Electroosmotic flow of non-Newtonian fluids in a constriction microchannel.

Insulator-based dielectrophoresis has to date been almost entirely restricted to Newtonian fluids despite the fact that many of the chemical and biological fluids exhibit non-Newtonian characteristics. We present herein an experimental study of the fluid rheological effects on the electroosmotic flow of four types of polymer solutions, i.e., 2000 ppm xanthan gum (XG), 5% polyvinylpyrrolidone (PVP), 3000 ppm polyethylene oxide (PEO), and 200 ppm polyacrylamide (PAA) solutions, through a constriction microchannel under DC electric fields of up to 400 V/cm. We find using particle streakline imaging that the fluid elasticity does not change significantly the electroosmotic flow pattern of weakly shear-thinning PVP and PEO solutions from that of a Newtonian solution. In contrast, the fluid shear-thinning causes multiple pairs of flow circulations in the weakly elastic XG solution, leading to a central jet with a significantly enhanced speed from before to after the channel constriction. These flow vortices are, however, suppressed in the strongly viscoelastic and shear-thinning PAA solution.

Sample preconcentration from dilute solutions on micro/nanofluidic platforms: A review.

Biochemical detection plays a critical role in many analytical fields. For example, blood samples include many proteins with relevance to disease diagnosis and therapeutic monitoring. Foods and beverages contain a large number of chemicals and compounds which must be quantified and characterized to ensure their compliance with safety standards. Detecting trace amounts of contaminants in ambient air or water samples is essential in monitoring the environment and protecting human health. Therefore, effective techniques for performing the rapid and reliable detection of targeted analytes are required. Compared to conventional macroscale devices, microfluidic systems have many advantages, including a greater sensitivity, a faster response time, a reduced sample and reagent consumption, and a greater portability. Accordingly, many microfluidic systems for sample detection have been proposed in recent years. The performance of such devices relies on the target analyte being present in a sufficient concentration to enable its detection. In many biomedical, food testing and environmental applications, the detection limit was restricted. Thus, the sample must first be concentrated before the detection process is carried out. Accordingly, this review provides a comprehensive review of recent advances for sample preconcentration with emphasis on utilizing ion concentration polarization (ICP) effects in micro/nanofluidics platforms. We start with a brief introduction regarding the importance of preconcentration using micro/nanofluidics platforms, followed by in-depth discussions of the ICP effects for the preconcentration and applications to biomedical analysis, food testing and environmental monitoring. Finally, the article concludes with a brief perspective on the future development of the field.

Particles small angle forward-scattered light measurement based on photovoltaic cell microflow cytometer.

A method is proposed for detecting microparticles in a microflow cytometer by means of small angle forward-scattered light measurements. The proposed cytometer comprises a commercial photovoltaic cell, an adjustable power laser module, and a PDMS microfluidic chip. The detection performance of the proposed device is evaluated using particles with dimensions of 5, 8, 10, and 15 µm, respectively, given forward-light scattering angles of 5 and 8° and laser powers ranging from 15-25 mW. It is shown that for a constant laser power and particle size, the S/N of the detected light signal increases with a reducing forward-scattering angle. Moreover, for a constant forward-scattering angle and particle size, the S/N increases with an increasing laser power. The intensity of the forward-scattered light signal is found to vary linearly with the particle size and has a correlation coefficient of R(2) = 0.967, 0.967, and 0.963 given laser powers of 15, 20, and 25 mW, respectively, and a forward-scattering angle of 5°. Moreover, the CV of the forward-scattered light intensity is found to lie within the range of 20-30% for both forward-scattering angles. Overall, the present results suggest that the proposed device has significant potential for detection applications in the medical, environmental monitoring, and biological science fields.

Rapid Microfluidic Immuno-Biosensor Detection System for the Point-of-Care Determination of High-Sensitivity Urinary C-Reactive Protein.

