Photochemically and electrochemically triggered Au nanoparticles "sponges"

Stimuli-triggered wettability of surfaces and controlled uptake and release of substrates by "smart" materials are essential for drug delivery and microfluidic control. A composite "sponge" consisting of bis-aniline-bridged Au nanoparticles (NPs), functionalized with photoisomerizable nitrospiropyran/nitromerocyanine that includes selective imprinted molecular recognition sites for N,N'-bis(3-sulfonatopropyl)-4,4'-bipyridinium (PVS) was electropolymerized on a Au electrode. The system is triggered by photonic and/or electrical signals to yield four different states exhibiting variable binding/release capacities for PVS and controlled wettability of the surface. The electrical/optical uptake and release of PVS to and from the Au NPs "sponge", respectively, is followed by CdSe/ZnS quantum dots, acting as an auxiliary photonic label.     

A quantitative, real-time assessment of binding of peptides and proteins to gold surfaces

Interactions of peptides and proteins with inorganic surfaces are important to both natural and artificial systems; however, a detailed understanding of such interactions is lacking. In this study, we applied new approaches to quantitatively measure the binding of amino acids and proteins to gold surfaces. Real‐time surface plasmon resonance (SPR) measurements showed that TEM1‐β‐lactamase inhibitor protein (BLIP) interacts only weakly with Au nanoparticles (NPs). However, fusion of three histidine residues to BLIP (3H‐BLIP) resulted in a significant increase in the binding to the Au NPs, which further increased when the histidine tail was extended to six histidines (6H‐BLIP). Further increasing the number of His residues had no effect on the binding. A parallel study using continuous (111)‐textured Au surfaces and single‐crystalline, (111)‐oriented, Au islands by ellipsometry, FTIR, and localized surface plasmon resonance (LSPR) spectroscopy further confirmed the results, validating the broad applicability of Au NPs as model surfaces. Evaluating the binding of all other natural amino acid homotripeptides fused to BLIP (except Cys and Pro) showed that aromatic and positively‐charged residues bind preferentially to Au with respect to small aliphatic and negatively charged residues, and that the rate of association is related to the potency of binding. The binding of all fusions was irreversible. These findings were substantiated by SPR measurements of synthesized, free, soluble tripeptides using Au‐NP‐modified SPR chips. Here, however, the binding was reversible allowing for determination of binding affinities that correlate with the binding potencies of the related BLIP fusions. Competition assays performed between 3H‐BLIP and the histidine tripeptide (3 His) suggest that Au binding residues promote the adsorption of proteins on the surface, and by this facilitate the irreversible interaction of the polypeptide chain with Au. The binding of amino acids to Au was simulated by using a continuum solvent model, showing agreement with the experimental values. These results, together with the observed binding potencies and kinetics of the BLIP fusions and free peptides, suggest a binding mechanism that is markedly different from biological protein–protein interactions.     

Electrochemical Recognition of Chiral Molecules with Poly(4‐bromoaniline) Modified Gold Electrode

A poly(4‐bromoaniline) (PBA) film is electrochemically synthesized on a gold electrode for the recognition of amino acids enantiomers. Scanning electron microscopy measurements show that the porous PBA films are made up of nano‐ribbons. At the PBA modified Au electrode differential pulse voltammograms of L ‐ and D ‐glutamic acids not only have very different current densities, but also produce different waveforms, providing an intuitive way to differentiate the two chiral molecules. Similar results are obtained in analyzing L ‐ and D ‐aspartic acids. Control experiments suggest that the observed sensing behavior arises from synergistic interactions between Au and the PBA film, where polymerization at the meta‐position creates a steric structure needed for differentiating chiral molecules.     

