The manipulation of fluids in channels with dimensions of tens of micrometres--microfluidics--has emerged as a distinct new field. Microfluidics has the potential to influence subject areas from chemical synthesis and biological analysis to optics and information technology. But the field is still at an early stage of development. Even as the basic science and technological demonstrations develop, other problems must be addressed: choosing and focusing on initial applications, and developing strategies to complete the cycle of development, including commercialization. The solutions to these problems will require imagination and ingenuity.

The origins and the future of microfluidics

This Minireview systematically examines optical properties of silver nanoparticles as a function of size. Extinction, scattering, and absorption cross-sections and distance dependence of the local electromagnetic field, as well as the quadrupolar coupling of 2D assemblies of such particles are experimentally measured for a wide range of particle sizes. Such measurements were possible because of the development of a novel synthetic method for the size-controlled synthesis of chemically clean, highly crystalline silver nanoparticles of narrow size distribution. The method and its unique advantages are compared to other methods for synthesis of metal nanoparticles. Synthesis and properties of nanocomposite materials using these and other nanoparticles are also described. Important highlights in the history of the field of metal nanoparticles as well as an examination of the basic principles of plasmon resonances are included.

https://nathan.instras.com/ResearchProposalDB/doc-220.pdf

Synthesis and Optical Properties of Silver Nanoparticles and Arrays

Micro total analysis systems. Latest advancements and trends.

Optofluidics - the synergistic integration of photonics and microfluidics - has recently emerged as a new analytical field that provides a number of unique characteristics for enhanced sensing performance and simplification of microsystems. In this review, we describe various optofluidic architectures developed in the past five years, emphasize the mechanisms by which optofluidics enhances bio/chemical analysis capabilities, including sensing and the precise control of biological micro/nanoparticles, and envision new research directions to which optofluidics leads.

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Optofluidic microsystems for chemical and biological analysis

A number of polydimethysiloxane (PDMS) bonding techniques have been reported in the literature over the last several years as the focus on multilayer PDMS microfluidic devices has increased Oxygen plasma bonding, despite cost, additional fabrication time and inconsistent bonding results, has remained a widely used method for bonding PDMS layers A comparative study of four rapid, inexpensive alternative PDMS?PDMS bonding approaches was undertaken to determine relative bond strength These include corona discharge, partial curing, cross-linker variation and uncured PDMS adhesive Partial curing and uncured PDMS adhesive demonstrated a considerable improvement in bond strength and consistency by retaining average bond strengths of over 600 kPa, which was more than double the average bond strength of oxygen plasma A description of each technique and their performance relative to oxygen plasma bonding is included

https://iopscience.iop.org/article/10.1088/0960-1317/18/6/067001/pdf

Determining the optimal PDMS–PDMS bonding technique for microfluidic devices

An issue in microfabrication of the fluidic channels in glass/poly (dimethyl siloxane) (PDMS) is the absence of a well-defined study of the bonding strength between the surfaces making up these channels. Although most of the research papers mention the use of oxygen plasma for developing chemical (siloxane) bonds between the participating surfaces, yet they only define a certain set of parameters, tailored to a specific setup. An important requirement of all the microfluidics/biosensors industry is the development of a general regime, which defines a systematic method of gauging the bond strength between the participating surfaces in advance by correlation to a common parameter. This enhances the reliability of the devices and also gives a structured approach to its future large-scale manufacturing. In this paper, we explore the possibility of the existence of a common scale, which can be used to gauge bond strength between various surfaces. We find that the changes in wettability of surfaces owing to various levels of plasma exposure can be a useful parameter to gauge the bond strength. We obtained a good correlation between contact angle of deionized water (a direct measure of wettability) on the PDMS and glass surfaces based on various dosages or oxygen plasma treatment. The exposure was done first in an inductively coupled high-density (ICP) plasma system and then in plasma enhanced chemical vapor deposition (PECVD) system. This was followed by the measurement of bond strength by use or the standardized blister test.

