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Micromixing devices often utilize complex architectures to mix miscible liquid streams and can be complex and expensive to fabricate. Here, we developed, built, experimentally tested, and computationally analyzed a serpentine micromixer that can be fabricated using simple tools and supplies available in non-microdevice dedicated laboratories. Fluorescence imaging was used to quantify its mixing effectiveness experimentally. A Computational Fluid Dynamics (CFD) software package (COMSOL) was used to model the micromixing process. The predictions were in excellent agreement with the experimental data. The serpentine micromixer can achieve significant levels of mixing efficiency. CFD predictions for a straight microfluidic channel of the same length as the serpentine favorably compared with previous theoretical predictions, indicating that the serpentine's mixing efficiency was vastly superior. Finally, CFD predictions were conducted for different and possibly improved designs of the basic serpentine. In all cases, the mixing efficiency was primarily associated with the number of 90o elbows in the device rather than the straight sections' length, with the first serpentine bend playing a significant role. Future design improvements should focus on incorporating as many elbows as possible in the device to maximize mixing efficiency and reduce the device size.

Microfluidic devices are constructed from polydimethylsiloxane (PDMS) due to their biocompatibility, fabrication ease, well-established protocols, and simplicity. PDMS-based microfluidic devices are constructed by (i) applying liquid PDMS to a negative mold (usually a silicon or 3D-printed mold) and (ii) curing the PDMS with heat exposure over a set time period. Unreacted resin monomers in 3D-printed molds prevent PDMS from fully curing, resulting in improper channel formation in PDMS and reducing the PDMS device’s efficacy. An in-house protocol that uses SU-8 as a “non-stick” coating on 3D-printed molds facilitates the successful casting of PDMS. Contact angle, surface profile, optical profile, and force testing prove that PDMS cast from SU-8-treated molds resembles pristine PDMS, unlike PDMS cast from untreated molds. Further, this method is generalized to commercial 3D prints using different 3D printing resins. To demonstrate this technique’s viability in microfluidic devices, a microfluidic tree using PDMS from treated 3D prints shows vibrant colors and clear lines. This is absent from an untreated PDMS.

An NP-μFEC is a reusable, novel microfluidic electrochemical cell with multiple non-planar interdigitated microelectrode arrays, minimal sample volume, and enhanced electric field penetration for highly sensitive electrochemical analysis. (i) The NP-μFEC features spatial 3-electrode architecture, and a small sample volume (∼4 μL). (ii) Here, [Fe(CN)

In this work we report the use of a gas sensor that can be used in inline configuration for applications like organ-on-a-chip. The key element of the device is a microfluidic channel with a thickness of 140 μm and width of 500 μm. This microfluidic channel is sandwiched between a top and bottom substrate, each substrate containing microelectrodes making this a non-planar interdigitated microelectrode (NP-IμE) configuration. Room temperature ionic liquids (RTILs) are used as electrolyte in the microfluidic channel. Due to the dimensions of the microfluidic channel only low volume of RTILs are required as electrolyte. RTILs can be tuned to selectively capture specific gases. This in addition to other favourable properties such as wide electrochemical window, thermal stability and negligible vapor pressure makes it a good candidate as the selective electrolyte in electrochemical gas sensor. The use of NP-IμE makes the electric field penetrate through the channel. This allows us to register the perturbations in signal caused by absorption of CO2 from the entire cross-section of the channel, thereby increasing the sensitivity of the device (as compared to a planar architecture). 1-ethyl-3-methylimidazolium 2-cyanopyrolide ([EMIM][2-CNpyr]) was used as the RTIL, as it has been shown to be a good sorbent of CO2 with high capacity at low partial pressures due to its chemical affinity. The RTILs exposed to different concentrations of CO2 was injected into the microfluidic channel. Cyclic Voltammetry (CV), Differential pulse voltammetry (DPV) and Electrochemical impedance spectroscopy (EIS) experiments were done using our microfluidic device. During the CV and DPV experiments, RTIL exposed to CO2 shows a reduction peak (of CO2). This along with the changes in EIS spectrum (Nyquist plot) can be used to detect the presence of CO2. We used CO2 as a test gas to analyse the sensitivity of our microfluidic device combined with RTIL. In future we will be using this same setup to sense biomarker gases and other toxic gases by changing the RTIL and tuning its affinity towards the target analytes.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are human-made chemicals with high chemical resistance and thermal stability. The extremely stable fluoro-carbon (F-C) skeletons enable PFAS molecules can exist stably in nature especially in the water sources for a long time concerning thermal, chemical, and biodegradation. Perfluorooctanoic acid (PFOA) is one of the most dominant environmental contributors, and its half-life in water has been estimated to be longer than 92 years. Therefore, the monitoring of PFOA level in the water source is needed. It is reported that Zirconium (Zr) based metal-organic frameworks (MOFs) have shown considerable affinity to PFOA molecules. In addition, electrochemical impedance spectroscopy (EIS) as a rapid and sensitive detection method (based on measuring the impedance changes at the electrode/solution interface) is perhaps the most frequently used technique in the investigation of affinity-based transducers. In the pursuit of building a highly efficient screening sensor to PFOA molecules. In this work, the application of Zr based MOF in NP-μFEC as a combined sensing platform to PFOA molecules is conducted. Here, the NP-μFEC is our group proposed new impedance sensing platform with enhanced, three-dimensional distributed electric field. To validate the feasibility of Zr based MOF packed NP-μFEC’s sensing performance. The work is conducted with a ranging concentration of PFOA (in 0.1X PBS) from 150 to 10 ng/L. We finally find that the proposed combination of Zr based MOF and NP-μFEC can show an excellent response to the PFOA molecules, which offers a detection limit lower than the established US Environmental Protection Agency (EPA)'s water contamination level (70 ng/L).