One Step Fabrication of Au Nanoparticles‐Ni‐Al Layered Double Hydroxide Composite Film for the Determination of L‐Cysteine

This paper reports the fabrication of Au nanoparticles (Au NPs)‐Ni‐Al layerd double hydroxide (LDH) composite film by one step electrochemical deposition on the surface of a glass carbon electrode from the mixture solution containing HAuCl₄ and nitrate salts of Ni²⁺ and Al³⁺. Improved conductivity was obtained by Au NPs codeposited on LDH film. The synergic effect of LDHs and Au NPs dramatically improves the performance of L ‐cysteine electro‐oxidation, displaying low oxidation peak potential (0.16 V) and high current response. Thus the electrode was used to sense L ‐cysteine, showing good sensitivity and selectivity.     

Chiral Recognition Sites Converted from Tetrapeptide Derivatives Adopting Racemates as Print Molecules

Molecularly imprinted polymeric membranes were prepared from polystyrene resin bearing tetrapeptide derivatives H‐Asp(OcHex)‐Leu‐Asp(OcHex)‐Glu(OBzl)‐OCH₂‐ (DLDE) consisting of D ‐amino acid residues or L ‐amino acid residues. The tetrapeptide derivatives were converted into chiral recognition sites by using not only an optically pure Boc‐Trp but also racemic Boc‐Trps as a print molecule. The chiral recognition ability depends on the combination of the absolute configuration of the print molecule and that of constituting amino acid residues. The membrane prepared from a DLDE derivative consisting of D ‐amino acid residues and imprinted by Boc‐D ‐Trp recognized the D ‐isomer in preference to the corresponding L ‐isomer and vice versa. In the present study, it was also made clear that racemic print molecules were effective in generating chiral recognition sites. The affinity constant of the generated chiral recognition site was determined to be 9.6 × 10³ mol^?1 · dm³, which was independent of the molecular imprinting conditions. Enantioselective permeation was attained by applying electrodialysis. An optimum permselectivity of 5.9, which corresponds to the adsorption selectivity, was attained.

Summary of the molecularly imprinted polymeric membranes studied.     

Optical resolution of racemic amino acid derivatives with molecularly imprinted membranes bearing oligopeptide tweezers

Molecularly imprinted polymeric membranes were prepared from various oligopeptide tweezers by the adoption of N‐α‐tert‐butoxycarbonyl‐D ‐tryptophan (Boc‐D ‐Trp) or N‐α‐tert‐butoxycarbonyl‐L ‐tryptophan (Boc‐L ‐Trp) as a print molecule. The chiral recognition ability of the formed molecular recognition sites was dependent on the absolute configuration of the print molecule adopted in the membrane preparation (molecular imprinting) process, whereas the candidate oligopeptide tweezers consisted of the L ‐amino acid residues. In other words, the membranes imprinted by the D ‐isomer recognized the D ‐isomer in preference to the corresponding L ‐isomer, and vice versa. The affinity constant between the target molecule and the chiral recognition site from the oligopeptide tweezers was higher than that from a single‐strand oligopeptide derivative. Those membranes selectively transported the enantiomer, which was preferentially incorporated into the membrane by dialysis. The permselectivities for these membranes exceeded their adsorption selectivities. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 385–396, 2005     

Efficient synthesis of molecularly imprinted polymers with bio‐recognition sites for the selective separation of bovine hemoglobin

We developed a facile approach to the construction of bio‐recognition sites in silica nanoparticles for efficient separation of bovine hemoglobin based on amino‐functionalized silica nanoparticles grafting by 3‐aminopropyltriethoxylsilane providing hydrogen bonds with bovine hemoglobin through surface molecularly imprinting technology. The resulting amino‐functionalized silica surface molecularly imprinted polymers were characterized using scanning electron microscope, transmission electronic microscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and thermogravimetric analysis. Results showed that the as‐synthesized imprinted polymers exhibited spherical morphology and favorable thermal stability. The binding adsorption experiments showed that the imprinted polymers can reach equilibrium within 1 h. The Langmuir isotherm and pseudo‐second‐order kinetic model fitted the adsorption data well. Meanwhile, the imprinted polymers possessed a maximum binding capacity up to 90.3 mg/g and highly selectivity for the recognition of bovine hemoglobin. Moreover, such high binding capacity and selectivity retained after eight cycles, indicating the good stability and reusability of the imprinted polymers. Finally, successful application in the selective recognition of bovine hemoglobin from a real bovine blood sample indicated that the imprinted polymers displayed great potentials in efficient purification and separation of target proteins.     

