Spectral and photobleaching analysis using confocal laser scanning microscopy: a comparison of modern and archaeological bone fluorescence

Since the 1950s, tetracycline (TC) administration has been used to create fluorescent ‘labels’ in bone for histomorphometric analysis. Similar fluorescence discovered in ancient human bone from Egypt and Sudan has been attributed to bacterially contaminated food-stores. It has been suggested that TC from this source could have affected the health of exposed ancient populations. However, no efficient means for the quantitative comparison of fluorescent labels within or between individuals or populations has been proposed. In the current study, confocal laser scanning microscopy (CLSM) was shown to be an effective tool for fluorescence detection and spectral analysis in bone. Well-preserved archaeological bone recovered from the Dakhleh Oasis, Egypt was compared to modern pig bone labeled with tetracycline and stained decalcified dog bone. TC fluorescence, whether archaeological or modern, was accurately identifiable by its spectrum. Photobleaching experiments suggest some difference exists in the photoresilience of archaeological and modern TC labels and that scans of one plane and area of focus can be made for more than an hour without complete loss of signal intensity. Results encourage the use of CLSM imaging and spectral analysis for further study on the nature of fluorescence in ancient and modern bone.