Probing Spatiotemporal pHi and pHe Dynamics in Tumor Spheroids during Growth and Alkaline Therapy via Surface-Enhanced Raman Spectroscopy

The acidic microenvironment in solid tumors is not merely a metabolic byproduct of the Warburg effect but actively promotes disease aggressiveness and treatment failure. Tumor alkalization therapy, which aims to neutralize or alkalinize the TME, has therefore emerged as a promising adjunct to conventional cancer treatments. In this study, we fabricated both SERS nanosensors and microsensors for parallel spatiotemporal monitoring of intracellular pH (pHi) and extracellular pH (pHe) within tumor spheroids derived from three human cancer cell lines: lung adenocarcinoma (H1975), pancreatic cancer (SW1990), and colorectal cancer (SW480). Over a 7-day culture period, distinct pHi and pHe profiles were observed among the different cell types. We then examined the pH modulation elicited by administration of sodium bicarbonate (NaHCO3), a clinically employed alkaline agent. Exposure to 75 mM NaHCO3 for 24 h induced a marked elevation of pHe (∼0.78 units) and a modest increment in pHi (∼0.37 units). This integrated nanosensor-microsensor system, which leverages the size effect for precise spatial localization, offers a versatile approach for elucidating the complex interactions within the tumor microenvironment and helps optimize pH-modulating cancer therapies.