Pendant structure governed anion sensing property for sulfonamide‐functionalized poly(phenylacetylene)s bearing various α‐amino acids

The colorimetric detection of anionic species has been studied for α‐amino acid‐conjugated poly(phenylacetylene)s, which were prepared by the polymerization of the ethyl esters of N‐(4‐ethynylphenylsulfonyl)‐L ‐alanine, L ‐isoleucine, L ‐valine, L ‐phenylalanine, L ‐aspartic acid, and L ‐glutamic acid using Rh⁺(2,5‐norbornadiene)[(η⁶‐C₆H₅)B^?(C₆H₅)₃] as the catalyst in CHCl₃. The one‐handed helical conformations of all the sulfonamide‐functionalized polymers were characterized by Cotton effects in the circular dichroism spectra. The addition of anions with a relatively high basicity, such as tetra‐n‐butylammonium acetate and fluoride, induced drastic changes in both the optical and chiroptical properties. On the other hand, anions with a relatively low basicity, such as tetra‐n‐butylammonium nitrate, azide, and bromide, had essentially no effects on the helical conformation of all the sulfonamide‐functionalized polymers. The anion signaling property of the sulfonamide‐functionalized polymers possessing α‐amino acid moieties was significantly affected by the installed residual amino acid structures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1683–1689, 2010     

Photoirradiation surface molecularly imprinted polymers for the separation of 6‐O‐α‐d‐maltosyl‐β‐cyclodextrin

Photoirradiation surface molecularly imprinted polymers for the separation of 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin were synthesized using functionalized silica as a matrix, 4‐(phenyldiazenyl)phenol as a light‐sensitive monomer, and 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin as a template. Fourier transform infrared spectroscopy results indicated that 4‐(phenyldiazenyl)phenol was grafted onto the surface of functionalized silica. The obtained imprinted polymers exhibited specific recognition toward 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin. Equilibrium binding experiments showed that the photoirradiation surface molecularly imprinted polymers obtained the maximum adsorption amount of 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin at 20.5 mg/g. In binding kinetic experiments, the adsorption reached saturation within 2 h with binding capacity of 72.8%. The experimental results showed that the adsorption capacity and selectivity of imprinted polymers were effective for the separation of 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin, indicating that imprinted polymers could be used to isolate 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin from a conversion mixture containing β‐cyclodextrin and maltose. The results showed that the imprinted polymers prepared by this method were very promising for the selective separation of 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin.     

Hydrophobic Cysteine Poly(disulfide)‐based Redox‐Hypersensitive Nanoparticle Platform for Cancer Theranostics

Selective tumor targeting and drug delivery are critical for cancer treatment. Stimulus‐sensitive nanoparticle (NP) systems have been designed to specifically respond to significant abnormalities in the tumor microenvironment, which could dramatically improve therapeutic performance in terms of enhanced efficiency, targetability, and reduced side‐effects. We report the development of a novel L ‐cysteine‐based poly (disulfide amide) (Cys‐PDSA) family for fabricating redox‐triggered NPs, with high hydrophobic drug loading capacity (up to 25 wt % docetaxel) and tunable properties. The polymers are synthesized through one‐step rapid polycondensation of two nontoxic building blocks: L ‐cystine ester and versatile fatty diacids, which make the polymer redox responsive and give it a tunable polymer structure, respectively. Alterations to the diacid structure could rationally tune the physicochemical properties of the polymers and the corresponding NPs, leading to the control of NP size, hydrophobicity, degradation rate, redox response, and secondary self‐assembly after NP reductive dissociation. In vitro and in vivo results demonstrate these NPs’ excellent biocompatibility, high selectivity of redox‐triggered drug release, and significant anticancer performance. This system provides a promising strategy for advanced anticancer theranostic applications.     

