Sensor Array-Based Optical Portable Instrument For Determination Of Ph

A portable optical instrument is presented that makes it possible to determine pH with a colorimetric sensor array. The use of four membranes containing acid-base indicators makes it possible to cover the full range of pH using the H (hue) coordinate measurements of the HSV colour space. pH sensitive membranes were directly cast onto a plastic support to form a two-dimensional array, located between an OLED display as the programmable light source and a set of digital colour detectors. The resulting microcontroller-based system is immune to optical and electrical interferences. A complete optical and electrical characterization and optimization of the hand-held instrument was carried out. The instrument was used to determine pH using a simple algorithm to select the sensor output that was programmed in the microcontroller. The initial eleven candidate pH membranes were reduced to only four, which permit to obtain reliable pH values. The pH response of the selected four sensing elements was modelled, and calibration curves were applied to a validation set and real samples obtaining positive correlations between the real and predicted data.Ministerio de Ciencia e Innovación, Dirección General de Investigación y Gestión del Plan Nacional de I+D+i (Spain) (Projects CTQ2009-14428-C02-01 and CTQ2009-14428-C02-02)Junta de Andalucía (Proyecto de Excelencia P08-FQM-3535)Partially supported by European Regional Development Funds (ERDF

Computer Vision-Based Portable System for Nitroaromatics Discrimination

A computer vision-based portable measurement system is presented in this report. The system is based on a compact reader unit composed of a microcamera and a Raspberry Pi board as control unit. This reader can acquire and process images of a sensor array formed by four nonselective sensing chemistries. Processing these array images it is possible to identify and quantify eight different nitroaromatic compounds (both explosives and related compounds) by using chromatic coordinates of a color space.The system is also capable of sending the obtained information after the processing by aWiFi link to a smartphone in order to present the analysis result to the final user.The identification and quantification algorithm programmed in theRaspberry board is easy and quick enough to allow real time analysis. Nitroaromatic compounds analyzed in the range of mg/L were picric acid, 2,4-dinitrotoluene (2,4-DNT), 1,3-dinitrobenzene (1,3-DNB), 3,5-dinitrobenzonitrile (3,5-DNBN), 2-chloro-3,5-dinitrobenzotrifluoride (2-C-3,5-DNBF), 1,3,5-trinitrobenzene (TNB), 2,4,6-trinitrotoluene (TNT), and tetryl (TT)

Wireless wearable wristband for continuous sweat pH monitoring

Several studies have shown that the determination of pH in sweat, which is one of the most accessible body fluids, can be an indicator of health and wellness, and even be used for potential disease diagnosis. On that basis, we present herein a wearable wristband for continuous and wireless monitoring of sweat pH with potential applications in the field of personal health assessment. The developed wristband consists of two main parts: a microfluidic cloth analytical device (μCAD) to collect continuously the sweat from skin with a color-based pH sensing area; and a readout and processing module with a digital color sensor to obtain the pH of sweat from the color changes in the μCAD. In addition, the readout module includes a low-power Bluetooth interface to transmit the measurements in real-time to a custom-designed smartphone application. To allow continuous operation, an absorbent pad was included in the design to retire and store thsweat from the sensing area through a passive pump path. It was found that the Hue parameter (H) in the HSV color space can be related to the sweat pH and fitted to a Boltzmann equation (R2 = 0.997). The range of use of the wristband device goes from 6 to 8, which includes the pH range of sweat, with a precision at different pH values from 3.6 to 6.0 %. Considering the typical human sweat rate, the absorbent pad allows continuous operation up to more than 1000 minutes

Real time monitoring of glucose in whole blood by smartphone

A combined thread-paper microfluidic device (μTPAD) is presented for the determination of glucose in blood. The device is designed to include all the analytical operations needed: red blood cell separation, conditioning, enzymatic recognition, and colorimetric transduction. The signal is captured with a smartphone or tablet working in video mode and processed by custom Android-based software in real-time. The automatic detection of the region of interest on the thread allows for the use of either initial rate or equilibrium signal as analytical parameters. The time needed for analysis is 12 s using initial rate, and 100 s using the equilibrium measurement with a LOD of 48 μM and 12 μM, respectively, and a precision around 7%. The μTPAD allows a rapid de- termination of glucose in real samples using only 3 μL of whole blood.This study was supported by the CTQ2016-78754-C2-1-R project from the Spanish MINEC

A cost-effective microfluidic device for determination of biodiesel content in diesel blends

The increasing production and extensive use of biodiesel in the latest years call for the development of fast and cost-effective procedures for point-of-care analysis. One of the main quality parameters is the biodiesel content in diesel blends, which needs to conform to regional legislations. In this work, a microfluidic device exploiting chemical derivatization of alkyl esters and detection by smartphone-based digital-image colorimetry was developed. It was designed to ensure proper experimental conditions for chemical derivatization, including re- agent release, and photometric measurements. Analytes reacted with alkaline hydroxylamine yielding the cor- responding alkyl hydroxamates, measured as colored Fe(III) complexes. Analytical response was based on the measurement of the G (green) channel from RGB color system. By taking methyl linoleate as a model compound, a linear response was obtained from 0.1% to 0.6%(v/v) (Analytical signal = 69.6 +2.1 C, r = 0.999), coefficient of variation (n = 10) of 4.0% and limit of detection (99.7% confidence) of 0.04%(v/v). Procedure consumes 1.2 µL of sample, 230 µg of hydroxylamine, 480 µg of NaOH, 14 µg of Fe(III) and equivalent to 1.2 µL of 69%(v/v) HNO3. Accurate results were achieved in relation to the MIR reference method, with agreement at the 95% confidence levelThe authors gratefully acknowledge the financial support from Fundaç˜ao de Amparo `a Pesquisa do Estado de S˜ao Paulo FAPESP (proc. 2021/12242–5 and 2018/07687–5). and the support from the Spanish “Ministerio de Economía y Competitividad” (Project PID2019–103938RB- I00) and Junta de Andalucía (Projects B-FQM-243-UGR18 and P18-RT- 2961)