The ESSENCE platform is an electrochemical sensor system that utilizes non-planar porous microelectrode microfluidic chips with a fully programmable fluidic/sample system to be a “portable, automatic, rapid, sensitive, and selective” for different emerging contaminants and liquid biopsy. The system is designed with non-planar porous microelectrode interfaces, containing different functional capturing probes for specific sensing tasks. From our previous report, this 3D non-planar structure has advantages such as increased flow’s convective fluxes and disrupts diffusive processes like the electric double layer (EDL). The porous electrode structure utilized the packing material’s higher Zeta potential than the bare glass surface, resulting in the EDL length will be significantly smaller than the clear channel. Due to a smaller EDL length, the relaxation frequency will increase, which shifts the EIS signal to a higher frequency range (1kHz to 100MHz) and results in a fast response with a higher signal-to-noise ratio in Electrochemical Impedance Spectroscopy (EIS) measurements. From the perspective of electric field penetration, the top-down electric direction covers all the packing sensing areas, providing a generally higher electronic signal response than the traditional planar electrode system, leading to a higher signal-to-noise ratio. A second feature from the perspective of microfluidics is the significant fluidic shear force generated due to flow through the porous electrode surface. This higher shear force on the surface can unbind most false-positive signals generated by non-specific binding, such as physical adhesive or biofouling. These unique benefits provide physical enhancements of sensitivity and selectivity without manipulating the chemical material in the system. Earlier we showed that our detection of the biomolecules like DNA (fM sensitivity, which can distinguish against a mismatched DNA), proteins (breast cancer biomarker p53, fM sensitivity, which can distinguish it against another breast cancer biomarker HER2), PFOS (Perfluorooctanesulfonate, 0.5 ng) under the traditional desktop Electrochemical Impedance Spectroscopy (EIS) analyzer in the total process of hourly. In this talk, we have further developed our previous ESSENCE platform to a modular, automatic, and portable, one-stop instrument for clinicians to screen for infectious diseases, liquid biopsy, and toxin detection to detect emerging pathogens while significantly reducing false positives and false negatives, but also decreasing our detecting process to 15 mins in much more hazard background conditions to meet the criteria of POC. Second, A small (15 cm x 17cm) USB programable fluidic/oscilloscope base with a 15 minutes total detecting protocol is applied to our ESSENCE system for a fast Point-of-care (POC) diagnostic. This portable ESSENCE platform can respond to the measurable EIS signals from the oscilloscope with 25 ul samples size (DNA and HER2 proteins in undiluted artificial Urine) with a fully automatic process at the uM to pM regions in 15 minutes. Each ESSENCE chip is also significantly cheaper than the ELISA; the chip costs about $20 (for an academic lab) and can be reused. Figure 1

One approach to reduce increasing concentrations of toxic per- and polyfluoroalkyl substances (PFAS) involves the capture of PFAS from aqueous media using porous materials. The use of highly porous, tunable metal organic framework (MOF) materials is appealing for targeted liquid phase sorption. In this work, we demonstrate the excellent capture of perfluorooctanesulfonate (PFOS) using both the chromium and iron analogs of the MIL-101 framework. Experimental characterization of PFOS uptake reveals unique differences in sorption properties between these two analogs, providing key implications for future PFOS sorbent design. Specifically, STEM-EDS and IR spectroscopy show definitive proof of sorption. Furthermore, XPS analysis shows evidence of a strong interaction between sulfur atoms of the polar headgroup of PFOS and the metal center of the framework in addition to the fluorinated nonpolar tail. Additionally, in situ