Electrochemically controlled assembly and logic gates operations of gold nanoparticle arrays

The reversible assembly of β-cyclodextrin-functionalized gold NPs (β-CD Au NPs) is studied on mixed self-assembled monolayer (SAM), formed by coadsorption of redox-active ferrocenylalkylthiols and n-alkanethiols on gold surfaces. The surface coverage and spatial distribution of the β-CD Au NPs monolayer on the gold substrate are tuned by the self-assembled monolayer composition. The binding and release of β-CD Au NPs to and from the SAMs modified surface are followed by surface plasmon resonance (SPR) spectroscopy. The redox state of the tethered ferrocene in binary SAMs controls the formation of the supramolecular interaction between ferrocene moieties and β-CD-capped Au NPs. As a result, the potential-induced uptake and release of β-CD Au NPs to and from the surface is accomplished. The competitive binding of β-CD Au NPs with guest molecules in solution shifted the equilibrium of the complexation-decomplexation process involving the supramolecular interaction with the Fc-functionalized surface. The dual controlled assembly of β-CD Au NPs on the surface enabled to use two stimuli as inputs for logic gate activation; the coupling between the localized surface plasmon, associated with the Au NP, and the surface plasmon wave, associated with the thin metal surface, is implemented as readout signal for "AND" logic gate operations.     

Highly Stereoselective Recognition and Deracemization of Amino Acids by Supramolecular Self‐Assembly

The highly stereoselective supramolecular self‐assembly of α‐amino acids with a chiral aldehyde derived from binol and a chiral guanidine derived from diphenylethylenediamine (dpen) to form the imino acid salt is reported. This system can be used to cleanly convert D ‐amino acids into L ‐amino acids or vice versa at ambient temperature. It can also be used to synthesize α‐deuterated D ‐ or L ‐amino acids. A crystal structure of the ternary complex together with DFT computation provided detailed insight into the origin of the stereoselective recognition of amino acids.     

Reconstituted Enzymes on Electropolymerizable FAD‐Modified Metallic Nanoparticles: Functional Units for the Assembly of Effectively “Wired” Enzyme Electrodes

Au nanoparticles are functionalized with thioaniline electropolymerizable units and mercaptophenyl boronic acid ligands. Flavin adenine dinucleotide (FAD) is linked to the boronic acid ligands and apo‐glucose oxidase, apo‐GOx, is reconstituted on the FAD cofactor units to yield enzymes in a structurally‐aligned configuration in respect to the Au NPs. Electropolymerization of the enzyme‐functionalized Au NPs on a thioaniline‐modified Au electrode yields a three‐dimensional bis‐aniline‐crosslinked Au NPs/reconstituted glucose oxidase matrix on the electrode that reveals effective electrical contacting with the electrode.     

Chiral SiO2 and Ag@SiO2 Materials Templated by Complexes Consisting of Comblike Polyethyleneimine and Tartaric Acid

A facile avenue to fabricate micrometer‐sized chiral (L ‐, D ‐) and meso‐like (dl ‐) SiO₂ materials with unique structures by using crystalline complexes (cPEI/tart), composed of comblike polyethyleneimine (cPEI) and L ‐, D ‐, or dl ‐tartaric acid, respectively, as catalytic templates is reported. Interestingly, both chiral crystalline complexes appeared as regularly left‐ and right‐twisted bundle structures about 10 μm in length and about 5 μm in diameter, whereas the dl ‐form occurred as circular structures with about 10 μm diameter. Subsequently, SiO₂@cPEI/tart hybrids with high silica content (>55.0 wt %) were prepared by stirring a mixture containing tetramethoxysilane (TMOS) and the aggregates of the crystalline complexes in water. The chiral SiO₂ hybrids and calcined chiral SiO₂ showed very strong CD signals and a nanofiber‐based morphology on their surface, whereas dl ‐SiO₂ showed no CD activity and a nanosheet‐packed disklike shape. Furthermore, metallic silver nanoparticles (Ag NPs) were encapsulated in each silica hybrid to obtain chiral (D and L forms) and meso‐like (dl form) Ag@SiO₂ composites. Also, the reaction between L ‐cysteine (Lcys) and these Ag@SiO₂ composites was preliminarily investigated. Only chiral L ‐ and D ‐Ag@SiO₂ composites promoted the reaction between Lcys and Ag NPs to produce a molecular [Ag–Lcys]_n complex with remarkable exciton chirality, whereas the reaction hardly occurred in the case of meso‐like (dl ‐) Ag@SiO₂ composite.     

