Fluorescent paper-based sensor integrated with headspace thin-film microextraction for the detection of acyclic N-nitrosamines following in situ photocatalytic decomposition

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGBackground: In this work, a novel analytical approach based on the photocatalytic decomposition of N-nitrosamines combined with headspace thin-film microextraction of the generated nitrogen oxides such as NO has been developed for the determination of the acyclic N-nitrosamine fraction in drinking water samples. A hydrophilic cellulose substrate modified with fluorescent silver nanoclusters (Ag NCs) was used both as extractant and sensing platform. A quenching effect of Ag NCs fluorescence occurs as the concentration of N-nitrosamines increases. Front-face fluorescence spectroscopy with a solid sample holder was employed for directly measuring the fluorescence quenching onto the cellulose substrate. Results: In order to achieve an optimal analytical response, different parameters involved in the photocatalytic reaction as well as those concerning the microextraction step were fully investigated. It is demonstrated that the photodegradation rate of cyclic N-nitrosamines at acidic pH is much lower than that of acyclic ones, which can be the basis for the determination of the later fraction in waters. Under optimal conditions, a detection limit for the acyclic N-nitrosamine fraction around 0.08 μg L−1 using N-nitrosodimethylamine (NDMA) as model compound for calibration was obtained. Several drinking waters were spiked with acyclic N-nitrosamines showing recoveries in the range of 98–102% with a relative standard deviation of 3–4% (N = 3). Significance and novelty: N-nitrosamines generated as by-products during disinfection processes applied to water cause multiple adverse effects on human health being classified as potential human carcinogens. This study highlights the suitability of a fluorescent paper-based sensor for the rapid analysis of the acyclic N-nitrosamine fraction (i.e. the most abundant fraction) as a total index in drinking water, being useful as screening tool before exhaustive chromatographic analysis, which saves costs, time and reduces waste generation.Agencia Estatal de Investigacion | Ref. RTI2018- 093697-B-I00Xunta de Galicia | Ref. ED481D-2021-02

A paper-based colorimetric assay with non-instrumental detection for determination of boron in water samples

The present work reports on the combination of paper-based analytical devices (PADs) and information technology (IT) equipment for non-instrumental determination of boron. PADs prepared with curcumin as a receptor and ethanolic extracts of Curcuma longa L. powder were evaluated for sensing. The colorimetric assay is based on a two step-strategy involving initially the formation of rosocyanin in the PAD under acidic conditions, with subsequent color change (from red to blue-green) at alkaline pH. The color change produced in the PAD is then exploited for determination of boron by digitization and image processing with IT devices (scanner and tablet camera) and an image analysis program, respectively. Under optimal conditions, the proposed assay showed limits of detection in the range 0.2–0.8 mg/L depending on the PADs and IT devices used for colorimetric reaction and digitization, respectively. In addition, the repeatability, expressed as relative standard deviation, was found to be below 5% (5 mg/L, N = 10). PADs prepared with curcumin and ethanolic extracts of Curcuma longa L. powder showed excellent lifetime and successful applicability to the analysis of water samples of different complexity with recoveries in the range 93–105%.Agencia Estatal de Investigación | Ref. RTI2018-093697-B-I0

Silver nanocluster-based colorimetric/fluorimetric dual-mode sensor for the detection of bromide and sulfite in waters and wastewaters

In this work, the development of a fluorimetric/colorimetric dual-mode nanosensor for the determination of sulfite and fluorimetric determination of bromide involving silver nanoclusters (AgNCs) is reported. SO2 and Br2 were found to significantly modify the optical properties of AgNCs. Particularly, both volatiles weakened the fluorescence of AgNCs, whereas a color change from nearly colorless to yellowish/brown occurred upon exposure of AgNCs to SO2. Accordingly, three smartphone-based optical assays were devised for sulfite and bromide determination, involving in situ volatile generation and enrichment/trapping of the selectively formed volatiles by AgNCs confined in a droplet and exposed to the headspace above the sample. A hydrophobized cellulose substrate acting as drop holder enabled integrating both the enrichment and the subsequent smartphone-based optical detection in a straightforward manner. Smartphone-based digitization of the enriched AgNCs microdrops and subsequent image processing using a smartphone and its integrated App, respectively, were used for quantitative purposes. Under optimal conditions, limits of detection (LODs) of 1.1 μM and 1.5 μM were achieved for the fluorimetric determination of sulfite and bromide, respectively, whereas sulfite was alternatively determined by colorimetric readout, yielding a LOD of 37.0 μM. The repeatability, expressed as relative standard deviation, was found to be in the range of 5.1–5.9 % in all cases (N = 8). The applicability of the method was demonstrated in aqueous samples of increasing complexity, with recoveries in the range 91–109 %. In addition, the responsiveness of AgNCs to SO2 and Br2 rendered them suitable for the monitoring of bromide and sulfite in increasingly relevant advanced reduction processes such as the UV/sulfite system, as demonstrated in this work.Agencia Estatal de Investigación | Ref. PID2022-136337OB-I00Universidade de Vigo/CISU

