Fabrication Of Microfluidic Devices Research Articles

Batch fabrication of electrochemical sensors on a glycol-modified polyethylene terephthalate-based microfluidic device

Developing low-cost methods for the fabrication of electrochemical microfluidic devices is urgently needed for transferring such devices from fundamental research to daily-life technology. Herein, glycol-modified polyethylene terephthalate (PETG)-based microfluidic devices with embedded channels and gold film electrode (GFE) are developed by a one-step, low-cost, straightforward, and mass-producible method, and are sealed by a reversible hydrophilic tape-based mechanism. Easily accessible poly (methyl methacrylate) (PMMA), polyethylene terephthalate (polyester, PET), and PETG are explored as substrate options for fabricating electrochemical sensors. The results demonstrated that PETG can be an excellent substrate for fabricating the electrode. The electrochemical stability and morphology of the device are investigated. Both redox ions ([Fe(CN)6]3-/4-) and redox organic compounds (dopamine) are used as model analytes to prove the electrochemical performance of the device. The PETG-based microfluidic devices integrated with electrochemical sensors can be used as alternative electrochemical devices for the detection of biological and chemical analytes. Meanwhile, batch-fabricated flexible electrochemical sensors based on PETG film and their electrochemical performance are reported.

Inexpensive and nonconventional fabrication of microfluidic devices in PMMA based on a soft‐embossing protocol

This study describes an inexpensive and nonconventional soft-embossing protocol to produce microfluidic devices in poly(methyl methacrylate) (PMMA). The desirable microfluidic structure was photo-patterned in a poly(vinyl acetate) (PVAc) film deposited on glass substrate to produce a low-relief master. Then, this template was used to generate a high-relief pattern in stiffened PDMS by increasing of curing agent /monomer ratio (1:5) followed by thermal aging in a laboratory oven (200°Cfor 24 h). The stiffened PDMS masters were used to replicate microfluidic devices in PMMA based on soft embossing at 220-230°Cand thermal sealing at 140°C.Bothembossing and sealing stages were performed by using binder clips. The proposed protocol has ensured the replication of microfluidic devices in PMMA with great fidelity (>94%). Examples of MCE devices, droplet generator devices and spot test array were successfully demonstrated. For testing MCE devices, a mixture containing inorganic cations was selected as model and the achieved analytical performance did not reveal significant difference from commercial PMMA devices. Water droplets were successfully generated in an oil phase at rate of ca. 60 droplets/min (fixing the continuous phase flow rate at 100μL/h) with size of ca. 322± 6μm. Glucose colorimetric assay was performed on spot test devices and good detectability level (5 μmol/L) was achieved. The obtained results for two artificial serum samples revealed good agreement with the certified concentrations. Based on the fabrication simplicity and great analytical performance, the proposed soft-embossing protocol may emerge as promising approach for manufacturing PMMA devices.

Rapid Fabrication of Membrane-Integrated Thermoplastic Elastomer Microfluidic Devices.

Leveraging the advantageous material properties of recently developed soft thermoplastic elastomer materials, this work presents the facile and rapid fabrication of composite membrane-integrated microfluidic devices consisting of FlexdymTM polymer and commercially available porous polycarbonate membranes. The three-layer devices can be fabricated in under 2.5 h, consisting of a 2-min hot embossing cycle, conformal contact between device layers and a low-temperature baking step. The strength of the FlexdymTM-polycarbonate seal was characterized using a specialized microfluidic delamination device and an automated pressure controller configuration, offering a standardized and high-throughput method of microfluidic burst testing. Given a minimum bonding distance of 200 μm, the materials showed bonding that reliably withstood pressures of 500 mbar and above, which is sufficient for most microfluidic cell culture applications. Bonding was also stable when subjected to long term pressurization (10 h) and repeated use (10,000 pressure cycles). Cell culture trials confirmed good cell adhesion and sustained culture of human dermal fibroblasts on a polycarbonate membrane inside the device channels over the course of one week. In comparison to existing porous membrane-based microfluidic platforms of this configuration, most often made of polydimethylsiloxane (PDMS), these devices offer a streamlined fabrication methodology with materials having favourable properties for cell culture applications and the potential for implementation in barrier model organ-on-chips.