β‐Cyclodextrin‐Functionalized Gold Nanoparticles/Poly(L‐cysteine) Modified Glassy Carbon Electrode for Sensitive Determination of Metronidazole

A simple electrochemical method was developed to determine metronidazole based on β‐cyclodextrin‐functionalized gold nanoparticles/poly(L ‐cysteine) modified glassy carbon electrode (β‐CD‐GNPs/poly(L ‐cys)/GCE). The electropolymerized film of poly(L ‐cys) provides a stable matrix for the fabrication of a sensing interface. β‐CD‐GNPs can form inclusion complexes with metronidazole and act as a modifier with catalytic function. The modified electrode exhibited excellent electrocatalytic activity towards metronidazole. The reaction of metronidazole at the modified electrode was an irreversible process controlled by diffusion. Under optimum experimental conditions, the logarithm of catalytic currents shows a good linear relationship with that of the metronidazole concentration in the range of 0.1–600 µmol/L with a low detection limit of 14 nmol/L. In addition, the modified electrode exhibited satisfactory stability, sensitivity and reproducibility, and could be applied to the determination of metronidazole in an injection solution.     

In-situ polymerized molecularly imprinted polymeric thin films used as sensing layers in surface plasmon resonance sensors: Mini-review focused on 2010–2011

This review provides a short overview of polymeric thin films incorporating molecular imprints within their 3D macromolecular structure as synthetic recognition elements and prepared by in situ polymerization for surface plasmon resonance application. This review starts with a brief reminder of the principle of surface plasmon resonance detection. The second section is focused on molecularly imprinted materials. Bulk and thin film polymer formats can be obtained by free radical polymerization, where the functional monomer interacts specifically with the template and the cross-linker controls the rigidity of the imprinted cavities. Grafting polymerization is presented as a method of choice for covalent attachment of ultra-thin molecularly imprinted films on a surface plasmon resonance metallic substrate. Examples of electropolymerized thin films are also provided. In the rest of this contribution, surface plasmon resonance applications of molecularly imprinted polymers reported mainly over the last two years are presented with respect to the preparation mode. Also, applications of gold nanoparticle/molecularly imprinted polymer composites for the design of surface plasmon resonance-based sensors with enhanced sensitivity due to the phenomenon of localized surface plasmon resonance induced by the presence of gold nanoparticles are summarized.     

Poly(γ‐benzyl‐L‐glutamate)‐functionalized single‐walled carbon nanotubes from surface‐initiated ring‐opening polymerizations of N‐carboxylanhydride

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate) (PBLG) by ring‐opening polymerizations of γ‐benzyl‐L ‐glutamic acid‐based N‐carboxylanhydrides (NCA‐BLG) using amino‐functionalized SWCNTs (SWCNT‐NH₂) as initiators. The SWCNT functionalization has been verified by FTIR spectroscopy and transmission electron microscopy. The FTIR study reveals that surface‐attached PBLGs adopt random‐coil conformations in contrast to the physically absorbed or bulk PBLGs, which exhibit α‐helical conformations. Raman spectroscopic analysis reveals a significant alteration of the electronic structure of SWCNTs as a result of PBLG functionalization. The PBLG‐functionalized SWCNTs (SWCNT‐PBLG) exhibit enhanced solubility in DMF. Stable DMF solutions of SWCNT‐PBLG/PBLG with a maximum SWCNTs concentration of 259 mg L^?1 can be readily obtained. SWCNT‐PBLG/PBLG solid composites have been characterized by differential scanning calorimetry, thermogravimetric analysis, wide/small‐angle X‐ray scattering (W/SAXS), scanning electron microscopy, and polarized optical microscopy for their thermal or morphological properties. Microfibers containing SWCNT‐PBLG and PBLG can also be prepared via electrospinning. WAXS characterization reveals that SWCNTs are evenly distributed among PBLG rods in solution and in the solid state where PBLGs form a short‐range nematic phase interspersed with amorphous domains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2340–2350, 2010     

