共查询到20条相似文献,搜索用时 31 毫秒
1.
Excited light and corresponding intrinsic fluorescence diffusion inside teeth tissue are an essential problem for light-based
carious lesion detection. Based on finite element numerical analysis of diffusion equation, the photon density distribution
of both excited light and autofluorescence of 2D premolar teeth model is obtained. The dependence of excited light and autofluorescence
density distribution inside the teeth model on the scattering coefficient of enamel (5–25 mm−1) and dentine (100–140 mm−1) is numerically simulated and analyzed. The fitted results reveal that fluorescence intensity decreases exponentially. Optical
penetration depth and fluorescence relative depth declined with the increment of scattering coefficient of enamel. And the
dentine had the opposite effect. Finally, the experiment of measurement of fluorescence intensity on the teeth surface is
conducted and the result is compared with the numerical computation. 相似文献
2.
The validity of laser induced fluorescence spectroscopy for early diagnosis of occlusal caries irradiated by 403 nm diode
laser compared to commercial device DIAGNOdent pen was investigated. The quantitative evaluation parameter based on the fluorescence
intensity area ratio of different bands F(440–480 nm)/F(540–700 nm) was built. And the linear correlation analysis between
fluorescence result and corresponding DIAGNOdent reading is performed to be r = −0.9085. Moreover, the factors of irradiation laser power and excited site influencing the fluorescence distribution was
experimentally investigated. The result shows that the fluorescence spectra at different site of sound occlusal surface is
different and the higher laser power will lower the sensitivity of evaluation parameter based on the red fluorescence region
increasing. The work is of great significance for practical application of laser induced fluorescence at 403 nm. 相似文献
3.
Nina Sadlej-Sosnowska 《Journal of fluorescence》1997,7(3):195-200
It was found that the fluorescence intensity in solutions of three estrogens—estradiol, ethinyloestradiol, and estriol—increased
upon the addition of Β- or γ-cyclodextrin, the effect being greater with the first ligand. These changes in fluorescence intensity were used for
the determination of association constants of the compounds with the two cyclodextrins. An iterative procedure was used to
calculate the concentrations of free (uncomplexed) ligand, which are needed for the calculation of the association constants.
These values were compared with the constants previously determined by HPLC. The fluorometric association constants with Β-cyclodextrin
were ower than the corresponding HPLC values, whereas for the complexes with γ-cyclodextrin the results of both methods coincide. 相似文献
4.
Gil-García MD Martínez-Galera M Parrilla-Vázquez P Mughari AR Ortiz-Rodríguez IM 《Journal of fluorescence》2008,18(2):365-373
This work describes the optimization of a photochemically induced method for the detection of eight phenylureas has been developed
by response surface methodology (RSM). These pesticides do not show native fluorescence but they were photolyzed into strongly
fluorescent photoproducts under UV irradiation. The effect of the main variables affecting the yield of the photoderivatization
reaction, and hence the fluorescence intensity, such as solvent, UV irradiation time and pH were optimized for each pesticide.
A Doehlert design was applied in order to obtain maximum intensity fluorescence using response surface methodology. In general,
a maximum was found for all pesticides using MeOH as organic solvent, except for diuron, whereas the effect of pH and irradiation
time was different, according to each pesticide. Finally, the addition of β-cyclodextrin upon the photochemically induced
fluorescence intensity was investigate. The fluorescence intensity was only improved for monolinuron at a concentration of
4 × 10−3 M of β-cyclodextrin. 相似文献
5.
A fluorimetric method based on fluorescence enhancement effect was developed for the determination of adenosine 5′-monophosphate
(AMP) with 9-anthracene carboxylic acid (9-ANCA)–cetyl trimethyl ammonium bromide (CTAB) system. Fluorescence intensity of
9-ANCA was decreased by the addition of CTAB but addition of AMP again rose the intensity of 9-ANCA gradually. The observed
fluorescence enhancement is attributed to the competitive binding reaction of 9-ANCA and adenosine to CTAB. The enhancement
in the fluorescence intensity was found proportional to the concentration of AMP over the range 2.0 × 10−4 to 1.2 × 10−3 mol dm−3. The ion pair complex is formed spontaneously between 9-ANCA and CTAB. Since the binding interaction is larger for the adenosine–CTAB
pair, the fluorophore 9-ANCA will be released. The quantum yield of free 9-ANCA is higher therefore its fluorescence observed
at 417 nm wavelength is enhanced. This mechanism of competitive molecular interaction is further confirmed by conductometric
measurements. The method was applied successfully for the determination of AMP from pharmaceutical sample. The method is more
selective, sensitive and relatively free from interferences. 相似文献
6.
