In the last time, experts estimate that industrial processes introduce up to a million different pollutants into the atmosphere and the aquatic ecosystem, and heavy metals are one group of these substances.

In this presentation the absorption (transient absorption) and emission (steady state and time-resolved fluorescence) spectroscopy were used to study, investigate and characterize the mechanisms of fluorescence quenching and obtaining new sensors for detecting toxic environments: heavy metals from water. For these purpose new compounds, lanthanide complexes were obtained by condensation between the siloxane diamine and dialdehyde, and were synthesized to have a high quantum yield, stability and selective sensibility. The fluorescence quenching of these metal complexes by different metal ions such: Ni²⁺, Cu²⁺, Co²⁺, Zn²⁺, Fe³⁺, Mn²⁺, Ca²⁺, Pb²⁺, Cd²⁺, Sr²⁺, Mg²⁺, were studied in solution/film at different variation in time, to demonstrate that these samples have a good stability and can be used as fluorescence sensors for the selective detection of metal ions.

For fundamental study, theory of dynamic quenching, theory of static quenching and combined dynamic and static quenching were used, and constants of the process, the lifetime in excited state, the quantum yield were estimated and depend on the substitution of metal ions.

A sensor for detecting Fe in water was proposed

This work demonstrates a hydrogen (H₂) sensor composed of a tapered optical fiber coated with polyaniline (PANI) nanofibers that operates at room temperature. A transducing platform was fabricated using multimode optical fiber (MMF) with cladding and core diameters of 125 µm and 62.5 µm, respectively. To enhance the light evanescent field surrounding the fiber, it was tapered from the diameter of 125 µm to a waist diameter of 20 µm, a waist-length of 10 mm and coated with PANI using the drop-casting technique. To establish the PANI’s properties, various characterization techniques were applied, such as Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray (EDX), X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The optical properties of PANI layer changes when it is exposed to H₂, leading to a change in the light absorbance. The fabricated sensor was tested by exposing it to H₂ at different concentrations of 0.125% to 1.00%. In this case, the sensitivity, response and recovery times were 15.928/vol%, 110 s and 160 s, respectively. Owing to its room temperature operation, the developed hydrogen sensor is promising for environmental and industrial applications.

Organic solvents are widely used as reaction media and/or for separation and purification of synthetic products in chemical and pharmaceutical industries. Many of those solvents, among them acetone, are considered to be harmful to human health. Detecting vapors of such volatile solvents present in the air can be achieved by multiple devices, but optical detection have few important advantages- easy room temperature detection without need of electrical power supply and detection based only on color/reflectance change. Among the great variety of materials, that can be implemented as sensitive media in optical chemical sensors excel polymers which change their refractive index, extinction coefficient or thickness in presence of solvent’s vapors.

In this work, acetone-sensitive thin films were deposited on a silica substrates by spin-coating of aqueous dispersions of poly(vinyl alcohol)-graft-poly(methyl acrylate) of different copolymer characteristics. In order to study the optical and sensing properties of the films thickness d, refractive index n and extinction coefficient k were calculated from measured reflectance spectra by using two-stage nonlinear curve fitting method. Sensing properties of the films were studied by measuring reflectance spectra before and after exposure to acetone vapors at room temperature and maximum reflectance change ∆R_max was calculated. The influence of copolymer characteristics on the acetone vapor-responsive properties of studied films is demonstrated and discussed.

Acknowledgments: S. Bozhilova acknowledge the National Scientific Program for young scientists and postdoctoral fellows, funded by the Bulgarian Ministry of Education and Science (MES) with DCM 577/17.08.2018.

The inner core system of metal-free (‘free base’) porphyrins has continually served as a ligand for various metal ions, but only recently was studied in organocatalysis due its highly tuneable basicity. Highly conjugated porphyrin systems offer spectrophotometric sensitivity towards geometrical and/or electronic changes and thus, utilizing the porphyrin core for selective detection of substrates in solution offers significant potential for a multitude of applications. However, solvation and dilution drastically affect weak interactions by dispersing the binding agent to its surroundings. Thus, spectroscopic detection of N–H···X-type binding in porphyrin solutions is almost impossible without specially designing the binding pocket.

