Latest developments and opportunities for 3D analysis of biological samples by confocal XRF

R.D. PÉREZ; H. J. SÁNCHEZ; C. A. PÉREZ; M. RUBIO

RADIATION PHYSICS AND CHEMISTRY (OXFORD)

Año: 2009

0969-806X

X-ray fluorescence analysis performed with a primary radiation focused in the micrometer rangeis known as micro x-ray fluorescence (μXRF). It is characterized by a penetration depth higher than othermicro-analytical methods, reaching hundreds of micrometers in biological samples. This characteristic ofthe x-ray beam can be employed in 3D analysis. An innovative method to performed 3D analysis byμXRF is the so-call confocal setup.The confocal setup consists of x-ray lenses in the excitation as well as in the detection channel.In this configuration, a micro volume defined by the overlap of the foci of both x-ray lenses is analyzed.Scanning this micro volume through the sample can be used to perform a study in three dimensions.At present, x-ray lenses used in confocal μXRF experiments are mainly glass capillaries andpolycapillaries. Glass capillaries are used in the excitation channel with sources of high photon flux likesynchrotron radiation. Half polycapillaries or conical polycapillary concentrators are used almostexclusively in the detection channel. Spatial resolution of the confocal μXRF depends on the dimensionsof the foci of both x-ray lenses. The overlap of these foci forms an ellipsoid which is the probing volumeof the confocal setup. The axis length of the probing volume reported in confocal μXRF experiments areof order of few tens of m.In our confocal setup, we used a commercial glass monocapillary in the excitation channel and amonolithic half polycapillary in the detection channel. The polycapillary was home-made by means ofdrawing of multibundles of glass capillaries in a heating furnace. The experiment was carried out at thebeamline D09B-XRF of the Synchrotron Light National Laboratory (Laboratório Nacional de LuzSíncrotron, LNLS) using white beam.A model for the theoretical description of x-ray fluorescence intensity registered by confocalXRF was introduced by Malzer and Kanngieer in 2005. These authors showed that the measuredscanning of fluorescent intensity is the spatial convolution of the sensitivity and the x-ray fluorescenceemission rate detected. In a previous work we demonstrated that the convolution theorem can simplify thecalibration and quantification process in confocal XRF. In the present work, we applied these ideas toanalyze samples of aquatic plants and a sample of tooth by confocal XRF. We showed that confocalXRF can be successfully applied to help the study of the effects of water bioremediation