AVS2016 Session TF+BI-ThA: Thin Films for Bio-related Applications

Organic monolayers or polymer brushes, often in combination with surface structuring, are widely used to prevent nonspecific adsorption of polymeric or biological material on sensor and microfluidic surfaces. Here we show how robust, covalently attached alkyne– derived monolayers or ATRP-produced polymer brushes, with a varying numbers of fluorine atoms, on atomically flat Si(111), effectively repel a wide range of apolar polymers without the need for micro– or nanostructuring of the surface. We have studied the antifouling property of fluoro-hydro monolayers and of fluorine-containing polymer brushes towards a range of commonly used polymers/plastics with comparable molecular weight in non– aqueous solvent, and have investigated the effect of polymer molecular weight on the fouling behavior. In addition, we show how for fluorinated polymer brushes this property can be self-repaired upon damage. These studies relied on a range of characterization methods: wettability studies, ellipsometry, X– ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). We developed a novel surface morphology survey by AFM characterization that can accurately quantify the degree of fouling.

These findings and analysis offer significant potential for antifouling applications of ultrathin and covalently bound fluorine– containing coatings for a range of micro– and nanotechnological applications.

Lit:

J. Mater. Chem. A, 2016, 4, 2408–2412

Adv. Mater. Interfaces 2016, 3, 1500514

Bloch surface waves (BSWs) are electromagnetic excitation modes that exist at the interface of truncated dielectric multilayer structures and a homogeneous medium. Although BSWs are intrinsically present at such interfaces, they cannot be directly excited by light incident from the homogeneous medium due to their non-radiative and evanescent nature. The use of a grating coupler or a prism mitigates this inability by providing an additional momentum to the free-space wave vector required to satisfy the phase matching condition with the BSW wave vector. Since Grating-coupled Bloch surface wave resonance (GCBSWR) bio-sensors do not require a bulky prism to couple light into BSWs, they are strong candidates for nanoscale bio-sensors. But GCBSWR bio-sensors, based on either wavelength or angular interrogation, are observed to be less sensitive compared to prism-coupled Bloch surface wave resonance (PCBSWR) bio-sensors. However, due to their inhomogeneous surface architecture, GCBSWR bio-sensors can be interrogated by rotating the grating platform azimuthally. Exploiting this ability, here we present a new method for improving sensing capability of GCBSWR bio-sensors. We demonstrate computationally, using a three-dimensional scattering matrix based rigorous coupled wave analysis method, that the proposed azimuthal angle interrogation technique highly enhances the sensitivity of GCBSWR bio-sensors. For our study we use a sixteen layered TiO₂-SiO₂ multilayer with SiO₂ gratings on the top sensing platform. We fix the wavelength and incident angle of the incoming light, and sweep over the azimuthal angle to simulate the sensitivity as a function of changing refractive index of the sensing layer. Furthermore, we show that contrary to conventional GCBSWR bio-sensors that only work for transverse electric mode, azimuthal angle based GCBSWR bio-sensors work for both transverse electric and transverse magnetic modes.

Amine-functionalized substrates are among the most commonly used materials in solid-phase peptide synthesis. Chemical stability and amine loading of the amino coating are two important properties that determine silane selection as a building layer in peptide synthesis. We synthesized three different amino coatings i.e., APTES (3-aminopropyltriethoxysilane), APDEMS (3-aminopropyldiethoxymethylsilane) and APDIPES (3-aminopropyldiisopropylethoxysilane), and determined their strengths and limitations as a building layer in peptide array synthesis. Here, amino coatings were synthesized via gas-phase deposition of the corresponding silanes on thermal oxide-terminated silicon substrates in a commercial chemical vapor deposition system. A 16-mer peptide coating was then synthesized on the amino surfaces and the chemical stability of the surface to highly acidic side chain deprotection (SCD) treatments was determined. After SCD, the coating thicknesses decrease to different degrees on the surfaces: it is greatest for the APDIPES surface, lowest for the APTES surface and intermediate for the APDEMS surface, which indicates that peptide-functionalized APTES and APDIPES surfaces are chemically most and least stable to SCD treatment, respectively. The effect of amine loading on peptide density and purity was also determined for the three amino surfaces. Four different trimers were synthesized on the amino surfaces, and the density and purity of these trimers for the three surfaces was determined. A positive correlation between the amine loadings and peptide densities was observed; peptide density was highest for the APTES surface and lowest for the APDIPES surface. However, high amine loading is found to have a negative impact on peptide purity; peptide purity is highest for the APDIPES surface and lowest for APTES surface. Coated surfaces were characterized by spectroscopic ellipsometry, contact angle goniometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), spectrophotometry, and MALDI-MS.

The aim of this research is to fabricate an electrically conducting, smooth, continuous and sensitive nanofiber using polystyrene (PS), triblock copolymer (PS-b-PDMS-b-PS) and single-walled carbon nanotubes (SWCNTs) by electrospinning. The electronic nanofibers may be utilized for effective bio-sensing applications. The SWCNTs have been of great interest to researchers because of their exceptional electrical, mechanical, and thermal properties. The nanoscale diameter, high aspect ratio, and low density make them an ideal reinforcing candidate for novel nano composite material.

Electrically conducting nanofibers have been prepared by electrospinning a solution of PS, PS-b-PDMS-b-PS and functionalized SWCNTs in the ratio 5:1:0.05 using solvent DMF. The nanofibers formed had an average diameter of 5 µm and height 4 µm. These nanofibers were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy and electrical characterization.

The electrical characterization of a single fiber shows an almost linear graph of current vs voltage using four-point probe (also known as Kelvin sensing) method. This linear graph exemplifies the conducting nature of the nanofiber. From the graph, a resistance, resistivity and conductivity of the single were measured. The study suggests that the SWCNT/block copolymer nanofibers have superior performance in the development of ultra-high sensitive sensor for the detection of single molecule relative to conventional materials due to significantly larger surface-to-volume ratio. Future work includes preparing nanofibers decorated with functional groups and binding with specific type of enzyme or protein to study their I-V behavior. This approach or method can be utilized for bio-sensing activities, especially for the detection of various antibodies and protein molecules.

References:

[1] Ramakrishna, S.; Fujihara, K.; Teo, W.-E.; Lim, T.-C.; Ma, Z. An Introduction to Electrospinning and Nanofibers; World Scientific: Singapore, 2005.

[2] Charlier, J.-C.; Issi, J.-P. Electrical Conductivity of Novel Forms of Carbon. Journal of Physics and Chemistry of Solids. 1996, 57, 957–965.

[3] Zhao, B.; Hu, H.; Haddon, R. C. Synthesis and Properties of a Water-Soluble Single-Walled Carbon Nanotube–Poly (m-Amino benzene Sulfonic Acid) Graft Copolymer. Advanced Functional Materials. 2004, 14, 71–76.

Funder Acknowledgement(s): This research was funded and supported by the National Science Foundation, CREST, DMR-0934142 and the Center for Functional Nanoscale Material Research program at Clark Atlanta University.

Faculty Advisor/ Mentor: Dr. Michael D. Williams, mdwms@cau.edu