A microfluidic immuno-biosensor detection system consisting of a microfluidic spectrum chip and a micro-spectrometer detection device is presented for the rapid point-of-care (POC) detection and quantification of high-sensitivity C-reactive protein (hs-CRP) in urine. The detection process utilizes a highly specific enzyme-linked immunosorbent assay (ELISA) method, in which capture antibodies and detection antibodies are pre-deposited on the substrate of the microchip and used to form an immune complex with the target antigen. Horseradish peroxidase (HRP) is added as a marker enzyme, followed by a colorimetric reaction using 3,3',5,5'-tetramethylbenzidine (TMB). The absorbance values (a.u.) of the colorimetric reaction compounds are measured using a micro-spectrometer device and used to measure the corresponding hs-CRP concentration according to the pre-established calibration curve. It is shown that the hs-CRP concentration can be determined within 50 min. In addition, the system achieves recovery rates of 93.8-106.2% in blind water samples and 94.5-104.6% in artificial urine. The results showed that the CRP detection results of 41 urine samples from patients with chronic kidney disease (CKD) were highly consistent with the conventional homogeneous particle-enhanced turbidimetric immunoassay (PETIA) method's detection results (R2 = 0.9910). The experimental results showed its applicability in the detection of CRP in both urine and serum. Overall, the results indicate that the current microfluidic ELISA detection system provides an accurate and reliable method for monitoring the hs-CRP concentration in point-of-care applications.

Finger pump microfluidic detection system for methylparaben detection in foods.

A novel assay platform consisting of a finger pump microchip (FPM) and a WiFi-based analytical detection platform is presented for measuring the concentration of methylparaben (MP) in commercial foods. In the presented approach, a low quantity (5 µL) of distilled food sample is dripped onto the FPM and undergoes a modified Fenton reaction at a temperature of 40 °C to form a green-colored complex. The MP concentration is then determined by measuring the color intensity (RGB) of the reaction complex using APP software (self-written) installed on a smartphone. The color intensity Red(R) + Green(G) value of the reaction complex is found to be linearly related (R2 = 0.9944) to the MP concentration for standard samples with different MP concentrations ranging from 100 to 3000 ppm. The proposed method is used to detect the MP concentrations of 12 real-world commercial foods. The MP concentrations measurements are found to deviate by no more than 5.88% from the results obtained using a conventional benchtop method. The presented platform thus offers a feasible and low-cost alternative to existing macroscale techniques for measuring the MP concentration in commercial foods.

Light-shading reaction microfluidic PMMA/paper detection system for detection of cyclamate concentration in foods.

Cyclamate is an artificial sweetener with high sweetness and low calories, and is a common sugar substitute for weight control and diabetic patients. However, excessive cyclamate consumption is associated with various health disorders, and hence it is prohibited as a food additive in many countries around the world. The current research proposes a light-shading reaction microfluidic PMMA/paper detection (MPD) system for determining the cyclamate concentration in food. In the current system, inject 10 µL of the extracted sodium cyclamate sample into the sample chamber of the MPD device, perform the diazotization reaction under shading conditions, and then suck it into the detection area through a paper strip, which consists of a paper chip embedded with modified Bratton-Marshall reagent. Once the paper chip is thoroughly wetted, the MPD device is inserted into a microanalysis box, where a fuchsia azo reaction compound is produced through heating at 40 °C for 3 min. The reaction complex is observed by a camera and the reaction image is wirelessly transmitted to a smartphone, and the concentration of sodium cyclamate is measured through the self-developed grayscale software. The results obtained for the sodium cyclamate samples with a concentration in the range of 50-1000 ppm show that the measured gray value changes linearly with the sodium cyclamate concentration, and the correlation coefficient (R2) is 0.9898. By analyzing the concentration of sodium cyclamate in 10 real-world samples, the practical feasibility of the current MPD system is proved. The results showed that the concentration measurement value did not deviate by more than 4.8 % from the value obtained using the conventional liquid chromatography/tandem mass spectrometry (LC-MS/MS) method.

Microfluidic Distillation System for Separation of Propionic Acid in Foods.

