Tao Dong

Capacitance variation induced by microfluidic two-phase flow across insulated interdigital electrodes in lab-on-chip devices

Microfluidic two-phase flow detection has attracted plenty of interest in various areas of biology, medicine and chemistry. This work presents a capacitive sensor using insulated interdigital electrodes (IDEs) to detect the presence of droplets in a microchannel. This droplet sensor is composed of a glass substrate, patterned gold electrodes and an insulation layer. A polydimethylsiloxane (PDMS) cover bonded to the multilayered structure forms a microchannel. Capacitance variation induced by the droplet passage was thoroughly investigated with both simulation and experimental work. Olive oil and deionized water were employed as the working fluids in the experiments to demonstrate the droplet sensor. The results show a good sensitivity of the droplet with the appropriate measurement connection. This capacitive droplet sensor is promising to be integrated into a lab-on-chip device for in situ monitoring/counting of droplets or bubbles.

A Capacitive Touch Screen Sensor for Detection of Urinary Tract Infections in Portable Biomedical Devices

Incidence of urinary tract infections (UTIs) is the second highest among all infections; thus, there is a high demand for bacteriuria detection. Escherichia coli are the main cause of UTIs, with microscopy methods and urine culture being the detection standard of these bacteria. However, the urine sampling and analysis required for these methods can be both time-consuming and complex. This work proposes a capacitive touch screen sensor (CTSS) concept as feasible alternative for a portable UTI detection device. Finite element method (FEM) simulations were conducted with a CTSS model. An exponential response of the model to increasing amounts of E. coli and liquid samples was observed. A measurable capacitance change due to E. coli presence and a tangible difference in the response given to urine and water samples were also detected. Preliminary experimental studies were also conducted on a commercial CTSS using liquid solutions with increasing amounts of dissolved ions. The CTSS was capable of distinguishing different volumes of liquids, also giving an exponential response. Furthermore, the CTSS gave higher responses to solutions with a superior amount of ions. Urine samples gave the top response among tested liquids. Thus, the CTSS showed the capability to differentiate solutions by their ionic content.

Development and optimization of an integrated capillary-based opto-microfluidic device for chemiluminescence quantitative detection

A capillary-action driven device amenable for integration of organic photodiodes (OPDs) was developed for monitoring parallel chemiluminescence (CL) reactions. Device characterization was conducted using finite element method (FEM) simulations. Definition of the simulation setup, dimensional optimization of the reaction chamber and overall geometrical characterization of the microfluidic device were the main simulation results. Furthermore, a non-uniform filling process was observed during the final simulation of the capillary device. Validation of this result and the proposed capillary-driven filling process was later confirmed by experimental results. Experimental testing performed on a single chamber defined an optimal exposure time to the luminescent substrate of 5 min, indicating a quick analyte detection time. Further tests using one chamber presented a linear relation between the signal-to-noise ratio and increasing concentrations of the protein used. A measured limit of detection of 28 nM was obtained for streptavidin. Regarding the tests performed on the whole device, acceptable values of 39 s ± 5 s were obtained for the luminescent substrate total filling times. Also, the microfluidic device showed the capability to perform a quantitative detection of the occurring CL reactions. Weaker optical signals, due to the occurrence of CL reactions, were detected in the chambers with a later filling process, as predicted by simulation results. Notwithstanding these results, the capillary-based device is promising for quantitative detection of proteins in future point-of-care systems, presenting an unprompted filling process and parallel quantitative detection capability.

Modelling and design of a capacitive touch sensor for urinary tract infection detection at the point-of-care

Due to great use of touchscreens in mobile telephones and other electronic devices, there has been great evolution in this technology. Its wide applicability makes the touch sensor technology suitable for detection of specific components in urine, responsible for urinary tract infection (UTI). Integration of a touch sensor in a disposable probe tip to be used in UTI detection represents a powerful tool to develop new point-of-care testing (POCT) devices. The simplified structure of an electrodes array touch screen was simulated using the software COMSOL Multiphysics to prove that capacitive based touch screens can be used for detection of UTI. Besides we assumed presence of E.coli, one of the major causes of UTI urine. Results show that global capacitance increases if an E.coli sphere is present near the active electrodes, remaining approximately constant when further apart electrodes are excited. The output simulated voltage varies according to the capacitance value, decreasing when the capacitance is increased.

Quantitative detection of Escherichia coli and measurement of urinary tract infection diagnosis possibility by use of a portable, handheld sensor

Electrochemical nitrite sensor was used to quantitatively detect the nitrite concentration in urine and by building the approximate relationship between the nitrite concentration and number of E.coli bacterias, electrochemical nitrite sensor can count the numbers of Escherichia coli and do the Urinary Tract Infection (UTI) Diagnosis. Electrochemical nitrite sensor was assembled and calibrated, the artificial urine sample was detected; the feasibility of electrochemical nitrite sensor including the errors effect had been checked and proved at around -5.1~2.3%; the possibility to detect artificial UTI urine sample out is around 95.5%; the approximate relationship between the number of E.coli and electrode potential had been built as E=228.3193-3.78225×Ln (N+2.29101e6), thereby building the relationship between UTI possibilities and the measurement. Finally, the conception and design of electrochemical sensor array had been made, thus to measure different biomarkers for the maximum possibilities of UTI and can show the data of the possibility of UTI directly on the screen. Furthermore, it can easily be used and transported for the home-users or patients in hospitals.

