Correction: Inkjet-printed O2 gas sensors in intelligent packaging.

Correction for 'Inkjet-printed O2 gas sensors in intelligent packaging' by M. D. Fernández-Ramos et al., Analyst, 2021, 146, 3177-3184, https://doi.org/10.1039/D1AN00295C.

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

Correction for 'An optical sensor for the sensitive determination of formaldehyde gas based on chromotropic acid and 4-aminoazobenzene immobilized in a hydrophilic membrane' by M. D. Fernández-Ramos et al., Analyst, 2023, 148, 4533-4538, https://doi.org/10.1039/D3AN01056B.

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.

Design of colorimetric nanostructured sensor phases for simple and fast quantification of low concentrations of acid vapors.

Two colorimetric nanostructured sensor phases (Color-NSPs) for the determination of low concentrations of acid vapors in the atmosphere of paper storage rooms have been designed and characterized. The acid vapor determination is based on the color change that occurs in polyaniline (PANI) in the presence of acids when it goes from its emeraldine base form (blue) to its emeraldine salt form (green). To synthesize the Color-NSPs, two methods have been used, a one-step method performed by grafting polyaniline onto a cellulose membrane (Cellu-PANI) and a two-step method in which in the first step, polyaniline is grafted onto the surface of polymeric nanoparticles (NPs-PANI), and in a second step, NPs-PANI are immobilized into the pores of a nylon membrane (Nylon-NPs PANI). The response of the sensors versus acid vapor was measured by color coordinates with a photographic camera. A linear response range from 1 ppmv to 7 ppmv was found for both sensors, and the detection limits were 0.95 ppmv (1.2 % RSD) and 0.40 ppmv (0.8 % RSD) for Cellu-PANI and Nylon-NPs PANI, respectively. In addition, both sensors showed complete reversibility and a short exposition time (5 min). The potential applicability of the Color-NSPs in the control of the exposure of paper heritage collections to outdoor- and indoor-generated gaseous pollutants was demonstrated by determining acid vapors in museums. The method was validated with an external reference method; the paired test was applied, and p-values greater than 5% were obtained, indicating an excellent correlation and showing that the Color-NSPs reported are simple, fast, and an economical alternative to control and protect cultural heritage materials in indoor environments.

Inkjet-printed O2 gas sensors in intelligent packaging.

An inkjet printed membrane is presented as a colorimetric sensor for oxygen for use in smart packaging, in order to quickly inform the consumer about possible degradation reactions in modified atmosphere products (MAP). The colorimetric sensor is based on the redox dye, toluidine blue (TB), a sacrificial electron donor, glycerol, and, hydroxypropyl methylcellulose, as the hydrophilic polymeric matrix. The UVC-wavelength activated TB is photoreduced by SnO2 nanoparticle ink. This colorimetric oxygen indicator stays colourless upon exposure in nitrogen atmosphere to 7 min UVC light (6 W·cm-2). The photoreduced TB to leuco TB recovers its original colour upon exposure to oxygen for 55 min under ambient conditions (∼21 °C, ∼55%RH, 21% O2). The characteristics of the sensor have been evaluated, including its functionality through the colorimetric response to different oxygen concentrations as well as the influence of experimental variables such as humidity and temperature using a digital camera as the detector. The results obtained show that: (1) the colorimetric sensor remains stable in the absence of oxygen; (2) relative humidity greater than 60% significantly affects the reoxidation process; and (3) the temperature has a significant influence on the colour recovery, although the stability increases considerably when the sensor is kept refrigerated at 4 °C. A real application to packaged ham was performed, demonstrating that the printed colorimetric sensor is stable for at least 48 hours once activated and when the container deteriorates upon the entrance of oxygen, the sensor returns to its original blue colour, demonstrating its utility as a UVC-activated colorimetric oxygen sensor.

NIR optical carbon dioxide gas sensor based on simple azaBODIPY pH indicators.

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.

Ionic liquids on optical sensors for gaseous carbon dioxide.

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. Graphical abstract ᅟ.