A microfluidic distillation system is proposed to facilitate the separation and subsequent determination of propionic acid (PA) in foods. The system comprises two main components: (1) a polymethyl methacrylate (PMMA) micro-distillation chip incorporating a micro-evaporator chamber, a sample reservoir, and a serpentine micro-condensation channel; and (2) and a DC-powered distillation module with built-in heating and cooling functions. In the distillation process, homogenized PA sample and de-ionized water are injected into the sample reservoir and micro-evaporator chamber, respectively, and the chip is then mounted on a side of the distillation module. The de-ionized water is heated by the distillation module, and the steam flows from the evaporation chamber to the sample reservoir, where it prompts the formation of PA vapor. The vapor flows through the serpentine microchannel and is condensed under the cooling effects of the distillation module to produce a PA extract solution. A small quantity of the extract is transferred to a macroscale HPLC and photodiode array (PDA) detector system, where the PA concentration is determined using a chromatographic method. The experimental results show that the microfluidic distillation system achieves a distillation (separation) efficiency of around 97% after 15 min. Moreover, in tests performed using 10 commercial baked food samples, the system achieves a limit of detection of 50 mg/L and a limit of quantitation of 96 mg/L, respectively. The practical feasibility of the proposed system is thus confirmed.

Optical microflow cytometer based on external total reflection.

A novel optical microflow cytometer based on external total reflection comprising a laser-induced fluorescence system, a PDMS chip, a plane mirror and a dichroic beamsplitter is proposed for the simultaneous detection, enumeration and sizing of labeled and nonlabeled microparticles. In the proposed approach, the total number and size of the particles passing through the detection region is determined via the nonscattered light signal reflected from a plane mirror positioned over the microchip, while the number of fluorescence-labeled particles is determined via the back scattered fluorescence signal. The experimental results confirm the ability of the proposed system to count and size fluorescent and nonfluorescent particles with nominal diameters ranging from 6 to 10.2 µm. In addition, it is shown that for a mixed sample containing both labeled and nonlabeled particles, the number of nonlabeled particles can be determined by subtracting the number of peaks in the fluorescence signal from that in the reflected light signal.

Microfluidic Sliding Paper-Based Device for Point-of-Care Determination of Albumin-to-Creatine Ratio in Human Urine.

A novel assay platform consisting of a microfluidic sliding double-track paper-based chip and a hand-held Raspberry Pi detection system is proposed for determining the albumin-to-creatine ratio (ACR) in human urine. It is a clinically important parameter and can be used for the early detection of related diseases, such as renal insufficiency. In the proposed method, the sliding layer of the microchip is applied and the sample diffuses through two parallel filtration channels to the reaction/detection areas of the microchip to complete the detection reaction, which is a simple method well suited for self-diagnosis of ACR index in human urine. The RGB (red, green, and blue) value intensity signals of the reaction complexes in these two reaction zones are analyzed by a Raspberry Pi computer to derive the ACR value (ALB and CRE concentrations). It is shown that the G + B value intensity signal is linearly related to the ALB and CRE concentrations with the correlation coefficients of R2 = 0.9919 and R2 = 0.9923, respectively. It is additionally shown that the ALB and CRE concentration results determined using the proposed method for 23 urine samples were collected from real suffering chronic kidney disease (CKD) patients are in fine agreement with those acquired operating a traditional high-reliability macroscale method. Overall, for point-of-care (POC) CKD diagnosis and monitoring in clinical applications, the results prove that the proposed method offers a convenient, real time, reliable, and low-spending solution for POC CKD diagnosis.

Microfluidic aptasensor POC device for determination of whole blood potassium.

An integrated microfluidic Au nanoparticle (AuNP) aptasensor device is proposed for monitoring the concentration of potassium (K+) ions in the bloodstream of patients with chronic kidney disease (CKD). In the proposed detection device, the AuNPs in the AuNP/aptamer complex are displaced by the serum K+ ions and react with NaCl to produce a color change in the detection region from which the K+ ion concentration is then inversely derived. The microfluidic device comprises two main components, namely an AuNP aptasensor PMMA (Poly(methyl methacrylate))/paper-microchip and a colorimetric analysis system for the quantitative detection of K+ ion concentration in whole blood. The functions of PMMA/paper microchips include reagent storage, K+ ion/aptamer reaction, and separation of serum from whole blood samples (blood filter). Experimental results show that the microfluidic device provides a linear response over the K+ ion concentration in range of 0.05-9 mM in artificial serum and has a detection limit (LOD) of 0.01 mM. Moreover, the detection results obtained for the 137 whole blood and 287 serum samples of CKD patients are very consistent (R2 = 0.968 and R2 = 0.980) with the measurement results obtained using an ion-selective electrodes (ISE) method. Results confirm that the current microfluidic aptasensor device provides a highly-sensitive and convenient method for performing the point-of-care (POC) monitoring of the whole blood K+ ion concentration.