Test for arsenic speciation in waters based on a paper-based analytical device with scanometric detection

A rapid, simple and affordable method for arsenic speciation analysis is described in this work. The proposed methodology involves in situ arsine generation, transfer of the volatile to the headspace and its reaction with silver nitrate at the detection zone of a paper-based analytical device (PAD). Thus, silver nitrate acts as a recognition element for arsine in the paper-based sensor. The chemical reaction between the recognition element and the analyte derivative results in the formation of a colored product which can be detected by scanning the detection zone and data treatment with an image processing and analysis program. Detection and injection zones were defined in the paper substrate by formation of hydrophobic barriers, thus enabling the formation of the volatile derivative without affecting the chemical stability of the recognition element present in the PAD. Experimental parameters influencing the analytical performance of the methodology, namely color mode detection, composition of the paper-based sensor and hydride generation and mass transfer conditions, were evaluated. Under optimal conditions, the proposed method showed limits of detection and quantification of 1.1 and 3.6 ng mL−1, respectively. Remarkably, the limit of detection of the method reported herein was much lower than the maximum contaminant levels set by both the World Health Organization and the US Environmental Protection Agency for arsenic in drinking water, unlike several commercially available arsenic test kits. The repeatability, expressed as relative standard deviation, was found to be 7.1% (n = 8). The method was validated against the European Reference Material ERM®-CA615 groundwater and successfully applied to the determination of As(III), As(V) and total inorganic As in different water samples. Furthermore, the method can be used for the screening analysis of total arsenic in waters when a cut-off level of 7 ng mL−1 is used.Ministerio de Economía y Competitividad | Ref. CTQ2015-68146-

Droplet-based luminescent sensor supported onto hydrophobic cellulose substrate for assessing fish freshness following smartphone readout

In this work, two sensitive droplet-based luminescent assays with smartphone readout for the determination of trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) are reported. Both assays exploit the luminescence quenching of copper nanoclusters (CuNCs) produced when exposed to volatile nitrogen bases. In addition, hydrophobic-based cellulose substrates demonstrated their suitability as holders for both in-drop volatile enrichment and subsequent smartphone-based digitization of the enriched colloidal solution of CuNCs. Under optimal conditions, enrichment factors of 181 and 153 were obtained with the reported assays for TMA-N and TVB-N, respectively, leading to methodological LODs of 0.11 mg/100 g and 0.27 mg/100 g for TMA-N and TVB-N, respectively. The repeatability, expressed as RSD, was 5.2% and 5.6% for TMA-N and TVB-N, respectively (N = 8). The reported luminescent assays were successfully applied to the analysis of fish samples, showing statistically comparable results to those obtained with the reference methods of analysis.Agencia Estatal de Investigación | Ref. RTI2018-093697-B-I00Universidade de Vigo/CISU

A 3D microfluidic paper-based analytical device with smartphone-assisted colorimetric detection for iodine speciation in seaweed samples

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGThe present work reports on the development of a 3D origami microfluidic paper-based analytical device (3D µPAD) for the determination of iodide and iodate in edible seaweeds by smartphone-based colorimetric detection. In addition, a methacrylate holder was designed and fabricated to enhance interlayer contact in 3D µPADs, obtaining excellent sensitivity and precision, also allowing real-time monitoring in a straightforward and expeditious way. The reported assay, based on the formation of a blue colored triiodide-starch complex at the detection areas of the 3D µPAD, represents an affordable, fast and greener alternative for the simultaneous determination of inorganic iodine species. Under optimal conditions, the proposed method showed limits of detection and quantification of 9.8 and 32.7 µM for I- and 0.6 and 1.8 µM for IO3-, respectively. The repeatability, expressed as relative standard deviation, was 1.7% and 3.3% for I- and IO3-, respectively. The proposed 3D µPAD was applied to the determination of iodine species in extracts of edible seaweeds and related food additives, showing satisfactory recoveries (90–109%).Agencia Estatal de Investigación | Ref. RTI2018-093697-B-I0

Silver nanoparticle-cellulose composite for thin-film microextraction of Cd and Pb as dithiocarbamate derivatives followed by inductively-coupled plasma mass spectrometry determination