Printed disposable colorimetric array for metal ion discrimination.

One of the main limiting factors in optical sensing arrays is the reproducibility in the preparation, typically by spin coating and drop casting techniques, which produce membranes that are not fully homogeneous. In this paper, we increase the discriminatory power of colorimetric arrays by increasing the reproducibility in the preparation by inkjet printing and measuring the color from the image of the array acquired by a digital camera, using the H coordinate of the HSV color space as the analytical parameter, which produces robust and precise measurements. A disposable 31 mm × 19 mm nylon membrane with 35 sensing areas with 7 commercial chromogenic reagents makes it possible to identify 13 metal ions and to determine mixtures with up to 5 ions using a two-stage neural network approach with higher accuracy than with previous approaches.

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.

Point-of-care assay platform for uric acid, urea, and triglycerides with a microfluidic paper device (µPAD) controlled by stimulus-sensitive valves.

A microfluidic biosensor paper-based analytical device, or µPAD, was developed as a point-of-care assay platform for the simultaneous determination of three clinically important markers: uric acid, urea, and triglycerides. To achieve a simultaneous determination, thermosensitive valves based on N-isopropylacrylamide polymers controlled the flow of fluid in the µPAD. The evaluation of the analytical characteristics of the µPAD was done using a photographic camera at room temperature. The detection limits were 4.5·10-5, 2.5·10-3, and 1.5·10-3 mg mL-1, for uric acid, urea, and triglycerides, respectively, and the precision expressed as relative standard deviation (% RSD) 3.2, 1.2, and 1.6%. The obtained µPAD devices were validated with real human plasma samples, demonstrating high accuracy and precision. Multiple analyte point-of-care tests such as those developed here have excellent characteristics, being easy to manufacture, cost-effective, easy to use, and highly sensitive.

LED-LED portable oxygen gas sensor.

A portable instrument for oxygen determination, based on the quenching of phosphorescent octaethylporphyrin by gaseous O(2), has been developed using the fluorimetric paired emitter-detector diode technique (FPEDD). The instrument configuration consists of two light-emitting diodes (LEDs) facing each other, with an interchangeable support containing a phosphorescent membrane in between, in which one of the LEDs is used as the light source (emitter LED) and the other, working in reverse bias mode, as the light detector. The feasibility of using a LED as a luminescence detector is studied. Its small size enables integration of the instrument into a portable measurement system. A systematic study of the system capabilities as a portable instrument was performed to optimize range, sensitivity, short term and long term stability, dynamic behaviour, effect of temperature and humidity, and temporal drift.

Smart facemask for wireless CO2 monitoring.

The use of facemasks by the general population is recommended worldwide to prevent the spread of SARS-CoV-2. Despite the evidence in favour of facemasks to reduce community transmission, there is also agreement on the potential adverse effects of their prolonged usage, mainly caused by CO2 rebreathing. Herein we report the development of a sensing platform for gaseous CO2 real-time determination inside FFP2 facemasks. The system consists of an opto-chemical sensor combined with a flexible, battery-less, near-field-enabled tag with resolution and limit of detection of 103 and 140 ppm respectively, and sensor lifetime of 8 h, which is comparable with recommended FFP2 facemask usage times. We include a custom smartphone application for wireless powering, data processing, alert management, results displaying and sharing. Through performance tests during daily activity and exercise monitoring, we demonstrate its utility for non-invasive, wearable health assessment and its potential applicability for preclinical research and diagnostics.

Copolymerization of luminol on screen-printed cells for single-use electrochemiluminescent sensors.

An efficient electrochemiluminescent (ECL) single-use sensor for H(2)O(2) is presented based on an electropolymerized film prepared on screen-printed gold electrode (gold SPE). A study of the copolymerization of luminol in the presence of different monomers was carried out. The polymeric films were grown potentiodynamically with a potential interval between -0.2 and 1.0 V in 0.2 M H(2)SO(4) and were characterized by their electrochemical, electrochemiluminescent, and superficial features. The polymer with the most efficient growth and ECL emission was poly(luminol-3,3',5,5'-tetramethylbenzidine) at 1:5 ratio. These prepared SPE cells present good mechanical and photoemissive properties. A semi-logarithmic linearization shows a noticeable four decade-width concentration range with a limit of detection (LOD) of 2.6 × 10(-9) M and a precision of 10.2% (n = 5; as relative standard deviation, RSD) in the medium range level. The described SPE ECL sensors will be useful for the determination of oxidase substrates in ECL single-use biosensors.