Numerical analysis of a rapid magnetic microfluidic mixer.

This paper presents a detailed numerical investigation of the novel active microfluidic mixer proposed by Wen et al. (Electrophoresis 2009, 30, 4179-4186). This mixer uses an electromagnet driven by DC or AC power to induce transient interactive flows between a water-based ferrofluid and DI water. Experimental results clearly demonstrate the mixing mechanism. In the presence of the electromagnet's magnetic field, the magnetic nanoparticles create a body force vector that acts on the mixed fluid. Numerical simulations show that this magnetic body force causes the ferrofluid to expand significantly and uniformly toward miscible water. The magnetic force also produces many extremely fine finger structures along the direction of local magnetic field lines at the interface in both upstream and downstream regions of the microchannel when the external steady magnetic strength (DC power actuation) exceeds 30 Oe (critical magnetic Peclet number Pe(m),cr = 2870). This study is the first to analyze these pronounced finger patterns numerically, and the results are in good agreement with the experimental visualization of Wen et al. (Electrophoresis 2009, 30, 4179-4186). The large interfacial area that accompanies these fine finger structures and the dominant diffusion effects occurring around the circumferential regions of fingers significantly enhance the mixing performance. The mixing ratio can be as high as 95% within 2.0 s. at a distance of 3.0 mm from the mixing channel inlet when the applied peak magnetic field supplied by the DC power source exceeds 60 Oe. This study also presents a sample implementation of AC power actuation in a numerical simulation, an experimental benchmark, and a simulation of DC power actuation with the same peak magnetic strength. The simulated flow structures of the AC power actuation agree well with the experimental visualization, and are similar to those produced by DC power. The AC and DC power actuated flow fields exhibited no significant differences. This numerical study suggests approaches to maximize the performance of the proposed rapid magnetic microfluidic mixer, and confirms its exciting potential for use in lab-on-a-chip systems.

Microfluidic mixing: a review.

The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either "active", where an external energy force is applied to perturb the sample species, or "passive", where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers.

Experimental and numerical analysis of high-resolution injection technique for capillary electrophoresis microchip.

This study presents an experimental and numerical investigation on the use of high-resolution injection techniques to deliver sample plugs within a capillary electrophoresis (CE) microchip. The CE microfluidic device was integrated into a U-shaped injection system and an expansion chamber located at the inlet of the separation channel, which can miniize the sample leakage effect and deliver a high-quality sample plug into the separation channel so that the detection performance of the device is enhanced. The proposed 45° U-shaped injection system was investigated using a sample of Rhodamine B dye. Meanwhile, the analysis of the current CE microfluidic chip was studied by considering the separation of Hae III digested ϕx-174 DNA samples. The experimental and numerical results indicate that the included 45° U-shaped injector completely eliminates the sample leakage and an expansion separation channel with an expansion ratio of 2.5 delivers a sample plug with a perfect detection shape and highest concentration intensity, hence enabling an optimal injection and separation performance.

Lab-on-Paper Devices for Diagnosis of Human Diseases Using Urine Samples-A Review.

In recent years, microfluidic lab-on-paper devices have emerged as a rapid and low-cost alternative to traditional laboratory tests. Additionally, they were widely considered as a promising solution for point-of-care testing (POCT) at home or regions that lack medical infrastructure and resources. This review describes important advances in microfluidic lab-on-paper diagnostics for human health monitoring and disease diagnosis over the past five years. The review commenced by explaining the choice of paper, fabrication methods, and detection techniques to realize microfluidic lab-on-paper devices. Then, the sample pretreatment procedure used to improve the detection performance of lab-on-paper devices was introduced. Furthermore, an in-depth review of lab-on-paper devices for disease measurement based on an analysis of urine samples was presented. The review concludes with the potential challenges that the future development of commercial microfluidic lab-on-paper platforms for human disease detection would face.

