Matejka Turel

Detection of nanomolar concentrations of copper(II) with a Tb-quinoline-2-one probe using luminescence quenching or luminescence decay time.

We present a time-resolved (gated) luminescence-based method for determination of Cu2+ ions in microtiterplate format in the nanomolar concentration range using the novel long-lived terbium-[1-methyl-4-hydroxy-3-(N-2-ethyl-5-aminothiadiazolyl-)-carbamoyl-quinoline-2-one] (TbL) complex. The probe works best in Tb:L = 1:2 stoichiometry at neutral pH. The dynamic range is from 10 to 300 nmol L(-1) of Cu2+ and the limit of detection is 4.3 nmol L(-1). This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for copper. It is shown that gating can efficiently suppress intense, short decaying background fluorescence e.g. that of Rhodamine 6G. The assay can be performed by measurement of luminescence decay time, as well. Stern-Volmer studies indicate that static quenching dominates over dynamic quenching. TbL2 was tested for the effect of some relevant interferents and the assay was applied to the determination of copper in tap water samples. The results achieved were in good agreement with those of a reference method.

Optical Chemical Sensors:Design and Applications

Optical sensors, or opt(r)odes, represent a group of chemical sensors in which electromagnetic (EM) radiation is used to generate the analytical signal in a transduction element. The interaction of this radiation with the sample is evaluated from the change of a particular optical parameter and is related to the concentration of the analyte (Blum, 1997). Typically, an optical chemical sensor consists of a chemical recognition phase (sensing element or receptor) coupled with a transduction element (Fig. 1). The receptor identifies a parameter, e.g., the concentration of a given compound, pH, etc., and provides an optical signal proportional to the magnitude of this parameter. The function of the receptor is fulfilled in many cases by a thin layer that is able to interact with the analyte molecules, catalyse a reaction selectively, or participate in a chemical equilibrium together with the analyte. The transducer translates the optical signal produced by the receptor into a measurable signal that is suitable for processing by amplification, filtering, recording, display, etc. (Grundler, 2007; Nagl & Wolfbeis, 2008).

Microtiterplate phosphate assay based on luminescence quenching of a terbium complex amenable to decay time detection

We describe a terbium-ligand complex (TbL) for a microtiterplate assay for phosphate (P) in the 0.3-100 micromol L(-1) range based on luminescence quenching. As the pH optimum is at neutral pH (7.4) the probe is quenched by both, primary (H(2)PO(4)(-)) and secondary phosphate (HPO(4)(2-)). The LOD is 110 nmol L(-1). A Stern-Volmer study revealed that quenching is mostly static. Due to the ms-decay time of TbL, the first luminescence lifetime assay for phosphate could also be developed. The lifetime-based calibration plot is linear between 0.5 and 5 micromol L(-1) of P. The effect of various surfactants on assay performance and a study on interferents are presented. The probe was successfully applied to determination of P in commercial plant fertilizers and validated against the molybdenum blue test. The probe is the most sensitive lanthanide-based probe for phosphate.

Fluorescence-Based Determination of Agmatine in Dietary Supplements

This study presents an optical determination of agmatine at pH 13. The fluorescent product formed between the indicator reagent o-phthaldialdehyde and agmatine sulfate reached its maximum intensity within twenty minutes of incubation time when excited at 340 nanometers. The determination of agmatine sulfate was linear within a concentration range between 6.0 × 10−7 and 8.0 × 10−6 moles per liter and the limit of detection was 1.5 × 10−8 molar. Under the optimized conditions, the fluorescent intensity of o-phthaldialdehyde in the presence of other biogenic amines (histamine, tyramine, putrescine, noradrenaline, etc.) was at least fourteen-fold lower than that of the o-phthaldialdehyde–agmatine sulfate product. The method was applied for the determination of agmatine sulfate in dietary supplements.

Assay for optical determination of biogenic amines using microtiterplates

Direct determination of catecholamine noradreanaline (NOR) is presented using o-phthaldialdehyde (OPA) as an indicator reagent. The fluorescent assay in which OPA forms with NOR a fluorescent complex (OPA-NOR) can be monitored at neutral, physiological conditions (pH 7) and performed in microtiterplates. The determination of NOR is optimal in the concentration range from 4.0×10-7 to 1.0×10-5 M and limit of detection is 4.0×10-7 M. The OPA-NOR complex maximum intensity is reached within 5 minutes. Dopamine and adrenaline could not be determined using the same approach.

Design and Characterization of Dicyanovinyl Reactive Dyes for the Colorimetric Detection of Thiols and Biogenic Amines

The synthesis of two new azobenzene dyes, namely CR-528 and CR-555, and their spectral properties in ethanol solution are described. The recognition of sulfur-containing analytes (2-mercaptoethanol (2-ME), sodium hydrosulfide (NaHS)), and biogenic amines (spermine, spermidine, ethanolamine) bestowed significant spectral changes with color changes from pink/purple to pale yellow/orange-yellow. The nitro acceptor group in the dicyanovinyl reactive dye contributes to higher sensitivity and lower detected analyte concentrations. The absorption maxima of both the dyes are at wavelengths compatible with low-cost light sources and detectors, making them excellent candidates for optical probes that are economic, simple to use, and do not require well-trained personnel.

Effects of Ultrasound Irradiation on the Preparation of Ethyl Cellulose Nanocapsules Containing Spirooxazine Dye

This article presents the influence of low frequency, high intensity ultrasonic irradiation on the characteristics (average size, polydispersity index) of ethyl cellulose nanocapsules encapsulating a photochromic dye. Photochromic nanocapsules were prepared by the emulsion-solvent evaporation method. The acoustic densities entering the system were systematically studied with respect to their abilities to modify and reduce the average sizes and polydispersity indexes of the nanocapsules. Scanning electron microscope, confocal laser microscope, and dynamic light scattering were utilised to characterise the structure, shape, size, and polydispersity of ethyl cellulose photochromic nanocapsules. We were able to tailor the size of the photochromic nanocapsules simply by varying the acoustic densities entering the system. At an acoustic density of 1.5 W/mL and 60 s of continuous irradiation, we were able to prepare an almost monodispersed population of the nanocapsules with an average size of 193 nm.

Magnetic Silica Nanocomposites as Optical Tools in Biomedical Applications

As a result of their size and versatile chemistry, today’s nanomaterials represent powerful tools for several biomedical applications. Various types of nanomaterials have proven to be practical, not only for determining clinically relevant parameters, but also for diagnostics, drug delivery and the treatment of diseases (e.g., cancer). Of particular promise are those nanocomposite structures with multifunctional capabilities. In this chapter we focus on magnetic silica nanocomposites, combined with an optical component, such as organic fluorescent dyes or quantum dots. The most important characteristics of these nanomaterials are presented, together with their specific uses in biomedical applications. It was observed that findings based on in-vitro measurements were not always in agreement with in-vivo applications. Additionally, the use of these nanocomposites in clinical trials remains a long-term goal.

Optical Chemical Nanosensors in Clinical Applications

Because of their size and versatile chemistry, nanomaterials represent today powerful tools for (bio) sensing applications. Various types of nanomaterials have proven to be practical, not only for the determination of clinically relevant parameters, but also for diagnostics, drug delivery and treatment of diseases (e.g. cancer). In this short review, types of nanomaterials used in medical applications are briefly described along with some of their applications where the nanomaterials optical properties can be exploited. The question of the toxicity of nanomaterials and the issue of future trends are also raised.