Development And Application Of Microanalysis Systems In The Environmental Monitoring

This study describes the development and application of three microanalysis systems. The application domain is concentrated on environmental contaminations, mainly heavy metal ions in surface water and endocrine disrupting chemicals in sewage.A microfabricated device has been developed for the selective detection of lead in water. It is based on the use of a selective and sensitive fluorescent molecular sensor (Calix-DANS4) for lead which contains a calix[4]arene bearing four dansyl groups. The principle of this sensor is photoinduced charge transfer (PCT) which can cause a slight blue shift of both the absorption and fluorescence spectra in acidic condition after binding with lead ion. The microchip-based lead sensor is a Y-shape microchannel structured with a passive mixer and stuck on a glass substrate. The detection is performed by using a configuration in which the sensing molecules are excited by two optical fibres, each connected to a 365 nm UV LED, and the emitted light is collected by another optical fibre coupled with a photomulti-plier.A detection limit of 2.5×10^-8 mol L^-1 (i.e. 5.2μg L^-1) could be reached, which is lower than the maximum level of lead allowed in drinking water after 2013, according to European regulation.In order to improve the sensitivity of the previous microfluidic device and to get rid of interfering calcium ion, we developped a solid phase extraction preconcentration (SPE) stage with a micro-column filled with silica beads functionalized with aminopropyl groups (APS). During SPE, the APS groups selectively adsorb the lead ions at basic pH (pH = 10) which allows its separation from others (Ca²⁺, Na⁺). In acidic medium (pH = 2), lead is reversibly released and can be recovered in a 100 times more concentrated. The combination of SPE and previous fluorimetric microfluidic device was carried out for lead solutions of known concentrations in tap water. The results were proved by Atomic Absorption Spectroscopy.The study of the mechanism of the complexation between fluorescence molecular sensor (Calix-DANS4) and lead ion allows us to optimize the chip where the complexation occurs. The large difference between the calibration curves obtained for reactants mixed inside the chip and for injection of a premixed solution shows that the complexation is not finished at the end of the microchannel. A new microchip with a longer channel has permitted to approach the equilibrium state. Conventional stopped-flow method was also applied here to determine the real reaction kinetics and rate constants. The results show that this complexation at pH 3.2 is a relatively slow reaction, which takes several minutes for weak Pb²⁺ concentrations. It proves that the complexation in our microfluidic chips has not yet finished, as the transit times in all these microfluidic chips are less than 40 s.Another microanalysis system for metal ion sensing is an optofluidic sensor which combines optical elements (such as waveguide, laser...) and microfluidics for biological and chemical assays. A preliminary study of polymer microcavity laser for metal ions sensor in microfluidic channel is introduced in this thesis. The search of the microcavity laser materials is focused on diblock copolymers, especially two diblock copolymers (PS-b-P2VP, PS-b-P4VP), which can form microphase separation to load laser dye (e.g. DCM) in the hydrophobic phase and metal ion in the hydrophilic phase. The morphologies and refractive index of their cast films are studied before fabricating the microcavity laser. Their responses to different environments (e.g. water, metal ion solutions...) are characterized by AFM and ellipsometry. The results show that PS-b-P4VP can exhibit remarkable changes both of morphology and refractive index when contacting with zinc ion solution, while zinc ion has no effect on PS-b-P2VP. The first optofluidic sensor is fabricated with a microcavity laser which is made of PS-b-P4VP doped with a laser dye (DCM) and placed in a PDMS microfluidic channel. Its laser spectral shifts in presence of pure water and zinc ion are both observed.Endocrine Disrupting Chemicals (EDCs) are anthropogenic substances that can interfere with the endocrine systems of living organisms. Their harmful effects on human health, when they reach a certain amount, have been discovered and are still being studied precisely. An integrated analytical method to monitor five environmental endocrine disrupting chemicals (EDCs): 2,4-dichlorophenol (DCP), 4-tert-butylphenol (BP), bisphenol A (BPA), 17α-ethynylestradiol (EE2) and 4-n-nonylphenol (NP), is developed for the first time. This third microanalysis system is based on a solid-phase extraction and miniaturized micellar electrokinetic chromatography (MEKC) with amperometric detection (AD). In order to get the optimum conditions of their separation and detection, several parameters including pH and concentration of running buffer, concentration of micelle, separation voltage and injection time are studied and optimized. The five EDCs are well separated under the optimum conditions within 12 min. This method is successfully applied for the determination of these five EDCs in sewage influent sample. Satisfactory extraction performances from sewage sample are obtained by solid-phase extraction (SPE), using a HLB (waters) cartridge. Quantitative analysis shows that DCP, BP and BPA exist atμg L^-1 level in the selected sample, while EE2 and NP are not detected.