Studies on surface wettability of poly(dimethyl) siloxane (PDMS) and glass under oxygen-plasma treatment and correlation with bond strength

The fabrication and testing of Teflon AF-coated channels on silicon and bonding of the same to a similarly coated glass wafer are described. With water or aqueous solutions in such channels, the channels exhibit much better light conduction ability than similar uncoated channels. Although the loss is greater than extruded Teflon AF tubes, light throughput is far superior to channels described in the literature consisting of [110] planes in silicon with 45/spl deg/ sidewalls. Absorbance noise levels under actual flow conditions using an LED source, an inexpensive photodiode and a simple operational amplifier circuitry was 1/spl times/ 10/sup -4/ absorbance units over a 10-mm path length (channel 0.17-mm deep /spl times/0.49-mm wide), comparable to many commercially available macroscale flow-through absorbance detectors. Adherence to Beer's law was tested over a 50-fold concentration range of an injected dye, with the linear r/sup 2/ relating the concentration to the observed absorbance being 0.9993. Fluorescence detection was tested with fluorescein as the test solute, a high brightness blue LED as the excitation source and an inexpensive miniature PMT. The concentration detection limit was 3 /spl times/ 10/sup -9/ M and the corresponding mass detection limit was estimated to be 5 /spl times/ 10 /sup -16/ mol.

/pdf/microfabrication-and-characterization-of-teflon-af-coated-1uonzygjfp.pdf

Microfabrication and characterization of teflon AF-coated liquid core waveguide channels in silicon

We report on the microfabrication and testing of liquid core waveguides (LCW) using Teflon AF for integration in microfabricated microanalysis systems. Teflon AF has an index of refraction less than that of water allowing it to function as a waveguide when used as a cladding layer surrounding an aqueous core. Straight microchannels (400-/spl mu/m width, 60-/spl mu/m depth) etched into Pyrex and soda-lime glass wafers were coated with Teflon AF and sealed with a Teflon AF coated capping wafer. Aqueous fluorescein solutions with varying concentrations were injected into the channels and were illuminated transversely using an ultraviolet light emitting diode. For studying the waveguide attenuation performance, light was focused to a point on the channel. Fluorescence generated in the channel was used to quantify the light collection and waveguide characteristics. The Teflon coating produces a significant enhancement in the amount of light collected in the channel, allowing light to be collected from the 16-mm length tested. This is compared to a control microchannel in glass (no coating), for which the fluorescence drops to the background level in an illumination-detection separation of <4 mm. For sensitivity performance, the entire channel was illuminated. The lower detection limit for spectroscopically resolved fluorescence was /spl sim/10 nMolar.

Microfabrication and characterization of liquid core waveguide glass channels coated with Teflon AF

Nanofluidic channels by anodic bonding of amorphous silicon to glass to study ion-accumulation and ion-depletion effect.

Reports on the microfabrication of liquid core waveguides (LCW) using Teflon/sup /spl reg// AF for integration in microfabricated micro total analysis systems. Teflon/sup /spl reg// AF has an index of refraction less than that of water. Straight micro channels (/spl les/500 /spl mu/m width, /spl les/100 /spl mu/m depth) etched into a Pyrex wafer were coated with Teflon AF and sealed with a Teflon AF coated Pyrex capping wafer. This formed a low index of refraction channel in which a higher index, aqueous solution was flowed. Light generated in the lumen propagated by total internal reflection (TIR) to the end of the channel where the light was detected using either a photomultiplier or a miniature spectrometer. An optical microscope was used to transversely illuminate the channel at various distances from the end to measure the waveguide properties.

A. Datta

Papers

Studies on surface wettability of poly(dimethyl) siloxane (PDMS) and glass under oxygen-plasma treatment and correlation with bond strength

Microfabrication and characterization of teflon AF-coated liquid core waveguide channels in silicon

Microfabrication and characterization of liquid core waveguide glass channels coated with Teflon AF

Nanofluidic channels by anodic bonding of amorphous silicon to glass to study ion-accumulation and ion-depletion effect.

Microfabricated liquid core waveguides for microanalysis systems