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 - A technology for advancements in aerospace engineering

The evolution of real-time PCR machines to real-time PCR chips.

Thermal uniformity within a specific area is a key point for precise thermal control, especially crucial for micro biomedical applications. In this study, a new approach to improve the thermal uniformity inside a specific area was reported and used for reverse transcription polymerase chain reaction (PCR) applications. The temperature uniformity inside the reaction region of a microthermal cycler was significantly enhanced by using array-type microheaters with a two-dimensional, symmetrical, self-compensation (SC) design. With this approach, the edges of thermal profile in the heating area which commonly had significant temperature gradients can be self-compensated with an automatic function. Experimental results from infrared images showed that the percentages of the uniformity area with a thermal variation <1°C were 90.3, 99.9, and 96.8% at three PCR thermocycling temperatures (94, 55, and 72°C, respectively). It was a significant improvement over conventional block-type or serpentine-type microheaters. The performance of this proposed microthermal cycler was successfully verified by amplifying a detection gene associated with the dengue virus serotype 2. The amplification efficiency of the new microthermal cycler was statistically higher than the microheaters without SC function.

A two-dimensional, self-compensated, microthermal cycler for one-step reverse transcription polymerase chain reaction applications

The formation of emulsification droplets is crucial for many industrial applications. This paper reports a new microfluidic chip capable of formation and collection of micro-droplets in liquids for emulsion applications. This microfluidic chip comprising microchannels, a micro-chopper and a micro-switch was fabricated by using micro-electro-mechanical-systems (MEMS) technology. The microfluidic chip can generate uniform droplets with tunable sizes by using combination of flow-focusing and liquid-chopping techniques. The droplet size can be actively fine-tuned by controlling either the relative sheath/sample flow velocity ratios or the chopping frequency. The generated droplets can be then sorted to a specific collection area utilizing an active pneumatic micro-switch formed with three micro-valves. Experimental data showed that the olive oil and sodium-alginate (Na-alginate) droplets with diameters ranging from 3 μm to 70 μm with a variation less than 14% is successfully generated and collected. The development of this microfluidic system can be promising for emulsion, drug delivery and nano-medicine applications.

A microfluidic chip for formation and collection of emulsion droplets utilizing active pneumatic micro-choppers and micro-switches

This paper reports at innovative microfluidic chip capable of performing DNA amplification (polymerase chain reaction, PCR), electrokinetic sample injection and separation, and on-line optical detection of DNA. All microfluidic modules are integrated on cheap and biocompatible soda-lime glass substrates using a simple and reliable fabrication process. With this approach, DNA samples could be first duplicated using the micro PCR module, then injected and separated in the micro electrophoretic channels driven by electrokinetic forces, and finally detected optically by buried optical waveguides downstream the separation channel. In order to have a better separation efficiency for DNA samples, a novel surface treatment method by coating a thin layer of spin-on-glass (SOG) is developed. Experimental data show that DNA samples can be successfully duplicated using the micro PCR device with less sample and reagent volumes in a shorter period thanks to lower thermal inertia of the micro devices. DNA samples can be injected, separated and detected successfully in the subsequent microfluidic channels. The integrated microfluidic device could be crucial for genetic analysis.

Gwo-Bin Lee

Papers

MEMS - A technology for advancements in aerospace engineering

The evolution of real-time PCR machines to real-time PCR chips.

A two-dimensional, self-compensated, microthermal cycler for one-step reverse transcription polymerase chain reaction applications

A microfluidic chip for formation and collection of emulsion droplets utilizing active pneumatic micro-choppers and micro-switches

Microfluidic chips for DNA amplification, electrophoresis separation and on-line optical detection