Selective Xenon Recovery Using Aluminum-Based Metal-Organic Frameworks with Conserved Pore Topology.

Xenon (Xe) is a commercially valuable element found in trace amounts in the off-gas from used nuclear fuel. Recovering Xe from these streams provides a cost-effective means to increase its supply. However, achieving high-purity Xe recovery is challenging due to the need for separation from nearly identical krypton (Kr). Metal-organic frameworks (MOFs), a class of crystalline porous materials, show potential to separate Xe and Kr by utilizing differences in their kinetic diameters, allowing for selective separation. In this work, we study the impact of pore aperture and volume on selective Xe recovery using four robust aluminum MOFs: Al-PMOF, Al-PyrMOF, Al-BMOF and MIL-120, all with conserved structural topology. The pore topology in each MOF is dictated by the dimensions of the tetracarboxylate ligand employed, with larger ligands leading to MOFs with increased pore size and volume. Our experimental and computational investigations revealed that MIL-120 exhibits the highest affinity (21.94 kH(Xe) = 21.94 mmol g-1 bar-1) for Xe among all MOFs, while Al-BMOF demonstrates the highest Xe/Kr selectivity of 14.34. We evaluated the potential of both MIL-120 and Al-BMOF for Xe recovery through breakthrough analysis using a mixture of 400 ppm Xe:40 ppm Kr. Our results indicate that due to its larger pore volume, Al-BMOF captured more Xe than MIL-120, demonstrating superior Xe/Kr separation efficiency.

Selective laser ablation for in situ fabrication of enclosed channel porous-media microfluidic analytical devices.

This work describes a new method for fabrication of enclosed channel porous-media microfluidic analytical devices using selective laser ablation. Microfluidic structures can be readily produced inside the enclosed devices within two fabrication steps. A sheet of porous material was first sandwiched and bonded between two sheets of polymeric film. The porous substrate inside the film layers was then selectively ablated using a laser cutter to create hollow barriers for microfluidic channels. Selective ablation of only the porous layer was achieved because the porous substrate layer is susceptible to ablation by the laser beam, whereas the film layer is resistant to laser ablation due to its light transmission properties. This selective laser ablation processing is not limited by laser type. As a proof-of-concept, two different laser systems, a 10.6 µm CO2 laser and a 455 nm diode laser, were employed for this purpose. A variety of porous materials, including cellulose, nitrocellulose, and glass microfiber, were combined with a wide variety of polymeric films to fabricate enclosed microfluidic devices. The developed method is versatile; depending on material combination and number of layers of materials in the devices, enclosed microfluidic devices with 2D, passive 3D, or compression-activated 3D fluid flow can be created. Quantitative assays for albumin, glucose, and cholesterol in human serum performed using devices produced via this method demonstrated the utility of this fabrication approach. This unique, simple, and scalable method for fabrication of enclosed microfluidic devices not only ensures protection of devices from contamination and prevention of fluid evaporation, but also offers a method for commercial fabrication of porous-media analytical devices.

Wicking microfluidic approach to separate blood plasma from whole blood to facilitate downstream assays.

Separation of blood plasma or serum from blood is essential for accurate analysis. Conventional blood separation requires instrumentation, reagents, and large sample volumes, limiting this process to laboratory environments with trained personnel. Full implementation of effective blood separation and analysis on microliter sample volumes for point of care (POC) diagnostics has proven extremely challenging resulting in a growing market demand, with common challenges such as expensive device fabrication processes or devices being comprised of materials which are not easily disposable. We developed a membrane-based wicking microfluidic device which is made using a simple fabrication process. This device uses a unique 3D flow channel geometry, fabricated in a polycaprolactone-filled glass microfiber membrane, to efficiently separate microliter sample volumes of blood. Colorimetric assay chemistries were integrated to demonstrate utility of these devices in POC diagnostics. The devices are capable of separating both fresh and anticoagulant-treated blood at microscale sample volumes (<15.0 µL). Modifications to the base device are also reported herein which increased sample volume capacity and separation efficiency. Integrated colorimetric assay enabled semi-quantitative detection of conjugated bilirubin in real blood samples (1.0-1.5 mg/dL). These blood separation devices, fabricated on polycaprolactone-filled glass microfiber, enabled effective blood plasma (anticoagulant-treated blood) and serum (fresh blood) separation with microscale sample volumes. Sample volume capacity and separation efficiency are customizable for specific applications and devices can be integrated with downstream assay chemistries to develop complete POC devices that offer blood separation and diagnostics at the same time on a single membrane.

