Comparison of infrared-excited up-converting phosphors and europium nanoparticles as labels in a two-site immunoassay

Research in the field of immunoassays and labels used in the detection has been recently focused on particulate reporters, which possess very high specific activity that excludes the label as a sensitivity limiting factor. However, the large size and shape of the particulate labels may produce additional problems to immunoassay performance. The aim of this work was to study with two identical non-competitive two-site immunoassays whether up-converting phosphor (UCP) particles are comparable in performance with europium(III) chelate-dyed nanoparticles as particulate labels. In addition we strived to verify the common assumption of the photostability of up-converting phosphor particles supporting their potential applicability in imaging. Detection limits in two-site immunoassay for free prostate-specific antigen (free-PSA) were 0.53 ng L⁻¹ and 1.3 ng L⁻¹ using two different up-converting phosphors and 0.16 ng L⁻¹ using europium(III) nanoparticle. Large size distribution and non-specific binding of up-converting phosphor particles caused assay variation in low analyte concentrations and limited the analytical detection limit. The non-specific binding was the major factor limiting the analytical sensitivity of the immunoassay. The results suggests the need for nanoscaled and uniformely sized UCP-particles to increace the sensitivity and applicability of up-converting phosphor particles. Anti-Stokes photoluminescence of up-converting phosphor particles did not photobleach when measured repeatedly, on the contrary, the time-resolved fluorescence of europium nanoparticles photobleached relatively rapidly.     

Investigation of photobleaching and saturation of single molecules by fluorophore recrossing events

A method for investigation of photobleaching and saturation of single molecules by fluorophore recrossing events in a laser beam is described. The diffraction-limited probe volumes encountered in single-molecule detection (SMD) produce high excitation irradiance, which can decrease available signal. The single molecules of several dyes were detected and the data was used to extract interpeak times above a defined threshold value. The interpeak times revealed the number of fluorophore recrossing events. The number of molecules detected that were within 2 ms of each other represented a molecular recrossing for this work. Calcein, fluorescein and R-phycoerythrin were analyzed and the saturation irradiance and photobleaching effects were determined as a function of irradiance. This approach is simple and it serves as a method of optimizing experimental conditions for single-molecule detection.     

聚合物PMMA/DR1薄膜棱镜的制备

本文研究了用光漂白方法制备ＰＭＭＡ／ＤＲ１聚合物光棱镜的方法,测量了这种波导棱镜对１．０６４μｍ光的ＴＥ模和ＴＭ模在波导内传播光束的方向改变,并从理论上对测量结果进行了分析。     

Photocatalytic bleaching of p-nitrosodimethylaniline in TiO2 aqueous suspensions: A kinetic treatment involving some primary events photoinduced on the particle surface

The photocatalytic bleaching of p-nitrosodimethylaniline (P) has been investigated in aqueous suspensions of TiO₂. It was found that both charge carriers (hole and electron) were reactive to P to result in a bleaching. The roles of O₂ and several hole scavengers (HCOO⁻, EDTA, I⁻) have also been examined. A reaction mechanism has been proposed with consideration of several primary processes photoinduced on TiO₂ surface. The results of the kinetic analysis fit fairly well to those of the experiments. The rate constant (k^h_p) of the reaction between P and the adsorbed hydroxyl radical was estimated to be in the order 10¹⁰ M⁻¹ s⁻¹, which is in good agreement with that obtained from the homogeneous reaction of P with free OH radicals. Of particular interest is the pH dependence of the photobleaching rate. Around both pK_a of P and pH_ZPC of TiO₂, the photobleaching of P was steeply enhanced. This can be reasonably attributed to the mutual interaction (repulsion versus attraction) between P and TiO₂ particles in different pH ranges.     

