Room-temperature Phosphorescence Measurements Research Articles

Electrochemical and spectrophotometric detection of malachite green in aqueous system using imprinted sol–gel polymer-capped quantum dots

ABSTRACTIn this study, malachite green-imprinted sol-gel polymer (MG-imp) has been anchored on the surface of mercaptopropyltrimethoxysilane-capped Mn-doped ZnS quantum dots (MPTMS-Mn:ZnS) and characterised by Fourier Transform-Infrared Spectroscopy and Scanning Electron Microscopy. Surface imprinting property of MPTMS-Mn:ZnS (QDs) covered by MG-imprinted sol-gel (MG-imp-QDs) was elucidated by differential pulse voltammetry and room temperature phosphorescence (RTP) measurements. Selective determination of MG in the presence of analogue molecules was managed upon optimised solution parameters based on the RPT quenching efficiency of MG-imp-QDs nanoparticles. Electrochemical measurement was also carried out by fabricating electrode modified with MG-imp-QDs nanoparticles in order to confirm the existence of imprinting effect and spectral overlap causing to inner filter effect during the RTP measurements. The linear concentration range and limit of detection for determining of MG in buffer solution were found to be 0.03–1.84 µM and 3.2 nM, respectively.

Insecticide as a precursor to prepare highly bright carbon dots for patterns printing and bioimaging: A new pathway for making poison profitable

Halophenols (HPs) inflict adverse impacts on human and environment due to their toxic, carcinogenic as well as teratogenic properties. Additionally, it is of great importance and urgency for the development of simple, efficient and inexpensive approaches to minimize the harm of HPs. Here we report an innovatively making poison profitable method to prepare carbon dots (C-dots) using 3-bromophenol residual as a precursor. The effects of solvent and carbonization temperature on the preparation of insecticide-based C-dots were investigated. The results indicate that higher organic solvent content in solution and higher carbonization temperature are in favor of the formation of C-dots with smaller size and higher quantum yields. Meanwhile, all C-dots displayed excellent water solubility and high photostability against ionic strengths and light illumination. The possible mechanisms of polymerization and carbonization of C-dots were rationally proposed, and the incompact framework structure of C-dots was reasonably inferred by room-temperature phosphorescence measurement. Also, a kind of low toxicity, good biocompatibility and photostability C-dots, which were synthesized via a lab-leveled mimetic insecticide residuals approach, were utilized as colorless inks for printing patterns and as fluorescence probe for bioimaging. This proposed approach opened up a potential prospect to efficiently utilize pesticide residuals and other hazardous chemicals for biolabeling and bioimaging.

Design of a Room-Temperature Phosphorescence-Based Molecular Beacon for Highly Sensitive Detection of Nucleic Acids in Biological Fluids

Ultrasensitive fluorescent analysis or monitoring of significant molecules in complex samples is important for many biological studies, clinical diagnosis, and forensic investigations, the major obstacle for which is the background signals from ubiquitous endogenous fluorescent components of the environments. Herein, a room-temperature phosphorescence (RTP)-based molecular beacon (MB), employing a Eu(3+) complex of chlorosulfonylated tetradentate β-diketone (L) and the quencher BHQ-2, was engineered for highly sensitive detection of DNA sequences in biological fluids. Complexation of Eu(3+) with the ligand L formed a strongly luminescent complex EuL(2). But when EuL(2) and BHQ-2 were labeled to two ends of a DNA molecule with hairpin structure, the luminescence of EuL(2) was quenched by BHQ-2 due to the stem-closed conformation of the beacon. Due to very low background luminescence from the probe molecule, >200-fold signal enhancement was achieved when nanomolar target sequence was introduced. This sensitivity is about 20-fold higher than the level achieved with conventional fluorescence-based molecular beacons. Furthermore, because the Eu(3+) complex has a much longer luminescence lifetime (≈0.8 ms) than that of the background (<10 ns), RTP measurements were used to directly detect as low as 500 pM DNA in cell media quantitatively without any sample pretreatment.

