David Dandy

David Dandy
Colorado State University | CSU · Department of Chemical & Biological Engineering

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138
Publications
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Introduction
Skills and Expertise

Publications

Publications (138)
Article
Analyte affinity capture by surface-immobilized diagnostic agents is a routinely used assay format for profiling numerous medically and technologically important target analytes. These assays suffer from numerous performance limitations, including sensitivity and rapidity. Assay miniaturization is advocated to improve surface-capture performance, s...
Article
Urinary tract infections (UTIs) are one of the most common infections across the world and can lead to serious complications such as sepsis if not treated in a timely manner. Uropathogenic Escherichia coli account for 75% of all UTIs. Early diagnosis is crucial to help control UTIs, but current culturing methods are expensive and time-consuming and...
Article
Point-of-care (POC) methods currently available for detecting SARS-CoV-2 infections still lack accuracy. Here, we report the development of a highly sensitive electrochemical immunoassay capable of quantitatively detecting the presence of the SARS-CoV-2 virus in patient nasopharyngeal samples using stencil-printed carbon electrodes (SPCEs) function...
Article
Rapid and inexpensive serological tests for SARS-CoV-2 antibodies are needed to conduct population-level seroprevalence surveillance studies and can improve diagnostic reliability when used in combination with viral tests. Here, we report a novel low-cost electrochemical capillary-flow device to quantify IgG antibodies targeting SARS-CoV-2 nucleoca...
Preprint
Full-text available
A disposable enzyme-linked immunosorbent assay (dELISA) device for ate-home or doctor’s office use was developed to detect SARS-CoV-2 antibodies. Serology testing for SARS-CoV-2 antibodies is currently run using well-plate ELISAs in centralized laboratories. However, the scale of serology testing needed for epidemiological and clinical screening st...
Preprint
A disposable enzyme-linked immunosorbent assay (dELISA) device for ate-home or doctor’s office use was developed to detect SARS-CoV-2 antibodies. Serology testing for SARS-CoV-2 antibodies is currently run using well-plate ELISAs in centralized laboratories. However, the scale of serology testing needed for epidemiological and clinical screening st...
Article
Sensitive, reliable and cost-effective detection of pathogens has wide ranging applications in clinical diagnostics and therapeutics, water and food safety, environmental monitoring, biosafety and epidemiology. Nucleic acid amplification tests (NAATs)...
Article
Capillary-driven microfluidic devices are of significant interest for on-site analysis because they do not require external pumps and can be made from inexpensive materials. Among capillary-driven devices, those made from paper and polyester film are among the most common and have been used in a wide array of applications. However, since capillary...
Article
Microfluidic magnetophoresis is a powerful technique that is used to separate and/or isolate cells of interest from complex matrices for analysis. However, mechanical pumps are required to drive flow, limiting portability and making translation to point-of-care (POC) settings difficult. Microfluidic paper-based analytical devices (μPADs) offer an a...
Preprint
A disposable enzyme-linked immunosorbent assay (dELISA) device for ate-home or doctor’s office use was developed to detect SARS-CoV-2 antibodies. Serology testing for SARS-CoV-2 antibodies is currently run using well-plate ELISAs in centralized laboratories. However, the scale of serology testing needed for epidemiological and clinical screening st...
Preprint
Capillary-driven microfluidic devices are of significant interest for on-site analysis because they do not require external pumps and can be made from inexpensive materials. Among capillary-driven devices, those made from paper and polyester film are among the most common and have been used in a wide array of applications. However, since capillary...
Article
Pathogen detection is crucial for human, animal, and environmental health; crop protection; and biosafety. Current culture-based methods have long turnaround times and lack sensitivity. Nucleic acid amplification tests offer high specificity and sensitivity. However, their cost and complexity remain a significant hurdle to their applications in res...
Article
Microfluidic paper-based analytical devices (μPADs) are simple but powerful analytical tools that are gaining significant recent attention due to their many advantages over more traditional monitoring tools. These include being inexpensive, portable, pump-free, and having the ability to store reagents. One major limitation of these devices is slow...
Article
Detection of viral infection is commonly performed using serological techniques like the enzyme-linked immunosorbent assay (ELISA) to detect antibody responses. Such assays may also be used to determine the infection phase based on isotype prevalence. However, ELISAs demonstrate limited sensitivity and are difficult to perform at the point of care....
