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.

Micro capillary electrophoresis chips integrated with buried SU-8/SOG optical waveguides for bio-analytical applications (vol 107, pg 125, 2003)

Periprosthetic joint infection (PJI) is difficult to treat and the incidence is between 1% and 2% in primary arthroplasties. Implant-associated infections usually arise via either primary infections from bacterial invasion at the time of implant surgery or secondary infections from hematogenous sources. The two-stage re-implantation protocol that consists of extensive debridement at the first stage followed by delayed re-implantation is currently the standard process for chronic PJI with a success rate between 82% to 95%. Furthermore, re-implantation arthroplasty should be only performed after ensuring the complete eradication of bacterial infection to avoid devastating complications. However, it is still a challenge in clinical practice to accurately determine the eradication of infections before or during implantation. Conventional diagnostic methods such as measurements of serum C-reactive protein or interleukin-6 levels, culture of joint aspirates, and microscopic examination of tissue biopsy are either non-specific or relatively time-consuming. For critical decision-making before or during the re-implantation surgery, a quick method with high sensitivity and specificity is therefore of great need. Previous studies reported bacterial ribosomal ribonucleic acids (rRNAs) as a target for the diagnosis of infections since rRNAs are highly conserved among bacterial species and abundant in amount. By using universal primers, the presence of bacterial rRNA could be amplified by using reverse-transcription polymerase chain reaction (RT-PCR). Currently the RT-PCR method for detection of bacterial rRNA is highly sensitive with a limit of detection (LOD) as low as a pictogram level. However, RT-PCR signals could only indirectly distinguish live from dead bacteria based on the degradation of rRNA in the tissue. Furthermore, the whole detection procedure of 16s rRNA RT-PCR is labor-intensive. Therefore, an integrated microfluidic system was presented in this work, which could distinguish the existence of live bacteria within 1 hour with a LOD of 104 colony formation unit (CFU). In this study, the fabrication of the microfluidic chip was improved so that the consistency of the transported liquid volume was increased. Moreover, by using an ethidium monoazide (EMA) assay, the cumbersome pre-treatment process of rRNA in live bacteria can be alleviated. This is the first time that a microfluidic platform was reported to detect live bacteria successfully in PJI samples.

An integrated microfluidic system for rapid isolation and detection of live bacteria in periprosthetic joint infections

Integrated Microfluidic System for DNA Amplification

A new method which allows assembly of carbon nanoparticles (CNPs) into predesigned patterns by using optically induced dielectrophoretic (ODEP) force is presented in this study. Theoretical analysis of ODEP working principle and operational regimes are investigated. Moreover, experimental parameters including AC frequency and solution conductivity are optimized for manipulating micro/nano particles. Finally, experimental results clearly demonstrate that CNP patterns and arrays with arbitrary geometry (including a 16×16 array covering an area of 0.4×0.4 mm2) can be successfully realized. Our results proved that ODEP is a highly-effective, low-cost, reconfigurable, and parallel manipulating approach for potential applications in fabricating CNPs sensors and micro-printing.

Deposition of carbon nanoparticles using optically induced dielectrophoretic force

This current study presents a new miniature, integrated system capable of rapid extraction of genomic DNA (gDNA) from saliva samples. Three major components of the DNA extraction chip, including six symmetrical, normally-closed microvalves, a sample transport/mixing unit and a waste unit are integrated in this device. The microfluidic DNA extraction chip was made of CNC machining and PDMS casting processes to integrate a liquid channel layer, an air chamber layer and a glass layer on a single chip. Liquid samples can be transported and mixed by the suction-type sample transport/mixing unit by using micropumps, micromixers and normally-closed microvalves. Experimental results showed the pumping rate can be as high as 400 µL/min at an applied pressure of −70 KPa for an air chamber with a depth of 1.5 mm. A mixing efficiency as high as 96.5% can be achieved within 3 sec. Experimental data also showed that gDNA with an average concentration of 45 ± 3 ng/µL and an optical intensity (OD) value (260/280) of 1.5 ± 0.2 from ten measurements can be successfully achieved within 25 minutes. Consequently, the proposed miniature system can provide a powerful platform for automatic, rapid DNA extraction.

Gwo-Bin Lee

Papers

Micro capillary electrophoresis chips integrated with buried SU-8/SOG optical waveguides for bio-analytical applications (vol 107, pg 125, 2003)

An integrated microfluidic system for rapid isolation and detection of live bacteria in periprosthetic joint infections

Integrated Microfluidic System for DNA Amplification

Deposition of carbon nanoparticles using optically induced dielectrophoretic force

A suction-type, pneumatic microfluidic device for rapid DNA extraction