Determination of norfloxacin residues in foods by exploiting the coffee-ring effect and paper-based microfluidics device coupling with smartphone-based detection.

A major goal of green chemistry is to avoid the use of toxic organic solvents. In particular, there are few green methods allowing extraction and quantification of chromium species in environmental samples. Here, we developed home-made, dual-gel electromembrane extraction combined with a microfluidic paper-based analytical device for the simultaneous determination of Cr(III) and Cr(VI) in water, without using any organic solvent. The positively charged Cr(III) and negatively charged Cr(VI) migrated selectively into the cathodic (pH 2.0) and anodic (pH 3.0) aqueous acceptor phases, respectively. After extraction, the anodic acceptor phase containing Cr(VI) was analyzed directly by a microfluidic paper-based analytical device, after the addition of the diphenylcarbazide colorimetric reagent. The cathodic acceptor phase containing Cr(III) was mixed with Ce(IV) to oxidize Cr(III) to Cr(VI), and then, Cr(VI) ions were detected on the microfluidic paper-based analytical device after adding diphenylcarbazide. Under the optimized conditions, limits of detection of 2.0 and 3.0 ng/mL and extraction recoveries of 58.8% and 83.3% were achieved for Cr(VI) and Cr(III), respectively.

Multi-dimensional microfluidic paper-based analytical devices (μPADs) for noninvasive testing: A review of structural design and applications

• In-tube gel electro-membrane was for the first time introduced as a scaled-down version of G-EME. • Extractions in transparent tube enable visual monitoring during the extraction processes. • With this new set-up, the DP/AP volume ratio can be easily increased to achieve a high enrichment factor. • Gel membrane and microfluidic paper-based analytical devices (µPADs) were a homemade fabrication. • The proposed workflow shows the ease of operation and is highly environmentally friendly. For the first time, in-tube gel electro-membrane microextraction (IT-G-EME) system followed by microfluidic paper-based analytical devices (µPADs) as a low-cost reading platform was fabricated for the speciation of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) as model cationic and anionic compounds. In this new miniaturized extraction mode, a transparent narrow-bore polymeric tube was used as housing of the aqueous acceptor phase (AP, 30 µL), while an agarose gel membrane was placed as a micro plug (2.5 mm) at the beginning of the tube. A circular shape vial (1.5 mL, pH 5.5) containing chromium species as donor phase (DP) was connected between two tubes which previously filled with gel membrane and aqueous AP. By applying electric potential, the positively charged Cr(III) and negatively charged Cr(VI) in the DP migrated selectively toward cathodic and anodic tubes, respectively. After extraction, each AP was analyzed by µPAD, which had already been modified with diphenylcarbazide (DPC). Under the optimized extraction conditions, a good limit of detection (LOD) equal to 7.0 µg L –1 was achieved for both analytes, while the extraction recoveries for Cr(VI) and Cr(III) were 72% and 84%. In addition, the developed approach was used for the quantification of chromium species in water samples.

This work presents a microfluidic paper-based analytical device (μPAD) for glucose determination using a supported metal-organic framework (MOF) acting as a peroxidase mimic. The catalytic action of glucose oxidase (GOx) on glucose causes the formation of H2O2, and the MOF causes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to form a blue-green product with an absorption peak at 650nm in the detection zone. A digital camera and the iOS feature of a smartphone are used for the quantitation of glucose with the S coordinate of the HSV color space as the analytical parameter. Different factors such as the concentration of TMB, GOx and MOF, pH and buffer, sample volume, reaction time and reagent position in the μPAD were optimized. Under optimal conditions, the value for the S coordinate increases linearly up to 150μmol·L-1 glucose concentrations, with a 2.5μmol·L-1 detection limit. The μPAD remains stable for 21days under conventional storage conditions. Such an enzyme mimetic-based assay to glucose determination using Fe-MIL-101 MOF implemented in a microfluidic paper-based device possesses advantages over enzyme-based assays in terms of costs, durability and stability compared to other existing glucose determination methods. The procedure was applied to the determination of glucose in (spiked) serum and urine. Graphical abstract Schematic representation of microfluidic paper-based analytical device using metal-organic framework as a peroxidase mimic for colorimetric glucose detection with digital camera or smartphone and iOS appreadout.

