Nourdin Yaakoubi

Design of a polypyrrole MIP-SAW sensor for selective detection of flumequine in aqueous media. Correlation between experimental results and DFT calculations

A shear horizontal surface acoustic wave sensor (SH-SAW) operating at 104 MHz was functionalized with a polypyrrole (PPy) molecularly imprinted polymer (MIP) for selective detection of flumequine (FLU) in aqueous media. In order to prevent the formation of FLU complexes with the gold sensing area of the SH-SAW sensor, a thin blocking polypyrrole layer was deposited by chronoamperometry before the MIP electrochemical deposition. The detection limit of the designed sensor was of the order of 1 μM and the sensitivity was estimated to be at 9.36 ± 0.39° mM−1. Selectivity tests were made with levofloxacin (LEVO), an interfering fluoroquinolone antibiotic. Results indicate that the designed PPy-MIP recognition layer is selective of flumequine. Quantum chemical calculations, based on density functional theory (DFT), have permitted us to highlight the importance of the PPy blocking layer, on the one hand, and the nature of interactions between the polypyrrole matrix and FLU and LEVO analytes, on the other hand.

Discriminating DNA mismatches by electrochemical and gravimetric techniques

A silicon nitride functionalized electrode and a 104 MHz lithium tantalate (LiTaO₃) surface acoustic wave (SAW) sensor have been used to investigate target-probe recognition processes. Electrochemical and gravimetric measurements have been considered to monitor hybridization of single base mismatch (SBM) in synthetic oligonucleotides and single-nucleotide polymorphisms ApoE in real clinical genotypes. Obvious discrimination of SBM in nucleotides has been shown by both gravimetric and electrochemical techniques, without labeling nor amplification. Investigations on mismatches nature and position have also been considered. For guanine-adenine (GA), guanine-thymine (GT) and guanine-guanine (GG) mismatches, the sensors responses present a dependence upon positions. Considering the capacitance variations and hybridization rates, results showed that gravimetric transduction is more sensitive than electrochemical one. Moreover, the highest value of GT hybridization rate (in the middle position) was found in accordance with the nearest-neighbor model, where the considered configuration appears as the most thermodynamically stable. For the real samples, where the electrochemical transduction, by combining capacitance and flat-band potential measurements, were found more sensitive, the results show that the realized sensor permits an unambiguous discrimination of recognition between fully complementary, non-complementary and single base mismatched targets, and even between the combination of differently matched strands.

Laser doping for microelectronics and microtechnology

The future CMOS generations for microelectronics will require advanced doping techniques capable to realize ultra-shallow, highly-doped junctions with abrupt profiles. Recent experiments have shown the potential capabilities of laser processing of Ultra Shallow Junctions (USJ). According to the International Technology Roadmap for Semiconductors, two laser processes are able to reach ultimate predictions: laser thermal processing or annealing (LTP or LTA) and Gas Immersion Laser Doping (GILD). Both processes are based on rapid melting/solidification of the substrate. During solidification, the liquid silicon, which contains the dopants, is formed epitaxially from the underlying crystalline silicon. In the case of laser thermal annealing dopants are implanted before laser processing. GILD skips the ion-implantation step: in this case dopants are chemisorbed on the Si surface before the laser shot. The dopants are then incorporated and activated during the laser process. Activation is limited to the liquid layer and this chemisorption/laser shot cycle can be repeated until the desired concentration is reached. In this paper, we investigate the possibilities and limitations of the GILD technique for two different substrates: silicon bulk and SOI. We also show some laser doping applications for the fabrication of micro and nanoresonators, widely used in the MEMS Industry.

Highly Selective Polypyrrole MIP-Based Gravimetric and Electrochemical Sensors for Picomolar Detection of Glyphosate

There is a global debate and concern about the use of glyphosate (Gly) as an herbicide. New toxicological studies will determine its use in the future under new strict conditions or its replacement by alternative synthetic or natural herbicides. In this context, we designed biomimetic polymer sensing layers for the selective molecular recognition of Gly. Towards this end, complementary surface acoustic wave (SAW) and electrochemical sensors were functionalized with polypyrrole (PPy)-imprinted polymer for the selective detection of Gly. Their corresponding limits of detection were on the order of 1 pM, which are among the lowest values ever reported in literature. The relevant dissociation constants between PPy and Gly were estimated at [Kd1 = (0.7 ± 0.3) pM and Kd2 = (1.6 ± 1.4) µM] and [Kd1 = (2.4 ± 0.9) pM and Kd2 = (0.3 ± 0.1) µM] for electrochemical and gravimetric measurements, respectively. Quantum chemical calculations permitted to estimate the interaction energy between Gly and PPy film: ΔE = −145 kJ/mol. Selectivity and competitivity tests were investigated with the most common pesticides. This work conclusively shows that gravimetric and electrochemical results indicate that both MIP-based sensors are perfectly able to detect and distinguish glyphosate without any ambiguity.

Self assembled monolayers versus iron oxide nanoparticles modified surfaces: Two functionalization strategies for femtomolar detection of prostate specific antigen: Comparative study between two electrochemical biosensors for femtomolar detection of prostate specific antigen

Two electrochemical immunosensors were investigated for prostate specific antigen detection. The first one was functionalized with 3-glycidypxypropyltrimethoxysilane self-assembled monolayer, while the second one was based on iron oxide nanoparticles functionalized with 3-aminopropyltriethoxysilane. Electrochemical impedance spectroscopy and square wave voltammetry have been investigated to follow-up the prostate specific antigen detection in a phosphate buffer solution and in a human serum. The limit of detection of both immunosensors was found of order of 10 fg/ml.

Integration of commercial microspeakers in an acoustic absorbing liner

In this work, the fabrication of an acoustic sound absorbing surface (i.e. liner) made of commercial Visaton™ K16 microspeakers is presented. The acoustic liner is made of a circular surface composed of a 10 cm diameter fix support with 7 embedded microspeakers covering 8.5% of th overall surface. Different electrical connections of the microspeakers using no added electronic circuit are tested and the obtained absorption coefficient is 0.2 close to the natural resonance frequency of the microspeakers. A Negative Impedance Converter is used to electrically compensate the losses occurring in the acoustic liner. The maximum sound absorption is raised to 0.31 using the NIC again close to the natural resonance frequency of the microspeakers with a 7 microspeakers configuration covering 8.5% of the wall surface. The back cavity of the microspeakers is found to slightly move the maximum absorption peak but not to modify the maximum absorption. The influence of the microspeakers density is measured in open circuit configuration. The surface covered by the microspeakers ranges from 2.85% up to 12.35% of the wall surface. The maximum sound absorption ranges then from 0.1 to 0.34.

High acoustic performance MEMS microspeaker

In this paper, a theoretical approach for the electrodynamic motor optimization has been presented. The analytical simulations of the electroacoustic efficiency were validated with an experimental measurements were we have seen a very good agreement. The same assembled device was characterized in an anechoic chamber, where we have detected an SPL around 80 dB for 0.5 W.

Acoustic vs electric power response of a high-performance MEMS microspeaker

This paper presents the characterization of the acoustic performance of an electrodynamic MEMS microspeaker and the influence of magnets position, which allows halving device size while intensifying the force factor. This work is based on the previously reported MEMS microspeaker dedicated to handheld electronics. A vacuum-formed seal has been designed and applied to enhance acoustic performance at low frequencies. The efficiency of the electroacoustic conversion is increased by a factor 5-10 compared to conventional microspeakers and low harmonic distortions were observed. Measurements of the acoustic power versus electrical input power were carried out in an anechoic room within the hearing range.