13 research outputs found
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Method for the detection and quantification of analytes using three-dimensional paper-based devices
Described herein are three-dimensional (3-D) paper fluidic devices. The entire 3-D device is fabricated on a support layer formed from a single sheet of material and assembled by folding the support layer. The folded structure may be enclosed in an impermeable cover or package. Chemically sensitive particles may be disposed in the support layer for use in detecting analytes.Board of Regents, University of Texas Syste
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Microfluidics for bioanalytical research : transitioning into point-of-care diagnostics
textIn this dissertation, three different microfluidic devices with bioanalytical applications are presented. From chapter to chapter, the bioanalytical focus will gradually become the development of a point-of-care sensor platform able to yield a reliable and quantitative response in the presence of the desired target. The first device consists of photolithographically-patterned gold on glass bipolar electrodes and PDMS Y-shaped microchannels for the controlled enrichment, separation from a mixture, and delivery of two charged dyes into separate receiving microchannels. The principle for the permanent separation of these dyes is based on the concept of bipolar electrochemistry and depended on the balancing/unbalancing of convective and electromigrating forces caused by the application of a potential bias, as well as the activation/deactivation of the bipolar electrodes. Two different bipolar electrode configurations are described and fluorescence is used to optimize their efficiency, speed, and cleanliness of delivery. The second device is a DNA sensor fabricated on paper by wax printing and folding to form 3D channels. DNA is detected by strand-displacement induced fluorescence of a single-stranded DNA. A multiplexed version of this sensor is also shown where the experiment results in âORâ and âANDâ Boolean logic gate operations. In addition, the nonspecific adsorption of the reagents to cellulose is studied, demonstrating that significant reduction of nonspecific adsorption and increased sensitivity can be achieved by pre-treating the substrate with bovine serum albumin and by preparing all analyte solutions with spectator DNA. The third device, also made of paper, has a novel design and uses a versatile electrochemical detection method for the indirect detection of analytes via the direct detection of AgNP labels. A proof-of-concept experiment is shown where streptavidin-coated magnetic microbeads and biotin-coated AgNPs are used to form a composite model analyte. The paper device, called oSlip, and electrochemical method used are easily coupled so the resulting sensor has a simple user-device interface. LODs of 767 fM are achieved while retaining high reproducibility and efficiency. The fourth device is the updated version of the oSlip. In this case, the objective is to show the current progress and limitations in the detection of real analytes using the oSlip device. A sandwich-type immunoassay approach is used to detect human chorionic gonadotrophin (pregnancy hormone) present in human urine. Various optimization steps are performed to obtain the ideal reagent concentrations and incubation time necessary to form the immunocomposite in one step, that is, by mixing all reagents at the same time in the oSlip. Additionally, improvements to the electrochemical detection step are demonstrated.Chemistr
Electrochemically-gated delivery of analyte bands in microfluidic devices using bipolar electrodes
A method for controlling enrichment, separation, and delivery of analytes into different secondary microchannels using simple microfluidic architecture is described. The approach, which is based on bipolar electrochemistry, requires only easily fabricated electrodes and a low-voltage DC power supply: no pumps or valves are necessary. Upon application of a voltage between two driving electrodes, passive bipolar electrodes (BPEs) are activated that result in formation of a local electric field gradient. This gradient leads to separation and enrichment of a pair of fluorescent analytes within a primary microfluidic channel. Subsequently, other passive BPEs can be activated to deliver the enriched tracers to separate secondary microchannels. The principles and performance underpinning the method are described
Recent applications of carbon-based nanomaterials in analytical chemistry: Critical review
The objective of this review is to provide a broad overview of the advantages and limitations of carbon-based nanomaterials with respect to analytical chemistry. Aiming to illustrate the impact of nanomaterials on the development of novel analytical applications, developments reported in the 2005-2010 period have been included and divided into sample preparation, separation, and detection. Within each section, fullerenes, carbon nanotubes, graphene, and composite materials will be addressed specifically. Although only briefly discussed, included is a section highlighting nanomaterials with interesting catalytic properties that can be used in the design of future devices for analytical chemistry.Fil: Scida, Karen. University of Texas; Estados UnidosFil: Stege, Patricia Wanda. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Luis. Instituto de QuĂmica de San Luis. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia. Instituto de QuĂmica de San Luis; ArgentinaFil: Haby, Gabrielle. University of Texas; Estados UnidosFil: Messina, GermĂĄn Alejandro. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Luis. Instituto de QuĂmica de San Luis. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia. Instituto de QuĂmica de San Luis; ArgentinaFil: GarcĂa, Carlos D.. University of Texas; Estados Unido
