Marta Elena Díaz-García

Multifunctional nanoparticles: Analytical prospects

Abstract Multifunctional nanoparticles are among the most exciting nanomaterials with promising applications in analytical chemistry. These applications include (bio)sensing, (bio)assays, catalysis and separations. Although most of these applications are based on the magnetic, optical and electrochemical properties of multifunctional nanoparticles, other aspects such as the synergistic effect of the functional groups and the amplification effect associated with the nanoscale dimension have also been observed. Considering not only the nature of the raw material but also the shape, there is a huge variety of nanoparticles. In this review only magnetic, quantum dots, gold nanoparticles, carbon and inorganic nanotubes as well as silica, titania and gadolinium oxide nanoparticles are addressed. This review presents a narrative summary on the use of multifuncional nanoparticles for analytical applications, along with a discussion on some critical challenges existing in the field and possible solutions that have been or are being developed to overcome these challenges.

Molecularly Imprinted Polymers and Optical Sensing Applications

ABSTRACT The development of optical sensing approaches for analytes of biological, industrial, or environmental concern has reached an enormous significance. Different natural systems such as enzymes or antibodies have been employed in the development of these kind of sensors, but they often lack of stability. Molecular imprinting has become a universal tool for preparation of artificial and robust recognition materials mimicking natural systems. Molecular imprinting polymers (MIPs) are easily obtained by copolymerization of suitable functional monomers and crosslinkers in the presence of the target molecule. These polymers exhibit a tremendous thermal, chemical, and mechanical stability besides having selectivity similar to that of natural systems. Here we report an overview of molecular imprinting technique focussed to its sensing applications, emphasizing those systems based on an optical transduction.

Sol–gel immobilized room-temperature phosphorescent metal-chelate as luminescent oxygen sensing material

Abstract The chelate formed by 8-hydroxy-7-iodo-5-quinolinesulfonic acid (ferron) with aluminium exhibits strong room-temperature phosphorescence (RTP) when retained on a solid support. In a previous paper we have found that sol–gel technology is a very useful approach for developing RTP optical sensors as a new way to immobilize lumiphors. Sol–gel active phases proved to exhibit a high physical rigidity that enhanced relative RTP intensities and triplet lifetimes of the immobilized probe. In this paper we present an optical sensing phase prepared using the Al–ferron chelate which displays RTP entrapped in a sol–gel glass matrix for the determination of very low levels of oxygen both dissolved in water and organic solvents and in gaseous media. The sol–gel sensing material has proved to be chemically stable for at least 6 months under ambient storage conditions. Besides a high reproducibility in the formation of the sensing materials and no leaching or bleaching of the trapped reagent (neither in the gas phase nor in water or organic solvents) was observed. Oxygen was determined by continuous flow and flow injection methods using both intensity and triplet lifetime measurements. Both methods provided a fast response, good reproducibility and detection limits of 0.0005% (v/v) in the gas phase and

Flavonol fluorescent flow-through sensing based on a molecular imprinted polymer

Molecular imprinting has become a universal tool for the preparation of artificial and robust recognition materials useful for diagnostics, industry and environmental analysis. Molecular imprinting polymers (MIPs) are easily obtained by copolymerization of suitable functional monomers and cross-linkers in presence of the desired molecule. In this work, an MIP selective for 3-hydroxyflavone (flavonol) has been prepared. Various polymerization conditions were examined in order to determine their influence on the binding strength and selectivity of the binding materials. Finally, this MIP has been utilized as a recognition element in a flow-through optosensing system with fluorescence detection, showing desirable sensitivity and selectivity characteristics.

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.

FLUORIMETRIC MONITORING OF MOLECULAR IMPRINTED POLYMER RECOGNITION EVENTS FOR ALUMINIUM

ABSTRACT Novel molecular imprints were prepared against aluminium. Sensing materials were prepared via non-covalent imprinting technique, using the aluminium(III)–morin chelate as the template. Based on the fluorescent properties of the chelate, it was possible to design a selective optical flow-through sensor for Al3+. The affinity of the polymer binding sites was higher for aluminium than for other di- and trivalent ions (e.g., Be2+, Ca2+, Mg2+, Eu3+, Zn2+, Fe3+), suggesting that the nature of the metal ion, its ionic radius, and the metal–morin stoichiometry play important roles in the ionic recognition.