Article
Viral pathogens are a serious health threat around the world, particularly in resource limited settings, where current sensing approaches are often insufficient and slow, compounding the spread and burden of these pathogens. Here, we describe a la-bel-free, point-of-care approach towards detection of virus particles, based on a microfluidic paper-b...
Article
Microfluidic paper-based analytical devices (μPADs) are a versatile and inexpensive point-of-care (POC) technology, but their widespread adoption has been limited by slow flow rates and the inability to carry out complex in field analytical measurements. In the present work, we investigate multilayer μPADs as a means to generate enhanced flow rates...
Article
Full-text available
The ability to study individual bacteria or subcellular organelles using inertial microfluidics is still nascent. This is due, in no small part, to the significant challenges associated with concentrating and separating specific sizes of micrometer and sub-micrometer bioparticles in a microfluidic format. In this study, using a rigid polymeric micr...
Article
The dilute conditions under which microalgae suspensions are cultured have negatively impacted economical routes for cell harvesting using conventional approaches. A promising alternative has arisen, for which a microfluidic concentration approach has been developed for harvesting Cyanobacterium Synechocystis sp. PCC 6803. This method uses passive...
Article
Since the first microfluidic paper-based analytical device (µPAD) was introduced by Whitesides and coworkers in 2007,1 the field has continued to develop at an exponential rate with notable impacts to academic and industrial communities. Generally, µPADs fabricated from cellulose paper as a substrate can process 0.1 to 100 µL of liquids using fluid...
Conference Paper
Chemical gradients drive many processes in biology, ranging from nerve signal transduction to ovulation. At present, microscopy is the primary tool used to understand these gradients. Microscopy has provided many important breakthroughs in our understanding of the fundamental biology, but is limited due to the need to incorporate fluorescent molecu...
Article
Full-text available
Chemical gradients drive a diverse set of biological processes ranging from nerve transduction to ovulation. At present, the most common method for quantifying chemical gradients is microscopy. Here, a new concept for probing spatial and temporal chemical gradients is reported that uses a multi-layer microfluidic device to measure analyte concentra...
Article
Full-text available
A local evanescent array coupled biosensor is used to detect spherical polystyrene nanoparticles with diameters of 40 nm and 200 nm, whose sizes and refractive index are similar to virus particles. The sensitivity is similar to 1%/particle for 200 nm particles and 0.04%/particle for 40 nm particles. Mie scattering in an evanescent field theory is u...
Article
A prototype microfluidic platform has been developed for spatially and temporally resolved sampling of biomarkers expressed by organotypic tissue slices. The device draws liquid from the sample reservoir through discrete sampling ports into separate analysis microchannels. By monitoring the concentrations of specific biomarkers it is possible to ma...
Article
The spatial and temporal distributions of an extensive number of diffusible molecules drive a variety of complex functions. These molecular distributions often possess length scales on the order of a millimeter or less; therefore, microfluidic devices have become a powerful tool to study the effects of these molecular distributions in both chemical...
Article
CVD diamond is an enabling material for diverse applications. In recent years, multiscale modelling of CVD growth in conjunction with experimental studies of the deposition processes has made a substantial progress towards our understanding of the fundamental growth chemistry and material quality. Macroscopic gas phase simulations of the CVD reacto...
Article
The spatial and temporal distributions of diffusible molecules play an important role in a wide variety of biological and chemical processes. Molecular diffusion creates gradients that carry critical temporal and spatial information, yet little is known at this point regarding the mechanisms of gradient formation, maintenance, or elimination. Here...
Article
The detection and quantification of aqueous suspensions of virus particles is critical for a wide variety of applications, ranging from medical diagnostics, homeland security, food and drug production, to water sanitation. Advances in virus detection technologies are expected to yield significant savings in cost and time. Here we present the use of...
Article
Nanoparticles with diameter and refractive index similar to viruses were detected by using a local evanescent array coupled biosensor with an integrated photodetector array on a CMOS chip.
Article
Measurements of pollutants such as toluene are critical for the characterization of contaminated sites and for the monitoring of remediation processes and wastewater treatment effluents. Fiber optic enzymatic biosensors have the potential to provide cost-effective, real time, continuous, in situ measurements. In this study, a fiber optic enzymatic...
Article
The first demonstration of a label-free LEAC biosensor immunoassay is reported. CMOS chips with integrated detection arrays detected tuberculosis related antibodies and 18kDa protein antigens. The limit of detection for thickness change was 120 pm.