A Membrane-based Disposable Well-Plate for Cyanide Detection Incorporating a Fluorescent Chitosan-CdTe Quantum Dot.

A novel approach to building a membrane-based disposable well-plate, here applied to cyanide detection, is described. Chitosan encapsulated CdTe quantum dots with a maximum emission at 520 nm (CS-QD520) were used as fluorophores. The CS-QD520 nanoparticle was specifically quenched by copper(II), and the quenched CS-QD520 (Cu-CS-QD520) was deposited onto a glass microfiber filter (GF/B). Subsequent introduction of cyanide ion resulted in fluorescence recovery. The "signal-ON" fluorescence linearly correlated to cyanide concentrations in the range of 38.7 to 200 µM with a limit of detection of 11.6 µM. The assay was incorporated into a membrane-based well-plate format to enhance sample throughput. A three-layer paper/glass microfiber well plate design was cut using a laser cutter and assembled using a polycaprolactone (PCL) as a bonding agent in a low-cost laminator. The experimental conditions were optimized and applied to detect cyanide in drinking water with rapid, high-throughput, low-cost analysis.

A copper oxide-ionic liquid/reduced graphene oxide composite sensor enabled by digital dispensing: Non-enzymatic paper-based microfluidic determination of creatinine in human blood serum.

A paper-based analytical device (PAD) with an integrated composite electrode for non-enzymatic creatinine sensing was developed. The electrode was produced and optimization was efficiently accomplished using a rapid digital dispensing approach. The electrochemical sensor was fabricated using an HP D300 digital dispenser to deliver a copper oxide and ionic liquid composite onto an electrochemically reduced graphene modified screen-printed carbon electrode (CuO/IL/ERGO/SPCE) on a PAD. The modified electrode was characterized using electrochemical and microscopic techniques. Electrochemical detection of creatinine was performed on the SPCE using amperometry at a constant potential. Under optimized conditions, the paper-based sensor exhibited a linear range of 0.01-2.0 mM (R2 = 0.99) and the limit of detection was 0.22 µM (S/N = 3, IUPAC definition) for creatinine. The simple fabrication process, low cost, and clinically appropriate creatinine sensitivity make this device applicable for point-of-care use.

Chromatographic Separation and Visual Detection on Wicking Microfluidic Devices: Quantitation of Cu2+ in Surface, Ground, and Drinking Water.

Copper is widely applied in industrial and technological applications and is an essential micronutrient for humans and animals. However, exposure to high environmental levels of copper, especially through drinking water, can lead to copper toxicity, resulting in severe acute and chronic health effects. Therefore, regular monitoring of aqueous copper ions has become necessary as recent anthropogenic activities have led to elevated environmental concentrations of copper. On-site monitoring processes require an inexpensive, simple, and portable analytical approach capable of generating reliable qualitative and quantitative data efficiently. Membrane-based lateral flow microfluidic devices are ideal candidates as they facilitate rapid, inexpensive, and portable measurements. Here we present a simple, chromatographic separation approach in combination with a visual detection method for Cu2+ quantitation, performed in a lateral flow microfluidic channel. This method appreciably minimizes interferences by incorporating a nonspecific polymer inclusion membrane (PIM) based assay with a "dot-counting" approach to quantification. In this study, hydrophobic polycaprolactone (PCL)-filled glass microfiber (GMF) membranes were used as the base substrate onto which the PIM was evenly dispensed as an array of dots. The devices thus prepared were then selectively exposed to oxygen radicals through a mask to generate a hydrophilic surface path along which the sample was wicked. Using this approach, copper concentrations from 1 to 20 ppm were quantified from 5 µL samples using only visual observation of the assay device.

Patterned polycaprolactone-filled glass microfiber microfluidic devices for total protein content analysis.