Rapid and sensitive detection and quantification of trace and ultra-trace analytes is critical to environmental remediation, analytical chemistry and defense from chemical and biological contaminants. Though affinity based electrochemical sensors have gained immense popularity, they frequently do not meet the requirements of desired sensitivity and detection limits. Here, we demonstrate a complementary luminescence mode that can significantly enhance sensitivity of impedance or voltammetric electrochemical sensors. Our methodology involves using a redox probe, whose luminescence properties change upon changing the oxidation state. By tailoring the system such that these luminescence changes can be correlated with the capture of target analytes, we are able to significantly lower the detection limit and improve the efficiency of detection compared to the electrochemical modes alone. Our proof-of-concept demonstration, using a model system designed for Ca2+ capture, illustrated that the luminescent mode allowed us to lower the limits of detection by three-orders of magnitude compared to the impedance or voltammetric modes alone without requiring any modification of electrode design or cell configuration. Further, the linear ranges of detection are 10−8 to 10−3 M in the voltammetry mode, 10−8 to 10−5 M in the impedance mode and 2.5 × 10−11 to 10−7 M in the luminescent mode, providing a large range of operational flexibility.

INTRODUCTION: Directed fibroblast migration is central to highly proliferative processes in regenerative medicine and developmental biology. However, the mechanisms by which single fibroblasts affect each other’s directional decisions, while chemotaxing in microscopic pores, are not well understood. METHODS: We explored effects of cell sequence and mitosis on fibroblast platelet-derived growth factor-BB (PDGF-BB)-induced migration in microfluidic mazes with two possible through paths: short and long. Additionally, image-based modeling of the chemoattractant’s diffusion, consumption and decay, was used to explain the experimental observations. RESULTS: It both cases, the cells displayed behavior that is contradictory to expectation based on the global chemoattractant gradient pre-established in the maze. In case of the sequence, the cells tend to alternate when faced with a bifurcation: if a leading cell takes the shorter (steeper gradient) path, the cell following it chooses the longer (weaker gradient) path, and vice versa. Image-based modeling of the process showed that the local PDGF-BB consumption by the individual fibroblasts may be responsible for this phenomenon. Additionally, it was found that when a mother cell divides, its two daughters go in opposite directions (even if it means migrating against the chemoattractant gradient and overcoming on-going cell traffic). CONCLUSIONS: It is apparent that micro-confined fibroblasts modify each other’s directional decisions in a manner that is counter-intuitive to what is expected from classical chemotaxis theory. Consequently, accounting for these effects could lead to a better understanding of tissue generation in vivo, and result in more advanced engineered tissue products in vitro. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s12195-018-0551-x) contains supplementary material, which is available to authorized users.

The rapid, sensitive, and selective detection of target analytes using electrochemical sensors is challenging. ESSENCE, a new Electrochemical Sensor that uses a Shear-Enhanced, flow-through Nanoporous Capacitive Electrode, overcomes current electrochemical sensors' response limitations, selectivity, and sensitivity limitations. ESSENCE is a microfluidic channel packed with transducer material sandwiched by a top and bottom microelectrode. The room-temperature instrument less integration process allows the switch of the transducer materials to make up the porous electrode without modifying the electrode architecture or device protocol. ESSENCE can be used to detect both biomolecules and small molecules by simply changing the packed transducer material. Electron microscopy results confirm the high porosity. In conjunction with the non-planar interdigitated electrode, the packed transducer material results in a flow-through porous electrode. Electron microscopy results confirm the high porosity. The enhanced shear forces and increased convective fluxes disrupt the electric double layer's (EDL) diffusive process in ESSENCE. This disruption migrates the EDL to high MHz frequency allowing the capture signal to be measured at around 100 kHz, significantly improving device timing (rapid detection) with a low signal-to-noise ratio. The device's unique architecture allows us multiple configuration modes for measuring the impedance signal. This allows us to use highly conductive materials like carbon nanotubes. We show that by combining single-walled carbon nanotubes as transducer material with appropriate capture probes, NP-μIDE has high selectivity and sensitivity for DNA (fM sensitivity, selective against non-target DNA), breast cancer biomarker proteins (p53, pg/L sensitivity, selective against non-target HER2).

