Free indium concentration determined with AGNES

Ethyl 3-aminobenzo[b]thiophene-2-carboxylate Derived Ratiometric Schiff Base Fluorescent Sensor for the Recognition of In3+ and Pb2

An ethyl 3-aminobenzo[b]thiophene-2-carboxylate derived ratiometric Schiff base fluorescent sensor R was devised and synthesized. R exhibited a highly sensitive and selective ratiometric response to In3+ in DMF/H2O tris buffer solution. R exhibited a colorimetric/fluorescent dual-channel response to In3+. More importantly, R can distinguish In3+ from Ga3+ and Al3+ in less than 5 min. R exhibited a good linear correlation with the concentration of In3+ in the 5-25 μM range and the limit of detection for In3+ was found to be 8.36 × 10-9 M. According to the job`s plot and MS spectra, R formed a complex with In3+ at 1:2 with a complexation constant of 8.24 × 109 M2. Based on Gaussian theory calculations, the response mechanism of R to In3+ can be explained by photo-induced electron transfer (PET) and intramolecular charge transfer (ICT) mechanisms. In addition, R can be used for the detection of indium in tap water with satisfactory recoveries. Meanwhile, R displayed a linear relationship to micromolar concentrations (0-50 μM) of Pb2+ and recognized Pb2+ in a ratiometric response with a detection limit of 8.3 × 10-9 M.

Physicochemical Rationale of Matrix Effects Involved in the Response of Hydrogel-Embedded Luminescent Metal Biosensors

There is currently a critical need for understanding how the response and activity of whole-cell bacterial reporters positioned in a complex biological or environmental matrix are impacted by the physicochemical properties of their micro-environment. Accordingly, a comprehensive analysis of the bioluminescence response of Cd(II)-inducible PzntA-luxCDABE Escherichia coli biosensors embedded in silica-based hydrogels is reported to decipher how metal bioavailability, cell photoactivity and ensuing light bioproduction are impacted by the hydrogel environment and the associated matrix effects. The analysis includes the account of (i) Cd speciation and accumulation in the host hydrogels, in connection with their reactivity and electrostatic properties, and (ii) the reduced bioavailability of resources for the biosensors confined (deep) inside the hydrogels. The measurements of the bioluminescence response of the Cd(II) inducible-lux biosensors in both hydrogels and free-floating cell suspensions are completed by those of the constitutive rrnB P1-luxCDABE E. coli so as to probe cell metabolic activity in these two situations. The approach contributes to unraveling the connections between the electrostatic hydrogel charge, the nutrient/metal bioavailabilities and the resulting Cd-triggered bioluminescence output. Biosensors are hosted in hydrogels with thickness varying between 0 mm (the free-floating cell situation) and 1.6 mm, and are exposed to total Cd concentrations from 0 to 400 nM. The partitioning of bioavailable metals at the hydrogel/solution interface following intertwined metal speciation, diffusion and Boltzmann electrostatic accumulation is addressed by stripping chronopotentiometry. In turn, we detail how the bioluminescence maxima generated by the Cd-responsive cells under all tested Cd concentration and hydrogel thickness conditions collapse remarkably well on a single plot featuring the dependence of bioluminescence on free Cd concentration at the individual cell level. Overall, the construction of this master curve integrates the contributions of key and often overlooked processes that govern the bioavailability properties of metals in 3D matrices. Accordingly, the work opens perspectives for quantitative and mechanistic monitoring of metals by biosensors in environmental systems like biofilms or sediments.