Local photo-polymer deposition-assisted fabrication of multilayer paper-based devices

In this paper, we report on the use of a local acrylate-based negative photo-polymer deposition technique for the fabrication of 3D microfluidic paper-based analytical devices (3D-μPADs) where the sample flows in both the lateral and vertical directions through multiple stacked layers of porous materials. A simple and inexpensive manufacturing method was used, which is based on the local deposition of a photo-polymer (deposition speed 30 mm/s) on a porous cellulose paper substrate followed by the subsequent exposure (scanning speed 30 mm/s) to a laser source (fibre coupled continuous wave at 405 nm with maximum power of 60 mW), to stack four layers of cellulose paper and make 3D multilayer μPADs. With this technique, we provide a pathway to eliminate the limitations that other reported methods have during the fabrication of μPADs such as the need for multiple sophisticated alignments between adjoining layers and the use of additional tools to ensure adequate contact between the layers. In this study, we demonstrate the usefulness of our four-layer 3D-μPAD for simultaneous detection of three analytes, namely BSA, glucose, nitrite spiked in artificial urine and also the pH of the tested sample, through single step colorimetric assays with the limit of detection found at 0.4 mg/mL for BSA, 14.5 μg/mL for glucose and 2.5 μg/mL for nitrite. Our 3D-μPAD fabrication methodology can also be adapted in more complex analytical assays where multiple steps are needed for applications in point-of-care diagnostics.

Rapid fabrication of high-resolution multi-scale microfluidic devices based on the scanning of patterned femtosecond laser.

Femtosecond-laser-induced two-photon polymerization has distinct advantages in micro-nanofabrication due to its intrinsic three-dimensional processing capability and high precision with sub-100 nanometer fabrication resolution. However, the high resolution causes a drawback in fabricating large-scale structures due to unacceptably long processing times. To solve this problem, we applied the patterned focus as the basic element for scanning processing. Theoretically, the relationship between patterned-focus scanning parameters and the uniformity of scanned light field was analyzed and optimized. Experimentally, we quantitatively investigated the relationship between the microstructure surface quality and the parameters of patterned-focus scanning. Based on above, we put forward a hybrid method that combines the femtosecond laser patterned exposure with direct-writing fabrication to rapidly fabricate large-scale microfluidic devices for various practical applications.

Rapid Fabrication of Poly(methyl methacrylate) Devices for Lab-on-a-Chip Applications Using Acetic Acid and UV Treatment.

In the present study, we introduce a new approach for rapid bonding of poly(methyl methacrylate) (PMMA)-based microdevices using an acetic acid solvent with the assistance of UV irradiation. For the anticipated mechanism, acetic acid and UV irradiation induced free radicals on the PMMA surfaces, and acrylate monomers subsequently formed cross-links to create a permanent bonding between the PMMA substrates. PMMA devices effectively bonded within 30 s at a low pressure using clamps, and a clogging-free microchannel was achieved with the optimized 50% acetic acid. For surface characterizations, contact angle measurements and bonding performance analyses were conducted using predetermined acetic acid concentrations to optimize bonding conditions. In addition, the highest bond strength of bonded PMMA was approximately 11.75 MPa, which has not been reported before in the bonding of PMMA. A leak test was performed over 180 h to assess the robustness of the proposed method. Moreover, to promote the applicability of this bonding method, we tested two kinds of microfluidic device applications, including a cell culture-based device and a metal microelectrode-integrated device. The results showed that the cell culture-based application was highly biocompatible with the PMMA microdevices fabricated using an acetic acid solvent. Moreover, the low pressure required during the bonding process supported the integration of metal microelectrodes with the PMMA microdevice without any damage to the metal films. This novel bonding method holds great potential in the ecofriendly and rapid fabrication of microfluidic devices using PMMA.

