Abstract
In this tutorial review, we will explore recent advances for the design, construction and application of two-photon excited fluorescence (TPEF)-based small-molecule probes. The advantages of TPEF-based probes include deep tissue penetration and minimal photo-damage. We discuss the underlying two-photon (TP) fluorophores including hemicyanine and design strategies such as Förster resonance energy transfer (FRET). Moreover, we emphasize applications for the detection or imaging of cations, anions, small neutral molecules, biomacromolecules, cellular microenvironments, subcellular localization and dual-responsive systems. Examples of photodynamic therapy (PDT) using TP irradiation are also illustrated.
Highlights
Small-molecule probes are powerful tools to monitor specific cellular processes via fluorescence detection and/or imaging.[1]
With water fraction increasing from 0% to 70%, the fluorescence intensity decreased due to enhanced twisted intramolecular charge transfer (TICT) processes caused by increased polarity
We describe the development of dual-responsive sensors and theranostic systems based on two-photon excited fluorescence (TPEF), which we believe will pave a way in providing a deeper understanding of the complex role that different species play in disease-specific processes
Summary
Small-molecule probes are powerful tools to monitor specific cellular processes via fluorescence detection and/or imaging.[1] These molecular probes change their fluorescence emission when they respond to a specific analyte or environment. The main causes include: (1) short-wavelength excitation light that limits the penetration depth in biological samples; (2) photobleaching which makes the probe inappropriate for long-time imaging; (3) photo damage to biological samples; and (4) autofluorescence from biological species that interfere with the fluorescence signal. These problems of OPM can be overcome by two-photon excited fluorescence (TPEF) to different degrees. As such TPM reduces photobleaching and increases penetration depth and provides higher spatial resolution than OPM.[3,4]
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