Release of indium from In2O3 nanoparticles in model solutions and synthetic seawater

Indium oxide (In2O3) nanoparticles (NPs) are used in electronic devices, from which indium (as its nanoparticulate form or as other generated chemical species) can be released to natural waters. To assess for the impacts of such releases (e.g. toxic effects), information on the kinetics and thermodynamics of the In2O3 dissolution processes is key. In this work, the evolution with time of the dissolution process was followed with the technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) by measuring the free indium concentration ([In3+]). AGNES can determine the free ion concentration in the presence of nanoparticles without a prior separation step, as shown in the case of ZnO nanoparticles, a procedure that is more accurate than the typical sequence of centrifugation+filtration+elemental analysis. Excess of indium oxide NPs were dispersed in 0.1 mol L-1 KNO3 at various pH values ranging from 2 to 8. Additional dispersions with bulk In2O3 at pH 3 or NPs in synthetic seawater at pH 8 were also prepared. The temperature was carefully fixed at 25 °C. The dispersions were continuously stirred and samples were taken from time to time to measure free indium concentration with AGNES. 180-day contact of In2O3 to solutions at pH 2 and 3 was not enough to reach equilibrium. The dissolution of the NPs at pH 3 was faster than that of the bulk (i.e. non nanoparticulate) material. Equilibrium of the NPs with the solution was reached at pH 4 and 5 in KNO3 and at pH 8 in seawater, in shorter times for higher pH values, with free indium concentrations decreasing by a factor of 1000 for each increase in one pH unit. The solubility products of In(OH)3 and In2O3 were compared. Equilibration of NPs with synthetic seawater took <18 days, with an average free [In3+] (up to 196 days) of 1.03 amol L-1.

Electroanalytical Trace Metal Cations Quantification and Speciation in Freshwaters: Historical Overview, Critical Review of the Last Five Years and Road Map for Developing Dynamic Speciation Field Measurements

An historical overview covering the field of electroanalytical metal cations speciation in freshwaters is presented here, detailing both the notable experimental and theoretical developments. Then, a critical review of the progress in the last five years is given, underlining in particular the improvements in electrochemical setups and methodologies dedicated to field surveys. Given these recent achievements, a road map to carry out on-site dynamic metal speciation measurements is then proposed, and the key future developments are discussed. This review shows that electroanalytical stripping techniques provide a unique framework for quantitatively assessing metals at trace levels while offering access to both thermodynamic and dynamic features of metal complexation with natural colloidal and particulate ligands.

Selective ratiometric red-emission detection of In3+ in aqueous solutions and in live cells using a fluorescent peptidyl probe and metal chelating agent

Indium has been regarded as one of the most rarely used metal ions; however, the consumption of indium has increased intensively due to its increasing use in electrodes of liquid crystal displays (LCDs). In recent years, warnings have been issued about the toxicity of indium to aquatic ecosystems and humans. Thus, the development of efficient and selective detection methods for In³⁺ in aquatic environments as well as in live cells is highly required. However, the selective and sensitive detection of In³⁺ in the presence of trivalent metal ions and other metal ions is highly challenging. In the present study, we synthesized a fluorescent probe (1) for In³⁺ and Al³⁺ based on an unnatural peptide receptor and an aggregation-induced emission fluorophore and developed a selective fluorescent detection method for In³⁺ in aqueous solutions and live cells using the probe and a metal chelating agent. 1 recognized In³⁺ and Al³⁺ selectively among 19 metal ions in aqueous solutions depending on pH by the enhancement of the red emission at 600 nm and decrease in the green emission at 530 nm. 1 sensitively detected In³⁺ and Al³⁺ by ratiometric response in a wide pH range (3.5-7.4), and the ratiometric response was complete within 20 seconds in an aqueous buffered solution at pH 5.0. Interestingly, the addition of EDTA to the complex of 1 with In³⁺ or Al³⁺ did not induce the Al³⁺-free spectrum but instead induced the In³⁺-free spectrum; thus, In³⁺ and Al³⁺ could be easily differentiated. The detection limit of 1 for In³⁺ ions was 211 nM (R² = 0.981) in purely aqueous solutions. The fluorescence ratiometric detection method using 1 could quantify low concentrations of In³⁺ in ground water and tap water. Fluorescence cell image studies revealed that the probe was cell-permeable, and low concentrations of In³⁺ inside the cells could be recognized by the enhancement of the red emission at 600 nm. The binding mode study via NMR, IR, and CD spectroscopy revealed how the peptide receptor of 1 interacted with In³⁺ and resulted in the enhancement of the red emission in an aqueous solution.

