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

Nanoparticles containing magnetic materials, such as magnetite (Fe3O4), are particularly useful for imaging and separation techniques. As these nanoparticles are generally considered to be biologically and chemically inert, they are typically coated with metal catalysts, antibodies or enzymes to increase their functionality as separation agents. Here, we report that magnetite nanoparticles in fact possess an intrinsic enzyme mimetic activity similar to that found in natural peroxidases, which are widely used to oxidize organic substrates in the treatment of wastewater or as detection tools. Based on this finding, we have developed a novel immunoassay in which antibody-modified magnetite nanoparticles provide three functions: capture, separation and detection. The stability, ease of production and versatility of these nanoparticles makes them a powerful tool for a wide range of potential applications in medicine, biotechnology and environmental chemistry.

Intrinsic peroxidase-like activity of ferromagnetic nanoparticles

http://lovely-physics.persiangig.com/document/DLLME.pdf

Determination of organic compounds in water using dispersive liquid-liquid microextraction

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of “the dose makes the poison,” because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from...

/pdf/hormones-and-endocrine-disrupting-chemicals-low-dose-effects-2vn32zoqc8.pdf

Hormones and endocrine-disrupting chemicals: Low-dose effects and nonmonotonic dose responses

Background: Thyroid disease in pregnancy is a common clinical problem. Since the guidelines for the management of these disorders by the American Thyroid Association (ATA) were first published in 2...

https://www.thyca.org/download/document/486/PregnancyandPostpartum.pdf

2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum

Solubility of ammonia in liquid water and generation of trace levels of standard gaseous ammonia

Hydrogen sulfide evolved from an acidified sample is pre-concentrated by permeation in a stationary alkaline acceptor solution enclosed in a silicone rubber sample loop. Depending on the sample volume pre-concentrated, the applicable analytical range spans low micrograms/L to tens of mg/L for both methods. The methylene blue method is more sensitive by a factor of approximately 30 and actually permits practical determinations in the sub-micrograms/L levels. The limit of detection (LOD) for the nitroprusside method ranges from 20 micrograms/L for a 20 microL sample by conventional flow-injection determination (no membrane, throughput 30 samples/h) to less than 2 micrograms/L for 12 mL sample pre-concentrated in the membrane system (throughput 5 samples/h). The membrane is highly resistant to fouling and permits analysis of untreated wastewater samples bearing suspended solids, oil, grease, etc. without any pretreatment. No significant interference is observed with either chemistry. Although the nitroprusside chemistry is less sensitive, it does not involve the use of concentrated aggressive reagents and is recommended unless ultratrace determinations are essential. Viable reaction mechanisms are proposed for both of these chemistries.

Nitroprusside and methylene blue methods for silicone membrane differentiated flow injection determination of sulfide in water and wastewater.

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

A new approach is introduced for the quantitative collection of aerosol particles to submicrometer size. The design and construction of a continuously operating system is described. Particles are continuously transferred to a liquid stream utilizing condensation of supersaturated vapor to promote particle growth followed by collection that relies on impaction and the thermophoretic effect. The automated system is simple to construct and operate and provides quantitative collection of aerosol particulate matter even at a flow rate of 10 L/min. Individual measurements of aerosol particles and soluble gases are achieved by combining the system with a wetted wall parallel plate diffusion denuder

Continuous Automated Measurement of the Soluble Fraction of Atmospheric Particulate Matter

A luminescence detector with a liquid-core waveguide. For detecting photoluminescence, the exciting radiation is provided transversely instead of axially, thus eliminating the need for monochromators and focusing optics. For detecting chemiluminescence, the chemiluminescent reagents are mixed in situ in the detector, thus eliminating time loss which results in loss of chemiluminescence. A further aspect of the invention is the electrogeneration of an unstable reagent for the production of chemiluminescence. The unstable reagent is generated in such a way that there is complete separation of anodic and cathodic products without the use of a physical barrier.

Purnendu K. Dasgupta

Papers

Solubility of ammonia in liquid water and generation of trace levels of standard gaseous ammonia

Nitroprusside and methylene blue methods for silicone membrane differentiated flow injection determination of sulfide in water and wastewater.

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

Continuous Automated Measurement of the Soluble Fraction of Atmospheric Particulate Matter

Luminescence detector with liquid-core waveguide