An IUPAC-based approach to estimate the detection limit in co-extraction-based optical sensors for anions with sigmoidal response calibration curves.

An approach based on IUPAC methodology to estimate the limit of detection of bulk optode-based analytical methods for anions has been developed. The traditional IUPAC methodology for calculating the detection limit was modified to be adapted to particular cases where the calibration curves have a sigmoidal profile. Starting from the different full theoretical models for every co-extraction mechanism of the analyte in the membrane in bulk optodes, several particular simplified models at low analyte concentration were obtained and validated. The slope of the calibration curve at low analyte concentration was calculated from the first derivative of the simplified equation and, subsequently, the detection limit was estimated. This fitted-for-purpose estimation strategy was applied to anion quantification for in-house bulk optode-based analytical methods, and the estimated limits of detection were compared with those obtained by applying classical geometrical methodology. This way of establishing the detection limit yields values that maintain their true statistical and probabilistic aspects. It can be easily applied to any analytical system which yields non-linear calibration curves at low analyte concentration.

Analysis of phenolic compounds in health care products by low-pressure liquid-chromatography with monolithic column and chemiluminescent detection.

This paper presents a new application for monolithic columns with low-pressure chromatographic separation using an flow injection analysis configuration with chemiluminescent detection for the determination of a mixture of phenolic compounds: phloroglucinol, 2,4-dihydroxybenzoic acid, salicylic acid, methyl paraben and n-propyl gallate. The procedure consists of the separation of these compounds on a reverse-phase ultra-short monolithic column with pH 3.0 acetate buffer and 5% acetonitrile as carrier phase. The detection is based on a chemiluminescence measurement coming from Ce(IV)-Rhodamine 6G chemistry with the incorporation of two different chemiluminescent chemical conditions in the chromatographic setup in order to enhance the sensitivity for the different phenolic compounds. All separation and detection variables were optimized to propose a determination method. The analysis is performed in 280?s, with the sampling frequency being some 13 h(-1) . The calibration function is a double reciprocal function obtaining good results within two orders of magnitude. The limits of detection were 8.8 × 10 (-8) m (phloroglucinol), 2.7 × 10 (-8) m (2,4-dihydroxybenzoic acid); 2.3 × 10 (-8) m (salicylic acid); 5.2 × 10 (-8) m (methyl paraben) and 4.1 × 10 (-6) m (n-propyl gallate), and the relative standard deviations at a medium level of the linear range were 4.4% (phloroglucinol), 2.8% (2,4-dihydroxybenzoic acid), 5.2% (salicylic acid), 3.6% (methyl paraben) and 6.8% (n-propyl gallate). The method was applied and validated satisfactorily for the determination of these compounds in healthcare products, comparing the results against an HPLC reference method.

Use of the hue parameter of the hue, saturation, value color space as a quantitative analytical parameter for bitonal optical sensors.

The hue or H component of the hue, saturation, value (HSV) color space has been studied as a quantitative analytical parameter for bitonal optical sensors. The robust nature of this parameter provides superior precision for the measurement of sensors which change colors with the speciation of some indicator molecule. This parameter has been compared to red, green, blue (RGB) intensity and RGB absorbance along with differences and ratios of both intensity and absorbance and has been demonstrated to be 2 to 3 times superior. The H value maintains this superior precision with variations in indicator concentration, membrane thickness, detector spectral responsivity, and illumination. Because this parameter is stable, simple to calculate, easily obtained from commercial devices such as scanners and digital cameras, continuous over the entire color gamut, and bound between values of 0 and 1, it shows great promise for use in a variety of sensing applications including imaging, automated analysis, pharmaceutical sensing, lab-on-a-chip devices, and quality control applications.

