Gold nanoparticles (AuNPs) have shown great promise as a universal platform for biosensing and are often functionalized with a densely packed DNA for intracellular detection. While DNA–AuNP conjugates, such as nanoflares, have been used for single and multiple mRNA molecules detection in living cells, the target recognition reaction is triggered once they enter into cells, making it impossible to control the initial reaction at the desired time. To solve this problem, we have designed photoactivated (PA) nanoflares for intracellular mRNA analysis with high spatiotemporal control. PA nanoflares consist of AuNP and photoresponsive DNA hairpin probes. Without UV irradiation, the DNA hairpin could be kept unawakened and show no reactivity to target the probe. Upon UV activation, the hairpin structures are destroyed and expose the sticky domains, which act as toeholds to mediate strand displacement reactions, making flares release from the gold surface and causing an increase of fluorescence. By tuning light irradiation, PA nanoflares for mRNA detection in living cells can be temporally controlled. With the benefit from two-photon laser illumination, PA nanoflares can detect mRNA in selective cells at a desired time point at the single-cell level. Compared to the traditional nanoflares, the novel PA nanoflares have increased the detection sensitivity and achieved intracellular biomarkers detection at the single-cell level with high spatiotemporal control.

Cyclodextrins (CDs), one of the host molecules in supramolecular chemistry, can host guest molecules to form inclusion complexes via non-covalent and reversible host-guest interactions. CD-based light-responsive supramolecular systems are typically constructed using CDs and guest molecules with light-responsive moieties, including azobenzene, arylazopyrazole, o-nitrobenzyl ester, pyrenylmethyl ester, coumarin, and anthracene. To date, numerous efforts have been reported on the topic of CD-based light-responsive supramolecular systems, but these have not yet been highlighted in a separated review. This review summarizes the efforts reported over the past ten years. The main text of this review is divided into five sections (vesicles, micelles, gels, capturers, and nanovalves) according to the formation of self-assemblies. This feature article aims to afford a comprehensive understanding of the light-responsive moieties used in the construction of CD-based light-responsive supramolecular systems and to provide a helpful guide for the further design of CD-based light-responsive supramolecular systems.

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N-doped carbon dots used as a fluorescence probe can distinguish cancer cells from normal cells by pH and evaluate intracellular GSH.

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