A new optical molecular thermometer, based on the thermally activated delayed fluorescence of C70 dispersed in a polystyrene film, was developed. In the presence of oxygen, the fluorescence intensity of the C70 film is essentially temperature independent in a wide range. In the absence of oxygen, however, the fluorescence intensity markedly increases with temperature. At room temperature (25°C), and after degassing the sample, the fluorescence intensity of C70 increases 22 times, while at 100°C the fluorescence intensity is increased by 70 times. With our system, the very weak fluorescence of C70 (ΦF ≅ 5 × 10−4, in toluene) can be increased up to 91 times (up to an estimated maximum value ΦF = 0.046). The estimate value of the singlet-triplet gap (29 kJ mol−1) and the fluorescence lifetime (0.63 ns) of the C70 in film are in agreement with the values reported in the literature for C70 in solution. The values of the phosphorescence lifetime at room temperature (23 ms) and the quantum yield of triplet formation (0.989) were also determined. The system is completely reversible with respect to heating-cooling cycles. 相似文献
7.
We study the forced aspiration of small ( mm) and large ( cm) liquid drops, deposited on prewetted porous membranes, and pumped mechanically with a constant current J. Two kinds of membranes are used where the pores are i) disconnected, cylindrical and calibrated or ii) interconnected “sponge-like”.
Whatever the size of the drops and the intensity J of the current, two suction regimes are observed versus time: 1) a “locked” regime, when the drop is pinned, with a dynamic contact angle decreasing from advancing () to finite receding () contact angle; 2) an “unlocked” regime, where the contour line recedes with a constant contact angle closed to . In both regimes, the shape of the drop remains quasistatic, during the suction process, i.e. a spherical cap for small drops and a flat “gravity pancake” for large ones.
Received 19 January 2000 相似文献
8.
The value of intrinsic chlorophyll fluorescence polarization, and the intensity in emission spectrum were investigated in
leaf segments of Alocasia macrorrhiza under several stress conditions including different temperatures (25–50°C), various concentrations of NaCl (0–250 mM), methyl
viologen (MV, 0–25 μM), SDS (0–1.0%) and NaHSO3 (0–80 μM). Fluorescence emission spectrum of leaves at wavelength regions of 500–800 nm was monitored by excitation at 436 nm.
The value of fluorescence polarization (P value), as result of energy transfer and mutual orientation between chlorophyll molecules, was determined by excitation at
436 nm and emission at 685 nm. The results showed that elevated temperature and concentrations of salt (NaCl), photooxidant
(MV), surfactant (SDS) and simulated SO2 (NaHSO3) treatments all induced a reduction of fluorescence polarization to various degrees. However, alteration of the fluorescence
spectrum and emission intensity of F685 and F731 depended on the individual treatment. Increase in temperature and concentration of NaHSO3 enhanced fluorescence intensity mainly at F685, while an increase in MV concentration led to a decrease at both F685 and F731. On the contrary, NaCl and SDS did not cause remarkable change in fluorescence spectrum. Among different treatments, the
negative correlation between polarization and fluorescence intensity was found with NaHSO3 treatments only. We concluded that P value being measured with intrinsic chlorophyll fluorescence as probe in leaves is a susceptible indicator responding to
changes in environmental conditions. The alteration of P value and fluorescence intensity might not always be shown a functional relation pattern. The possible reasons of differed
response to various treatments were discussed. 相似文献
9.
Correia M Neves-Petersen MT Parracino A di Gennaro AK Petersen SB 《Journal of fluorescence》2012,22(1):323-337
Continuous 295 nm excitation of whey protein bovine apo-α-lactalbumin (apo-bLA) results in an increase of tryptophan fluorescence
emission intensity, in a progressive red-shift of tryptophan fluorescence emission, and breakage of disulphide bridges (SS),
yielding free thiol groups. The increase in fluorescence emission intensity upon continuous UV-excitation is correlated with
the increase in concentration of free thiol groups in apo-bLA. UV-excitation and consequent SS breakage induce conformational
changes on apo-bLA molecules, which after prolonged illumination display molten globule spectral features. The rate of tryptophan
fluorescence emission intensity increase at 340 nm with excitation time increases with temperature in the interval 9.3–29.9°C.
