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Supplementary data to this article can be found online at https://doi. org/10.1016/j.bios.2023.115268, The COVID-19 pandemic has highlighted the need for innovative approaches to its diagnosis. Here we present CoVradar, a novel and simple colorimetric method that combines nucleic acid analysis with dynamic chemical labeling (DCL) technology and the Spin-Tube device to detect SARS-CoV-2 RNA in saliva samples. The assay includes a fragmentation step to increase the number of RNA templates for analysis, using abasic peptide nucleic acid probes (DGL probes) immobilized to nylon membranes in a specific dot pattern to capture RNA fragments. Duplexes are formed by labeling complementary RNA fragments with biotinylated SMART bases, which act as templates for DCL. Signals are generated by recognizing biotin with streptavidin alkaline phosphatase and incubating with a chromogenic substrate to produce a blue precipitate. CoVradar results are analysed by CoVreader, a smartphone-based image processing system that can display and interpret the blotch pattern. CoVradar and CoVreader provide a unique molecular assay capable of detecting SARS-CoV-2 viral RNA without the need for extraction, preamplification, or pre-labeling steps, offering advantages in terms of time (similar to 3 h/test), cost (similar to epsilon 1/test manufacturing cost) and simplicity (does not require large equipment). This solution is also promising for developing assays for other infectious diseases., FEDER/Junta de Andalucia-Consejeria de Economia y Conocimiento CV20-77741, A-FQM-760-UGR20, PID 2019-110987RB-I00, PID 2019-103938RB-I00, Spanish MCIN/AEI P18-RT-2961, P18-TP-4160, FEDER/Junta de Andalucia-Consejeria de Salud y Familias PIP-0232-2021, European Commission, MCIN/AEI PTQ 2020-011388, IJC 2020-043307-I, European Union NextGenerationEU/PRTR PTQ 2020-011388, IJC 2020-043307-I

Alonso Cano is considered one of the most original and brilliant artists from the Spanish Golden Age (known in Spanish as Siglo de Oro), a period of flourishing in arts and literature. He was also ...

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

Two simple boron-dipyrromethene-type fluorophore (azaBODIPYs) dyes are synthesized and tested for the determination of CO2 gas by an inner filter process. The indicators are noncovalently entrapped in suitable polymers according to their polarity, featuring absorption maxima at 620 nm and fluorescent emission maxima in the range 675–720 nm. Molar absorptivity and fluorescence quantum yield data were determined for these two synthesized azaBODIPYs. These indicators have high molar absorption coefficients of 7.1 × 104 and 2.1 × 104 M−1 cm−1 and quantum yields of 21 and 9%. The pKa values of the indicators are determined from absorbance and fluorescence measurements with values of 7.9 and 8.5, depending on the positioning of the substitution pattern of the electron-donating functionalities. The two azaBODIPYs present excellent photostability, making them suitable for long duration measurements. These azaBODIPY dyes act as fluorescent pH indicators in a polymeric sensing membrane along with microcrystalline powder of chromium-doped gadolinium aluminium borate as the luminophore, a transfer phase agent (tetraoctyl or tetramethyl ammonium hydroxide) and a plasticizer or surfactant to improve membrane permeability to gaseous CO2. The response time ranges from 42 to 60 s and recovery time from 103 to 120 s, with a detection limit of 0.04 and 0.57% CO2. The store time of the sensing membranes is longer than 570 days in the best case, and it does not need to be kept in any special atmosphere other than darkness.

Thermal sintering has traditionally been the most popular sintering method to enhance conductivity after the printing process in the manufacturing of printed electronics. Nevertheless, in recent years, there has been a growing interest in electrical sintering as an alternative method to overcome some of the limitations of thermal curing. This paper makes a comparative study of both sintering methods in terms of surface morphology, electrical dc conductance, and radiofrequency performance for different applied voltage waveforms. To this end, microstrip transmission lines have been inkjet-printed using nanoparticle-based silver ink on flexible polyimide substrate. The traces have been tested under different sintering conditions, achieving electrical sintering resistivity values only 2.3 times higher than that of bulk silver. This implies a 62% reduction in comparison with the best resistivity value achieved using thermal sintering in our samples. The main novelty of this contribution lies in the analysis of RF behavior as a function of electrical sintering conditions. Lower resistivities have been achieved with slower voltage ramps or allowing higher density current during sintering. It has also been proved that electrically sintered lines have similar RF performance than high-temperature thermally sintered lines in terms of insertion losses, regardless of their very different surface topology. Therefore, we can take advantage of the benefits that electrical sintering offers over thermal sintering regarding significant shorter sintering times maintaining suitable RF performance., This work was supported in part by the Spanish Ministry of Economics and Competitiveness under Grant CTQ2016-78754-C2-1-R.

In this work we propose for the first time, a paper-based test strip to analyse Cu

Encapsulation of magnetic nanoparticles (MNPs) of iron (II, III) oxide (Fe3O4) with a thermopolymeric shell of a crosslinked poly(2-(2-methoxyethoxy)ethyl methacrylate) P(MEO2MA) is successfully developed. Magnetic aggregates of large size, around 150–200 nm are obtained during the functionalization of the iron oxide NPs with vinyl groups by using 3-butenoic acid in the presence of a water soluble azo-initiator and a surfactant, at 70 °C. These polymerizable groups provide a covalent attachment of the P(MEO2MA) shell on the surface of the MNPs while a crosslinked network is achieved by including tetraethylene glycol dimethacrylate in the precipitation polymerization synthesis. Temperature control is used to modulate the swelling-to-collapse transition volume until a maximum of around 21:1 ratio between the expanded: shrunk states (from 364 to 144 nm in diameter) between 9 and 49 °C. The hybrid Fe3O4@P(MEO2MA) microgel exhibits a lower critical solution temperature of 21.9 °C below the corresponding value for P(MEO2MA) (bulk, 26 °C). The MEO2MA coating performance in the hybrid microgel is characterized by dynamic light scattering and transmission electron microscopy. The content of preformed MNPs [up to 30.2 (wt%) vs. microgel] was established by thermogravimetric analysis while magnetic properties by vibrating sample magnetometry.

