21 research outputs found
Wax-Printed Fluidic Controls for Delaying and Accelerating Fluid Transport on Paper-Based Analytical Devices
In this work, we explore a new method for controlling fluid transport rate on paper-based analytical devices that enables both the delay and the acceleration of fluid flow. The delays were incorporated by wax printing linear patterns of variable width within the flow channel and melted to penetrate the paper. In this manner, the surface tension of the fluid decreases while its contact angle increases, causing a pressure drop along the fluid path that reduces capillary flow. The acceleration of flow was accomplished by overlaying hydrophobic stripes (prepared by wax printing and melting the wax) on the hydrophilic path (top or top–bottom). In this manner, the fluid was repelled from two dimensions (vertical and applicate), increasing the flow rate. The combination of these methods on the same devices could adjust wicking time in intermediate time internals. The method enabled a wide timing of fluid transport, accomplishing a change in wicking times that extended from −41% to +259% compared to open paper channels. As a proof of concept, an enzymatic assay of glucose was used to demonstrate the utility of these fluid control methods in kinetic methods of analysis
Generic Assay of Sulfur-Containing Compounds Based on Kinetics Inhibition of Gold Nanoparticle Photochemical Growth
This
work describes a new, equipment-free, generic method for the
determination of sulfur-containing compounds that is based on their
ability to slow down the photoreduction kinetics of gold ions to gold
nanoparticles. The method involves tracking the time required for
a red coloration to appear in the tested sample, indicative of the
formation of gold nanoparticles, and compare the measured time relative
to a control sample in the absence of the target analyte. The method
is applicable with minimal and simple steps requiring only two solutions
(i.e., a buffer and a gold solution), a source of light (UV or visible),
and a timer. The method responds to a large variety of sulfur-containing
compounds including thiols, thioesters, disulfides, thiophosphates,
metal–sulfur bonds, and inorganic sulfur and was therefore
applied to the determination of a variety of compounds such as dithiocarbamate
and organophosphorous pesticides, biothiols, pharmaceutically active
compounds, and sulfides in different samples such as natural waters
and wastewater, biological fluids, and prescription drugs. The analytical
figures of merit of the method include satisfactory sensitivity (quantitation
limits at the low μM levels), good recoveries (from 93 to 109%),
and satisfactory reproducibility (from 4.8 to 9.8%). The method is
easily adoptable to both laboratory settings and nonlaboratory conditions
for quantitative and semiquantitative analysis, respectively, is user-friendly
even for the minimally trained user, and can be performed with limited
resources at low cost
Gold-Modified Micellar Composites as Colorimetric Probes for the Determination of Low Molecular Weight Thiols in Biological Fluids Using Consumer Electronic Devices
This work describes a new, low-cost and simple-to-use method for the determination of free biothiols in biological fluids. The developed method utilizes the interaction of biothiols with gold ions, previously anchored on micellar assemblies through electrostatic interactions with the hydrophilic headgroup of cationic surfactant micelles. Specifically, the reaction of AuCl4− with the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) produces an intense orange coloration, due to the ligand substitution reaction of the Br− for Cl− anions, followed by the coordination of the AuBr4− anions on the micelle surface through electrostatic interactions. When biothiols are added to the solution, they complex with the gold ions and disrupt the AuBr4−–CTAB complex, quenching the initial coloration and inducing a decrease in the light absorbance of the solution. Biothiols are assessed by monitoring their color quenching in an RGB color model, using a flatbed scanner operating in transmittance mode as an inexpensive microtiter plate photometer. The method was applied to determine the biothiol content in urine and blood plasma samples, with satisfactory recoveries (i.e., >67.3–123% using external calibration and 103.8–115% using standard addition calibration) and good reproducibility (RSD < 8.4%, n = 3)
Concentration of organic compounds in natural waters with solid-phase dispersion based on advesicle modified silica prior to liquid chromatography
Abstract The ability of vesicle-coated silica to aid the extraction of organic compounds from water prior to liquid chromatographic analysis is presented for the first time. The method is based on the formation of silica supported cationic multi-lamellar vesicles of gemini surfactants inherently ensuring the presence of hydrophilic and hydrophobic sites for the partitioning of analytes bearing different properties. Method development is illustrated by studying the adsolubilization of UV absorbing chemicals from swimming pool water. Due to the requirement for external energy input (intense shearing) a method based on solid-phase dispersion (SPD) was applied producing better results than off-line solid-phase extraction (SPE). Meticulous investigation of the experimental parameters was conducted in order to elucidate the mechanisms behind the proposed extraction pattern. Analyte recoveries were quantitative under the optimum experimental conditions offering recoveries higher than 96% with RSD values below 5%
Metal ion determination by flame atomic absorption spectrometry through reagentless coacervate phase separation-extraction into lamellar vesicles
