Shortwave infrared quantum dots (QDs) are promising probes for in vivo imaging in depth. Here, we present two strategies to design pH-sensitive ratiometric QD in vivo probes. In the first one, central fluorescent QDs are coated with a copolymer ligand and conjugated to gold nanoparticle (AuNP) quenchers. As the pH decreases from physiological (7.5) to slightly acidic (5.5−6), the copolymer reversibly shrinks, which modulates the QD fluorescence signal through energy transfer. In a second design, QDs and AuNPs are encapsulated into micelles using pH-sensitive copolymer surfactants, providing stability in serum, sharp pH transitions and high contrast.
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