Increasingly used in industrial coatings, polyelectrolytes multilayers (PEMs) are self-assembled systems made of the alternate deposition of oppositely charged polymers on substrates, usually built by the traditional layer-by-layer method. Their properties strongly depend on environmental physico-chemical parameters. Due to the variety of conditions used in the literature on the one hand and the diversity of polyelectrolytes systems on the other hand, it remains difficult to bring out general principles, leading now to a lack of a real understanding of the PEM buildup, from the macro- to the nanoscale. Here, combining acoustic and electrochemical methods with atomic force microscopy, in a systematic approach, we uncover the critical role of the deposition protocol in the growth regime of PEMs made of cationic poly (allylamine hydrochloride) and anionic poly(4-styrene sulfonate, sodium). Traditional dipping leads to thick, heterogeneous and relatively isolating PEMs whereas a spin-coating assisted method leads to thinner, homogeneous and more permeable PEMs. We also highlight that the pH and the ionic strength influence not only the electrostatic interactions and polyelectrolyte conformation in solution but also their organization after their adsorption on the substrate. Finally, our easily and rapidly adaptable protocol paves the way for promising potential bio-applications, since PEMs are applied to the bacterial immobilization on substrates or as a coating for nanostructured biosensor transducer.

Cellular membrane is one of the main targets of photodynamic therapy. Its high complexity has led to the study of the efficiency of photosensitizers on artificial lipid systems mimicking membranes. However, the preliminary analysis of this efficiency remains limited due to difficulty of the model construction and/or implementation of the required measurement techniques. Hereby, we propose a quite simple way for the rapid comparative assessment of novel photosensitizers in terms of membrane photodegradation, based on simple and fast measurements, such as wetting angle and surface plasmon resonance spectroscopy. As a proof of concept, we applied this methodology to two bacteriopurpurinimide derivatives. We have shown in particular that such complementary techniques can be employed not only for the multiparametric monitoring of the kinetics of the photodegradation, but also for the comparison of the damaging efficiency of the photosensitizers in the lipid structures as well.

An amperometric biosensor based on tyrosinase immobilized on the sensor surface has been used for the detection of polyphenols extracted from green tea. The immobilization was ensured by the crosslinking method on thins films of CoAlSO4 layered double hydroxide recovering screen-printed gold electrodes. Electrochemical measurements show that this biosensor is able to detect tea polyphenols by following the reduction of compounds enzymatically generated. Its response is linear in the concentration range of [0 - 2,4 μM] with high sensitivity and stability, since it retains 90% of its original response after 20 days.

Oxidation of unsaturated lipids promotes important changes in the lipid packing or phase separation in cellular membranes or membrane models. Here, we study by Atomic Force Microscopy (AFM) the behavior of oxidized lipids in Langmuir-Blodgett (LB) films by using two strategies : either following the evolution of LB films of POPC (palmitoyloleoyl-phosphatidylcholine) naturally ageing in contact of atmospheric oxygen, or incorporating a known amount of a defined oxidized derivative of POPC (ALDO-PC) in POPC monolayers before their LB transfer. AFM images of naturally ageing POPC LB films show the appearance of small circular domains after 2 days of exposure to air. These domains (not observed if the samples are kept under vacuum) are characterized by a higher thickness (+0.8 nm) as compared to the intact POPC regions, likely due to a reversal of the oxidized chain which is more polar that intact hydrophobic chains. In the second case, surface pressure measurements show that ALDO-PC induces a slight expansion of the mixed monolayers, suggesting that they are rather homogenous. This hypothesis is confirmed by their smooth and homogenous AFM images. Finally, these results confirm that oxidation in POPC LB films occurs locally in areas presenting likely a looser packing or a defect.

A dried biomass of Arthrospira platensis, called Spirulina (Sp), a filamentous cyanobacterium, a blue-green microalga, is known to bind a wide range of heavy metals [1]. In this work, we propose an innovative approach, based on Spirulina as bioreceptor, combined with highly sensitive Love wave platform for the real-time detection of HM in liquid medium. The real time response to various concentrations of Cadmium (Cd2+) and Mercury (Hg2+), pumped through the microchannels, has been investigated. A detection limit as low as 10-12 mol.l-1 has been obtained. This response has been attributed to changes of microalgae visco-elastic equivalent parameters in presence of heavy metals.

A biosensor based on Escherichia coli Bacteria for determination of heavy metal ions with an acoustic Love wave device and Polydimethylsiloxane (PDMS) microfluidic network has been previously developed, that provides fast detection of toxic chemical compounds.Bacteria were immobilized on the transducer coated with self-assembled molecular multilayers of polyelectrolytes.In this study, we emphasize Love wave and AFM-based complementary characterization methods, which allowed an optimization of some physicochemical parameters of polyelectrolyte solutions, such as pH, ionic strength or molecular weight, in order to increase the immobilization of bacteria as well as the sensor lifetime.For instance, an increase density of bacteria was observed when using alternative pH of 9 for cationic solution.

This work deals with the design of a highly sensitive acoustic Love waves biosensor for heavy metal detection in liquid medium. Biorecepting Escherichia coli bacteria are immobilized on polyelectrolyte multilayers, and are used to detect the presence of cadmium by modification of viscoelastic properties of bacteria. The different setups of sensor elaboration are measured through the real-time resonant frequency shifts of the sensor. The impact of the addition of a titania mesoporous coating is studied, and compared to previous results [1]. Frequency variation for bacteria immobilization is doubled with titania compared with bare silicon dioxide surface. The improvement of the acoustic platform sensitivity is highlighted with cadmium as typical heavy metal. A complementary study was done by Atomic Force Microscopy (AFM) and allowed us to validate the assumptions.

Arthrospira platensis, called spirulina (Sp), is known to bind a wide range of heavy metals [1]. We propose an innovative approach, based on Spirulina as bioreceptor combined with highly sensitive Love wave platform for fast detection of heavy metals in solution. Our goal is to optimize the biofunctionalization of the sensor surface with microalgae, based on realtime responses of the acoustic sensor during Spirulina immobilization then heavy metals detection, combined with atomic force microscopy characterization to improve understanding of interaction phenomena. Both methods have proved the efficiency of a microfluidic chip to control the hydrodynamical flow, resulting in a biofunctional layer of microalgae. This work is an application of three generations of PDMS chips already manufactured in IMS of Bordeaux1. In particular, the protocol is optimized from that previously proposed for E. coli bacteria [2], by using the real-time oscillating frequency due to mass loading during layers deposition : the microalgae is fixed onto the sensor surface coated with a polyelectrolyte multilayer (PEM), and the bioreceptor immobilization response time is greatly reduced using the microfluidic set up.