Solid-supported room temperature phosphorescence from aflatoxins for analytical detection of Aspergillus spp. strains

A simple, direct and rapid analytical methodology for the detection of aflatoxin producing Aspergillus spp. strains based on the measurement of room temperature phosphorescence from aflatoxins is presented here.

Flow-through optosensing of 1-naphthaleneacetic acid in water and apples by heavy atom induced–room temperature phosphorescence measurements

A sensitive and selective phosphorimetric method for the determination of 1-naphthaleneacetic acid (1-NAA) based on a flow-injection system connected to a flow cell packed with a solid support and placed in the sample compartment of a conventional luminescence spectrometer is described. A non-ionic solid polymeric resin Amberlite XAD-7 is used for the packing. After injection of the sample, 1-NAA is on-line retained in the packed resin and measurements of the heavy atom induced (HAI)–room temperature phosphorescence (RTP) emission ( λ ex/ λ em = 292/490 nm) from this native luminescent compound are taken. The optimum experimental conditions were investigated by injecting 2 ml samples of an aqueous solution of 1-NAA in the flow system. A concentration 0.15 mol l −1 of thallium(I) ions, as heavy atom, both in the samples and the carrier flow, was finally selected. Also, a concentration of 6 mmol l −1 of sulphite was optimal for ensuring the necessary deoxygenation of the system at the selected flow rate of 0.8 ml min −1. After measurement, the solid support was efficiently regenerated by injecting 1 ml of a mixture water:acetone in a ratio 1:1 (v/v) into the flow. The detection limit (3 σ criterion) was 1.2 ng ml −1 of 1-NAA. The repeatability (R.S.D.) for five replicates of a sample containing 50 ng ml −1 of analyte turned out to be ±3% and the calibration graphs proved to be linear up to 500 ng ml −1 of 1-NAA (maximum concentration assayed). The effect of potential interferences from other organic species which can be also used as plant growth regulators, as well as from various inorganic cations and anions, has been investigated as well. The method was successfully applied to the determination of low levels of this plant growth regulator in natural waters (river and fountain waters) and apples.

Investigation of atypical germination changes during accelerated ageing of pea seeds

Pea seeds with initial germinability of 100, 82 and 56% were subjected to accelerated ageing for 16 days at 40°C and 85% relative humidity (RH). Upon ageing of seeds with initial germinability of 82 and 56%, multiphasic changes in germination (production of normal seedlings) were observed: after 5 or 7 days of ageing, germinability decreased to 72 and 22%, respectively, but after 8 or 10 days it rose to 92 and 60%, respectively. Prolongation of ageing led to deterioration of both germinability and seed viability. When the seed sample with initial germinability of 56% was pre-treated for three days at 20°C and 85% RH (during which the moisture content (MC) reached 15% fresh weight (FW)) before being subjected to accelerated ageing, the initial decrease and subsequent increase of germination were observed 3 days earlier. When the seed lot with germinability of 82% was subjected to controlled ageing at 20% MC, only a consistent steady decline in germination was observed. A similar decline was also observed during accelerated and controlled ageing of seeds with almost 100% germinability (MC 18, 20, 21 and 22%). Measurement of room temperature phosphorescence (RTP) of seeds, was used to divide the sample of air-dry low-germination seeds into three fractions (sub-lots): viable seeds of fraction I (produced normal seedlings), viable seeds of fraction II (produced abnormal seedlings) and dead seeds (fraction III). Changes in germination during ageing were due to changes in the proportion of seeds occurring in fractions I and II. Fraction II seeds differed from fraction I by characteristically higher rate of water uptake during the imbibition. However, the high rate of imbibition was not caused by changes in seed-coat permeability of fraction II seeds. After slowing seed imbibition by PCMB (a mercurial closing aquaporin water channels), seeds of fraction II produced normal seedlings and germinability increased. It is proposed that the atypical increase in germination capacity during accelerated ageing was due to lower permeability of cell membranes for water.