Preparation of Ag Nanowire @ Au Nanoparticle Hybrid Nanowires and their Influence on the Fluorescence Properties of P3HT

In this study, the galvanic displacement reaction between silver and AuCl₄⁻ was carried out to synthesize a series of silver nanowire (Ag NW) @ gold nanoparticle (Au NP) hybrid nanowires. The influence of Ag NW @ Au NP hybrid nanowires on the fluorescence properties of the poly (3‐hexylthiophene) (P3HT) was investigated. The particle sizes of Au NPs on the hybrid nanowires could be adjusted by varying the reaction time and the concentration of the HAuCl₄ solution. Furthermore, steady‐state fluorescence measurements showed that the fluorescence intensity of the P3HT films was higher on various Ag NW @ Au NP hybrid nanowires compared to that on a bare silicon substrate. This was due to the increase in the intensity of electromagnetic field by the localized surface plasmon resonances of Au NPs and surface plasmon polaritons of Ag NWs from the hybrid nanowires. The results were further confirmed by the Raman spectra of the P3HT films on different substrates.     

Selective and Sensitive Electrochemical Sensor for L‐Methionine at Physiological pH Using Functionalized Triazole Polymer Film Modified Electrode

This communication describes the determination of an essential amino acid, L ‐methionine (L ‐Met) in the presence of important interferents, ascorbic acid (AA) and uric acid (UA) at physiological pH using a glassy carbon electrode modified with an electropolymerized film of 3‐amino‐5‐mercapto‐1,2,4‐triazole (p‐AMTa). The bare glassy carbon electrode fails to show a voltammetric signal for L ‐Met in the presence of AA and UA at pH 7.2. However, the p‐AMTa electrode separates the voltammetric signals of AA, UA and L ‐Met with pronounced oxidation currents. The amperometric current of L ‐Met was increased linearly from 1.0×10^?7 to 1×10^?4 M and the detection limit was found to be 4.12×10^?10 M (S/N=3).     

An Amperometric Immunosensor Based on Layer‐by‐Layer Assembly of L‐Cysteine and Nanosized Prussian Blue on Gold Electrode for Determination of Human Chorionic Gonadotrophin

A novel amperometric immunosensor based on L ‐cysteine/nanosized Prussian blue bilayer films ({NPB/L ‐cys}₂) and gold nanoparticles (nano‐Au) was fabricated for determination of human chorionic gonadotrophin (HCG). First, L ‐cys and NPB was self‐assembled by layer‐by‐layer (LBL) technology to form {NPB/L ‐cys}₂ bilayer films on the gold electrode. Subsequently, nano‐Au layer was immobilized on the {NPB/L ‐cys}₂ bilayer films by electrodepositing gold chloride tetrahydrate and then anti‐HCG was assembly on the nano‐Au layer. Finally hemoglobin (Hb) was employed to block sites against nonspecific binding. With the electrocatalytic ability of Hb and NPB for the reduction of H₂O₂, the current signal of the antigen‐antibody reaction was amplified and the enhanced sensitivity was achieved. In this study, the assembly process and performance of the immunosensor were characterized by cyclic voltammetry (CV) and the morphology was researched by scanning electron microscopy (SEM). The immunosensor performed a high sensitivity and a wide linear response to HCG in two ranges from 0.5 to 10 mIU/mL and from 10 to 200 mIU/mL with a relatively low detection limit of 0.2 mIU/mL at 3 times the background noise, as well as good stability and long‐term life.