Gold-coated Glass Slides Research Articles

Solid-state optical coupling for surface plasmon resonance sensors

An optical coupling methodology using a removable and strippable polymer is reported. Poly(dimethylsiloxane) films (PDMS) are used to bond two optical components and are compared to the coupling provided by conventional refractive index matching oils and gels. The detection limit and sensitivity of the solid-state PDMS coupled optical components are investigated, using a commercially available surface plasmon resonance (SPR) instrument. Films are prepared either by an in situ curing of the PDMS pre-polymer and cast between the prism and the gold-coated glass slide of an SPR sensor or using a self standing thin film of pre-cured PDMS sandwiched between the two optical components. Both approaches lead to an efficient optical and mechanical coupling. The PDMS films may be stripped and removed very easily from the optical component surfaces after usage, due to their very low surface adhesion characteristics, reducing the messiness of the conventional optical oils and gels. The response of the PDMS-coupled SPR sensors is validated with calibration curves for both increasing sucrose and ethanol/water mass fractions. This work presents the first application of an all solid-state polymer film as an optical coupling medium in SPR and may find applications in other optical networks.

Dielectric Properties of Electrostatic Self-Assembled (ESA) Films

AbstractCapacitance measurements were conducted to determine the dielectric constant of electrostatic self assembly (ESA) films over various temperature and frequency ranges at 1 mV and 15% relative humidity. Measurement electrodes were fabricated on the ESA films using silver grease and a brass bar. In these tests, polymeric nanofilms were fabricated on gold-coated glass slides using the ESA process. Thicknesses of the films were between 100 nm and 600 nm obtained by depositing different number bilayers of negatively charged Poly s-119 (PS-119) or heparin and positively charged poly(diallyldimethylammonium chloride) (PDDA). The test results showed that dielectric constant values were around 2. Based on the test results, we concluded that this is a technique that might prove useful to estimate the capacitance and dielectric constant values of nanostructured ESA films, which can be largely used in the near future.

Immobilization of gold nanorods onto acid-terminated self-assembled monolayers via electrostatic interactions.

We report the immobilization of gold nanorods onto self-assembled monolayers (SAMs) of 16-mercaptohexadecanoic acid (16-MHA). The simple two step protocol involves formation of a SAM of 16-MHA molecules onto gold-coated glass slides and subsequent immersion of these slides into the gold nanorod solution. The nanorods, formed by a seed-mediated, surfactant-assisted synthesis protocol, are stabilized in solution due to surface modification by the surfactant cetyltrimethylammonium bromide (CTAB). Attractive electrostatic interactions between the carboxylic acid group on the SAM and the positively charged CTAB molecules are likely responsible for the nanorod immobilization. UV-vis spectroscopy has been used to follow the kinetics of the nanorod immobilization. The nature of interaction between the gold nanorods and the 16-MHA SAM has been probed by Fourier transform infrared spectroscopy (FTIR). The surface morphology of the immobilized rods is studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements. SEM was also used to determine the density of the immobilized nanorods as a function of the pH of immobilization. Control over the surface coverage of the immobilized gold nanorods has been demonstrated by simple pH variation. Such well-dispersed immobilized gold nanorods with control over the surface coverage could be interesting substrates for applications such as surface-enhanced Raman spectroscopy (SERS).

Effect of substratum surface chemistry and surface energy on attachment of marine bacteria and algal spores.

Two series of self-assembled monolayers (SAMs) of omega-substituted alkanethiolates on gold were used to systematically examine the effects of varying substratum surface chemistry and energy on the attachment of two model organisms of interest to the study of marine biofouling, the bacterium Cobetia marina (formerly Halomonas marina) and zoospores of the alga Ulva linza (formerly Enteromorpha linza). SAMs were formed on gold-coated glass slides from solutions containing mixtures of methyl- and carboxylic acid-terminated alkanethiols and mixtures of methyl- and hydroxyl-terminated alkanethiols. C. marina attached in increasing numbers to SAMs with decreasing advancing water contact angles (theta(AW)), in accordance with equation-of-state models of colloidal attachment. Previous studies of Ulva zoospore attachment to a series of mixed methyl- and hydroxyl-terminated SAMs showed a similar correlation between substratum theta(AW) and zoospore attachment. When the hydrophilic component of the SAMs was changed to carboxylate, however, the profile of attachment of Ulva was significantly different, suggesting that a more complex model of interfacial energetics is required.