Development of a Prototype Instrument for Multiposition Sensing of Dissolved Oxygen by Using Room-Temperature Phosphorescence Measurements

Development of a Prototype Instrument for Multiposition Sensing of Dissolved Oxygen by Using Room-Temperature Phosphorescence Measurements

Room-temperature phosphorescence fiber-optic instrumentation for simultaneous multiposition analysis of dissolved oxygen

The design and analytical characterization of a fiber-optic instrument for simultaneous multiposition water-dissolved oxygen monitoring by room-temperature phosphorescence (RTP) measurements is presented. The sensing principle is based on the RTP quenching by oxygen of the phosphorescent light emitted by the metal chelate formed by Al with 8-hydroxy-7-iodo-5-quinolinesulfonic acid (Al-ferron) trapped in a sol–gel solid support. Four RTP oxygen sensor flow-cells are assembled in order to measure the oxygen content in four different water streams. A xenon flash-lamp is used as the single excitation source for the four sensing regions, while multichannel phosphorescence detection is achieved by using a cooled intensified charge-coupled device (ICCD). Four bifurcated optical fibers are used to carry the light from the excitation source to the sensing active surface in the flow-cell and to bring the emitted RTP to the detector. The RTP light coming from each of the optical fibers was focused onto different sites (rows of pixels) of the ICCD. In this way, the RTP signals from each of the four sensing materials packed in the flow-cells can be differentiated and measured. Simultaneous dissolved oxygen monitoring in several water streams containing different dissolved oxygen levels is demonstrated by using the proposed instrumentation. Also, the relatively long phosphorescence lifetime of the materials used allow the use of the developed instrumentation to perform lifetime room-temperature phosphorescence measurements.

Determination of p-aminobenzoic acid in the presence of bovine serum albumin by room-temperature phosphorimetry on a poly(vinyl alcohol) substrate

Solid substrate room-temperature phosphorimetry on a poly(vinyl alcohol) (PVA) substrate was applied to the analysis of p-aminobenzoic acid (PABA) in the presence of bovine serum albumin (BSA). The buffer solution containing PABA and BSA was spotted on the PVA substrate and after sufficient drying, room-temperature phosphorescence (RTP) measurements were performed on both the front and the back side of the substrate. The BSA was separated on the front surface of the substrate and it emitted a negligibly weak RTP signal. Therefore, the RTP measurement of PABA on the reverse of the sample spotted side was not interfered by BSA, whereas, impurities in the BSA permeated into the PVA and emitted a weak RTP signal on the back side of the substrate. However, the RTP intensities of the impurities were weak enough as compared to that of PABA under the experimental conditions, so that their interference could be neglected. To improve the RTP intensity and reproducibility of PABA in the presence of BSA, a new substrate that consisted of Millipore-VS and PVA layer was prepared. The analytical figures of merit of this substrate obtained under the best experimental condition for maximum phosphorescence emission are a relative standard deviation of 6.0% ( n=5) at a level of 2 nmol/spot and a linear calibration curve from 0.5 to 20 nmol/spot with a correlation coefficient of 0.996 for 25 data points.

Long Time-Scale Probing of the Protein Globular Core Using Hydrogen-Exchange and Room Temperature Phorphorescence

Preliminary room temperature phosphorescence measurements of the highly buried Trp109 inE. colialkaline phosphatase have been used to report on the kinetics of protein hydrogen–deuterium exchange. Upon dilution in D2O the phosphorescence lifetime increases (at 20°C) in a biphasic manner with an immediate change (<30 seconds) followed by a slow change occurring on an extremely long timescale (days). The immediate D2O-induced lifetime increase is similar to that observed upon dilution into glycerol, a known protein hydrating agent. On the other hand, the slow D2O-induced first order growth in Trp109 lifetime is due to exchange at highly protected protein groups. As the phosphorescence lifetime of Trp109 is dependent on local rigidity, this increase in lifetime reflects changes in alkaline phosphatase structure. This first use of room temperature phosphorescence to monitor proton exchange shows promise as a sensitive and selective probe of protein core dynamics.

