Microfluidics for Biosensing and Diagnostics

Efforts to miniaturize sensing and diagnostic devices and to integrate multiple functions into one device have caused massive growth in the field of microfluidics and this integration is now recognized as an important feature of most new diagnostic approaches. These approaches have and continue to change the field of biosensing and diagnostics. In this Special Issue, we present a small collection of works describing microfluidics with applications in biosensing and diagnostics

Developing a spectral and colorimetric database of artist paint materials

As the project of the author\u27s Master\u27s thesis, the development of a spectral and colorimetric database of artist paint materials for acrylic paints was started. The goal of this research project was to: - provide the academic resource of colorant spectral characteristics - give scientifc explanations on various paint-particular phenomena (paint mixing, gloss effects and color gamut expansion by varnishing) These tasks were planned to satisfy possible interests on paint research from not only conservators in museums but also color educators in schools and color reproduction engineers in imaging companies

Biosensing by “Growing” Antennas and Error-correcting Codes

Food-borne disease outbreaks not only cause numerous fatalities every year but also contribute to significant economic losses. While end-to-end supply chain monitoring can be one of the keys to preventing these outbreaks, screening every food product in the supply chain is not feasible considering the sheer volume and prohibitive test costs. Fortunately, two converging economic trends promise to make this end-to-end supply chain monitoring possible. The first trend is that passive radio-frequency identification (RFID) tags and quick response (QR) codes are now widely accepted for food packaging. The second trend is that smartphones are now equipped with the capability to interrogate RFID tags or to decode QR codes. Together, they have opened up the possibility of monitoring food quality by endowing these tags and error-correcting codes with the capability to detect pathogenic contaminants. This dissertation investigates a biosensing paradigm of growing\u27\u27 transducer structures, such as RFID tags and QR codes, which is triggered only when analytes of interest are present in the sample. This transducer growth or self-assembly process relies on a silver enhancement technique through which silver ions reduce into metallic form in the presence of a target analyte, which in turn leads to changes in electrical or optical properties. By exploiting this, we first demonstrate two remote biosensor platforms, a RFID tag-based biosensor and a QR code-based biosensor, respectively. For the RFID-based biosensor, a chain of silver-shelled particles is assembled during the analyte detection process, which directly modulates the antenna\u27s effective impedance, and hence leads to an improvement in the tag\u27s reflection efficiency. For the QR code-based biosensor, the operating principle relies on the optical absorption changes resulting from silver enhancement. The target detection process assembles an invalid code-word into a valid QR code. This self-assembly sensing approach should produce few false positives since it is a process which transits from a high entropy state (disassembled transducer) to a low entropy state (assembled transducer). While there can be numerous states of a disassembled transducer structure, there are only a few configurations representing the assembled transducer state. Given that there are no active power sources on the RFID tag or the QR code, it is challenging for the proposed biosensors to perform sample acquisition and pre-processing since they are envisioned to be embedded inside food packages eventually. Paper-based microfluidics have been explored and integrated on the biosensors to provide a self-powered approach for reagent sampling and processing. One use case is to trigger target detection remotely by an end consumer. Thermal absorption properties of graphite have been exploited such that the end user can initiate the process of analyte sampling in paper-based biosensors by shining a beam of light on the sensor

FROM DOCUMENTATION IMAGES TO RESTAURATION SUPPORT TOOLS: A PATHFOLLOWING THE NEPTUNE FOUNTAIN IN BOLOGNA DESIGN PROCESS

The sixteenth-century Fountain of Neptune is one of Bologna's most renowned landmarks. During the recent restoration activities of the monumental sculpture group, consisting in precious marbles and highly refined bronzes with water jets, a photographic campaign has been carried out exclusively for documentation purposes of the current state of preservation of the complex. Nevertheless, the highquality imagery was used for a different use, namely to create a 3D digital model accurate in shape and color by means of automated photogrammetric techniques and a robust customized pipeline. This 3D model was used as basic tool to support many and different activities of the restoration site. The paper describes the 3D model construction technique used and the most important applications in which it was used as support tool for restoration: (i) reliable documentation of the actual state; (ii) surface cleaning analysis; (iii) new water system and jets; (iv) new lighting design simulation; (v) support for preliminary analysis and projectual studies related to hardly accessible areas; (vi) structural analysis; (vii) base for filling gaps or missing elements through 3D printing; (viii) high-quality visualization and rendering and (ix) support for data modelling and semantic-based diagrams

