Typical PeT-based fluorescent probes are multi-component systems where a fluorophore is connected to a recognition/activating group by an unconjugated linker. PeT-based fluorescent probes are powerful tools for cell imaging and disease diagnosis due to their low fluorescence background and significant fluorescence enhancement towards the target. This review provides research progress towards PeT-based fluorescent probes that target cell polarity, pH and biological species (reactive oxygen species, biothiols, biomacromolecules, etc.) over the last five years. In particular, we emphasise the molecular design strategies, mechanisms, and application of these probes. As such, this review aims to provide guidance and to enable researchers to develop new and improved PeT-based fluorescent probes, as well as promoting the use of PeT-based systems for sensing, imaging, and disease therapy.

Changes in adenosine triphosphate (ATP) and peroxynitrite (ONOO^–) concentrations have been correlated in a number of diseases including ischemia-reperfusion injury and drug-induced liver injury. Herein, we report the development of a fluorescent probe ATP-LW, which enables the simultaneous detection of ONOO^– and ATP. ONOO^– selectively oxidizes the boronate pinacol ester of ATP-LW to afford the fluorescent 4-hydroxy-1,8-naphthalimide product NA-OH (λ_ex = 450 nm, λ_em = 562 nm or λ_ex = 488 nm, λ_em = 568 nm). In contrast, the binding of ATP to ATP-LW induces the spirolactam ring opening of rhodamine to afford a highly emissive product (λ_ex = 520 nm, λ_em = 587 nm). Due to the differences in emission between the ONOO^– and ATP products, ATP-LW allows ONOO^– levels to be monitored in the green channel (λ_ex = 488 nm, λ_em = 500–575 nm) and ATP concentrations in the red channel (λ_ex = 514 nm, λ_em = 575–650 nm). The use of ATP-LW as a combined ONOO^– and ATP probe was demonstrated using hepatocytes (HL-7702 cells) in cellular imaging experiments. Treatment of HL-7702 cells with oligomycin A (an inhibitor of ATP synthase) resulted in a reduction of signal intensity in the red channel and an increase in that of the green channel as expected for a reduction in ATP concentrations. Similar fluorescence changes were seen in the presence of SIN-1 (an exogenous ONOO^– donor).

An overview of cyanine dye-based phototherapy agents, including the design strategies, relationships between molecular structures and properties, as well as applications in photodynamic therapy, photothermal therapy, and multimodal combined therapy.

This review highlights the uniqueness of smart photosensitizers to increase the efficacy of photodynamic therapy while enhancing treatment biosafety, as well as their future prospects in clinical applications.