Used in bioimaging and cellular labeling due to the fluorescent properties of rhodamine B (RhB) combined with the biocompatibility and solubility provided by the PEG linker. The primary amine (NH2) group allows for easy conjugation to biomolecules such as antibodies, peptides, or proteins, enabling targeted fluorescence labeling in biological systems. Commonly applied in fluorescence microscopy, flow cytometry, and drug delivery tracking. Also utilized in surface modification of nanoparticles and biosensors where a fluorescent signal is needed. The PEG spacer reduces non-specific binding and enhances stability in physiological environments.