A practical molecular clip for immobilization of receptors and biomolecules on devices’ surface: Synthesis, grafting protocol and analytical assay

Highly stable protein immobilizationviamaleimido-thiol chemistry to monitor enzymatic activity

Combining a novel protein immobilisation method with multivariate curve resolution enables the direct observation of biocatalysis by ATR-FTIR spectroscopy.

Chemical Functionalization of Germanium with Dextran Brushes for Immobilization of Proteins Revealed by Attenuated Total Reflection Fourier Transform Infrared Difference Spectroscopy

Protein immobilization studied by attenuated total reflection Fourier transform infrared (ATR-FT-IR) difference spectroscopy is an emerging field enabling the study of proteins at atomic detail. Gold or glass surfaces are frequently used for protein immobilization. Here, we present an alternative method for protein immobilization on germanium. Because of its high refractive index and broad spectral window germanium is the best material for ATR-FT-IR spectroscopy of thin layers. So far, this technique was mainly used for protein monolayers, which lead to a limited signal-to-noise ratio. Further, undesired protein-protein interactions can occur in a dense layer. Here, the germanium surface was functionalized with thiols and stepwise a dextran brush was generated. Each step was monitored by ATR-FT-IR spectroscopy. We compared a 70 kDa dextran with a 500 kDa dextran regarding the binding properties. All surfaces were characterized by atomic force microscopy, revealing thicknesses between 40 and 110 nm. To analyze the capability of our system we utilized N-Ras on mono-NTA (nitrilotriacetic acid) functionalized dextran, and the amount of immobilized Ras corresponded to several monolayers. The protein stability and loading capacity was further improved by means of tris-NTA for immobilization. Small-molecule-induced changes were revealed with an over 3 times higher signal-to-noise ratio compared to monolayers. This improvement may allow the observation of very small and so far hidden changes in proteins upon stimulus. Furthermore, we immobilized green fluorescent protein (GFP) and mCherry simultaneously enabling an analysis of the surface by fluorescence microscopy. The absence of a Förster resonance energy transfer (FRET) signal demonstrated a large protein-protein distance, indicating an even distribution of the protein within the dextran.

Light-Induced Functionalization of Amphiphilic Block Copolymers: Application to Nanoparticles for Drug Targeting

Photografting of bifunctional photolinker on biocompatible amphiphilic copolymers, such as PCL-b-PEGs and PLGA-b-PEGs, has been developed as a practical and versatile strategy for the materials functionalisation. Depending on the copolymer nature (block length, % of crystallinity) and the experimental conditions we could selectively direct the grafting on the hydrophilic PEG segments. The resulting copolymers were further derivatized with molecules of interest (RGD-peptides, LDV-peptides, “home-made”peptidomimetics, mannose derivatives,…) by substitution of the O-succinimidyl ester of the photolinker. The derivatization rates were controlled by radiolabelling, colorimetric assay and XPS spectroscopy. The functionalized copolymers were used in the formulation of nanoparticles displaying the ligands on their outer-shell. This nanoparticulate system was successfully employed for the oral vectorisation of antigen and for the targeted delivery of an anticancer drug.

Determination of accessible amino groups on surfaces by chemical derivatization with 3,5-bis(trifluoromethyl)phenyl isothiocyanate and XPS/NEXAFS analysis

The determination of amino groups on surfaces capable of binding biomolecules is important for the understanding and optimization of technologically relevant coupling processes. In this study, three different types of amino-functionalized model surfaces, amino thiolate on Au, amino siloxane on Si, and polyethylene (PE) foils and films reacted with 1,2-diaminoethane (DAE) were derivatized with 3,5-bis(trifluoromethyl)phenyl isothiocyanate. Subsequently, these samples were analyzed by chemical derivatization X-ray photoelectron spectroscopy (CD-XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The determination of amino groups by this analytical approach allows gaining insight into the availability of groups on surfaces that can actually serve as attachment sites for biomolecules in technical applications. In the case of the amino thiolate on Au, almost 90% of the expected amino groups were detected by CD-XPS. Investigation of the amino siloxane films revealed lower yields for the derivatization reaction in the order of 30%. The lowered reaction yields are thought to be due to interactions between the amino siloxane's amino and silanol groups or the underlying substrate, making them inaccessible to the derivatization agent. The aminated PE samples are characterized by a complex surface chemistry and structure, and reaction yields of the derivatization reaction cannot be unequivocally derived. However, 1-3% of the total carbon atoms in the surface layer were found to be bound to amino groups accessible to the derivatization agent. It can be concluded that, depending on the detailed character of the investigated amino-terminated surface, the amount of amino groups accessible to CD-XPS can be substantially lower than the total amount of amino groups present at the surface.

Surface functionalization of germanium ATR devices for use in FTIR-biosensors

Biosensors based on intrinsic detection methods have attracted growing interest. The use of Fourier transform infra-red (FTIR) spectroscopy with the attenuated internal total reflection (ATR) mode, in the biodetection context, requires appropriate surface functionalization of the ATR optical element. Here, we report the direct grafting of a thin organic layer (about 20 A depth) on the surface of a germanium crystal. This covering, constructed with novel amphiphilic molecules 2b (namely, 2,5,8,11,14,17,20-heptaoxadocosan-22-yl-3-(triethoxysilyl) propylcarbamate), is stable for several hours under phosphate buffered saline (PBS) flux and features protein-repulsive properties. Photografting of molecule 5 (namely, O-succinimidyl 4-(p-azidophenyl)butanoate) affords the activated ATR element, ready for the covalent fixation of receptors, penicillin recognizing proteins BlaR-CTD for instance. The different steps of the previous construction have been monitored by water contact angle (theta(w)) measurements, spectroscopic ellipsometry (covering depth), X-ray photoelectron spectroscopy (XPS) by using a fluorinated tag for the control of surface reactivity, and FTIR-ATR spectroscopy for the structural analysis of grafted molecules. Indeed, contrarily to silicon device, germanium device offers a broad spectral window (1000-4000 cm(-1)) and thus amide I and II absorption bands can be recorded. This work lays the foundations for the construction of novel FTIR biosensors.

