The manipulation of biological substrates is becoming more popular route toward generating novel computing devices. Physarum polycephalum is used as a model organism in biocomputing because it can create “wires” for use in hybrid circuits; programmable growth by manipulation through external stimuli and the ability withstanding a current and its tolerance to hybridization with a variety of nano/microparticles. Lettuce seedlings have also had previous interest invested in them for generating plant wires, although currently there is little information as to their suitability for such applications. In this study both P. polycephalum and Lettuce seedlings were hybridized with gold nanoparticles — functionalized and unfunctionalized — to explore their uptake, toxicological effects and, crucially, any alterations in electrical properties they bestow upon the organisms. Using various microscopy techniques it was shown that P. polycephalum and lettuce seedlings are able to internalize nanoparticles and assemble them in vivo, however some toxicological effects were observed. The electrical resistance of both lettuce seedlings and P. polycephalum was found to decrease, the most significant reduction being with lettuce seedlings whose resistance reduced from 3MΩΩs to 0.5MΩΩs. We conclude that gold is a suitable nanomaterial for biohybridization specifically in creating conductive pathways for more efficient biological wires in self-growing hybrid circuitry.
Poly(4-vinylpyridine) swollen in pyridine displays changes in electrical conductivity in response to white light and to low level thermal perturbation; protonation of the side-chain nitrogen is believed to play a role. Here we present spectroscopic evidence that the proton donor is the methyne group CH on the polymer chain.
In this contribution we describe the formation of gold nanoparticles (AuNP) and polyaniline (PANI) AuNP-PANI nanocomposite via in-situ enzymatic polymerization. The method consists of electrostatic adsorption of anilinium monomers on AuNPs citrate stabilized surface of 50 nm diameters, followed by oxidation with horseradish peroxidase (HRP) enzyme and its cofactor H2O2. All reaction steps were monitored by UV-Vis-NIR spectroscopy including in-situ detection of the polymerization process. UV-Vis-NIR, Cyclic voltammetry (CV) and surface enhanced Raman scattering (SERS) measurements supported the formation of a nanoshell of PANI on the AuNP core. Two templates for anilinium assembly were compared revealing a strong dependence of the enzymatic kinetics on the template. The kinetic study had shown that the rigid template of the AuNP contributes to higher reaction rate on the AuNP compared with the more flexible polyanion template. The mild reaction’ condition enables an easy and precise method for obtaining PANI nano-shell on anionic templates for advanced bioelectronic applications.
An electrochemical biosensor has been developed for ultrasensitive, label-free determination of protein kinase activity. The sensor is composed of a unique peptide monolayer on a gold electrode. It identifies the order change in the monolayer upon phosphorylation, via square wave voltametry (SWV) measurements. Disorder caused by the introduction of the phosphate groups onto the middle of the peptide sequence results in pinhole formation and therefore an increase in the electrochemical signal. The measured sensitivity was 100 nM of kinase and the dynamic range was 100 nM up to 11 μM. Sensitivity was an order of magnitude higher, and the dynamic range wider by two orders of magnitude, as compared to our previously reported impedimetric method, in which the sensitivity was 1 μM, and the dynamic range was 1-20 μM.
We present an integrated approach for highly sensitive identification and validation of substrate-specific kinases as cancer biomarkers. Our approach combines phosphoproteomics for high throughput cancer-related biomarker discovery from patient tissues and an impedimetric kinase activity biosensor for sensitive validation. Using non-small-cell lung cancer (NSCLC) as a proof-of-concept study, label-free quantitative phosphoproteomic analysis of a pair of cancerous and its adjacent normal tissues revealed 198 phosphoproteins that are over-phosphorylated in NSCLC. Among the differentially regulated phosphorylation sites, the most significant alteration was in residue S165 in the Hepatoma Derived Growth Factor (HDGF) protein. Hence, HDGF was selected as a model system for the electrochemical studies. Further motif-based analysis of this altered phosphorylation site revealed that extracellular-signal-regulated kinase 1/2 (ERK1/2) are most likely to be the corresponding kinases. For validation of the kinase–substrate pair, densely packed peptide monolayers corresponding to the HDGF phosphorylation site were coupled to a gold electrode. Phosphorylation of the monolayer by ERK2 and dephosphorylation by alkaline phosphatase (AP) were detected by electrochemical impedance spectroscopy (EIS) and surface roughness analysis. Compared to other methods for quantification of kinase concentration, this label-free electrochemical assay offers the advantages of ultra-sensitivity as well as higher specificity for the detection of cancer-related kinase–substrate pair. With implementation of multiple kinase–substrate biomarker pairs, we expect this integrated approach to become a high throughput platform for discovery and validation of phosphorylation-mediated biomarkers.