Membrane based microfluidic devices have gained much popularity in recent years, as they make possible rapid, inexpensive analytical techniques that can be applied to a wide variety of areas. The ability to modify device hydrophilicity and hydrophobicity is critically important in fabricating membrane based microfluidic devices. Polar hydrophilic membranes, such as glass microfiber (GMF) membranes, hold great potential as they are inexpensive, chemically inert, and stable. Filling of these membranes with non-polar polymers such as polycaprolactone (PCL) converts the hydrophilic GMF into a hydrophobic medium. Controlled alteration of the surface chemistry of PCL/GMF substrates allows for the fabrication of microfluidic patterns on the surface. Using this approach, we have developed a simple and rapid technique for fabrication of highly adaptable complex multidimensional (2D and 3D) microfluidic pathways on a single membrane. PCL-filled GMF media were masked and selectively exposed to oxygen radicals so that the exposed surface became permanently superhydrophilic in its behavior. The desired microfluidic pattern was cut into the mask prior to assembly and exposure, and the mask was removed after exposure to reveal the ready-to-use microfluidic device. To verify and demonstrate the performance of this novel fabrication method, a colorimetric total protein assay was applied to the determination of protein concentrations in real samples.

Centrifugal partition chromatography: A preparative tool for isolation and purification of xylindein from Chlorociboria aeruginosa.

A centrifugal partition chromatography (CPC) method was developed for the preparative-scale isolation and purification of xylindein from the wood-staining fungi, Chlorociboria aeruginosa. Xylindein, a blue-green pigment naturally secreted from the hyphae and fruiting bodies of the fungus, has great value in the decorative wood industry and textile coloration. Xylindein has great potential for use as a fluorescent labeling agent as well as in organic semiconductor applications. However, a primary limitation of xylindein is its poor solubility in most common HPLC solvents. Consequently, it is arduous to purify using preparative liquid chromatography or solid-phase extraction (SPE). Support-free, liquid-liquid chromatographic methods, including CPC, where solutes are separated based on their different distribution coefficients (KD) between two immiscible solvent systems, are promising alternatives for the purification of the compound on a preparative scale. In this work, a new biphasic solvent system suitable for CPC separation of xylindein was developed. Various groups of solvents were assessed for their suitability as xylindein extractants. A new solvent system suitable for CPC separation of xylindein, composed of heptane/THF/MEK/acetonitrile/acetic acid/water, was developed. This solvent system yielded a KD value for xylindein of 1.54±0.04, as determined by HPLC (n=3). The compositions of the upper phase and lower phase of the solvent system were determined by Heteronuclear Single Quantum Correlation (HSQC) NMR and proton NMR. A CPC system, equipped with a fraction collector, was used for the isolation of xylindein from crude extracts. The xylindein fractions isolated by the CPC were then analyzed using HPLC and presented as a fractogram. Based on the CPC fractogram, the purified xylindein fractions were achieved after 30min CPC separation time, yielding 71% extraction efficiency. The developed CPC method allowed for isolation of this naturally sourced xylindein in amounts suitable for further study.

A capillary electrophoretic method for separation and characterization of carbon dots and carbon dot-antibody bioconjugates.

Capillary electrophoresis (CE) coupled with UV absorbance detection has been applied as an analysis tool for carbon dots (C-dots), which were hydrothermally synthesized from precursors citric acid (CA) and ethylene diamine (EDA). An alkaline working buffer (100mM tris acetate, pH 8.4) was found to be optimal for rapid and reliable analysis of C-dots. A calibration curve was established over a broad concentration range (0.5-10mg/mL) with excellent linearity (R2=0.9989). The CE method was also applied to enhance understanding of and facilitate optimization of ensuing C-dot biolabeling reactions. The novel CE method was used to confirm and quantify production of C-dot labeled antibodies. The optimum concentration of antibody for use in the labeling reaction was determined.

Rapid Synthesis of a Long Double-Stranded Oligonucleotide from a Single-Stranded Nucleotide Using Magnetic Beads and an Oligo Library.