Pushing the Limits of Spatial Assay Resolution for Paper-Based Microfluidics Using Low-Cost and High-Throughput Pen Plotter Approach.

To transform from reactive to proactive healthcare, there is an increasing need for low-cost and portable assays to continuously perform health measurements. The paper-based analytical devices could be a potential fit for this need. To miniaturize the multiplex paper-based microfluidic analytical devices and minimize reagent use, a fabrication method with high resolution along with low fabrication cost should be developed. Here, we present an approach that uses a desktop pen plotter and a high-resolution technical pen for plotting high-resolution patterns to fabricate miniaturized paper-based microfluidic devices with hundreds of detection zones to conduct different assays. In order to create a functional multiplex paper-based analytical device, the hydrophobic solution is patterned on the cellulose paper and the reagents are deposited in the patterned detection zones using the technical pens. We demonstrated the effect of paper substrate thickness on the resolution of patterns by investigating the resolution of patterns on a chromatography paper with altered effective thickness. As the characteristics of the cellulose paper substrate such as thickness, resolution, and homogeneity of pore structure affect the obtained patterning resolution, we used regenerated cellulose paper to fabricate detection zones with a diameter as small as 0.8 mm. Moreover, in order to fabricate a miniaturized multiplex paper-based device, we optimized packing of the detection zones. We also showed the capability of the presented method for fabrication of 3D paper-based microfluidic devices with hundreds of detection zones for conducting colorimetric assays.

Fabrication of Paper-based Microfluidic Devices Using a Laser Beam Scanning Technique.

This paper describes a novel method for fabricating paper-based microfluidic devices using a laser beam scanning technique. Cellulose chromatography papers were treated with octadecyltrichlorosilane (OTS) to make them entirely hydrophobic. A photoacid generator (CPI-410S) was soaked into the paper, and irradiated with a 405-nm laser beam to induce acid generating reactions. Since the silyl ether bond between cellulose and OTS was cleaved by the hydrolysis reaction, the photo-irradiated area changed to hydrophilic. By scanning the laser beam using a Galvo mirror system, arbitrary shaped hydrophilic patterns were successfully created on the paper in 50 μm resolution. To the best of our knowledge, this is the first report on the fabrication of hydrophilic channels on the OTS-treated paper using photo-induced acid generation processes coupled with the laser beam scanning technique. Quantification of nitrite was demonstrated with the paper device made by this method.

Microwave irradiation-based rapid curing of PDMS for microfluidic applications

Microfluidic devices are routinely fabricated using replica moulding. The master relief structure is generally constructed on a silicon substrate and the stamps are made using polydimethylsiloxane (PDMS), cured via the slow process of hot-air convective heating. An alternative method that greatly reduces this cure time is presented here. It employs a low-cost, consumer-grade microwave oven and speeds up the curing process by permitting a much higher heat flux to be applied to the prepolymer. A specific pulsed irradiation protocol has been devised which achieves precisely controlled energy delivery for this purpose. This is necessary because silicon’s relatively much stronger microwave absorption causes uncontrollable temperature overshoots that could degrade PDMS if continuously irradiated. The protocol has been arrived at after due optimization of operational parameters, achieved via simulation of a finite element model. It has been implemented by modifying the control circuitry of the consumer grade oven. Cure times as low as two minutes have been demonstrated. Optical and mechanical characterization results show no adverse effect on the performance of PDMS cured using the proposed method. Thus, it can be used for the rapid fabrication of PDMS-based microfluidic devices and would be especially beneficial for research labs looking to speed up microfluidic device development iterations.

