Development of a "turn off" fluorescent molecularly imprinted nanoparticle-based sensor for selective captopril quantification in synthetic urine and wastewater samples.

The combination of silica nanoparticles with fluorescent molecularly imprinted polymers (Si-FMIPs) prepared by a one-pot sol-gel synthesis method to act as chemical sensors for the selective and sensitive determination of captopril is described. Several analytical parameters were optimized, including reagent ratio, solvent, concentration of Si-FMIP solutions, and contact time. Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and the ninhydrin assay were used for characterization. The selectivity was evaluated against molecules belonging to other drug classes, such as fluoroquinolones, nonacid nonopioids, benzothiadiazine, alpha amino acids, and nitroimidazoles. Under optimized conditions, the Si-FMIP-based sensor exhibited a working range of 1-15 µM, with a limit of detection (LOD) of 0.7 µM, repeatability of 6.4% (n = 10), and suitable recovery values at three concentration levels (98.5% (1.5 µM), 99.9% (3.5 µM), and 99.2% (7.5 µM)) for wastewater samples. The sensor provided a working range of 0.5-15 µM for synthetic urine samples, with an LOD of 0.4 µM and a repeatability of 7.4% (n = 10) and recovery values of 93.7%, 92.9%, and 98.0% for 1.0 µM, 3.5 µM, and 10 µM, respectively. In conclusion, our single-vessel synthesis approach for Si-FMIPs proved to be highly effective for the selective determination of captopril in wastewater and synthetic urine samples.

Transparent, flexible, and eco-friendly starch-based films for reversible optoelectronic noses for food spoilage monitoring in smart packaging.

A reversible optoelectronic nose is presented consisting of ten acid-base indicators incorporated into a starch-based film, covering a wide pH range. The starch substrate is odorless, biocompatible, flexible, and exhibits high tensile resistance. This optical artificial olfaction system was used to detect the early stages of food decomposition by exposing it to the volatile compounds produced during the spoialge process of three food products (beef, chicken, and pork). A smartphone was used to capture the color changes caused by intermolecular interactions between each dye and the emitted volatiles over time. Digital images were processed to generate a differential color map, which uses the observed color shifts to create a unique signature for each food product. To effectively discriminate among different samples and exposure times, we employed chemometric tools, including hierarchical cluster analysis (HCA) and principal component analysis (PCA). This approach detects food deterioration in a practical, cost-effective, and user-friendly manner, making it suitable for smart packaging. Additionally, the use of starch-based films in the food industry is preferable due to their biocompatibility and biodegradability characteristics.

Fabrication of Low-Cost Miniaturized Gas Cells via SLA 3D-Printing for UV-Based Gas Sensors.

The use of 3D-printing technology for producing optical devices (i.e., mirrors and waveguides) remains challenging, especially in the UV spectral regime. Gas sensors based on absorbance measurements in the UV region are suitable for determining numerous volatile species in a variety of samples and analytical scenarios. The performance of absorbance-based gas sensors is dependent on the ability of the gas cell to propagate radiation across the absorption path length and facilitate interaction between photons and analytes. In this technical note, we present a 3D-printed substrate-integrated hollow waveguide (iHWG) to be used as a miniaturized and ultralightweight gas cell used in UV gas-sensing schemes. The substrates were fabricated via UV stereolithography and polished, and the light-guiding channel was coated with aluminum for UV reflectivity. This procedure resulted in a surface roughness of 11.2 nm for the reflective coating, yielding a radiation attenuation of 2.25 W/cm2. The 3D-printed iHWG was coupled to a UV light source and a portable USB-connected spectrometer. The sensing device was applied for the quantification of isoprene and acetone, serving as a proof-of-concept study. Detection limits of 0.22 and 0.03% in air were obtained for acetone and isoprene, respectively, with a nearly instantaneous sensor response. The development of portable, low-cost, and ultralightweight UV optical sensors enables their use in a wide range of scenarios ranging from environmental monitoring to clinical/medical applications.

AirQuality Lab-on-a-Drone: A Low-Cost 3D-Printed Analytical IoT Platform for Vertical Monitoring of Gaseous H2S.

