Controlled release of nafcillin using biocompatible "dummy" molecularly imprinted sol-gel nanospheres.

Different silicon-based xero-gel molecularly imprinted spheres in the nano boundary range with recognition capabilities for nafcillin have been synthesised, using tetraethylorthosilicate (TEOS) and (3- aminopropyl) triethoxysilane (APTEOS) as precursors. Imprinting has been achieved using both nafcillin (NAF) or structural analogous 'dummies' such as (+)-6-aminopenicillenic acid (APA), or ampicillin ((+)-6- aminobenzylpenicillin)sodium salt (AMP). Materials were fully characterized using ATR-FTIR, (29)Si solidstate NMR, TGA, TEM and BET. Adsorption isotherms for all the materials fit with a continuous Freundlich model with correlation coefficients better than 0.988 and mean affinity constants between 10(5) and 10(6) L·mol(-1). The use of 'dummies' as well as the template itself in the imprinting process resulted in materials with different release speed. Combinations of these materials allow designing mixtures with a continuous, controlled and constant release longer than four days. Thus, the non-imprinted and the AMP-imprinted material have a rapid release during the first five hours, nafcillin and APA imprinted ones release antibiotic mainly after a latency-period of 24 hours.

Molecularly imprinted silica-silver nanowires for tryptophan recognition.

We report on silver nanowires (AgNWs) coated with molecularly imprinted silica (MIP SiO2) for recognition of tryptophan (Trp). The use of AgNWs as a template confers an imprinted material with adequate mechanical strength and with a capability of recognizing Trp due to its nanomorphology when compared to spherical microparticles with a similar surface-to-volume ratio. Studies on adsorption isotherms showed the MIP-SiO2-AgNWs to exhibit homogeneous affinity sites with narrow affinity distribution. This suggests that the synthesized material behaves as a 1D nanomaterial with a large area and small thickness with very similar affinity sites. Trp release from MIP-SiO2-AgNWs was demonstrated to be dominated by the diffusion rate of Trp as controlled by the specific interactions with the imprinted silica shell. Considering these results and the lack of toxicity of silica sol-gel materials, the material offers potential in the field of drug or pharmaceutical controlled delivery, but also in optoelectronic devices, electrodes and sensors.

Enhanced resonance light scattering properties of gold nanoparticles due to cooperative binding.

The interaction of 11-mercaptoundecanoic acid capped gold nanoparticles (MUA-GNPs) with europium ions and aminoacids has been studied by UV-Vis spectrophotometry, fluorescence, confocal fluorescence microscopy, resonance light scattering and TEM. Results demonstrated that hyper-Rayleigh scattering emission occurs upon the addition of lysine to the MUA-GNPs-Eu(III) system, thus providing an inherently sensitive method for lysine determination. The effects of geometrical factors of the gold nanoparticles (aspect ratio, particle size, cluster formation) and the surrounding medium (pH) on this behavior are discussed. The cooperative binding interactions of Eu(3+) and lysine with gold nanoparticles permitted the discrimination of lysine from other amino acids. The probable mechanism for the spectral changes and the enhanced resonance light scattering observed is outlined.

Synthesis of metallothionein-mimic decapeptides with heavy atom signaling properties.

The automated parallel solid-phase synthesis of a 17-member library of metallothionein-mimic decapeptides carrying a Lariat ether group is described. The peptides were synthesized in good yield and the identity and quality of each product were performed by mass spectrometry and IR. Subsequently, in the presence of europium(III) ions as fluorescent reporter, each compound was screened, both attached to the resin and cleaved off, for their sensing behavior towards metal ions (Cd(2+),Hg(2+), Cu(2+), Mg(2+) and Ca(2+)) using fluorimetric techniques. Several of these Cys-enriched synthetic peptides showed surprisingly low detection limits for Cd(2+) and Hg(2+). The analytical potential of these metallothionein-mimic decapeptides as metal ion recognition materials for sensor development is outlined. Finally, the sensing response mechanism, based on an energy transfer process and a metal ion allosteric interaction, is proposed.

Molecular imprinted ormosils for nafcillin recognition by room temperature phosphorescence optosensing.

Nafcillin imprinted sol-gels were used as specific binding materials for the room temperature phosphorescence (RTP) recognition of nafcillin using a flow injection system. Selective and reversible binding of the template to imprinted sol-gels could be observed by tailoring the hydrophobic/hydrophilic balance of the materials. Also, the possibility of minimizing non-specific interactions was evaluated by end-capping with trimethyl silyl groups. Control experiments were performed with non imprinted reference sol-gels. The recognition mechanism and the analytical potential of these materials for developing stable, selective and sensitive approaches for nafcillin recognition in real samples are outlined.