Chemical synthesis of oligonucleotides is a widely used tool in the field of biochemistry. Several methods for gene synthesis have been introduced in the growing area of genomics. In this paper, a novel method of constructing dsDNA is proposed. Short (28-mer) oligo fragments from a library were assembled through successive annealing and ligation processes, followed by PCR. First, two oligo fragments annealed to form a dsDNA molecule. The double-stranded oligo was immobilized onto magnetic beads (solid support) via streptavidin-biotin binding. Next, single-stranded oligo fragments were added successively through ligation to form the complete DNA molecule. The synthesized DNA was amplified through PCR and gel electrophoresis was used to characterize the product. Sanger sequencing showed that more than 97% of the nucleotides matched the expected sequence. Extending the length of the DNA molecule by adding single-stranded oligonucleotides from a basis set (library) via ligation enables a more convenient and rapid mechanism for the design and synthesis of oligonucleotides on the go. Coupled with an automated dispensing system and libraries of short oligo fragments, this novel DNA synthesis method would offer an efficient and cost-effective method for producing dsDNA.

Development of a carbon dot (C-Dot)-linked immunosorbent assay for the detection of human α-fetoprotein.

A sensitive, selective, environmentally friendly, high-throughput, well-plate-based immunosorbent assay was developed to detect human α-fetoprotein (AFP) using carbon dots (C-Dots). Highly fluorescent C-Dots were synthesized using a one-step hydrothermal reaction, with citric acid serving as the carbon source and ethylene diamine acting as the nitrogen source. The reaction conditions were optimized to obtain the desired surface functionality. Then, the C-Dots were used to label one member of the anti-AFP pair (Ab2) via amine-amine coupling using glutaraldehyde. The capture anti-AFP (Ab1) was coated onto polystyrene well plates and bovine serum albumin (BSA) was used to block unsaturated binding sites. AFP was incubated in Ab1-coated wells; unbound AFP was then washed away with Tween-20. Next, the C-Dot-labeled Ab2 was added to form a sandwich immunocomplex with the AFP bound to the Ab1-coated wells. The fluorescence intensities detected from the C-Dots on these sandwich immunocomplexes were positively correlated to the concentrations of AFP antigen. A five-parameter logistic regression calibration curve was established between fluorescence and clinically important AFP concentrations (range: 0-350 ng/mL with a correlation coefficient of R(2) = 0.995). The results from the C-Dot-based immunoassay were in agreement with results from traditional immunoassays, which used horseradish peroxidase (HRP, R(2) = 0.964) and fluorescein isothiocyanate (FITC, R(2) = 0.973). These results indicated that C-Dots have great potential to be applied as biolabels for high-throughput well-plate-based immunoassays.

Detection of water contamination from hydraulic fracturing wastewater: a µPAD for bromide analysis in natural waters.

Due to the rapid expansion in hydraulic fracturing (fracking), there is a need for robust, portable and specific water analysis techniques. Early detection of contamination is crucial for the prevention of lasting environmental damage. Bromide can potentially function as an early indicator of water contamination by fracking waste, because there is a high concentration of bromide ions in fracking wastewaters. To facilitate this, a microfluidic paper-based analytical device (µPAD) has been developed and optimized for the quantitative colorimetric detection of bromide in water using a smartphone. A paper microfluidic platform offers the advantages of inexpensive fabrication, elimination of unstable wet reagents, portability and high adaptability for widespread distribution. These features make this assay an attractive option for a new field test for on-site determination of bromide.

Clinical chemistry measurements with commercially available test slides on a smartphone platform: Colorimetric determination of glucose and urea.