In this study, we have developed a thread-paper microfluidic analytical device (µTPAD) for the determination of glucose directly in a whole blood sample. The analytical device is based on the enzymatic method for glucose in plasma using glucose oxidase and horseradish peroxidase combined with the chromogen TMB. Besides, all the analytical operations needed to perform the glucose determination have been included in the device itself, as it is red blood cell separation, conditioning, enzymatic recognition, and colorimetric transduction. To be possible the use of whole blood samples directly, a piece of separation membrane was located at the extreme of the cotton thread, where 3 µL of sample is dropped, retaining the blood cells from the sample and reaching to the cotton thread the free of cells plasma from sample. Later, it will be buffered to pH 7.4 thanks to the dry buffer retained along the thread. Finally, the sensing area of the device will turn into blue, depending on the glucose concentration in the sample. In order to register the analytical parameter, R/B from RGB color space, from the sensing area, a smartphone running a homemade app that is capable to analyze, in real time, the color of the sensing area was used. Consequently, the app analyzes the sensing area, determines when the R/B signal is steady and, finally, calculates the glucose concentration in the sample.

A microfluidic paper-based analytical device integrating carbon dot (CDs) is fabricated and used for a fluorometric off-on assay of biothiols. Vinyl sulfone (VS) click immobilization of carbon dots (CDs) on paper was accomplished by a one-pot simplified protocol that uses divinyl sulfone (DVS) as a homobifunctional reagent. This reagent mediated both the click oxa-Michael addition to the hydroxyl groups of cellulose and ulterior covalent grafting of the resulting VS paper to NH2-functionalized CDs by means of click aza-Michael addition. The resulting cellulose nanocomposite was used to engineer an inexpensive and robust microfluidic paper-based analytical device (μPAD) that is used for a reaction-based off-on fluorometric assay of biothiols (GSH, Cys, and Hcy). The intrinsic blue fluorescence of CDs (with excitation/emission maxima at 365/450 nm) is turned off via the heavy atom effect of an introduced iodo group. Fluorescence is turned on again due to the displacement of iodine by reaction with a biothiol. The increase in fluorescence is related to the concentration over a wide range (1 to 200 μM for GSH and 5–200 μM for Cys and Hcy, respectively), and the assay exhibits a low detection limit (0.3 μM for GSH and Cys and 0.4 μM for Hcy). The method allows for rapid screening and can also be used in combination with a digital camera readout.

Creatinine is a metabolite present in urine, and its concentration is used to diagnose and monitor kidney performance. For that reason, the development of new sensors to analyze this metabolite and obtain accurate results in a short period of time is necessary. An optical disposable sensor for monitoring creatinine levels in urine is described. The system, based on a new aryl-substituted calix[4]pyrrole synthetic receptor, has an unusual coextraction scheme. Due to the low pKa values of creatininium (pKa 4.8), a careful selection of a lipophilic pH indicator that works in acid medium is required. The sensor components were optimized, and the new sensor displays a good response time to creatinine (approximately 3 min) over a wide dynamic range (from 1 × 10−5 to 1 × 10−2 M). Moreover, the optical selectivity coefficients obtained for creatinine over common cations present in urine meet the requirements for real sample measurements. With a good sensor-to-sensor reproducibility (RSD, 5.1−6.9% in the middle of the range), this method provides a simple, quick, cost-effective, and selective alternative to the conventional methodology based on Jaffé’s reaction, FQM-118, MINECO (CTQ2016-78754-C2-1-R), Spanish Ministry of Economy and Competitiveness and European Regional Development Fund (ERDF) CTQ2016-77128-R, MINECO (CTQ2017-84319-P), Severo Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319, FEDER funds (Project CTQ2017- 84319-P), CERCA Programme/Generalitat de Catalunya and AGAUR (2017 SGR 1123)

In this paper we present the design, fabrication and characterization of electro-textile inductor and capacitor patterns on denim fabric as a basis for the development of wearable e-textiles. Planar coil inductors have been harnessed as antenna structures for the development of near field communication tags with temperature sensing capability, while interdigitated electrode capacitors have been used as humidity sensors for wearable applications. The effect of bending in the electrical performance of such structures was evaluated, showing variations below 5% in both inductance and capacitance values for bending angles in the range of interest; that is, those fitting to human limbs. In the case of the fabricated near field communication tags, a shift in the resonance frequency below 1.7% was found, meaning that the e-textile tag would still be readable by a near field communication-enabled smartphone. In respect of the capacitive humidity sensor, we obtained a minimum capacitance variation of 40% for a relative humidity range from 10% to 90%. Measured thermal shift was below 5% in the range from 10 to 40℃. When compared with the 4% variation due to bending, it can be concluded that this capacitive structure can be harnessed as a humidity sensor even under bending strain conditions and moderate temperature variations. The development and characterization of such structures on denim fabrics, which is one of the most popular fabrics for everyday clothing, combined with the additional advantage of affordable and easy fabrication methodologies, means a further step towards the next generation of smart e-textile products.