Chemical engineering (ChE) is a historically-relevant degree that is experiencing an emergence of diverse research and industrial trends. However, adapting to them is a challenge, because the overloaded nature of the ChE curriculum makes adding new courses, without removing older ones, difficult. The problem is further exacerbated by the need to justify any modifications to various university committees while satisfying accreditation organizations' criteria. With the ultimate goal of guiding and/or justifying potential curricular changes, this manuscript presents a thorough statistical analysis of the current state of the ChE curricula in the United States of America (USA). Specifically, publically-available undergraduate degree sheets are aggregated from the majority of established ChE departments in the USA, and subject-specific descriptive statistics are reported for core ChE courses. Among the significant findings are two different approaches to teaching Transport Phenomena , the rise of Bio , and the scarcity of traditional Statics and Strength of Materials and Process Safety courses. Ultimately, the results of this study are intended to be used by the other departments interested in improving their curriculum.

Electrical impedance spectroscopy (EIS) sensors, though rapid and cost-effective, often suffer from poor sensitivity. EIS sensors modified with carbon-based transducers show a higher conductance, thereby increasing the sensitivity of the sensor toward biomolecules such as DNA. However, the EIS spectra are compromised by the parasitic capacitance of the electric double layer (EDL). Here, a new shear-enhanced, flow-through nonporous, nonplanar interdigitated microelectrode sensor has been fabricated that shifts the EDL capacitor to high frequencies. Enhanced convective transport in this sensor disrupts the diffusion dynamics of the EDL, shifting its EIS spectra to high frequency. Concomitantly, the DNA detection signal shifts to high frequency, making the sensor very sensitive and rapid with a high signal to noise ratio. The device consists of a microfluidic channel sandwiched between two sets of top and bottom interdigitated microelectrodes. One of the sets of microelectrodes is packed with carbon-based transducer material such as carboxylated single-walled carbon nanotube (SWCNT). Multiple parametric studies of three different electrode configurations of the sensor along with different carbon-based transducer materials are undertaken to understand the fundamental physics and electrochemistry. Sensors packed with SWCNT show femtomolar detection sensitivity from all the different electrode configurations for a short target-DNA. A 20-fold jump in the signal is noticed from the unique working electrode configuration in contrast to the other electrode configurations. This demonstrates the potential of the sensor to have a significant increase in detection sensitivity for DNA and other biomolecules.

We report the functionalized carbon nanotubes (fCNTs) and graphene oxide (GO) doped polyvinyl alcohol (PVA) based gel electrolytes (GEs). The multiwalled carbon nanotubes (CNTs) were treated via microwave irradiation to alter the degree of carboxylation. The fCNT doped gel electrolyte (fCNTGE) showed significantly improved ionic conductivity, mechanical strength as well as electrochemical stability when compared to the pure GE and graphene oxide doped gel electrolyte (GOGE). The homogeneous distribution of ionic channels provided by fCNTs served as redox shuttle and facilitated the ion migration in the gel. The fCNTGE exhibited the best performance when the oxygen content was 12.8% by weight. The ionic conductivity was significantly improved by introducing fCNTs into the PVA gel and reached 6.9 × 10−2 S cm−1, revealing that the diffusion and transport of ions into electrolyte were much better than the GE and GOGE. A significant enhancement in the gel mechanical properties was observed as the Young's module (E = 2.3) and tensile strength (22.3 kPa) of fCNTGE was higher than that of GE and GOGE. Furthermore, the composite Zn–Ag2O batteries were made and tested using the fCNTGE, GE, and GOGE in the 3D-printed battery casings. The fCNTGE based batteries demonstrated good electrochemical stability with specific capacity reaching 204.3 mAh g−1 (C/20).

In this paper, a novel plasmonic grating sensor platform was developed and tested for feasibility using a lights-ON fluorescence-based DNA assay. The sensor platform combined the fluorescence enhancement of a grating-based plasmonic platform with the electric field intensifying effects of nanoscale cones and cavities. The gratings were made through a microcontact printing process that replicated HD-DVD disks in polymethylsilsesquioxane and coated with a thin gold film. Nanocavities were incorporated into the sensor platform during the printing process and nanocones were incorporated during the 100-nm gold deposition process. Fluorescently tagged single-strand (ss) DNA molecules were immobilized onto the surface and were designed such that the molecules would fluoresce when bound to a complementary sequence. Sensor substrates were imaged after exposure to a mismatched and matched ssDNA to quantify the fluorescence enhancement of the sensor. Exposure to matched ssDNA resulted in fluorescent emission from the grating that was $13.6\times $ brighter than flat gold, while the nanocones and nanocavities were $37.5\times $ and $47.4\times $ brighter than flat gold, respectively.