FTIR study of polycaprolactone chain organization at interfaces

Polycaprolactone (PCL), extensively known as a biomaterial, is the subject of this paper. Knowing well that some biomaterial applications exhibit specific chain organization, we focused our study on the orientation of PCL chains when this polymer is adsorbed (spin-coated) on inert substrates such as gold-coated glass slides. The main technique allowing adsorbed thin films analysis that we chose is polarization–modulation infrared reflection–absorption spectroscopy (PM-IRRAS), which permits qualitative and quantitative determination of chain anisotropy in the confined layers at the interface. Based on our spectroscopic results, we achieved an adsorption model of PCL chains and we calculated orientation angles with respect to the substrate normal. Calculated values show a quasi-perpendicular deposition of PCL chains on the gold substrate. Moreover, PCL thin films remain highly crystalline, a fact which could be the basis of the important anisotropy of PCL chains.

Microspotting streptavidin and double-stranded DNA arrays on gold for high-throughput studies of protein-DNA interactions by surface plasmon resonance microscopy.

We present two strategies for microspotting 10 x 12 arrays of double-stranded DNAs (dsDNAs) onto a gold-coated glass slide for high-throughput studies of protein-DNA interactions by surface plasmon resonance (SPR) microscopy. Both methods use streptavidin (SA) as a linker layer between a biotin-containing mixed self-assembled monolayer (SAM) and biotinylated dsDNAs to produce arrays with high packing density. The primary mixed SAM is produced from biotin- and oligo(ethylene glycol)-terminated thiols bonded as thiolates onto the gold surface. In the first method, a robotic microspotter is used to deliver nanoliter droplets of dsDNA solution onto a uniform layer of this SA ( approximately 2 x 10(12) SA/cm(2)). SPR microscopy shows a density of (5-6) x 10(11) dsDNA/cm(2) (0.2-0.3 dsDNA/SA) in the array elements. The second method uses instead a microspotted array of this SA linker layer, onto which the microspots of dsDNA are added with spatial registry. SPR microscopy before addition of the dsDNA shows a SA coverage of 2 x 10(12) SA/cm(2) within the spots and a dsDNA density of 8.5 +/- 3.5 x 10(11) dsDNA/cm(2) (0.3-0.7 dsDNA/SA, depending on the length of dsDNA) after dsDNA spotting. We demonstrate the ability to simultaneously monitor protein binding with the SPR microscope in many 200-microm spots with 1-s time resolution and sensitivity to <1 pg of protein.

PM‐IRRAS spectroscopy for the characterization of polymer nanofilms: chains conformation, anisotropy and crystallinity

AbstractThis paper is focused on the use of the Polarization‐Modulation Infrared Reflection‐Absorption Spectroscopy (PM‐IRRAS) for studying thin polymer films at interfaces. When forming a polymer film on a metallic substrate, for instance by spin‐coating, the characterization of the polymeric layer becomes very difficult given the small amount of matter deposited and also because of the contact with the metal. Among the techniques well adapted to surface and interface analyses, the PM‐IRRAS spectroscopy represents an excellent tool to probe ultra‐thin films.Different systems have been selected in this study such as polyamides (PA) and ethylene‐co‐vinyl acetate (EVA) nanofilms spin‐coated onto chemically controlled surfaces (i.e. thiol self‐assembled monloayers grafted onto gold coated glass slides). PM‐IRRAS spectroscopy allowed us to characterize the polymer anisotropy (chains orientation and conformation), to suggest a model for chain organization at the polymer/substrate interface, and to calculate the orientation angles. Moreover, we were able to determine, by using PM‐IRRAS, the degree of crystallinity of PA and EVA films of nanometric dimensions without any calibration procedure needed by other techniques.

