PDMS lens for a fiber probe for detecting low-intensity fluorescence signals from advanced glycation endproducts.

Fluorescence-based biomedical diagnostics such as cancers and advanced glycation endproducts (AGEs) face important challenges, primarily the weak fluorescence emission and optical attenuation in highly scattering and absorbing biological tissues. We aim to develop an attachable polydimethylsiloxane (PDMS) lens for an optical fiber probe that can detect low-intensity collagen-linked fluorescence (CLF) due to the AGE formation, despite high melanin concentration, and provide a non-invasive AGE detection system irrespective of skin color. We employed a Y-shaped multimode fiber-optic (MMFO) probe-based fluorescence spectroscopy for the detection of AGEs. We fabricated the PDMS-based plano-convex milli-lens for the MMFO probe using a hanging droplet technique and characterized for numerical aperture to maximize light collection. Skin mimicking phantoms containing AGEs, NADH, FAD, and varying concentrations of melanin (100-400 µM) were prepared. The PDMS lens-assisted fiber probe was used to measure the CLF spectrum (440-560 nm) from phantoms at an excitation of 405 nm. The phantom-based studies revealed that increasing concentration of melanin made the acquisition of CLF spectra difficult. The lens-assisted fluorescence measurement from these phantoms resulted in significant improvement in the collection of CLF spectra. The collection of the CLF signals with lens improved by 200%. The peak prominence of the CLF spectrum improved from 1 to 6.4.