Electrochemical Impedance Spectroscopy Study of Concanavalin A Binding to Self-Assembled Monolayers of Mannosides on Gold Wire Electrodes.

The interactions of the lectin Concanavalin A (Con A) with self-assembled monolayers (SAMs) of thiolated mono-, di-, and tri-mannosides were studied on the surface of gold wires using electrochemical impedance spectroscopy (EIS). The SAMs of mannosides were prepared either pure or along with thiolated triethylene glycol (TEG) at different molar ratios (1:1, 1:2, 1:4, 1:9, and 1:19) to better understand and optimize the interaction conditions. The charge-transfer resistance of the [Fe(CN)]/ redox probe was compared before and after the interaction at different concentrations of Con A to determine the equilibrium dissociation constant () and limit of detection (LOD).

Selective capture of glycoproteins using lectin-modified nanoporous gold monolith.

The surface of nanoporous gold (np-Au) monoliths was modified via a flow method with the lectin Concanavalin A (Con A) to develop a substrate for separation and extraction of glycoproteins. Self-assembled monolayers (SAMs) of α-lipoic acid (LA) on the np-Au monoliths were prepared followed by activation of the terminal carboxyl groups to create amine reactive esters that were utilized in the immobilization of Con A. Thermogravimetric analysis (TGA) was used to determine the surface coverages of LA and Con A on np-Au monoliths which were found to be 1.

Lectin-carbohydrate interactions on nanoporous gold monoliths.

Monoliths of nanoporous gold (np-Au) were modified with self-assembled monolayers of octadecanethiol (C-SH), 8-mercaptooctyl α-D-mannopyranoside (αMan-C-SH), and 8-mercapto-3,6-dioxaoctanol (HO-PEG-SH), and the loading was assessed using thermogravimetric analysis (TGA). Modification with mixed SAMs containing αMan-C-SH (at a 0.20 mole fraction in the SAM forming solution) with either octanethiol or HO-PEG-SH was also investigated.

The influence of gold surface texture on microglia morphology and activation.

Microglial cells play a critical role in the propagation of neuroinflammation in the central nervous system. Microglia sense and respond to environmental signals including chemical, physical and biological cues from the surrounding cell/tissue components. In this project, our goal was to examine the effects of surface texture on BV-2 microglia morphology and function by comparing flat and nanoporous gold (np-Au) surfaces to the more conventional glass.

Surface-tethered iterative carbohydrate synthesis: a spacer study.

Comparative study of Surface-Tethered Iterative Carbohydrate Synthesis (STICS) using HPLC-assisted experimental setup clearly demonstrates benefits of using longer spacer-anchoring systems. The use of mixed self-assembled monolayers helps provide the required space for glycosylation reaction around the immobilized glycosyl acceptor. Both extension of the spacer length and using mixed self-assembled monolayers help promote the reaction, and the beneficial effects may include moving the glycosyl acceptor further out into solution and providing additional conformational flexibility.

Electrochemical characterization of globotriose-containing self-assembled monolayers on nanoporous gold and their binding of soybean agglutinin.

Self-assembled monolayers (SAMs) of α-D-Gal-(1→4)-β-D-Gal-(1→4)-β-D-Glc-mercaptooctane (globotriose, Gb3-C8-SH) were prepared both as single-component SAMs and as mixed SAMs with either octanethiol (OCT) or 8-mercapto-3,6-dioxaoctanol (HO-PEG2-SH), on flat gold and on nanoporous gold (NPG) electrodes. The binding of soybean agglutinin (SBA) to the globotriose (Gb3) unit in the SAMs was then studied using electrochemical impedance spectroscopy (EIS), which is a label free method found to be quite sensitive to SAM composition and to the differences in SAM structure on NPG versus on flat Au. The affinity of SBA to the mixed SAM of HO-PEG2-SH and Gb3-C8-SH on NPG is found to be greater on NPG than on flat gold, and indicates a potential advantage for NPG as a substrate.

Surface area and pore size characteristics of nanoporous gold subjected to thermal, mechanical, or surface modification studied using gas adsorption isotherms, cyclic voltammetry, thermogravimetric analysis, and scanning electron microscopy.

