Stimuli Response of Eu3+-Based Metallo-Supramolecular Polymers toward Pharmaceutical Amines.

Metallo-supramolecular polymers offer a highly controllable platform for sensing. Their modular characteristics obtained by the ability of varying both building blocks, the metal ion and the organic ligand, provide tunability of their optical and chemical properties. Specifically, polymers based on lanthanide ions and conjugated aromatic ligands exhibit enhanced luminescence properties that can be altered by external stimulation. Herein, using europium-based polymers, we demonstrate the ability to detect different pharmaceutical amines, including in complex biological media, based on their luminescence quenching efficiency as a result of their polymer dissociation capacity. A combination of absorption, luminescence, and NMR measurements reveals combined static and dynamic quenching mechanisms that enable selective sensing of strong basic amines with high pKa values.

Core-shell nanoparticles for gas phase detection based on silver nanospheres coated with a thin molecularly imprinted polymer adsorbed on a chemiresistor.

We present a novel gas phase detection prototype based on assembling core-shell nanospheres made of a silver core and coated with a molecularly imprinted polymer (MIP) adsorbed onto an interdigitated array (IDA) electrode chemiresistor (CR). The core-shell nanospheres, AgNP@MIPs, were imprinted with linalool, a volatile terpene alcohol, as a model system. The thickness of the MIP layer was tuned to a few nanometers to enable the facile ingress and egress of the linalool, as well as to enhance the electrical transduction through the Ag core. The AgNP@MIPs were spread onto the IDA-CR modified with various positively charged polymers, by drop casting and dip-coating. The AgNP@MIPs were characterized by various techniques such as extra high-resolution scanning and tunnelling electron microscopy and X-ray diffraction. The MIP recognition event was transduced into a measurable increase in the resistance. The response to linalool exposure and removal was fast and the device was fully recovered and could be reused. Finally, the difference in the resistance change between imprinted and non-imprinted nanospheres was substantial.

Highly Stable Lyophilized Homogeneous Bead-Based Immunoassays for On-Site Detection of Bio Warfare Agents from Complex Matrices.

This study shows the development of dry, highly stable immunoassays for the detection of bio warfare agents in complex matrices. Thermal stability was achieved by the lyophilization of the complete, homogeneous, bead-based immunoassay in a special stabilizing buffer, resulting in a ready-to-use, simple assay, which exhibited long shelf and high-temperature endurance (up to 1 week at 100 °C). The developed methodology was successfully implemented for the preservation of time-resolved fluorescence, Alexa-fluorophores, and horse radish peroxidase-based bead assays, enabling multiplexed detection. The multiplexed assay was successfully implemented for the detection of Bacillus anthracis, botulinum B, and tularemia in complex matrices.

Gold fibers as a platform for biosensing.

A new form of high surface bioelectrode based on electrospun gold microfiber with -immobilized glucose oxidase was developed. The gold fibers were prepared by electroless deposition of gold nanoparticles on a poly(acrylonitrile)-HAuCl(4) electrospun fiber. The material was characterized using electron microscopy, XRD and BET, as well as cyclic voltammetry and biochemical assay of the immobilized enzyme. The surface area of the gold microfibers was 2.5 m(2)/g. Glucose oxidase was covalently crosslinked to the gold surface using cystamine monolayer and glutardialdehyde, and portrayed characteristic catalytic currents for oxidizing glucose using a ferrocene methanol mediator. Limit of detection of glucose is 0.1 mM. The K(m) of the immobilized enzyme is 10 mM, in accordance with other reports of immobilized glucose oxidase. The microfiber electrode was reproducible and showed correlation between fiber weight, cathodic current and enzymatic loading.

Electrospun gold nanofiber electrodes for biosensors.

A new form of high surface area bioelectrode, based on nanofibers of electrospun gold with immobilized fructose dehydrogenase, was developed. The gold fibers were prepared by electroless deposition of gold nanoparticles on an electrospun poly(acrylonitrile)-HAuCl(4) fiber. The material was characterized using electron microscopy, XRD and BET, as well as cyclic voltammetry and biochemical assay of the immobilized enzyme. The electrochemical surface area of the gold microfibers was 0.32 ± 0.04 m(2)/g. Fructose dehydrogenase was covalently coupled to the gold surface through glutaraldehyde crosslinks to a cystamine monolayer. The enzyme exhibited mediated electron transfer directly to the gold electrode and catalytic currents characteristic of fructose oxidation in the presence of a ferrocene methanol mediator were observed. The limit of detection of fructose was 11.7 µM and the K(M) of the immobilized enzyme was 5mM. The microfiber electrode was stable over 20 cycles with a 3.05% standard deviation. The response time of the sensor was less than 2.2s and reached half maximum value within 3.6s. The sensor was proven to be accurate and precise in both serum and popular beverages sweetened with high fructose corn syrup. The addition of glucose isomerase enabled the sensor to perform with glucose, thus expanding the available analyte selection for the sensor.

Kinetic study of the thermal inactivation of cholinesterase enzymes immobilized in solid matrices.