Paper-Based Device for Sweat Chloride Testing Based on the Photochemical Response of Silver Halide Nanocrystals
A new method for the determination of chloride anions in sweat is described. The novelty of the method relies on the different photochemical response of silver ions and silver chloride crystals when exposed to UV light. Silver ions undergo an intense colorimetric transition from colorless to dark grey-brown due to the formation of nanosized Ag while AgCl exhibits a less intense color change from white to slightly grey. The analytical signal is obtained as mean grey value of color intensity on the paper surface and is expressed as the absolute difference between the signal of the blank (i.e., in absence of chloride) and the sample (i.e., in the presence of chloride). The method is simple to perform (addition of sample, incubation in the absence of light, irradiation, and offline measurement in a flatbed scanner), does not require any special signal processing steps (the color intensity is directly measured from a constant window on the paper surface without any imager processing) and is performed with minimum sample volume (2 μL). The method operates within a large chloride concentration range (10–140 mM) with good detection limits (2.7 mM chloride), satisfactory recoveries (95.2–108.7%), and reproducibility (<9%). Based on these data the method could serve as a potential tool for the diagnosis of cystic fibrosis through the determination of chloride in human sweat
A Family of RuIIPhotosensitizers with High Singlet Oxygen Quantum Yield: Synthesis, Characterization, and Evaluation
A series of RuII-based photosensitizers were synthesized and extensively characterized. The ligand utilized to coordinate ruthenium was a pyridine-quinoline hybrid bearing an anthracene moiety, and it was combined with commercially available 2,2'-bipyridine (bpy) for the heteroleptic complexes. The produced bichromophoric complexes show very strong and wide UV/Vis absorption bands. The ability of these complexes to act as triplet photosensitizers in the production of singlet oxygen was thoroughly studied by utilizing the photooxidation of 1,3-diphenylisobenzofuran as the test reaction. The most efficient photosensitizer in this new family of RuII complexes affords singlet oxygen quantum yields and production-rate efficiencies up to two times higher than those of the benchmark [Ru(bpy)3] 2+ parent complex. A series of ruthenium complexes bearing a pyridine-quinoline hybrid ligand were synthesized and extensively characterized. The 1O2 generation quantum yield of these complexes is enhanced in comparison with that of the benchmark parent complex [Ru(bpy) 3]Cl2 (bpy = 2,2'-bipyridine), and the most efficient complex outperforms the parent complex by up to two times. Copyright © 2013 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim
Ultratrace Determination of Silver, Gold, and Iron Oxide Nanoparticles by Micelle Mediated Preconcentration/Selective Back-Extraction Coupled with Flow Injection Chemiluminescence Detection
A new method has been developed for
the ultrasensitive determination
of silver, gold, and iron oxide nanoparticles in environmental samples.
Cloud point extraction was optimized and used as a means to extract
and preconcentrate all nanoparticle species simultaneously from the
same sample. The extracted nanoparticles were sequentially isolated
from the surfactant-rich phase by a new selective back-extraction
procedure and dissociated into their precursor metal ions. Each ion
solution was injected in a flow injection analysis (FIA) manifold,
accommodating the chemiluminogenic oxidation of luminol, in order
to amplify chemiluminescence (CL) emission in a manner proportional
to its concentration. Under the optimum experimental conditions, the
detection limits were brought down to the picomolar and femtomolar
concentration levels with satisfactory analytical features in terms
of precision (2.0–13.0%), selectivity against dissolved ions,
and recoveries (74–114%). The method was successfully applied
to the determination of iron oxide, silver, and gold nanoparticles
in environmental samples of different complexity, ranging from unpolluted
river water to raw sewage. The developed method could also serve as
a basis for future deployment of molecular spectrometry detectors
for the selective determination and speciation analysis of nanoparticles
in environmental applications
Programming Fluid Transport in Paper-Based Microfluidic Devices Using Razor-Crafted Open Channels
Manipulating
fluid transport in microfluidic, paper-based analytical
devices (μPADs) is an essential prerequisite to enable multiple
timed analytical steps on the same device. Current methods to control
fluid distribution mainly rely on controlling how slowly the fluid
moves within a device or by activating an on/off switch to flow. In
this Article, we present an easy approach for programming fluid transport
within paper-based devices that enables both acceleration as well
as delay of fluid transport without active pumping. Both operations
are programmed by carving open channels either longitudinally or perpendicularly
to the flow path using a craft-cutting tool equipped with a knife
blade. Channels are crafted after μPADs fabrication enabling
the end user to generate patterns of open-channels on demand by carving
the porous material of the paper without cutting or removing the paper
substrate altogether. Parameters to control the acceleration or delay
of flow include the orientation, length, and number of open channels.
Using this method, accelerated as well as reduced fluid transport
rates were achieved on the same device. This methodology was applied
to μPADs for multiple and time-programmable assays for metal
ion determination