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGPreconcentration of Cd and Pb at ultratrace level in waters following filtration through silver nanoparticles-cellulose composites used for thin-film microextraction was performed. The new procedure was based on the formation of pyrrolidine dithiocarbamate (APDC) derivatives, which showed a large affinity toward the AgNPs. For this purpose, cellulose filters modified with AgNPs were prepared in situ upon reduction of silver ions by sodium tetrahydroborate. The effect of several experimental parameters such as the kind of derivatization agent and its concentration, sample pH, desorption conditions and volume of filtered sample was assessed. Cd and Pb were quantitated in the eluates by inductively coupled plasma-mass spectrometry (ICP-MS). Filters were characterized by scanning electron microscopy (SEM) in backscattering electron mode and combined with energy dispersive X-ray spectrometry, showing the presence of Ag and S in the cellulose filter. The repeatability expressed as relative standard deviation (RSD,%) was 1.4% for Cd and 5.8% for Pb. Methodological detection limits were 0.6 and 8.5 ng/L for Cd and Pb, respectively. The method was applied to several environmental waters.Agencia Estatal de Investigación | Ref. RTI2018-093697-B-I0

Turn–on fluorescent sensor for the detection of periodate anion following photochemical synthesis of nitrogen and sulphur co–doped carbon dots from vegetables

In this work, a novel one–step ‘bottom–up’ synthetic approach is described for obtaining highly fluorescent nitrogen (N) and sulphur (S) co–doped carbon dots (CDs) following photochemical oxidation of carbohydrates naturally occurring in vegetables. N and S co–doping allows more active sites in the CDs surface resulting in an enhancement of their luminescent properties. Among the 18 vegetables studied as green precursors of CDs, those rich in proteins and glucosinolates (natural S–linked glucosides), such as cruciferous vegetables (Brassicaceae family), i.e. broccoli, cauliflower and Romanesco, facilitate an efficient N and S co–doping of the CDs during the photochemical reaction without the need for further post–synthetic treatments. A comprehensive characterization of CDs obtained from broccoli was performed by transmission electron microscopy, elemental analysis, X–ray fluorescence (total reflection), UV–Vis absorption and Fourier transform–infrared spectroscopy. Quantum yields and fluorescence up–conversion properties were also investigated. Monodisperse CDs (∼8 nm average size) with up–conversion fluorescence properties and a quantum yield (QY) of 22% are obtained. More importantly, a dramatic increase in the CDs fluorescence (turn–on) is observed when the highly oxidant periodate anion (IO4−) is added to the reaction medium, which allowed us to construct a sensitive and selective fluorescent assay for the detection of periodate anion in wastewater samples. The detection limit was 19 μM IO4− and the repeatability expressed as the relative standard deviation was 3.2% (N = 5)Ministerio de Economía y Competitividad | Ref. CTQ2015–68146–

Fluorescent poly(vinylpyrrolidone)-supported copper nanoclusters in miniaturized analytical systems for iodine sensing

Poly(vinylpyrrolidone)-supported copper nanoclusters (CuNCs) are employed in the present work as luminescent probes for iodide determination in water samples. The method involves the combination of two miniaturized analytical systems, namely nanoparticle-enhanced liquid-phase microextraction and microvolume fluorospectrometry. The proposed method is based on the in situ generation of iodine and trapping of the evolved volatile into a CuNCs-containing aqueous microdrop, thus leading to fluorescence quenching. The fluorescence quenching mechanism for iodine sensing can be presumably ascribed to a ‘sphere of action’ static quenching model. Instrumental conditions, as well as a number of experimental parameters affecting extractant phase composition, iodine generation conditions and mass transfer of the volatile, have been evaluated. An outstanding enrichment factor of ca. 1100 was achieved under optimal conditions, yielding limits of detection and quantification of 1.0 ng/mL and 3.4 ng/mL, respectively. The repeatability, expressed as relative standard deviation, was found to be 7.4% (N = 7). The method was validated against a certified reference material and successfully applied to the analysis of different water samples. Furthermore, paper-based analytical devices containing CuNCs have been evaluated for the non-instrumental sensing of iodine generated in situ, showing promise as an inexpensive and portable alternative for iodide determination.Agencia Estatal de Investigación | Ref. RTI2018-093697-B-I00Xunta de Galici

Detection of gases and organic vapors by cellulose-based sensors

The growing interest in the development of cost-effective, straightforward, and rapid analytical systems has found cellulose-based materials, including cellulose derivatives, cellulose-based gels, nanocellulosic materials, and the corresponding (nano)cellulose-based composites, to be valuable platforms for sensor development. The present work presents recent advances in the development of cellulose-based sensors for the determination of volatile analytes and derivatives of analytical relevance. In particular, strategies described in the literature for the fabrication and modification of cellulose-based substrates with responsive materials are summarized. In addition, selected contributions reported in the field of paper-based volatile sensors are discussed, with a particular emphasis on quick response (QR) code paper-based platforms, intelligent films for food freshness monitoring, and sensor arrays for volatile discrimination purposes. Furthermore, analytical strategies devised for the determination of ionic species by in situ generation of volatile derivatives in both paper-based analytical devices (PADs) and microfluidic PADs will also be described.Universidade de Vigo/CISUGAgencia Estatal de Investigación | Ref. RTI2018-093697-B-I0