Chromophore-appended cyclodextrins combine the supramolecular loading capabilities of cyclodextrins (CDs) with the optical properties of the affixed chromophores. Among fluorescent materials, carbon dots (CNDs) are attractive and the feasibility of CND-appended CDs as sensors has been demonstrated by different authors. However, CNDs are intrinsically heterogeneous materials and their ulterior functionalization yields hybrid composites that are not well defined in terms of structure and composition. Inspired by the fluorescence properties of 5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-7-carboxylic acid (IPCA), the most paradigmatic of the molecular fluorophores detected in CNDs, herein we report two highly efficient synthetic chemical strategies for the preparation of IPCA-appended CDs that behave as CND-based CD “turn off–on” biosensors suitable for the analysis of cholesterol and β-galactosidase activity. We have deconstructed the CND–CD systems to demonstrate that (i) the role of CNDs is limited to acting as a support for the molecular fluorophores produced during their synthesis and (ii) the molecular fluorophores suffice for the determination of the enzymatic activity based on the quenching by p-nitrophenol as a sacrificial quencher., Ministerio de Economía, Industria y Competitividad, Spain CTQ2017-86125-P CTQ2016-78754-C2-1-R

Creatinine level in urine is a key factor to monitor kidney performance. The use of an alternative microfluidic platform based on cellulose substrates is an interesting option to integrate sample treatment, creatinine re- cognition by ionophore extraction chemistry and quantification by color measurement through consumer electronics imaging devices. The inclusion of ionophore extraction chemistry based on aryl-substituted calix[4] pyrrole synthetic receptor on 8.7 mm long cotton thread permit the sample treatment, optical recognition of creatinine and their quantification by smartphone running app in unfiltered urine samples diluted 1:100 ratio. The device shows a short response time, 30 s, to creatinine over a wide dynamic range (from 1.6× 10 6 to 5 10–2 M) with precision between 2.9–4.3%. The low interference level of representative species in urine is studied and justified by density functional theory (DFT) calculations., “Ministerio de Economía y Competitividad” under Project CTQ2016-78754-C2-1-R

In this work, a freshness colorimetric sensor has been integrated with pork meat packages. The sensor tracks rising CO2 levels in the package associated with meat spoilage, as CO2 levels increase with bacterial population. The color of the sensor changes depending on the quantity of bacteria present, therefore it can be correlated with the freshness of meat, in this case pork loin. Detection is achieved by a simple photograph using a smartphone, and analyzing the grey scale from the RGB space color with a custom made app. Only 2 μL of the cocktail (all components are nontoxic) is needed to prepare the sensor, which have been integrated inside meat packages using a variety of support materials prior to sealing. The Smartphone measurements have been validated using a reference method (Checkpoint Analyzer) and the results suggest it can provide the basis for a quick test of the quality of the packaged pork.

A platina sample brought to Spain in the last quarter of the 18th century is nowadays exhibited at the National Museum of Natural Sciences in Madrid. It originated from the ancient Mineralogical Museum of the School of Applied Chemistry at El Turco Street in Madrid and most probably corresponds to the material used by François Chabaneau for his experiments to purify platinum metal in the late 18th century. The sample is a heavy-mineral concentrate consisting of Pt–Fe alloys and gold nuggets associated with ilmenite–hematite, chromian spinel, goethite and minor quartz, sphene, rutile, magnetite, hornblende, garnet, calcite, pyrite, native bismuth and bismite. The Pt–Fe alloys exhibit a characteristic composition (81.97–90.75 wt.% Pt and 5.08–10.81 wt.% Fe with minor amounts of Cu, Os, Ir, Ru, Rh and Pd) and mineralogy of solid inclusions (abundant inclusions of Ir alloy as well as Os alloy, laurite–erlichmanite, bowieite, tulameenite and undetermined Pt–Pd–Ir–Rh antimonides and tellurides) that are very similar to those Pt–Fe alloys currently mined in western Colombia (the Chocó Department). These features allow us to discuss the provenance of the sample (probably from the proximal or medial reaches of any of the Chocó rivers) and evaluate the suitability of the Chabaneau's method for purifying platina. Our results show that the method became effective only with platina samples depleted or lacking iridium.

The development of a contactless readout system for High Frequency (HF) tags and its application to relative humidity monitoring is presented. The system consists of a Colpitts oscillator circuit whose frequency response is determined by a built-in logic counter of a microcontroller unit. The novel readout strategy is based on the frequency response change due to the inductive coupling between the coil of the Colpitts oscillator and the load impedance of a parallel LC resonator tag, as a result of the variation of the humidity sensing capacitor. The frequency is monitored with a low cost microcontroller, resulting in a simple readout circuit. This passive LC tag has been directly screen-printed on a humidity-sensitive flexible substrate. The readout circuit experimental uncertainty as frequency meter was 4 kHz in the HF band. A linear temperature drift of (-1.52 ± 0.17) kHz/⁰C was obtained, which can be used to apply thermal compensation if required. The readout system has been validated as a proof of concept for humidity measurement, obtaining a significant change of about 260 kHz in the resonance frequency of the Colpitts oscillator when relative humidity varies from 10% to 90%, with a maximum uncertainty of ±3% (±2 SD). Therefore, the proposed readout system stands as a compact, low-cost, contactless solution for chipless HF tags that avoids the use of bulky and costly equipment for the analog reading of wireless passive LC sensors., This work was supported by project CTQ2016-78754-C2-1-R from the Spanish Ministry of Economics and Competitivity. P. Escobedo wants to thank the Spanish Ministry of Education, Culture and Sport (MECD) for a pre-doctoral grant (FPU13/05032).

This work presents a study of high-performance capacitive sensors based on a novel design of interdigitated electrode structure. In the proposed layout, electrodes are placed out of plane and the bottom electrode is a mixed interdigitated-planar plate electrode. Thanks to this layout, the sensor sensitivity is significantly enhanced. This structure has been characterized as humidity sensor manufactured by printing techniques on a flexible substrate. In particular, the sensitive layer is made of cellulose acetate butyrate deposited by screen printing, using silver ink to define the interdigitated electrodes. The capacitance is in the range of hundreds of pF with an area of 95.5 mm2 at ambient conditions. The response of this sensor shows a sensitivity substantially dependent on the frequency but this sensitivity is considered to be enough to use this device as capacitive sensor in the whole range of frequency studied, for example 5 pF/%RH at 1 MHz. Further characterization was carried out to study the reliability of the manufacturing process and to measure the effect of temperature in the determination of the relative humidity (RH). The capacitive humidity sensor showed a thermal dependence of 0.39%RH/K at 1 MHz.