Recent advances in lab-on-paper diagnostic devices using blood samples.

Lab-on-paper, or microfluidic paper-based analytical devices (µPADs), use paper as a substrate material, and are patterned with a system of microchannels, reaction zones and sensing elements to perform analysis and detection. The sample transfer in such devices is performed by capillary action. As a result, external driving forces are not required, and hence the size and cost of the device are significantly reduced. Lab-on-paper devices have thus attracted significant attention for point-of-care medical diagnostic purposes in recent years, particularly in less-developed regions of the world lacking medical resources and infrastructures. This review discusses the major advances in lab-on-paper technology for blood analysis and diagnosis in the past five years. The review focuses particularly on the many clinical applications of lab-on-paper devices, including diabetes diagnosis, acute myocardial infarction (AMI) detection, kidney function diagnosis, liver function diagnosis, cholesterol and triglyceride (TG) analysis, sickle-cell disease (SCD) and phenylketonuria (PKU) analysis, virus analysis, C-reactive protein (CRP) analysis, blood ion analysis, cancer factor analysis, and drug analysis. The review commences by introducing the basic transmission principles, fabrication methods, structural characteristics, detection techniques, and sample pretreatment process of modern lab-on-paper devices. A comprehensive review of the most recent applications of lab-on-paper devices to the diagnosis of common human diseases using blood samples is then presented. The review concludes with a brief summary of the main challenges and opportunities facing the lab-on-paper technology field in the coming years.

Design and Application of MEMS-Based Hall Sensor Array for Magnetic Field Mapping.

A magnetic field measurement system based on an array of Hall sensors is proposed. The sensors are fabricated using conventional microelectromechanical systems (MEMS) techniques and consist of a P-type silicon substrate, a silicon dioxide isolation layer, a phosphide-doped cross-shaped detection zone, and gold signal leads. When placed within a magnetic field, the interaction between the local magnetic field produced by the working current and the external magnetic field generates a measurable Hall voltage from which the strength of the external magnetic field is then derived. Four Hall sensors are fabricated incorporating cross-shaped detection zones with an identical aspect ratio (2.625) but different sizes (S, M, L, and XL). For a given working current, the sensitivities and response times of the four devices are found to be almost the same. However, the offset voltage increases with the increasing size of the detection zone. A 3 × 3 array of sensors is assembled into a 3D-printed frame and used to determine the magnetic field distributions of a single magnet and a group of three magnets, respectively. The results show that the constructed 2D magnetic field contour maps accurately reproduce both the locations of the individual magnets and the distributions of the magnetic fields around them.

Microfluidic colorimetric detection platform with sliding hybrid PMMA/paper microchip for human urine and blood sample analysis.

A microfluidic colorimetric detection (MCD) platform consisting of a sliding hybrid PMMA/paper microchip and a smart analysis system is proposed for the convenient, low-cost and rapid analysis of human urine and whole blood samples. The sliding PMMA/paper microchip comprises a PMMA microfluidic chip for sample injection and transportation, a paper strip for sample filtration (urine) or separation (blood), and a sealed paper-chip detection zone for sample reaction and detection. In the proposed device, the paper-chip is coated with bicinchoninic acid (BCA) and biuret reagent and is then assembled into the PMMA microchip and packaged in aluminum housing. In the detection process, the PMMA/paper microchip is slid partially out of the housing, and 2 µL of sample (urine or whole blood) is dripped onto the sample injection zone. The chip is then slid back into the housing and the sample is filtered/separated by the paper strip and transferred under the effects of capillary action to the sealed paper-chip detection zone. The housing is inserted into the color analysis system and heated at 45 °C for 5 min to produce a purple-colored reaction complex. The complex is imaged using a CCD camera and the RGB color intensity of the image is then analyzed using a smartphone to determine the total protein (TP) concentration of the sample. The effectiveness of the proposed method is demonstrated using TP control samples with known concentrations in the range of 0.03-5.0 g/dL. The detection results obtained for 50 human urine samples obtained from random volunteers are shown to be consistent with those obtained from a conventional hospital analysis system (R2 = 0.992). Moreover, the detection results obtained for the albumin (ALB) and creatine (CRE) concentrations of 50 whole blood samples are also shown to be in good agreement with the results obtained from the hospital analysis system (R2 = 0.982 and 0.988, respectively).