The thermal inactivation of immobilized cholinesterase enzymes (ChE) in solid matrices where the protein unfolding is blocked was studied, thus enabling investigation of the kinetics of the inactivation process directly from the native structure to the inactivated state. The thermal inactivation of butyrylcholinesterase (BChE), recombinant human acetylcholinesterase (rHuAChE), and eel acetylcholinesterase (AChE) enzymes was studied in dry films composed of poly(vinyl pyrollidone) (PVP), bovine serum albumin (BSA) and trehalose at 60 degrees -120 degrees C. The kinetics follows a bi-exponential decay equation representing a combination of fast and slow processes. The activation enthalpy DeltaH(#) and the activation entropy DeltaS(#) for each of the three enzymes have been evaluated. The values of DeltaH(#) for the fast process and for the slow process of BChE are 33+/-3, and 28+/-2 kcal/mol, respectively, and the values of DeltaS(#) are 0.84+/-0.04, and -18.2+/-0.5 cal/deg, respectively. The appropriate value of DeltaH(#) for rHuAChE is 26+/-2 Kcal/mol, for both processes and the values of DeltaS(#) are -17.6+/-0.9, and -23.0+/-0.9 cal/deg, respectively. Similarly, the values of DeltaH(#) for eelAChE are 30+/-3, 31+/-1 kcal/mol, and the values of DeltaS(#) are -6.7+/-0.5, -9.1+/-0.2 cal/deg respectively.

The investigation of water diffusion into teflon copolymer revealed by fiber-optic evanescent wave spectroscopy.

Fiber-optic evanescent wave infrared spectroscopy was used for the study of water diffusion in Teflon and has provided valuable information about the structure of water in amorphous hydrophobic polymers. Time-dependent absorption measurements were carried out in two spectral ranges: 3000-3800 cm(-1), associated with the O-H stretching mode, and 1620-1670 cm(-1), associated with the H-O-H bending mode of water. The results indicate that the IR spectra could be expressed as a superposition of spectra due to two species of water molecules: strongly and weakly hydrogen-bonded. We suggest that water molecules form clusters with strongly hydrogen-bonded molecules at the cores and with weakly hydrogen-bonded molecules at the external parts of the clusters. A mathematical model, based on a linear diffusion equation with a moving boundary, gave a ratio of 3.5 between the total number of molecules in a cluster and the number of water molecules at the core of the cluster.

The induction of chirality in sol-gel materials.

We review the different approaches that lead to chiral sol-gel materials. These methods include the use of silanes bearing a chiral group for silylating the surface of the porous sol-gel (SG) material, the use of such silanes as monomers or co-monomers in SG polycondensations, the physical entrapment of chiral molecules by SG procedures, the imprinting of SG materials with chiral templates and the creation of chiral pores, and the induction of chirality in the matrix skeleton itself. Analytical methods for detecting chirality are reviewed, including fluorescence methods, electrochemical methods, NMR, and induced CD. Applications are reviewed as well, including sensing, catalysis, chromatography, and optics. While most of the examples are focused on silicas and derivatized silicas, the methods and the analytical tools are generally applicable to other oxides and to preparation procedures other than sol-gel processes.

Chiral electrochemical recognition by very thin molecularly imprinted sol-gel films.

Thin films with enantioselective properties for electrochemically active chiral probes were developed. Enantioselectivity was accomplished via molecular imprinting. The films were fabricated through the sol-gel technique and were spin-coated on ITO electrodes. The chiral selectivity recognition was detected using two enantiomer pairs: D- and L-3,4-dihydroxyphenylalanine (D- and L-dopa) and (R)- and (S)-N,N'-dimethylferrocenylethylamine [(R)-Fc and (S)-Fc]. A defined chiral cavity was obtained by selection of functional monomers that interact with the template molecule, followed by its removal. Chiral selection properties were measured by cyclic voltammetry and square wave voltammetry. For both template molecules, very good chiral recognition was revealed by electrochemical measurement. The nonspecific adsorption measured for reference nonimprinted films was negligible (less than 5%). Dopa imprinted films revealed both high sensitivity, by the detection of 1 nM (0.2 ppb) concentration, and excellent selectivity, when challenged with a series of catechol derivatives. Fc-imprinted films were able to detect ca. 2 ppm of the target molecule, with very good enantioselectivity and low nonspecific adsorption. To our knowledge, this is the first report of successful molecular imprinting of a ferrocene derivative.

Enantioselective, chirally templated sol-gel thin films.

Enantioselective surfactant-templated thin films were fabricated through the sol-gel (SG) process. The enantioselectivity is general in the sense that it discriminates between pairs of enantiomers not used for the imprinting process. The chiral cationic surfactant (-)-N-dodecyl-N-methylephedrinium bromide (1) was used as the surfactant template, and after its extraction chiral domains were created. The chiral discriminative feature of these films was examined by challenging with pure enantiomer solutions for rebinding. Selective adsorption was shown using (R)- and (S)-propranolol, (R)-2 and (S)-2, respectively, and (R)- and (S)-2,2,2-trifluoro-1-(9-anthryl)ethanol, (R)-3 and (S)-3, respectively, as the chiral probes. The selective adsorption was measured by fluorescence analysis, and the chiral selectivity factors were found to be 1.6 for 2 and 2.25 for 3. In both cases, (R)-enantiomer was adsorbed preferably. The resulting material was characterized by transmission electron microscopy, by diffraction, and by surface area measurements, and was found to be semicrystalline with short-range ordered domains (50 A) of hexagonal symmetry.