Compact, non-invasive frequency domain lifetime differentiation of collagens and elastin

• Frequency domain system was developed to measure tissue fluorescence lifetimes.
• The LED and photodiode based system was low cost and low complexity.
• Collagen I versus III lifetimes are distinct at 3.95 ns and 5.01 ns, respectively.
• Elastin lifetime is distinct from collagen at 6.78 ns.
• Detection was demonstrated with bovine ocular tissue and murine skin wounds.

Changes in the composition of type I and type III collagen in tissue can shed light on various diseases. However, many of the current collagen detection techniques require invasive and destructive tissue sampling. In this study, a low cost, low complexity light emitting diode (LED) based system was developed to realize both non-invasive detection and specific discrimination of collagen and elastin variations in tissue based on fluorescence lifetimes. Modulated LED excitation was applied to frequency domain (FD) fluorescence lifetime spectroscopy to calculate tissue autofluorescence lifetimes. Using this method, fluorescence lifetimes from collagen type I versus type III were clearly separated at 3.95 ns and 5.01 ns, respectively, distinct from the elastin lifetime at 6.78 ns. The probe was tested on bovine ocular tissues, with cornea showing much shorter average lifetime of 4.27 ns than sclera at 7.48 ns. Furthermore, measurements of an 8 mm murine skin wound at 14 days post-wounding also showed distinct, longer average lifetimes at 9.74 ns versus normal skin at 6.72 ns. This FD tissue detection technique can potentially offer a way to examine tissue structures and discern the underlying pathology nondestructively.