BACKGKROUND: Rapidly increasing healthcare costs in economically advantaged countries are currently unsustainable, while in many developing nations, even 50-year-old technologies are too expensive to implement. New and unconventional technologies are being explored as solutions to this problem. In this study, we examined the use of a smartphone as the detection platform for 2 well-developed, relatively inexpensive, commercially available clinical chemistry assays as a model for rapid and inexpensive clinical diagnostic testing. METHODS: An Apple iPhone 4 camera phone equipped with a color analysis application (ColorAssist) was combined with Vitros® glucose and urea colorimetric assays. Color images of assay slides at various concentrations of glucose or urea were collected with the iPhone 4 and quantitated in three different spectral ranges (red/green/blue or RGB) using the ColorAssist app. When the diffuse reflectance data was converted into absorbance, it was possible to quantitate glucose or blood urea nitrogen (BUN) over their clinically important concentration ranges (30-515mg/dl for glucose or 2-190mg/dl for BUN), with good linearity (R(2)=0.9994 or 0.9996, respectively [n=5]). RESULTS: Data collected using the iPhone 4 and canine serum samples were in agreement with results from the instrumental "gold standard" (Beckman Coulter AU480 Chemistry System) (R(2)=0.9966 and slope=1.0001 for glucose; R(2)=0.9958 and slope=0.9454 for BUN). Glucose determinations of serum samples made using this smartphone method were as accurate as or more accurate than a commercial colorimetric dry slide analyzer (Heska® Element DC Chemistry Analyzer, Loveland, CO) and 2 glucometers: ReliOn® Ultima (Abbott Diabetes Care Inc) and Presto® (AgaMatrix Inc.H). BUN determinations made using the smartphone approach were comparable in accuracy to the Heska instrument. CONCLUSION: This demonstration shows that smartphones have the potential to be used as simple, effective colorimetric detectors for quantitative diagnostic tests, and may be applicable for both point-of-care applications in the developed world and field deployment in developing nations.

Low-cost, high-speed identification of counterfeit antimalarial drugs on paper.

With the emergence of artesunate antimalarial counterfeiting in Southeast Asia and sub-Saharan Africa, we present the production of a rapid, inexpensive and simple colorimetric-based testing kit for the detection of counterfeit artesunate in order to preserve life and prevent the development of multi-drug resistant malaria. The kit works based on paper microfluidics which offer several advantages over conventional microfluidics, and has great potential to generate inexpensive, easy-to-use, rapid and disposable diagnostic devices. Here, we have developed a colorimetric assay that is specific to artesunate and turns yellow upon addition of the sample. The test can be done within minutes, and allows for a semi-quantitative analysis of the artesunate tablets by comparing the developed yellow color on the paper test to a color-coded key chart that comes with the kit. A more accurate and precise analysis is done by utilizing a color analyzer on an iPhone camera that measures the color intensity of the developed color on the paper chip. A digital image of the chip was taken and analyzed by measuring the average gray intensity of the color developed on the paper circle. A plot of the artesunate concentration versus the average gray scale intensity was generated. Results show that the intensity of the yellow color developed on the paper test was consistent and proportional to the amount of artesunate present in the sample. With artesunate concentrations ranging from 0.0 to 20mg/mL, a linear calibration plot was obtained with a detection limit of 0.98 mg/mL.

Scalable graphene field-effect sensors for specific protein detection.

We demonstrate that micron-scale graphene field-effect transistor biosensors can be fabricated in a scalable fashion from large-area chemical vapor deposition derived graphene. We electrically detect the real-time binding and unbinding of a protein biomarker, thrombin, to and from aptamer-coated graphene surfaces. Our sensors have low background noise and high transconductance, comparable to exfoliated graphene devices. The devices are reusable and have a shelf-life greater than one week.

Synthesis and characterization of low-generation polyamidoamine (PAMAM) dendrimer-sodium montmorillonite (Na-MMT) clay nanocomposites.

Polymer-inorganic nanocomposites are a recently developed class of materials that have altered physical or chemical properties with respect to the pure polymer, inorganic host, or their micro- and macrocomposites. Lower generation (G0.0-2.0) polyamidoamine (PAMAM) dendrimer/sodium montmorillonite (Na-MMT) nanocomposites were synthesized in a solution-phase exfoliation adsorption reaction. These are the first reports of the G0.0/ and G1.0/Na-MMT nanocomposites and of a structurally-ordered G2.0/Na-MMT. The materials were characterized using powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). PAMAM characteristics at acidic and basic aqueous media were studied using capillary zone electrophoresis (CZE). Pseudospherical PAMAM dendrimers in aqueous medium attain a highly flattened conformation within the confined space between MMT sheets upon nanocomposite formation. The nanocomposite structure depends on the PAMAM generation and the starting dendrimer/organic composition. G0.0 always forms monolayer structures (d = 0.42 nm), while G2.0 forms monolayer structure, mixed phase, and bilayer structures (d = 0.84 nm) at lower, intermediate, and higher organic content, respectively, showing an interesting monolayer to bilayer transition. G1.0 showed an intermediate behavior, with monolayer to mixed-phase transition at the reactant ratios studied. This monolayer arrangement of PAMAM/clay nanocomposites is reported for the first time. Maximum organic contents of G0.0 monolayer and G2.0 bilayer nanocomposites were ∼7% and ∼14%, respectively. Gallery expansions were similar to those observed with linear polymer intercalates, but the packing fractions (0.31-0.32) were 2-3 times lower. At acidic pH, the nanocomposites forming only monolayer structures are obtained, indicating a stronger electrostatic attraction between MMT and protonated PAMAM, and these nanocomposites formed more slowly and were more ordered. Na(+) ions play a significant role in nanocomposite formation. At high pH, PAMAMs show high mobility, ζ potential, and surface charge densities due to Na(+) complexation in solution. FTIR data indicates that both Na-MMT and PAMAM structural units are preserved in the nanocomposites obtained.

