Effect of physicochemical anomalies of soda-lime silicate slides on biomolecule immobilization

Photografting and Patterning of Poly(ethylene glycol) Methacrylate Hydrogel on Glass for Biochip Applications

An efficient procedure for chemical initiator-free, in situ synthesis of a functional polyethylene glycol methacrylate (PEG MA) hydrogel on regular glass substrates is reported. It is demonstrated that self-initiated photografting and photopolymerization driven by UV irradiation can yield tens of nanometer-thick coatings of carboxy-functionalized PEG MA on the aldehyde-terminated borosilicate glass surface. The most efficient formulation for hydrogel synthesis contained methyl methacrylic acid (MAA), 2-hydroxyethyl methacrylate (HEMA), and PEG methacrylate (PEG₁₀MA) monomers (1:1:1). The resulting HEMA/PEG₁₀MA/MAA (HPMAA) coatings had a defined thickness in the range from 11 to 50 nm. The physicochemical properties of the synthesized HPMAA coatings were analyzed by combining water contact angle measurements, stylus profilometry, imaging null ellipsometry, and atomic force microscopy (AFM). The latter technique was employed in the quantitative imaging mode not only for direct probing of the surface topography but also for swelling behavior characterization in the pH range from 4.5 to 8.0. The estimated high swelling ratios of the HPMAA hydrogel (up to 3.2) together with its good stability and resistance to nonspecific protein binding were advantageous in extracellular matrix mimetics via patterning of fibronectin (FN) at a resolution close to 200 nm. It was shown that the fabricated FN micropatterns on HPMAA were equally suitable for single-cell arraying, as well as controlled cell culture lasting at least for 96 h.

Fabricating customized hydrogel contact lens

Contact lenses are increasingly used in laboratories for in vivo animal retinal imaging and pre-clinical studies. The lens shapes often need modification to optimally fit corneas of individual test subjects. However, the choices from commercially available contact lenses are rather limited. Here, we report a flexible method to fabricate customized hydrogel contact lenses. We showed that the fabricated hydrogel is highly transparent, with refractive indices ranging from 1.42 to 1.45 in the spectra range from 400 nm to 800 nm. The Young’s modulus (1.47 MPa) and hydrophobicity (with a sessile drop contact angle of 40.5°) have also been characterized experimentally. Retinal imaging using optical coherence tomography in rats wearing our customized contact lenses has the quality comparable to the control case without the contact lens. Our method could significantly reduce the cost and the lead time for fabricating soft contact lenses with customized shapes, and benefit the laboratorial-used contact lenses in pre-clinical studies.

Surface-Controlled Orientational Transitions in Elastically Strained Films of Liquid Crystal That Are Triggered by Vapors of Toluene

We report the fabrication of chemically patterned microwells that enable the rapid and facile preparation (by spin coating and patterned dewetting) of thin films of liquid crystals (LCs) that have precise thicknesses (0.7-30 μm), are supported on chemically defined substrates, and have free upper surfaces. We use these microwells to prepare elastically strained nematic LC films supported on silica glass, gold, or polystyrene substrates and thereby characterize the response of the strained LC films to vapors of toluene. We report that low concentrations of toluene vapor (<500 ppm) can partition into the LC to lower the anchoring energy of the LC on these substrates, thus allowing the elastic energy of the strained LC film to drive the LC films through an orientational transition. The central role of the toluene-induced change in surface anchoring energy is supported by additional experiments in which the response of the nematic LC to changes in film thickness and substrate identity are quantified. A simple thermodynamic model captures these trends and yielded estimates of anchoring energies (8-22 μJ/m(2)). Significantly, the orientational transitions observed in these strained LC thin films occur at concentrations of toluene vapor that are almost 1 order of magnitude below those which lead to bulk phase transitions, and they are not triggered by exposure to water vapor. Overall, these results hint at principles for the design of responsive LC-based materials that can be triggered by concentrations of aromatic, volatile organic compounds that are relevant to human health.

Stick-jump mode in surface droplet dissolution

The analogy between evaporating surface droplets in air to dissolving long-chain alcohol droplets in water is worked out. We show that next to the three known modi for surface droplet evaporation or dissolution (constant contact angle mode, constant contact radius mode, and stick-slide mode), a fourth mode exists for small droplets on supposedly smooth substrates, the stick-jump mode: intermittent contact line pinning causes the droplet to switch between sticking and jumping during the dissolution. We present experimental data and compare them to theory to predict the dissolution time in this stick-jump mode. We also explain why these jumps were easily observed for microscale droplets but not for larger droplets.

Release of colloids from primary minimum contact under unfavorable conditions by perturbations in ionic strength and flow rate

Colloid release from surfaces in response to ionic strength and flow perturbations has been mechanistically simulated. However, these models do not address the mechanism by which colloid attachment occurs, at least in the presence of bulk colloid-collector repulsion (unfavorable conditions), which is a prevalent environmental condition. We test whether a mechanistic model that predicts colloid attachment under unfavorable conditions also predicts colloid release in response to reduced ionic strength (IS) and increased fluid velocity (conditions thought prevalent for mobilization of environmental colloids). The model trades in mean-field colloid-collector interaction for discrete representation of surface heterogeneity, which accounts for a combination of attractive and repulsive interactions simultaneously, and results in an attached colloid population (in primary minimum contact with the surface) having a distribution of strengths of attraction. The model moderates equilibrium separation distance by inclusion of steric interactions. By using the same model parameters to quantitatively predict attachment under unfavorable conditions, simulated release of colloids (for all three sizes) from primary minimum attachment in response to perturbations qualitatively matched experimental results, demonstrating that both attachment and detachment were mechanistically simulated.

