Synthesis of a thermoresponsive crosslinked MEO2MA polymer coating on microclusters of iron oxide nanoparticles

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.Andalusian Knowledge AgencyEuropean Commission 291780Ministry of Economy, Innovation, Science and Employment of the Junta de AndalucíaSpanish "Ministerio de Economía y Competitividad" PID2019-103938RB-I00 CTQ2017-86125-PJunta de Andalucía B-FQM-243-UGR18 P18-RT-2961CEI-Biotic CEI2013-MP-1

Thread-based microfluidic sensor for lithium monitoring in saliva

Lithium administration is a commonly prescribed treatment for some mental disorders, e.g. bipolar disorder. However, Li+ level must be regularly monitored to maintain therapeutical effect and avoid adverse side effects. Currently, it is determined in blood, using complex instrumentation, which excludes self-monitoring of lithium concentration by patients themselves. That creates a need for simple, reliable and fast sensors for Li monitoring in biological fluids. In this paper, we introduced a microfluidic thread-based analytical device for optical determination of lithium in saliva. Lithium ion recognition was achieved by incorporating of chromoionophore- ionophore chemistry onto thread. To ensure appropriate selectivity over other alkaline metal ions, it was necessary to include an efficient lithium extractant in the sensing cocktail, alongside its usual components. After optimization of cocktail composition, the developed sensors allowed for lithium determination in a range from 8.8⋅10−4 to 0.95 mol L−1 with remarkable precision of 0.3% (at 10−2 mol L−1) and within a very short time of ca. 10 s. The analytical usefulness of the developed sensors was tested with saliva samples, which were analyzed without any prior processing. A comparison of the obtained results with a reference method revealed high ac- curacy (relative error < ±20% in most cases).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). These investigations were also supported by Polish National Science Centre (Project PRELUDIUM no. 2021/41/N/ST4/00299)

An optical sensor for the sensitive determination of formaldehyde gas based on chromotropic acid and 4-aminoazobenzene immobilized in a hydrophilic membrane

Formaldehyde is a common contaminant in occupational and environmental atmospheres, prolonged exposure leads to health risks, and its determination is necessary to protect health. There is a great demand for portable, rapid, and sensitive methods that can be used in resource-limited settings. In this respect, a colorimetric sensor has been developed based on the colour change from pink to purple of co-immobilized chromotropic acid and 4-aminoazobenzene in hydroxypropyl methylcellulose when it is exposed to different concentrations of formaldehyde. The concentration of formaldehyde in the gas phase was quantified by measuring the change of the appropriate colour coordinates in response to the concentration of formaldehyde. A calibration curve was obtained for formaldehyde, with a useful concentration range from 0.08 to 0.6 ppmv. The detection limit was 0.016 ppmv, which is lower than the maximum exposure concentrations recommended by both the World Health Organization (WHO) and the Occupational Safety and Health Administration (OSHA). The optical sensor was found to have good reproducibility, with a relative standard deviation of 2.3 and 1.7% at 0.08 and 0.25 ppmv, respectively. The sensor can operate at room temperature and environmental humidity, 25 °C, and 50% RH, respectively. In addition, a study of interferents (acetaldehyde, toluene, methanol, ethyl acetate, acetone, acetic acid, carbon dioxide and ammonia) showed high selectivity for formaldehyde, which indicates that this membrane is a simple, fast, and economical alternative for quantifying the concentration of formaldehyde in different environments.Spanish “Ministerio de Ciencia e Innovación/Agencia Estatal de Innovación” Project: PID2019-103938RB-I00Spanish “Ministerio de Ciencia e Innovación/Agencia Estatal de Innovación” Project: PID 2021-126579OB-C31Junta de Andalucía Projects: B-FQM-243-UGR18 and P18-RT-296

Near Infrared Sensor to Determine Carbon Dioxide Gas Based on Ionic Liquid

In this study we present an NIR carbon dioxide gas sensor based on an inner filter process that includes an ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4), to improve its stability, dynamic behavior and lifetime, which are usually the main drawbacks with these sensors. The presence of CO2 causes a displacement of a simple boron-dipyrromethene-type fluorophore, azaBODIPY, as the pH indicator towards its acid form. This increases the emission intensity of Cr(III)-doped gadolinium aluminium borate (GAB) as the luminophore. The characterization of the prepared sensor was carried out and a discussion of the results is presented. The response and recovery times improved considerably, 23 and 49 s, respectively, with respect to the sensor without IL, at 60 and 120 s, respectively,. Additionally, the measurement range is extended when using IL, able in this case to measure in the complete range up to 100% CO2; without IL the measurement range is limited to 60% CO2. The detection limit ranges from 0.57% CO2 without IL to 0.26% CO2 when IL is added. The useful lifetime of the sensing membrane was 20 days for membranes with IL and only 6 days for membranes without IL, with the sensor always kept in the dark and without the need to maintain a special atmosphere

