Programmable graphene-based microfluidic sensor for DNA detection

Nonaqueous redox flow batteries (NAqRFB) utilizing redox active organic molecules offer an attractive alternative to metal-based aqueous redox flow batteries for achieving cost-effective, grid-scale energy storage. In particular, nonaqueous electrolytes provide large electrochemical windows, enabling 3 – 4 V cells, and organic active materials span a broad materials design space.1 While several studies report on the discovery of new redox active organic molecules2,3 and even demonstrate organic-based NAqRFB prototypes4, few efforts discuss advances in NAqRFB reactor design. A lack of materials specific knowledge of new nonaqueous electrolytes makes translating aqueous flow cell design principles to nonaqueous systems difficult, especially considering the increased viscosities and decreased conductivities associated with nonaqueous systems. Additionally, prototyping laboratory-scale flow cells employing newly discovered active materials leads to difficulty in determining whether cell failure arises from active material degradation or inadequate flow cell design. Thus, advancing NAqRFB cell design requires development of chemistry-agnostic design guidelines and systematic investigation of device configurations using well-characterized electrolytes with near practical active species concentrations. This work combines experimental and modeling efforts to quantify performance-limiting factors in nonaqueous flow cell design. First, numerical modeling of electrochemical processes in high performance interdigitated flow fields predicts cell polarization as a function of various characteristic dimensionless groups relating to electrolyte properties, electrode morphology, and cell geometry. To capture the wide array of possible materials and cell design configurations, we perform a parametric sweep of the numerical model across the feasible design space, computing dimensionless polarization curves for the characteristic dimensionless groups. From the dimensionless polarization curves, cell designs that minimize area specific resistance (ASR) for a particular set of input materials properties can be identified (Figure 1), guiding flow cell design. Second, we prove 4-acetylamino-2,2,6,6-tetramethyl-1-oxo-piperidine-1-oxyl (AcNH-TEMPO) as a redox pair with the required traits to serve as a platform chemistry for systematic cell-level performance analysis. Both AcNH-TEMPO and its oxidized cation salt are commercially available, stable over many cycles, and soluble in the electrolyte of interest (≥ 0.5 M in 1 M lithium tetrafluoroborate (LiBF4) / propylene carbonate (PC)); additionally the AcNH-TEMPO couple exhibits fast redox kinetics. Using this model redox pair, we investigate critical electrolyte properties including viscosity, conductivity, and UV-vis absorbance spectra as a function of state-of-charge (SOC). Across all SOCs of the model electrolyte (0.5 M AcNH-TEMPO / 1 M LiBF4 / PC), conductivity varies by only 13 %, but viscosity swings drastically by 45 %. Well-defined absorbance peaks at visible wavelengths suggest that electrolyte SOC could even be monitored in-situ with UV-vis. Furthermore, cyclic voltammetry helps to determine the redox potential and reversibility of both the reduced and oxidized forms of AcNH-TEMPO. The redox potential of AcNH-TEMPO conveniently lies well within the electrochemical window of many common nonaqueous electrolytes, allowing for controlled flow cell studies with no electrolyte decomposition. Third, after validating the model compound, a single-electrolyte flow cell study5 exploits the AcNH-TEMPO couple to explore experimental pathways towards achieving an aggressive area specific resistance (ASR) target of ≤ 5 Ω cm2 and validating the numerically computed design rules. A state-of-the-art vanadium flow cell5 (Figure 2a) serves as the initial architecture with various nonaqueous compatible separators and membranes. For each flow cell configuration, impedance (Figure 2a) and polarization (Figure 2b) measurements are recorded at several flow conditions, quantifying the total ASR, as well as the ohmic, kinetic, and mass transfer impedance contributions. Specifically, we demonstrate the effects of separator conductivity, electrode thickness, and flow rate on ASR. We also investigate, for the first time, the performance enhancements afforded by operating NAqRFBs at elevated temperatures. This work culminates in a demonstration of a NAqRFB reactor, which achieves our ASR target, showing promise for economically viable NAqRFBs with high performance reactors. Acknowledgments We gratefully acknowledge the financial support of the Joint Center for Energy Storage Research and the National Science Foundation Graduate Research Fellowship Program.

