Reversible affinity interactions of antibody molecules at functionalized dendrimer monolayer: affinity-sensing surface with reusability

Dendrimers: synthesis, applications, and properties

Dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure that has a typically symmetric core, an inner shell, and an outer shell. Their three traditional macromolecular architectural classes are broadly recognized to generate rather polydisperse products of different molecular weights. A variety of dendrimers exist, and each has biological properties such as polyvalency, self-assembling, electrostatic interactions, chemical stability, low cytotoxicity, and solubility. These varied characteristics make dendrimers a good choice in the medical field, and this review covers their diverse applications.

Site-specific conjugation of metal carbonyl dendrimer to antibody and its use as detection reagent in immunoassay

We describe here the conjugation of polyclonal goat anti-rabbit antibody to generation 4 polyamidoamine (G4-PAMAM) dendrimers carrying (i) (η(5)-cyclopentadienyl) iron dicarbonyl succinimidato complexes as infrared (IR) probes, (ii) nitroaniline entities as nuclear magnetic resonance (NMR) probes, (iii) acetamide groups for surface neutralization, and (iv) hydrazide-terminated spacer arms for the reaction with aldehyde. To preserve a high binding affinity, the conjugation was performed on the carbohydrate moieties located on the Fc fragment. The resulting conjugates were characterized by Fourier transform-IR, ultraviolet (UV), and high-mass matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. On the basis of relative concentration ratios of IR probes and antibody, an average labeling of 30 IR probes per antibody was reached (i.e., more than twice the value obtained with our previous strategy that generated no spacer arm). Immunoassays revealed that the antibody-dendrimer conjugates retained 55.1% of immunoreactivity on average with respect to underivatized antibody. Finally, the conjugates were used to quantify their antigen by solid-phase carbonyl metallo immunoassay (CMIA). Results showed a significant enhancement of the IR signal, demonstrating the efficiency of the new conjugation strategy and the potential of the new antibody-dendrimer conjugates as universal immunoanalytical reagents.

Multifunctional Dendrimer-templated Antibody Presentation on Biosensor Surfaces for Improved Biomarker Detection

Dendrimers, with their well-defined globular shape and a high density of functional groups, are ideal nanoscale materials for templating sensor surfaces. This work exploits dendrimers as a versatile platform for capturing biomarkers with improved sensitivity and specificity. Synthesis, characterization, fabrication, and functional validation of the dendrimer-based assay platform are described. Bifunctional hydroxyl/thiol functionalized G4-polyamidoamine (PAMAM) dendrimer is synthesized and immobilized on to the polyethylene-glycol (PEG)-functionalized assay plate by coupling PEG-maleimide and dendrimer thiol groups. Simultaneously, part of the dendrimer thiol groups are converted to hydrazide functionalities. The resulting dendrimer-modified surface is coupled to the capture antibody in the Fc region of the oxidized antibody. This preserves the orientation flexibility of the antigen binding region (Fv) of the antibody. To validate the approach, the fabricated plates are further used as a solid phase for developing a sandwich type ELISA to detect IL-6 and IL-1β, important biomarkers for early stages of chorioamnionitis. The dendrimer-modified plate provides assays with significantly enhanced sensitivity, lower nonspecific adsorption, and a detection limit of 0.13 pg ml-1 for IL-6 luminol detection and 1.15 pg ml-1 for IL-1β TMB detection, which are significantly better than those for the traditional ELISA. The assays were validated in human serum samples from normal (non-pregnant) woman and pregnant women with pyelonephritis. The specificity and the improved sensitivity of the dendrimer-based capture strategy could have significant implications for the detection of a wide range of cytokines and biomarkers since the capture strategy could be applied to multiplex microbead assays, conductometric immunosensors and field effect biosensors.

Quantitative FT-IRRAS Spectroscopic Studies of the Interaction of Avidin with Biotin on Functionalized Quartz Surfaces

