of the cladding layer strongly influence the photonic gap parameters. In particular, the existence of dielectric cladding reduces the absolute PBG in case of air rods drilled in a dielectric host, but may lead to larger absolute gaps in case of dielectric rods embedded in air. We also discuss the practical technological feasibility of these structures and their experimental realization.

Two-dimensional photonic crystals of rods with a dielectric cladding

The absolute maximum value of the voltage devel- oped across an electrostatic actuator when driven by a current source has been calculated as well as an absolute minimum for the pull-in time. These two results are calculated for a drive using a -pulse of current and numerical assessment is given to show that for a nonzero parasitic capacitance, a realistic shape of the cur- rent pulse, or a finite value of the damping coefficient do not in- crease the maximum value of the voltage developed beyond that limit and that the pull-in time is always larger than the analytical minimum. A scaled-up macromodel of an electrostatic actuator has been used to register voltage transients to validate the theoretical predictions. (728)

Voltage and Pull-In Time in Current Drive of

The main contribution of our work is a technique to accelerate the real-time simulation of deformable objects using a stable finite element method. Our purpose is to construct a preconditioner matrix for the coefficient matrix of the implicit integration scheme based on the global rotation matrix of the object. We describe some required steps to compute an optimal preconditioner in an off-line step. Our technique can be used to accelerate the element stiffness warping method and could be used to solve the system directly for objects with small deformations or for objects that appear outside of the users' interest zone. Copyright © 2006 John Wiley & Sons, Ltd.

Optimized linear FEM for modeling deformable objects: Research Articles

The characteristics of reflection and transmission peaks in the spectra of photonic crystals have been studied theoretically and the results compared to measurements performed in fabricated samples. The aim of this work is to investigate the relation between material losses and the effective Q factors that can be obtained in photonic crystals made with it. Photonic crystals have been designed with defects of periodicity to introduce states in the band gap that give place to reflectance and transmittance peaks at adjustable specific wavelengths. The fabricated structures are described together with their reflection and transmission spectra. The influence of losses in the material in these spectra is evaluated.

/pdf/impact-of-the-absorption-in-transmittance-and-reflectance-on-x45i5qbtws.pdf

Angel Rodríguez

Papers

Macroporous silicon microreactor for the preferential oxidation of CO

Two-dimensional photonic crystals of rods with a dielectric cladding

Voltage and Pull-In Time in Current Drive of

Optimized linear FEM for modeling deformable objects: Research Articles

Impact of the absorption in transmittance and reflectance on macroporous silicon photonic crystals