Around 1970 Intel discovered it could put 2,000 transistorsor perhaps a few moreon a single NMOS chip. In retrospect, this may be said to mark the beginning of very large-scale integration (VLSI), ...

e15185 Background: Solid tumor specimen collection during clinical trials often follows a standard histology protocol, ending in the generation of FFPE sections mounted onto 1 mm histology slides. Though a common sample format for researchers developing tissue-based biomarkers, slides present a data quality challenge for multiplexed spatial biology workflows. Here we present data describing an innovative flow cell design fully compatible with pre-slided tissue specimens. We collected spatial biology data using this slide-compatible flow cell and compared it to the gold standard direct mounting on coverglass. Several rounds of marker staining and imaging demonstrate equivalency in method outcomes including image resolution, signal to noise, and re-interrogation capacity. Methods: FFPE biopsy tissue specimens (tumor punch biopsies and a tonsil section) were mounted on standard histology slides. These specimens were incorporated into flow cells using a new glass coverslip and porting device, CellScape™ Slide, that pairs with a standard histology slide to form a microfluidic chamber. After mounting, each sample was probed for consensus CD markers (CD45, CD3, CD4,CD8,CD20, etc.) through several rounds of iterative immunofluorescence staining using CellScape™ Precise Spatial Multiplexing. The resulting multi-layered whole slide image dataset was then interrogated for spatial resolution and signal-to-noise using digital image analysis. Results: Spatial resolution and signal-to-noise ratio (SNR) were assessed through comparison to data collected from similar samples using the existing CellScape microfluidic chip. The lowest intensity signal collected with at least a 30:1 SNR (acceptable for image analysis) was equivalent or lower in the CellScape Slide preparation (equivalent sensitivity). The highest intensity signal collected was equivalent between the two flow cell designs. Comparing stain quality (specificity, sensitivity) among markers stained through multiple rounds of iterative staining, imaging, and signal remove via photoinactivation showed that the CellScape Slide flow cell is on par with or better than the existing CellScape chip. Further, the usable clear window of the CellScape Slide flow chamber, measuring 16 mm x 44 mm, was found to be greater than twice that of the existing chip. Literature review determined this to also be the largest imaging window available among commercially available spatial biology platforms. Conclusions: Assessment of the CellScape Slide flow cell, innovative in providing access to the CellScape spatial biology workflow for pre-mounted FFPE tissue, determined that the optical performance of the new flow cell is at least on par with the existing flow cell. Further, the usable window is over twice the area, and the new flow cell is fully capable of supporting re-interrogation of the sample.

Microfluidic system for DNA sequence detection

An electrochemical DNA sensor for Legionella pneumophila detection was constructed using O2 plasma functionalized multi-walled carbon nanotube (MWCNT) film as a working electrode (WE). The cyclic voltammetry (CV) results revealed that the electrocatalytic activity of plasma functionalized MWCNT (pf-MWCNT) significantly changed depending on O2 plasma treatment time due to some oxygen containing functional groups on the pf-MWCNT surface. Scanning electron microscope (SEM) images and X-ray photoelectron spectroscopy (XPS) spectra were also presented the changes of their surface morphologies and oxygen composition before and after plasma treatment. From a comparison study, it was found that the pf-MWCNT WEs had higher electrocatalytic activity and more capability of probe DNA immobilization: therefore, electrochemical signal changes by probe DNA immobilization and hybridization on pf-MWCNT WEs were larger than on Au WEs. The pf-MWCNT based DNA sensor was able to detect a concentration range of 10 pM–100 nM of target DNA to detect L. pneumophila.

