Chouki Zerrouki

Ultrasensitive and selective detection of dopamine using cobalt-phthalocyanine nanopillar-based surface acoustic wave sensor.

A highly selective and sensitive surface acoustic wave (SAW) sensor of dopamine (DA) was developed by depositing cobalt phthalocyanine (CoPc) nanopillars on gold-coated sensing platform of SAW sensor. The developed biosensor presents a sensitivity of 1.6°/nM, has a low limit of detection (LOD) on the order of 0.1 nM, and imparts more selectivity toward DA, since the detection limit of the interfering ascorbic acid (AA) is as high as 1 mM. To understand the selectivity mechanisms of this sensor toward DA, density functional theory-based chemical calculations were carried out. Calculations suggest two different types of interactions: dative bond with a very strong character for DA-CoPc complexes, and significant ionic character in the case of AA-CoPc ones. The interaction energies, in liquid phase, were estimated to be equal to -81 kJ mol(-1) and -38 kJ mol(-1) for DA-CoPc and AA-CoPc complexes, respectively, therefore accounting for the selective detection of DA over AA using tandem CoPc nanopillar-based SAW sensor device. This work demonstrates a simple and efficient design of SAW sensors employing thin nanostructured CoPc biomolecular recognition layers for DA detection.

Tosylcellulose synthesis in aqueous medium

p-Toluenesulfonyl cellulose was prepared by reacting cellulose in aqueous medium, instead of via traditional routes, which involve the use of DMAc/LiCl, or more recently, ionic liquids. The influence of several parameters on the reaction efficiency has been studied; amount of tosylchloride, presence of triethylamine, reaction time and use of sodium hydroxide or sodium chloride. The resulting p-toluenesulfonyl cellulose samples were characterized by means of FTIR and NMR spectroscopy. The effects of solvent on the crystalline change during tosylation were investigated by X-ray diffraction (XRD). The degree of substitution (DS) was determined by 1H NMR and confirmed by X-ray photoelectron spectroscopy (XPS). Tosylcelluloses with DS from 0.1 to 1.7 have been prepared.

Biological investigation using a shear horizontal surface acoustic wave sensor: Small “Click generated” DNA hybridization detection

We have used a 104 MHz lithium tantalate (LiTaO(3)) surface acoustic wave (SAW) sensor to investigate DNA probes grafting and their further hybridization with natural and click generated (Cg-DNA) oligonucleotides. Natural DNA targets of different strand lengths, tosyl-di(tri, tetra) thymidine and azido-di(tri, tetra) thymidine oligonucleotides were tested. In our case, and besides the follow-up of a 34mer DNA hybridization, we detected complementarity between natural DNA probes and azido-tetra-thymidine for the first time, whereas previous hybridization studies reported a minimal of 10-mer oligonucleotides recognition length. We also demonstrated that contrarily to natural DNA, the synthesized oligonucleotides present stable bonds with complementary DNA strands. Frequency responses of both grafting and hybridization have shown the same shape: an exponential decay with different time constants, (187±1)s and (68±19) s for grafting and hybridization respectively. We have also shown that recognition between DNA strands and tetranucleotide analogues is comparable to natural 34mer DNA bases and presents the same time constant within uncertainties.

Study and comparison of two polishing methods for platinum?iridium surfaces, by means of three characterization techniques

Machining the surface of mass standards is still of great importance. This paper details a comparative study of the roughness of two plane surfaces of a platinum?iridium alloy (90% of platinum and 10% of iridium). Using the BIPM processes, the surfaces were initially machined on a lathe using diamond tools; in addition, one of these was manually polished with a diamond paste.Three techniques for surface characterization are used: shear-force microscopy (ShFM), optical roughness-meter and x-ray reflectometer. The first technique uses the shear-force interaction between the probe and the sample. The ShFM is part of a scanning near-field optical microscope that has the advantage of providing two images simultaneously, a topographical one and a near-field optical one. Only the topographic images will be presented in this paper; the results obtained in optical near-field will be the subject of another publication. To avoid any confusion, we will speak here of ShFM. The topographic images and their associated statistical and physical parameters, such as power spectral densities (PSDs), root-mean-square height, etc, are discussed in this paper. The PSDs of the surface are also determined experimentally from x-ray and visible light scattering measurements using angle-resolved scattering theory. This theory, which is well adapted for visible radiation, is extended to x-rays. The measurements made with the three instruments demonstrate that the two surfaces present a roughness of the same order of magnitude. However, the defects that contribute in a preponderant manner to their roughness spectrum do not belong to the same spatial bandwidth but depend on the polishing process.

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.

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.

Identification of an in vivo orally active dual-binding protein-protein interaction inhibitor targeting TNFα through combined in silico/in vitro/in vivo screening

TNFα is a homotrimeric pro-inflammatory cytokine, whose direct targeting by protein biotherapies has been an undeniable success for the treatment of chronic inflammatory diseases. Despite many efforts, no orally active drug targeting TNFα has been identified so far. In the present work, we identified through combined in silico/in vitro/in vivo approaches a TNFα direct inhibitor, compound 1, displaying nanomolar and micromolar range bindings to TNFα. Compound 1 inhibits the binding of TNFα with both its receptors TNFRI and TNFRII. Compound 1 inhibits the TNFα induced apoptosis on L929 cells and the TNFα induced NF-κB activation in HEK cells. In vivo, oral administration of compound 1 displays a significant protection in a murine TNFα-dependent hepatic shock model. This work illustrates the ability of low-cost combined in silico/in vitro/in vivo screening approaches to identify orally available small-molecules targeting challenging protein-protein interactions such as homotrimeric TNFα.

Surface acoustic wave sensors: From design to chemical and biological applications

Surface acoustic wave (SAW) sensors are versatile devices, as they can be used to sensing temperature, pressure, strain, torque or mass. Theses abilities can be extended to chemical and biological investigations by suitable functionalisation of the sensing area. Depending on the intended application, the sensitive layer which must to specifically detect the chemical or the biological analyt of interest, may be: single strand DNA, antibody, antigen proteins, self-assembled monolayers, molecularly or ionic imprinted polymers,… This presentation will focus on some chemical and biological applications we have developed, to highlight the potential of this kind of sensors.

Ultrasensitive Electrochemical Sensors for PSA Detection: Related Surface Functionalization Strategies

Prostate cancer is the most common male cancer in the world. The diagnosis, staging, prognosis and monitoring are usually done with Prostate Specific Antigen (PSA). Biosensors are emerging as a novel analytical technology for PSA detection. They provide several advantages for clinical applications and will benefit clinicians, patients and forensic workers in the future. Among them, electrochemical immunosensors have gained growing interests. Hence, their sensitivity is often improved by modifying them with nanoparticles especially iron oxide (IONP). Functionalized IONP attracted much attention in the fabrication of biosensing systems, due to their multiple properties, such as biocompatibility and signal amplification, and their ability to bind covalently to antibodies via their functional groups. In the present study, two electrochemical immunosensors were investigated for PSA detection. The first one was functionalized with 3- glycidoxypropyltrimethoxysilane self-assembled monolayer, while the second one was based on iron oxide nanoparticles functionalized with 3-aminopropyltriethoxysilane. Square wave voltammetry (SWV) has been investigated to follow-up the PSA detection in a phosphate buffer solution, in an artificial serum and in a human serum. The limit of detection (LOD) of both immunosensors was found of order of 10 fg/ml. When estimated in human serum this value increases up to 50 pg/ml.

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.