Physicochemical rationale of matrix effects involved in the response of hydrogel-embedded luminescent metal biosensors
Elise Rotureau, Christophe Pagnout, Jérôme F.L. Duval
Biosensors (2024) DOI: xxx
There is currently a critical need for understanding how the response and activity of whole-cell bacterial reporters positioned in 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 ac-cumulation 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 situa-tions. The approach contributes to unravel 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 a quantitative and mechanistic monitoring of metals by biosensors in environmental systems like biofilms or sediments.
Towards improving the electroanalytical speciation analysis of indium
Elise Rotureau, Pepita Pla-Vilanova, Josep Galceran, Encarna Companys, José Paulo Pinheiro
Analytica Chimica Acta, 1052, 57-64 (2019)
DOI: 10.1016/j.aca.2018.11.061
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.
Structural effects of soft nanoparticulate ligands on trace metal complexation thermodynamics
Elise Rotureau, Yves Waldvogel, José P. Pinheiro, José Paulo S. Farinha, Isabelle Bihannic, Romain M. Présent, and Jérôme F. L. Duval
Physical Chemistry Chemical Physics, 2016, 18, 31711-311724
DOI: 10.1039/C6CP06880D
Abstract
Metal binding to natural soft colloids is difficult to address due to the inherent heterogeneity of their reactive polyelectrolytic volume and the modifications of
their shell structure following changes in e.g. solution pH, salinity or temperature. In this work, we investigate the impacts of temperature- and salinity-mediated modifications of the shell
structure of polymeric ligand nanoparticles on the thermodynamics of divalent metal ions Cd(II)-complexation. The adopted particles consist of a glassy core decorated by a fine-tunable
poly(N-isopropylacrylamid) anionic corona. According to synthesis, the charges originating from the metal binding carboxylic moieties supported by the corona chains are located preferentially
either in the vicinity of the core or at the outer shell periphery (p(MA-N) and p(N-AA) particles, respectively). Stability constants of cadmium-nanoparticle complexes are measured under
different temperature and salinity conditions using electroanalytical techniques. The obtained is clearly impacted by the location of the carboxylic functional groups within the shell as p(MA-N)
leads to stronger nanoparticulate Cd complexes than p(N-AA). The dependence of on solution salinity for p(N-AA) is shown to be consistent with a binding of Cd to peripheral carboxylic groups
driven by coulombic interactions (Eigen-Fuoss mechanism for ions-pairing) or with particle electrostatic features operating at the edge of the shell Donnan volume. For p(MA-N) particulate
ligands, a scenario where metal binding occurs within the intraparticulate Donnan phase correctly reproduces the experimental findings. Careful analysis of electroanalytical data further
evidences that complexation of metal ions by core-shell particles significantly differ according to the location and distribution of the metal-binding sites throughout the reactive shell. This
complexation heterogeneity is basically enhanced with increasing temperature i.e. upon significant increase of particle shell shrinking, which suggests that the contraction of the reactive phase
volume of the particulate ligands promotes cooperative metal binding effects.
Addressing metal biouptake dynamics from cell concentration-dependent kinetics of bulk metal depletion
Elise Rotureau, Patrick Billard, Jérôme F.L. Duval
Environmental Science and Technology, 2015, 49, 990-998
Abstract
Bioavailability of trace metals is a key parameter for assessment of toxicity on living organisms. Proper evaluation of metal bioavailability requires monitoring the various interfacial processes that control metal partitioning dynamics at the biointerface, which includes metal transport from solution to cell membrane, adsorption at the biosurface, internalization and possible excretion. In this work, a methodology is proposed to quantitatively describe the dynamics of Cd(II) uptake by Pseudomonas putida. The analysis is based on thekinetic measurement of Cd(II) depletion from bulk solution at various initial cell concentrations using electroanalytical probes. On the basis of a recent formalism on dynamics of metal uptake by complex biointerphases, cell concentration-dependent depletion timescale and plateau value reached by metal concentration at long exposure times (>3 hrs) are successfully rationalized in terms of limiting metal uptake flux, rate of metal excretion and metal affinity to internalization sites. The analysis demonstrates the inapplicability here of approximate analytical depletion models valid in the extremes of high and weak metal affinities. The contribution of conductive diffusion transfer of metals from solution to cell membrane in governing the rate of Cd(II) uptake is further discussed from estimation of the resistances for metal membrane transfer and extracellular mass transport.