Here we present the first report on spectroscopic detection of the N–H···X-type interplay in porphyrins formed by weak interactions. Protonated 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetrakis(2-aminophenyl)porphyrin contains coordination sites for selective binding of charge-bearing analytes, revealing characteristic spectroscopic responses. While electronic absorption spectroscopy proved to be a particularly useful tool for the detection of porphyrin-analyte interactions in the supramolecular complexes, X-ray crystallography helped to pinpoint the orientation, flexibility, and encapsulation of substrates in the corresponding atropisomers.

This charge‐assisted complexation of analytes in the anion-selective porphyrin inner core system is ideal for the study of atropisomers by high-resolution NMR, since it reduces the proton exchange rate, generating static proton signals. Therefore, we were able to characterize all four rotamers of the nonplanar 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetrakis(2-aminophenyl)porphyrin by performing 1D and 2D NMR spectroscopic analyses of host‐guest systems consisting of benzenesulfonic acid (BSA) and each porphyrin atropisomer, . Lastly, detailed assignment of the symmetry operations that are unique to porphyrin atropisomers, allowed us to accurately identify the rotamers using NMR techniques only. Overall, the N–H···X-type interplay in porphyrins formed by weak interactions that form restricted H-bonding complexes shows to be the key to unravel the atropisomeric enigma.

The sensing of gas molecules is of fundamental importance for environmental monitoring, control of chemical processes, and non-invasive medical diagnostics based on human’s breath analysis [1,2]. In recent years, graphene-based gas sensors have attracted much attention and different materials have been developed [2]. However, they still suffer from several problems, which could be overcome by covering the graphene surface with metal oxides (MOS). Besides, thanks to the high chemical versatility, promising results could be also obtained by coupling porphyrin-based macrocycles to MOS. As such, boosted potentialities, especially in terms of tuned selectivity and low water interference, may be obtained. Therefore, the present work is aimed at evaluating and comparing the sensing at both mild temperatures (also exploiting the UV light) of SnO₂ matrix coupled with different porphyrins and graphene oxide (GO, in a fixed SnO₂/GO weight ratio [4]) materials towards the sensing of acetone molecules. Specifically, three zinc porphyrins were adopted: zinc tetraphenylporphyrin (ZnTPP) and two perfluorinated derivatives of ZnTPP. The sensor responses at 150 °C of the latter resulted about ten times more intense than those of ZnTPP@Sn and Sn32@GO, whose intensities are similar. By computing the response and recovery times, it can be stated that the former for the three hybrids is comparable, whereas the recovery time of SnO₂–porphyrins are significantly longer. Switching the UV lamp on, the samples ability to sense acetone drastically changed: the LOD reached the 200 ppb for all the materials, while perfluorinated derivatives can still guarantee the more intense response. A possible explanation of the role of both GO and porphyrins in boosting the SnO₂ sensing of oxidizing molecules (as acetone) is reported, according to the recent literature related to hybrid chemoresistors [3,4] and DSSC devices [5].

References

[1] A. Tricoli, N. Nasiri, S. De, Adv. Funct. Mater. 2017, 27, 1605271.

[2] J. Chen, B. Yao, C. Li, G. Shi, Carbon 2013, 64, 225–229.

[3] E. Pargoletti, U. H. Hossain, I. Di Bernardo, H. Chen, T. Tran-Phu, et al., Nanoscale 2019, 11, 22932

[4] E. Pargoletti, U. H. Hossain, I. Di Bernardo, H. Chen, T. Tran-Phu, Get al., ACS App. Mat. and Interf. 2020, 12, 39549−39560

[5] S. Berardi, St. Caramori, E. Benazzi, N. Zabini, A. Niorettini, A. Orbelli Biroli, M. Pizzotti, F. Tessore, G. Di Carlo, Appl. Sci. 2019, 9, 2739

Following the great success of graphene, 2D layered materials based on the elements of group VA (also known as pnictogens) open up many possibilities in the field of sensors. This group of materials include phosphorene, bismuthene, antimonene, and arsenene and offer many desirable features for electrochemical sensors such as high surface area, excellent mobility, morphology tunability, and the possibility to modify their surface properties [1].