Nitrogen adsorption/desorption isotherms are used to investigate the Brunauer, Emmett, and Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) pore size distribution of physically modified, thermally annealed, and octadecanethiol functionalized np-Au monoliths. We present the full adsorption-desorption isotherms for N(2) gas on np-Au, and observe type IV isotherms and type H1 hysteresis loops. The evolution of the np-Au under various thermal annealing treatments was examined using scanning electron microscopy (SEM).

HPLC-assisted automated oligosaccharide synthesis.

A standard HPLC was adapted to polymer supported oligosaccharide synthesis. Solution-based reagents are delivered using a software-controlled solvent delivery system. The reaction progress and completion can be monitored in real time using a standard UV detector.

Comparative Study of the Binding of Concanavalin A to Self-Assembled Monolayers Containing a Thiolated α-Mannoside on Flat Gold and on Nanoporous Gold.

We have prepared SAMs containing 8-mercaptooctyl α-D-mannopyranoside, either as a single component or in mixed SAMs with n-octanethiol on flat gold surfaces and on nanoporous gold. Electrochemical impedance spectroscopy showed that the mixed SAMs on flat gold surfaces showed the highest Con A binding near 1:9 solution molar ratio of thiolatedα-mannoside to n-octanethiol whereas those on NPG showed the highest response at 1:19 solution molar ratio of thiolated α-mannoside to n-octanethiol. Atomic force microscopy was employed to image the monolayers, and also to image the bound Con A protein.

Reverse orthogonal strategy for oligosaccharide synthesis.

Herein, we report the invention of a novel expeditious concept for oligosaccharide synthesis. Unlike the classic orthogonal strategy based on leaving groups, the reverse approach is based on orthogonal protecting groups, herein p-methoxybenzyl and 4-pentenoyl, which allows for efficient oligosaccharide assembly in the reverse direction.

Characterization of protein immobilization on nanoporous gold using atomic force microscopy and scanning electron microscopy.

Nanoporous gold (NPG), made by dealloying low carat gold alloys, is a relatively new nanomaterial finding application in catalysis, sensing, and as a support for biomolecules. NPG has attracted considerable interest due to its open bicontinuous structure, high surface-to-volume ratio, tunable porosity, chemical stability and biocompatibility. NPG also has the attractive feature of being able to be modified by self-assembled monolayers.

Well-defined, size-tunable, multifunctional micelles for efficient paclitaxel delivery for cancer treatment.

We have developed a well-defined and biocompatible amphiphilic telodendrimer system (PEG-b-dendritic oligo-cholic acid) which can self-assemble into multifunctional micelles in aqueous solution for efficient delivery of hydrophobic drugs such as paclitaxel. In this telodendrimer system, cholic acid is essential for the formation of stable micelles with high drug loading capacity, owing to its facial amphiphilicity. A series of telodendrimers with variable length of PEG chain and number of cholic acid in the dendritic blocks were synthesized.

A nanoengineering approach for investigation and regulation of protein immobilization.

It is known that protein attachment to surfaces depends sensitively upon the local structure and environment of the binding sites at the nanometer scale. Using nanografting and reversal nanografting, both atomic force microscopy (AFM)-based lithography techniques, protein binding sites with well-defined local environments are designed and engineered with nanometer precision. Three proteins, goat antibiotin immunoglobulin G (IgG), lysozyme, and rabbit immunoglobulin G, are immobilized onto these engineered surfaces.

Structural characterization of aldehyde-terminated self-assembled monolayers.

The structure of aldehyde-terminated alkanethiol self-assembled monolayers (SAMs) on Au(111) is investigated using scanning tunneling microscopy (STM), atomic force microscopy (AFM), and density functional theory (DFT) calculations. For the first time, the structures of aldehyde-terminated SAMs are revealed with molecular resolution. SAMs of 11-mercapto-1-undecanal exhibit the basic (radical3xradical3)R30 degrees periodicity and form various c(4x2) superstructures upon annealing.

A nanoengineering approach to regulate the lateral heterogeneity of self-assembled monolayers.

Using a scanning probe lithography method known as nanografting in conjunction with knowledge of self-assembly chemistry, regulation of the heterogeneity of self-assembled monolayers (SAMs) is demonstrated. While nanografting in single-component thiols produces areas of SAMs with designed geometry and size, nanofabrication in mixed thiol solution yields segregated domains. The reaction mechanism in nanografting differs significantly from self-assembly in mix-and-grow methods, as proven in systematic studies reported in this article and a companion paper of theoretical calculations of the nanografting process.