A Surface-Enhanced Raman Scattering and Fluorescence Seesaw Nanosensor for the Detection of Cathepsin B Activity in Breast Cancer Cells

Cathepsin B (CTSB) plays a key role in several processes that promote breast cancer progression, making its activity detection crucial for cancer analysis. In this study, we developed a surface-enhanced Raman scattering (SERS) and fluorescence seesaw nanosensor for probing CTSB activity in breast cancer cells. The nanosensor, termed Au-pep-TAMRA, was fabricated by conjugating carboxytetramethylrhodamine (TAMRA)-labeled peptide substrates (pep-TAMRA) to gold nanoparticles (Au NPs). The peptide substrates served dual functions: (1) as recognition units specifically cleavable by CTSB and (2) as linkers bridging the plasmonic Au NPs and TAMRA signal molecules. Upon CTSB-mediated proteolytic cleavage, the altered distance between Au NPs and TAMRA generated inversely correlated signal changes in the SERS (reduction) and fluorescence (recovery) channels. This dual-mode nanosensor exhibited an expanded detection range of 5–200 ng/mL (compared to the single-mode detection) while achieving a low limit of detection of 1.16 ng/mL. Cell experiment validated the nanosensor’s capacity to precisely determine CTSB activity in MDA-MB-231 cell lysates. The SERS-fluorescence switchable nanosensor demonstrates potential for advancing accurate diagnosis and personalized therapeutic strategies for breast cancer in clinical settings.