Methods and Applications in Fluorescence最新文献

This work describes the relationship between the complex of photosystem I and photosystem II in the senescence process of rice leaves observed through changes in the optical response. We studied three varieties of rice plants at different aging times using time-resolved photoluminescence to measure the time decay of the emission, and stationary photoluminescence, to measure the emission wavelength. The spectra obtained with the former technique were fitted with decreasing exponential functions. Two relaxation times were obtained, one ranging between 1.0 and 1.7 ns, and the other, from 5.0 to 10.5 ns. They are associated with the electron's deexcitation of PSI and PSII, respectively, and these decay times increase as the leaf senescence process takes place. The spectra obtained with stationary photoluminescence were fitted with Voigt functions. These spectra exhibit two main peaks around 683 and 730 nm, which could be associated mainly with PSII and PSI emissions, respectively. The PSI de-excitation exhibits higher dispersive processes because chlorophyll-a molecules in it move away from each other, decreasing their concentration. Therefore, it takes longer for electrons to recombine during photosynthesis, as seen in the time-resolve response. Articulating the results of both photoluminescence techniques, the changes in the response of the photosystems of the living rice leaves during senescence are evidenced.

Polyvinylpyrrolidone (PVP) can be used to produce upconversion nanoparticles (UCNPs) in an advantageous manner, i.e. at modest temperatures in open-to-air conditions with simple hotplate and flask apparatus. However, the influence of PVP parameters on the formation of UCNPs has not been previously investigated. In this exploratory study, we establish that PVP molecular weight and relative amount of PVP can greatly influence the morphology and diameter of NaYF₄:Yb,Er UCNPs produced via the PVP-assisted route. At nominal amounts of PVP, varying the molecular weight of PVP in synthesis between 10,000 g mol^-1(PVP10), 40,000 g mol^-1(PVP40), and 55,000 g mol^-1(PVP55), had minimal effect on UCNP morphology, whereas reducing the quantity of PVP10 and PVP40 in the reaction to 10% of the nominal amount resulted in two notable effects: (1) the generation of a greater range of UCNP diameters and (2) the production of an unexpected sub-population of rhombus-shaped UCNPs. Bulk and individual nanoparticle analysis indicates that all UCNP morphologies were cubic (α-phase) crystal structure and consisted of NaYF₄:Yb,Er. Optical emission properties exhibited only modest green and red luminescence emission ratio when PVP parameters were varied. However, separately produced PVP40 NaYF₄:Yb,Tm UCNPs exhibited a much more intense and dual-band blue/red emission. This exploratory work demonstrates that tailoring PVP content in synthesis of UCNPs can greatly alter morphology of UCNPs produced and should be carefully considered in experimental design. However, the underlying mechanisms of action of the role PVP plays in this synthesis remain unclear. Ultimately, significant further work is still required to fully elucidate the relevant chemistry to achieve full control of PVP-UCNP synthesis.

Two different pairs of laser dyes, Rhodamine-110 (Rh-110)/Rhodamine-6G (Rh-6G) and Rhodamine-19 (Rh-19)/Rhodamine-B (Rh-B) (the first dye in each pair as a donor and the second as an acceptor) were impregnated in silica samples prepared by the sol-gel method and spectroscopically studied using absorption and steady-state fluorescence techniques. The critical transfer distance (R₀), actual distance (r) between the donor and acceptor, overlap integral [J(υ¯)], FRET (fluorescence resonance energy transfer) efficiency (E), and antenna effect efficiency (AE) were investigated in detail based on the variation in acceptor concentration. The FRET efficiency, antenna effect efficiency, and actual donor-acceptor distance for Rh-110/Rh-6G and Rh-19/Rh-B dye pairs corresponding to acceptor concentration ranges (3.83 to 7.65) × 10^-5M l^-1and (3.71 to 8.34) × 10^-5M l^-1, respectively, were found to be in the ranges of 57.38% to 74.89%, 36.97% to 24.13%, 5.44 nm to 4.77 nm, and 77.01%. Furthermore, maximum FRET efficiencies of 85.68% and 87.63% and antenna effect efficiencies of 36.97% and 40.95% for Rh-110/Rh-6G and Rh-19/Rh-B, respectively, were also reported. Our results demonstrate the superior FRET efficiency of Rh-19/Rh-B over Rh-110/Rh-6G dye pair in sol-gel glasses, while the antenna effect efficiency of Rh-110/Rh-6G is higher than that of Rh-19/Rh-B for the same donor to acceptor (D/A) ratio. Finally, Rh-110/Rh-6G is a better energy harvester than the Rh-19/Rh-B dye pair at the common D/A ratio. These results are explained in terms of molecular structure similarity, polarity, and rigidity of donor and acceptor.

The wavelength-ratiometric techniques gain increasing popularity in fluorescence probing and sensing for providing inner reference to output signal and removing instrumental artefacts, in this way increasing the sensitivity and reliability of assays. Recent developments demonstrate that such approach can allow achieving much more, with the application of broad range of novel molecular and nanoscale fluorophores (luminophores), exploring the whole power of photophysical and photochemical effects and using extended range of assay formats. Simplicity of detection and potentially rich content of output data allows realizing these techniques in different simplified, miniaturized and multiplexing devices. The latter issues are discussed in Pt. II of these series.