Poly(vinyl alcohol) as Solid Substrate Material for Room-Temperature Phosphorimetry

A mixture of poly(vinyl alcohol) (PVA) and a small amount (5%) of cellulose (CLL) was pressed under ∼280 kg/cm 2 to form a disk of 1 mm thickness, and the prepared disk was used as a solid substrate for room-temperature phosphorescence (RTP). The addition of CLL was to reduce the fragility of the disk and enhance the permeability of sample solutions into the disk surface. The sample solution spotted PVA-CLL solid substrates were dried in a microwave oven conveniently. The efficiency of PVA-CLL solid substrates was monitored by RTP intensity of p-aminobenzoic acid (PABA) spotted on them, and the results showed that the RTP signal of PABA was largely enhanced as compared to that on the conventional paper solid substrates. Another prominent feature of the PVA-CLL solid substrate is that the RTP signal can be observed sufficiently even without a dry gas flush during the RTP measurement, while a dry gas flush is essential for the conventional substrates. A calibration curve for PABA was linear from 7.3 to 1200 pmol/spot. The results for the RTP measurements of chlorpromazine hydrochloride and tetracaine hydrochloride were also reported. The limits of detection of PABA and the other two drugs were 0.03, 0.16 and 1.26 ng, respectively.

Comparing organized media types using fluorescence probe characterization methods

Organized media, such as surfactant micelles and cyclodextrins, have been shown to provide increased selectivity and lower detection limits in the spectrofluorimetric analyses of many compounds. Analysis performance is generally improved because the medium shields the analyte from quenchers or because inclusion in the medium increases the efficiency of a requisite interaction, as in the case of energy transfer and room-temperature phosphorescence measurements. The ability of other types of microheterogeneous media, such as phospholipid vesicles, to solubilize non-electrolytes is also well known, but the microenvironmental properties of many of these systems have not been characterized under the conditions likely to be used in spectrofluorimetric analysis. In a step toward evaluating the suitability of a wider range of compounds in spectrofluorimetric applications, several medium properties including the microheterogeneity, partition coefficient, sequestering efficiency and apparent polarity of a typical lipid vesicle, dimyristoyl phosphatidylcholine (DMPC), and surfactant micelle, sodium dodecyl sulfate (SDS), were compared using a single fluorescence probe. The results indicate that DMPC vesicles are less microheterogeneous, less polar and partition hydrophobic molecules more readily than SDS micelles. However, probe molecules were sequestered from interferents less effectively in DMPC than in SDS.

Screening Benzo(a)pyrene Metabolites in Urine Using Synchronous Room Temperature Phosphorescence

Abstract We have developed a simple measurement procedure for screening of polycyclic aromatic hydrocarbons (PAC) and their metabolites in urine using room temperature phosphorescence (RTP). The signal intensities were proportional to the amounts of benzo(a)pyrene-r-7,t-8,9,10,tetrahydrotetrol (BPT) below 75 pmol per spot. The presence of unknown substances in urine of exposed rats caused photochemical interferences in the measurement of RTP. The removal of polar interferants restored the RTP spectra. These substances were removed by selective absorption of the target compounds to hydrocarbon-bonded silica particles (RP) imbedded in Whatman 42 filter paper discs. The sensitivity and linear response range are dependent on the signal to noise ratio of the instrument. Up to 1000 pmol of BPT can be adsorbed to 40 μg of imbedded RP. When an instrument with signal to noise ratio capabilities of 300 is used, 5 pmol of BPT can be detected with an S/N of 3. Room temperature phosphorescence measurements of urine fr...