Article
The evanescent field surrounding the core of an optical waveguide is very sensitive to refractive index changes near the core. This sensitivity can be exploited to form the basis for a quantitative sensor with high specificity and sensitivity. Selective probe molecules may be attached to the surface of a waveguide core and the evanescent field loca...
Article
Bending of lamellar microdomains of block copolymers on nonselective surfaces has been reported. Symmetric diblock copolymers self-assemble into lamellar microdomains which can be used to create line and space patterns on substrates by controlling the orientation of microdomains. The fabrication of topographic guiding patterns began with patterning...
Article
A label-free optical waveguide immunosensor was designed, fabricated and tested. Different from other popular resonance-based biosensors, such as surface-plasmon-resonance (SPR) or ring/disk resonance biosensors, the local evanescent array coupled (LEAC) biosensor relies on a local evanescent field shift mechanism and can be readily manufactured us...
Article
Full-text available
Controlled pumping of fluids through microfluidic networks is a critical unit operation ubiquitous to lab-on-a-chip applications. Although there have been a number of studies involving the creation of passive flows within lab-on-a-chip devices, none has shown the ability to create temporally stable flows for periods longer than several minutes. Her...
Conference Paper
Diagnostic protocols based on protein-antigen affinity interactions have become increasingly popular in both clinical and research settings. Heterogeneous affinity assays, in which antigens (or antibodies) immobilized to a surface capture analytes of interest from an aqueous solution, offer many advantages over their traditional homogeneous well-ba...
Conference Paper
Halogenated hydrocarbons are among the most common environmental contaminants in groundwater, due to their widespread use and their recalcitrance to natural attenuation. Halogenated alkanes (1,2-dichloroethane, 1,2-dibromoethane) could cause health problems and could be found in most environmental groundwater monitoring sites. Traditional laborator...
Article
Full-text available
An integrated, inexpensive, label-free photonic waveguide biosensor system with multi-analyte capability has been implemented on a silicon photonics integrated circuit from a commercial CMOS line and tested with nanofilms. The local evanescent array coupled (LEAC) biosensor is based on a new physical phenomenon that is fundamentally different from...
Article
Full-text available
As a result of very large surface area to volume ratios, evaporation is of significant importance when dealing with lab-on-a-chip devices that possess open air/liquid interfaces. For devices utilizing a reservoir as a fluid delivery method to a microfluidic network, excessive evaporation can quickly lead to reservoir dry out and overall device fail...
Article
Immunoassays represent a core workhorse methodology for many applications ranging from clinical diagnostics to environmental monitoring. In traditional formats such as the enzyme linked immunosorbent assay (ELISA), analytes are measured singly or in small sets. As more biomarkers are identified for disease states, there is a need to develop methods...
Conference Paper
Protein patterning is ubiquitous in the creation of sensing motifs that rely on receptor-ligand binding for selectivity. Autonomous micro-fluidic networks (FNs) have the potential to greatly aid in the development of simple, robust methods for deposition of biological capture agents onto a solid substrate. Unfortunately, FN-based micro-immunoassays...
Conference Paper
Controlled pumping of fluids through microfluidic networks is a critical step in many lab-on-a-chip applications. Traditional methods of fluid delivery, such as syringe pumps or electrokinetic phenomena, generally require bulky equipment that at a minimum is several orders of magnitude larger in size than the microfluidic network itself. Due to the...
Conference Paper
Optoelectronic enzymatic biosensors are a next generation biosensing technology that have been adroitly applied to sensing environmental contaminants such as dichloroethane (DCA). As environmental biosensing technology moves towards efficient in situ measurement methods, emphasis is focused not only on novel stratagems but also on iterative experim...
Conference Paper
Groundwater monitoring plays an important role in safeguarding our water supply, especially drinking water resources. Toluene and trichloroethylene (TCE) are two common groundwater contaminants, as well as critical contaminants in the National Primary Drinking Water Regulations. Traditional monitoring for groundwater contaminants usually involves f...
Article
Full-text available
A new micromixer incorporating integrated electrodes deposited on the bottom surface of a glass/PDMS microchannel is used to induce a localized, perpendicular electric field within pressure driven axial flow. The presence of the electric field drives electro-osmotic flow in the transverse direction along the channel walls, creating helical motion t...
Article
The following explores the issue of how reductions in contaminant loading to plumes will effect downgradient water quality. An idealized scenario of two adjacent layers of uniform geologic media, one transmissive and the other low permeability, is considered. A high concentration source, similar to a thin DNAPL pool, is introduced in the transmissi...