Soft-Lithography Patterning of Functionalized Regioregular Polythiophenes

Poly(3-(6-thiohexyl)-4‘-dodecyl-2,2‘-bithiophene) (1) was successfully synthesized by postpolymerization functionalization of poly(3-(6-bromohexyl)-4‘-dodecyl-2,2‘-bithiophene) (12). 3-(6-Bromohexyl)-4‘-dodecyl-2,2‘-bithiophene (10), a key intermediate in the synthesis of polymer 12, was synthesized via Stille coupling of 2-bromo-3-(bromohexy)thiophene (8) and 2-trimethylstannyl-4-dodecylthiophene (9) in 30% isolated yield. Microstructure patterns of poly(3-(6-thiohexyl)-4‘-dodecyl-2,2‘-bithiophene) (1) were fabricated on a gold-coated glass slide through microcontact printing and microtransfer molding techniques. Circuit patterns of poly(3-hexylthiophene)s were constructed from a patterned silicon wafer via capillary force lithography methodology.

The interaction of ozone with polyphenylsulfide thin films studied by ellipsometry and SPR

Thin films of polyphenylsulfide (PPS) have been deposited onto silicon wafers and gold-coated glass slides by the method of spin coating. Ellipsometry and surface plasmon resonance (SPR) were performed in order to determine film thickness and index of refraction. It was found that the derived film thickness depends on spin speed as ω − s , with s varying between 0.5 and 0.6, depending on the concentration of PPS solution, which was in good agreement with hydrodynamic theory. An accurate value of films' index of refraction of n=1.59 was determined. The index of refraction of PPS films was found to increase on exposure to 2 ppm ozone. These results can be exploited for further development of real-time detection systems for ozone at low concentration based upon more sensitive optical techniques, such as integrated optic interferometry.

Detection of Staphylococcus aureus enterotoxin B at femtomolar levels with a miniature integrated two-channel surface plasmon resonance (SPR) sensor

Surface plasmon resonance (SPR) biosensors offer the capability for continuous real-time monitoring. The commercial instruments available have been large in size, expensive, and not amenable to field applications. We report here an SPR sensor system based on a prototype two-channel system similar to the single channel Spreeta™ devices. This system is an ideal candidate for field use. The two-channel design provides a reference channel to compensate for bulk refractive index (RI), non-specific binding and temperature variations. The SPR software includes a calibration function that normalizes the response from both channels, thus enabling accurate referencing. In addition, a temperature-controlled enclosure utilizing a thermo-electric module based on the Peltier effect provides the temperature stability necessary for accurate measurements of RI. The complete SPR sensor system can be powered by a 12V battery. Pre-functionalized, disposable, gold-coated thin glass slides provide easily renewable sensor elements for the system. Staphylococcus aureus enterotoxin B (SEB), a small protein toxin was directly detectable at sub-nanomolar levels and with amplification at femtomolar levels. A regeneration procedure for the sensor surface allowed for over 60 direct detection cycles in a 1-month period.

Stamping of monomeric SAMs as a route to structured crystallization templates: patterned titania films.

Gold-coated glass slides have be patterned by using self-assembled monolayers (SAM) of alkane thiols. Through the use of a special thiol terminated with a styrene monomer, microstructures of 5 to 10 microm width and 70 A height have been formed on the surface by graft polymerization of styrene. These patterned gold slides have then been used to template the precipitation of thin titania films from ethanolic solutions of titanium isopropoxide to create microstructured architectures in the film. Plasmon resonance spectra have established the presence of different steps in the process and have been used to follow the kinetics of the precipitation of titania on the surface. The structured TiO2 films have been characterized by scanning electron microscopy.