A custom-built mask aligner (CBMA), which fundamentally covers all the key features of a commercial mask aligner, while being low cost and light weight and having low power consumption and high accuracy, is constructed. The CBMA is composed of a custom high fidelity light emitting diode light source, a vacuum chuck, a mask holder, high-precision translation and rotation stages, and high resolution digital microscopes. The total cost of the system is under $7500, which is over ten times cheaper than a comparable commercial system. It produces a collimated ultraviolet illumination of 1.8–2.0 mW cm(−2) over an area of a standard 4-in. wafer, at the plane of photoresist exposure, and the alignment accuracy is characterized to be

Exploiting the functionalization chemistry of graphene, long-range electrostatic and short-range covalent interactions were harnessed to produce multifunctional energetic materials through hierarchical self-assembly of nanoscale oxidizer and fuel into highly reactive macrostructures. Specifically, we report a methodology for directing the self-assembly of Al and Bi2O3 nanoparticles on functionalized graphene sheets (FGS) leading to the formation of nanocomposite structures in a colloidal suspension phase that ultimately condense into ultradense macrostructures. The mechanisms driving self-assembly were studied using a host of characterization techniques including zeta potential measurements, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), particle size analysis, micro-Raman spectroscopy, and electron microscopy. A remarkable enhancement in energy release from 739 ± 18 to 1421 ± 12 J/g was experimentally measured for the FGS self-assembled nanocomposites.

Classical methods for enhancing the electromagnetic field from substrates for spectroscopic applications, such as surface-enhanced Raman spectroscopy (SERS), have involved the generation of hotspots through directed self-assembly of nanoparticles or by patterning nanoscale features using expensive nanolithography techniques. A novel large-area, cost-effective soft lithographic technique involving glancing angle deposition (GLAD) of silver on polymer gratings is reported here. This method produces hierarchical nanostructures with high enhancement factors capable of analyzing single-molecule SERS. The uniform ordered and patterned nanostructures provide extraordinary field enhancements that serve as excitatory hotspots and are herein interrogated by SERS. The high spatial homogeneity of the Raman signal and signal enhancement over a large area from a self-assembled monolayer (SAM) of 2-naphthalenethiol demonstrated the uniformity of the hotspots. The enhancement was shown to have a critical dependence on the underlying nanostructure via the surface energy landscape and GLAD angles for a fixed deposition thickness, as evidenced by atomic force microscopy and scanning electron microscopy surface analysis of the substrate. The nanostructured surface leads to an extremely concentrated electromagnetic field at sharp nanoscale peaks, here referred to as 'nano-protrusions', due to the coupling of surface plasmon resonance (SPR) with localized SPR. These nano-protrusions act as hotspots which provide Raman enhancement factors as high as 108 over a comparable SAM on silver. Comparison of our substrate with the commercial substrate Klarite™ shows higher signal enhancement and minimal signal variation with hotspot spatial distribution. By using the proper plasmon resonance angle corresponding to the laser source wavelength, further enhancement in signal intensity can be achieved. Single-molecule Raman spectra for rhodamine 6G are obtained from the best SERS substrate (a GLAD angle of 60°). The single-molecule spectrum is invariant over the substrate, due to the patterned ordered nanostructures (nano-protrusions).