Article
Full-text available
The response of a compact photonic immunoassay biosensor based on a planar waveguide to variation in antigen (C-reactive protein) concentration as well as waveguide ridge height has been investigated. Near-field scanning optical microscope measurements indicate 1.7%nm and 3.3%nm top surface optical intensity modulation due to changes in effective a...
Article
Biomolecular patterning is essential for the creation of sensing motifs that rely on receptor-ligand binding for selectivity. Microfluidic devices have the potential to aid in the development of simple, robust methods for biomolecular patterning and therefore contribute to the generation of protein, DNA, and cell microarrays. In microfluidic patter...
Article
New high-throughput immunoassay methods for rapid point-of-care diagnostic applications represent an unmet need and current focus of numerous innovative methods. We report a new micromosaic competitive immunoassay developed for the analysis of the thyroid hormone thyroxine (T4), inflammation biomarker C-reactive protein (CRP), and the oxidative dam...
Conference Paper
A compact photonic immunoassay biosensor that can simultaneously sense multiple analytes has been implemented. NSOM results indicate 8% modulation of the local evanescent field due to an 18 nm biological adlayer on the waveguide's surface.
Article
Full-text available
Owing to the enhancement of surface effects at the micro-scale, patterned grooves on a micro-channel floor remain a powerful method to induce helical flows within a pressure driven system. Although there have been a number of numerical studies on geometrical effects concerning fluid mixing within the staggered herringbone mixer, all have focused ma...
Article
Low-cost, label-free immunoassay biosensors are needed for point-of-care clinical diagnostics, food safety, environmental monitoring, and biosecurity applications. A novel local, evanescent-field, array coupled (LEAC) photonic biosensor that can simultaneously sense multiple viruses, proteins, or DNA oligomers is being investigated. The sensing mec...
Article
A novel optical sensor is developed on the concept that the evanescent field surrounding the core of an appropriately designed waveguide can be very sensitive to the local refractive index of the cladding surrounding the core. The formation of a protein- or ssDNA-based adlayer via specific binding of an analyte target to one of several localized pa...
Article
As with their macroscale counterparts, laminar fluid mixing becomes a very important, albeit inherently difficult step at the microscale. Micromixers based on electro-osmotic flow (EOF) rely on either a modification of microchannel geometries or a modification of the zeta-potential of the microchannel surfaces to enhance fluid mixing. Here we prese...
Article
The need for a selective, multianalyte biosensor capable of detecting target molecules with high sensitivity has long been recognized. In this project, a novel means of detecting target affinity binding interactions is under development, whereby a shift in the evanescent wave surrounding the core of an ultra thin (< 1 micron) optical waveguide is m...
Article
The evanescent field of an appropriately designed waveguide can be very sensitive to the local refractive indices of the cladding layers surrounding the core. In this study, a planar waveguide has been fabricated on a chip that contains buried p-Si photo-detectors, located about 1 micron from the waveguide core and arrayed down the length of the wa...
Article
Full-text available
Computational fluid dynamics are applied to the study of three-dimensional fluid flow in a dense medium plasma reactor (DMPR) under different operating conditions. Reaction mechanisms and rates for the removal of methyl t-butyl ether (MTBE) in a DMPR are developed from experimental data to determine the plasma volume, the rate of interphase mass tr...
Article
A compact dielectric waveguide sensor with buried detector arrays, which demonstrates high optical sensitivity to thin biological adlayers, is designed and implemented. Real-time, reagent-less, multi-analyte sensing is possible with this device
Article
The response of a novel waveguide biosensor to 30 nm thick, ~1 mum diameter organic features is evaluated using near-field scanning optical microscopy and compared with numerical simulations
Article
Experiments on planar optical waveguide based local evanescent array coupled biosensors using low-index photoresist and polystyrene nanoparticle adlayers are reported. Near-field scanning optical microscopy measurements are in close agreement with beam propagation method simulations.
Article
Experiments have yielded a number of important insights into the energy distribution, sparging and oxidation of methyl tert-butyl ether (MTBE), benzene, ethylbenzene, toluene, m- and p-xylene, and o-xylene (BTEX) in a dense medium plasma reactor (DMPR). It has been found that the DMPR transferred a relatively small amount of electrical energy, appr...
