Nanostars on Nanopipette Tips: A Raman Probe for Quantifying Oxygen Levels in Hypoxic Single Cells and Tumours

Multiple sharp-edged gold nanostars were efficiently assembled on nanopipette tips through electrostatic interactions for use as a potent intracellular hypoxia-sensing Raman probe. Colloidal stability and surface immobilization were checked using scanning electron microscopy, light scattering, and zeta potential measurements. Site-specific intracellular hypoxia levels can be estimated in vitro and in vivo using Raman lancets (RL). Distinct Raman spectral changes for the nitro-(NO₂ ) functional group of the redox marker 4-nitrothiophenol (4NTP) can be quantified according to the intracellular oxygen (O₂ ) content, ranging from 1 % to 10 %. Redox potential changes in mitochondrial respiration were also examined through serial injections of inhibitors. 3D-cultured cells and in vivo tests were used to validate our method, and its application in the assessment of the aggressiveness of cancer cells by differentiating spectral changes between malignant and benign cells was demonstrated.