The measurement of gaseous compounds in the atmosphere is a multichallenging task due to their low concentration range, long and latitudinal concentration variations, and the presence of sample interferents. Herein, we present a quadcopter drone deployed with a fully integrated 3D-printed analytical laboratory for H2S monitoring. Also, the analytical system makes part of the Internet of Things approach. The analytical method applied was based on the reaction between fluorescein mercuric acetate and H2S that led to fluorescence quenching. A 5 V micropump at a constant airflow of 50 mL min-1 was employed to deliver constant air into a flask containing 800 µL of the reagent. The analytical signal was obtained using a light-emitting diode and a miniaturized digital light detector. The method enabled the detection of H2S in the range from 15 to 200 ppbv, with a reproducibility of 5% for a sampling time of 10 min and an limit of detection of 9 ppbv. All devices were controlled using an Arduino powered by a small power bank, and the results were transmitted to a smartphone via Bluetooth. The proposed device resulted in a weight of 300 g and an overall cost of ∼50 USD. The platform was used to monitor the concentration of H2S in different intervals next to a wastewater treatment plant at ground and vertical levels. The ability to perform all analytical steps in the same device, the low-energy requirements, the low weight, and the attachment of data transmission modules offer new possibilities for drone-based analytical systems for air pollution monitoring.

Design and application of a paper-based optoelectronic nose for the on-site discrimination of essential oils using a chemometric web app.

Essential oils are appreciated worldwide for their pleasant aroma, in addition to their therapeutic, pharmacological, and cosmetic functions. For these reasons, adulteration is a common practice that decreases product quality causing economic and health issues. In this study, we present for the first time the application of a simple, inexpensive and disposable paper-based optoelectronic nose (i.e. colorimetric sensor array) to (i) discriminate sixteen different types of essential oils and (ii) detect adulterated samples. The colorimetric array was prepared by adding 1.5 µL of 9 chemo-responsive dyes with different chemical properties to each circular spot of the paper-based device. 1 mL of each essential oil was transferred to a flask and bubbled with synthetic air at an airflow of 200 mL min-1. Then, the optoelectronic nose was exposed to the airstream containing the volatiles from the sample for 5 minutes. Digital images from before and after exposure were obtained using a smartphone and the RGB values were extracted using appropriate software. The color changes provided a unique color map fingerprint for each essential oil. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) were successfully employed using a customized smartphone app, showing suitable discrimination of all studied essential oils as well as among adulterated and non-adulterated samples. The proof-of-concept showed the potential of the optoelectronic nose approach for the discrimination of different essential oils and the identification of adulterated samples, providing a valuable tool for quality control procedures.

Combination of headspace single-drop microextraction (HS-SDME) with a nickel-embedded paper-based analytical device for cyanide quantification.

BACKGROUND: Cyanide anion can be found in foodstuffs, tobacco smoke and a variety of types of waters, mainly originating from anthropogenic activities. Due to its highly toxic nature, several agencies have established limits for cyanide levels in water. Additionally, monitoring cyanide levels in biological samples, such as blood and urine, is crucial for obtaining clinical information about the health condition of patients. Therefore, there is a pressing need for the development of simple, cost-effective, and reliable analytical methods capable of quantifying cyanide at low concentrations. RESULTS: This study presents a novel analytical method for the selective and sensitive determination of cyanide based on analyte volatilization, pre-concentration via single-drop microextraction (SDME) using a selective reagent, and colorimetric quantification using a paper-based analytical device. For this, 10 mL of a liquid sample was acidified with phosphoric acid and the generated HCN was collected using a single drop of 3 µL of a palladium dimethylglyoximate solution (Pd (DMG)22-) positioned in the flask headspace using a syringe. The reaction of Pd (DMG)22- leads to the formation of Pd(CN)42- and the demasking of the organic ligand. After 15 min of extraction time, the reagent drop was added to a paper-based analytical device that has been previously impregnated with 3 µL of nickel chloride, resulting in the formation of a red precipitate of nickel (II) dimethylglyoximate. Digital images of the paper-based device were captured and the red channel (R) was used for quantification purposes. Under optimized conditions, the method demonstrates a suitable linear relation (r2 > 0.99) ranging from 26 to 286 µg L-1 and a limit of detection of 5 µg L-1. SIGNIFICANCE: As a proof of concept, cyanide levels were quantified in water and urine samples using this method. The proposed approach offers high sensitivity and selectivity while requiring only a small volume of reagents. Furthermore, it exhibits a high degree of portability for in-situ applications.

