Luminescence temperature sensing using poly(vinyl alcohol)-encapsulated Ru(bpy)(3)(2+) films

The ruthenium(II) diimine complexes, such as ruthenium(II) tris( bipyridyl), Ru(bpy)(3)(2+), possess highly luminescent excited states that are not only readily quenched by oxygen but also by an increase in temperature. The former effect can be rendered insignificant by encapsulating the complex in an oxygen impermeable polymer, although encapsulation often leads also to a loss of temperature sensitivity. The luminescence properties of Ru(bpy)(3)(2+) encapsulated in PVA were studied as a function of oxygen concentration and temperature and found to be independent of the former, but still very sensitive towards the latter. The results were fitted to an established Arrhenius-type equation, based on thermal quenching of the emitting state by a slightly higher (Delta E = 3100 cm(-1)) (3)d-d state that deactivates very rapidly (10(-13) s) via a non-radiative process.

Development of a novel UV indicator and dosimeter film

A novel UV indicator is described, comprising nanocrystalline particles of titania dispersed in a film of a polymer, hydroxyl ethyl cellulose (HEC), containing: a mild reducing agent, triethanolamine (TEOA) and a redox indicator, methylene blue (MB). The UV indicator film is blue-coloured in the absence of UV light and loses colour upon exposure to UV light, attaining within a few min a steady-state degree of bleaching that can provide a measure of the irradiance of the incident light. The original blue colour of the film returns once the source of UV light is removed. The spectral characteristics of a typical UV indicator film, and its components, are discussed and the UV-absorbing action of the titania particles highlighted. From the measured %bleaching undergone by a typical UV indicator as a function of light irradiance the indicator appears fully bleached, within 7 min, by a UV irradiance of 3 mW cm (-) or greater. The mechanism by which the UV indicator works is described. The reversible nature of the UV indicator is removed by covering a typical UV indicator with a thin, largely oxygen impermeable, polymer film, such as the regenerated cellulose found in Sellotape(TM). The product is a UV dosimeter, the response of which is related to the intensity and duration of the incident UV light, as well as the amount of titania in the film. A typical UV dosimeter film is fully bleached by 250 mJ cm(-2) of UV light. The possible use of these novel indicators to measure UV exposure levels, irradiance and dose, is discussed.

Response characteristics of optical sensors for oxygen: models based on a distribution in tau(o) or kappa(q)

The features of two popular models used to describe the observed response characteristics of typical oxygen optical sensors based on luminescence quenching are examined critically. The models are the 'two-site' and 'Gaussian distribution in natural lifetime, tau(o),' models. These models are used to characterise the response features of typical optical oxygen sensors; features which include: downward curving Stern-Volmer plots and increasingly non-first order luminescence decay kinetics with increasing partial pressures of oxygen, pO(2). Neither model appears able to unite these latter features, let alone the observed disparate array of response features exhibited by the myriad optical oxygen sensors reported in the literature, and still maintain any level of physical plausibility. A model based on a Gaussian distribution in quenching rate constant, k(q), is developed and, although flawed by a limited breadth in distribution, rho, does produce Stern-Volmer plots which would cover the range in curvature seen with real optical oxygen sensors. A new 'log-Gaussian distribution in tau(o) or k(q)' model is introduced which has the advantage over a Gaussian distribution model of placing no limitation on the value of rho. Work on a 'log-Gaussian distribution in tau(o)' model reveals that the Stern-Volmer quenching plots would show little degree in curvature, even at large rho values and the luminescence decays would become increasingly first order with increasing pO(2). In fact, with real optical oxygen sensors, the opposite is observed and thus the model appears of little value. In contrast, a 'log-Gaussian distribution in k(o)' model does produce the trends observed with real optical oxygen sensors; although it is technically restricted in use to those in which the kinetics of luminescence decay are good first order in the absence of oxygen. The latter model gives a good fit to the major response features of sensors which show the latter feature, most notably the [Ru(dpp)(3)(2+)(Ph4B-)(2)] in cellulose optical oxygen sensors. The scope of a log-Gaussian model for further expansion and, therefore, application to optical oxygen sensors, by combining both a log-Gaussian distribution in k(o) with one in tau(o) is briefly discussed.