A fluorescence probe based on 6-phenylimidazo[2,1-b]thiazole and salicylaldehyde for the relay discerning of In3+ and Cr3+

A new fluorescence probe, (E)-N′-(2-hydroxybenzylidene)-6-phenylimidazo[2,1-b]thiazole-3-carbohydrazide (LB1), based on 6-phenylimidazo[2,1-b]thiazole and salicylaldehyde was designed and synthesized.

Double Schiff base from thiophene-2,5-dicarboxylic acid as an “off–on–off” fluorescence sensor for the sequential detection of In3+ and PPi

A double Schiff base T as acceptor for metal ions derived from thiophene-2,5-dicarboxylic acid was designed and synthesized, and showed a high selectivity for In³⁺ in a DMF/H₂O buffer solution.

Towards improving the electroanalytical speciation analysis of indium

The geochemical fate of indium in natural waters is still poorly understood, while recent studies have pointed out a growing input of this trivalent element in the environment as a result of its utilisation in the manufacturing of high-technology products. Reliable and easy-handling analytical tools for indium speciation analysis are, then, required. In this work, we report the possibility of measuring the total and free indium concentrations in solution using two complementary electroanalytical techniques, SCP (Stripping chronopotentiometry) and AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) implemented with the TMF/RDE (Thin Mercury Film/Rotating Disk Electrode). Nanomolar limits of detection, i.e. 0.5 nM for SCP and 0.1 nM for AGNES, were obtained for both techniques in the experimental conditions used in this work and can be further improved enduring longer experiment times. We also verified that AGNES was able (i) to provide robust speciation data with the known In-oxalate systems and (ii) to elaborate indium binding isotherms in presence of humic acids extending over 4 decades of free indium concentrations. The development of electroanalytical techniques for indium speciation opens up new routes for using indium as a potential tracer for biogeochemical processes of trivalent elements in aquifers, e.g. metal binding to colloidal phases, adsorption onto (bio)surfaces, etc.

Dissolution and Phosphate-Induced Transformation of ZnO Nanoparticles in Synthetic Saliva Probed by AGNES without Previous Solid-Liquid Separation. Comparison with UF-ICP-MS

The variation over time of free Zn²⁺ ion concentration in stirred dispersions of ZnO nanoparticles (ZnO NPs) prepared in synthetic saliva at pH 6.80 and 37 °C was followed in situ (without solid-liquid separation step) with the electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). Under these conditions, ZnO NPs are chemically unstable due to their reaction with phosphates. The initial stage of transformation (around 5-10 h) involves the formation of a metastable solid (presumably ZnHPO₄), which later evolves into the more stable hopeite phase. The overall decay rate of ZnO NPs is significantly reduced in comparison with phosphate-free background solutions of the same ionic strength and pH. The effective equilibrium solubilities of ZnO (0.29-0.47 mg·L^-1), as well as conditional excess-ligand stability constants and fractional distributions of soluble Zn species, were determined in the absence and presence of organic components. The results were compared with the conventional ultrafiltration and inductively coupled plasma-mass spectrometry (UF-ICP-MS) methodology. AGNES proves to be advantageous in terms of speed, reproducibility, and access to speciation information.

A Highly Selective Fluorescent Chemosensor for Detecting Indium(III) with a Low Detection Limit and its Application

A highly selective chemosensor BHC ((E)-N-benzhydryl-2-((2-hydroxynaphthalen-1-yl)methylene)hydrazine-1-carbothioamide) for detecting indium(III) was synthesized. Sensor BHC can detect In(III) by a fluorescence turn-on method. The detection limit was analyzed to be 0.89 μM. Importantly, this value is the lowest among those previously known for fluorescent turn-on In(III) chemosensors. Based on the analytical methods like ESI-mass, Job plot, and theoretical calculations, the detection mechanism for In(III) was illustrated to be chelation-enhanced fluorescence (CHEF) effect. Additionally, sensor BHC was successfully applied to test strips.