Capillary action arising from surface tension-based forces has been demonstrated to be an effective means of passively actuating various fluids through simple and sophisticated microfluidic channel networks. Systems based on this technique are advantageous compared with standard pumping strategies, as they have zero power requirements, are readily integrated into the overall fluidic chip design, and can be fabricated rapidly in a single manufacturing step. This paper comprehensively investigates time lapsed average velocity profiles of various capillary action microfluidic systems, including channels and pumping structures, and compares experimental data against prominent, competing, and flow-based theoretical models. We demonstrate that the average meniscus flow velocity of CO 2 laser ablated capillary systems can be adequately predicted and characterize smooth fluidic velocity profiles in simple microchannels and complex interlinking channel pump/filling structures. Such systems offer a useful, rapid, and low cost alternative to traditional fluidic actuation and flow control systems such as those found in on-chip based biological and chemical analysis.

Detection of DNA hybridization and extension reactions by an extended-gate field-effect transistor: Characterizations of immobilized DNA–probes and role of applying a superimposed high-frequency voltage onto a reference electrode

This paper presents a single chip efficient FPGA implementation of RSA and DES for Digital Envelope Scheme that targets the Altera Apex 20KE EP20k200EBC356. Implementation of cryptographic algorithms on programmable devices like FPGAs run much faster than on software while preserving physical security of hardware solutions. The high throughput in the implementation of cryptographic algorithms for digital envelope scheme is achieved by means of exploiting the parallelism present in the DES and RSA operations as well as the features of Altera Apex 20KE device family which best suit for system-on-a-programmable-chip (SOPC) applications. The parallelized single chip implementation of DES and RSA for performing the Encryption/Decryption for the Digital envelope scheme offers a throughput of 3.5 Gbits/sec at a system clock rate of 54.7 MHz. This implementation even provides a means for using the DES and RSA separately.

The assessment of candidate materials for redox flow batteries requires effective diagnostic techniques for monitoring the evolution of electrolyte state of charge and state of health to interrogate time-dependent changes in system behavior. Further, such tools can be applied in practical embodiments to inform maintenance schedules and optimize energy utilization. In this work, we develop and test a flow-through, microelectrode-based electrochemical sensor to continuously measure active species concentrations in redox flow cells. A gold microelectrode (working electrode) and platinum wire (pseudoreference electrode) are sealed into a stainless steel fitting (counter electrode), and three-electrode electroanalytical techniques (i.e., voltammetry, chronoamperometry) are performed to correlate steady-state current to concentration. To validate transport and thermodynamics that govern the sensing mechanism, we combine multiphysics simulation with ex situ experimental testing, confirming that the device is capable of accurately determining individual species concentrations. We then evaluate the microelectrode sensor in a symmetric redox flow cell, demonstrating the utility of this approach for measuring operando concentrations, and discuss additional considerations for successful implementation (e.g., measurement protocol, material selection, flow cell design). Assembled from commercially available, off-the-shelf components, the sensor can be readily adopted by research laboratories and integrated into existing experimental workflows, making it a promising tool for studying flow battery materials.

A direct electrochemical detection procedure for DNA hybridization by using the electrochemical signal changes of conductive poly(m-aminobenzenesulfonic) acid (PABSA)/TiO(2) nanosheet membranes, which were electropolymerized by using the pulse potentiostatic method, is reported. Due to the unique properties of TiO(2) nanoparticles, m-aminobenzenesulfonic acid monomers tend to be adsorbed around the particles, and the electropolymerization efficiency is greatly improved. The combination of TiO(2) nanoparticles and PABSA resulted in a nanocomposite membrane with unique and novel nanosheet morphology that provides more activation sites and enhances the surface electron-transfer rate. These characteristics were propitious for the magnification of PABSA electrochemical signals and the direct detection of DNA hybridization. Owing to the presence of abundant sulfonic acid groups, PABSA could overcome the drawbacks of polyaniline and be used to detect bioanalytes at physiological pH. DNA probes could be covalently attached to the sulfonic groups through the amines of DNA sequences by using an acyl chloride cross-linking reaction. After immobilization of probe DNA, the electrochemical impedance value increased significantly compared to that of PABSA/TiO(2) nanosheet membranes, and then decreased dramatically after the hybridization reaction of the probe DNA with the complementary DNA sequence compared to that of the probe-immobilized electrode. Electrochemical impedance spectroscopy was adopted for indicator-free DNA biosensing, which had an eminent ability for the recognition between double-base mismatched sequences or non-complementary DNA sequences and complementary DNA sequences. A gene fragment, which is related to one of the screening genes for the transgenically modified plants, the cauliflower mosaic virus 35S gene was satisfactorily detected. This is the first report for the indicator-free impedance DNA hybridization detection by using PABSA/TiO(2) membranes under neutral conditions.