Library preparation of derivatives of 1,4,10,13-tetraoxa-7,16-diaza-cycloctadecane and their fluorescence behavior for signaling purposes.

In the present work, we report the library preparation on solid supports of 20 derivatives of 1,4,10,13-tetraoxa-7,15-diaza-cycloctadecane 1(a-e)(w,x,y,z) carrying a fluorescent dansyl group. The sensing fluorescence behavior of these materials toward alkali and alkali earth metal ions was studied by packing the beads into a conventional flow-through cell in a FIA (flow injection analysis) approach. The fluorescence emission of these materials' responses shows a fluorescence increase to Li+, Na+, K+, NH4+, Ca2+, and Mg2+ with maximum sensitivity for Mg2+ over the rest of the ions. The analytical potential of these materials is outlined, and the sensing response mechanism, based on a photoinduced electron-transfer process, is proposed.

Fluorometric monitoring of organic reactions on solid phase.

The direct monitoring of reaction progress on solid supports by fluorescence spectroscopy is described. An immobilized fluorescent tracer molecule (dansyl chloride) is used to monitor the reaction on OH resins (Argopore Wang, PS Wang, and Argogel Wang), both in batch and in parallel chemistry. Fluorescence measurements were obtained directly on solid phase. The method demonstrated to be a valuable tool for the quantitative determination of resin-bound hydroxyl groups, to study reaction kinetics and for continuously monitoring the progress of the conversion of the hydroxyl resins into the chlorinated ones. The procedure proposed is highly sensitive compared to the traditional ones. The system can be extended to monitor a variety of reactions on solid supports, and in conjunction with a well-established technique such as flow analysis, basic studies on solid-phase become possible.

Assessment of molecularly imprinted sol-gel materials for selective room temperature phosphorescence recognition of nafcillin.

Sol-gel imprinted materials were prepared against nafcillin, a semisynthetic beta-lactamic antibiotic employed in the treatment of serious infections caused by penicillinase-producing staphylococci. Two approaches were addressed for preparation of the imprinted materials and the controls: as conventional monoliths, which were ground and sieved to a desired particle size for rebinding analysis, and as films on supporting glass slides. The specific binding sites that are created during the imprinting process are analyzed via selective room temperature phosphorescence (RTP) (sol-gel films) measurements as well as via competitive room temperature phosphorescence ligand assay. Results demonstrated the importance of the physical configuration of the imprinted material for minimizing non-specific binding. The close similarities between the structures of different beta-lactamic antibiotics made it possible to interpret the roles of the template structure on specific molecular recognition. In this article, we introduce the use of room temperature phosphorescence as selective transduction method for the template. The imprinted sol-gel films displayed enhanced specific binding characteristics respect to the monolithic sol-gel and can be envisaged for the use as recognition matrices for the screening and rapid selection of antibiotics from a combinatorial library or for the rapid control of nafcillin in biological samples (e.g. milk, serum, urine).

Comparative study of the micellar enhanced spectrophotometric determination of beta-lactamic antibiotics by batch and flow injection analysis using a multisimplex design.

A study has been made on the spectrophotometric determination of the beta-lactamic antibiotics, amoxicillin and ampicillin, in micellar media using Cu ions as catalyst. Batch and flow injection approaches were compared. Multisimplex design was used to determine the optimal values of the flow injection analysis (FIA) system. Chemical (buffer, pH and Cu(II) concentrations) and physical (flow rate, temperature and reaction coil length) variables were considered. The analytical performance characteristics were as follows: the detection limits for batch and flow-through systems were 2.5 x 10(-7) and 2 x 10(-6) M, respectively, and a relative standard deviation less than 1% was found for both methods. The proposed FIA methodology was satisfactorily applied to the determination of the antibiotics in pharmaceutical formulations.

Fluorescent competitive flow-through assay for chloramphenicol using molecularly imprinted polymers.

It is a fact that molecular imprinting techniques have reached tremendous importance in the research of new artificial recognition systems. These methods resemble the mechanism of natural recognition, generally based on non-covalent interactions, but improving their stability by means of a simple and inexpensive technique. Molecular imprinting polymers (MIPs) are easily obtained by copolymerisation of suitable functional monomers and crosslinkers in the presence of the print molecule. Removal of the template leaves a polymer that selectively recognises it. In this work, different imprinted polymers for chloramphenicol (CAP) obtained using different monomers and polymerisation conditions were tested in a HPLC system, in order to obtain a highly selective material for CAP. The optimised MIP was then used as recognition phase in a fluorescent competitive flow assay to determine chloramphenicol.