Recent Advances in Microfluidic Devices for Contamination Detection and Quality Inspection of Milk.

Milk is a necessity for human life. However, it is susceptible to contamination and adulteration. Microfluidic analysis devices have attracted significant attention for the high-throughput quality inspection and contaminant analysis of milk samples in recent years. This review describes the major proposals presented in the literature for the pretreatment, contaminant detection, and quality inspection of milk samples using microfluidic lab-on-a-chip and lab-on-paper platforms in the past five years. The review focuses on the sample separation, sample extraction, and sample preconcentration/amplification steps of the pretreatment process and the determination of aflatoxins, antibiotics, drugs, melamine, and foodborne pathogens in the detection process. Recent proposals for the general quality inspection of milk samples, including the viscosity and presence of adulteration, are also discussed. The review concludes with a brief perspective on the challenges facing the future development of microfluidic devices for the analysis of milk samples in the coming years.

Rapid electrochemical-biosensor microchip platform for determination of microalbuminuria in CKD patients.

An electrochemical-biosensor (EC-biosensor) microchip consisting of screen-printed electrodes and a double-layer reagent paper detection zone impregnated with amaranth is proposed for the rapid determination of microalbuminuria (MAU) in human urine samples. Under the action of an applied deposition potential, the amaranth is adsorbed on the electrode surface and the subsequent reaction between the modified surface and the MAU content in the urine sample prompts the formation of an inert layer on the electrode surface. The inert layer impedes the transfer of electrons and hence produces a drop in the response peak current, from which the MAU concentration can then be determined. The measurement results obtained for seven artificial urine samples with known MAU concentrations in the range of 0.1-40 mg/dL show that the measured response peak current is related to the MAU concentration with a determination coefficient of R2 = 0.991 in the low concentration range of 0.1-10 mg/dL and R2 = 0.996 in the high concentration range of 10-40 mg/dL. Furthermore, the detection results obtained for 82 actual chronic kidney disease (CKD) patients show an excellent agreement (R2 = 0.988) with the hospital analysis results. Overall, the results confirm that the proposed detection platform provides a convenient and reliable approach for performing sensitive point-of-care testing (POCT) of the MAU content in human urine samples.

Microfluidic colorimetric analysis system for sodium benzoate detection in foods.

Sodium benzoate (SBA) is a widely-used additive for preventing food spoilage and deterioration and extending the shelf life. However, the concentration of SBA must be controlled under safe regulations to avoid damaging human health. Accordingly, this study proposes a microfluidic colorimetric analysis (MCA) system composing of a wax-printed paper-microchip and a self-made smart analysis equipment for the concentration detection of SBA in common foods and beverages. In the presented method, the distilled SBA sample is mixed with NaOH to obtain a nitro compound and the compound is then dripped onto the reaction area of the paper-microchip, which is embedded with two layers of reagents (namely acetophenone and acetone). The paper-microchip is heated at 120 °C for 20 min to cause a colorimetric reaction and the reaction image is then obtained through a CMOS (complementary metal oxide semiconductor) device and transmitted to a cell-phone over a WiFi connection. Finally, use the self-developed RGB analysis software installed on the cell-phone to obtain the SBA concentration. A calibration curve is constructed using SBA samples with known concentrations ranging from 50 ppm (0.35 mM) to 5000 ppm (35 mM). It is shown that the R + G + B value (Y) of the reaction image and SBA concentration (X) are related via Y = -0.034 X +737.40, with a determination coefficient of R2 = 0.9970. By measuring the SBA concentration of 15 commercially available food and beverage products, the actual feasibility of the current MCA system can be demonstrated. The results show that the difference from the measurement results obtained using the macroscale HPLC method does not exceed 6.0%. Overall, the current system provides a reliable and low-cost technique for quantifying the SBA concentration in food and drink products.