Neutron, fluorescence, and optical imaging: An in situ combination of complementary techniques

Abstract

An apparatus which enables the simultaneous combination of three complementary imaging techniques, optical imaging, fluorescence imaging, and neutron radiography, is presented. While each individual technique can provide information on certain aspects of the sample and their time evolution, a combination of the three techniques in one setup provides a more complete and consistent data set. The setup can be used in transmission and reflection modes and thus with optically transparent as well as opaque samples. Its capabilities are illustrated with two examples. A polymer hydrogel represents a transparent sample and the diffusion of fluorescent particles into and through this polymer matrix is followed. In reflection mode, the absorption of solvent by a nile red-functionalized mesoporous silica powder and the corresponding change in fluorescent signal are studied.

Solvent and solute ingress into hydrogels resolved by a combination of imaging techniques

“…A detailed description of the home-built imagingapparatus to perform optical transmission imaging (OI) and fluorescence imaging (FI) experiments concurrently with neutron radiography (NR) can be found elsewhere. 31 The sample was irradiated with a parallel beam of light and a collimated neutron beam at the cold neutron imaging facility ICON at the Paul Scherrer Institute (Villigen, Switzerland) and time series of images were recorded with separate CCD cameras for each imaging technique. The chosen distance of the neutron source aperture, L, and diameter of the aperture, D ap , yielded L/D ap = 343.…”

“…In a typical experiment, the sample was constrained between two glass plates in a specifically designed sample cell that consisted of an aluminum body and quartz glass windows. 31 The cell was aligned with respect to the neutron and light beams. As neutron radiography experiments can only be performed at large scale facilities where beam time is severely limited, time series of images were recorded for a maximum of 3-8 h. It was found that for the FI experiments, and especially when the larger dextran molecules were used as diffusants, much longer measurement times would be favorable.…”

“…(Note that the dependence on position, (x, y), and time since the start of the experiment, t, is not explicitly given in the following equations.) As described elsewhere in more detail, 31,32 based on I raw , the absolute transmission of the sample, T S , and then the concentration or composition was determined.…”

“…This was done using a novel setup, which combines neutron radiography (NR), fluorescence imaging (FI), and optical brightfield imaging (OI). 31 These three imaging techniques monitor different properties of the samples. In the optical images, contrast is generated by differences in the local optical density of the sample.…”

“…The number of transmitted neutrons, i.e., intensity, provides spatially and temporally resolved information about the composition of the sample. [31][32][33] This has already successfully been applied to investigate the flux of liquids. [34][35][36][37][38][39] Exploiting this effect, this allowed us to monitor solvent diffusion into and out of the hydrogel.…”