Table 1.

Summary table of the smart theranostics discussed in this section and their pH-responsive mechanisms

Smart theranostic	Structure of responsive linker	Responsive trigger	Responsive Mechanism	Ref
PMN/Ce6		pH	pH = 6.5-7: Ionisation of imidazole groups cause swelling. pH = 5.5: Further ionisation of imidazole groups causes disassembly and release of photosensitiser.	113
DOX@ES-MION3@RGD2@mPEG3		pH	pH = 5.5: Cleavage of β-propionate linker leads to exposure of RGD2 ligand and tumour cell internalisation.	119
Gd2O3@MSN-DOX		pH	pH = 5.0: Charge reversal and disintegration of polyelectrolyte P(DMA-co-TPAMA) leads to DOX release.	115
MTX-Mn@PEG		pH	pH = 5.5: Protonation of carboxylic acids and nitrogen heterocycle of MTX reduces coordination and releases Mn2+ from MTX complex.	117
SPA-SPIO-IR780		pH	pH = 6.5: Cleavage of bond between PEI and HHPA and exposure of positive amino groups enhances tumour cell internalisation.	116
Fe3O4@TA-PEG/ICG		pH ATP	pH = 5.5: Protonation of hydroxyl groups of TA leads to disassembly by weakening of coordinate and hydrogen bonds. Quenching of ICG is reduced. ATP (10 mM): Displacement of TA from the nanoparticles and disassembly.	32
Bi-MSx-PEG/DOX NFs		pH NIR light	pH = 5.5: Solubility of DOX is increased. NIR laser: Temperature increase reduces binding of DOX to NPs, facilitating its release.	118
MCDION-Se		pH	pH = 5.5: Degradation of MnCO3 component of nanoparticles leads to release of Mn2+ and Se in tumour cells.	128
Gd-texaphyrin-DOX complex		pH	pH = 5.5: Cleavage of hydrazone linker leads increase of FL signal of DOX due to separation from the Gd-texaphyrin complex.	132