A one-step polymer screen-printing method for fabrication of microfluidic cloth-based analytical devices

We report the first use of a one-step polymer screen-printing method for fabrication of microfluidic cloth-based analytical devices (µCADs). The method involves a simple, low-cost and one-step fabrication process and requires only polystyrene and a patterned screen. Firstly, polystyrene solution is poured through the patterned screen and allowed to penetrate through the cotton fabrics to create a three-dimensional hydrophobic barrier which defined the test zones. Different types of cotton fabric and polystyrene concentrations were first investigated. By adjusting polystyrene concentration, various types of cotton cloth can be successfully fabricated. Under optimal condition, the smallest hydrophilic channel and hydrophobic barrier that the fabrication method can provide were 678 ± 59 µm and 329 ± 27 µm, respectively. High device-to-device repeatability was achieved with a relative standard deviation (%RSD) in the range of 1.10–2.03% (n = 64) obtained from the measured diameter of the circular-shaped fabricated test zones with a designed diameter of 5 and 7 mm. The cloth treatments using hot water, Na2CO3 and NaOH solutions were found to affect the wicking ability of the cloths where the highest wicking rate was found in the Na2CO3 treated-cloth followed by NaOH, hot water treated-cloths and untreated-cloth. To demonstrate the significance of the fabricated µCAD, the analysis of glucose and albumin in control human serum was carried out. The results showed no significant difference at 95% confident intervals of the glucose and albumin levels obtained from the µCAD analysis and the certified values verifying that the polymer-screen printing method can be alternatively used as a method for µCAD fabrication.

Sealing 3D-printed parts to poly(dimethylsiloxane) for simple fabrication of Microfluidic devices

Microfluidics has revolutionized the fields of bioanalytical chemistry, cellular biology, and molecular biology. Advancements in microfluidic technologies, however, are often limited by labor, time, and resource-intensive fabrication methods, most commonly a form of photolithography. The advent of 3D printing has helped researchers fabricate proof-of-concept microfluidics more rapidly and at lower costs but suffers from poor resolution and tedious post-processing to remove uncured resin from enclosed channels. Additionally, custom resins and printers are often needed to create entirely enclosed channels, which increases cost and complexity of fabrication. In this work we demonstrate the ability to create microfluidic devices by covalently sealing 3D-printed parts with open-faced channels to polydimethylsiloxane (PDMS). Open-faced channels are easier to print than fully enclosed channels and can be printed using an inexpensive and commercially available stereolithography 3D printer and resin. The 3D-printed parts are sealed to PDMS, a common substrate used in traditional microfluidic fabrication, using two different techniques. The first involves coating the part with a commercially available silicone spray before sealing to PDMS via plasma treatment. In the second technique, the cured methacrylate resin is silanized with (3-Aminopropyl)triethoxysilane (APTES) before binding to PDMS with plasma treatment. Both methods create a strong seal between the two substrates, which is demonstrated with several types of microfluidic devices including droplet and gradient generators.

Designing and Fabrication of Low Cost Microfluidic Electrochemical Paper Analytical Device (ePAD) for Sensing

The development of electrochemical sensors as miniaturized and low-cost platforms for the rapid and sensitive detection of biomolecules demands for the requirement of disposable economically viable and easy manufacturable devices. Moreover, it should ASSURES (Affordable, Sensitive, Specific, User-friendly, Robust, Electrode for Sensing) the simple DIY (Do It Yourself) strategy. This could be achievable only if the substrate for the electrodes are inexpensive, easily manufacturable and should be from renewable and reusable resources. Simple paper offers unique advantages such as, easily printable, impregnable, and because of its innate cellulose structures, paper is protein and biomolecules friendly. In addition, porous structure acts as a good filter, and facilitates lateral flow. On the other hand, papers also have been used to make paper analytical devices (PAD), which have the advantages to incorporate microfluidic channels and reagent prestorage zones with mixing opportunities for colorimetric and electrochemical sensing units. Recently, these PADs have been recognized as low-cost and disposable sensing platforms.Considering the aforementioned properties, herein paper has been explored as a substrate for the fabrication of microfluidic ePAD. Using simple photo-lithography technique, we could achieve the hydrophobic and hydrophilic regions for making a 3 in 1 electrode patterns consists of working, counter and reference electrodes along with the reservoirs for analyte of interests (sample inlet) and reagents (prestorage zones). The designed and fabricated ePAD with colorimetric detection zones (Fig.1) was further characterized by surface morphological and electrochemical studies. As a proof-of-concept, we were able to use ePAD as an electrochemical sensor for trolox (analogue of Vitamin E, an antioxidant), and a probe for selective detection of dopamine in the presence of ascorbic acid. On the other hand, the electrochemical investigations further revealed the interplay between edge plane sites, oxygen functionalities, and the carbon structures π-π interactions with pyrene conjugates towards biomolecules detection. The calibration plot for the trolox sensor showed linear range from 5 µM to 400 µM with a detection limit of (S/N=3) of 1.17 µM. The modified ePAD were able to detect dopamine in real sample with satisfactory results. Aforementioned observations indicated that ePAD have great potential to establish point-of-care testing platform for clinical applications. The findings also demonstrated simple fabrication of microfluidic ePAD is possible, unlike the widely used wax printing technique, and laser scribing or screen printing, or inkjet printing of electrodes onto different substrates, which requires sophisticated instrumentation and skilled personal. Figure 1

