Jakub Rysz

Device performance of APFO-3/PCBM solar cells with controlled morphology

Polymer/fullerene solar cells with three different device structures: A) diffuse bilayer, B) spontaneously formed multilayer, and C) vertically homogenous thin films, are fabricated. The photocurrent/voltage performance is compared and it is found that the self-stratified structure (B) yields the highest energy conversion efficiency.

Breath figures in polymer and polymer blend films spin-coated in dry and humid ambience.

We investigate effects of two spin-coating parameters, relative humidity (5% < or = RH < or = 80%) in ambient atmosphere and water content (3 wt % < or = f(H2O) < or = 20 wt %) in solution (rich in tetrahydrofuran), on the structure of breath figures (BF) formed in spin-cast films of polar poly(methyl methacrylate) (PMMA) and PMMA mixed with nonpolar polystyrene (PS). Film morphologies, examined with atomic and lateral force microscopy, are analyzed with integral geometry analysis to yield morphological BF measures. In PMMA, water added to solution has much stronger impact than that from moisture on formed BFs, which could be ordered (with conformational entropy S approximately 0.9-1.0). In PMMA/PS, BFs decorate exclusively polar PMMA domains, resulting in morphologies with two length scales (sub-micrometer BFs and domains >10 microm). This suggests a novel strategy for herarchic structure formation in multicomponent polymer films. In PS/PMMA, BFs are better developed than in pure PMMA spin-coated in identical conditions. These observations show that the air boundary layer facing the spin-cast polymer film (region) is more important than the ambient atmosphere.

Selective protein adsorption on polymer patterns formed by self-organization and soft lithography.

Thin films, with both isotropic and ordered patterns of polymer domains, are used as substrates to study selective adsorption of two proteins (concanavalin A and lentil lectin) and to test reconstruction of polymer patterns by these proteins. Integral geometry approach is used to compare quantitatively fluorescence micrographs of protein patches with AFM images of original isotropic patterns, formed during blend casting of polystyrene/poly(methyl methacrylate) and PS/poly(ethylene oxide). Preferential adsorption of both lectins to PMMA phase domains, enhanced for PS/PMMA interfaces is concluded. In turn, protein binding to PS phase regions of PS/PEO blends is highly selective. Ordered protein grouping is obtained as a result of selective adsorption to alternating stripes of polystyrene (partly brominated to enable identification) and cross-linked PEO, prepared with solvent-assisted micromolding applied to PBrS/PEO bilayers. Biological activity test, performed with concanavalin A, confirms preserved functionality of a complementary protein, carboxypeptidase Y, adsorbed to polymer patterns.

Spectroscopic and microscopic characterization of biosensor surfaces with protein/amino-organosilane/silicon structure.

Composition and structure of biorecognition protein layers created on silicon substrates modified with amino-organosilanes determine the sensitivity and specificity of silicon based biosensing devices. In the present work, diverse spectroscopic and microscopic methods were applied to characterize model biosensor surfaces, formed on Si(3)N(4) or SiO(2) by modification with (3-aminopropyl)triethoxysilane, coating with rabbit gamma-globulins (IgGs) through physical adsorption, blocking with bovine serum albumin (BSA) and specific binding of an anti-rabbit IgG antibody. In addition, silanized substrates with directly adsorbed BSA or anti-rabbit IgG antibody were examined as reference surfaces. The protein/amino-organosilane/silicon structure of all surfaces was confirmed by X-ray photoelectron spectroscopy. Homogeneity of protein coverage was verified with near-field scanning optical microscope, working in reflection and fluorescence mode. Surface coverage with proteins was determined with angle-resolved XPS using a previously established bilayer approach. Inner structure of protein layers was examined with atomic force microscopy. Vertical arrangement of carbon functional groups was revealed by high resolution ARXPS. Combined spectroscopic and microscopic data reveal the complex character of interactions with the immobilized IgG molecules during blocking with BSA and immunoreaction with anti-IgG antibody. Within experimental error, neither surface coverage nor lateral structural scales of protein layer (provided by Fourier and auto-correlation analysis of topographic and phase images) increase during blocking procedure. On the other hand, coverage and all structural measures rise considerably after immunoreaction. In addition, it was found that polar functional groups orient towards substrate for all protein layers, independently of coverage, prior to and after both blocking and specific binding.

Thiolate versus Selenolate: Structure, Stability, and Charge Transfer Properties

Selenolate is considered as an alternative to thiolate to serve as a headgroup mediating the formation of self-assembled monolayers (SAMs) on coinage metal substrates. There are, however, ongoing vivid discussions regarding the advantages and disadvantages of these anchor groups, regarding, in particular, the energetics of the headgroup-substrate interface and their efficiency in terms of charge transport/transfer. Here we introduce a well-defined model system of 6-cyanonaphthalene-2-thiolate and -selenolate SAMs on Au(111) to resolve these controversies. The exact structural arrangements in both types of SAMs are somewhat different, suggesting a better SAM-building ability in the case of selenolates. At the same time, both types of SAMs have similar packing densities and molecular orientations. This permitted reliable competitive exchange and ion-beam-induced desorption experiments which provided unequivocal evidence for a stronger bonding of selenolates to the substrate as compared to the thiolates. Regardless of this difference, the dynamic charge transfer properties of the thiolate- and selenolate-based adsorbates were found to be nearly identical, as determined by the core-hole-clock approach, which is explained by a redistribution of electron density along the molecular framework, compensating the difference in the substrate-headgroup bond strength.