Quantitative Analysis of Molecular Oxygen Using Palladium Porphyrins

A simple optical method for the quantitative determination of dissolved oxygen under physiological conditions is described. The technique involves measurement of room temperature phosphorescence from palladium(II) porphyrins. Such emission is rare for large organic molecules, and its long lifetime, together with the favourable absorption characteristics of the porphyrin receptor, ensure that the phosphorescence can be resolved easily, even in heterogeneous media. Phosphorescence yields and lifetimes are shown to be highly sensitive to the concentration of dissolved oxygen, but do not depend upon the nature of the environment, and can be used separately or together to determine oxygen levels within a biological substrate. This technique should be applicable to all areas of clinical, medicinal and biomedical chemistry.

Phosphorescence measurements of calf γ-II, III, and IV crystallins at 77 and 293 K

Structural and dynamical features of bovine γ-crystallin tryptophan residues were investigated by phosphorescence measurements at 77 and 293 K. The low temperature phosphorescence spectra and lifetimes of calf γ-II, III, and IV crystallins did not reflect heterogeneity among the γ-crystallins. The 0-0 bands were all at 414±1 nm and the emission lifetimes were all single-exponential with lifetimes of 5·1, 5·3 and 5·3±0·3 sec, respectively. In contrast, phosphorescence measurements at room temperature were sensitive to subtle differences in exposure, accessibility, and flexibility of γ-crystallin tryptophan residues. Thorough deoxygenation allowed for measurement of the normally-quenched room-temperature phosphorescence, and we report the first native phosphorescence measurements of lens crystallins at ambient temperature. The emission maxima for γ-II, III and IV were 446, 442, and 440±2 nm, respectively. The intensity decay curves were all non-single exponential, and the decays were fit to a sum of two exponentials with lifetimes of 9·1 and 93 msec (γ-II), 11 and 75 msec (γ-III), and 4·2 and 68 msec (γ-IV), ±10%. The components of the γ-II emission were assigned to the four tryptophans based on X-ray structural information. Quantum yields of the phosphorescence emission were in the ratio of 20:7:1 for γ-II, III and IV, and comparison of lifetimes and quantum yields suggests that tryptophan rigidity increases in the order γ-IV < III < II. Acrylamide quenching constants for the long-lived components of γ-II and III were roughly equal, while the short-lived tryptophans of γ-III were an order of magnitude more accessible than those of γ-II. The wide range of phosphorescence lifetimes and quenching constants allowed for discrimination of distinct contributions to the phosphorescence emission, and we suggest that room-temperature phosphorescence measurements will be an effective tool for studying conformational changes of lens crystallins.

New substrate for room-temperature phosphorescence—Inorganic compound plate

Room-temperature phosphorescence (RTP) is becoming an important tool for the analysis of drugs, PAHs, pesticides, etc., because of its selectivity, ease of sample handling, ease of automation, and small amount of sample needed for the analysis. Thus far, the solid substrates used in RTP measurement have been limited to filter paper (3, 6, 7, 9, IO), silica gel (I, 2), and sodium acetate (4, 5). Filter paper is the most popular, useful, and convenient substrate at the present time although it still suffers from a relatively high background which hampers the possibility of lowering the detection power for most analytes (6). The search for means of reducing the background signal of filter paper (7), and for other low-background substrates is critical to the analytical usefulness of RTP.

Some aspects of room-temperature phosphorescence in liquid solutions

Experimental requirements for room-temperature phosphorescence measurements in liquids (RTPL) are discussed. Phosphorescence quantum yields and triplet lifetimes of some brominated naphthalenes and halogenated biphenyls at 77 K in 2-methyltetrahydrofuran and at room temperature in hexane are reported and compared. Surprisingly the naphthalenes show only little loss in quantum yields in going from 77 K to room temperature. Sensitized phosphorescence is discussed as a means of expanding the analytical potential of RTPL. Results with a model system of benzophenone as a donor (analyte) and 1,4-dibromonaphthalene as an acceptor are presented.