Functionalized nanoparticle networks offer a model system for the study of charge transport in low-dimensional systems as well as a potential platform to implement and test electronic functionalities. The electrical response of a nanoparticle network is expected to sensitively depend on the molecular inter-connects, i.e. on the linker chemistry. If these linkers have complex charge transport properties, then phenomenological models addressing the large scale properties of the network need to be complemented with microscopic calculations of the network building blocks. In this study we focus on the interplay between conformational fluctuations and electronic $π$-stacking in single molecule junctions and use the obtained microscopic information on their electrical transport properties to parametrize transition rates describing charge diffusion in mesoscopic nanoparticle networks. Our results point out at the strong influence of mechanical degrees of freedom on the electronic transport signatures of the studied molecules. This is then reflected in the varying charge diffusion at the network level. The modeling studies are complemented with first charge transport measurements at the single-molecule level of $π$-stacked molecular dimers using state of the art mechanically controllable break junction techniques in a liquid environment.
We report on the fabrication and characterization of porous-silicon/conjugated-polymer hybrids, created by combining a host columnar matrix of mesoporous silicon and a network of organic nanowires made from poly(N-vinylcarbazole) (PVK). A uniform and homogeneous filling of the pores by the polymers was accomplished by electrochemical polymerization of organic monomers inside the pores by using cyclic voltammetry. Spectroscopic measurements showed that polymerization inside the confined environment of the nanometric pores results in a tighter and denser packing of the polymer due to a change of the polymerization process from the vinyl groups to the conjugated carbazole groups, giving rise to a redshift of the absorption spectra and better electrical conductivity. Current-voltage characterization of the hybrids under dark conditions and under illumination were investigated. We demonstrate a simple method to control the band alignment between the organic polymer and the porous silicon, altering it from a type-I to a type-II interface by changing the doping polarity of the silicon substrate (from p-type to n-type, respectively). An efficient photoinduced charge separation was observed for the type-II interface (n-type porous-silicon–polymer interface), while no such effect was observed for the type-I organic–inorganic interface.
There is continuing interest in determining essential structural features of polymer gels, which display photoelectric and/or thermoelectric behavior. One such gel is the blend, poly(4-vinylpyridine-co-butyl methacrylate)/poly(4-vinylpyridine), dissolved in liquid pyridine. Following extended aeration of a three-component mixture, which serves as a model for the gel side chain interactions, crystallization of a new molecule, 4-isopropylpyridine hydroxide (IPPOH), occurs. X-ray diffraction, DFT modeling, and spectroscopy were used to determine the structural, electronic, and luminescent properties of the crystal. The crystal structure reveals molecules forming head-to-tail, hydrogen-bonded chains without base stacking or marked interchain interaction. The molecular chains are characterized by moderately long-lived, blue-violet luminescence excited in the near-UV. Because these photoluminescent properties resemble those of the gel from which the crystals are derived, we may posit similar structural features in the gel for which direct structural analysis is not available.
Sensing from the ultraviolet to the infrared is important for a number of scientific and industrial applications. Poly(4-vinyl pyridine) swollen in liquid pyridine functions as a photoconductive gel sensitive to irradiation in the ultraviolet. By blending poly(4-vinyl pyridine) with poly(4-vinyl pyridine-co-butyl methacrylate), we have now succeeded in expanding the range of wavelength sensitivity of the gel to cover the whole visible spectrum. Furthermore, addition of a small amount of 4-hydroxypyridine to the polymer blend results in unusually high thermal sensitivity (TCR = (0.1–0.16)/1 °C). Spectroscopic measurements show that the combined processes of proton transfer and electron transfer, occurring in a DC electric field, contribute to the gel properties. The optimized system has potential application as a simple and inexpensive active layer in organic photovoltaic cells as well as a thermal sensor.