Capillary microfluidic platform for sulfite determination in wines

A microfluidic paper-based analytical device integrating a chromoreactand – a formylazo dye– has been fabri- cated and used for a colorimetric assay of sulfites. The chromoreactand was covalently linked to paper by vinyl sulfone chemistry. This work presents two robust capillary microfluidic devices to determine sulfite in wine without any pretreatment. One of them based on thread (µTPAD) useful to determine it in white wine and another based on paper (µPAD) to specifically determine sulfite in red wine as well as in white wine. Both are based on the selective recognition of sulfite by means of a chromoreactand that turns from orange to yellow in the presence of sulfite. The colour information acquired (H coordinate) using a digital camera readout allows for a range of appli- cation of the µTPAD from 7.8⋅10−5 M (8.1 mg L−1) to 2.7⋅10−3 M (279.3 mg L−1) with a limit of detection (LOD) of 78 µM. The strong interference caused by the dyes present in red wine is eliminated by including a laminated paper channel in the µPAD structure that allows for the separation of colorants from red wine before the recognition of the sulfite. This makes it possible to adjust the µPAD procedure to the usual sulfite concentration in wine, with an LOD of 2.2⋅10−4 M (22.7 mg L−1) and a CV of 2.6%.This work was founded by Spanish “Ministerio de Economía y Competitividad” (Projects PID2019-103938RB-I00) and Junta de Andalucía (Projects B-FQM-243-UGR18 and P18-RT-2961). The projects were partially supported by European Regional Development Funds (ERDF)

Flexible Passive NFC Tag for Multi-Gas Sensing

In this work we present a full-passive flexible multigas sensing tag for the determination of oxygen, carbon dioxide, ammonia, and relative humidity readable by a smartphone. This tag is based on near field communication (NFC) technology for energy harvesting and data transmission to a smartphone. The gas sensors show an optic response that is read through high-resolution digital color detectors. A white LED is used as the common optical excitation source for all the sensors. Only a reduced electronics with very low power consumption is required for the reading of the optical responses and data transmission to a remote user. An application for the Android operating system has been developed for the power supplying and data reception from the tag. The responses of the sensors have been calibrated and fitted to simple functions, allowing a fast prediction of the gases concentration. Cross-sensitivity has also been evaluated, finding that in most of the cases it is negligible or easily correctable using the rest of the readings. The election of the target gases has been due to their importance in the monitoring of modified atmosphere packaging. The resolutions and limits of detection measured are suitable for such kinds of applications.This work was supported by project CTQ2013-44545-R from the Ministry of Economy and Competitiveness (Spain) and Junta de Andalucía (Proyecto de Excelencia P10- FQM-5974). These projects were partially supported by European Regional Development Funds (ERDF). P. Escobedo wants to thank the Spanish Ministry of Education, Culture and Sport (MECD) for a pre-doctoral grant (FPU13/05032)

Thread based microfluidic platform for urinary creatinine analysis

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-

WEARABLE DEVICE FOR REAL TIME pH MEASUREMENT IN SWEAT

Nowadays, it is more and more common to find devices that permits to everybody carry out analysis of different analytes of interest as glucose in blood or creatinine in urine by themselves, thanks to the development of the Point-of-Care (POC) devices. POC’s permit the in situ analysis of the samples, in an easy way, quickly and by the use of a small amount of sample in the sampling area of the device, obtaining result with no need of instrumentation or by the use of a very simple one. In order to match these objectives and make the device useful for everybody in any condition, the WHO has described the ASSURED guidelines for the POC devices[1]. In the recent years, and thanks to the capillary properties of different materials as paper, thread or cloth, the development of the POC devices are turning to a new strategy that implies the inclusion of the POC devices in t-shirts, bracelets or patches obtaining in this way wearables sensors. In this kind of sensor, instead of the addition of the sample in the sampling area, it moves through the device arriving to recognition/transduction area were the property of the sensor changes and can be measured and related to the concentration of the analyte. In this work, we present a wearable POC that permits the real-time determination of the pH in sweat. For this purpose, we have developed a μCAD (Figure) that contains a pH indicator (4-[4-(2-hydroxyethanesulfonyl)-phenylazo]-2,6-dimethoxyphenol (GJM-534) [2]) covalently immobilized on cotton cloth, which color is going to change from yellow (pH around 6) to pink (pH around 9) depending on the pH. The size and shape of the μCAD (see Figure) was designed taking into account the low flow rate of sweat generated in the wrist when sweating (0.01 μL/min) including a superabsorbent material working as passive pump to avoid the saturation of sample of the μCAD. The colorimetric device was calibrated using the H parameter from the HSV color space as analytical parameter, obtaining the calibration function and analytical parameters of the device, the reversibility of the μCAD, response time and stability. Finally, the μCAD was integrated into a bracelet that includes a color detector and a microprocessor that registered the color of the μCAD in real-time and send the information via Bluetooth to a smartphone, obtaining and registering the pH of the sweat while doing exercise.This study was supported by project from the Spanish MINECO (CTQ2016-78754-C2-1-R)