The temperature-dependent 340 nm emission kinetic traces were fitted by a 1st order reaction model. Native apo-bLA molecules
with intact SS bonds and low tryptophan emission intensity are gradually converted upon excitation into apo-bLA molecules
with disrupted SS, molten-globule-like conformation, high tryptophan emission intensity and red-shifted tryptophan emission.
Experimental Ahrrenius activation energy was 21.8 ± 2.3 kJ.mol−1. Data suggests that tryptophan photoionization from the S1 state is the likely pathway leading to photolysis of SS in apo-bLA. Photoionization mechanism(s) of tryptophan in proteins
and in solution and the activation energy of tryptophan photoionization from S1 leading to SS disruption in proteins are discussed. The observations present in this paper raise concern regarding UV-light
pasteurization of milk products. Though UV-light pasteurization is a faster and cheaper method than traditional thermal denaturation,
it may also lead to loss of structure and functionality of milk proteins. 相似文献
10.
Fluorescence imaging of cells and tissue can be used to evaluate β-NADH redox and location. At low temperature, β-NADH fluorescence
intensity increases and therefore sensitivity of imaging increases. In this paper, the temperature dependence of fluorescence
was evaluated for β-NADH in glycerol/water solution and in trehalose/sucrose glass. The average fluorescence lifetime for
NADH in glycerol/water is 0.66 ns, compared with 5.3 ns in trehalose/ sucrose at 20°C. Emission spectra were recorded from
290 to 12 K. The fluorescence of β-NADH in glycerol/water increases ∼16 fold and the emission shifts about 35 nm to the blue
as temperature decreases. Much smaller change is seen for fluorescence of β-NADH in sugar glass. Below 77 K, the β-NADH spectral
features did not change significantly with temperature change, and so no increase in sensitivity is obtained by going to very
low temperatures. It is suggested that the sensitivity of β-NADH fluorescence is related to water relaxation around the excited
state molecule. Differences in water in various tissues may contribute to β-NADH fluorescence changes when cells are altered. 相似文献
11.
D. B. Rogozkin 《Journal of Experimental and Theoretical Physics》1997,84(5):916-939
The long-range correlations in the reflected and transmitted fluxes in the case of the coherent transport of waves in an unordered
medium with discrete inhomogeneities are considered. The correlator and spectrum of the intensity fluctuations are expressed
in a general form in terms of the one-center scattering amplitude and the propagators of the mean radiated intensity. The
random interference of the waves and the fluctuations of the number of scattering centers in a microvolume of the medium are
taken into account simultaneously. Detailed calculations are performed for two limiting radiation propagation regimes, viz.,
spatial diffusion and small-angle multiple scattering. It is shown that the conservation of the total flux upon elastic scattering
leads to the formation of a dip in the spectrum and, accordingly, a negative correlation between the intensities at large
distances. In the case of spatial diffusion this feature is displayed upon reflection, and in the case of small-angle multiple
scattering it is displayed upon transmission through a slab. The relative roles of the various sources of intensity fluctuations,
as well as the sensitivity of the correlations to factors that influence the wave propagation regime, viz., the finite size
of the scattering sample, absorption in the medium, and the presence of a frequency shift in the incident waves, are analyzed.
We find that fluctuations in the distribution of the scatterers show up most strongly in a medium with strong, i.e., “non-Born,”
centers, especially if they exhibit absorption.
Zh. éksp. Teor. Fiz. 111, 1674–1716 (May 1997) 相似文献
12.
The quenching of 2,5-diphenyloxazole (PPO) fluorescence by nucleotides has been investigated by electronic absorption and
steady state fluorescence spectra. Five purine nucleotides AMP, ADP, ATP, GMP and dGMP, one pyrimidine nucleotide UMP and
one dinucleotide NAD have been employed in the present study. Electronic absorption studies indicate that there is no ground
state complexation between the nucleotides and PPO. The quenching of PPO fluorescence was investigated at two different wavelengths.
