There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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.

基礎講座 電気泳動(Electrophoresis)

This protocol provides an introduction to soft lithography--a collection of techniques based on printing, molding and embossing with an elastomeric stamp. Soft lithography provides access to three-dimensional and curved structures, tolerates a wide variety of materials, generates well-defined and controllable surface chemistries, and is generally compatible with biological applications. It is also low in cost, experimentally convenient and has emerged as a technology useful for a number of applications that include cell biology, microfluidics, lab-on-a-chip, microelectromechanical systems and flexible electronics/photonics. As examples, here we focus on three of the commonly used soft lithographic techniques: (i) microcontact printing of alkanethiols and proteins on gold-coated and glass substrates; (ii) replica molding for fabrication of microfluidic devices in poly(dimethyl siloxane), and of nanostructures in polyurethane or epoxy; and (iii) solvent-assisted micromolding of nanostructures in poly(methyl methacrylate).

/pdf/soft-lithography-for-micro-and-nanoscale-patterning-21e1ngmrqv.pdf

Soft lithography for micro- and nanoscale patterning

A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production.

MEMS has been an enabling technology for biomedical applications recently. Not only does it provide an instrument to obtain information on molecular level, but it also allows us to manipulate bio-molecules efficiently. Micro devices and systems for manipulation of biological objects such as cells, proteins and DNA have been demonstrated. In this study, we report a technique using dielectrophoretic forces to manipulate micro particles. First, the concept of several manipulation techniques is reviewed. Then we focus on novel manipulation modes. With the help of these biochips, we are able to perform manipulation of micro particles/cells.

Platform technology for manipulation of cells, proteins and DNA

Rapid and accurate diagnosis of C-reactive protein (CRP) is crucial for monitoring cardiovascular diseases because it is a well-known biomarker for evaluating risks of cardiovascular diseases. This study presents a dual-aptamer assay for detection of CRP by using field-effect transistors (FET). This is the first time that two aptamers, which are specific to CRP, were used to form a sandwich assay such that the CRP concentration could be detected by FET devices. Furthermore, a microfluidic system was used to automate the dual-aptamer sandwich assay such that the entire diagnosis process could be automated. In addition to electric signals from the FET device, fluorescent signals were also used to confirm this assay. Experimental results revealed that the first aptamer (1st aptamer) and the second aptamer (c aptamer) could be specifically binded with target CRP. Furthermore, the microfluidic chip integrated with FET can be re-used if the binded CRP and 2nd aptamer was eluted. Besides, in order to prevent the interference materials like proteins, cells and any nonspecific molecules from adhering onto the gate region of the FET device even after immobilization of 1st aptamer, we used ethanolamine as the blocking agent to prevent nonspecific adhesion. The experimental results confirmed that blocking using ethanolamine could successfully prevent nonspecific binding.

Dual-aptamer assay for C-reactive protein detection by using field-effect transistors on an integrated microfluidic system

The determination of the mechanical properties of cells plays an important role in biological studies and has gained acceptance recently as a possible label-free biomarker for cell status determination or diseases detection. Investigations on how external cellular properties affect cell mechanics are helpful in understanding cell disease processes and cell morphogenesis, which are of large significance in medical science. Although most researchers have focused on individual cell mechanics, or the effect of substrate stiffness on cells, cell mechanical response due to interactions among cells is yet to be examined. A reason for this is that the study of cell mechanical response to cell shape requires one to use a cell patterning process. However, existing cell patterning methods are very complex and time-consuming. In this paper, we describe a practical and rapid technique that can easily pattern cells into desired shapes, which allows investigations of the effect of external environment on cell stiffness. In the new technique, Poly-(ethylene) glycol diacrylate (PEGDA) hydrogel film with thickness 70n100 nm is controllably patterned on a hydrogenated amorphous silicon (a-Si:H) substrate by polymerizing PEGDA molecules in-situ using programmable visual light patterns. The idea is to enable the confinement of cells cultured on the hydrogels into special areas. The elastic modulus of the patterned cells is measured using an atomic force microscope. Experimental results have demonstrated the versatility of the technique as a tool for cell pattering and exploration of cell mechanics under external mechanical stimuli.

Regulating the mechanical properties of cells using a non-UV light-addressable hydrogel patterning process

Mono-disperse emulsion is of great significance for both chemical and industrial applications. The current study reports a new microfluidic system capable of formation of micro-droplets in liquids for emulsification applications. The new emulsion chip can precisely generate uniform droplets using a novel combination of hydrodynamic-focusing and liquid-chopping techniques. Experimental data show that micro-droplets with a diameter ranging from several to tens of micrometers could be precisely generated. The emulsification behavior at different ratios of sample flow rate (v 1 ) and sheath flow rate (v 2 ) and chopping frequency is systematically investigated. The micro-droplets have a uniform size while compared to previous studies. This novel device can be promising for emulsification and other related applications.

Gwo-Bin Lee

Papers

Platform technology for manipulation of cells, proteins and DNA

Dual-aptamer assay for C-reactive protein detection by using field-effect transistors on an integrated microfluidic system

Regulating the mechanical properties of cells using a non-UV light-addressable hydrogel patterning process

A New Microfluidic Chip for Formation of Micro-Droplets in Liquids Utilizing Active Pneumatic Choppers

Partial Nephrectomy Without Renal Ischemia Using an Electromagnetic Thermal Surgery System in a Porcine Model