Thermoplastic polyurethane-based flexible multilayer microfluidic devices

Background: Microfluidics has been widely used in the biological and medical fields, and polymers are the most widely used materials in microfluidics at present due to their low cost and ease of processing. Both thermoplastics and thermosets were used as the bulk materials in microfluidics. The third option of a material with both advantages from thermoplastics and thermosets will be of great significance. Aim: We try to establish a low cost and rapid fabrication approach for thermoplastic polyurethane (TPU)-based microfluidics. Several demonstrations were also provided with the proposed fabrication method for TPU-based microfluidics. Approach: A CO2 laser ablation instrument was used for the fabrication of the TPU-based microfluidic devices. The width and depth of microchannels fabricated with various laser scan speeds and energies were studied in detail. For sealing the fabricated channels, a thermal fusion bonding method was also proposed with the bonding strength testing. Several types of the most commonly used microfluidic chips were fabricated for demonstration of the proposed fabrication method. Results: A comprehensive fabrication approach for TPU-based microfluidic devices was achieved. A series of microfluidic chips were designed, fabricated, and tested. Conclusions: TPU-based microfluidics is achievable and could be used as an alternative material for polydimethylsiloxane or thermoplastics for the fabrication of microfluidic devices. The proposed method could have broad potential applications in biological and chemical fields.

Fabrication of microwell plates and microfluidic devices in polyester films using a cutting printer

This study reports, for the first time, the possibility to manufacture analytical devices on polyester substrates using a cutting printer. The protocol involves the design of a layout in a graphical software, the cut into polyester films and the lamination against one or multiple polyester films coated with a thermosensitive layer. The feasibility of the proposed approach was demonstrated through the fabrication of 96-microwell plates, 3D microfluidic mixing and distance-based microfluidic devices. The printer has enabled cutting microchannels wider than 300 μm on polyester films and a thickness of 250 μm. Urea and glucose assays were performed on microwell plates aiming for their quantification in artificial urine and serum samples. The presented results revealed good agreement with the expected values. The complexation reaction between Fe2+ and o-phenanthroline was selected as model to investigate the feasibility of the 3D mixing device. Absorbance measurements were recorded for the reaction product performed in both on and off-chip modes. Considering the achieved data, the on-chip mixing exhibited similar behavior when compared to off-chip reaction, thus demonstrating to be efficient to perform mixtures due to the turbulence generated inside three-dimensional channels. Lastly, a distance-based device was designed to detect H2O2 based on the displacement of a dye plug promoted by the oxygen generation using a copper-modified paper sheet. The distance-based peroxymeter revealed a linear behavior in the concentration range between 1 and 5% (v/v) and a LOD equal to 0.5% (65.2 mM). Based on the results herein reported, the proposed method represents a simple and alternative protocol to produce microdevices, using affordable and inexpensive raw materials, within 10 min, and at a cost lower than US$ 0.10 per unit.

Integrating Microstructured Electrospun Scaffolds in an Open Microfluidic System for in Vitro Studies of Human Patient-Derived Primary Cells.