Bioactive microfluidic paper device for pesticide determination in waters.

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 acetylcholine 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 coordinate. 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 determination of pesticides in different water samples, with no sample preparation.

Optical portable instrument for the determination of CO2 in indoor environments.

A portable device based on a colorimetric sensor to determine the atmospheric level of CO2 gas is presented in this work. The system is based on a low-cost, low-power System on a Chip (SoC) microcontroller with integrated Wi-Fi. A user-friendly application was developed to monitor and log the CO2 measurements when the system is connected to a Wi-Fi network. The sensing membrane is directly deposited on the surface of the colour detector, thus reducing the complexity of the system. This sensing membrane is formed by a pH indicator α-naphtholphthalein, tetramethylammonium hydroxide pentahydrate, 1-ethyl-3-methylimidazolium tetrafluoroborate, Tween 20 and hydroxypropyl methylcellulose as the hydrophilic polymer. The system has been fully characterized, obtaining response and recovery times of 1.3 and 2.5 s, respectively, a limit of detection of 51 ppm, and an average resolution of 6.3 ppm. This portable device was applied for the in-situ determination of CO2 gas in the atmosphere inside classrooms in several secondary schools. The measurements were taken during complete workdays and the results were statistically compared with the same measurements taken using a commercially available non-dispersive infra-red (NDIR) device. No significant statistical differences were found between the results obtained using both devices. A complete statistical treatment of the measurements made with the proposed portable device was carried out. The obtained results show that the concentration of CO2 gas in some schools was higher than the desired concentration, with regard to influencing the student's health, safety, productivity and comfort. This demonstrates the need to control this parameter to ensure appropriate indoor environmental quality (IEQ).

Disposable electrochemiluminescent biosensor for lactate determination in saliva.

An electrochemiluminescence-based disposable biosensor for lactate is characterized. The lactate recognition system is based on lactate oxidase (LOx) and the transduction system consists of luminol. All the needed reagents, luminol, LOx, BSA, electrolyte and buffer have been immobilized by a Methocel membrane placed on the working electrode of the screen-printed electrochemical cell. The measurement of the electrochemiluminescence (ECL) is made possible via a photocounting head when 50 microl of sample is placed into the screen-printed cell with a circular container containing the disposable sensing membrane. The compositions of the membrane and reaction conditions have been optimized to obtain adequate sensitivity. The disposable biosensor responds to lactate after 20 s when two 1 s pulses at 0.5 V are applied to obtain the analytical parameter, the ECL initial rate. The linearized double logarithmic dependence for lactate shows a dynamic range from 10(-5) to 5 x 10(-4) M with a detection limit of 5 x 10(-6) M and a sensor-to-sensor repeatability, as relative standard deviation, RSD, of 3.30% at the medium level of the range. The ECL disposable biosensor was applied to the analysis of lactate in human saliva as an alternative procedure for obtaining the lactate level in a non-invasive way. Interferences coming from components of saliva were studied and eliminated in a simple way that was easy to handle. The procedure was validated for use in human saliva, comparing the results against an enzymatic reference procedure. The proposed method is quick, inexpensive, selective and sensitive and uses conventional ECL instrumentation.

Colourimetric characterisation of disposable optical sensors from spectroradiometric measurements.

Spectroradiometric measurements of reflectance and CIELAB hue-angle, were tested for K(I) determination using disposable optical sensors based on ion exchange mechanism. The linearisation of the sigmoidal response function, using a logistic regression, increases the linear range noticeably to 7.65 x 10(-8)-1.5 M and 1.22 x 10(-7)-1.5 M for CIELAB hue-angle and reflectance, respectively. The trueness of both procedures was demonstrated comparing it with results obtained by a DAD spectrophotometer used as a reference measurement procedure. The usefulness of the procedure was checked by analysing K(I) in different types of waters and beverages. Additionally, we studied the possible visual discrimination for the whole potassium range tested, obtaining the possibility of discriminating twelve groups of concentrations.