In this work, the modification of screen-printed electrodes with 2D layered pnictogens was explored for the enhanced anodic stripping voltammetric determination of metal ions. Particular emphasis was placed on bismuthene and antimonene given both their lower toxicity and the ability of bismuth and antimony films to mirror the analytical performance of mercury electrodes for metal ion determination. Thus, bismuthene and antimonene, as well as some of their derivatives, were tested and compared looking for an improved analytical performance (i.e, low limit of detection, LOD, high sensitivity), which was evaluated for the simultaneous determination of Pb(II) and Cd(II). Out of all the tested materials, bismuthene demonstrated the best analytical performance, providing, for a 120 s preconcentration time, a linear response from 0.2 to 25.0 μg L⁻¹ for both Pb(II) and Cd(II) and LODs of 0.06 and 0.07 μg L^-1 for Pb(II) and Cd(II), respectively [2]. The achieved LODs also represent an improvement over other bismuth-based electrochemical sensors such as those based on bismuth nanoparticles or commercially available sputtered screen-printed electrodes.

[1] M.A. Tapia, R. Gusmão, N. Serrano, Z. Sofer, C. Ariño, J.M. Díaz-Cruz, et al., Phosphorene and other layered pnictogens as a new source of 2D materials for electrochemical sensors, TrAC Trends Anal. Chem. 139 (2021) 116249. doi:10.1016/j.trac.2021.116249.

[2] M.A. Tapia, C. Pérez-Ràfols, R. Gusmão, N. Serrano, Z. Sofer, J.M. Díaz-Cruz, Enhanced voltammetric determination of metal ions by using a bismuthene-modified screen-printed electrode, Electrochim. Acta. 362 (2020) 137144. doi:10.1016/j.electacta.2020.137144.

Aged distilled beverages namely cognac and brandy contain natural phenolic antioxidants to be considered as one of the quality markers. Different types of chromatography are usually applied for their quantification. Electrochemical sensors being simple, reliable and cost-effective could be an effective alternative tool for this purposes. The only problem of the electrochemical approaches is the low selectivity of phenolics determination due to the structural similarity of analytes. This limitation can be overcome using chemically modified electrodes. Novel voltammetric sensors based on the carbon nanotubes and electropolymerized pyrocatechol violet or p-aminobenzoic acid (ABA) have been developed for the simultaneous determination of phenolic antioxidants in cognac and brandy for the first time. Application of carbon nanotubes (polyaminobenzene sulfonic acid functionalized single-walled carbon nanotubes (f-SWNT/GCE) and multi-walled carbon nanotubes (MWNT/GCE)) as a substrate provide high surface area and conductivity while polymeric film provides structural similarity to the analytes and the porous structure leading to the increase of the determination sensitivity. Polymerization conditions of pyrocatechol violet and ABA in potentiodynamic mode has been optimized. Sensors has been characterized with SEM, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The polymeric films exhibit porous structure with the shape of particles and their aggregates deposited on the surface of carbon nanomaterials that confirms the successful electropolymerization. Statistically significant increase of the effective surface area and low charge transfer resistance of the sensors developed in comparison to GCE and GCE modified with carbon nanotubes have been obtained. Sensors developed have been applied for the simultaneous sensitive determination of gallic and ellagic acids as well as syringaldehyde and vanillin under conditions of differential pulse voltammetry. The analytical characteristics obtained are improved vs. other modified electrodes. The sensors selectivity in the presence of typical interferences and other natural phenolics has been obtained that is important advantage. The sensors developed have been successfully tested on the cognac and brandy samples. The results obtained agree well with chromatographic data confirming the accuracy of the sensors developed. Thus, the novel highly sensitive and selective voltammetric sensors for the simultaneous determination of structurally related phenolic antioxidants are characterized by simplicity of the fabrication, reliability, cost-efficiency and can be applied for the routine analysis as an alternative to chromatographic methods.