Paper-based colorimetric sensor array for the rapid and on-site discrimination of green tea samples based on the flavonoid composition.

Green tea is a worldwide appreciated food product with Chinese production estimated to reach over 3m tons in 2027 and with many valuable health effects. The development of analytical methods to discriminate among green tea samples is induced by economic benefits and to avoid deliberate origin mislabeling and adulteration. In this study, we present a paper-based colorimetric sensor array comprised of six ordinary reagents tailored for the discrimination of green tea extracts of different brands according to differences in the composition of flavonoids. The colorimetric array was rationally designed based on indicators that differentially react with a variety of flavonoids via specific functional groups. 4 µL of each reagent was impregnated onto the paper surface followed by the addition of the green tea extract. After 1 minute, digital images were acquired using a smartphone and the color changes were employed to build differential maps with a unique fingerprint for each green tea sample. Moreover, principal component analysis (PCA) and hierarchical component analysis (HCA) were employed to successfully discriminate among the samples, enabling the origin and adulteration identification of the samples. Therefore, this study provides a simple, effective, low-cost, and portable method for quick discrimination and quality control of green tea samples.

An indirect electrochemical method for aqueous sulfide determination in freshwaters using a palladium chelate as a selective sensor.

Sulfide anion is a highly toxic and corrosive compound and its presence above the threshold concentrations (i.e. µmol L-1) in freshwaters may indicate environmental pollution. Besides, the increase in sulfide concentration results in modifications of the organoleptic proprieties of water and air. Many analytical methodologies have been designed for aqueous sulfide quantification, however, due to the high reactivity and instability of sulfide, the pursue of a simple, sensitive, selective, and portable analytical method is still a current demand. In this study, an indirect electrochemical method for the determination of sulfide based on its interaction with a palladium complex - bis(2-aminobenzoate) palladium(II) - acting as a selective chemosensor is described. The reaction leads to the demasking of the electroactive ligand 2-aminobenzoic acid (i.e. anthranilic acid) and square wave voltammetry is employed to monitor its concentration using a glassy carbon electrode (GCE). Experimental conditions were optimized and the reaction was performed in Britton-Robinson (BR) buffer at pH 5 for 4 min, providing the higher magnitude of the analytical signal. A linear relation (r2 > 0.99) from 3 to 30 µmol L-1 of sulfide was obtained with a limit of detection of 0.10 µmol L-1. Recovery experiments using freshwater samples spiked with sulfide revealed overall satisfactory results for the limit concentration levels permitted by regulatory agencies. Therefore, the proposed methodology shows advantages in terms of portability, selectivity, sensitivity, low-cost, and easiness-to-use enabling monitoring of sulfide in a variety of waters.

3D-printed and fully portable fluorescent-based platform for sulfide determination in waters combining vapor generation extraction and digital images treatment.

The determination of sulfide anion in a variety of waters (e.g. wastewaters and natural waters) even at low concentration (i.e. in the µM range) is essential due to its high toxicity, corrosivity and unpleasant smelling proprieties. Despite several methodologies are dedicated to aqueous sulfide determination, most of them need sampling/transport steps - which is no adequate to sulfide due to its reactivity and instability - resulting in critical analytical bias. In this study, we present a fully modular and portable 3D-printed platform for in-situ aqueous sulfide determination. The analytical device is based on H2S vapor generation from the sulfide sample solution by addition of H3PO4 followed by collection in a miniaturized cuvette (µCuvette) containing few microliters of Fluorescein Mercury Acetate (FMA), a fluorescent dye. The chemical reaction results in fluorescence quenching of the dye at 530 nm when excited at 470 nm. A light-emitted diode (LED) emitting at 470 nm and powered with 9 V-battery based circuitry was employed to provide stable excitation light source at 20 mA. Digital images from the light emitted by FMA were captured by a smartphone and the Green channel intensity was used as analytical signal. Under optimized conditions, a linear relation (r2 > 0.99) from 0.1 to 5 µM of sulfide was obtained using 10 mL of standard/sample solution. The portable platform was applied to the in-situ monitoring of sulfide in tap water and river water with no loss of analyte, no need for external power supplies or powered pumps. and the analysis results were obtained in 20 min. The proposed device shows advantages in terms of high degree of portability, low-power consumption, easiness to use, minimal use of reagents yet enabling on-site determination of sulfide with high sensitivity. By using the vapor generation approach combined with the modular building blocks concept presented herein for the first time, we anticipate the development of a tailored "plug-and-play" platform enabling the multiplexed determination of volatile substances using absorbance, reflectance or fluorescence measurements with smartphones.