A new water-based sensor for carbon dioxide containing an ionic liquid is presented. The sensor is based on the acidity of the CO2 molecule. The sensor incorporates an ionic liquid in the matrix, which enhances CO2 solubility, and minimising the response and recovery times of the sensor. The entire concentration range (0–100%) of CO2 has been studied. The sensor is more sensitive at low CO2 concentrations as is usual in this kind of optical sensor. As the sensor is intended for smart food packaging, one of the most important characteristics is stability, and this has been studied under different conditions of light, temperature and relative humidity. The sensor was found to be stablef or more than 14 days, which is the period of use for the intended application. Pork chops were packed at 4 °C and the production of CO2 studied in conjunction with total bacterial counts over a period of 14 days. The results show that the concentration of CO2 dioxide increases in time, in correlation with bacterial counts. As the threshold of CO2 content for human consumption of this meat is 20%, the sensor has been optimised for detection around this concentration., Talentia Postdoc Program launched by the Andalusian Knowledge Agency, co-funded by the European Union’s Seventh Framework Program, Marie Skłodowska-Curie actions (COFUND – Grant Agreement n° 267226), Ministry of Economy, Innovation, Science and Employment of the Junta de Andalucía., the Science Foundation Ireland INSIGHT Centre for Data Analytics (Grant Number SFI/12/RC/2289)

The astonishing boom of radio-frequency identification (RFID) technology is stimulating plenty of new RFID-based industrial applications. Consequently, in the very near future, an almost unlimited number of RFID tags could be embedded into manufactured goods of various shapes, assets, and machineries to enable their communication abilities. As a result, prototyping techniques of RFID tags on flexible substrates are becoming more crucial. In this article, four different techniques suitable for prototyping flexible tags are briefly explained and tested from many points of view: ease of use, processing time, cost, tag sensitivity, radiation pattern, impedance, and robustness of the realized prototype. Characterization methods and experimental setups are presented, and two tag layouts, one commercial and one appositely designed, are used to compare the different techniques.

An interdigitated capacitive structure whose fingers have branches across them is described in this article. By changing the traditional interdigitated electrodes (IDE), the area where the sensor is defined can be reduced by a third, while its capacitance and sensitivity are maintained. This enhancement with respect to the traditional one is obtained thanks to the contribution to the capacitance not only in the finger length direction (unidimensional) but also in the finger width dimension (2-D). In order to test the sensitivity enhancement of this device in comparison with the conventional IDE, two version of this structure and the classical IDE have been manufactured by inkjet printing on flexible foil and characterized as relative humidity (RH) sensor. For this purpose, a substrate whose electrical permittivity changes with moisture content has been selected. Their capacitances have been measured as a function of RH in a wide range of frequencies at different temperatures, obtaining comparable results as a function of the RH and temperature. However, in the case of the sensor with closer branches, the response changes above 50%RH, showing a significantly higher sensitivity due to the fact that electrodes are much closer than in the other structures. The accumulation of water molecules between consecutive fingers occurs at lower values of moisture content than in the other layouts, resulting in higher capacitance values due to the higher electrical permittivity of water.

FDM (Fused Deposition Modelling) 3D printing emerged in the last few years as one of the most promising additive manufacturing techniques for fast prototyping. In this work, this technique is used to fabricate UHF (Ultra High Frequency) RFID (Radiofrequency Identification) flexible tag antennas, using a plastic-based conductive filament with copper inclusions, called Electrifi. A comparison with other prototypes with similar shape but fabricated through different and already investigated techniques [1] has been performed in terms of ease of use, processing time, cost, tag sensitivity, radiation pattern, and impedance. More specifically, 3D-printing technology for RFID tag fabrication is compared with inkjet printing, screen printing, wax-based deposition, and cutting plotter. The conductive properties of the antennas realized with the Electrifi filament, as expected, are lower than those of the antennas realized with the other techniques. Nevertheless, a slight degradation in terms of tag performances, is balanced by the extremely high versatility of the fabrication technique. Moreover, the capability to easily fabricate a fully 3D printable antenna, together with the possibility to print complex and not only planar geometries, pave the way to interesting and meaningful future developments. © 2019 IEEE.

A combined thread-paper microfluidic device (μTPAD) is presented for the 15 determination of glucose in blood. The device is designed to include all the analytical 16 operations needed: red blood cell separation, conditioning, enzymatic recognition, and 17 colorimetric transduction. The signal is captured with a smartphone or tablet working in 18 video mode and processed by custom Android-based software in real-time. The automatic 19 detection of the region of interest on the thread allows for the use of either initial rate or 20 equilibrium signal as analytical parameters. The time needed for analysis is 12 s using 21 initial rate, and 100 s using the equilibrium measurement with a LOD of 48 μM and 12 22 μM, respectively, and a precision around 7%. The μTPAD allows a rapid determination 23 of glucose in real samples using only 3 μL of whole blood.

The traditional role of food packaging is the isolation of foods from the outer atmosphere to extend their shelf life. In response to current necessities, traditional food packaging has led to smart packaging. CO2 inside food packages is a key factor to control. CO2 sensors can give information about the modified atmosphere integrity, indicating that the inner atmosphere is intact or if it has been broken and therefore the used by date must not be trusted, or about how fresh is the packaged product. This article briefly describes the types of packaging (traditional and smart) and how CO2 sensors can be used in the food industry. Different approaches for their integration in packaged food are described and the characteristics that must comply in order to be integrated in the agro-food industry.