Protein adsorption and covalent bonding to silicon nitride surfaces modified with organo-silanes: comparison using AFM, angle-resolved XPS and multivariate ToF-SIMS analysis.

Organo-silanes provide a suitable interface between the silicon-based transducers of various biosensing devices and the sensing proteins, immobilized through physical adsorption, as for (3-aminopropyl)triethoxysilane (APTES), or covalent binding, e.g. via protein amine groups to (3-glycidoxypropyl)trimethoxysilane (GOPS) modified surface. Immobilization of rabbit gamma globulins (RgG) to silicon nitride surfaces, modified either with APTES or GOPS, was examined as a function of incubation time using atomic force microscopy (AFM), angle-resolved X-ray photoelectron spectroscopy (ARXPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Multivariate technique of principal component analysis was applied to ToF-SIMS spectra in order to enhance sensitivity of immobilized RgG detection. Principal component regression shows a linear relationship with surface density determined rigorously from ARXPS following an organic bilayer approach, allowing for protein coverage quantification by ToF-SIMS. Taking it overall the surface immobilized amount of RgG is higher and develops faster on the surfaces silanized with APTES rather than with GOPS. Similar, although less distinct, difference is observed between the two surface types concerning the temporal evolution of average AFM height. The average height of protein overlayer correlates well with ARXPS and ToF-SIMS data expressed in terms of protein surface density. However, determined linear regression coefficients are distinctively higher for the surfaces modified with epoxy- rather than amino-silane, suggesting different surface density and conformation of the proteins immobilized through to covalent binding and physical adsorption.

Ordering domains of spin cast blends of conjugated and dielectric polymers on surfaces patterned by soft- and photo-lithography

Spin casting polymer blends of conjugated and dielectric macromolecules onto chemically patterned metal and oxidized silicon surfaces might provide a simple method to fabricate polymer-based circuitries that can be integrated with conventional electronics. Such solution-processing of the blend components offers simultaneous deposition and pattern-directed alignment of the phase separated polymer domains. The alignment is driven by self-organization guided by preferential surface segregation. Here we demonstrate that the laterally arranged domain structures in spin cast films of the conjugated poly(3-alkylthiophenes) (P3ATs): P3BT, P3DDT and regioregular R-P3HT, blended with dielectric polystyrene (PS), can be ordered by three different surface templates. The templates are formed by a patterned self-assembled monolayer (SAM), micro-contact printed on the surface of interest, i.e. hexadecanethiols on gold (for alignment of P3DDT/PS blend) and octadecyltrichlorosilanes on oxidized silicon (for R-P3HT/PS). Additionally gold lines are micro-patterned on SiO2 with photo-lithography (for P3BT/PS mixture). The forces driving pattern-directed self-organization of the polymers are discussed based on complementary studies of preferential surface segregation, observed for blend films spin cast on homogeneous surfaces that correspond to the different regions of the surface templates.

PDMS substrate stiffness affects the morphology and growth profiles of cancerous prostate and melanoma cells.

A deep understanding of the interaction between cancerous cells and surfaces is particularly important for the design of lab-on-chip devices involving the use of polydimethylsiloxane (PDMS). In our studies, the effect of PDMS substrate stiffness on mechanical properties of cancerous cells was investigated in conditions where the PDMS substrate is not covered with any of extracellular matrix proteins. Two human prostate cancer (Du145 and PC-3) and two melanoma (WM115 and WM266-4) cell lines were cultured on two groups of PDMS substrates that were characterized by distinct stiffness, i.e. 0.75 ± 0.06 MPa and 2.92 ± 0.12 MPa. The results showed the strong effect on cellular behavior and morphology. The detailed analysis of chemical and physical properties of substrates revealed that cellular behavior occurs only due to substrate elasticity.

Three-dimensional information on the phase domain structure of thin films of polymer blends revealed by secondary ion mass spectrometry

We describe the technique of dynamic secondary ion mass spectrometry developed to determine three-dimensional phase domain structures of films of polymer blends. The polymers are composed of light elements or are labeled with deuterium or heavy elements. The applicability of this method to various polymer blends forming thin and ultrathin films with flat and undulated air/film interface is discussed.

Temperature and pH dual-responsive coatings of oligoperoxide-graft-poly(N-isopropylacrylamide): wettability, morphology, and protein adsorption.

Poly(N-isopropylacrylamide) (PNIPAM) coatings attached to glass with novel approach involving polymerization from oligoperoxide grafted to surface with (3-aminopropyl)triethoxysilane exhibit not only temperature- but also pH-dependence of wettability and protein adsorption. Wettability and composition of coatings, fabricated with different polymerization times, were determined using contact angle measurements and Time Of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS), respectively. Thermal response of wettability, measured between 20 and 40°C, was prominent at pH 9 and 7 and diminished or absent at pH 5 and 3. This indicates a transition between hydrated loose coils and hydrophobic collapsed chains that is blocked at low pH. Higher surface roughness and dramatically increased adsorption of model protein (lentil lectin labeled with fluorescein isothiocyanate) were observed with AFM and fluorescence microscopy to occur in hydrophobic phases (at pH 3, for pH varied at constant temperature of 22°C and at ∼33°C, for temperature varied at constant pH 9). Protein adsorption response to pH was confirmed by TOF-SIMS and Principal Component Analysis.