The interaction of avidin with biotin was studied on functionalized quartz surfaces terminated with 3-aminopropyltrimethoxysilane (3-APTMS), 2,2'-(ethylenedioxy)bis(ethylenediamine) (DADOO), and fourth-generation amine-terminated polyamidoamine (G4-NH2 PAMAM) dendrimers with the use of Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS). In particular, the molecular recognition ability of these surfaces was quantified through FT-IRRAS in combination with the use of an alkyne dicobalt hexacarbonyl probe coupled with avidin. The degree of nonspecific adsorption of avidin was determined by exposure of the amine-terminated and/or biotinylated surfaces to solutions of biotin-saturated avidin. The results indicate that the biotinylated 3-APTMS layer exhibits a very low specific binding capacity for avidin (on the order of 0.15 pmol of avidin/cm2) and substantial nonspecific adsorption. Both the binding capacity and the specificity were greatly improved when the 3-APTMS layer on quartz was modified through serial chemisorption of glutaraldehyde (GA), DADOO, and/or G4-NH2 PAMAM dendrimer layers. Among these layers, the biotinylated G4-NH2 PAMAM dendrimer layer exhibited the highest capacity for avidin binding (2.02 pmol of avidin/cm2) with a specificity of approximately 90%. This effect can be attributed to the efficient packing/ordering of the binding dendrimer layer, leading to a more dense and better organized layer of biotin headgroups on the subsequent biotinylated surface.

Dendrimers as guests in molecular recognition phenomena

Dendrimers are highly branched macromolecules which may engage in host-guest interactions, acting as either hosts or guests; this review is specifically concerned with the binding behavior of dendrimers containing single or multiple guest residues interacting with individual, freely diffusing hosts.

FT-IRRAS spectroscopic studies of the interaction of avidin with biotinylated dendrimer surfaces

The interaction of avidin with biotin on a functional Au surface containing fourth generation amine-terminated polyamidoamine (G4-NH(2) PAMAM) dendrimers was investigated through the use of Fourier transform infrared reflection-adsorption spectroscopy (FT-IRRAS). The first step in the fabrication of the functional surfaces used was the construction of an aldehyde-terminated self-assembled monolayer (SAM) through the treatment of Au-coated glass slides with ethanol solutions of self-synthesized 2-hydroxypentamethylene sulfide (HPMS). The as-formed aldehyde-terminated monolayer was subsequently immersed in methanol solutions of G4-NH(2) PAMAM dendrimer to obtain well-organized primary amine-terminated surfaces. Biotinylation of the amine-terminated layers thus obtained was accomplished by use of the N-succinimidyl ester of biotin. Each step of the synthetic process, as well as the performance of final surface for protein recognition was monitored by FT-IRRAS. In particular, the molecular recognition ability was examined and quantified by use of an alkyne dicobalt hexacarbonyl probe coupled with avidin. Non-specific adsorption of avidin was determined by exposure of the amine-terminated and/or biotinylated surfaces to solutions of biotin-saturated avidin. The results indicate that the biotinylated G4-NH(2) PAMAM dendrimer layers formed according to this procedure have a high capacity for binding avidin with relatively high specificity. The performance of these layers (i.e. both binding capacity and specificity) improve substantially when 6-mercapto-1-hexanol (MH) is present as a co-adsorbent during the formation of the initial aldehyde-terminated layers. This effect can be attributed to the dilution of the initial aldehyde-terminated SAM, leading to a more favorable spatial arrangement of the subsequent biotinylated surfaces.

Synthesis and characterization of tri(ethylene oxide)-attached poly(amidoamine) dendrimer layers on gold

This paper describes the synthesis of a tri(ethylene oxide)-attached fourth-generation poly(amidoamine) dendrimer (EO3-dendrimer) and the characterization of its layers on gold. NMR analysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that about 61 amine groups of a G4 PAMAM dendrimer were covalently conjugated with tri(ethylene oxide) units, accounting for a 95% modification level. Layers of the EO3-dendrimer were formed on gold, and the resulting surface was characterized by infrared reflection absorption spectroscopy, ellipsometry, and contact angle goniometry. The EO3-dendrimer resulted in more hydrophilic and less compact layers with no substantial deformation of the molecule during layer formation by virtue of the EO3 units, compared to a PAMAM dendrimer. Interestingly, the specific binding of avidin to the biotinylated layers of the EO3-dendrimer approached a surface density of 5.2 +/- 0.2 ngmm-2, showing about 92% of full surface coverage. The layers of the EO3-dendrimer were found to be more resistant to nonspecific adsorption of proteins than PAMAM dendrimer layers when bovine serum albumin and serum proteins were tested.

Biological applications of dendrimers

In the past year, significant advances have been made in the synthesis and study of glycodendrimers and peptide dendrimers. Application of these dendrimers to the study of carbohydrate-protein and protein-protein interactions has facilitated the understanding of these processes. In addition, dendrimers show great promise as DNA- and drug-delivery systems.