Resorcinol calixarenes (resorcarenes): Langmuir-Blodgett films and optical properties

Specially synthesized amphiphilic resorcinol calixarene (resorcarene 2) molecules have been deposited as Langmuir-Blodgett (LB) films on a variety of substrates including hydrophobically treated glass slides, silicon and gold-coated glass slides. A value of 1.9 nm 2 is obtained for the area per molecule from measurements of pressure/area isotherms of the floating layer. Optical absorption studies within the ultraviolet-visible frequency region have been performed on these molecules in both LB films and in solution of resorcarene 2 in chloroform, containing 10% ethanol. Molecular aggregation in the form of dimerization is believed to take place during film formation. Further analysis has been carried out for Langmuir-Blodgett films of resorcarene 2 by using Fourier transform infra-red spectroscopy, low-angle X-ray diffraction and surface plasmon resonance (SPR) techniques. The monolayer thickness of 1.6 nm found from SPR measurements is consistent with that from other experimental observations.

Electropolymerization of a phenol-modified peptide for use in receptor–ligand interactions studied by surface plasmon resonance

In this paper, the combination of surface plasmon resonance (SPR) with an electrochemical method for surface modification is presented. The SLP1 sequence of the sodium channel protein of rat cardiac muscle cells was N-terminally modified with an electropolymerizable group and immobilized on a gold-coated glass slide by oxidative polymerization. The resulting peptide-functionalized substrate was incubated with a polyclonal-specific anti-SLP1 serum. Growth of the peptide layer and the immunological reaction between ligand and receptor were detected on-line by SPR. The applicability of this approach for the rapid and selective analysis of receptor–ligand interactions is demonstrated.

Physicochemical and biochemical characterization of biosurfactants released by Lactobacillus strains

Biosurfactants from Lactobacillus casei subsp. rhamnosus 36 and ATCC 7469, Lactobacillus fermentum B54 and Lactobacillus acidophilus RC14 were isolated from bacteria in their mid-exponential (4–5 h) and stationary growth phases (18 h) and physicochemical and biochemical properties of the freeze-dried biosurfactants from both growth phases were compared. The mid-exponential and stationary phase biosurfactants were similar in their surface activities, but the latter had a lower and better defined critical micelle concentration. In particular, the stationary phase biosurfactant from L. acidophilus RC14 reached a low liquid surface tension of 39 mJ m −2 in phosphate buffered saline, with a critical micelle concentration of 1.0 mg ml −1. All biosurfactants consisted of a mixture of protein and polysaccharides, possibly containing bound phosphate groups, but the stationary phase biosurfactants were richest in protein, as concluded from Fourier transform infrared spectroscopy on biosurfactants in KBr pellets and from X-ray photoelectron spectroscopy on biosurfactants deposited on gold-coated glass slides. Infrared spectra of mid-exponential phase biosurfactants showed an absorption band around 2500 cm −1, which was absent in the spectra of stationary phase biosurfactants and was assigned to nitrogen-containing compounds with > NH 2 +, >(NH +)−, or = (NH +)− groups. Amino acid analysis of the hydrolyzed mid-exponentil and stationary phase biosurfactants from L. casei subsp. rhamnosus 36 demonstrated a high occurrence of alanine, which is possibly present as the free amino acid. The L. acidophilus RC14 mid-exponential phase biosurfactant also had a high alanine content, but the L. acidophilus RC14 stationary phase biosurfactant had an approximately four-fold lower alanine occurrence. We suggest that the protein-rich biosurfactants released by certain Lactobacillus strains in their stationary growth phases may interfere with uropathogen adhesion, for which we propose the name “surlactin”.