In this work we propose for the first time, a paper-based test strip to analyse Cu2+ content in sugar cane spirits, which, due to its simplicity, high portability and fast analytical response (3 min), can be easily applied to in situ analyses by producers. The test strip was developed aiming: i) identify qualitatively the Cu2+ content in sugar cane spirits, and, ii) determine quantitatively the Cu2+ content using a digital image method employing a smartphone. The paper-based test strip was functionalized with cuprizone and optimized through a Box-Behnken, an experimental design for obtaining the best reaction conditions. Based on qualitative method with naked eyes approach performed by six volunteers analyst untrained, the method present a percentage of accuracy of 93%. For the quantitative analysis, it was determined the metal content at a level of statistical agreement with the reference method, as well as it was obtained the dynamic linear range from 2 to 13 mg L−1 with limits of detection and quantification of 0.034 and 0.103 mg L−1, respectively. Furthermore, the quantitative method showed a reliable precision with an RSD of 4.3% (n = 10) and the recovery of Cu2+ ranged from 80 to 103.8%.

We report a simple, rapid, low-resource and one-step method for formation of fluorescent silicon nanodots (SNDs) in a microfluidic paper-based analytical device (μPAD) incorporated in a reusable, portable and flexible heater for determination of total carbohydrates. The synthesis of SNDs is based on the redox reaction between (3-aminopropyl) triethoxysilane (APTS) reagent and carbohydrates, which act as a reducer. The graphene-based heater was fabricated by laser ablation of Kapton polyimide. Thereby, the developed system heat the μPAD during the synthesis of SNDs at 80 °C for 30 min. The blue emitting SNDs formed have an emission peak wavelength at 475 nm. We used a digital camera and smartphone for the quantitative analysis of total carbohydrates expressed such as index of glucose or fructose with grey scale value as the analytical parameter. Under the optimal conditions, the method has a low detection limit (0.80 μM for glucose and 0.51 μM for fructose, respectively), and a linear response (10–200 μM for glucose and 10–100 μM for fructose). The method has been applied to the determination of glucose in biological fluids (serum and urine samples). In addition, determination of total carbohydrates in commercial juices and teas have been carried out.

We present a new chemistry to determine nitrites implemented in a microfluidic paper-based analytical device (µPAD). The device is fabricated in cellulose paper with a sample reception area and three replicate detection areas with recognition chemistry immobilized by adsorption. The method involves the use of nitrite in an acid medium reaction to generate nitrous acid, which produces the oxidation of s-dihydrotetrazine: 1,2-dihydro-3,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazine (DHBPTz), which change the detection zone from colorless to pink. We used a digital camera and smartphone for the quantitative analysis of nitrite with the color coordinate S of the HSV color space as the analytical parameter. Parameters such as concentration and volume of s-dihydrotetrazine, pH, sample volume and reaction time were studied. The detection limit for this method is 1.30µM nitrite. To estimate the selectivity of the method an interference study of common ions in water samples was performed. The procedure was applied to natural water and compared with reference procedures.

In this work we describe a passive screen printed flexible tag for gas monitoring that can be used in sealed environments. The developed measurement system is based on chemical sensors that are sensitive to gases concentration presenting optical response, luminescent or colourimetric. The measuring electronics consist of a LED for optical excitation of the sensing membrane and a high resolution digital colour detector for the reading of the optical signal. A microcontroller receives and processes the data enabling the detection threshold for the corresponding gas. The whole system is powered by two miniaturized solar cells that provide 4 V and up to 250 μA each one. This system can run in sunlight or using a bright artificial light as the only energy source. The information of the inner environmental conditions regarding the gas concentration is transmitted to the user through a simple optical code using colour light-emitting diodes. These LEDs are activated to indicate whether the concentration of the monitored gas is within the expected limits, or not. Two prototypes based on this architecture and only changing the sensing module have been developed and applied for the determination of two common gases: oxygen and carbon dioxide. In the first case, a luminescent chemical sensor is used while in the second, the sensing membrane presents a colourimetric response. Both types of sensors can be used in this design. Resulting limits of detection are compatible with assessment of modified atmosphere packaging.

Bevacizumab (BVZ), cetuximab (CTX) and trastuzumab (TTZ) are monoclonal antibodies (mAbs) used worldwide for the treatment of several widespread kinds of cancer. They are marketed as medicines under their respective tradenames: Avastin(®), Erbitux(®) and Herceptin(®). The aim of this research was to develop in-house specific enzyme-linked immunosorbent assays (ELISA) to assess the long-term stability of these three mabs. These assays assess the biological functionality of the mAbs by quantifying their biological activity. For this purpose, we developed an indirect ELISA procedure whereby the specific antigens against which the mAbs are directed are used as specific "capturing" antibodies on the ELISA plates. We therefore used vascular endothelial growth factor (VEGF) in the ELISA for BVZ; human epidermal growth factor receptor (hEGFR) in the ELISA for CTX and human receptor HER2 (hHER2) in the ELISA for TTZ. After the mAbs had attached to their antigen, we used an anti-human IgG (whole molecule) peroxidase-conjugate and o-phenylenediaminedihydrochloride substrate. The reaction was stopped using sulphuric acid and absorbance was recorded at a wavelength of 450nm. The three ELISA methods were validated in terms of calibration models, range of the assay, limits of detection and quantitation, intra and interday precision and accuracy, and specificity by cross reactions. Forced degradation studies were also conducted on the medicines, providing useful information. Finally, the proposed ELISA were successfully used in a long-term stability study to quantify the remaining biological activity in medicines that had been opened and then stored under two different storage conditions, i.e. refrigerated at 4°C and frozen at -20°C. Results indicated that BVZ (Avastin(®)) is the most stable of the three in terms of its biological functionality.