Porous Silicon Photonics for Label-Free Interferometric Biosensing and Flat Optics

This dissertation uses porous silicon as a material platform to explore novel optical effects in three domains: (i) It studies dispersion engineering in integrated waveguides to achieve high performance group index sensing. With proper design parameters, the sensor waveguides can theoretically achieve 6 times larger group index shift compared to the actual bulk effective refractive index shift. We demonstrate the guided mode confinement factor to be a key parameter in design and implementation of these waveguides. (ii) It explores multicolor laser illumination to experimentally demonstrate perceptually enhanced colorimetric sensing, overcoming the limitations faced by many contemporary colorimetric sensors. Our technique allows our sensor to achieve ~ 7 to 30 times higher sensitivities and ~ 30 to 1000 times lower limits of detection compared to current colorimetric sensors. (iii) It develops a novel imprinting technique to laterally pattern arbitrary refractive index on the porous silicon surface to realize nanoscale flat optical components. We demonstrate and characterize imprinted flat lens arrays and show how myriads of possible applications are to be implemented using this nanoimprinting technique. While the material primarily used in this dissertation is porous silicon, many of the demonstrated techniques are generalizable and can be extended towards other materials of interest to achieve high performance patterning and sensing

Point-of-care immunoassay system using carbon nanotube labels

The goal of this research was to develop enhanced signal detection mechanisms for immunosensing using carbon nanotubes (CNTs). The utilization of CNT labels for direct electrical measurement was implemented on lateral flow system and microfluidic integrated interdigitated array microelectrodes. These sensing mechanisms in simple and miniaturized system provided higher sensitivity and autonomous flow control for rapid detection aimed at point-of-care diagnostics. Specific functionalization protocols were carried out to chemically modify the surface of the CNTs for uniform dispersion and antibody conjugation in aqueous solution. Surfactant assisted dispersion of the CNTs was studied using PVP and PEG. Covalent conjugation of antibodies on the carboxyl groups of the CNTs was accomplished using EDC/Sulfo-NHS coupling chemistry. The adsorption of surfactant and antibodies were manipulated in order to optimize immunoassay detection capability based on electrical measurements. Following surface functionalization methods, CNTs as a sensing label were employed on a lateral flow system. Competitive and sandwich immunoassay formats were demonstrated based on antibody and antigen binding. The lateral flow system was used for immobilization of capture molecules and passive sample transport by capillary action. CNTs conjugated to antibodies formed conductive network at the capture zone providing a visual indication corresponding to the amount of binding. Most importantly, significant change in electrical conductance was measured for varying low antigen concentrations, detecting anti-human Immunoglobulin G concentration below 1 ng/ml. Research was also conducted to obtain on-chip immunoassay detection using CNT labels. An IDA microelectrode was used as a binding surface and integrated within a PDMS microfluidic system. The sample and reagents were delivered to the sensing area through a microchannel. The capture of target analyte was indicated by the conjugated CNTs that formed a conducting matrix across the IDA. The detection was based on the selective binding between HSA and anti-HSA, where the conductimetric signal of the binding reaction was monitored through the IDA. The developed miniaturized system provided simple and sensitive immunosensing with detection capability below 1 ng/ml concentration using only 5 ìl of sample volume. Simulation was performed in order to understand the influence of the parameters in the microfluidic detection system

Resonant sensors for passive, real-time, and wireless characterization of biological analytes

