Mina Hoorfar

Microfluidics Integrated Biosensors: A Leading Technology towards Lab-on-a-Chip and Sensing Applications

A biosensor can be defined as a compact analytical device or unit incorporating a biological or biologically derived sensitive recognition element immobilized on a physicochemical transducer to measure one or more analytes. Microfluidic systems, on the other hand, provide throughput processing, enhance transport for controlling the flow conditions, increase the mixing rate of different reagents, reduce sample and reagents volume (down to nanoliter), increase sensitivity of detection, and utilize the same platform for both sample preparation and detection. In view of these advantages, the integration of microfluidic and biosensor technologies provides the ability to merge chemical and biological components into a single platform and offers new opportunities for future biosensing applications including portability, disposability, real-time detection, unprecedented accuracies, and simultaneous analysis of different analytes in a single device. This review aims at representing advances and achievements in the field of microfluidic-based biosensing. The review also presents examples extracted from the literature to demonstrate the advantages of merging microfluidic and biosensing technologies and illustrate the versatility that such integration promises in the future biosensing for emerging areas of biological engineering, biomedical studies, point-of-care diagnostics, environmental monitoring, and precision agriculture.

Online Drinking Water Quality Monitoring: Review on Available and Emerging Technologies

Online drinking water quality monitoring technologies have made significant progress for source water surveillance and water treatment plant operation. The use of these technologies in the distribution system has not been favorable due to the high costs associated with installation, maintenance, and calibration of a large distributed array of monitoring sensors. This has led to a search for newer technologies that can be economically deployed on a large scale. This paper includes a brief description of important parameters for drinking water and current available technologies used in the field. The paper also provides a thorough review of the advances in sensor technology for measurement of common water quality parameters (pH, turbidity, free chlorine, dissolved oxygen, and conductivity) in drinking water distribution systems.

Leakage detection and location in water distribution systems using a fuzzy-based methodology

Loss of water due to leakage is a common phenomenon observed practically in all water distribution systems (WDS). However, the leakage volume can be reduced significantly if the occurrence of leakage is detected within minimal time after its occurrence. This paper proposes a novel methodology to detect and diagnose leakage in WDS. In the proposed methodology, a fuzzy-based algorithm has been employed that incorporates various uncertainties into different WDS parameters such as roughness, nodal demands, and water reservoir levels. Monitored pressure in different nodes and flow in different pipes have been used to estimate the degree of membership of leakage and its severity in terms of index of leakage propensity (ILP). Based on the degrees of leakage memberships and the ILPs, the location of the nearest leaky node or leaky pipe has been identified. To demonstrate the effectiveness of the proposed methodology, a small distribution network was investigated which showed very encouraging results. The proposed methodology has a significant potential to help water utility managers to detect and locate leakage in WDS within a minimal time after its occurrence and can help to prioritise leakage management strategies.

Two-dimensional flow dynamics in digital microfluidic systems

A two-dimensional model for the fluid flow in a digital microfluidic system is introduced, and the results are compared to experimental data. Resistive flow effects based upon contact line forces, filler effects and shear forces are applied in the model. It is found that the induced vertical velocity components are critical to the overall motion, as velocity and pressure gradients, together with microdroplet surface deformations, can limit the desired horizontal velocity. These effects are particularly important for digital microfluidic systems characterized by higher Reynolds numbers.

Systematic analysis of geometrical based unequal droplet splitting in digital microfluidics

This paper presents the thorough analysis of a new operator developed for unequal droplet splitting by geometrical modification of a conventional electrode in digital microfluidic (DMF) platforms. This operator functions in an area as small as the size of a conventional electrode divided into several smaller sub-electrodes addressable independently. Using this operator, droplets can be precisely split unequally with a high volume ratio, as well as being dispensed with a wide range of sizes from a reservoir. This operator functions without complications in the fabrication process and the need for additional external modules such as feedback control systems. To characterize the range of the applicability of this operator, the effects of the applied voltage, the gap height between the two plates, and the sub-electrode geometry on the splitting performance are studied. For high applied voltages, splitting is performed with an error close to 5% (similar to the splitting precision obtained in conventional DMF devices); whereas, for voltages close to the threshold value, the error is less than 1%. In this way the droplet size becomes fairly independent of the geometry and the gap height. The threshold splitting voltage versus gap height has also been studied and shows a linear behavior, facilitating the selection of proper voltages for high precision splitting. For the three sub-electrode patterns studied here (i.e. square, horizontal stripe, and vertical stripe), the results show that the square sub-electrodes provide higher reliability and a wider range of sizes for the split droplet as compared to the other patterns. The final part of the study illustrates that there is a linear relation between the area of the split droplets and the number of actuated sub-electrodes. This linear behavior allows for the selection of an appropriate number of the sub-electrodes to be actuated based on the desired volume of the droplet.