The most promising biosensor platforms are electrochemical biosensors due to their simple, low manufacturing and usage costs, multiplexed detection capabilities, short response time, as well as ease of miniaturization for portable point-of-care diagnostics. In this talk, we investigate new electrochemical sensing that utilizes a shear-enhanced, flow-through, nanoporous and capacitive electrode technology (hereafter called “ESSENCE”). ESSENCE consists of three layers, a top and bottom nonplanar interdigitated microelectrode array (IDμE) and a middle layer of vertically grown Carbon Nanotubes (CNTs). The fabrication protocol of ESSENCE is unique as unlike most fabrication protocols; it is neither top-down nor bottom-up. We call the technique side-to-side, where the final layer is a sidewall of the device. The steps are: (1) First, fabricate the bottom IDμE on a suitable substrate like glass or silicon. (2) Deposition and the etching process are used to make the microfluidic channel above the bottom IDμE. (3) The catalyst to grow the CNT pillars in the microchannel is patterned on the exposed bottom portion of the channel. (4) A sacrificial layer to support the upper electrode and protect catalyst is introduced on the bottom IDμE. (5) Top electrodes and catalyst are patterned on the top of the sacrificial layer. (6) The CNT’s are grown using well-established techniques. (7) Finally; the chip wall is closed to finish a non-panned interdigitated microfluidic sensor. The functionalization of the CNT is carried out using an in-house on-chip protocol. We exploited the unique electrochemical impedance spectroscopy signal from ESSENCE. Interestingly the tightly packed, porous, flow-through electrode of ESSENCE leads to a substantive increase in diffusion, leading to the formation of the parasitic double layer capacitor at highly elevated frequencies (MHz). This allows for measurement of the charge transfer resistance, an electrochemical signature of the binding of the target biomolecule at high frequencies. This leads to a significant increase in the signal to noise ratio. Further, the nano-porous nature of ESSENCE tremendously boosts the shear force in the device increasing selectivity. Thus, the use of ESSENCE technology boosts both sensitivities (decrease the occurrence of false negatives) and selectivity (decrease the occurrence of false positives), mitigates biofouling and decreases artifacts in the electrochemical signal like the parasitic double layer capacitance (polarization error). Hence, ESSENCE has four significant benefits over the current generation of electrochemical biosensors. (1) The electrode nanoporosity facilitates the development of shear forces of the order of a hydrogen bond, which significantly increases selectivity by mitigating non-specific adsorption. (2) Our preliminary results indicate that the interdigitated, nanoporous microelectrode design, results in a high signal to noise ratio (SNR) which is realized by increases in both sensitivity and specificity. As the ionic flux is confined to nanodomains due to nanostructured electrodes (nanoconfinement effects), it enables the ESSENCE technology to tremendously increase sensitivity and boosts the signal so significantly that even the surface functionalization of the electrodes can be resolved and characterized. (3) The nanoporous electrode architecture increases convective transport of the analyte of interest to the sensing element, thus overcoming diffusion limitations and reducing assay times. Additionally, the convection-mediated transport enhancement negates signal artifacts such as the parasitic double layer capacitance, thus facilitating rapid, high resolutions characterization of the binding signal due to a significant reduction in noise. (4) Finally, given the ease of controlling shear force through flow rate, challenges related to sensitivity and, device selectivity can be decoupled from each other (and each parameter investigated individually) using the shear force as a tuning design parameter. This decoupling allows us to mitigate the problems of biofouling, false positives, and false negatives, among others. Here, electrode fabrication involves many different well-established micro-fabrication techniques. Preliminary tests show very high sensitivity and selectivity with DNA, and a modified ELISA assay for p53, a biomarker for cancer. Acknowledgement: The authors are supported by the National Science Foundation (NSF) Career grant (#1751759): "ASSURED" electrochemical platform for multiplexed detection of Cancer Biomarker Panel using Shear-Enhanced Nanoporous-Capacitive Electrodes Figure Caption: The left figure shows the schematic of the different layers of the ESSENCE electrochemical sensor. The right figure shows an assembled chip with connection wires and inlet/outlet ports for fluid entry. Figure 1

Here we present an electrochemical platform that meets the “ASSURED” criteria for Point-of-Care devices set by the World Health Organization. The proposed research will integrate technologies for 1) a flow-through, nanoporous and capacitive electrode, 2) electrochemical sensor capable of label-free, multiplexed, rapid, portable, sensitive and selective detection, 3) non-planar interdigitated microelectrodes, and 4) integrates multiple electrochemical sensing techniques in one chip. Furthermore, the proposed work assesses the applicability of using this platform technology with both faradaic (cyclic voltammetry) and non-faradaic (electrochemical impedance spectroscopy, EIS) electrochemical measurements from the same sensor. The device architecture consists of three layers, namely, a top and bottom glass layer with gold interdigitated microelectrode array (IDμE) and a middle tape layer with the desired channel pattern. Here, Carbon Nanotubes (CNTs) are loaded in the channel, between the two non-planar interdigitated IDμEs, as shown in the figure below. The microfluidic channel in the device is fabricated using medical grade, acrylic double-sided, pressure-sensitive tapes from ARcare® (Tape No: 90880). The tape is cut into shape using a commercially available cutting machine, Cricut®. The CNTs are oxidized to introduce –COOH group into the nanotubes following established protocols. Post -COOH functionalization, the CNT’s are placed in the channel. The double-sided tape is then ripped off, and the device is closed. This room temperature assembly of the device allows us to do multiple tasks like pre-functionalization of the CNT’s, replacing the CNT’s with other nanomaterials that often do not survive harsh microfluidic chip integration. Post-chip assembly, an in-house EDC-NHS on-chip protocol is used to attach a capture biomolecule (oligo DNA or capture antibody) to the –COOH functionalized CNT. Target biomolecule (target DNA or antigen) attachment to CNTs is sensed by observing the shift in EIS/CV/DPV that occurs because of this binding. As shown in the figure, due to the innovative design of the electrode architecture, the electrodes can be connected in multiple different modes and 2/3 electrode connections. It is worthwhile to note that exchanging the CNT with another material like metal-organic framework (MOF) not only changes the electrochemical signal but also results in entirely new electrochemical measurement methodology. The MOF filled chip has been used for Ultrasensitive Detection of Perfluorooctanesulfonate (PFAS). Further, the chip is also used to cascade multiple electrochemical techniques at the same time for enhanced sensitivity and selectivity. The different electrode connections allow us to obtain a rich plethora of physical and chemical characteristics of the flow-through, nonporous, non-planar interdigitated IDμE system. It has allowed us to optimize the electrode architecture for significant improvement in the sensitivity and selectivity of the electrochemical platform. Acknowledgement: The authors are supported by the National Science Foundation (NSF) Career grant (#1751759): "ASSURED" electrochemical platform for multiplexed detection of Cancer Biomarker Panel using Shear-Enhanced Nanoporous-Capacitive Electrodes. Figure Caption: The left figure shows the schematic of the different layers of the electrochemical sensor. The right figure shows the multitude of electrical connections and electrode set-ups that can be accomplished with this sensor. In particular we show here the sensor in a 3 electrode set-up with a nanoporous flow-through working electrode that is made of CNT trapped between two non-planar interdigitated micoelectrodes. Figure 1