Monitoring of degradation of porous silicon photonic crystals using digital photography

We report the monitoring of porous silicon (pSi) degradation in aqueous solutions using a consumer-grade digital camera. To facilitate optical monitoring, the pSi samples were prepared as one-dimensional photonic crystals (rugate filters) by electrochemical etching of highly doped p-type Si wafers using a periodic etch waveform. Two pSi formulations, representing chemistries relevant for self-reporting drug delivery applications, were tested: freshly etched pSi (fpSi) and fpSi coated with the biodegradable polymer chitosan (pSi-ch). Accelerated degradation of the samples in an ethanol-containing pH 10 aqueous basic buffer was monitored in situ by digital imaging with a consumer-grade digital camera with simultaneous optical reflectance spectrophotometric point measurements. As the nanostructured porous silicon matrix dissolved, a hypsochromic shift in the wavelength of the rugate reflectance peak resulted in visible color changes from red to green. While the H coordinate in the hue, saturation, and value (HSV) color space calculated using the as-acquired photographs was a good monitor of degradation at short times (t  pSi-ch.We acknowledge the financial support from Ministerio de Educación y Ciencia (Spain), Dirección General de Enseñanza Superior (Spain) (CTQ2009-14428-C02-01), and Junta de Andalucía (Spain) (P10-FQM-5974). A.N. wants to acknowledge Fundación Alfonso Martín Escudero for a postdoctoral fellowship. This material is based upon the work supported by the U.S. National Science Foundation under Grant No. DMR-1210417

Smartphone-based simultaneous pH and nitrite colorimetric determination for paper microfluidic devices

In this work, an Android application for measurement of nitrite concentration and pH determination in combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed imageprocessing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L−1 of resolution and 0.52 mg L−1 as the limit of detection was achieved

Handheld colorimeter for determination of heavy metal concentrations

A portable instrument that measures heavy metal concentration from a colorimetric sensor array is presented. The use of eight sensing membranes, placed on a plastic support, allows to obtain the hue component of the HSV colour space of each one in order to determinate the concentration of metals present in a solution. The developed microcontroller-based system captures, in an ambient light environment, an image of the sensor array using an integrated micro-camera and shows the picture in a touch micro-LCD screen which acts as user interface. After image-processing of the regions of interest selected by the user, colour and concentration information are displayed on the screen

Fast prototyping of paper-based microfluidic devices by contact stamping using indelible ink

This work was supported by Science Foundation Ireland under CLARITY CSET award (grant 07/CE/I1147). Thanks to Staedtler Mars GmbH & Co. KG for providing the LumocolorE Permanent Universal Black InkHere we present a fast and cheap prototyping technique for the realisation of paper-based microfluidic devices simply by using a stamp and indelible ink. The proposed mechanism involves contact stamping of indelible ink to laboratory filter paper using a PDMS stamp, which defines the microfluidic structure. It is a cleanroom and washing steps-free method which provides a reproducible method for the production of functional paper-based microfluidic devices in a single step in less than 10 s. The method is fully characterised and the concept has been applied, as a proof-of-principle, for the realisation of a low-cost colorimetric glucose sensor.Supported by Science Foundation Ireland under CLARITY CSET award (grant 07/CE/I1147

Screen Printed Flexible Radiofrequency Identification Tag for Oxygen Monitoring

In this work, a radiofrequency identification (RFID) tag with an optical indicator for the measurement of gaseous oxygen is described. It consists of an O2 sensing membrane of PtOEP together with a full electronic system for RFID communication, all printed on a flexible substrate. The membrane is excited by an LED at 385 nm wavelength and the intensity of the luminescence generated is registered by means of a digital color detector. The output data corresponding to the red coordinate of the RGB color space is directly related to the concentration of O2, and it is sent to a microcontroller. The RFID tag is designed and implemented by screen printing on a flexible substrate for the wireless transmission of the measurement to a remote reader. It can operate in both active and passive mode, obtaining the power supply from the electromagnetic waves of the RFID reader or from a small battery, respectively. This system has been fully characterized and calibrated including temperature drifts, showing a high-resolution performance that allows measurement of very low values of oxygen content. Therefore this system is perfectly suitable for its use in modified atmosphere packaging where the oxygen concentration is reduced below 2%. As the reading of the O2 concentration inside the envelope is carried out with an external RFID reader using wireless communication, there is no need for perforations for probes or wires, so the packaging remains completely closed. With the presented device, a limit of detection of 40 ppm and a resolution as low as 0.1 ppm of O2 can be reached with a low power consumption of 3.55 mA.Junta de Andalucía (Proyecto de Excelencia P10-TIC-5997 and P10-FQM-5974)Project PYR-2012-12, CEI BioTIC (CEB09-0010 and CEI2013-P-2) from CEI program of MICINNEuropean Regional Development Funds (ERDF