The efficacy of photostabilizers on the color change of wood filled plastic composites

In this study, we compared the performance of different hindered amine light stabilizers and ultraviolet absorbers as photostabilizers of wood plastic composites (WPC). We showed how their functional groups and molecular weights influence the photostabilization of WPC subjected to natural weathering for 2000 h. The changes were followed using color measurements and FTIR spectroscopy which provided insight into the photodegradation mechanism of weathered WPC.The results indicate that weathering causes color fading and changes in yellowing. We propose that WPC undergo two competing redox reactions upon UV exposure. The first is the oxidation of lignin which leads to the formation of paraquinone chromophoric structures which is dominant in the first 250 h of exposure. The second is the reduction of the paraquinone structures to hydroquinones which leads to photobleaching.High molecular weight diester HALS were found to be the most effective in controlling long term fading and yellowing changes. Furthermore, the addition of a benzotriazole ultraviolet absorber shows great synergism in controlling fading when added to a diester HALS.     

Photoinduced absorption edge shift of As20Se60Tl20 films

As₂₀Se₆₀Tl₂₀ bulk material was prepared firstly then thermal evaporation method was used to prepare As₂₀Se₆₀Tl₂₀ films. Illumination effect at room temperature for the mentioned films has been studied within the homogeneous glass-forming region. The prepared film samples were amorphous, this is depicted by X-ray chart. Optical properties have been studied using spectrophotometric measurements. The absorption edge was shifted to shorter wavelengths due to light exposure or photobleaching effect. It was found that the extinction coefficient and the optical band gap have opposite character after illumination.     

利用分子梳方法研究单个DNA-YOYO-1复合体的光漂白性质

利用分子梳方法结合荧光显微术对单个DNA-YOYO-1复合体的光漂白过程进行了研究,发现单个DNA-YOYO-1复合体的光漂白是一个随光照时间指数衰减的过程,并给出了DNA拓扑结构以及光照强度对光漂白过程的影响.     

厦门湾有色溶解有机物光漂白的三维荧光光谱研究

利用荧光激发-发射矩阵光谱(excitation-emission matrix spectroscopy,EEMs)研究了厦门湾九龙江河口中、低盐度区表层水样中有色溶解有机物在秋季天然太阳辐照下的光化学漂白。结果表明,光漂白未引起水样中类腐殖质(C, A, M)和类蛋白质(T,B)荧光峰位置的移动。5个峰的荧光强度均随辐照时间的增加而减少,其中低盐度水样的降低幅度更大,并以指示陆源河流输入的特征荧光峰C的光漂白程度最大。根据漂白速率可将各荧光团区分出易漂白和难漂白两类组分。光漂白导致T、C峰及A、C峰之间的荧光强度比值增加,说明光漂白可引起海水中溶解有机物性质的明显改变,并且也是近海类蛋白质荧光相对类腐殖质荧光占优势的一个重要控制因素。研究结果对于探究陆源有机物在近海的转化及去除过程以及海洋光学有一定的参考价值。     

Fluorescence Recovery Under Decaying Photobleaching Irradiation: Concept and Experiment

A novel modification of photobleaching method for measurement of lateral diffusion is developed. In this approach fluorescence recovery kinetics is measured under decaying photobleaching irradiation, termed as fluorescence recovery under decaying photobleaching (FRDP). The time evolution of fluorescence intensity normalized to input irradiation starts from the photobleaching kinetics and transforms into the kinetics of fluorescence recovery at a later stage resulting in appearance of minimum. The analytical solution for the kinetics of fluorescence for Gaussian lineshape of laser beam and hyperbolic decay of irradiation in the first order approximation on bleaching rate was obtained. The accuracy of the analytical function was evaluated with exact numerical solution computed with finite differentiates method. The FRDP method was successfully applied to fluorescein solution in the glycerol/water mixture (80%) under various experimental settings using home-made experimental set-up. The FRDP approach demonstrated 25–30 fold enhancement in signal intensity over classical fluorescence recovery after photobleaching (FRAP) method at 3–5 fold increase in total irradiation. Among other advantages of the FRDP is the opportunity to perform measurements on varying time scales under constant size of the bleaching spot, including “safe” long time measurements. The potential extra advantage of FRDP method for analysis of complex diffusion in the biological system is discussed.