Evaluating Water Quality Failure Potential in Water Distribution Systems: A Fuzzy-TOPSIS-OWA-based Methodology

The goal of a water distribution system (WDS) is to deliver safe water with desirable quality, quantity and continuity to the consumers. In some cases, a WDS fails to deliver safe water due to the compromise/ failure of water quality which may have devastating consequences. The frequency and consequence of a water quality failure (WQF) can be reduced if prognostic analysis and necessary remedial measures are taken on time. This study developed a prognostic model to predict WQF potential in a WDS. The study identifies important factors (parameters) which can directly and/or indirectly linked to WQFs. These factors are classified into two groups—the causes of WQF such as lack of free residual chlorine, or excess of total organic carbon, and the symptoms of WQF such as taste & odor, color which are in fact the effects of certain causes of WQF. The interrelationships among the symptoms and the causes have been established based on extensive literature review and elicited expert opinion. A fuzzy-TOPSIS-OWA-based model has been developed to identify the impacts of different influencing parameters on the overall WQF potential. The developed model has been implemented for a WDS in Quebec City (Canada). To study the impacts of uncertainties of the influencing factors, a Monte Carlo simulation-based sensitivity analysis has been carried out. It is anticipated that the developed model can help water utilities to understand the role of different factors on WQF.

Evidential reasoning using extended fuzzy Dempster–Shafer theory for handling various facets of information deficiency

This work investigates the problem of combining deficient evidence for the purpose of quality assessment. The main focus of the work is modeling vagueness, ambiguity, and local nonspecificity in information within a unified approach. We introduce an extended fuzzy Dempster–Shafer scheme based on the simultaneous use of fuzzy interval‐grade and interval‐valued belief degree (IGIB). The latter facilitates modeling of uncertainties in terms of local ignorance associated with expert knowledge, whereas the former allows for handling the lack of information on belief degree assignments. Also, generalized fuzzy sets can be readily transformed into the proposed fuzzy IGIB structure. The reasoning for quality assessment is performed by solving nonlinear optimization problems on fuzzy Dempster–Shafer paradigm for the fuzzy IGIB structure. The application of the proposed inference method is investigated by designing a reasoning scheme for water quality monitoring and validated through the experimental data available for different sampling points in a water distribution network.

Ultra-Portable Smartphone Controlled Integrated Digital Microfluidic System in a 3D-Printed Modular Assembly

Portable sensors and biomedical devices are influenced by the recent advances in microfluidics technologies, compact fabrication techniques, improved detection limits and enhanced analysis capabilities. This paper reports the development of an integrated ultraportable, low-cost, and modular digital microfluidic (DMF) system and its successful integration with a smartphone used as a high-level controller and post processing station. Low power and cost effective electronic circuits are designed to generate the high voltages required for DMF operations in both open and closed configurations (from 100 to 800 V). The smartphone in turn commands a microcontroller that manipulate the voltage signals required for droplet actuation in the DMF chip and communicates wirelessly with the microcontroller via Bluetooth module. Moreover, the smartphone acts as a detection and image analysis station with an attached microscopic lens. The holder assembly is fabricated using three-dimensional (3D) printing technology to facilitate rapid prototyping. The holder features a modular design that enables convenient attachment/detachment of a variety of DMF chips to/from an electrical busbar. The electrical circuits, controller and communication system are designed to minimize the power consumption in order to run the device on small lithium ion batteries. Successful controlled DMF operations and a basic colorimetric assay using the smartphone are demonstrated.

A dielectrophoretic-gravity driven particle focusing technique for digital microfluidic systems

In the present study, a particle focusing technique functioning based on the cumulative effects of gravity and negative dielectrophoresis (nDEP) is developed for digital microfluidic (DMF) systems. This technique works using the conventional electrodes used for droplet manipulation without a need for geometrical modification. Particle manipulation is performed by applying an AC voltage to the electrode above which there is the droplet containing the non-buoyant particles. The particles sediment due to the difference between the gravitational and the vertical component of the nDEP forces, while the horizontal component of the nDEP force concentrates them on the center of the electrode. Therefore, the magnitude of the voltage must be kept within an effective range to have simultaneous effects of sedimentation (dominated by gravity) and concentration (due to the horizontal component of the nDEP force). The physics of the phenomenon is explained using simulation. The effects of the magnitude of the applied vo...

Comparative study of fuzzy evidential reasoning and fuzzy rule-based approaches: an illustration for water quality assessment in distribution networks

This paper presents the use of two multi-criteria decision-making (MCDM) frameworks based on hierarchical fuzzy inference engines for the purpose of assessing drinking water quality in distribution networks. Incommensurable and uncertain water quality parameters (WQPs) at various sampling locations of the water distribution network (WDN) are monitored. Two classes of WQPs including microbial and physicochemical parameters are considered. Partial, incomplete and subjective information on WQPs introduce uncertainty to the water quality assessment process. Likewise, conflicting WQPs result in a partially reliable assessment of the quality associated with drinking water. The proposed methodology is based on two hierarchical inference engines tuned using historical data on WQPs in the WDN and expert knowledge. Each inference engine acts as a decision-making agent specialized in assessing one aspect of quality associated with drinking water. The MCDM frameworks were developed to assess the microbial and physicochemical aspects of water quality assessment. The MCDM frameworks are based on either fuzzy evidential or fuzzy rule-based inference. Both frameworks can interpret and communicate the relative quality associated with drinking water, while the second is superior in capturing the nonlinear relationships between the WQPs and estimated water quality. More comprehensive rules will have to be generated prior to reliable water quality assessment in real-case situations. The examples presented here serve to demonstrate the proposed frameworks. Both frameworks were tested through historical data available for a WDN, and a comparison was made based on their performance in assessing levels of water quality at various sampling locations of the network.