Aromatic polyamides or aramids are materials with exceptional thermal and mechanical properties. For this reason, they are considered high-performance materials with a multitude of applications in fields such as civil security (bullet-proof body armour or fire, chemical and saw protection suits), transport (automotive and aerospace) and civil engineering, among many others. The remarkable properties arise from the high cohesive energy as a consequence of their chemical structure, including the rigidity of the main chain due to the wholly aromatic structure conjugated with the amide groups, the high average bond energy and a strong and highly directional interchain hydrogen bonds between the amide moieties. Although in some industrial applications the natural yellowish colour of the fibres is used, generally most of the applications require coloured fibres. However, aramid fibres have poor dyeing properties, for the same reasons that make them thermally and mechanically resistant, and traditional dyeing methods such as dope dying, are inefficient and aggressive, which impairs fibres properties.

Ideal colour fastness of fibres is achieved by intrinsically, inherently or self-coloured polymers, by introducing a dye motif or chromophore monomer in the chemical structure of the polymer. In addition, the colour hue can be controlled by means of tuning the chromophore monomer molar content in the final composition. In a previous research, we successfully obtained inherently blue coloured aramids, with blue chromophore motifs unable to migrate and evenly distribute along the polymer chain and maintaining their high performance properties, and our aim now is to obtain red coloured aramids prepared in the same fashion.

Arsenic is amongst the most hazardous heavy metals released into the environment by natural or human-induced sources. A known carcinogen and irritant, its trivalent and pentavalent forms are the most common in aqueous media rendering their onsite monitoring and removal crucial. In this work, different adsorbents based on iron oxide nanoparticles (Fe­₃O₄ NPs) coated with (3-aminopropyl)triethoxysilane (APTES) were prepared. The nanoparticles were then functionalized with one of the three nucleobase derivatives: adenine hydrazide (AH), guanine hydrazide (GH) or uracil hydrazide (UH). The successful functionalization of the nanoparticles was confirmed using Fourier transform infrared spectroscopy. Boron-doped diamond electrodes were modified using the different functionalized nanoparticles, and the interaction of the nucleobases with trivalent arsenic ions was assessed using square wave voltammetry, the adsorption efficiency being extracted from the decrease of the nucleobase peak maximum intensity. The electrochemical evaluation of adsorption isotherms showed that the Langmuir model was a better fit compared to Freundlich, and that the adsorption capacity increased in the following order: AH < UH < GH. Furthermore, it was shown that the adsorption follows a pseudo-second order kinetic model implying the involvement of chemisorption in the process. The electrochemical detection of arsenic utilizing the magnetic nanoparticles functionalized with guanine hydrazide showed a better analytical performance compared to adenine and uracil hydrazide, with a sensitivity of 1.92 µA.µg^-1.L and limit of detection of 1.6 µg/L.

Tripeptide glutathione (GSH) is an abundant and ubiquitous metabolite in living organisms that plays critical roles in various cellular bioprocesses. In this work, we report the development of a new nanoprobe (MnO₂-PEI-FITC) for GSH detection and imaging through exploiting the response mechanism of specific GSH-triggered reduction of manganese dioxide (MnO₂) nanosheet. The MnO₂-PEI-FITC nanoprobe was developed by coating negatively charged MnO₂ nanosheet with positively charged polyethylenimine (PEI) polymer, followed by coupling with fluorescein isothiocyanate (FITC) through a thiourea linkage. The MnO₂-PEI-FITC nanoprobe showed weak fluorescence due to the quenching of FITC emission by MnO₂’s absorption, while FITC’s emission at 518 nm was observed in the presence of GSH. The MnO₂-PEI-FITC nanoprobe featured rapid response to GSH (< 12 min), high sensitivity (detection limit, 164 nM) and selectivity. Application of this nanoprobe for GSH imaging in in fresh yeast cells and onion inner-layer epidermal tissues were then successfully demonstrated. This work thus provides a new nanoprobe for GSH detection and imaging in biological samples.