A passive, low-cost resonant sensor was developed with the potential application of wireless monitoring of hydrolytic enzyme activity in closed systems. The resonators are rapidly prototyped from polyimide substrates (25õm thickness) which are coated with a thin layer of copper (35õm thickness). The patterns of the resonators, which are Archimedean spirals, are drawn on these substrates using an indelible marker with an XY plotter. These substrates are etched with a solution containing hydrogen peroxide and hydrochloric acid in order to remove the undesired copper. The initial resonant frequency of these resonators can be controlled by the Archimedean coil length and pitch size of the spiral. The frequency response window is tuned for the 1-100 MHz range for better penetration through soil, water, and tissue. The resonant frequency can be measured up to 5cm stand-off distance by a 3D-printed coplanar, two-loop coil reader antenna. This reader is attached to a vector network analyzer for monitoring the magnitude of S21 scattering parameter. The central hypothesis is that the Archimedean spiral sensors respond to any change in relative permittivity of the medium in contact with the resonator. This response is represented as a clear shift in the resonant frequency of the resonator. For instance, changing the medium from air to water results in approximately 50MHz redshift in the resonant frequency. In order to measure hydrolytic enzyme activity, the resonant sensors are coated by an enzyme substrate (e.g. hydrogel). The degradation of the enzyme substrate causes a change in the relative permittivity which results in a shift in the resonant frequency (up to 7MHz redshift). By fitting a transport-reaction model, which simulates the radial digestion profile, on the experimental data the activity (turnover rate, or kcat value) of the enzyme is calculated. This approach is used for testing purified Subtilisin A and unpurified bacterial protease samples at different concentrations ranging from 30mg/ml to 200mg/ml with kcat values of 0.003-0.002 and 0.009-0.004 gsubstrate/genzyme per second, respectively. The sensor response rate can be tuned by changing the substrate composition (i.e. changing the gelatin and glycerol plasticizer weight percentage in the hydrogel). Finally, the applicability of these resonant sensors in a real-life problem is demonstrated by wirelessly measuring the proteolytic activity of farm soil with a measured kcat of 0.00152 gsubstrate/(gsoil÷s) using 3D-printed plastic cases

A Portable Colorimetric Sensing Platform for the Evaluation of Carbon Dioxide in Breath

abstract: This work describes the development of a device for measuring CO2 in breath, which has applications in monitoring a variety of health issues, such as Chronic Obstructive Pulmonary Disease (COPD), asthma, and cardiovascular disease. The device takes advantage of colorimetric sensing technology in order to maintain a low cost and high user-friendliness. The sensor consists of a pH dye, reactive element, and base coated on a highly porous Teflon membrane. The transmittance of the sensor is measured in the device via a simple LED/photodiode system, along with the flow rate, ambient relative humidity, and barometric pressure. The flow is measured by a newly developed flow meter described in this work, the Confined Pitot Tube (CPT) flow meter, which provides a high accuracy with reduced flow-resistance with a standard differential pressure transducer. I demonstrate in this work that the system has a high sensitivity, high specificity, fast time-response, high reproducibility, and good stability. The sensor has a simple calibration method which requires no action by the user, and utilizes a sophisticated, yet lightweight, model in order to predict temperature changes on the sensor during breathing and track changes in water content. It is shown to be effective for measuring CO2 waveform parameters on a breath-by-breath basis, such as End-Tidal CO2, Alveolar Plateau Slope, and Beginning Exhalation Slope.Dissertation/ThesisDoctoral Dissertation Chemical Engineering 201