Conference Paper
A concept for a novel, compact, immunoassay biosensor that can simultaneously sense multiple analytes simultaneously is being investigated. The dielectric planar waveguide sensor relies on modulation of the local evanescent field coupled into an array detector. Proof of concept experiments carried out using near-field scanning optical microscopy (N...
Article
Near-field scanning optical microscopy was used to image transient interference between the guided mode and a leaky mode induced in a single-mode waveguide due to a localized adlayer. The observed field response in the adlayer region as well as the period and decay length of the subsequent interference are in good agreement with beam propagation ca...
Article
Multiple modes are directly imaged in a silicon nitride waveguide bend using near-field scanning optical microscopy. Since the high order mode attenuates faster than the fundamental mode, a transient interference is observed. Local loss at the bend-to-straight waveguide interface is found and attributed to modal mismatch. The observations are in go...
Article
Near-field scanning optical microscopy (NSOM) is used to directly measure transient interference between a guided and step induced leaky mode in a single mode waveguide.Simulations are in good agreement with the observed results.
Article
The chemical vapor deposition of polycrystalline carbon nitride in stagnation flow reactors is simulated. A model is used to predict the gas phase chemistry, temperature and velocity profiles, potential gaseous film growth precursors, and to evaluate the likelihood of bond rearrangement occurring in the bulk phase or on the deposition surface once...
Article
A kinetic model to predict the time evolution of a β-SiC intermediate layer under the operating conditions of diamond nucleation in hot filament chemical vapor deposition reactors was developed. The evolution of the layer was calculated by accounting for gas-phase and surface reactions, surface and bulk diffusions, the mechanism for intermediate la...
Article
Reinfusion of shed blood during surgery could avoid the need for blood transfusions. Prior to reinfusion of the red blood cells, the shed blood must be washed in order to remove leukocytes, platelets, and other contaminants. Further, the hematocrit of the washed blood must be increased. The feasibility of using computational fluid dynamics (CFD) to...
Article
A novel waveguide sensor capable of sensing multiple analytes directly and in real time with label-free, local detection has been investigated. Numerical simulations agree with analytical calculations of the sensor sensitivity. The waveguide parameters including detector to core distance, adlayer length, and surface roughness have been extensively...
Article
The feasibility of using computational fluid dynamics to guide the design of better centrifuges for processing shed blood is explored here. The velocity field and the rate of protein removal from the shed blood have been studied. The results indicate that computational fluid dynamics could help screen preliminary centrifuge bowl designs thus reduci...
Article
Plasma treatment of contaminated water appears to be a promising alternative for the oxidation of aqueous organic pollutants. This study examines the kinetic and oxidation mechanisms of methyl tert-butyl ether (MTBE) in a dense medium plasma (DMP) reactor utilizing gas chromatography-mass spectrometry and gas chromatography-thermal conductivity tec...
Article
A diagonally implicit method is shown to be an effective method for integrating the multicomponent species conservation equations. The constitutive equation for multicomponent diffusion is recast into a form analogous to that for binary diffusion, except that the diffusion coefficient is replaced with a matrix of effective multicomponent diffusion...
Article
Inertial migration has been used to fractionate feed streams containing latex particles and sheep leukocytes. For latex particles, a purified stream of small particles, less than 4 m, was obtained. For sheep leukocytes, a stream containing almost no large leukocytes greater than 16 m was produced. The results obtained show that this method could be...
Article
A series of calculations has been carried out to examine the relationship between gas phase composition and film composition in diamond chemical vapor deposition. It is predicted that the ability to carry out in situ doping of films with N and S, and the inability to dope with O, can be explained from a simple thermodynamic perspective. Probable pr...
Article
A thermodynamic analysis has been applied to systematically study III–V semiconductor alloy deposition, including nitrides grown by metalorganic vapor phase epitaxy. The predicted solid compositions of a number of ternary and quaternary alloys, including AlxGa1−xPyAs1−y, are compared with experimental data. For phosphorus-containing alloys, introdu...
Article
The growth of β-SiC films via chemical vapor deposition (CVD) has been under intensive investigation because this is viewed to be an enabling material for a variety of new semiconductor devices in areas where silicon cannot effectively compete. However, the difficulty in achieving single-crystal or highly textured surface morphology in films with l...
Article
The shear induced inertial migration of a rigid sphere has been studies computationally by simulating the flow around a rigid sphere with a Fourier finite volume technique. The values of the lift force obtained by flow simulation have been compared with those predicted by asymptotic analyses for rotating and non-rotating spheres.