Comparison of synchrotron and laser sources in X-ray contact microscopy of metal-contaminated biological tissue

Soft X-ray contact imaging of ultrasections of lead- and cadmium-contaminated earthworm chloragogenous tissue has been achieved with both synchrotron and laser sources. Resolution of ≅70 nm was obtained with the synchrotron radiation source (SRS). The heterogeneous lead deposits associated with the chloragosome granules in highly polluted tissue imaged precisely with the SRS using a methacrylic copolymer (PM) type resist, thus producing a lead 'map', confirmed by X-ray microanalysis. Less satisfactory images of the lead localisation were obtained with the laser source using a terpolymer (TP) resist, and when the TP resist was used in the SRS, tissue with lower lead levels was also imaged, as was tissue contaminated with cadmium. In this latter case, the SRS and laser source gave comparable images using TP resists, the granules imaging clearly but the cadmium, present in vesicles within the cytoplasm, was not resolved, though a suggestion of its localisation was obtained with the SRS and the PM type resist. (orig.)