Effect of liposomal confinement on photothermal and photo-oximetric fluorescence lifetimes of photosensitizers with varying hydrophilicity.

The time-resolved fluorescence of photosensitizers (PSs) of varying hydrophobicities, di-and tetrasulfonated Al phthalocyanines (Al-2 and Al-4), and Photochlor (HPPH), was investigated in liposomes used as cell-mimetic models. Using frequency-and time-domain apparatus, the fluorescence lifetime, tau(fluo), was compared for PSs free in aqueous solution and in a liposome-associated state at varied temperatures (25 to 78 degrees C) and oxygen concentrations (0-190 microM). The analysis of tau(fluo) revealed different decay behaviors for the free-solution and liposome-confined PSs, most significantly for the lipophilic HPPH. Hydrophilic PS drugs (Al-4, Al-2) were less affected by the liposomal confinement, depending on the relative hydrophilicity of the compound and the consequent localization in liposomes. Changes in the emission decay due to confinement were detected as differences in the lifetime between the bulk solution and the liposome-localized PS in response to heating and deoxygenation. Specifically, hydrophilic Al-4 produced an identical lifetime trend as a function of temperature both in solu and in a liposome-confined state. Hydrophobic HPPH exhibited a fundamental transformation in its fluorescence decay kinetics, transitioning from a multiexponential (in free solution) to single-exponential (in liposome) decay. Deoxygenation resulted in a ubiquitous tau(fluo) increase for all PSs in free solution, while the opposite, a tau(fluo) decrease, occurred in all liposomal PSs.

Effect of liposomal confinement on photochemical properties of photosensitizers with varying hydrophilicity.

Preferential tumor localization and the aggregation state of photosensitizers (PSs) can depend on the hydrophilic/hydrophobic nature of the molecule and affect their phototoxicity. In this study, three PSs of different hydrophilicity are introduced in liposomes to understand the structure-photochemistry relationship of PSs in this cellular model system. Absorbance and fluorescence spectra of amphiphilic aluminum (III) phthalocyanine disulfonate chloride adjacent isomer (Al-2), hydrophilic aluminum (III) phthalocyanine chloride tetrasulfonic acid (Al-4), and lipophilic 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide (HPPH) are compared in a liposomal confined state with free PS in bulk solution. For fluorescence measurements, a broad range of concentrations of both bulk and liposomal confined PSs are examined to track the transition from monomers to dimers or higher order aggregates. Epifluorescence microscopy, absorbance, and fluorescence measurements all confirm different localization of the PSs in liposomes, depending on their hydrophilicity. In turn, the localization affects the aggregation of molecules inside the liposome cell model. Data obtained with such cellular models could be useful in optimizing the photochemical properties of photosensitizing drugs based on their structure-dependent interactions with cellular media and subcellular organelles.

Nondestructive measurement of fresh tomato lycopene content and other physicochemical characteristics using visible-NIR spectroscopy.

Measurement of fresh tomato fruit overall quality, and particularly lycopene content, is challenging in the context of high-volume production. An experiment was conducted to simultaneously measure various quality parameters of tomato in a nondestructive manner using vis-NIR reflectance spectroscopy and chemometrics. The sampling set included different cultivars that are obtainable from both retailers' shelves and two greenhouse producers. Results indicate that lycopene content was accurately predicted [r(2) = 0.98; root mean square error of cross-validation (RMSECV) = 3.15 mg/kg], along with color variables such as Hunter a (r(2) = 0.98), L, and b (r(2) = 0.92). Tomato color index (TCI) was better predicted (r(2) = 0.96) than the a/ b ratio (r(2) = 0.89). Firmness prediction, with an r(2) of 0.75, is comparable to what is reported in the literature for other fruits and may have a practical interest. Prediction of internal quality such as pH, soluble solids, titratable acidity, and electrical conductivity was less accurate, partly due to a low variability of these parameters among samples. Predictions were robust with regard to cultivars, except for pink variety tomato. The 400-1000 nm range gave results almost as accurate as the 400-1500 nm range.

Multivariate approach to the measurement of tomato maturity and gustatory attributes and their rapid assessment by Vis-NIR spectroscopy.

Standard methods for determining quality and maturity are time- and labor-consuming and generally measure individual criteria at a specific time, without considering relationships among quality parameters. To propose a rapid and nondestructive analysis method describing multidimensional quality variables, an experiment was undertaken with mature green to overripe tomato fruits found on the North American retail markets. Factor analysis was used to analyze results. Four factors were considered, representing 81% of total variance. The first one, tomato maturity stage (TMS), is related to color, lycopene content, firmness, titratable acidity (TA), pH, and soluble solids (SS). Nondestructive rapid assessment by vis-NIR spectroscopy can predict TMS (r(2)=0.93). Factors 2 and 3 are both related to taste and should be considered simultaneously. Factor 2, called the gustatory index, is linked to electrical conductivity (EC), SS, TA, and pH. Factor 3, defined by SS, can be directly measured by a refractometer. Four categories of taste are proposed; the most desirable one ranks high both in soluble solids (above 4.5 degrees Brix) and in gustatory index (above 0). It was not possible to measure the gustatory index by vis-NIR spectroscopy (r(2)=0.17), but it can be estimated by EC, using a simple formula. The proposed limit between high and low gustatory index then corresponds to an EC of 5.4 mS/cm. Factor 4, variety, mostly discriminates the pink tomato type and field-grown samples from other varieties.

Optical characterization of Pseudomonas fluorescens on meat surfaces using time-resolved fluorescence.

A scanning optical system for the detection of bacteria on meat surfaces based on fluorescence lifetime and intensity measurements is described. The system detects autofluorescent light emitted by naturally occurring fluorophores in bacteria. The technique only requires minimal sample preparation and handling, thus the chemical properties of the specimen are preserved. This work presents the preliminary results obtained from a time-resolved fluorescence imaging system for the characterization of a nonpathogenic gram-negative bacteria, Pseudomonas fluorescens. Initial results indicate that the combination of fluorescence lifetime and intensity measurements provides a means for characterizing biological media and for detecting microorganisms on surfaces.

Simple fiber-optic-based sensors for process monitoring: an application in wine quality control monitoring.

The goal of this research was to develop a simple and economical fiber-optic sensor technology for agrifood process monitoring. Toward this end, two fiber-optic sensors were developed to be used in combination: a single reflection V-bend sensor and a single fiber air-gap probe. The former is designed to be sensitive toward refractive index and the latter towards absorption. Experiments indicate that the micromachined V-bend fiber refractometer is most sensitive when the bend angle is centered around 140 degrees, at which angle the sensor may resolve changes in refractive index as small as 0.00015. Additionally, the V-bend sensor was found to be non-responsive toward sample absorption even in extremely absorbing solutions. The air-gap design absorption sensor, most commonly used for measurements in highly colored media, was found to be slightly sensitive towards refractive index. When the two sensors are used together, the response of the absorption sensor may be corrected for. This sensor combination is able to provide accurate measurements in situations where Beer's law is not obeyed. Results are presented that show that the sensor pair was successfully used to monitor wine sugar content (Brix), and color density and hue, parameters related to the age of the wine.