The problem of enhanced molecular emission in close proximity to dielectric and metallic interfaces is of great importance for many physical and biological applications. Here we present an exact treatment of the problem from the view point of classical electromagnetism. Self-consistent analytical theory of the surface enhanced fluorescence (SEF) is developed for configurations consisting of an emitter in proximity to core-shell metal-dielectric nanoparticles. The dependence of the fluorescence enhancement on the excitation laser and fluorescence frequencies and distance of the emitter to the nanoparticle interface are studied. The developed theory predicts enhanced fluorescence at intermediate distances as well as emission quenching into non-radiative surface plasmon (SP) modes dominating the response for short distances. The conditions for optimal emission enhancement for two core-shell configurations are determined and a comparison to published experimental data is performed showing a good correspondence between theory and experiment. The developed model can be applied toward analyzes and optimizations of various applications related to SP enhance fluorescence spectroscopy.

The wavelength-ratiometric techniques demonstrate strong advantages in fluorescence sensing and imaging over techniques employing variations of intensity at single wavelength. We present different possibilities for realization of these advantages in different simplified, miniaturized and multiplexing devices. They include the smartphone-based detection systems and strips, in which the color changes are observed with naked eye. The array-based techniques and different immunoassays withλ-ratiometric detection demonstrate strongly increased stability and sensitivity. The application areas extend from on-site monitoring of environment and point-of-care diagnostics to testing in personal need. Selected examples of sensing different analytes in chemical and biological systems demonstrate multiple possibilities of coupling the analyte-sensor interaction with the generation ofλ-ratiometric output signal. Among them, simultaneous detection of several analytes and performing logical operations that can be useful in analysis. Finally, the benefits of multicolor ratiometric fluorescence imaging are demonstrated by visualization the functionally important parameters of biological membranes.

In recent years, tetracyclines (TCs) is a hot research topic. Herein, we report an interesting discovery using the complexation of oxytetracycline and metal ions. In this study, according to the properties of Fe₃O₄nanoparticles (Fe₃O₄NPs) as a nanoenzyme, it can be used to catalyze the oxidation of KI by H₂O₂to produceI3-,while at the same timeI3-binds to rhodamine 6G (Rh6G) to form a conjoined particle (Rh6G ∼ I₃)_n, leading to a decrease in the fluorescence intensity of Rh6G. However, in the presence of TCs, Fe₃O₄NPs have a synergistic effect with TCs, leading to enhanced catalytic activity, as well as better selectivity compared to the activity of other reducing enzymes. Consequently,the fluorescent signal based on a resonance scattering effect between Rh6G andI3-is dependent on the concentration of TCs, thus achieving highly facile and robust detection of TCs. The limits of detection (LOD) of the method were 20 nM, 10 nM and 40 nM for oxytetracycline(OTC), tetracycline(TC) and chlortetracycline(CTC), respectively. Most importantly, the method can be successfully applied to the detection of TCs in milk, eggs, and honey. The recoveries of spiked samples ranged from 83.11 to 118.95%. Thus, a stable, hands-on strategy for the detection of TCs is proposed, which has potential applications in the field of food safety and environmental protection.

Phosphorescence emission of 5,6-Benzoquinoline embedded in poly (vinyl alcohol) film has been studied at room temperature. A strong green long-lived emission was observed in films doped with 5,6-Benzoquinoline while illuminated on a UV plate. A broad phosphorescence emission spectrum is centered at about 500 nm. The phosphorescence excitation spectrum follows the absorption spectrum of 5,6-Benzoquinoline, except for a long-wavelength part, which is well beyond the absorption band. This long-wavelength part of the absorption spectrum is responsible for the forbidden S₀-T₁transition. The excitation at 430 nm resulted in the long-lived emission with a spectrum similar to the phosphorescence spectrum obtained with UV excitation within the absorption of 5,6-Benzoquinoline. The phosphorescence anisotropy obtained with a direct S₀-T₁excitation is positive, while the UV excitation is negative. In contrast to fluorescence, the phosphorescence intensity strongly depends on temperature. Phosphorescence lifetimes with UV and long-wavelength excitation are similar, with a mean value of about 0.5 s.

Hybrid nanoparticles are innovative invention of last decade designed to overcome limitations of single-component nanoparticles by introducing multiple functionalities through combining two or more different nanoparticles. In this study, we are reporting development of magneto-fluorescent hybrid nanoparticles by combining iron oxide and carbon nanoparticles to enablein vivofluorescence imaging which also has all the required characteristic properties to use as Magnetic Resonance Imaging (MRI) contrast agent. In order to achieve dual-functional imaging, alginate and pullulan coated super paramagnetic iron oxide nanoparticles (ASPION and PSPION) and Carbon dots (Cdts) were synthesised separately. ASPIONs and PSPIONs were further chemically conjugated with Cdts and developed dual-functional nanohybrid particles ASPION-Cdts and PSPION-Cdts. Subsequently, evaluation of the materials for its size, functionalisation efficiency, fluorescence and magnetic properties, biocompatibility and cellular uptake efficiency has been carried out. Fluorescence imaging of liver fibrosis was performedin vivoin rodent model of liver fibrosis using the two nanohybrids, which is further confirmed by high fluorescence signal from the harvested liver.