Review: recent advances and current challenges in scanning probe microscopy of biomolecular surfaces and interfaces

The introduction of scanning probe microscopy (SPM) techniques revolutionized the field of condensed matter science by allowing researchers to probe the structure and composition of materials on an atomic scale. Although these methods have been used to make molecular- and atomic-scale measurements on biological systems with some success, the biophysical sciences remain on the cusp of a breakthrough with SPM technologies similar in magnitude to that experienced by fields related to solid-state surfaces and interfaces. Numerous challenges arise when attempting to connect biological molecules that are often delicate, dynamic, and complex with the experimental requirements of SPM techniques. However, there are a growing number of studies in which SPM has been successfully used to achieve subnanometer resolution measurements in biological systems where carefully designed and prepared samples have been paired with appropriate SPM techniques. We review significant recent innovations in applying SPM techniques to biological molecules, and highlight challenges that face researchers attempting to gain atomic- and molecular-level information of complex biomolecular structures.

Quantification of surface etching by common buffers and implications on the accuracy of label-free biological assays

High throughput analyses in biochemical assays are gaining popularity in the post-genomic era. Multiple label-free detection methods are especially of interest, as they allow quantitative monitoring of biomolecular interactions. It is assumed that the sensor surface is stable to the surrounding medium while the biochemical processes are taking place. Using the Interferometric Reflectance Imaging Sensor (IRIS), we found that buffers commonly used in biochemical reactions can remove silicon dioxide, a material frequently used as the solid support in the microarray industry. Here, we report 53 pm to 731 pm etching of the surface silicon oxide over a 12-h period for several different buffers, including various concentrations of SSC, SSPE, PBS, TRIS, MES, sodium phosphate, and potassium phosphate buffers, and found that PBS and MES buffers are much more benign than the others. We observe a linear dependence of the etch depth over time, and we find the etch rate of silicon dioxide in different buffers that ranges from 2.73±0.76 pm/h in 1M NaCl to 43.54±2.95 pm/h in 6×SSC. The protective effects by chemical modifications of the surface are explored. We demonstrate unaccounted glass etching leading to erroneous results with label-free detection of DNA microarrays, and offer remedies to increase the accuracy of quantitative analysis.

Demonstration of α-helical structure of peptides tethered to gold surfaces using surface infrared and circular dichroic spectroscopies

Gold and quartz surfaces terminated in an alkane thiol self-assembled monolayer (SAM) that were partially terminated with azide were reacted with a helical peptide containing two alkyne groups in a Cu(I)-catalyzed Huisgen cycloaddition. Surface grazing incidence angle reflection-absorption infrared spectroscopy (GRAS-IR) was used to determine that when the Au surface was terminated with 25% of the monolayer containing azide groups, 92% of available azide groups reacted with the peptide. The majority of peptides reacted with both alkynes, resulting in peptides tethered to the surface through two covalent bonds. This was confirmed by comparison to a control peptide containing only one reactive alkyne group. Surface circular dichroic (CD) spectroscopy showed that while the helical structure of the peptide was distorted in the reaction solution, α-helical structure was induced when tethered on the SAM functionalized Au surface. Demonstration of the preservation of desired secondary structure of helical elements at a chemically functionalized surface is an important advance in preparing robust biologically mimetic surfaces to integrate functioning proteins into inorganic materials.

Nanobiochips

The actual progress towards biological chip devices consisting of nanostructured functional entities is summarized. The practical aspects of molecular nanobiochips are discussed, including the main surface chemistry platforms, as well as conventional and unconventional fabrication tools. Several successful biological demonstrations of the first generation of nanobiochip devices (mainly, different nanoarrays) are highlighted with the aim of revealing the potential of this technology in life sciences, medicine, and related areas.

Plasma-based surface modification of polystyrene microtiter plates for covalent immobilization of biomolecules

In recent years, polymer surfaces have become increasingly popular for biomolecule attachment because of their relatively low cost and desirable bulk physicochemical characteristics. However, the chemical inertness of some polymer surfaces poses an obstacle to more expansive implementation of polymer materials in bioanalytical applications. We describe use of argon plasma to generate reactive hydroxyl moieties at the surface of polystyrene microtiter plates. The plates are then selectively functionalized with silanes and cross-linkers suitable for the covalent immobilization of biomolecules. This plasma-based method for microtiter plate functionalization was evaluated after each step by X-ray photoelectron spectroscopy, water contact angle analysis, atomic force microscopy, and bioimmobilization efficacy. We further demonstrate that the plasma treatment followed by silane derivatization supports direct, covalent immobilization of biomolecules on microtiter plates and thus overcomes challenging issues typically associated with simple physisorption. Importantly, biomolecules covalently immobilized onto microtiter plates using this plasma-based method retained functionality and demonstrated attachment efficiency comparable to commercial preactivated microtiter plates.

Critical aspects of biointerface design and their impact on biosensor development

The stable integration of a biological recognition element on a transducing substrate surface is the single most important step in the creation of a high-functioning sensor surface. The key factors affecting biotic and abiotic functionalities at the biointerface are both chemical and physical. Understanding the interactions between biomolecules and surfaces, and their emergent complexity, is critical for biointerface implementation for sensing applications. In this overview, we highlight materials and methods typically used for biosensor development. Particular emphasis has been given to the experimental evaluation of biointerfacial properties and functionality. Promising research directions for application of biointerfaces to biosensing are suggested.