Electrochemical Sensor Research at the Laboratoire d'Electrochimie of the EPFL

This review presents some recent developments in the field of electroanalytical sensors. We first explain the working principle of electrochemistry at the interface between two immiscible electrolyte solutions (ITIES), illustrated by the example of copper transferring through a water/1,2-dichloroethane interface when the ionophore 1,4,7,10-tetrathiacyclododecane is present in the organic phase. The obtained results show that assisted ion-transfer reactions take place with both CuI and CuII, but that the interfacial process is complicated by the fact that CuI disproportionates in water and that CuII can be reduced in the organic phase.Based on the same experimental methodology, a new type of amperometric detector for non-redox ions has been developed using a composite polymer membrane supporting a gelified organic phase that can incorporate an ionophore such as valinomycin. We report here the use of a (o-nitrophenyloctylether)-(poy(vinyl chloride) (NPOE-PVC) gel micro-interface as a detector for cations and anions in ion-exchange chromatography. The main advantage of this approach is that selectivity and sensitivity can be tailored by the choice of the ionophore and by the polarisation potential.This ion detector has also been incorporated in a miniaturised total-analysis system (µ-TAS) fabricated in a polymer sheet by UV-laser photoablation. This microfabrication technique is used for the prototyping of a disposable capillary-electrophoresis microsystem comprising on-chip injector, separation column and electrochemical detector. This system is further used with built-in carbon-ink electrodes for the detection of electroactive species. These microsystems are now under development for immuno-sensor applications

Acute Delta Hepatitis in Italy spanning three decades (1991–2019): Evidence for the effectiveness of the hepatitis B vaccination campaign

Updated incidence data of acute Delta virus hepatitis (HDV) are lacking worldwide. Our aim was to evaluate incidence of and risk factors for acute HDV in Italy after the introduction of the compulsory vaccination against hepatitis B virus (HBV) in 1991. Data were obtained from the National Surveillance System of acute viral hepatitis (SEIEVA). Independent predictors of HDV were assessed by logistic-regression analysis. The incidence of acute HDV per 1-million population declined from 3.2 cases in 1987 to 0.04 in 2019, parallel to that of acute HBV per 100,000 from 10.0 to 0.39 cases during the same period. The median age of cases increased from 27 years in the decade 1991-1999 to 44 years in the decade 2010-2019 (p < .001). Over the same period, the male/female ratio decreased from 3.8 to 2.1, the proportion of coinfections increased from 55% to 75% (p = .003) and that of HBsAg positive acute hepatitis tested for by IgM anti-HDV linearly decreased from 50.1% to 34.1% (p < .001). People born abroad accounted for 24.6% of cases in 2004-2010 and 32.1% in 2011-2019. In the period 2010-2019, risky sexual behaviour (O.R. 4.2; 95%CI: 1.4-12.8) was the sole independent predictor of acute HDV; conversely intravenous drug use was no longer associated (O.R. 1.25; 95%CI: 0.15-10.22) with this. In conclusion, HBV vaccination was an effective measure to control acute HDV. Intravenous drug use is no longer an efficient mode of HDV spread. Testing for IgM-anti HDV is a grey area requiring alert. Acute HDV in foreigners should be monitored in the years to come

Impact of Channel Geometry on the Discrimination of Mechanically Impaired Red Blood Cells in Passive Microfluidics

In this work, we aimed at the discrimination of mechanically impaired red blood cells (RBCs) using passive microfluidic approaches. We investigated the impact of the channel geometry on the behavior of healthy RBCs (hRBCs) and thermally rigidified RBCs (T-rRBCs) flowing in (i) a Unique and Long Constriction (ULC) and (ii) a series of Oscillating Width Constrictions (OWC). To confront the two geometries, we evaluated potential biomarkers for cell discrimination such as their speed V, deformation index D and relaxation time τ

Deformability as a new physical biomarker

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Flow of healthy and thermally rigidified erythrocytes in a microfluidic rheometer

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Analysis of Red Blood Cells relaxation time flowing out of microfluidic constrictions reveals the impact of buffer viscosity and flow speed.

International audienceFor the first time, we report that the relaxation time t of healthy human Red Blood Cells (RBCs) decreases upon increase of both the buffer viscosity and its speed, and can reach values as low as 20 ms. Such result is a decade smaller than measurements usually reported in the literature using micropipette aspiration[1], optical tweezers[2], ecktacytometry[3] or microfluidics[4]. These published values (t = 100 to 300 ms) are in good agreement with Hochmuth-Evans[1] analytical calculation of t using the Kelvin-Voigt model describing the RBC as a viscoelastic material. They predict that t only depends on intrinsic cell membrane mechanical properties such as its viscosity and shear modulus. Our finding was obtained from the analysis of video-microscopic recordings of healthy RBCs flowing in a PDMS microfluidic channel, with oscillating width (5-25 µm) as illustrated in Figure1a. More precisely, we focused on the cell behavior at the exit of the last geometrical restriction through the study of its shape relaxation. A large range of fluidic stresses was investigated by varying both the buffer viscosity (h out = 1-30 mPa.s) through the addition of Dextran and the flow velocity (100-2000 µm/s) through the modification of the applied pressure. The observations revealed two different modes of shape relaxation, according to the external flow parameters. The first mode is the stretching behavior illustrated in Figure 1b, as RBCs exit the last narrowing they undergo a large deformation normal to the flow direction before relaxing to their equilibrium parachute-like shape. The second mode is the unfolding behavior, where the RBCs relax directly from their passage in the last restriction and recover their equilibrium shape (Figure 1c). We report in the diagram Figure 2, that the unfolding behavior is mainly observed for the lowest viscosities where the hydrodynamic constraint at the exit is below the stretching modulus of RBCs, whereas the stretching behavior occurs at higher viscosity and RBCs speed, corresponding to higher constraint. For a buffer viscosity of 2 mPa.s, we observed a transition between the two modes according to the cell speed. Indeed, for intermediate velocities a mixed behavior, where both modes are represented among the cell population, is observed. As shown in Figure 3, at fixed buffer viscosity, 1/τ increases linearly with the cell velocity. Similarly, for a given RBC speed, 1/τ rises with the buffer viscosity. Upon very low buffer viscosity and low flow speed, we retrieve relaxation times similar to those reported in literature. We attribute the diminution of the cell relaxation time upon both buffer viscosity and flow velocity to a coupling between the RBC and the external medium. Indeed, the cell dissipates some of the energy accumulated during its deformation, in the suspending media when the buffer viscosity can no longer be neglected compared to the internal cell viscosity. Moreover, we showed that the velocity difference between the cell and the surrounding fluid increases with the flow speed as expected[5], leading to a larger dissipation in the buffer. Both our results and the already published data agree with this interpretation

Continuous-flow microfluidic method for octanol-water partition coefficient measurement

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Comparison of ITO and IrOx-Modified ITO Interdigitated Electrodes for Electrical Cell-Substrate Impedance Sensing (ECIS) Applications

This study compares the sensitivity of interdigitated electrodes (IDEs) used in Electrical Cell-Substrate Impedance Sensing (ECIS). IDEs made of indium tin oxide (ITO) and ITO coated with iridium oxide (IrOx) were used for ECIS measurements with the human breast cancer cell line, MCF-7. The results indicate that IrOx-modified ITO electrodes provide both biocompatibility and higher cell sensitivity compared to ITO electrodes. We also found that the quantity of IrOx required to generate such a sensitivity improvement is sufficiently low to not interfere with the visualization of the cells under study. IrOx-modified ITO electrodes are therefore promising sensors for ECIS applications