Uwe H. F. Bunz

Detection and identification of proteins using nanoparticle–fluorescent polymer ‘chemical nose’ sensors

A sensor array containing six non-covalent gold nanoparticle-fluorescent polymer conjugates has been created to detect, identify and quantify protein targets. The polymer fluorescence is quenched by gold nanoparticles; the presence of proteins disrupts the nanoparticle-polymer interaction, producing distinct fluorescence response patterns. These patterns are highly repeatable and are characteristic for individual proteins at nanomolar concentrations, and can be quantitatively differentiated by linear discriminant analysis (LDA). Based on a training matrix generated at protein concentrations of an identical ultraviolet absorbance at 280 nm (A280 = 0.005), LDA, combined with ultraviolet measurements, has been successfully used to identify 52 unknown protein samples (seven different proteins) with an accuracy of 94.2%. This work demonstrates the construction of novel nanomaterial-based protein detector arrays with potential applications in medical diagnostics.

Sensing of proteins in human serum using conjugates of nanoparticles and green fluorescent protein

There is a direct correlation between protein levels and disease states in human serum making it an attractive target for sensors and diagnostics. However this is made challenging because serum features more than 20,000 proteins with an overall protein content of greater than 1 mM. Here we report a hybrid synthetic-biomolecule based sensor that uses green fluorescent protein-nanoparticle arrays to detect proteins at biorelevant concentrations in both buffer and human serum. Distinct and reproducible fluorescence response patterns were obtained from five serum proteins (human serum albumin, immunoglobulin G, transferrin, fibrinogen and α-antitrypsin) in buffer and when spiked into human serum. Using linear discriminant analysis we identified these proteins with an identification accuracy of 100% in buffer and 97% in human serum. The arrays were also able to discriminate between different concentrations of the same protein as well as a mixture of different proteins in human serum.There is a direct correlation between protein levels and disease states in human serum, which makes it an attractive target for sensors and diagnostics. However, this is challenging because serum features more than 20,000 proteins, with an overall protein content greater than 1 mM. Here we report a sensor based on a hybrid synthetic-biomolecule that uses arrays of green fluorescent protein and nanoparticles to detect proteins at biorelevant concentrations in both buffer and human serum. Distinct and reproducible fluorescence-response patterns were obtained from five serum proteins (human serum albumin, immunoglobulin G, transferrin, fibrinogen and a-antitrypsin), both in buffer and when spiked into human serum. Using linear discriminant analysis we identified these proteins with an identification accuracy of 100% in buffer and 97% in human serum. The arrays were also able to discriminate between different concentrations of the same protein, as well as a mixture of different proteins in human serum.

Gold nanoparticle-fluorophore complexes: sensitive and discerning "noses" for biosystems sensing.

Gold nanoparticles (NPs) efficiently quench adsorbed fluorophores. Upon disruption of such complexes by an analyte, fluorescence turn-on is observed. By judicious choice of the functionalized NP and the fluorophore, these complexes display different responses to analytes, thus leading to versatile yet simple array-based sensor platforms. Using this strategy, we can identify proteins in buffer and serum, distinguish between both different species and different strains of bacteria, and differentiate between healthy, cancerous, and metastatic human and murine cells.

Polyethynylated cyclic π-systems: scaffoldings for novel two and three-dimensional carbon networks

All-carbon materials with novel topologies are of interest in regard to their materials properties. These novel structures include graphite-like two-dimensional networks as well as fullerene-like three-dimensional cages. This article reviews recent developments in the synthesis of scaffolds for novel forms of carbon made of a core π-system carrying alkyne appendages, such as hexaethynylbenzene and its derivatives, pentaethynylcyclopentadienyl metal complexes, and tetraethynylcyclobutadiene metal complexes. Also included are the syntheses and properties of macrocyclic π-systems derived of these units which represent important substructures for the infinite lattices of novel carbon allotropes.

Detection and differentiation of normal, cancerous, and metastatic cells using nanoparticle-polymer sensor arrays

Rapid and effective differentiation between normal and cancer cells is an important challenge for the diagnosis and treatment of tumors. Here, we describe an array-based system for identification of normal and cancer cells based on a ‘‘chemical nose/tongue’’ approach that exploits subtle changes in the physicochemical nature of different cell surfaces. Their differential interactions with functionalized nanoparticles are transduced through displacement of a multivalent polymer fluorophore that is quenched when bound to the particle and fluorescent after release. Using this sensing strategy we can rapidly (minutes/seconds) and effectively distinguish (i) different cell types; (ii) normal, cancerous and metastatic human breast cells; and (iii) isogenic normal, cancerous and metastatic murine epithelial cell lines.

Colorimetric bacteria sensing using a supramolecular enzyme-nanoparticle biosensor.

Rapid and sensitive detection of pathogens is a key requirement for both environmental and clinical settings. We report here a colorimetric enzyme-nanoparticle conjugate system for detection of microbial contamination. In this approach, cationic gold nanoparticles (NPs) featuring quaternary amine headgroups are electrostatically bound to an enzyme [β-galactosidase (β-Gal)], inhibiting enzyme activity. Analyte bacteria bind to the NP, which releases the β-Gal and restores its activity, providing an enzyme-amplified colorimetric readout of the binding event. Using this strategy, we have been able to quantify bacteria at concentrations of 1 × 10(2) bacteria/mL in solution and 1 × 10(4) bacteria/mL in a field-friendly test strip format.

