Gao and colleagues have developed a polymeric, micelle-based nanoprobe that is highly responsive to both the angiogenic tumor vasculature and the extracellular pH. First, Gao and colleagues introduced tertiary amines with controlled hydrophobic substituents as ionizable hydrophobic blocks for the pH-sensitive core. Nanoprobes with different transition pH values can thus be achieved by using tertiary amino groups that protonate at a different pH. Subsequently the polymers were derivatized with hydrophobic fluorophores. At physiological pH, the monomers spontaneously assemble with the fluorophores oriented into the centre of the particle and in close proximity with each other. As a result of this, the fluorophores tend to silence each other by a process called fluorescence resonance energy transfer. As the particle navigates the body and enters the tumor site, the drop in pH begins to protonate the amines. The extremely high sensitivity makes these nanoprobes promising candidates for clinical tumor diagnosis.