Paper-based microchannels are important components in paper-based microfluidic devices. Paper-based microchannels are usually manufactured by creating lines with hydrophobic patterns enclosing an area of hydrophilic paper inside. Among the many techniques for making hydrophobic lines, the printing method in general and inkjet printing in particular have become more common because of their advantages in terms of material saving, high precision, low-cost, etc. In this paper, the electrohydrodynamic (EHD) inkjet printing method, which has been studied and developed in recent years, has been used to drop glycol ether solvent-based ink onto a nitrocellulose paper. The results of the field emission scanning electron microscope (FE-SEM) show that the solvent based ink could dissolve through membrane and form a transparent hydrophobic layer on the created space. The width of the barrier lines can be controlled from about 200 μm to 260 μm, which is quite small when compared to other manufacturing methods. Based on this fabrication process, paper-based microfluidic analytical devices have been designed and fabricated for use in analytical biochemistry assays. Human chorionic gonadotropin (hCG) was selected as the biological target for this assay. Initial results have shown that the target for hCG can be quantitatively determined by these devices with a coefficient of determination (R2) of approximately 0.99. Therefore, EHD inkjet printing technology can be used for the manufacture of paper-based microfluidic analytical devices (μPADs) that may be applied in the future for analytical biochemistry assays.

Chapter 11 - Microfluidic paper-based devices

Technical aspects and challenges of colorimetric detection with microfluidic paper-based analytical devices (μPADs) - A review

Targeting iron speciation in wines: Design of a microfluidic paper-based device for determination of iron(II) and iron(III)

In this work, a microfluidic paper-based analytical device was further exploited by coupling with an electrophoretic separation technique for the first time. A low-cost, simple, portable, and disposable microfluidic paper-based electrophoretic device with an on-column wireless electro-generated chemiluminescence detector was demonstrated.

Naked eye Y amelogenin gene fragment detection using DNAzymes on a paper-based device

This research aimed to develop a microfluidic analytical device for determination of heavy metals, which can be divided into 3 parts. The first part is the development of microfluidic paper-based colorimetric device using thiosulfate catalytic etching of silver nanoplates for determination of copper. This device offers high sensitivity and selectivity for determination of copper over other metal ions. The color change can be monitored by the naked eye. The limit of detection was found to be 0.3 ng mL-1 and the relevant calibration curves was linear in the range of 0.5 - 200.0 ng mL-1 by ImageJ analysis. The second part is simultaneous determination of lead, cadmium and copper using microfluidic paper-based analytical device with dual electrochemical and colorimetric detection. Electrochemical detection was applied for determination of lead and cadmium using a bismuth film modified boron-doped diamond electrodes (Bi-BDDE). For the copper assay, the concentration of copper was measured by colorimetric detection based on the catalytic etching of silver nanoplates by thiosulfate. Under optimized conditions, the linear range obtained was found to be 0.5 - 70 ng mL-1 for lead and cadmium, 10 - 350 ng mL-1 for copper, and the detection limits were 0.1 ng mL-1 for lead and cadmium, and 5.0 ng mL-1 for copper. The final part is development of analytical method for the determination of heavy metal using a nafion/ionic liquid/graphene composite modified screen-printed carbon electrode. The composite-modified electrode was fabricated and evaluated for the highly sensitive simultaneous determination of zinc, cadmium and lead, which the detection limits of the simultaneous analyses were 0.09 ng mL-1, 0.06 ng mL-1 and 0.08 ng mL-1, respectively. This composite-modified electrode can be a candidate working electrode used in a microfluidic analytical device for determination of heavy metals in the future. Moreover, all proposed assays were applied to detect heavy metals in real samples (e.g. food, environmental and clinical samples), which the results were in good agreement with obtained from those of the standard methods.

Salivary calcium determination with a specially developed microfluidic paper-based device for point-of-care analysis

Microfluidic paper-based analytical devices (µPADs) convert ordinary cellulose into an active analytical platform where capillary gradients shape transport, surface chemistry guides recognition, and embedded electrodes or optical probes translate biochemical events into readable signals. Progress in fabrication-from wax and stencil barriers to laser-defined grooves, inkjet-printed conductive lattices, and 3D-structured multilayers-has expanded reaction capacity while preserving portability. Detection strategies span colorimetric fields that respond within porous fibers, fluorescence and ratiometric architectures tuned for low abundance biomarkers, and electrochemical interfaces resilient to turbidity, salinity, and biological noise. Applications now include diagnosing human body fluids, checking food safety, monitoring the environment, and testing for pesticides and illegal drugs, often in places with limited resources. Researchers are now using learning algorithms to read minute gradients or currents imperceptible to the human eye, effectively enhancing and assisting the measurement process. This perspective article focuses on the newest advancements in the design, fabrication, material selection, testing methods, and applications of µPADs, and it explains how they work, where they can be used, and what their future might hold.

Simple and sensitive colorimetric assay system for horseradish peroxidase using microfluidic paper-based devices

MoOx quantum dots with peroxidase-like activity on microfluidic paper-based analytical device for rapid colorimetric detection of H2O2 released from PC12 cells