Thin layer coulometry based on ion-exchanger membranes for heparin detection in undiluted human blood.

We explore here for the first time a potentially calibration-free methodology for the detection of protamine (and, by titration, heparin) in undiluted human blood in the therapeutic concentration range from 20 to 120 mg L(-1). The use of a thin layer sample (5.8 µL) confined between a tubular protamine selective membrane (inner diameter, 600 µm) and a Ag/AgCl wire (diameter 400 µm) achieves an exhaustive depletion from the sample. Coulometry detection was chosen for the interrogation of the thin layer, employing a double pulse technique with 120 s for each pulse. Protamine calibration curves were recorded at physiological concentrations and in undiluted human blood. A linear relationship was obtained in both cases, but a diminished sensitivity was observed in contact with blood, which is explained with a partial passivation of the inner Ag/AgCl element. Heparin-protamine titrations were performed in undiluted human blood samples, mimicking the final application with patients undergoing critical care. The observed values correlate satisfactorily with those of an alternative technique, so-called flash-chronopotentiometry on planar membranes.

A low-cost thin layer coulometric microfluidic device based on an ion-selective membrane for calcium determination.

A prototype of a low-cost and easy-to-use thin layer coulometric microfluidic device based on an ion-selective membrane for calcium detection is described. The microfluidic device was fabricated and consequently assembled with inexpensive materials without using sophisticated and centralized fabrication laboratory facilities. The linear range of the device is found to be 10-100 µM for a 60 s current integration time. Preliminary validations showed that the microfluidic device is suitable for the quantification of calcium in mineral water.

Enabling biomedical research with designer quantum dots.

Quantum Dots (QDs) are a new class of semiconductor nanoparticulate luminophores, which are actively researched for novel applications in biology and nanomedicine. In this review, the recent progress in the design and applications of QD labels for in vitro and in vivo imaging of cells is presented. Surface chemical engineering of hydrophobic QDs is required to render them water soluble and biocompatible. Further surface modification and attachment of bioactive molecules to the surface of QDs, such as peptides, aptamers, or antibodies are intensively explored for targeted imaging of living cells, and disease states in animals. Specially designed surface coatings can drastically decrease nonspecific interactions between QDs and cells, minimize degradation of QDs under in vivo physiological conditions, reduce the cytotoxicity of QDs, and prolong circulation lifetimes in animals. New generations of QD probes are also promising for imaging cellular processes at the single-molecule level. Ultimately, QDs as components of complex therapeutic nanosystems are poised to contribute significantly to the field of personalized medicine.

Imaging surface plasmon resonance for multiplex microassay sensing of mycotoxins.

A prototype imaging surface plasmon resonance-based multiplex microimmunoassay for mycotoxins is described. A microarray of mycotoxin-protein conjugates was fabricated using a continuous flow microspotter device. A competitive inhibition immunoassay format was developed for the simultaneous detection of deoxynivalenol (DON) and zearalenone (ZEN), using a single sensor chip. Initial in-house validation showed limits of detection of 21 and 17 ng/mL for DON and 16 and 10 ng/mL for ZEN in extracts, which corresponds to 84 and 68 µg/kg for DON and 64 and 40 µg/kg for ZEN in maize and wheat samples, respectively. Finally, the results were critically compared with data obtained from liquid chromatography-mass spectrometry confirmatory analysis method and found to be in good agreement. The described multiplex immunoassay for the rapid screening of several mycotoxins meets European Union regulatory limits and represents a robust platform for mycotoxin analysis in food and feed samples.

Visualizing resonance energy transfer in supramolecular surface patterns of ß-CD-functionalized quantum dot hosts and organic dye guests by fluorescence lifetime imaging.

Detection of an analyte via supramolecular host-guest binding and quantum dot (QD)-based fluorescence resonance energy transfer (FRET) signal transduction mechanism is demonstrated. Surface patterns consisting of CdSe/ZnS QDs functionalized at their periphery with ß-cyclodextrin (ß-CD) were obtained by immobilization of the QDs from solution onto glass substrates patterned with adamantyl-terminated poly(propylene imine) dendrimeric "glue." Subsequent formation of host-guest complexes between vacant ß-CD on the QD surface and an adamantyl-functionalized lissamine rhodamine resulting in FRET was confirmed by fluorescence microscopy, spectroscopy, and fluorescence lifetime imaging microscopy (FLIM).

Ferrocene-coated CdSe/ZnS quantum dots as electroactive nanoparticles hybrids.

Electrochemical properties of core-shell CdSe/ZnS quantum dots (QDs) in a non-aqueous solution are presented. Cathodic reduction and anodic oxidation processes involving the QD HOMO and LUMO levels as well as defect states were identified by cyclic voltammetry. The electrochemical bandgap was estimated from the anodic and cathodic redox peaks and found to match well with the optical bandgap estimated from the absorption spectrum. The trioctylphosphine oxide ligands on the surface of the QDs were exchanged to electroactive ferrocenyl thiols and the resulting material was characterized by NMR and optical spectroscopy. Cyclic voltammetry showed that the redox potentials of the QDs are modified due to the presence of ferrocene on the surface of the QD. The QD oxidation peak decreased and the reduction peak shifted to more negative potentials. The concurrent shift of the ferrocene redox peaks indicates that the system displays features of a 'molecular hybrid', where both the QD and the ligand influence each other.

Fabrication and luminescence of designer surface patterns with beta-cyclodextrin functionalized quantum dots via multivalent supramolecular coupling.

Supramolecular microcontact printing was used to obtain controlled patterns consisting of quantum dots (QDs) functionalized at their periphery with beta-cyclodextrin (beta-CD) in combination with adamantyl terminated dendrimeric "glues". Functionalization of core--shell CdSe/ZnS QDs was achieved by surface ligation. Immobilization of the QDs from solution onto glass substrates printed with (a) adamantyl-terminated poly(propylene imine) dendrimers and (b) via direct microcontact printing of QDs onto the dendrimer layer both yielded stable and robust multilayer structures. The stability of the patterns was primarily due to multivalent supramolecular host--guest interactions between beta-CD located at the QD surface and adamantyl groups at the dendrimer periphery as the dendrimers acted as a "supramolecular glue". The surface-immobilized QDs were capable of forming host--guest complexes with other molecules of interest at binding cavities not occupied by adamantyl groups. Complex formation with ferrocene-functionalized molecules at these sites led to partial quenching of the luminescence emission of QDs demonstrating the principle for sensing using the QD multilayer structures.

Reversible phase transfer of (CdSe/ZnS) quantum dots between organic and aqueous solutions.

Ttrioctylphosphine oxide (TOPO) stabilized CdSe/ZnS quantum dots (QD) were modified with 6-ferrocenyl-1-hexanethiol (FcHT) or 11-ferrocenyl-1-undecanethiol (FcUT) via ligand exchange. The presence of ferrocenyl thiol ligands on the surface of the QDs was proven by diffusion ordered NMR spectroscopy. Upon replacement of the initial TOPO ligand with ferrocene derivatives the emission of the QDs decreased. Phase transfer of ferrocene-modified QDs from organic solvents into water was achieved by complexation reactions with beta-cyclodextrin (beta-CD). The QDs coated with ferrocene thiols are soluble in nonpolar solvents and are transferred into the aqueous phase upon formation of host-guest complexes between the ferrocene units and the cavity of beta-CD. The reversibility of the phase transfer was probed by the addition of naphthalene and adamantane derivatives to the aqueous phase containing QD-[Fc-CD] adduct.