METHOD FOR THE DETERMINATION OF ABSORPTION CROSS SECTIONS OF FLUORESCENT SOLUTES

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。我们设计了一种与溶质浓度无关的测定吸收截面的方法。我们的方法利用了荧光起伏光谱的光子计数直方图(PCH)分析和一个可以作为校准标准的荧光团。我们演示了该方法的原理及其在纳摩尔浓度下测量有机荧光团双光子截面的应用，表明与文献值相比，我们得到了合理的数值。我们的方法在需要少量样品(飞摩尔或更少)以及吸收截面不能用其他方法确定的情况下特别有用。

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.