Real-Time and Simultaneous Monitoring of NO, NO2, and N2O Using Substrate-Integrated Hollow Waveguides Coupled to a Compact Fourier Transform Infrared (FT-IR) Spectrometer.

Nitrogen-based fertilizers have been used in modern agricultural activities resulting in a relevant emission source of nitrogen gases into the atmosphere, mainly nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O). Furthermore, the burning of fossil fuels is the most significant emission source of NOx (i.e., NO + NO2), being the controlling of vehicle exhaust system an essential task. Those compounds can be related to air pollution effects either directly, by emitting a powerful greenhouse gas (i.e., N2O), or indirectly, by formation of nitric acid (HNO3) or ammonium nitrate (NH4NO3) from NO or NO2, responsible for the increase of acid rain and particulate material into the atmosphere. This context requires appropriate sensor technology facilitating in situ and simultaneous monitoring of nitrogen emitted gases, with easiness of operation and compact dimensions. In this communication, we describe an innovative mid-infrared chemical sensor platform for the in situ, real-time, and simultaneous quantification of gaseous NO, NO2, and N2O by combining a compact Fourier transform infrared (FT-IR) spectrometer with the so-called substrate-integrated hollow waveguide (iHWG) as a miniaturized gas cell. The optical platform enabled limits of detection of 10, 1, and 0.5 ppm of NO, NO2, and N2O, respectively. The linear concentration range evaluated in this study is suitable for the application of the sensing platform in vehicle exhaust air samples. Given the high adaptability of the developed infrared sensing device toward preconcentration or ultraviolet conversion modules and also considering the potential for combining tunable interband cascade lasers (ICLs) in lieu of the FT-IR spectrometer, we anticipate the application of the sensing platform for in situ determination of nitrogen gases in a wide range of scenarios.

A portable luminescent thermometer based on green up-conversion emission of Er3+/Yb3+ co-doped tellurite glass.

The determination of temperature is essential in many applications in the biomedical, technological, and industrial fields. Optical thermometry appears to be an excellent alternative for conventional electric temperature sensors because it is a non-contact method that offers a fast response, electromagnetic passivity, and high temperature sensitivity. In this paper, we propose an optical thermometer probe comprising an Er3+/Yb3+ co-doped tellurite glass attached to the tip of an optical fibre and optically coupled to a laser source and a portable USB spectrometer. The ratio of the up-conversion green emission integrated peak areas when excited at 980 nm was temperature dependent, and it was used to calibrate the thermometer. The thermometer was operated in the range of 5-50 °C and 50-200 °C, and it revealed excellent linearity (r2 > 0.99), suitable accuracy, and precisions of ±0.5 and ±1.1 °C, respectively. By optimizing Er3+ concentration, we could obtain the high green emission intensity, and in turn, high thermal sensitivity for the probe. The probe fabricated in the study exhibited suitable properties for its application as a temperature sensor and superior performance compared to other Er3+ -based optical thermometers in terms of thermal sensitivity.

iCONVERT: an integrated device for the UV-assisted determination of H2S via mid-infrared gas sensors.