Effect of plasticizer viscosity on the sensitivity of an [RU(bpy)(3)(2+)(Ph4B-)(2)]-based optical oxygen sensor

The quenching of the electronically-excited, lumophoric state of [Ru(bpy)(3)(2+)(Ph4B-)(2)] by oxygen is studied in a wide variety of neat plasticizers. The Stern-Volmer constant, K-SV, is found to be inversely dependent upon the viscosity of the quenching medium, although the natural lifetime of the electronically excited state of [RU(bPY)(3)(2+)(Ph4B-)(2)] is largely independent of medium. The least viscous of the plasticizers tested, triethyl phosphate, did not, however, produce highly sensitive optical oxygen sensors when used to plasticize [RU(bPY)(3)(2+)(Ph4B-)(2)]-containing cellulose acetate butyrate (CAB) and poly(methyl methacrylate) (PMMA) films, Instead, the compatibility of the polymer-plasticizer combination, as measured by the difference in the values of the solubility parameter of the two, appears to be a major factor in determining the overall oxygen sensitivity of the thin plastic films. For highly compatible polymer-plasticizer combinations, the plasticizer with the lowest viscosity produces films of the highest oxygen sensitivity. This situation arises because in the film the quenching process is partly diffusion-controlled and, as a result, the quenching rate constant is inversely proportional to the effective viscosity of the reaction medium.

Fluorescence-based thin plastic film ion-pair sensors for oxygen

A general method of preparation of thin-film sensors for O-2, incorporating the dye ion-pair tris(4,7-diphenyl-1,10-phenanthroline) rutheninm(II) ditetraphenylborate, in a variety of different thin film polymer/plasticizer matrices is described, The sensitivity of the sensor depends upon the nature of the polymer matrix and plasticizer, A detailed study of one of these systems utilising the polymer poly(methyl methacrylate), PMMA, is reported. The sensitivity of this O-2 sensor depends markedly upon the plasticizer concentration and is largely independent of temperature (24,5-52.5 degrees C) and age (up to 30 d), When exposed to an alternating atmosphere of O-2 and N-2, a typical oxygen film sensor in PMMA exhibits a 0-90% response and recovery time of 0.4 and 4.5 s, respectively.

Thin plastic film colorimetric sensors for carbon dioxide: Effect of plasticizer on response

Different plasticizers, including phosphate-, phthalate-and adipate-based types were used in the creation of a range of colorimetric plastic film sensors for CO2, The different types of plasticizer used in the formulation of a colorimetric plastic film sensor for CO2 affect the response and recovery times of the sensor differently, An effective plasticizer was taken as one that decreased the response and recovery times of the final film sensor when exposed to an alternating atmosphere of 0-5% CO2. On this basis, the most efficient plasticizers appeared to be phosphate-based, followed by phthalate- and adipate-based plasticizers, This trend appears to reflect the degree of the polymer-plasticizer compatibility. Increasing the amount of plasticizer in the film formulation decreased the response and recovery times of the sensor dramatically, The sensitivity of the film sensor towards CO2 appears to decrease with increasing plasticizer effectiveness; thus, the general order of film CO2 sensitivity with respect to plasticizer type was found to be adipate > phthalate > phosphate. In general, the response of the optical films towards CO2 was found to be temperature sensitive [typically, Delta H = -(44-55) kJ mol(-1)], The phosphate-based plasticized films appear to be less temperature sensitive than the other plasticized films, and 2-ethylhexyl diphenylphosphate appears particularly effective in this respect (Delta H = -18.5 kJ mol(-1)).

