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

PEREZ, R.D; SÁNCHEZ H.J.; PEREZ, C.A.; RUBIO, M.

RADIATION PHYSICS AND CHEMISTRY (OXFORD)

Elsevier Science Limited

Lugar: Exeter (UK); Año: 2010 vol. 79 p. 195 - 200

0969-806X

X-ray fluorescence analysis performed with a primary radiation focused in the micrometer range is known as micro x-ray fluorescence (mXRF). It is characterized by a penetration depth higher than other micro-analytical methods, reaching hundreds of micrometers in biological samples. This characteristic of the x-ray beam can be employed in 3D analysis. An innovative method to performed 3D analysis by mXRF 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 mXRF experiments are mainly glass capillaries and polycapillaries. Glass capillaries are used in the excitation channel with sources of high photon flux like synchrotron radiation. Half polycapillaries or conical polycapillary concentrators are used almost exclusively in the detection channel. Spatial resolution of the confocal mXRF depends on the dimensions of the foci of both x-ray lenses. The overlap of these foci forms an ellipsoid which is the probing volume of the confocal setup. The axis length of the probing volume reported in confocal mXRF experiments are of order of few tens of mm.  In our confocal setup, we used a commercial glass monocapillary in the excitation channel and a monolithic half polycapillary in the detection channel. The polycapillary was home-made by means of drawing of multibundles of glass capillaries in a heating furnace. The experiment was carried out at the beamline D09B-XRF of the Synchrotron Light National Laboratory (Laboratório Nacional de Luz Síncrotron, LNLS) using white beam. A model for the theoretical description of x-ray fluorescence intensity registered by confocal mXRF was introduced by Malzer and Kanngieber in 2005. These authors showed that the measured scanning of fluorescent intensity is the spatial convolution of the sensitivity and the x-ray fluorescence emission rate detected. In a previous work we demonstrated that the convolution theorem can simplify the calibration and quantification process in confocal mXRF. In the present work, we applied these ideas to analyze samples of aquatic plants and a sample of tooth by confocal mXRF. We showed that confocal mXRF can be successfully applied to help the study of the effects of water bioremediation on aquatic plants. We also showed that confocal mXRF can be used to make topological studies of teeth.