Super-resolution imaging has been advantageous in studying biological and chemical systems, but the required equipment and platforms are expensive and unable to observe single-molecules at the high (μM) fluorophore concentrations required to study protein interaction and enzymatic activity. Here, a plasmonic platform was designed that utilized an inexpensively fabricated plasmonic grating in combination with a scalable glancing angle deposition (GLAD) technique using physical vapor deposition. The GLAD creates an abundance of plasmonic nano-protrusion probes that combine the surface plasmon resonance (SPR) from the periodic gratings with the localized SPR of these nano-protrusions. The resulting platform enables simultaneous imaging of a large area without point-by-point scanning or bulk averaging for the detection of single Cyanine-5 molecules in dye concentrations ranging from 50 pM to 10 μM using epifluorescence microscopy. Combining the near-field plasmonic nano-protrusion probes and super-resolution technique using localization microscopy, we demonstrate the ability to resolve grain sizes down to 65 nm. This plasmonic GLAD grating is a cost-effective super-resolution imaging substrate with potential applications in high-speed biomedical imaging over a wide range of fluorescent concentrations.

We report the visualization of single molecule dynamics in epifluorescence mode through extraordinary plasmonic enhancement provided by silver grating with embedded nanocavities. Cy3/Cy5-labeled DNA/RNA hybrid duplexes were affixed to SiO2-capped silver gratings produced by soft lithography process. Tracking single-molecule fluorescence revealed damped sub-1 Hz periodic Cy3 intensity fluctuations with strong dependence on the bulk MgCl2 concentration. Extreme concentration of electric field at the nanocavity edge induces plasmonic heating, which sets up convection deep within the nanocavity. Local fluctuations in Mg2+ ion concentration promote a bent or unbent duplex conformational state, respectively, by varying degrees of negative charge screening along the duplex backbone. These oscillations continue until the duplex conformational state stabilizes or the dyes bleach. This unique molecular behavior in the nanocavity could be used to study duplex complementarity, structural polymorphisms, and protein-nucleic acid interactions at the single molecule level.

In this perspective article, we introduce a potentially transformative DNA/RNA detection technology that promises to replace DNA microarray and real-time PCR for field applications. It represents a new microfluidic technology that fully exploits the small spatial dimensions of a biochip and some new phenomena unique to the micro- and nanoscales. More specifically, it satisfies all the requisites for portable on-field applications: fast, small, sensitive, selective, robust, label- and reagent-free, economical to produce, and possibly PCR-free. We discuss the mechanisms behind the technology and introduce some preliminary designs, test results, and prototypes.

In this perspective article, we introduce a potentially transformative DNA/RNA detection technology that promises to replace DNA microarray and real-time PCR for field applications. It represents a new microfluidic technology that fully exploits the small spatial dimensions of a biochip and some new phenomena unique to the micro- and nanoscales. More specifically, it satisfies all the requisites for portable on-field applications: fast, small, sensitive, selective, robust, label- and reagent-free, economical to produce, and possibly PCR-free. We discuss the mechanisms behind the technology and introduce some preliminary designs, test results, and prototypes.