Design and evaluation of analogues of the bacterial cell-wall peptidoglycan motif L-Lys-D-Ala-D-Ala for use in a vancomycin biosensor

Four small molecular receptors of vancomycin have been designed to make part of a novel biosensor device based on the FTIR-ATR detection: N-Boc (2a) or N-Ac (2b)-6-aminocaproyl-D-Ala-D-Ala and N-Boc (3a) or N-Ac (3b)-6-aminocaproyl-D-Ala-d-Ser. Using an original microbiological approach to assess the competition of compounds with the natural target of vancomycin in bacteria, EC(50) values of 6.3-8.0 x 10(-5)M (2a-b) and 7.1-9.3 x 10(-4)M (3a-b) were determined. Vancomycin:2b complex was characterized by MS.

PEGylated PLGA-based nanoparticles targeting M cells for oral vaccination

To improve the efficiency of orally delivered vaccines, PEGylated PLGA-based nanoparticles displaying RGD molecules at their surface were designed to target human M cells. RGD grafting was performed by an original method called "photografting" which covalently linked RGD peptides mainly on the PEG moiety of the PCL-PEG, included in the formulation. First, three non-targeted formulations with size and zeta potential adapted to M cell uptake and stable in gastro-intestinal fluids, were developed. Their transport by an in vitro model of the human Follicle associated epithelium (co-cultures) was largely increased as compared to mono-cultures (Caco-2 cells). RGD-labelling of nanoparticles significantly increased their transport by co-cultures, due to interactions between the RGD ligand and the beta(1) intregrins detected at the apical surface of co-cultures. In vivo studies demonstrated that RGD-labelled nanoparticles particularly concentrated in M cells. Finally, ovalbumin-loaded nanoparticles were orally administrated to mice and induced an IgG response, attesting antigen ability to elicit an immune response after oral delivery.

Biochemical interaction analysis on ATR devices: a wet chemistry approach for surface functionalization

A new generic device suitable for the investigation of ligand-receptor interactions is presented. In particular, the research focused on optical waveguides constituted by an attenuated total internal reflection (ATR) element, transparent in the infrared and whose surfaces were activated in view of covalently binding a receptor. Silicon and germanium ATR elements were considered. The original method is based on the grafting of bifunctional spacer molecules directly at the surface of the germanium crystal, avoiding the deposition of an intermediate metal layer. The grafting of these binding molecules (under their N-hydroxysuccinimidyl ester forms) was performed either by wet chemistry or by photochemistry. The functionalized surfaces, which allow the binding of molecules bearing peripherical NH2 groups, were successfully used, e.g., for the detection of proteins (streptavidin) or of small molecules (biotin). In the latter case, the biotin was readily detected for concentrations as low as 10(-12) M.

Prospects of conducting polymers in biosensors

Applications of conducting polymers to biosensors have recently aroused much interest. This is because these molecular electronic materials offer control of different parameters such as polymer layer thickness, electrical properties and bio-reagent loading, etc. Moreover, conducting polymer based biosensors are likely to cater to the pressing requirements such as biocompatibility, possibility of in vivo sensing, continuous monitoring of drugs or metabolites, multi-parametric assays, miniaturization and high information density. This paper deals with the emerging trends in conducting polymer based biosensors during the last about 5 years.

Immobilization of Thrombin Inhibitors on Polyesters Surface: An Original Approach towards Materials Blood Compatibilization

Piperazinyl-amide derivatives of N--(3-trifluoromethyl-benzenesulfonyl)-L-arginine were synthesized as graftable thrombin inhibitors. Their biological activity was evaluated in vitro, against human -thrombin, and in blood coagulation assay. The piperazinyl-amide derivatives were found to inhibit the activity of -thrombin in the micromolar range. The designed molecules were fixed on poly(ethylene terephthalate) (PET), and poly(butylene terephthalate) (PBT) by wet chemistry treatment (activation of hydroxyl chain-ends) and photochemistry (nitrene insertion by photoactivation of aromatic azide). The protocols were validated by X-ray photoelectron spectroscopy (XPS) and by radiochemical assay (liquid scintillation counting, LSC).

Design, synthesis and evaluation of graftable thrombin inhibitors for the preparation of blood-compatible polymer materials

Piperazinyl-amide derivatives of N-alpha-(3-trifluoromethyl-benzenesulfonyl)-L-arginine (1) were synthesized as graftable thrombin inhibitors. The possible disturbance of biological activity due to a variable spacer-arm fixed on the N-4 piperazinyl position was evaluated in vitro, against human alpha-thrombin, and in blood coagulation assay. Molecular modelling (in silico analysis) and X-ray diffraction studies of thrombin-inhibitor complexes were also performed. The fixation of bioactive molecules on poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) membranes was performed by wet chemistry treatment and evaluated by XPS analysis. Surface grafting of inhibitor 1d improved the membrane hemocompatibility by reducing blood clot formation on the modified surface.