In this work we show dipole-assisted photogated switching by covalent grafting of photoactive molecules to conducting polymers. Photochromic spiropyran molecules were covalently attached to polyaniline (PANI) nanowires via N-alkylation reaction to the quinoic part of PANI. Upon irradiation with ultraviolet light spiropyran transformed to a large dipole containing molecule, merocyanine form. We show that this transformation leads to a substantial (ca. 2 orders of magnitude) increase in conductance of the photochromic PANI nanowires, which were evident by an increase in field-effect mobility and calculated band gap narrowing of the system. Finally, this transformation was found to be fully reversible with no significant photofatigue.
We report on a novel approach to synthesize hybrid nanostructures of meso porous silicon and conjugated organic polymers that are suitable for solar cell applications. Meso-porous silicon substrates with relatively large pores (\~100 nm) have been exploited for electrochemical polymerization of organic monomers, which were introduced into the porous silicon matrices and electro-polymerized to create poly-vinyl-carbazole (PVK). We present electrical characteristics of a device having relatively thin films of the hybrid medium, which exhibits a photovoltaic mode of operation
This paper describes remarkably high sensitivities in the label-free detection of kinase-promoted phosphorylation for 14 different peptide substrates on electrode-immobilized monolayers (gold or nitride) using serine/threonine kinases PKA, PKC, and CaMK2. Peptide substrates were preselected using 33P-labeling in a microarray of 1024 substrates. The three most active peptides (A1–A3, C1–C3, and M1–M3) were investigated using electrochemical impedance spectroscopy (EIS) and ion-sensitive field effect transistors (ISFETs). Some of the peptide substrates, for example, the PKC-specific substrate PPRRSSIRNAH (C1), showed a remarkably high sensitivity in the EIS-based sensor measurements. Our studies revealed that this high sensitivity is primarily due to the monolayer’s packing density. Nanoscopic studies demonstrated a distinct disordering of the C1-monolayer upon phosphorylation, while phosphatase-promoted dephosphorylation regenerated the highly ordered peptide monolayer. As a matter of fact, the initial surface packing of the peptide monolayer mainly determined the level of sensitivity, whereas electrostatic repulsion of the redox-active species was found to be much less important.
Selectivity is one of the most challenging issues in biosensor design. Several methods have been proposed in the past to overcome nonspecific interference. In particular, it has been shown that temperature curves can be used to simultaneously measure two similar analytes. Here, the performance of such thermal-based systems is analyzed, using least squares estimation and existing models for affinity-based sensing, and it is shown that a D-optimal difference for the sensor temperatures exists. Analysis at this optimized condition yields bounds on the sensitivity and selectivity of this class of sensors. For the first time, thermal discrimination is employed for an affinity-based sensor: an artificial receptor-based system for the detection of the neurotransmitter acetylcholine and its metabolite choline. The system performance demonstrates the practicality of the theoretical results presented.
Self-assembled monolayers (SAMs) of polar and polarizable organic molecules are widely used to tune semiconductors’ electronic properties for various applications. In the case of the dipoles’ arrangement in a dense and ordered SAM, intermolecular interaction between neighboring dipoles arises, inducing a change in the electrostatic properties of the polar SAM. These intermolecular long-range dipole interactions give rise to a molecular cooperative effect (MCE) through the layer, thus influencing the magnitude of the net surface dipole and suppressing the substrate contribution to dipole formation. Molecular engineering of the desired MCE could be a useful tool in various molecular electronics derived applications. In this work, we propose an experimental design to tailor the magnitude of the MCE through an organic monolayer. We constructed a mixed dipole monolayer containing parallel and antiparallel randomly organized dipoles. The creation of a mixed dipole monolayer enables controlling the MCE through the layer by giving rise to a smaller normal component to the surface coefficient and larger parallel component to the surface dipole coefficient. A deeper understanding of the MCE can be obtained by comparing the experimental and calculated values of such mixed dipole monolayers. The experimental values were obtained from contact potential difference measurements, and the calculated values were extracted by using the modified Helmholtz equation, based on the relative dipole contribution introduced in this work. This comparison enables analyzing the limit of the expected MCE, based on the evaluated surface dipole density along with its individual longitudinal molecular dipole.
