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During the winemaking process, wine is frequently exposed to oxygen which can affect the organoleptic characteristics and therefore the quality of the finished wine. Most phenolic molecules in wine serve as oxidation substrates affecting colour and flavour. Transition metal ions namely copper and iron act as electron pumps; in fact, Fe(III) is reduced to Fe(II) as a consequence of the oxidation of phenols to quinones and, in the presence of oxygen, Fe(II) is oxidised back to Fe(III). Consequently, speciation analysis by the oxidation state is critical and even more relevant than the total ion concentration when one wants to evaluate the risk for wine oxidation. Interestingly the different reactivity of Fe(III) and Fe(II) makes spectrophotometric methods, namely colorimetric reactions, ideally suited for speciation analysis. In this work, a microfluidic paper-based analytical device (µPAD) was designed for the iron speciation in wine samples. The colorimetric reaction between bathophenanthroline and iron(II) was chosen and the oxidation of Fe(III) to Fe(II), using hydroxylamine, was carried out within the same device. Aiming for application to different types of wine, the developed device also enabled to account for the potential sample colour (subtraction of interfering signal). The designed µPAD enabled the iron speciation in both white and red wines.

Nowadays, developing a cost-effective, easy-to-operate, and efficient signal amplification platform is of important to microfluidic paper-based analytical devices (μPAD) for end-use markets of point-of-care (POC) assay applications. Herein, an ultrasensitive, paper-based photoelectrochemical (PEC) bioassay platform is constructed by in situ grown ZnO/ZnIn2S4 heterojunctions onto paper fibers, which acted as photoactive signal amplification probes for enhancing the sensitivity of antibodies-based diagnostic assays, for the sensitive detection of alpha-fetoprotein (AFP) targets. The crystalline flake-like ZnIn2S4 composited with hexagonal nanorods (NRs) morphology of ZnO is an in situ grown, at the first time, onto cellulose fibers surface supported with Au nanoparticle (Au NP) modification to improve conductivity of the device working zone. The obtained composites on paper fibers are implemented as a flexible paper-based photoelectrode to realize remarkable performance of the fabricated μPAD, resulting from the enhanced PEC activity of heterojunctions with effective electron-hole pair separation for accelerating photoelectric conversion efficiency of the sensing process under light irradiation. Once the target AFP was introduced into the biosensing interface assistant, with a specific recognition interaction of AFP antibody, a drastically photocurrent response was generated, in view of the apparent steric effects. With the concentration increase of AFP targets, more immune conjugates could be confined onto the biosensing interface, eventually leading to the quantitative decrease of photocurrent intensity. Combined with an ingenious origami design and permitting the hydrophobic/hydrophilic conversion procedure in the bioassay process, the ultrasensitive PEC detection of AFP targets was realized. Under the optimized conditions, the level of AFP could be sensitively tracked by the prepared μPAD with a liner range from 0.1 to 100 ng mL−1 and limit of detection of 0.03 ng mL−1. This work provides a great potential application for highly selective and sensitive POC testing of AFP, and finally, developments for clinical disease diagnosis.

Here, we propose a microfluidic paper-based analytical device (mu PAD) implemented with a near-field communication (NFC) tag as a portable, simple and fast colorimetric method for glutathione (GSH) determination. The proposed method was based on the fact that Ag+ could oxidize 3,3';,5,5'-tetramethylbenzidine (TMB) into oxidized blue TMB. Thus, the presence of GSH could cause the reduction of oxidized TMB, which resulted in a blue color fading. Based on this finding, we developed a method for the colorimetric determination of GSH using a smartphone. A mu PAD implemented with the NFC tag allowed the harvesting of energy from a smartphone to activate the LED that allows the capture of a photograph of the mu PAD by the smartphone. The integration between electronic interfaces into the hardware of digital image capture served as a means for quantitation. Importantly, this new method shows a low detection limit of 1.0 mu M. Therefore, the most important features of this non-enzymatic method are high sensitivity and a simple, fast, portable and low-cost determination of GSH in just 20 min using a colorimetric signal., BBVA Foundation, European Commission European Commission Joint Research Centre H2020-MSCA-IF-2017-794885-SELFSEN, Spanish Government PID2019-103938RB-I00 PID2020-117344RBI00, Junta de Andalucia BFQM-243-UGR18 P18-RT-2961, European Commission

The main problem for the expansion of the use of microfluidic paper-based analytical devices and, thus, their mass production is their inherent lack of fluid flow control due to its uncontrolled fabrication protocols. To address this issue, the first step is the generation of uniform and reliable microfluidic channels. The most common paper microfluidic fabrication method is wax printing, which consists of two parts, printing and heating, where heating is a critical step for the fabrication of reproducible device dimensions. In order to bring paper-based devices to success, it is essential to optimize the fabrication process in order to always get a reproducible device. Therefore, the optimization of the heating process and the analysis of the parameters that could affect the final dimensions of the device, such as its shape, the width of the wax barrier and the internal area of the device, were performed. Moreover, we present a method to predict reproducible devices with controlled working areas in a simple manner. The authors would like to acknowledge funding support from Gobierno de España, Ministerio de Economía y Competitividad, with Grant No. BIO2016-80417-P (AEI/FEDER, UE), the Gobierno Vasco Dpto. Educación for the consolidation of the research groups (IT1271-19) and from Proyectos Colaborativos from the University of the Basque Country UPV/EHU, BIOPLASMOF (COLAB19/05). This project received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778001.