Recent studies have suggested that microenvironmental stimuli play a significant role in regulating cellular proliferation and migration, as well as in modulating self-renewal and differentiation processes of mammary cells with stem cell (SCs) properties. Recent advances in micro/nanotechnology and biomaterial synthesis/engineering currently enable the fabrication of innovative tissue culture platforms suitable for maintenance and differentiation of SCs in vitro. Here, we report the design and fabrication of an open microfluidic device (OMD) integrating removable poly(ε-caprolactone) (PCL) based electrospun scaffolds, and we demonstrate that the OMD allows investigation of the behavior of human cells during in vitro culture in real time. Electrospun scaffolds with modified surface topography and chemistry can influence attachment, proliferation, and differentiation of mammary SCs and epigenetic mechanisms that maintain luminal cell identity as a function of specific morphological or biochemical cues imparted by tailor-made fiber post-treatments. Meanwhile, the OMD architecture allows control of cell seeding and culture conditions to collect more accurate and informative in vitro assays. In perspective, integrated systems could be tailor-made to mimic specific physiological conditions of the local microenvironment and then analyze the response from screening specific drugs for more effective diagnostics, long-term prognostics, and disease intervention in personalized medicine.

3D Printing of Inertial Microfluidic Devices

Inertial microfluidics has been broadly investigated, resulting in the development of various applications, mainly for particle or cell separation. Lateral migrations of these particles within a microchannel strictly depend on the channel design and its cross-section. Nonetheless, the fabrication of these microchannels is a continuous challenging issue for the microfluidic community, where the most studied channel cross-sections are limited to only rectangular and more recently trapezoidal microchannels. As a result, a huge amount of potential remains intact for other geometries with cross-sections difficult to fabricate with standard microfabrication techniques. In this study, by leveraging on benefits of additive manufacturing, we have proposed a new method for the fabrication of inertial microfluidic devices. In our proposed workflow, parts are first printed via a high-resolution DLP/SLA 3D printer and then bonded to a transparent PMMA sheet using a double-coated pressure-sensitive adhesive tape. Using this method, we have fabricated and tested a plethora of existing inertial microfluidic devices, whether in a single or multiplexed manner, such as straight, spiral, serpentine, curvilinear, and contraction-expansion arrays. Our characterizations using both particles and cells revealed that the produced chips could withstand a pressure up to 150 psi with minimum interference of the tape to the total functionality of the device and viability of cells. As a showcase of the versatility of our method, we have proposed a new spiral microchannel with right-angled triangular cross-section which is technically impossible to fabricate using the standard lithography. We are of the opinion that the method proposed in this study will open the door for more complex geometries with the bespoke passive internal flow. Furthermore, the proposed fabrication workflow can be adopted at the production level, enabling large-scale manufacturing of inertial microfluidic devices.

Microfluidic Point-of-Care Devices: New Trends and Future Prospects for eHealth Diagnostics.

Point-of-care (PoC) diagnostics is promising for early detection of a number of diseases, including cancer, diabetes, and cardiovascular diseases, in addition to serving for monitoring health conditions. To be efficient and cost-effective, portable PoC devices are made with microfluidic technologies, with which laboratory analysis can be made with small-volume samples. Recent years have witnessed considerable progress in this area with “epidermal electronics”, including miniaturized wearable diagnosis devices. These wearable devices allow for continuous real-time transmission of biological data to the Internet for further processing and transformation into clinical knowledge. Other approaches include bluetooth and WiFi technology for data transmission from portable (non-wearable) diagnosis devices to cellphones or computers, and then to the Internet for communication with centralized healthcare structures. There are, however, considerable challenges to be faced before PoC devices become routine in the clinical practice. For instance, the implementation of this technology requires integration of detection components with other fluid regulatory elements at the microscale, where fluid-flow properties become increasingly controlled by viscous forces rather than inertial forces. Another challenge is to develop new materials for environmentally friendly, cheap, and portable microfluidic devices. In this review paper, we first revisit the progress made in the last few years and discuss trends and strategies for the fabrication of microfluidic devices. Then, we discuss the challenges in lab-on-a-chip biosensing devices, including colorimetric sensors coupled to smartphones, plasmonic sensors, and electronic tongues. The latter ones use statistical and big data analysis for proper classification. The increasing use of big data and artificial intelligence methods is then commented upon in the context of wearable and handled biosensing platforms for the Internet of things and futuristic healthcare systems.