When excited at 304 nm, the λ
max of PPO, the fluorescence spectra of PPO is quenched following Stern–Volmer kinetics. The quenching ability of nucleotides
are in the order NAD > AMP > ADP > GMP > dGMP > UMP. The K
SV and k
q values obtained indicate that AMP is a better quencher of PPO fluorescence than GMP, which is contrary to commonly observed
pattern. The quenching is found to be dynamic in nature. However, when excited at 260 nm, the absorption maximum of the nucleotides,
the fluorescence intensity of PPO is reduced with increase in the concentration of the nucleotide. This is attributed to the
primary inner filter effect arising due to the absorption of the incident radiation by the nucleotides. Thus the inner filter
effect phenomenon can be employed to assay the non-fluorescent molecules by fluorimetry. 相似文献
13.
N. D. Gómez V. D’Accurso J. Codnia F. A. Manzano M. L. Azcárate 《Applied physics. B, Lasers and optics》2012,106(4):921-926
Laser-induced fluorescence (LIF) has been used to directly determine the dissociation probability per pulse in highly focused
infrared multiple-photon dissociation (IRMPD). The fluence dependence of CDCl3 IRMPD has been determined by LIF and FTIR spectrometry. The particular LIF irradiation and detection system’s geometry implemented
allowed us to monitor the local CCl2 radicals concentration in the intersection zone of the observation and the dissociation volumes. The fluence dependence of
the LIF intensity was modeled with the cumulative log-normal distribution. The dependence of the global values of the fraction
of molecules dissociated per pulse on fluence was obtained from FTIR spectrometry. The dissociation probabilities per pulse
were derived from the deconvolution of these values using the cumulative log-normal distribution. A very good agreement between
the values of the parameters σ and Φ
sat obtained from the deconvolution technique with those resulting from the fluorescence intensity fit was found, showing the
validity of the method proposed. 相似文献
14.
Characterization of the interaction between methylene blue (MB) and calf thymus deoxyribonucleic acid (ctDNA) was investigated
by UV absorption spectra, fluorescence spectra, fluorescence polarization and fluorescence quenching experiments by ferrocyanide.
The above results indicated that the binding modes of MB to ctDNA were relative to the molar ratio γ (γ=[DNA]/[MB]). At low
γ ratios (γ < 4), remarkable hypochromic effect with no shift of λmax in the absorption spectra of MB was observed in the presence of increasing amounts of ctDNA, the fluorescence of MB was efficiently
quenched by the ctDNA bases and the fluorescence polarization of MB was slightly increased, which indicated that MB cations
bound to phosphate groups of ctDNA by electrostatic interaction and then stacked on the surface of ctDNA helix. While at high
γ ratios (γ > 6), besides the fluorescence of MB was quenched efficiently by the ctDNA bases, a red shift (about 3 nm) in
the absorption spectra of MB was observed and the fluorescence polarization of MB was obviously increased, which indicated
the intercalation binding that MB molecules were intercalated into the space of two neighbouring DNA base pairs was the preferred
mode. Effects of K4Fe(CN)6 on the fluorescence quenching of the MB-ctDNA system at low and high γ ratios were also performed. The results showed that
at γ = 1.7, the quenching effect by ferrocyanide was higher than that of pure MB, while at γ = 13.6 a decreased quenching
of the fluorescence intensity was observed as compared with that of pure MB, which further proved the above conclusion. In
addition, the mechanisms of the hypochromic effect and the fluorescence quenching were also discussed in detail. 相似文献
15.
D.V. Kosachiov E.A. Korsunsky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):457-463
Frequency conversion process is studied in a medium of atoms with a configuration of levels, where transition between two lower states is driven by a microwave field. In this system, conversion
efficiency can be very high by virtue of the effect of electromagnetically induced transparency (EIT). Depending on intensity
of the microwave field, two regimes of EIT are realized: “dark-state” EIT for the weak field, and Autler-Townes-type EIT for
the strong one. We study both cases via analytical and numerical solution and find optimum conditions for the conversion.
Received 13 December 1999 and Received in final form 6 March 2000 相似文献
16.
The fluorescence system of the norfloxacin-Tb3+- sodium dodecylbenzene sulfonate (SDBS) was investigated in this paper. The experiments indicated that the fluorescence intensity
of the Tb3+-SDBS was greatly enhanced by the norfloxacin. On the basis of the above findings, a sensitive fluorimetric method for determining
the norfloxacin was established. The fluorescence intensity was measured by a 1-cm quartz cell with the excitation wavelength
of 290 nm and the emission wavelength of 545 nm. The enhanced fluorescence intensity of the system (Δ F) showed a good linear
relationship with the concentration of norfloxacin in the range of 5.0×10−9 mol L−1–2.0×10−6 mol L−1, its correlation coefficient was 0.9991 and the detection limit (S/N=3) was 1.2×10−9 mol L−1. The presented method was used to determine the norfloxacin in real pharmaceutical samples. The luminescence mechanism was
also discussed in detail. In the fluorescence system of the norfloxacin-Tb3+-SDBS, the SDBS not only acted as the surfactant, but also acted as the energy donor. 相似文献
17.