FLUORESCENCE PLASTIC THIN-FILM SENSOR FOR CARBON-DIOXIDE

The method of preparation of a novel plastic thin-film sensor that incorporates the fluorescent dye 8-hydroxypryrene-1,3,6-trisulfonic acid is described; the shelf-life of the film is over 6 months. The results of a study on the equilibrium response of the sensor towards different levels of gaseous CO2 fit a model there is a 1 + 1 equilibrium reaction between the deprotonated form of the dye (present in the film as an ion pair) and the concentration of gaseous CO2 present. In contrast to the situation in aqueous solution, in the plastic film the pK(a) of the excited form of the dye appears close to that of the ground-state form, although this does not interfere with its use as 8 CO2 sensor. The 0 to 90% response and recovery times of the film when exposed to an alternating atmosphere of air and 5% CO2 are typically 4.3 and 7.1 s, respectively.

MODELED DIFFUSION-CONTROLLED RESPONSE AND RECOVERY BEHAVIOR OF A NAKED OPTICAL FILM SENSOR WITH A HYPERBOLIC-TYPE RESPONSE TO ANALYTE CONCENTRATION

The diffusion-controlled response and recovery behaviour of a naked optical film sensor (i.e., with no protective membrane) with a hyperbolic-type response [i.e., S0/S = (1 + Kc), where S is the measured value of the absorbance or luminescence intensity of one form of the sensor dye in the presence of the analyte, S0 is the observed value of S in the absence of analyte and K is a constant] to changes in analyte concentration, c, in a system under test is approximated using a simple model, and described more accurately using a numerical model; in both models it is assumed that the system under test represents an infinite reservoir. Each model predicts the variations in the response and recovery times of such an optical sensor, as a function of the final external analyte concentration, the film thickness (I) and the analyte diffusion coefficient (D). From an observed signal versus time profile for a naked optical film sensor it is shown how values for K and D/I2 can be extracted using the numerical model. Both models provide a qualitative description of the often cited asymmetric nature of the response and recovery for hyperbolic-type response naked optical film sensors. It is envisaged that the models will help in the interpretation of the response and recovery behaviour exhibited by many naked optical film sensors and might be especially apposite when the analyte is a gas.

A specificity-enhanced time-resolved fluoroimmunoassay for zeranol employing the dry reagent all-in-one-well principle

A simple dry chemistry time-resolved fluorescence immunoassay (TR-FIA) method was developed for the measurement of zeranol in bovine urine samples. The samples were purified by immunoaffinity chromatography and a specificity-enhanced zeranol antibody was employed in the immunoassay. This resulted in a highly selective method, which had only negligible reactivity with Fusarium spp, toxins. The all-in-one-well dry chemistry concept made the assay very simple to use because all the assay-specific reagents were already present in the reaction wells in dry form. Only the addition of diluted sample extract was required to perform the competitive one-step TR-FIA and the results were available in less than 1 h. The analytical limit of detection (mean + 3s) for the immunoassay was 0.16 ng ml(-1) (n=12) and the functional limit of detection for the whole method, estimated by the analysis of zeranol-free samples, was 1.3 ng ml(-1) (n=20). The recovery of zeranol at the level of 2 ng ml(-1) was 99% (n=18) and the within-assay variation ranged between 4.5 and 9.0%.

DETECTION OF IRRADIATED CHICKEN MEAT BY ANALYSIS OF LIPID EXTRACTS FOR 2-SUBSTITUTED CYCLOBUTANONES USING AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY

The means to detect the irradiation of food has been investigated for many years. In recent times radiolytic products, termed 2-alkylcyclobutanones (2-CBs), have been identified as excellent markers of irradiation in lipid-containing foods. An ELISA test was developed, which was capable of detecting a number of these compounds in irradiated chicken meat. A polyclonal antiserum was raised to a 2-CB containing a terminal carboxyl group conjugated to a carrier protein. This antiserum was highly specific for cyclobutanones containing C-10 and C-12 side chains. During assay validation the limit of detection of the assay was calculated to be 0.064 pg of 2-CB per gram of fat, within- and between-assay variations ranged from 6.7 to 18%. During experimental studies, chicken meat irradiated at doses ranging from 2.5 to 10 kGy were assayed and correctly identified as being treated. Quantitative comparisons between the ELISA and CC-MS revealed a good correlation (r(2) = 0.913) between the two methodologies in concentrations of 2-CB detected in irradiated samples.