The detection of volatile organic compounds (VOCs) at low μg/L levels in aqueous solution is accomplished using a resistive sensor. In particular, a flexible sensor manufactured by printing techniques is presented: its electrodes are defined with silver nanoparticles ink by inkjet printing, while its sensitive layer based on graphite and polystyrene is deposited by screen printing. The influence of different manufacturing parameters is analyzed: mesh density of the screen, ink composition and electrode configuration. The lower the mesh density of the screen is, the higher the resolution obtained and the lower the resistance value achieved. Inks with higher graphite content results in lower resistance values and better time responses. Higher resistance values are obtained with the serpentine electrode. In addition, the response of the sensor to different VOCs in aqueous solution is shown, finding the highest sensitivity to benzene, followed by o-xylene, p-xylene, m-xylene and toluene, in this order. All these results foresee that it is a promising device.

This work discusses about four planar printed capacitive sensors with different geometrical layouts, fabricated by inkjet printing on a flexible substrate and used as humidity sensors. In particular, we show a comparison among interdigitated electrodes, meandered electrodes, spiral electrodes, and serpentine electrodes in terms of fabrication yields, sensitivities to relative humidity as well as thermal drift taking into account frequency dependencies. In addition, numerical simulations have been performed to further investigate the characteristics of these sensors. All sensors present similar behavior in frequency with humidity. Taking into account sensitivity within the same sensing area, the highest value is achieved by serpentine electrodes, followed by spiral electrodes, interdigitated and meandered electrodes, in this order. The best configuration will be dependent on the specific application and its requirements.

Research into the effects that exposure to light can have on therapeutic proteins is essential for ensuring the quality and safety of the medicines in which they are used. It is important to understand the effects of light on aggregation to help avoid undesirable colloidal instabilities, both in the original medicines and in the formats in which they are finally administered. In this study, 5 marketed therapeutic mAbs, namely bevacizumab, cetuximab, infliximab, rituximab, and trastuzumab, were investigated for this purpose. The medicines and 2 diluted preparations in 0.9 NaCl (2 mg/mL and 5 mg/mL)-commonly used in clinical practice-were subjected to controlled light-accelerated degradation. The formation of aggregates was monitored by size-exclusion chromatography. The results indicated that light induced protein aggregation. This process of protein damage was influenced above all by mAb concentration, although the particular characteristics of each mAb were also important. Photodegradation also produced the fragmentation of the mAbs. The damage caused to the mAbs as a result of light-induced aggregation and/or fragmentation was demonstrated both in the medicines and in the diluted preparation forms. These findings should be carefully considered when handling the medicines for administration and when recommending beyond-use dates in normal hospital conditions.

This work reports on the development of a 3D microfluidic paper-based device (3D µPAD) for glucose detection using organic-inorganic hybrid nanoflower technology to immobilize the bi-enzymatic system (glucose oxidase and horseradish peroxidase). The system is based on nanoflowerssupported on cellulose paper (the microreactor zone) coupled to 3,3',5,5'-tetramethylbenzidine (TMB) as the colorimetric probe in the detection zone. We used a digital camera for the quantitative analysis of glucose with the S coordinate of the HSV color space as the analytical parameter. Under optimal operational conditions, linearity was observed for glucose concentrations up to 300 μM, with a detection limit of 15.6 µM. The biosensor is reusable and remains stable for 75 days in conventional storage conditions.

A portable reconfigurable platform for copper (Cu(II)) determination based on luminescent carbon dot (Cdots) quenching is described. The electronic setup consists of a light-emitting diode (LED) as the carbon dot optical exciter and a photodiode as a light-to-current converter integrated in the same instrument. Moreover, the overall analog conditioning is simply performed with one integrated solution, a field-programmable analog array (FPAA), which makes it possible to reconfigure the filter and gain stages in real time. This feature provides adaptability to use the platform as an analytical probe for carbon dots coming from different batches with some variations in luminescence characteristics. The calibration functions obtained that fit a modified Stern-Volmer equation were obtained using luminescence signals from Cdots quenching by Cu(II). The analytical applicability of the reconfigurable portable instrument for Cu(II) using Cdots has been successfully demonstrated in tap water analysis.

The determination of creatinine levels is essential for the detection of renal and muscular dysfunction. Luminescent nanoparticles are emerging as fast, cheap and highly selective sensors for the detection and quantification of creatinine. Nevertheless, current nanosensors only have a short shelf life due to their poor chemical and colloidal stability, which limits their clinical functionality. In this work, we have developed a highly stable, selective and sensitive nanosensor based on europium-doped, amorphous calcium phosphate nanoparticles (Eu-ACP) for the determination of creatinine by luminescence spectroscopy. The colloidal stability of Eu-ACP nanoparticles in aqueous solutions was optimised to ensure a constant signal after up to 4 months in storage. The luminescence intensity of Eu-ACP decreased linearly with the creatinine concentration over the range of 1-120 μM (R2 = 0.995). This concentration–response relationship was used to determine creatinine levels in real urine samples resulting in good recovery percentages. Significantly, selectivity assays indicated that none of the potential interfering species provoked discernible changes in the luminescence intensity.

In this work we propose a thread-based microfluidic device (μTAD) for the preconcentration and colorimetric determination of Co(II) in water using a digital image. The reaction is based on complexation of Co(II) by 4-(2- pyridylazo) resorcinol (PAR), which changes the detection zone from yellow to red. PAR is immobilized in a chitosan membrane to retain the complex in the detection zone. The designed μTAD makes it possible to pre- concentrate and determine cobalt between 25 and 600 µg·L−1 with a relative standard deviation of 4% (n = 5), and a detection limit of 6.5 µg·L−1. The device permits an enhancement factor of 11 by combining the use of a chitosan retention membrane and a sample volume of 50 µL. Recovery experiments were performed in tap water to evaluate the accuracy of the method, and the results obtained compared to a reference method presents an error no higher than 5.7%, This work was founded by Spanish “Ministerio de Economía y Competitividad” under Project CTQ2016-78754-C2-1-R and Junta de Andalucía under Projects B-FQM-243-UGR18 and P18-RT-2961. The project was partially supported by European Regional Development Funds (ERDF). Supporting Research in the State of Minas Gerais (Fapemig) (CEX-APQ-02436-15).