Poly(aryleneethynylene)s

Poly(aryleneethynylene)s (PAE) are easily synthesized, chemically stable, and color-responsive towards their surroundings. These superbly chromic polymers are attractive as active transducers in sensors and advanced organic electronic devices. PAEs are generally fluorescent with emission maxima ranging from 420-600 nm, and can be either water- or organo-soluble. PAEs from linear building blocks are rigid rod molecules and display a host of supramolecular arrangements in solution and in the solid state. The poly(para-phenyleneethynylene)s (PPE) are lyotropic or thermotropic smectic liquid crystalline. In the solid state, PPEs display lamellar supramolecular structures that lead to distinct stranded nanoscale morphologies. The spectroscopy and the optical properties of the PAEs and in particular of the PPEs are dominated by their conformation, which is influenced by solid-state packing, solvent, temperature and other factors. The presence of twisted and planar forms and their interconversion leads to attractive structure/property relationships; PAEs are of use as ingredients for advanced supramolecular materials.

α‐Oligofurans: Molecules without a Twist

Organic electronics, the science of p-conjugated organic compounds and their applications, is a focus of chemistry, materials science, and engineering. Despite the thousands of p-conjugated compounds that are already available, the development of new materials is critical, as specifically desired properties (such as stability, solubility, high purity, molecular packing to maximize intermolecular interactions in the solid state, and the correct level of the frontier molecular orbitals) are difficult to obtain in the solid state. Enhanced solubility by introduction of alkyl or alkoxy chains will change packing and influence molecular conformation, but might also disrupt p–p interactions, leading to decreased intermolecular interactions, whereas the addition of donor or acceptor substituents will influence the gross electronic properties of organic semiconductors. Substituted a-oligoand a-polythiophenes, and pentacenes 5] and C60 derivatives [6] are important for the development of organic thin-film transistors and photovoltaics. In the case of thiophene-based materials, synthetic routes for oligomers of any size and also polymers with varying sidechain density, stereochemistry, and regiochemistries have been reported. However, the sexithiophene 1 is already almost completely insoluble in common organic solvents. A single-crystal specimen of 1 could only be obtained through high-vacuum/high-temperature sublimation. Whereas hexamer 1 is planar in the solid state, oligoand polythiophenes adopt twisted conformations in solution, as can be attested to by their normally broad and featureless absorption spectra. There have been more than 1000 articles published on oligothiophenes, and more than 4600 articles have been published on polythiophenes, but the corresponding polyfurans have attracted much less attention. Most publications dealing with polyfurans involve the electrochemical synthesis by electrolysis of the terfuryl monomer. As the oxidation potentials of furan, bifuryl, and terfuryl are very different, the synthesis of polyfuran by the electrolysis of furan is not very successful. However, even polymer films obtained from terfuryl are insoluble in organic solvents and therefore cannot be characterized by classic polymer analytical methods (gel permeation chromatography, NMR spectroscopy, light scattering). The first highly soluble and characterized polyfurans, poly(3-octylfuran)s 5 and 6, were prepared by Curtis et al. in

Enzyme Amplified Array Sensing of Proteins in Solution and in Biofluids

We have developed an enzyme-nanoparticle sensor array where the sensitivity is amplified through enzymatic catalysis. In this approach cationic gold nanoparticles are electrostatically bound to an enzyme (beta-galactosidase, beta-Gal), inhibiting enzyme activity. Analyte proteins release the beta-Gal, restoring activity and providing an amplified readout of the binding event. Using this strategy we have been able to identify proteins in buffer at a concentration of 1 nM, substantially lower than current strategies for array-based protein sensing. Moreover, we have obtained identical sensitivity in studies where the proteins are spiked into the complex protein matrix provided by desalted human urine ( approximately 1.5 muM total protein; spiked protein concentrations were 0.067% of the overall protein concentration), demonstrating the potential of the method for diagnostic applications.

Effects of electronegative substitution on the optical and electronic properties of acenes and diazaacenes

Large acenes, particularly pentacenes, are important in organic electronics applications such as thin-film transistors. Derivatives where CH units are substituted by sp(2) nitrogen atoms are rare but of potential interest as charge-transport materials. In this article, we show that pyrazine units embedded in tetracenes and pentacenes allow for additional electronegative substituents to induce unexpected redshifts in the optical transitions of diazaacenes. The presence of the pyrazine group is critical for this effect. The decrease in transition energy in the halogenated diazaacenes is due to a disproportionate lack of stabilization of the HOMO on halogen substitution. The effect results from the unsymmetrical distribution of the HOMO, which shows decreased orbital coefficients on the ring bearing chlorine substituents. The more strongly electron-accepting cyano group is predicted to shift the transitions of diazaacenes even further to the red. Electronegative substitution impacts the electronic properties of diazaacenes to a much greater degree than expected.