DNA Detection Using Origami Paper Analytical Devices
We
demonstrate the hybridization-induced fluorescence detection
of DNA on an origami-based paper analytical device (<i>o</i>PAD). The paper substrate was patterned by wax printing and controlled
heating to construct hydrophilic channels and hydrophobic barriers
in a three-dimensional fashion. A competitive assay was developed
where the analyte, a single-stranded DNA (ssDNA), and a quencher-labeled
ssDNA competed for hybridization with a fluorophore-labeled ssDNA
probe. Upon hybridization of the analyte with the fluorophore-labeled
ssDNA, a linear response of fluorescence vs analyte concentration
was observed with an extrapolated limit of detection <5 nM and
a sensitivity relative standard deviation as low as 3%. The <i>o</i>PAD setup was also tested against OR/AND logic gates, proving
to be successful in both detection systems
Fluorescence-Based Observation of Transient Electrochemical and Electrokinetic Effects at Nanoconfined Bipolar Electrodes
Bipolar electrodes (BPEs) are conductors that, when exposed to an electric field, polarize and promote the accumulation of counterionic charge near their poles. The rich physics of electrokinetic behavior near BPEs has not yet been rigorously studied, with our current understanding of such bipolar effects being restricted to steady-state conditions (under constant applied fields). Here, we reveal the dynamic electrokinetic and electrochemical phenomena that occur near nanoconfined BPEs throughout all stages of a reaction. Specifically, we demonstrate, both experimentally and through numerical modeling, that the removal of an electric field produces solution-phase charge imbalances in the vicinity of the BPE poles. These imbalances induce intense and short-lived nonequilibrium electric fields that drive the rapid transport of ions toward specific BPE locations. To determine the origin of these electrokinetic effects, we monitored the movement and fluorescent behavior (enhancement or quenching) of charged fluorophores within well-defined nanofluidic architectures via real-time optical detection. By systematically varying the nature of the fluorophore, the concentration of the electrolyte, the strength of the applied field, and oxide growth on the BPE surface, we dissect the ion transport events that occur in the aftermath of field-induced polarization. The results contained in this work provide new insights into transient bipolar electrokinetics that improve our understanding of current analytical platforms and can drive the development of new micro- and nanoelectrochemical systems
Simple, Sensitive, and Quantitative Electrochemical Detection Method for Paper Analytical Devices
We
report a new type of paper analytical device that provides quantitative
electrochemical output and detects concentrations as low as 767 fM.
The model analyte is labeled with silver nanoparticles (AgNPs), which
provide 250â000-fold amplification. AgNPs eliminate the need
for enzymatic amplification, thereby improving device stability and
response time. The use of magnetic beads to preconcentrate the AgNPs
at the detection electrode further improves sensitivity. Response
time is improved by incorporation of a hollow channel, which increases
the flow rate in the device by a factor of 7 and facilitates the use
of magnetic beads. A key reaction necessary for label detection is
made possible by the presence of a slip layer, a fluidic switch that
can be actuated by manually slipping a piece of paper. The design
of the device is versatile and should be useful for detection of proteins,
nucleic acids, and microbes
High Surface Area Electrodes Generated via Electrochemical Roughening Improve the Signaling of Electrochemical Aptamer-Based Biosensors
The
electrochemical, aptamer-based (E-AB) sensor platform provides
a modular approach to the continuous, real-time measurement of specific
molecular targets (irrespective of their chemical reactivity) in situ
in the living body. To achieve this, however, requires the fabrication
of sensors small enough to insert into a vein, which, for the rat
animal model we employ, entails devices less than 200 ÎŒm in
diameter. The limited surface area of these small devices leads, in
turn, to low faradaic currents and poor signal-to-noise ratios when
deployed in the complex, fluctuating environments found in vivo. In
response we have developed an electrochemical roughening approach
that enhances the signaling of small electrochemical sensors by increasing
the microscopic surface area of gold electrodes, allowing in this
case more redox-reporter-modified aptamers to be packed onto the surface,
thus producing significantly improved signal-to-noise ratios. Unlike
previous approaches to achieving microscopically rough gold surfaces,
our method employs chronoamperometric pulsing in a 5 min etching process
easily compatible with batch manufacturing. Using these high surface
area electrodes, we demonstrate the ability of E-AB sensors to measure
complete drug pharmacokinetic profiles in live rats with precision
of better than 10% in the determination of drug disposition parameters