This article reports on the development and validation of a disposable microfluidic paper-based analytical device (μPAD) for on-hand, in-situ, and cheap Fe(III) determination in natural waters complying with World Health Organization guidelines. The developed μPAD used 3-hydroxy-4-pyridinone (3,4-HPO) as a colour reagent due to its considerably lower toxicity than traditionally used iron analytical reagents. It was selected among a group of hydrophilic 3,4-HPO chelators containing ether-derived chains in their structure which were prepared using green methods. The relatively high water solubility of these chelators improved the detection limit and applicability as μPAD reagents. Under optimal conditions, the μPAD is characterised by a quantification range between 0.25 and 2.0 mg/L, a detection limit of 55 μg/L and 15 min of analysis time. The signal stability extends up to 4 h and the device is stable for at least one month. The reagent consumption is below 0.2 mg per analysis and the μPAD method was validated by analysis certified reference materials and by comparison with atomic absorption results (RD < 10%). The newly developed μPAD was successfully applied to the determination of iron in river, well and tap waters with no need of any prior sample pre-treatment.

This work presents a new optical microfluidic paper biosensor for the detection of organophosphate pesticides and carbamate pesticides. The assay strip is composed of a paper support (1 × 17.6 mm) onto which acet- ylcholine esterase (AChE) and acetylcholine chloride (AChCl) are deposited, in such a way that there is a small hole between them that ensures that they only come into contact in the reaction zone when they are carried by a solution of the sample by lateral flow to the reaction zone containing bromocresol purple (BCP) as the pH indicator, immobilized by sol-gel. The sensor operates at room temperature and the rate of the inhibited reaction serves as an analytical signal, which is measured using a camera by quantifying the appropriate colour co- ordinate. Calibration curves were obtained for chlorpyrifos and carbaryl, with a useful concentration range from 0.24 to 20 μg L−1 for carbaryl and from 2.00 to 45 μg L−1 for chlorpyrifos. The detection limits were 0.24 and 2.00 μg L−1, respectively, and with reproducibility around 4.2–5.5%. The method was applied to the de- termination of pesticides in different water samples, with no sample preparation., This study was supported by a project from the Spanish MINECO (CTQ2016-78754-C2-1-R), a project partially supported by European Regional Development Funds (ERDF).

The following article summarizes United States Patent Application No. US20180052155A1, titled ‘Assay Devices and Methods’ (filed 16 August 2016, published 22 February 2018). While lateral flow assays (LFAs) have revolutionized point-of-care diagnostics by enabling accurate, inexpensive, and rapid detection of biomarkers, they typically do not provide quantitative results. Hence, there is a significant need for quantitative assays at the point of care. This patent summary describes a novel method of chronometric biomarker quantitation via enzymatic degradation of a metastable gelatin-based biomatrix, principally suited for use in paper-based microfluidic devices (microPADs). This new quantitation mechanism was designed to meet the ASSURED criteria for point-of-care diagnostic devices laid forth by the World Health Organization and may ultimately provide increased access to healthcare, at a significantly reduced cost, around the world.

The design, optimization and evaluation of a micro paper-based analytical device (μPAD) for the simultaneous determination of fluoride and nitrite in real water samples was developed. In order to create hydrophilic and hydrophobic zones on the laboratory filter paper device, a wax ink printer was used. The μPAD has four reaction zones for each analyte where the respective colorimetric reactions took place using the SPADNS method and Griess method for fluoride and nitrite respectively. A Smartphone was used to capture the corresponding images which were then converted to the RGB colour space by the software ImageJ using a personal computer. Under the optimal conditions, the linear range was 0.23–2.26 mg L−1 for fluoride with limit of detection (LOD) and limit of quantification (LOQ) of 0.13 mg L−1 and 0.25 mg L−1. The working range for nitrite was 0.05–10.0 mg L−1 with LOD of 0.03 mg L−1 and LOQ 0.13 mg L−1. The μPAD was used to determine the analytes in water samples obtaining satisfactory results in both cases. The validation of fluoride determination was performed comparing the μPAD with the reference method and for nitrite determination, a recovery study was carried out. In both cases, the obtained results demonstrated a good agreement. Fil: Vidal, Ezequiel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Lorenzetti, Anabela Silvana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Lista, Adriana Guillermina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Domini, Claudia Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina