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In the last twenty years, the number of publications presenting generalized pH-sensitive devices proposed for food freshness monitoring has been steadily growing, but to date, none of them have succeeded in exiting the laboratory and reaching the supermarket shelf. To reach this scope, we developed a large-scale applicable pH-sensitive sensor array to monitor perishable foods’ degradation. We ensured freshness monitoring in domestic conditions, using sales packages and during chilled storage, by simple naked-eye readout and multivariate imaging analysis, and we fully corroborated the device by (i) projection of unknown independent samples in the PCA model, (ii) TVB-N quantification and (iii) microbiological assay. The choice of commercial and cheap dye and polymeric support already employed in food packaging ensures the low-cost and scalability of the device and the promising results obtained make this device an eligible candidate for large-scale implementation.

This work presents the development of a green paper-based analytical device (Green-PAD) array for pH detection.

In this study, a molecularly imprinted polymer (MIP)-based screen-printed cell is developed for detecting phenoxy herbicides using 2-methyl-4-chlorophenoxyacetic acid (MCPA) as the template. MCPA is a phenoxy herbicide widely used since 1945 to control broadleaf weeds via growth regulation, primarily in pasture and cereal crops. The potentiometric cell consists of a silver/silver chloride pseudo-reference electrode and a graphite working electrode coated with a MIP film. The polymeric layer is thermally formed after drop-coating of a pre-polymeric mixture composed of the reagents at the following molar ratio: 1 MCPA: 15 MAA (methacrylic acid): 7 EGDMA (ethylene glycol dimethacrylate). After template removal, the recognition cavities function as the ionophore of a classical ion selective electrode (ISE) membrane. The detected ion is the deprotonated MCPA specie, negatively charged, so the measurements were performed in phosphate buffer at pH 5.5. A linear decrease of the potential with MCPA concentration, ranging from 4 × 10−8 to 1 × 10−6 mol L−1, was obtained. The detection limit and the limit of quantification were, respectively, 10 nmol L−1 and 40 nmol L−1. A Nernstian slope of about −59 mV/dec was achieved. The method has precision and LOD required for MCPA determination in contaminated environmental samples.

There is an increasing interest in determining the concentration of furanic compounds naturally formed in food aqueous matrices, by in situ, fast and low-cost methods. A sensor presenting such characteristics is here proposed, and characterized. It is based on a molecularly imprinted polymer (MIP) as a receptor with electrochemical transduction on a screen printed cell (SPC). The molecularly imprinted polymer has been developed for a particular furanic derivative, 2-furaldehyde (2-FAL). The detection bases on the reduction of 2-FAL selectively adsorbed on the polymer layer in contact with the working electrode. The polymer layer is simply formed by in situ polymerization, directly over the SPC and it was characterized by IR, SEM and electrochemical methods. Even if based on an easy and fast preparation procedure, the layer sufficiently adheres to the cell surface giving a reusable sensor. Square wave voltammetry (SWV) was applied as the signal acquisition method. The sensor performance in aqueous solution (NaCl 0.1 M) was tested, obtaining that the dose-response curve is fitted by the Langmuir adsorption isotherm. The sensitivity, and so the limit of detection, were noticeably improved by a chemometric approach based on the Design of experiment method. (optimized conditions: Estep = 0.03 V, Epulse = 0.066 V, f = 31 s−1). In water solution at pH around neutrality the dynamic range was from about 50 μM to 20 mM. Similar results were obtained for a white wine containing 12% ethanol, which has been considered as a typical example of beverage possibly containing furhaldehydes. The higher limit of quantification can be modulated by the amount of MIP deposited, while the lower detection limit by the conditions of the electrochemical measurement.

An innovative smart label for naked-eye protein food freshness evaluation, based on polymeric sensing films, is presented. The proposed device consists of six miniaturized sensors, obtained by cova...

This work presents a colorimetric dye-based array for naked-eye detection of chicken meat spoilage. The array is obtained by fixing five acid-base indicators, m-cresol purple (1), o-cresol red (2), bromothymol blue (3), thymol blue (4), and chlorophenol red (5), and a sensing molecule specific for thiols, 5,5'-dithiobis(2-nitrodibenzoic acid), called Ellman's reagent (6), on a cellulose-based support. The dyes, being permanently charged, are fixed on the support via ion-exchange. The entire degradation process of beast poultry meat, at ambient temperature and in a domestic fridge, is followed by the change of the color of the array, placed in the headspace over the meat samples. The device is set after selection of the most suitable starting form, which could be the acidic or the basic color of indicators, being the proper dye concentration and the dimension of the spots already established. Basing on sensors colors, we identified three levels of the degradation process of chicken meat, named SAFE, WARNING, and HAZARD. By instrumental analysis, we demonstrated that sensors response was correlated to volatile organic compounds (VOCs) composition in the headspace and, thus, to meat spoilage progress. We demonstrated that biogenic amines (BAs), commonly considered a critical spoilage marker, are indeed produced into the samples but never present in the headspace, even in traces, during the investigated time-lapse. The VOC evolution nevertheless allows one to assign the sample as WARNING and further HAZARD. Some indicators turned out to be more informative than others, and the best candidates for a future industrial application resulted in a bromothymol blue (3)-, chlorophenol red (5)-, and Ellman's reagent (6)-based array.

A simple and rapid solid-phase spectrophotometric procedure to determine free Fe(III) in environmental and biological samples is proposed. In particular, a deferoxamine (DFO) self assembled monolayer on mesoporous silica (DFO SAMMS) is developed and here applied as a sensor for iron(III). The solid product became brownish when put in contact with iron(III) solutions; so an immediate application as colorimetric sensor is considered. In order to optimize the DFO SAMMS synthesis and to obtain the best product for iron(III) sensing, a factorial experimental design is performed selecting the maximum absorption at 425 nm as response. The robustness of the spectrophotometric method is also proved. Keywords: Free iron(III), Deferoxamine, Self assembled monolayer, Mesoporous silica, Solid-phase spectrophotometry

Carboxymethyl cellulose, the most promising cellulose-derivatives, pulls together low cost, abundancy, biocompatibility, unique properties and, unlike the precursor, chemical reactivity. This latter aspect arouses the curiosity of chemists around the possibility of chemical modification and the production of interesting functional materials. Here, a two-step reaction is proposed for the covalent anchoring of a wide variety of molecules containing sulfonic groups to CMC. The strength points of the proposed pathway have to be found in the quick and easy reactions and workup that allow to obtain ready-to-use functional materials with very high yields. Having in this case exploited a pH-sensitive dye as a sulfonated molecule, the functional material is an interesting candidate for the development of colorimetric miniaturized sensors via the following drop-casting deposition: once optimized sensors preparation by design of experiments, an example of application on real samples is reported.

Myriads of sensors have been proposed to signal the spoilage of a piece of meat. It is assumed and taken for granted that biogenic amines, BAs, harmful by-product indicating the last phase of degradation, must be present in the volatilome developed over the decaying meat. This chapter aims to clearly explain BAs’ role in protein food spoilage: undoubtedly produced inside the meat, never present in the headspace, where sensors are displayed. The BAs presence in the headspace represents a sort of myth. It is plenty of evidence that BAs cannot be present in the volatilome over the meat. The BAs’ volatility is pH-dependent. As shown by their protonation constants, the strongly buffered pH of proteinaceous food prevents their vapour phase transition. The chemical analyses made at the same degradation time, on the meat and the headspace above the meat, corroborate the real composition of the volatilome, demonstrating the BAs absence. The sensors here described, designed on volatilome evidence, succeed to follow the entire process, from the SAFE condition to the WARNING and the HAZARD. The final prototype works reliably on real protein foods (i.e. chicken, beef pork and fish), not enriched and stored at the home condition.

Intelligent packaging represents an emerging trend in the food industry, especially for highly perishable foods like milk and dairy products. Despite the apparent simplicity, miniaturized BCP-EVOH@ sensor, made of bromocresol purple (BCP) covalently bound to ethylene-vinyl alcohol (EVOH) copolymer, meets the goal of milk freshness monitoring during chilled storage, allowing both naked-eye evaluation and chemometric-assisted spoilage modelling and measurements.

Environmental contamination affects human health and reduces the quality of life. Therefore, the monitoring of water and air quality is important, ensuring that all areas are acquiescent with the current legislation. Colorimetric sensors deliver quick, naked-eye detection, low-cost, and adequate determination of environmental analytes. In particular, disposable sensors are cheap and easy-to-use devices for single-shot measurements. Due to increasing requests for in situ analysis or resource-limited zones, disposable sensors’ development has increased. This review provides a brief insight into low-cost and disposable colorimetric sensors currently used for environmental analysis. The advantages and disadvantages of different colorimetric devices for environmental analysis are discussed.

In this study, a portable, disposable, and low-cost ionophore-based optical sensor is presented for the monitoring of sulphides and thiols. This sensor was obtained by fixing a classical dye, 5,5′-dithiobis(2-nitrobenzoic acid) (Ellman's reagent, ELL), on an unusual solid support. Indeed, we decided to anchor the dye on the commercial paper sheet known as the “Colour Catcher®” (herein, named under the acronym CC), commonly used in the washing machine to prevent colour run problems. The device obtained can be regarded as an optical sensor since the indicator dye fixed on the solid material changes its spectral properties (colour and hence the UV-vis spectrum) upon contact with the analyte. The relationship between the analyte content and changes in the UV-vis spectrum of the sensor has been provided using partial least squares regression (PLS).

An economic and extremely selective device for Pd(II) determination in very acidic solutions, TazoC-Mar@, is presented. The sensor was prepared via an ion exchange technique of an azoic ligand, (2-(tetrazolylazo)-1,8 dihydroxy naphthalene-3,6,-disulphonic acid), named TazoC, on a Macroporous Strong Anion Exchange Resin, namely Marathon® (Dow Chemical-USA). The TazoC-Mar@ rapidly forms complexes with palladium(II) ions, which give an intense blue colour to the solid phase, even at low pH. The reaction is highly selective and no other metal ions react with the device at this pH. Moreover, the quantification of Pd(II) is reliable when applying partial least squares regression (PLS) to relate the signal to the metal ion concentration. The regression model gives a good fit and correct predictions of Pd(II) concentrations in unknown samples. The method presented here is highly sensitive with an LOD and LOQ equal to 0.2 nM and 0.5 nM, respectively.

Since the emergence of deferiprone as an iron(III) chelating drug, hydroxypyridinones have been intensively explored due to their high affinity for trivalent metal ions and ability to form complexes at physiological pH with low toxicity. For instance, they have been employed as carriers of La(III) in therapy for bone diseases and to remove Gd(III) from Gd-based contrast agents. We believe that a pyridinone-based sensor can be useful for iron(III) monitoring. Herein, we present a novel chelating solid-phase, resulting from the functionalization of a mesoporous silica MCM-41, with the hydroxypyridinone N(3′-aminopropyl)-3-hydroxy-2-methyl-4-pyridinone (AHP) as the active site. The physico-chemical characterization of the new solid-state device, named AHP-MCM41@, demonstrates that the AHP moiety is covalently anchored on the silica surface; the active site concentration was found to be around 0.4 mmol g−1. Furthermore, its sorption of Fe(III) from aqueous solution is rather rapid. The soluble AHP forms a rich variety of complexes with iron(III), which is typical of all analogous O,O donor ligands, and is dominated by M : L = 1 : 3 complexes. Could complexes with such high stoichiometry can be retained in the solid phase? The answer is yes. The existence of these different species in the solid phase is evidenced by the sorption isotherm results and from sorption experiments as a function of solution pH and also in the presence of a competitive ligand. Furthermore, the existence of complexes in the solid phase was demonstrated via solid vis-spectrophotometry, where these species showed identical colour variations to those formed in solution. Such complexes in the solid phase have never been reported in the literature. Additionally, the intense colour of the solid phase in the presence of iron(III) is promising for naked eye detection.

An optode for Cu(II), Cd(II), Zn(II) and Hg(II) sensing has been designed by immobilization of dithizone on a triacetylcellulose membrane (mem-DTZ). The sorption of the metal ions on the mem-DTZ has been thoroughly characterized, in particular sorption kinetics, sorption isotherms and profiles as a function of the pH have been studied. Methods to assess the concentrations of the cations, both individually and in a mixture, in unknown samples, have been developed. In particular, UV-vis spectra and digital information of pictures taken by using a common desktop scanner, of the mem-DTZ sensor after equilibration with different solutions, were acquired and they were correlated with the concentration of the metal ions in solutions. For the single analyte determination, the RGB parameters of the pictures were subjected to Principal Component Analysis (PCA); otherwise the UV-vis spectra of a mixture of two cations were elaborated by Partial Least Squares (PLS) Regression. The membrane responds to the divalent cations by changing colour reversibly. The response time of the mem-DTZ is about 1 h for Cd(II), Hg(II) and Zn(II), but longer for Cu(II): more than 10 h are required. The linear interval is in the range of about 10−7 to 10−5 M for all metal ions. The limit of detection (LOD) is around 10−6 M for Cu(II), Cd(II) and Hg(II); for Zn(II) a lower LOD of 10−7 M is obtained. The applicability of mem-DTZ to real samples has been proved by analysis of the four metal cations in a certificate material (Sewage Sludge CC136A), white wine, and drinking water samples.

This paper presents an easy, fast and economic synthesis of chelating agents for medical, environmental and analytical applications, and the evaluation of the stability of their complexes with Fe3+ and Al3+. Complex formation equilibria with Cu2+ and Zn2+ metal ions were also studied to evaluate if the chelating agents can perturb the homeostatic equilibria of these essential metal ions. Effective chelating agents for metal ions, in addition to their well-known medical uses, find an increasing number of applications in environmental remediation, agricultural applications (supplying essential elements in an easily available form), and in analytical chemistry as colorimetric reagents. Besides the stability of the complexes, the lack of toxicity and the low cost are the basic requisites of metal chelating agents. With these aims in mind, we utilized ethyl salicylate, a cheap molecule without toxic effects, and adopted a simple synthetic strategy to join two salicylate units through linear diamines of variable length. Actually, the mutual position of the metal binding oxygen groups, as well as the linker length, affected protonation and complex formation equilibria. A thorough study of the ligands is presented. In particular, the complex formation equilibria of the three ligands toward Fe3+, Al3+, Zn2+ and Cu2+ ions were investigated by combined potentiometric and spectrophotometric techniques. The results are encouraging: all the three ligands form stable complexes with all the investigated metal ions, involving the oxygen donor atoms from the 2-hydroxybenzamido unit, and nitrogen atoms in copper and zinc coordination.

The purpose of this study is to implement a work that is a part of a project funded by the Italian National Antarctic Research Program (PNRA, Piano Nazionale di Ricerche in Antartide) within the main thematic focus “Chemical Contamination-Global Change”. This research was devoted to detect and characterize micro and nano components with strong complexing capability towards metal ions at trace level in sea water, lakes and lacustrine sediments, sampled during the XXII expedition of PNRA. In particular, in the present work, the sorption complexation capacity of an Antarctic lacustrine sediments toward Cu(II) and Pb(II) is described. The characterization of the sorption was undertaken, studying kinetics and isotherm profiles. The lake here considered is Tarn Flat in the area of Terra Nova Bay. The sorption equilibria of Cu(II) and Pb(II) on the lacustrine sediments were reached in about 10 h, and they were best modelled by the Langmuir equation. Preliminary, to establish if the data here obtained were consistent with those reported for the same area in other expeditions, a common multivariate techniques, namely the principal component analysis (PCA), was applied and finally the consistency of the data has been confirmed.

This work presents a simple, fast, disposable and low-cost colorimetric sensor for the simultaneous detection of Fe(III) and Al(III). It is obtained by fixing a classical dye, Alizarin Red S, on an inert solid support, i.e., a product of the washing powder market known as “Colour Catcher®” (here named under the acronym CC) generally used in the washing machine to prevent colour run problems. The device so obtained is called Aliz-CC@. Fe(III) and Al(III) interaction with the Alizarin Red S-based sensor, generates a change in the adsorption spectra of the fixed dye, allowing to highlight a naked-eye colour change. The relationship between the Fe(III) and Al(III) content and the colour change profiles of the sensor, is provided by using Partial Least Squares regression (PLS).

Azo-dyes, molecules characterised by the presence of the azo-group (–N N–), are widely used in textile, leather, rubber, plastic, and food industries. Water-soluble azo-dyes are greatly resistant to biodegradation, and are characterised by a high thermal and photo stability due to their complex structures. The release of these molecules into the environment is of crucial concern due to their toxic, mutagenic and carcinogenic characteristics. Biosorption has been demonstrated an effective method to remove pollutants from wastewaters thus solving ecological tasks, being a low cost process and the sorbent biodegradable. The main requirements of an efficient sorbent are thermal, chemical and mechanical stability, and rapid sorption. In this work, the ability of both row cork and the same sorbent entrapped in a biopolymeric gel of calcium alginate, on the removal of chrysoidine from aqueous solutions was examined. The influence on the sorption of pH, initial dye concentration, and particle size, as well as the efficiency of the entrapment, have been investigated. The maximum sorption was found for cork samples of fine particle size (FC), in both row and entrapped forms, at pH 7; conversely, at pH 4 the difference is significant (0.12 mmol/g for row cork and 0.20 mmol/g for entrapped cork), evoking a cooperation of alginate in binding the positively charged chrysoidine molecule.

A wide range of substances is reported in the literature as emerging pollutants. Biomass sorption has been found an effective way to remove these pollutants from wastewaters. In this work the ability of cork for the removal of ofloxacin from aqueous solutions has been evaluated. Cork and ofloxacin have been chosen as representative of biomass and of antibiotics, respectively. Ofloxacin is one of the most used fluoroquinolones, a potent broad spectrum oral antibiotic class. The sorption of ofloxacin by cork has been studied by equilibrium isotherms at three pH values (4, 7 and 9) using cork of two different sizes. The K and Qmax values obtained by fitting the data with Langmuir equation are discussed as a function of pH and cork size. In order to know the variously protonated species of ofloxacin that interact with cork at different pH, a potentiometric–spectrophotometric characterization of the protonation equilibria has been performed. A new spectrophotometric method for the quantitative determination of ofloxacin, based on the formation of colored iron(III) complexes, has been developed.

The sorption properties of rice husk towards Cu(II), Cd(II) and Pb(II) were studied. The sorption isotherms are described by the Langmuir equation, and Pb(II) shows a higher affinity for rice husk compared to Cu(II) and Cd(II) under the same conditions. The kinetics of sorption obeys to a pseudo second-order equation for all metals. The sorption profiles as a function of the pH were used to characterize the stoichiometry of the sorption reaction. The competition for metal complexation by any ligand in solution is also accounted for. Upon increasing the ionic strength, the sorption curves of Pb(II) move to basic pH; this shift can be explained by considering the effect of nitrate complexes on the free metal ion concentration, since KNO(3) is used as the ionic medium. An attempt to employ rice husk in a dynamic system is presented.

The affinity of azacryptands towards perrhenate has been investigated by potentiometric, 1H NMR spectroscopic and ITC studies in aqueous solutions. The association constants could only be determined for the p-xylyl and m-xylyl azacryptands in the hexaprotonated form. The experimental results showed the outstanding affinity of the p-xylyl cryptand for perrhenate, attributable to the geometric complementarity between the anion and the cavity of the receptor. Single crystals of the inclusion complex could also be obtained. The X-ray diffraction studies indicate that the perrhenate anion is included in the cavity of the receptor and interacts with the ammonium groups by means of both direct and water-mediated H-bonding interactions. The receptors were also investigated in the presence of different anions (i.e. chloride, bromide, iodide, perchlorate and nitrate). The affinity trend demonstrates that the p-xylyl cryptand cavity is more suitable to host large anionic guests such as perrhenate, perchlorate and iodide, despite their low density charge. On the contrary, nitrate, bromide and chloride fit better into the smaller cavity of the m-xylyl cryptand. The higher affinity of the m-xylyl cage towards chloride over that of perrhenate was also demonstrated by the crystal structure of the 1:1 adduct.

An all-solid-state ISE for dopamine (DAHCl) has been developed based on a screen printed graphite electrode modified with a multiwalled carbon nanotubes layer as an ion to electron transducer. The selective membrane is an acrylic polymer molecularly imprinted with the ion of interest (MIP). The polymer is made up of methacrylic acid as functional monomer and ethyleneglycole dimethacrylate as cross linker. The polymerization at 75 °C in the presence of AIBN as initiator was carried out in situ, directly over the CNT-modified screen printed graphite. The specific site obtained after polymerization and template elution can be considered as the ionophore, and the carboxylic groups as the cation exchanger groups, similarly to the usual ISE membrane. The specificity of the electrode was evaluated by voltammetric methods, and was very good. The potential of the electrode, measured against a double junction Ag/AgCl/KCl (sat.), linearly increases with the dopamine concentration at concentration higher than 10−4 M, but only in salt solution at least 0.1 M. The sensibility was less than nernstian. Not any potential increase was found for the electrode modified with not imprinted polymer (NIP) at the same conditions. The effect of ions in solution was particularly considered.

A large number of new solid phases have been proposed in the literature during the past decade with a large variety of purposes: separation and preconcentration for the solid phase extraction, specific chromatographic applications, assemblies of devices for recognition of a family of substances, sensors for a single species identification. In spite of this variety of materials, their properties are mostly depicted by physical descriptors and operational exchange properties, instead of quantities independent of the experimental conditions. In the present review the methods proposed for the description of the sorption phenomena, from the thermodynamic, kinetic and dynamic point of view, will be critically reviewed, focusing on general methods to describe the sorption that could be used in alternative to descriptive and operational approaches.