Dielectrophoretic nanocolloid assay is a promising technique for sensitive molecular detection and identification, as target molecule hybridization onto the probe-functionalized nanocolloids can change their surface conductance and consequently their dielectrophoretic crossover frequencies. Thus, instead of relying on surface charge density increase after hybridization, as in many capacitive and field effect transistor impedance sensing techniques, the current assay utilizes the much larger surface conductance (and dielectrophoresis crossover frequency) changes to effect sensitive detection. Herein, we present a Poisson–Boltzmann theory for surfaces with finite-size molecular probes that include the surface probe conformation, their contribution to surface charge with a proper delineation of the slip and Stern planes. The theory shows that the most sensitive nanocolloid molecular sensor corresponds to a minimum in the dielectrophoretic crossover frequency with respect to the bulk concentration of the molecular probes (oligonucleotides in our case) during nanocolloid functionalization. This minimum yields the lowest number of functionalized probes that are also fully stretched because of surface probe-probe interaction. Our theory provides the surface-bulk oligonucleotide concentration isotherm and a folding number for the surface oligonucleotide conformation from the crossover frequency, the zeta potential, and the hydrodynamic radius data.

A rapid (minutes) electrospray bead-based DNA hybridization detection technique is developed by spraying a mixture of hybridized and unhybridized silica nanocolloids. With proper far-field control by external electrodes, the trajectory of the ejected nanobeads from the electrospray is governed by specific harmonics of the Laplace equation, which select discrete polar angles along well-separated field maxima near the conducting Taylor cone. Due to Rayleigh fission and evaporation, beads of different size acquire different total charge after ejection and suffer different normal electrophoretic displacement such that they are ejected along well-separated field maxima and are deposited in distinct rings on an intersecting plane. As the hybridized DNA is of the same dimension as that of the nanocolloid, the nanocolloids are hence easily differentiated from the unhybridized ones. This technique is highly specific as the high shear stress in the microjet shears away any non-specifically bound DNA from the nanocolloid surface.

Other than concentrating the target molecules at the sensor location, we demonstrate two distinct new advantages of an open-flow impedance-sensing platform for DNA hybridization on carbon nanotube (CNT) surface in the presence of a high-frequency AC electric field. The shear-enhanced DNA and ion transport rate to the CNT surface decouples the parasitic double-layer AC impedance signal from the charge-transfer signal due to DNA hybridization. The flow field at high AC frequency also amplifies the charge-transfer rate across the hybridized CNT and provides shear-enhanced discrimination between DNA from targeted species and a closely related congeneric species with three nucleotide mismatches out of 26 bases in a targeted attachment region. This allows sensitive detection of hybridization events in less than 20 min with picomolar target DNA concentrations in a label-free CNT-based microfluidic detection platform.

Electric induced dipoles of nanocolloids the size of the Debye length are shown to be one order stronger than predicted by the classical Maxwell-Wagner theory and its extensions. The difference is attributed to normal ion migration within the diffuse layer, and adsorption onto the Stern layer at the poles. The characteristic relaxation frequency (the crossover frequency for dielectrophoresis) is shown to be inversely proportional to the $RC$ time of the diffuse layer capacitance and resistance, and has an anomalous $\ensuremath{-}1$ scaling with respect to the product of the Debye length and the particle size.

We present an indium tin oxide/polymethylsilsesquioxane (ITO/PMSSQ) photonic crystal with grating structure. This topography exhibits multiple coupling resonances in specific regions of the solar spectrum, which can be controlled by tuning the angle and polarization of incident light. The ITO/PMSSQ grating structures are prepared via simple soft lithography procedures using HD-DVDs as templates. The surface topology also includes geometrical singularities such as nanogaps and nanocones, which lead to further enhanced light trapping characteristics as demonstrated by theoretical and experimental results. Together, these singularity-embedded photonic crystal gratings result in extremely concentrated electromagnetic fields at the aforementioned singularities, which could be especially helpful in separating the tightly bonded excitons in organic solar cells and, hence, improve the efficiency significantly.

Normal and tangential surface ionic currents around low-permittivity nanocolloids with surface charges are shown to produce three different conductive mechanisms for ac-induced dipoles, all involving dynamic space charge accumulation at the double layer∕bulk interface with a conductivity jump. However, the distinct capacitor dimensions and diffusive contributions produce three disparate crossover frequencies at which the induced dipole reverses direction relative to the bulk field. A highly conducting collapsed diffuse layer, with bulk ion mobility, renders the particle conductive and produces an ionic strength independent crossover frequency for weak electrolytes. A precipitous drop in crossover frequency occurs at high ionic strengths when charging occurs only at the poles through field focusing around the insulated colloid. A peculiar maximum in crossover frequency exists between these two asymptotes for colloids smaller than a critical size when normal charging of the diffuse layer occurs over the entire surface. The crossover frequency data for latex nanocolloids of various sizes in different electrolytes of wide ranging ionic strengths are collapsed by explicit theoretical predictions without empirical parameters.

Molecular dielectrophoresis (DEP) is employed to rapidly (