Nanoparticles of Fluorescent Conjugated Polymers: Novel Ion-Selective Optodes.

A novel type of ion-selective nano-optode is proposed, in which a conjugated polymer is used as optical transducer and nanoprobe material. Thus, contrary to most of the proposed optodes, the response does not require presence of pH-sensitive dye in the sensor. The conjugated polymer nanosensor material is in partially oxidized form-it is bearing positive charges and its emission is quenched. The receptor is an optically silent uncharged ionophore selective for the analyte cation. When a binding event occurs, positive charges are formed in the nanosphere, leading to a decrease in the oxidation state of the polymer, in the absence of redox potential change, resulting in increased emission. This general approach herein proposed results in a simple sensor, benefitting from a novel optical transduction mechanism and high lipophilicity of the polymer matrix that results in linear responses over a broad concentration range of analyte. For the model system studied, the linear dependence of emission intensity on the logarithm of analyte (K(+)) concentration was obtained for a broad range from 10(-5) M to 0.1 M.

Alternating polymer micelle nanospheres for optical sensing.

A novel concept of nanosized fluorimetric sensors is proposed, using alternating polymers as self assembling micelles that can be crosslinked resulting in stable polymeric nanoparticles. The thus obtained nanospheres have sizes close to 250 nm or 130 nm, depending on the preparation procedure and the negative surface charge, due to the presence of carboxyl groups on the surface. By a simple procedure, the nanospheres can be effectively loaded with compounds of choice, e.g. ionophores and ion-exchangers previously used to induce ionic sensitivity in polyacrylate or poly(vinyl chloride) micro- and nanospheres (miniature optrodes), thus allowing for optical or fluorimetric quantification of analytes. As a proof of concept, H(+) sensitive colorimetric and fluorimetric sensors and K(+) fluorimetric sensors using classical optrode approach were prepared and tested. The obtained sensors were characterized by high sensitivity, fast and reversible responses. Both K(+) and H(+) sensors were characterized by a broad response range resulting from the significant effect of processes occurring on the surface of the nanospheres. Due to this effect, the fluorimetric responses of the obtained spheres are significantly different from those typically observed for miniature optrode systems, and were linear within a range of at least 5 logarithmic units of analyte concentration. As shown, the surface groups of the herein proposed nanospheres can be used for the covalent linking of fluorophores that can be used as markers (if applied alone) or as reference dyes for fluorescent ion-sensitive nanospheres.

Rational design of nanoptodes architecture - Towards multifunctional sensors.

Liposome type nano-optodes are reported. Probe architecture allows tailored - yet spontaneous - positioning of the reporter dye with chromophore group facing the sample solution. As a result the emission signal - related to competition between analyte cations and hydrogen ions, ultimately leading to deprotonation of chromoionophore and emission increase - can be read instantly after contact of the sensor with sample but also allows observation of optical signal in unique for these sensors days' time scale, without loss of intensity. Possibility of optode signal observation in days' time scale allows exploration of solvatochromic properties of applied chromoionophore group and estimation of sensor sample contact time as minute change in the position of chromophore group emission maximum.

Critical assessment of polymeric nanostructures used as colorimetric ions probes.

In this study the effect of nature of nanostructural materials used as colorimetric optical probes on the analytical performance of the resulting sensors is compared. Different effects related to the nanoprobe materials - probe structure and properties: surface charge and stability, but also effects related to the analyte - receptor interactions - complex formation kinetics and transport of ions from the sample to the probe were taken into account. Presence of charge on the nanostructural colorimetric sensor effectively hinders ions exchange between the probe and the sample, leading to a linear dependence of absorbance on logarithm of analyte concentration changes. Interestingly, both anionic and cationic micelles are offering linear dependence on logarithm of concentration, covering 2 logarithmic units. Nanostructures, e.g. prepared from amphiphilic polymer Pluronic F127, lead to absorbance dependence on concentration observed in rather narrow concentration range. In this respect crosslinked poly(maleic anhydride-alt-1-octadecene) nanostructures of pH tunable surface charge, due to the presence of carboxyl and amine group on the surface, seem an attractive alternative, offering also the lowest detection limits among tested systems. This system is stable even in the presence of high concentration of background electrolyte in the sample and offers the lowest detection limit, what makes it useful as e.g. indicator for titration. Generally from the results obtained it follows that inert complexes, hindering ion transport to the probe, can be used to expose a linear dependence of the optical signal on logarithm of concentration, whereas for labile complexes formed sigmoidal type dependences of higher sensitivity over limited concentration range are obtained.

Ultrasensitive 4-methylumbelliferone fluorimetric determination of water contents in aprotic solvents.

A novel approach to the quantification of relatively small amounts of water present in low polarity, aprotic solvents is proposed. This method takes advantage of protolitic reaction of 4-methylumbelliferone dissolved in the solvent with water, acting as a base. The low emission intensity neutral 4-methylumbelliferone is transformed in reaction with water to a highly fluorescent anionic form. Thus the increase in emission intensity is observed for increasing water contents in aprotic solvents. For low water contents and highly lipophilic solvents, this method yields (in practical conditions) higher sensitivity compared to biamperometric Karl Fischer titration method in volumetric mode. It is also shown that organic compounds of protolitic character (amines, acids) not only interfere with water contents determination but increase the sensitivity of emission vs. water contents dependence. Introduction of aqueous solution of strong acid or base (HCl or NaOH) has similar effect on the system as introduction of pure water.

Optimizing calcium selective fluorimetric nanospheres.

Recently it was shown that optical nanosensors based on alternating polymers e.g. poly(maleic anhydride-alt-1-octadecene) were characterized by a linear dependence of emission intensity on logarithm of concentration over a few of orders of magnitude range. In this work we focus on the material used to prepare calcium selective nanosensors. It is shown that alternating polymer nanosensors offer competitive performance in the absence of calcium ionophore, due to interaction of the nanospheres building blocks with analyte ions. The emission increase corresponds to increase of calcium ions contents in the sample within the range from 10(-4) to 10(-1) M. Further improvement in sensitivity (from 10(-6) to 10(-1) M) and selectivity can be achieved by incorporating calcium ionophore in the nanospheres. The optimal results were obtained for core-shell nanospheres, where the core was prepared from poly(styrene-co-maleic anhydride) and the outer layer from poly(maleic anhydride-alt-1-octadecene). Thus obtained chemosensors were showing linear dependence of emission on logarithm of calcium ions concentration within the range from 10(-7) to 10(-1) M.

Synthesis of conducting polymer nanospheres of high electrochemical activity.

We propose a novel approach to obtain conducting polymer nanoparticles with high electrochemical activity and a narrow size distribution. The method - templateless and seedless - uses polyacrylate microspheres to deliver the monomer for the polymerization reaction. Thus the obtained nanostructures have an active - unblocked - surface allowing fast charge/ion-exchange and the formation of stable suspensions in water. The obtained nanostructures have the potential to be applied in different fields ranging from conductive coatings and additives for increasing electronic conductivity, to electrochemical sensors.