We have explored the use of a fiber-optic probe with surface-enhanced Raman scattering (SERS) sensing modality for
early, noninvasive and, rapid diagnosis of potential renal acute rejection (AR) and other renal graft dysfunction of kidney
transplant patients. Multimode silica optical fiber immobilized with colloidal Ag nanoparticles at the distal end was used
for SERS measurements of as-collected urine samples at 632.8 nm excitation wavelength. All patients with abnormal
renal graft function (3 AR episodes and 2 graft failure episodes) who were clinically diagnosed independently show
common unique SERS spectral features in the urines collected just one day after transplant. SERS-based fiber-optic
probe has excellent potential to be a bedside tool for early diagnosis of kidney transplant patients for timely medical
intervention of patients at high risk of transplant dysfunction.
We present a study on surface-enhanced Raman scattering (SERS) utilizing unclad single crystal sapphire fiber with Ag nanoparticles (NPs) immobilized either at the fiber distal end for direct excitation or on the fiber surface for evanescent-field interaction. The dependence of SERS intensity on the coverage density of Ag NPs was investigated. We demonstrated robust SERS sensitivity in both cases. For direct excitation-based sensing, we found that a sensitivity maximum exists with increased particle coverage beyond which the sensitivity starts to decline. More importantly though, for evanescent-field based measurements, we revealed that multimode sapphire fiber can accommodate Ag NPs at a far higher particle coverage density than single-mode fiber while maintaining the dominance of SERS gain despite competitive absorption and scattering loss by Ag NPs with a limit of detection of 10-9 M Rhodamine 6G solution.