In this technical note, we describe an integrated device platform for performing in-flow gaseous conversion reactions based on ultraviolet (UV) irradiation. The system combines, using the same footprint, an integrated UV-conversion device (iCONVERT), a preconcentrator unit (iPRECON), and a new generation of mid-infrared (MIR) gas cell simultaneously serving as a photon conduit, i.e., so-called substrate-integrated hollow waveguide (iHWG) optically coupled to a compact Fourier transform-infrared (FT-IR) spectrometer. The iCONVERT is assembled from two blocks of aluminum (dimensions, 75 mm × 50 mm × 40 mm; L × W × D) containing 4 miniaturized UV-lamps (47mm × 6 mm × 47 mm each). For the present study, the iPRECON-iCONVERT-iHWG sensing platform has specifically been tailored to the determination of H2S in gaseous samples. Thereby, the quantitative UV-assisted conversion of the rather weak IR-absorber H2S into the more pronouncedly responding SO2 is used for hydrogen sulfide detection. A linear calibration model was established in the range of 7.5 to 100 ppmv achieving a limit of detection at 1.5 ppmv using 10 min of sample preconcentration (onto Molecular Sieve 5A) at a flow rate of 200 mL min(-1). When compared to a conventional UV-conversion system, the iCONVERT revealed similar performance. Considering the potential for system miniaturization using, e.g., dedicated quantum cascade lasers (QCL) in lieu of the FT-IR spectrometer, the developed sensing platform may be further evolved into a hand-held device.

Monitoring of hydrogen sulfide via substrate-integrated hollow waveguide mid-infrared sensors in real-time.

Hydrogen sulfide is a highly corrosive, harmful, and toxic gas produced under anaerobic conditions within industrial processes or in natural environments, and plays an important role in the sulfur cycle. According to the U.S. Occupational Safety and Health Administration (OSHA), the permissible exposure limit (during 8 hours) is 10 ppm. Concentrations of 20 ppm are the threshold for critical health issues. In workplace environments with human subjects frequently exposed to H2S, e.g., during petroleum extraction and refining, real-time monitoring of exposure levels is mandatory. Sensors based on electrochemical measurement principles, semiconducting metal-oxides, taking advantage of their optical properties, have been described for H2S monitoring. However, extended response times, limited selectivity, and bulkiness of the instrumentation are common disadvantages of the sensing techniques reported to date. Here, we describe for the first time usage of a new generation of compact gas cells, i.e., so-called substrate-integrated hollow waveguides (iHWGs), combined with a compact Fourier transform infrared (FTIR) spectrometer for advanced gas sensing of H2S. The principle of detection is based on the immediate UV-assisted conversion of the rather weak IR-absorber H2S into much more pronounced and distinctively responding SO2. A calibration was established in the range of 10-100 ppm with a limit of detection (LOD) at 3 ppm, which is suitable for occupational health monitoring purposes. The developed sensing scheme provides an analytical response time of less than 60 seconds. Considering the substantial potential for miniaturization using e.g., a dedicated quantum cascade laser (QCL) in lieu of the FTIR spectrometer, the developed sensing approach may be evolved into a hand-held instrument, which may be tailored to a variety of applications ranging from environmental monitoring to workplace safety surveillance, process analysis and clinical diagnostics, e.g., breath analysis.

Determination of 2-methylimidazole and 4-methylimidazole in caramel colors by capillary electrophoresis.

The use of chemical preservative compounds is common in the food products industry. Caramel color is the most usual additive used in beverages, desserts, and breads worldwide. During its fabrication process, 2- and 4-methylimidazole (MeI), highly carcinogenic compounds, are generated. In these cases, the development of reliable analytical methods for the monitoring of undesirable compounds is necessary. The primary procedure for the analysis of 2- and 4-MeI is using LC- or GC-MS techniques. These procedures are time-consuming and require large amounts of organic solvents and several pretreatment steps. This prevents the routine use of this procedure. This paper describes a rapid, efficient, and simple method using capillary electrophoresis (CE) for the separation and determination of 2- and 4-MeI in caramel colors. The analyses were performed using a 75 µm i.d. uncoated fused-silica capillary with an effective length of 40 cm and a running electrolyte consisting of 160 mmol L(-1) phosphate plus 30% acetonitrile. The pH was adjusted to 2.5 with triethylamine. The analytes were separated within 6 min at a voltage of 20 kV. Method validation revealed good repeatability of both migration time (<0.8% RSD) and peak area (<2% RSD). Analytical curves for 2- and 4-MeI were linear in the 0.4-40 mg L(-1) concentration interval. Detection limits were 0.16 mg L(-1) for 4-MeI and 0.22 mg L(-1) for 2-MeI. The extraction recoveries were satisfactory. The developed method showed many advantages when compared to the previously used method.