In Situ Scanning Probe Techniques for Evaluating Electrochemical Systems

Falling technology costs are allowing renewable sources of energy to become increasingly more competitive with fossil fuel-based sources. However, challenges still remain in the widespread deployment of sources like wind and solar due to their intermittent nature and cost-prohibitive storage options. An attractive solution to address these issues is by using renewably derived energy to drive electrolysis reactions that generate useful chemicals and fuels. In order to do this effectively and economically, efficient and durable electrocatalysts are needed for the reactions of interest, such as hydrogen production from water electrolysis. Presently, the best catalysts for this process are noble metals such as platinum, which are expensive and in limited supply. The discovery and mechanistic understanding of earth abundant materials that can also efficiently catalyze these reactions remains a current research focus. Scanning probe microscopy (SPM) techniques can be used to aid in the discovery of these materials, as they are able to investigate catalyst surfaces in situ and at a higher resolution than conventional 3-electrode electroanalytical methods. This dissertation explores the use of two in situ SPM techniques, scanning electrochemical microscopy (SECM) and scanning photocurrent microscopy (SPCM), for evaluating both photocatalytic and electrocatalytic electrochemical systems. Three different studies that use these two techniques were carried out over the duration of my thesis work and are presented in Chapters 2 through 4. After providing an overview of solar fuels and SPM techniques in Chapter 1, Chapter 2 describes the design considerations, implementation and demonstration of a home-built SECM instrument for use with nonlocal continuous line probes (CLPs) that can achieve high areal imaging rates with compressed sensing (CS) image reconstruction. The CLP consists of an electroactive band electrode sandwiched between two insulating layers, where one of the insulating layers needs to be on the same length scale as the band electrode because it determines the average separation distance from the band electrode to the substrate. Similarly, the spatial resolution of the CLP is determined by the thickness of the band and the realizable imaging rate is determined by its width and linear scan rate. Like conventional SECM systems, a combination of linear motors and a bipotentiostat is needed. However, for the CLP-SECM system both linear and rotational motors are needed to scan at different substrate angles to obtain the necessary raw signal to reconstruct the target electrochemical image with CS algorithms. Detailed descriptions of the microscope design, CLP fabrication, and the procedures necessary to carry out the CLP-SECM imaging are given in this chapter. Measurements with this novel CLP-SECM microscope are done with flat platinum disk electrode samples of varying sizes. A substrate-generation-probe-collection mode is used during the SECM linescan measurements to illustrate procedures for position calibration of the system, CLP and substrate cleaning, as well as verifying the sensitivity along the length of the CLP. Finally, linescans over a three disk platinum sample were taken and CS image reconstruction was done, with as few as three linescans, to demonstrate the order of magnitude time advantage of this approach over conventional SECM scanning methods. In Chapter 3, colorimetric imaging studies are done using a pH dye indicator to visualize the plume of electroactive species that is generated during in situ SECM measurements for both conventional and CLP-SECM systems. In SECM, the signal recorded by the probe is facilitated by transport of electroactive species and not by direct contact between the probe and the substrate, which is typical of many scanning probe microscopy (SPM) techniques. One of the complexities with SECM is being able to fully understand the interaction between the electroactive species generated at the substrate and the probe. Thus in order to understand this further, a pH indicator dye is used to visualize pH gradients associated with the hydrogen product plume generated by water electrolysis during in situ SECM measurements. The in situ colorimetric experiments are then used to inform assumptions about the system and validate simulations using finite element modeling software. From this study, we are able to develop quantitative relationships to describe how the plume of electroactive species influences the recorded current at the probe for different probe geometries. Finally, we use this initial study as groundwork for investigating the influence of higher probe scan speeds where convection starts to play a role on the distortion of the signal and plume dynamics, and how it can be corrected using CS post-processing methods. Lastly, SPCM is employed in Chapter 4 to study the optical efficiency losses due to varying size bubbles on a photoelectrode surface. Individual single hydrogen bubbles ranging from 100 µm to 1000 µm were generated on a photoelectrode surface and a laser was used to scan over single isolated bubbles to create localized optical efficiency maps based on photocurrent and external quantum efficiency (EQE). Moreover, a ray-tracing model based on Snell’s law was also constructed to compare to experimental SPCM linescans. This model showed very good agreement to the experimental SPCM linescan results. This investigation showed that larger bubbles lead to higher optical efficiency losses, not only due to higher inactive electrochemically active surface areas (ECSAs) but also due to a larger region of total internal reflection of light from the edge regions of bubbles. A macroscale study over a large photoelectrode surface was also done where the images of the surface were taken while the “sawtooth” was measured under AM1.5 illumination. Consequently, a predictive current−time profile was generated from the single bubble SPCM empirical relationship between bubble size and optical losses and was compared to the experimental measurement. Understanding how bubbles can impact the efficiency of the overall system is important, as bubbles in a system and on an electrode surface increases ohmic resistances, optical losses, and kinetic losses. Overall, this study can be used as a starting point for designing systems, electrolyte, and catalyst surfaces to improve one or more of the aforementioned losses