Self-Assembled Monolayers of Alkanethiolates Presenting Tri(propylene sulfoxide) Groups Resist the Adsorption of Protein

Self-Assembled Monolayers of Alkanethiolates Presenting Tri(propylene sulfoxide) Groups Resist the Adsorption of Protein

Partial Electron Transfer in Octadecanethiol Binding to Gold

Langmuir-Blodgett transfer of octanedecanethiol (Cl&H) containing monolayers onto gold-coated glass slides under potentiostatic conditions leads to a quantitative characterization of Cl&H chemisorption on gold. The thiol-gold bond involves a partial electron transfer from sulfur to the gold substrate. The CL$H partial charge number was determined to vary linearly with the potential of gold substrates from 0.30 at -0.30 V to 0.45 at 0.70 V vs SCE. Only ca. 81% of Cl&H molecules appear to chemisorb upon LB transfer at 20 mNlm. This is likely a result of some orientational restrictions (e.g. tilt and registry with the gold surface lattice) imposed on the system by the lateral pressure during LB transfer. The requirement of monolayer charge neutrality, stemming from a negligible capacitance of the Au/LB monolayer interface, results in a dissociation of thiol's proton to an extent equal to the charge transferred due to C&H chemisorption.

Sol-Gel Glasses as New Waveguides for Optical Immunosensors

ABSTRACTIn order to develop an optical immunosensor based on Surface Plasmon Resonance (SPR) and guided waves propagation, the sol-gel process has been used to prepare thin films of amorphous silica, deposited by spin coating on a gold-coated glass slide, and possessing chemically active functional groups (SH, NH2...). After activation of the sol-gel film in aqueous buffers by a bifunctional coupling agent, biological molecules such as antibodies could be covalently bonded on or inside the sol-gel film. Therefore, the behaviour of the functionalized silica thin films in aqueous solutions has been analyzed by SPR and guided waves propagation. The matrix hydrophilicity has been studied with different mixtures of functionalized silicon precursors forming organic-inorganic hybrid films. Immunoassays outline the possibility of obtaining covalent binding of antibodies to the sol-gel matrix with optimal stability and biological activity.

Thin films of functionalized amorphous silica for immunosensors application

Within the framework of the development of an optical immunosensor, the sol-gel process has been used to prepare a thin film of amorphous silica, deposited by spin coating on a gold-coated glass slide, and possessing chemically active functional groups (SH, NH2...). After activation of the sol-gel film in aqueous buffers by a bifunctional coupling agent, biological molecules such as antibodies could be covalently bonded on or inside the sol-gel film. Therefore, the behavior in aqueous solutions of the functionalized silica thin films has been analysed by Surface Plasmon Resonance (SPR) and guided wave propagation. Results show a modification of the thickness and of the refractive index of the silica film. Pore size range has been deduced by the infiltration of different molecular weight dextran molecules diluted in water into the sol-gel material. Immunosassays have demonstrated biological activity of antibodies which are covalently linked to or entraped in the sol-gel film.

Preparation of a Tissue Model for Quantitative FT-IR Microspectroscopic Functional Group Imaging

There is much interest in the biological and pharmacological sciences in knowing the specific location, concentration, and chemical structure of biologically active molecules in tissue. Infrared spectroscopy can be a suitable method for addressing these considerations; it can give quantitative and qualitative information without destroying the sample. IR spectra of approximately 20-μm-thick slices of animal tissue, mounted on barium or calcium fluoride crystals, can be obtained in the transmittance mode. Also, 3–5-μm-thick tissue slices can be mounted on gold-coated glass slides, and IR spectra can be obtained in the reflection-absorption mode.

Bonding of vapor deposited gold to glass using organosilane primers

Organosilane primers are known to improve adhesion of thin metal films deposited on inorganic and plastic surfaces. The present study demonstrated that the initial peel adhesion of vapor deposited gold to silane-primed glass substrate is greater than 3.5 N/cm estimated from cross-hatch test and thus is generally consistent with the earlier reports. The gold coated glass slides when examined using a more severe test (i.e. chemically bonding to a polymer, and subsequent peeling), however, exhibited poor adhesion in all cases except when the glass substrate was primed with an oligomeric organosilane primer. The successful primer (Dow Corning® 1205) was found to develop peel adhesion between vapor deposited gold and glass which was better than 17.5 N/cm.