Chemometrics has proven to be a powerful tool for processing multivariate analytical data aimed at locating and extracting useful information relating to a particular analyte or material system in a complex sample from non-specific analytical signals that have been previously acquired and recorded by one or more analytical instruments or devices. In this paper, the basis for the application of both classification and quantitation multivariate methods is described, using a colorimetric twin sensor produced on a microfluidic paper-based analytical device (μPAD) as instructive example. The selected twin sensor provides a dual analytical signal for four anions (acetate, cyanide, fluoride and phosphate) in aqueous solution (concentration interval 0–0.1 M) from two reagent dyes (alizarin and 4-nitrophenol), which are immobilised in parallel on the same device containing four microfluidic channels designed in the form of an X. In this way, a data vector is obtained from each test whose elements are the colour coordinates obtained from the four responses, which is then used to build the chemometric models to be applied. Two multivariate classification methods (partial least squares discriminant analysis and support vector machine classification) are explored and the latter makes it possible to detect the presence or absence of each anion in an aqueous solution mixture. Single (each dye dataset separately) and fused (merging the two dye datasets) models were built and a support vector machine was shown to be the best classification method, obtaining sensitivity and precision values of 100% in almost all cases.

This work presents a study on the influence of eight different ionic liquids (ILs) in the composition of dry membranes used for gaseous CO2 optical sensing. The presence of CO2 causes a displacement of a colorimetric pH indicator toward its acid form that increases the emission intensity of the luminophore by an inner filter process. The influence of ILs in the membrane on the stability and dynamic behavior—usually the main drawbacks of these sensors—of the membranes is studied. The characterization of the different membranes prepared was carried out and the discussion of the results is presented. In all cases, the response and recovery times improved considerably, with the best case being response times of only 10 s and recovery times of 48 s, compared to response and recovery times of 41 and 100 s, respectively, for membranes without IL. The useful life of the detection membranes is also considerably longer than that of membranes that do not include IL, at least 292 days in the best case. The sensing membrane without luminophore and only containing the pH indicator is proposed for the color-based measurement of CO2 using a digital camera for possible use in food-packaging technology.

Several techniques to improve the limit of detection (LOD) of analytical systems for electrochemiluminescent (ECL) reactions are presented. This work focuses on ECL measurement based on photodiodes and techniques to improve it, which were implemented and tested in a portable instrument. Three different topologies of ECL measurement systems were compared. One system consisted of a photomultiplier (PMT) with a photocounting device and a commercial potentiostat. The other two topologies used an ad hoc potentiostat and a photodiode with different conditioning electronics: one with Field Programmable Analog Arrays (FPAA) and the other using conventional analog electronics with a programmable gain amplifier (PGA). The three systems were tested using triethylamine (TEA) as the analyte and tris(2,2′bipyridyl)ruthenium(II) as the transduction chemistry. The detection limit achieved with the system with conventional electronics and PGA was 0.02 mg l −1 , nine times lower than the system with FPAA and 45 times lower than the commercial system with the photomultiplier (PMT).

An optical humidity sensor based on a membrane of hydrophilic polymer has been developed. It is a solid state sensor where the components of the membrane are hydrophilic polymer hydroxypropyl methylcellulose (HPMC), methylene blue to indicate humidity changes and a non-ionic surfactant. The mechanism of the sensor is based on the methachromasy related to the dimerization of methylene blue observed upon exposure to humidity. Measurement were carried out in the range of 0–99.5% relative humidity with a detection limit of 0.034%RH, showing a linear response, with good reproducibility (S.D. 0.27 at 1.78%RH, n = 5) and stability, fast response and recovery times (60 and 90 s, respectively) and reversibility up to 50% at room temperature (291 K). This sensor displayed sufficient sensitivity that it could be used to detect low RH in environmental applications. Possible interferents were studied such as O 2 , CO 2 , CH 4 and H 2 gases, which did not show any interference whereas SO 2 and H 2 S cause serious interferences on the humidity sensor.

Suspended structures are an important element in the vast majority of electromechanical systems. The definition of this kind of structures is a not totally resolved problem in printing electronics where the definition of a smooth sacrificial layer makes difficult their fabrication. Based on a previous work using a sacrificial substrate, we present in this paper a significant improvement of this technique in terms of reproducibility and yield rate. The sacrificial substrate is a commercial polyvinyl alcohol film which can be removed by water. The structural material is silver paste which has shown better performance during the removal of the sacrificial substrate than the previous approach based on an acetone bath. Furthermore, this sacrificial material is biodegradable as well as its solvent. In this paper, we show the fabrication process for printed cantilevers, including a characterization of their peak to peak displacements as a function of the applied acceleration and frequency. Moreover, the variation of the capacitance for different acceleration values is presented.

This paper describes printed resonant structures on a flexible substrate for humidity detection. The devices consist of a screen-printed spiral inductor working as radio frequency identification (RFID) antenna and two different inkjet-printed planar capacitive structures forming LC resonators. The sensitive material is directly the chosen substrate: a polyimide whose electrical permittivity is dependent on the moisture content. Therefore, no extra sensitive layer is required to functionalize these structures. In particular, two different approaches can be followed to use it. On one hand, the resonant structure can be used as a threshold tag including an RFID chip. The tags will be detected or not by an RFID reader depending on the humidity. On the other hand, these structures can be directly used as quantitative humidity sensors where the moisture content is associated with the resonant frequency of the structure.