Smartphone-Based Rapid Screening of Urinary Biomarkers

An ambulatory pre-screening Point-of-Care (POC) device compatible with commercially available diapers has been developed to rapidly screen urine samples for incontinent or functionally impaired elderly. This POC device consists of a set of colorimetric reaction pads with accompanying reference colors. A smartphone with camera is a convenient tool for analysis of colorimetric assays; and a software application has been developed for smartphones to photograph the colorimetric assay and classify colorimetric reactions according to the reference colors. To facilitate detection of multiple biomarkers, e.g., 12 biomarkers with 2–7 references per biomarker, automatic localization of test/reference pads has been implemented through recognition of corner alignment marks and projective coordinate transformation for perspective removal. Each test run trains a set of classifiers from extracted reference data, which is used to classify the extracted test data. The smartphone application gives semi-quantitative results and functions independently of illumination intensity, illumination color, device type (smartphone brand/model), device settings (ISO, shutter speed, aperture) and automatic camera preprocessing. The smartphone application has been tested successfully on Samsung Galaxy S3, S6 Edge, S7 Edge, ZTE Nubia V7 mini and Iphone 6 in various illumination conditions.

A smart phone-based robust correction algorithm for the colorimetric detection of Urinary Tract Infection.

This paper presents the preliminary work of developing a smart phone based application for colorimetric detection of Urinary Tract Infection. The purpose is to make a smart phone function as a practical point-of-care device for nurses or medical personnel without access to strip readers. The main challenge is the constancy of camera color perception across different illuminations and devices, which is the first step towards a practical solution without additional equipment. A reported black and white reference correction and a comprehensive color image normalization have been utilized in this work. Comprehensive color image normalization appears to be quite effective at correcting the difference in perceived color due to different illumination, and is therefore a candidate for inclusion in the further work.

Counting of water-in-oil droplets for targeted drug delivery systems using capacitive sensing technique

Droplet-based microfluidics has drawn attention of scientists due to its broad applicability in medical devices for targeted drug delivery. The use of microfluidic droplets has several advantages, among which reduction of reagents volumes is one of the most important. We propose a low-cost sensor system based on capacitive sensing technique for monitoring of water droplets that can be incorporated in existing lab-on-chip devices. The sensing unit is composed of gold interdigital electrodes (IDEs) patterned on top of a glass substrate. There is an insulation layer to avoid cross contamination of fluids and a PDMS cover to form the microchannel. The sensor was tested for detection of water-in-oil droplets and main experimental results show that presence of water droplets will induce an increase in measured voltage due to higher relative permittivity of water when compared to oil. A LABVIEW interface allows real time visualization of signals and counting of droplets.

Microfluidic paper-based analytical devices for colorimetric detection of urinary tract infection biomarkers on adult diapers.

Urinary tract infections (UTI) are common infection diseases in elderly patients. The conventional method of detecting UTI involves the collection of significant urine samples from the elderly patients. However, this is a very difficult and time-consuming procedure. This paper addresses the development of a microfluidic paper-based analytical device (μPAD) to detect UTI from urine collected from adult diapers. The design and fabrication for the μPAD is shown. The fabrication process involves melting solid wax on top of filter paper using a hot plate, followed by pattern transfer using a mold with rubbed wax. To demonstrate the feasibility of the proposed method, the μPAD with deposited nitrite reagent had detected different concentrations of nitrite solutions from 0.5 ppm to 100 ppm spiked in urine samples. A calibration curve was obtained by plotting the gray scale intensity values against the various nitrite concentrations. The results showed that the proposed paper-based device holds great potential as low-cost, disposable solution to sensitively detect UTI markers in urine sampled from diapers.Urinary tract infections (UTI) are common infection diseases in elderly patients. The conventional method of detecting UTI involves the collection of significant urine samples from the elderly patients. However, this is a very difficult and time-consuming procedure. This paper addresses the development of a microfluidic paper-based analytical device (μPAD) to detect UTI from urine collected from adult diapers. The design and fabrication for the μPAD is shown. The fabrication process involves melting solid wax on top of filter paper using a hot plate, followed by pattern transfer using a mold with rubbed wax. To demonstrate the feasibility of the proposed method, the μPAD with deposited nitrite reagent had detected different concentrations of nitrite solutions from 0.5 ppm to 100 ppm spiked in urine samples. A calibration curve was obtained by plotting the gray scale intensity values against the various nitrite concentrations. The results showed that the proposed paper-based device holds great potential as low-cost, disposable solution to sensitively detect UTI markers in urine sampled from diapers.

An Experimental Study on capacitive touch sensor's response to E. coli bacteria

Escherichia coli or E. coli is the dominant pathogen in Urinary Tract Infections (UTIs) in more than 80 % of the cases. Laboratory urine culture is the standard detection method which is expensive and time consuming. This paper studies the possibility of using a capacitive sensor to diagnose UTIs. Experimental tests were carried out to investigate the touch sensors response to artificially prepared E.coli sample. The capacitive touch sensor gave a consistent result that could be used to design a portable diagnostic device for early detection of UTIs. An exponential response was observed to increasing volume (up to 100 microliter) and E.coli presence in the sample. When the volume reached 100 microliter, the capacitance in average RAW Count Difference value became constant. Urine sample mixed with liquid E. coli gave the highest capacitance change (in average RAW Count Difference value) and the sensitivity at 100 microliter was found to be 22 counts per picofarad (pF).