Room temperature phosphorescence optosensor for tetracyclines

Abstract A flow-through optosensor for tetracyclines based on the tetracycline-europium chelate room temperature phosphorescence energy transfer is proposed. The sensor is developed in conjunction with a flow-injection analysis system and is based on the transient immobilization on a non-ionic resin (packed in a flow-through cell) of the tetracycline-europium chelate. The analytical performance characteristics of the proposed sensor for semiautomated analysis and control of very low levels of tetracycline were as follows: the detection limits for tetracycline, oxytetracycline and chlortetracycline were 0.25, 0.30 and 0.40 ng ml −1 , respectively, with a relative standard deviation of 1% for determination of 0.24 μ ml −1 of each antibiotic ( n = 10). Most of the common meta ions in biological samples did not interfere, except Fe(III) which caused serious interference and should be masked with 1,10-phenanthroline. The recommended method has been successfully tested for determination of tetracyclines in clinical samples (urine and pharmaceutical preparations).

Fluorimetric flow injection and flow-through sensing systems for cyanide control in waste water

The high toxicity of cyanide and its great variety of uses in industrial processes make it necessary to develop sensitive and selective on-line methods for its determination in natural and waste waters. In this work, a flow injection analysis (FIA) system for cyanide determination was first developed and then experiments were performed in order to develop a flow-through sensing approach. Both systems are based on the interaction between the non-fluorescent copper–calcein complex and cyanide. The analytical features of the FIA system are: linear dynamic range from the quantification limit up to 0.4 mM CN− , detection limit 4 × 10−3 mM CN−, relative standard deviation 1.2% and sampling frequency 30 h−1 in the FIA system. The analytical figures for the flow-through approach were linear dynamic range from the quantification limit up to 0.2 mM CN−, detection limit 5 × 10−4 mM CN−, relative standard deviation 3.7% and sampling frequency 10 h−1. Interference studies were performed with typical cations and anions present in natural and waste waters. The proposed methodologies were applied to cyanide determination in natural water samples and in samples coming from an industrial bioreactor in order to evaluate its effectiveness in the biological cyanide degradation process of metallurgical waste waters.

Determination of Thiocyanate within Physiological Fluids and Environmental Samples: Current Practice and Future Trends

As the toxicological and physiological importance of thiocyanate has become more and more evident during the past 20 years, there has been an increasing interest in this anion. Thiocyanate is a detoxication product of cyanide and its content in human saliva is considered as a biomarker for identification of nonsmokers and smokers. Chronically elevated levels of thiocyanate in body fluids are known to be toxic and its relation to local goiter, vertigo, or unconciousness has been pointed out. On the other hand, thiocyanate-containing waste discharged into rivers is harmful to aquatic life due to its degradation to cyanide in the presence of oxidants. Therefore, precise knowledge of the thiocyanate content in biological fluids and environmental samples is mandatory. An overview of the existing analytical methodologies for thiocyanate is presented and their advantages and limitations are highlighted. This review is intended not only to provide a comparison of the different methods employed, but also to make it possible for the interested reader to quickly find developments and relevant work that have transpired over the past 10 years.

Selective fluorescent chemosensor for fructose

A chemosensing system for the selective recognition of fructose based on a reverse photoinduced electron transfer process was developed. A fluorescent boronic acid, m-dansylaminophenylboronic acid, reacts with fructose to produce an electron transfer, which results in the fluorescence quenching of the dye. The addition of the sugar shifted the pKa from 8.13 to 7.80. A possible sensing mechanism is proposed. The analytical figures determined in a batch approach were detection limit 5 × 10–6M, repeatability of 1% at the 1 × 10–4M fructose level and linear calibration up to 3 × 10–4M. A flow injection system was also examined and after the experimental conditions had been optimized a selectivity study showed that only galactose (at a 1:2 fructose to galactose molar ratio) gave a positive deviation. Several food samples were analysed by the proposed flow injection procedure and the results agreed with those obtained using an enzymatic kit for food analysis.