METHOD FOR THE DETERMINATION OF ABSORPTION CROSS SECTIONS OF FLUORESCENT SOLUTES

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。我们设计了一种与溶质浓度无关的吸收截面的测定方法。我们的方法利用光子计数直方图（PCH）分析的荧光波动光谱与荧光团，可以用作校准标准。我们证明了该方法的原理和它的应用，在纳摩尔浓度的有机荧光团的双光子截面的测量，表明我们得到合理的数字与文献值相比时。我们的方法是特别有用的情况下，少量的样品是必要的（毫微微摩尔，可能更少）和吸收截面不能通过其他方法确定。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We have devised a method for the determination of absorption cross sections which is independent of the concentration of solute. Our method makes use of the photon counting histogram (PCH) analysis of fluorescence fluctuation spectroscopy together with a fluorophore that can be used as a calibration standard. We demonstrate the principles of the method and its application to the measurement of two-photon cross sections of organic fluorophores at nanomolar concentrations; showing that we obtain reasonable numbers when comparing with literature values. Our method is particularly useful in cases where small amounts of sample are necessary (femtomoles and possibly less) and where the absorption cross section cannot be determined by other methods.