Cyclodextrin-based optosensor for the determination of warfarin in waters.

A flow-through optosensor for warfarin is described. The sensor is developed in conjunction with flow analysis systems and uses a commercial bound beta-cyclodextrin material as the sensing phase. A strong fluorescence signal was observed as a result of the formation of an inclusion complex between warfarin and beta-cyclodextrin. The analytical performance characteristics of the proposed sensor for analysis of low levels of warfarin were as follows: the detection limits for continuous and flow injection analysis systems were 2 and 19 ppb, respectively; the observed relative standard deviations at 0. 5 ppm warfarin level were less than 2.3%. A study of the interference of other naphthalenic toxic substances was carried out. The continuous flow method was satisfactorily applied to the determination of the rodenticide in natural waters.

Kalman filtering-aided time-resolved solid-surface room temperature phosphorimetry for simultaneous determination of anthracyclines in solution.

Daunorubicin, doxorubicin and epirubicin react with EuIII to form complexes which exhibit analytically useful room temperature phosphorescence (RTP). The RTP features of the three complexes are similar and the RTP spectra completely overlap. However, their three phosphorescence decay rates are different, and these differences were utilized to analyse the time-resolved RTP data by Kalman filtering. Simultaneous quantification of all three complexes is demonstrated and a method is proposed for the simultaneous determination of the three anthracyclines in mixtures by RTP optosensing. The analytical errors observed are within +/- 5%.

Fluorescent organofilms for oxygen sensing in organic solvents using a fiber optic system.

Oxygen quenching of the luminescence of the tris(2,2'-bipyridyl)ruthenium(II) complex [Ru(bpy)3]2+, entrapped in gelatin-containing microemulsion-based organogels, has been shown to be an accurate and precise method for measuring oxygen concentrations in organic solvents (such as toluene, hexane and isooctane). Film composition was investigated in order to obtain sensing phases with high sensitivity to oxygen and suitable response times. Using a fiber optic design combined with a continuous flow system configuration, the dynamic response of oxygen-sensing films was less than 1 min for a full signal change. A detection limit of 0.2 ppm of oxygen in hexane-5% chloroform was found.

Room-temperature phosphorescent palladium-porphine probe for DNA determination.

Room-temperature phosphorescence (RTP) enhancement of a palladium-porphine complex by DNA was studied. Studies involving calf thymus DNA and calf liver RNA revealed that the Pd-porphine complex bound to double-stranded DNA displayed intense RTP, while a very weak RTP emission was observed in the presence of equal molar concentrations of RNA. This fact founded a basis for selective determination of DNA in the presence of RNA. Maximum phosphorescence was observed at pH 7, with maximum excitation and emission wavelengths at 435 and 680 nm, respectively. Under optimal experimental conditions, the calibration graphs were linear up to 6 × 10(-)(5) µM DNA. The detection limit was 5 × 10(-)(8) µM and the relative standard deviation (10 replicates) ±2.6% in the linear range. DNA extracted from human colon tissues could be successfully determined.

Enzyme catalysis in organic solvents: a promising field for optical biosensing.

The ability of enzymes to work in non-aqueous media offers new and almost unexploited possibilities for the development of new optical biosensors. The advantages of performing biocatalytic reactions in non-aqueous media are discussed in relation to their possible application in optical biosensor design. Attention is focused on the factors that influence enzymatic catalysis in organic solvents, including the role of enzyme-associated water, criteria for solvent selection and the alteration of enzyme specificity. Recent examples of relevant applications and future prospects of organic-phase optical biosensing are discussed.

Serum analysis for potassium ions using a fibre optic sensor.

A fibre optic potassium ion sensor has been developed based on reflectance measurements of the pH-dependent chromogenic crown ether 'Takagi reagent' immobilized on the non-ionic polymeric resin Amberlite XAD2. The sensor response is in the 1.5-100 mM range with a detection limit of 0.25 mM K+. The selectivity factor over sodium is 20. The proposed sensor works with a reproducibility of +/- 0.8% at the 5 mM K+ level. Advantageous design features include ease of construction, simplicity of use, reversibility, short response time (approximately 1 min) and an optimum working pH range (7.0-8.0) for biological fluids. This optical sensor was applied successfully to the direct determination of potassium in human serum. Aqueous potassium standards containing 0.13 M NaCl and a buffer of pH 8 were used for calibration.