Preparation of water soluble carbon nanotubes and assessment of their biological activity in embryonic zebrafish.

Carbon nanotubes (CNTs) are currently one of the most important classes of nanomaterials with unique properties sparking off numerous applications in many fields, including electronics, material science and medicine. However, applications of CNTs in medicine and other biological fields are hampered by their insolubility in aqueous media and concerns regarding toxicity. In this study, seven types of CNTs, including two single-walled, one double-walled, and four multi-walled, were evaluated for possible toxicological effects. Soluble CNTs were prepared by treatment with a mixture of acids (D2SO4 and DNO3), washed with Milli-Q water and oven dried. Transmission electron microscopy, thermal gravimetric analysis, and other techniques were used to characterize the prepared CNTs. CNT toxicity was assessed using the embryonic zebrafish. Results showed that none of the CNTs studied caused significant adverse developmental effects. These results support the potential safe use of CNTs as components of indwelling medical devices and drug delivery tools.

Increasing the detection speed of an all-electronic real-time biosensor.

Biosensor response time, which depends sensitively on the transport of biomolecules to the sensor surface, is a critical concern for future biosensor applications. We have fabricated carbon nanotube field-effect transistor biosensors and quantified protein binding rates onto these nanoelectronic sensors. Using this experimental platform we test the effectiveness of a protein repellent coating designed to enhance protein flux to the all-electronic real-time biosensor. We observe a 2.5-fold increase in the initial protein flux to the sensor when upstream binding sites are blocked. Mass transport modelling is used to calculate the maximal flux enhancement that is possible with this strategy. Our results demonstrate a new methodology for characterizing nanoelectronic biosensor performance, and demonstrate a mass transport optimization strategy that is applicable to a wide range of microfluidic based biosensors.

Preparation and characterization of a tetrabutylammonium graphite intercalation compound.

The intercalation of tetrabutylammonium (TBA) cations into graphite by cation exchange from a sodium-ethylenediamine graphite intercalation compound yields a single-phase first-stage product, C(44)TBA, with a gallery expansion of 0.47 nm. The gallery dimension requires an anisotropic "flattened" cation conformation.

In-line extraction employing functionalized magnetic particles for capillary and microchip electrophoresis.

An approach to performing in-line extraction employing functionalized magnetic particles for CE and microchip electrophoresis is presented. Silica-coated iron oxide particles were synthesized and used as the solid support. The particles were functionalized with octadecylsilane and used as reverse-phase sorbents for in-line SPE followed by electrophoresis. Magnets were used to locally immobilize these sorbents inside the capillary or microchip. Extraction, elution, and detection of the analytes were performed sequentially without interruption or need for sample handling. Mixtures of hydrophobic analytes were successfully extracted from solution using the synthesized magnetic sorbents. CE was able to extract and separate mixture of parabens within 10 min. In-line extraction was also carried out on a disposable PMMA microfluidic device with LIF detection. Electrophoretic separation of fluorescent dyes, Rhodamine 110 and SulfoRhodamine B, was completed in under a minute. The results demonstrated the feasibility of performing the in-line extraction/separation technique in a microchip platform enabling rapid analysis, low sorbent consumption, and increased analyte recovery (relative to the capillary format).