Instrument-free fabrication of microfluidic paper-based analytical devices through 3D pen drawing

This paper describes for the first time the use of a 3D pen to fabricate paper-based analytical devices. 3D pens are usually commercialized as “toy for children” and a kit containing four units and a handheld flashlight can be found at cost of US$ 10−15. The protocol involves the 3D pen drawing of the desirable layout on paper using an acrylic resin followed by a curing stage through a handheld flashlight. The barriers created with 3D pen revealed good chemical resistance when exposed to acid and alkaline solutions, surfactants and organic solvents, except ethanol. The proposed approach enabled the creation of zones with 2 mm diameter and channels with 3 mm wide. The analytical feasibility of the devices created with 3D pen was investigated through colorimetric measurements of clinically and environmentally relevant analytes using a free application for image capture and analysis. Considering the instrumental simplicity and the satisfactory analytical performance, we believe the reported approach exhibits potentiality to be implemented in laboratories or research centers with limited resources, opening possibilities to create the desirable devices for the point-of-need applications using only a pen and a flashlight.

A three-dimensional origami microfluidic device for paper chromatography: Application to quantification of Tartrazine and Indigo carmine in food samples

Herein, we report three-dimensional paper chromatography (3D-PC) as a micro-chromatographic platform. The method was based on applying the origami microfluidic device for separation, coupled by colorimetric methods for simultaneous determination. The microfluidic device fabrication was a facile printing approach. Two azo food dyes, Tartrazine (E102) and Indigo carmine (E132), were selected as a model analyte, while carbonate-bicarbonate buffer was used as the mobile phase. Our micro-chromatographic device is associated with two big advantages including needing very small volume of mobile phase ( ~12 µL) and ultrafast separation time (~35 s). Under the optimal conditions, the method provided acceptable linear ranges of 0. 0 g L1–18.0 g L1 (R2 = 0.997) for E102 and 0.070 g L1–10.0 g L1 for E132 and the limits of detection (3σ/slope) were evaluated as 0.620 and 0.060 g L1, respectively. The proposed method was successfully applied in the separation and quantification of these dyes in commercial food products such as jelly, candy, and four kinds of drink samples without any sample preparation prior to analysis. The mean recovery values for the real sample analysis were in the range of 100.14%–102.38% for E132 and E102 respectively. The inter-device relative standard deviations were in the ranges of 1.5%–11.8%. In total, our chromatographic μPAD is small (1.0 cm × 1.0 cm × 0.5 cm), portable, inexpensive, no need of specialized user, requires low volumes of sample (0.5 μL), and can perform separation using 12 μL of aqueous mobile phase in very short time.

Fabrication of microfluidic device for Aflatoxin M1 detection in milk samples with specific aptamers

This study describes the colorimetric detection of aflatoxin M1 (Afl M1) in milk samples using a microfluidic paper-based analytical device (µPAD). Fabrication of µPADs was done using a simple and quick approach. Each μPAD contained a detection zone and a sample zone interconnected by microchannels. The colorimetric assay was developed using unmodified AuNPs as a probe and 21-mer aptamer as a recognition molecule. The free aptamers were adsorbed onto the surface of AuNPs in absence of Afl M1, even at high salt concentrations. The salt induced aggregation of specific aptamers occurred in presence of Afl M1. Under optimum conditions, the analytical linear range was found to be 1 µM to 1 pM with limit of detection 3 pM and 10 nM in standard buffer and spiked milk samples respectively. The proposed aptamer based colorimetric assay was repeatable, quick, selective, and can be used for on-site detection of other toxins in milk and meat samples.