A fluorescence enhancement phenomenon in the europium (Eu)–Ofloxacin (OF)–Sodium Dodecyl Benzene Sulfonate (SDBS) fluorescence
system was observed when Gd3+ was added. The fluorescence intensity of the systems was measured (λ
ex/λ
em = 280/612 nm) at pH 7.8. Under optimum conditions, a linear relationship between the enhanced fluorescence intensity and
the Eu3+ concentration in the range of 5.0 × 10−10 ∼ 2.0 × 10−7 mol·L−1 was observed. The detection limit of Eu3+ was 1.46 × 10−10 mol·L−1 (S/N = 3). This method was used for the determination of trace amounts of europium in synthetic rare earth samples with satisfactory
results. In addition, the interaction mechanism is also studied. 相似文献
18.
O. A. Bukin S. S. Golik P. A. Salyuk E. N. Baulo I. A. Lastovskaya 《Journal of Applied Spectroscopy》2007,74(1):115-119
We present the results of measurement of the laser-induced fluorescence spectra of sea water under laboratory conditions.
We show that during phytoplankton cell death caused by heating of sea water samples, the fluorescence intensity of dissolved
organic matter (DOM) increases. We observe different behaviors of the fluorescence intensity for excitation by 2nd harmonic
(532 nm) and 3rd harmonic (355 nm) emission from a Nd:YAG laser during degradation of dissolved organic matter. In the first
case, a monotonic decrease in the DOM532 fluorescence intensity occurs, while in the second case the fluorescence intensity remains constant. We give a possible explanation
for such behavior of the DOM fluorescence intensity.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 103–107, January–February, 2007. 相似文献
19.
L. K. Neudachina E. V. Dedyukhina O. V. Evdokimova N. V. Pechishcheva E. V. Osintseva K. Yu. Shunyaev 《Journal of Applied Spectroscopy》2010,77(2):206-212
The fluorescence properties of N,N-di(2-carboxyethyl)-p-anisidine (I) in solvents of various nature and in the crystalline state have been studied at room temperature (273 K) and at the boiling
point of liquid nitrogen (77 K). Fluorescence in aqueous solutions of I with protonated (λ
ex
/λ
fl
max
= 225/290 nm) and unprotonated (λ
ex
/λ
fl
max
= 270/380 nm) amino nitrogen has been detected. On going from aqueous solutions to nonaqueous, the fluorescence band of unprotonated
I experiences a blue shift and its intensity rises. The fluorescence intensity of the band in aprotic polar solvents is higher
than that in protic solvents. A linear dependence of the fluorescence intensity of deprotonated I on Cu(II) concentration (ranging from 1.0 to 5.0 mg/dm3) in aqueous solution has been found. The fluorescence intensity of I in aqueous solutions at 77 K and pH 1–6 has been shown to increase in the presence of Zn(II) (1–170 mg/dm3) and Cd(II) (2–330 mg/dm3) although a similar dependence is not observed at 293 K. 相似文献
20.
In our study, terbium-acetylacetone (Tb-acac) composite nanoparticles have been prepared under vigorous ultrasonic irradiation.
The nanoparticles are water soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies.
They were used as fluorescence probes in the determination of enoxacin (Enox) based on the fluorescence enhancement of nanoparticles
through fluorescence resonance energy transfer (FRET). The influence of buffer solution on the fluorescence intensity was
investigated. Under the optimum conditions, the fluorescence intensity of the Tb-acac-Enox system is linearly proportional
to the Enox concentration in the Enox concentration range of 2 × 10−7–1 × 10−4 M. The correlation coefficient for the calibration curve was 0.9976. The limit of detection as defined by IUPAC, C
LOD = 3S
b/m (where S
b is the standard deviation of the blank signals and m is the slope of the calibration graph) was found to be 3 × 10−8 M. The relative standard deviation (RSD) for six repeated measurements of 1 × 10−4 M Enox was 1.35%. The method was applied to the determination of Enox in pharmaceutical formulation and recovery results
were obtained from urine samples. 相似文献