Detection of disease-related gene expression by DNA hybridization is a useful diagnostic method. In this study a monolayer graphene field effect transistor (GFET) was fabricated for the detection of a particular single-stranded DNA (target DNA). The probe DNA, which is a single-stranded DNA with a complementary nucleotide sequence, was directly immobilized onto the graphene surface without any linker. The VDirac was shifted to the negative direction in the probe DNA immobilization. A further shift of VDirac in the negative direction was observed when the target DNA was applied to GFET, but no shift was observed upon the application of non-complementary mismatched DNA. Direct immobilization of double-stranded DNA onto the graphene surface also shifted the VDirac in the negative direction to the same extent as that of the shift induced by the immobilization of probe DNA and following target DNA application. These results suggest that the further shift of VDirac after application of the target DNA to the GFET was caused by the hybridization between the probe DNA and target DNA.

ABSTRACTA continuous flow analysis system, composed of a 1.2-cm laboratory-made antibubble flow cell and a spectrophotometer, was established. The system was evaluated for the determination of nitrite, phosphate, and silicate. Different from flow injection analysis and other flow analysis modes, an injection or multiposition valve was not needed. Even better, the system was free from interferences from air bubbles without the use of a debubbler device or electronic bubble gate. Without the formation of air bubbles, the chemical reaction was accelerated using a water bath. The experimental parameters for nutrient analysis, including reagent concentration, flow strategy, flow rate, and reaction temperature, were optimized based on a univariate experimental design. The carry-over effect was comprehensively evaluated and may be ignored using this protocol. The established system and analytical methods were especially suitable for laboratories with only basic instruments and limited budgets. The system had the advantages of high sample throughput (>60 h−1); great convenience without valve utilization; long linear dynamic ranges (0.2–80 µM for nitrite, 0.3–14 µM for phosphate, and 0.5–120 µM for silicate); low detection limits (0.06 µM for nitrite, 0.08 µM for phosphate, and 0.11 µM for silicate); and high recovery values (91.5 ± 1.01 to 108.7 ± 3.18%). In addition to water samples, national reference materials were analyzed, and the results were in good agreement with the certified values.

Microfluidics. Big things in narrow channels.

A combined circuit/device model for the analysis of integrated microfluidic systems is presented. The complete model of an integrated microfluidic device incorporates modeling of fluidic transport, chemical reaction, reagent mixing, and separation. The fluidic flow is generated by an applied electrical field or by a combined electrical field and pressure gradient. In the proposed circuit/device model, the fluidic network has been represented by a circuit model and the functional units of the /spl mu/-TAS (micro Total Analysis System) have been represented by appropriate device models. We demonstrate the integration of the circuit and the device models by using an example, where the output from the fluidic transport module serves as the input for the other modules such as mixing, chemical reaction and separation. The combined circuit/device model can be used for analysis and design of entire microfluidic systems with very little computational expense, while maintaining the desired level of accuracy.

An ultra-narrow width silicon field effect transistor (FET) with a suspended gate, integrated with on-chip microfluidic delivery system is described. The device is designed to be used as an FET based sensor for sequencing of DNA, RNA and proteins, by detecting the local charge variations along the chains of these molecules as they are passed between the gate and the channel of the FET in an aqueous solution. A side-gated FET structure is demonstrated with sub-10 nm width, successfully suppressing the electrical leakage currents at the device edges. Side-gated FET structure allows electrostatic confinement of the electrons in the channel for increased spatial resolution.