In this work a novel algorithm for the fitting of an exponential decay luminescence curve is proposed. It is based on the integration of the luminescence intensity over two or three temporal windows in different states of the sample: steady state with and without optical excitation and during the whole luminescence intensity decay. These measurements allow to obtain the amplitude of the signal, the offset and the lifetime respectively, not only for single exponential decays, but also for multiple exponential behavior, if averaged values are considered. The proposed approach does not require a very fast instrumentation, since the width of the integration windows are fixed to values much higher than the expected lifetime of the sample, which represents a clear advantage over other window-based methods for the determination of luminescence lifetime. In addition, no previous knowledge of the expected lifetime is necessary. Specifically, this algorithm is applied for the fitting of the luminescence curve of an oxygen sensor based on PtOEP, and implemented on a very reduced and simple electronics, consisting basically on a digital color detector of 12-bits resolution that allow to define integration times high enough for measurements of the intensity using this approach. Good results are achieved, proving the benefits of the method.

Cantilevers are a widely used structure in electronics, covering many applications from switches to different kinds of sensors. The majority of them have been manufactured with complimentary metal–oxide–semiconductor (CMOS) technologies, but the increasing demand on printed electronics also motivates its development with printing techniques. Here, we present a cantilever beam fabricated by printing techniques with a novel manufacturing process that simplifies the fabrication procedure in terms of cost and time. The sacrificial layer is a poly(methyl methacrylate) film, which is not placed between the substrate and the beam, but, as a peculiarity of this process, on top of the beam; that is to say, the sacrificial layer is used as a sacrificial substrate. Another challenge faced in this paper is the use of a plastic foil as the substrate of this structure. In addition, we show experimental results of the physical and electrical characterization of these devices, which are in a reasonable good agreement with simulations by a finite element modeling tool. We tested the deflection of these cantilevers at different values of acceleration and frequency to show the efficiency of the innovative process. [2014-0073]

This paper presents a flexible printed sensor to detect two different magnitudes: toluene content and relative humidity. This device has been manufactured by using two printing techniques: inkjet printing to define the electrodes and screen printing to deposit the sensitive material. The combination in the same area of two different sensors enables the monitoring of two different gaseous chemicals without interference between them. On one hand, moisture content is associated with changes in the electrical permittivity of the chosen substrate (capacitive effect). On the other hand, toluene concentration is measured through variations in volume of the developed composite (resistive effect). Changes to relative humidity and toluene content have been measured in both capacitive and resistive parts as well as their responses to temperature variations.

This article explores the use of multi-objective evolutionary machine learning techniques to find the minimum number of sensors from a pull of 6 sensors as well as the minimum number of analytical signals belonging to each selected sensor for the design of an optimal colourimetric temperature sensor. The analytical information was obtained with a calibrated neural network that provides the best temperature estimation with respect to the selected colourimetric sensor responses from a previously developed sensor array. The sensor array was developed by embedding the linear spin crossover material [Fe-(NH 2 trz) 3 ](BF 4 ) 2 into polymers with different polarity, offering different thermochromic responses related to different morphologies of the spin crossover particles when embedded in each polymer. The different thermochromic responses are tracked by the green component of the RGB colour space and the a * from CIEL* a * b * obtained with a conventional photographic digital camera. These two colour signals are used as analytical parameters for the subsequent computer processing and model calibration. The use of multi-objective optimization techniques for neural network calibration demonstrated that only 3 signals coming from 3 sensors of the 6 studied are sufficient to provide optimal temperature estimation. The optimized selection was the green channel from polyurethane hydrogel D6 and PVC prepared in THF and a * from PMMA prepared in toluene.

We present a disposable optical sensor for Ascorbic Acid (AA). It uses a polyaniline based electrochromic sensing film that undergoes a color change when exposed to solutions of ascorbic acid at pH 3.0. The color is monitored by a conventional digital camera working with the hue (H) color coordinate. The electrochromic film was deposited on an Indium Tin Oxide (ITO) electrode by cyclic voltammetry and then characterized by atomic force microscopy, electrochemical and spectroscopic techniques. An estimation of the initial rate of H, as ΔH/Δt, is used as the analytical parameter and resulted in the following logarithmic relationship: ΔH/Δt = 0.029 log[AA] + 0.14, with a limit of detection of 17 μM. The relative standard deviation when using the same membrane 5 times was 7.4% for the blank, and 2.6% (for n = 3) on exposure to ascorbic acid in 160 μM concentration. The sensor is disposable and its applicability to pharmaceutical analysis was demonstrated. This configuration can be extended for future handheld configurations. We acknowledge financial support from the Junta de Andalucía (Proyecto de Excelencia P10-FQM-5974) and from the Ministerio de Economía y Competitividad (CTQ2013-44545-R). These projects were partially supported by European Regional Development Funds (ERDF).

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 650 nm 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 150 μmol·L−1 glucose concentrations, with a 2.5 μmol·L−1 detection limit. The μPAD remains stable for 21 days 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.

Two printed single-chip UHF radio frequency identification (RFID) tags compatible with EPC Gen 2 protocol capable of measuring temperature and relative humidity are presented. The UHF RFID chip SL900A, which includes an on-chip temperature sensor, is used on both tags to drive the relative humidity (RH) sensors and the RF communication. These tags have been fabricated on polyimide substrate (Kapton HN) which presents a well known humidity dependence. Printed RH sensors consist of an array of 12 serpentine electrodes fabricated by inkjet printing and an array of 6 screen printed interdigitated electrodes, respectively, to achieve a capacitance of around 35 pF far from the capacitive parasites present in the structure. Both tags are able to provide temperature and relative humidity environmental parameters in digital form answering to the inquiries of a RFID reader in a passive energy mode (without batteries). With very low thermal drifts, below 0.05%RH/°C, a RH range of 30% is covered by both tag with sensitivities of 100 fF/RH% for the inkjetted serpentine structure and 54 fF/RH% for the screen-printed one. Therefore, we propose passive RFID tags with a single silicon chip providing a cost-effective solution to monitor environmental conditions based on printing technologies.