We describe an experimental and theoretical consideration of photoexcited proton transfer in a poly(4-vinyl pyridine)/pyridine gel. Evidence was found for two states of a multiple state process analyzed by DFT modeling. According to the latter, following irradiation at 385 nm, the proton donor is the CH group of the polymer main chain and the proton acceptor is the nitrogen of the polymeric pyridine side chain. Proton transfer is made possible through the assistance of a mobile pyridine solvent molecule acting as a transfer vehicle. Proton transfer promotes both a geometrical rearrangement of the vinyl side chain as well as electronic density redistribution. The photoproduct intermediate—the hydrogen-bonded complex between the protonated solvent pyridine molecule and the deprotonated polymeric pyridine side chain—is identified by its Curie law magnetic susceptibility, ESR spectrum, and fluorescence lifetime measurements. The proton transfer from the nitrogen of the solvent pyridine molecule to the pyridine side chain nitrogen, producing pyridinium, is a thermodynamically favorable relaxation process and occurs without an energy barrier. The protonation of nitrogen on the polymeric side chain was detected by solid state NMR spectroscopy performed on a 15N-polymer enriched gel. The calculations and experimental data suggest a central role for the gel solvent molecule as a catalytic agent and proton transfer vehicle. The process suggested by DFT modeling may have relevance for photosensitive devices in part due to the fact that we have been able to show that long-lived paramagnetism may be included among the inducible properties of soft polymer gels.
Functionalized carbon nanotubes are increasingly exploited as innovative components for the development of advanced biomedical devices. In this study we report a novel synthetic route for the formation of single-walled carbon nanotube (SWCNT)–polyaniline (PANI) hybrids by in situchemical polymerization. The surfactant sodium dodecylsulfate (SDS) is used as a template for monomer assembly and polymerization. The resulting composite preserves the surfactant and is characterized by a tight binding between SWCNTs and PANI. Having the idea of integrating these new types of SWCNT conjugates into advanced biomedical tools (i.e. implantable multi-electrode arrays), we explored their potential impact on the viability and function of cells from the immune system. We have compared the cytotoxic effects of SWCNT-COOH, SWCNT/SDS andSWCNT/SDS/PANI on mouse spleen cells and macrophages. The results indicate that biocompatibility of the different SWCNT conjugates is dependent both on the doses used and the type of cells.
We report the preparation and characterization of hybrid materials from conducting polymers and single walled carbon nanotubes. Electrochemical polymerization yields nanotubes wrapped by conducting polymers – polyaniline, polycarbazole and melanin (i.e., polydopamine). The materials were characterized by ultraviolet–visible–near infrared, infrared, Raman and impedance spectroscopy. We found that wrapping the nanotubes with polymers can decrease the impedance of such composite electrode and increase the rate of electron transfer from the electrolyte to the electrode. From the attenuation of in-plane vibrations in the infrared spectra and the bathochromically shifted polaron band, we infer that the strongest interaction occurs between polyaniline and the nanotube surface.
We model the interaction of side-chain and end-chain groups of poly(4-vinylpyridine) by a 5:1 molar ratio mixture of 4-isopropylpyridine (side-chain model) and 4-propylpyridine (end-chain model). We find that the 4-isopropylpyridine in the mixture is oxidized in a slow air flow to produce 4-isopropylpyridine hydroperoxide which in turn precipitates as lamellar crystals with monoclinic structure. The fact that the peroxide group is exchanged for the hydrogen of the tertiary carbon demonstrates the high activity of the latter and gives strong support for its involvement in the self-protonation mechanism proposed earlier for the poly(4-vinylpyridine)/pyridine gel.