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The hydroxyl substituent in flavonoids can cause the binding site to change from DS1 to DS2 and restore the ESIPT process of flavonoids, thereby leading to a unique dual-emissive response towards human serum albumin.

• The strategy of donor engineering to enhance fluorescence brightness is reported. • The methylpiperazine-substituted flavonoid shows high fluorescence brightness in water. • A novel fluorescent probe can sense cysteine both in water and in living cells. Increasing demand for detecting environmental and biological analytes in aqueous solutions based on fluorescent probes has raised the bar for the fluorophores used. Especially, the twisted intramolecular charge transfer (TICT) state of fluorophore can trigger the formation of a charge-separated non-emissive specie, leading to a low fluorescence brightness. In this work, we performed a simple donor engineering on the flavonoid-based fluorophores to regulate the TICT formation. A systematic study on relationship between donor structure and photophysical properties has been carried out. Among a series of flavonoids, the methylpiperazine-substituted one exhibited the strongest fluorescence brightness in water since the methylpiperazine could rigidify the rotation of donor moiety to suppress TICT state. Moreover, a novel fluorescent probe based on this flavonoid successfully realized the cysteine detection both in water and in living cells. This work confirmed the validity of design strategy by inhibiting TICT to enhance the fluorescence brightness, and also provided a practical flavonoid-based fluorophore for further bioimaging applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • The flavonol-based small-molecule fluorescent probes are reviewed. • ƒÜ The unique photophysical process of flavonol and its advantages in probe design are introduced. • ƒÜ The design mechanism of flavonol-based fluorescent probes has been discussed and categorized. • ƒÜ The sensing performances and applications of probes are summarized. Flavonols, named as 3-hydroxyl-2-phenyl-1-benzopyran-4-one, are important natural botanical functional pigments widely distributing in fruits, vegetables, and flowers. Owing to intramolecular hydrogen bond, the flavonols can undergo the excited-state intramolecular proton transfer (ESIPT) process upon irradiation, leading to unique environmental-sensitive dual emissions, which makes flavonol an ideal fluorophore skeleton for probe design. In this paper, we summarized the recent progress of flavonol-based small-molecule fluorescent probes for diverse sensing applications, including detection of anions, cations, reactive biological species, proteins, DNAs, environmental hazards, and microenvironmental factors. This review highlighted the basic characteristics of flavonol probes in the respect of design principles, photophysical processes, sensing mechanism, sensing performances, and biological applications. The present review article aims to offer a comprehensive summary for researchers to inspire new probe design, and push forward the advancement of flavonol-based fluorescent probes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel functional material as the host–guest supramolecular probe was reported. • This work for the first time reported a ratiometric detection method for cyfluthrin. • The probe enables fast, sensitive (LOD 70 ppb), and selective detection of cyfluthrin. • The paper-based testing device was utilized for the smartphone-based analysis. • On-site determination of cyfluthrin in real food samples could be successfully realized. The massive use of cyfluthrin pesticide in agriculture has brought growing concerns on the food safety due to its chemical stability, easy-to-accumulation, and several harmful effects on human health. Design of a rapid, reliable and portable analytical method for on-site monitoring cyfluthrin is of great significance. Although reported assays showed high sensitivity and selectivity to cyfluthrin, these intensity-based outputs suffered from the interference from a variety of analyte-independent factors, i.e. the instrumental parameters, which often led to the poor accuracy and repeatability of detection results. In this work, we reported a novel host–guest supramolecular probe by using albumin as the host and solvatofluorochromic flavonoid as the guest, for the first time, successfully realizing ratiometric determination of cyfluthrin. This probe was capable of detecting cyfluthrin with the fast response (10 s), high sensitivity (LOD ∼70 ppb) and selectivity, good anti-interference performance, and remarkably distinct emission color change from orange to green. Moreover, the portable paper-based test strips could be facilely obtained and utilized for ratiometric determination cyfluthrin pesticide in food samples, such as apple, tomato, cucumber. The signal outputs could be captured and analyzed by using a smartphone, demonstrating the application potential of this probe in on-site food analysis. We expected this work may open up a novel avenue for on-site determination of pesticides with the simple testing apparatuses. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel flavonoid probe is reported for fluorescence discrimination of HSA from BSA. • The sensing mechanism was studied by Job's plot, site-displacement experiment, and molecular docking. • The specific response to HSA was attributed to the albumin-induced restricted intramolecular rotation of flavonoid probe. Discrimination of human serum albumin (HSA) from bovine serum albumin (BSA) based on the fluorescence probe technique is still challenging due to similar chemical structures. In this work, a novel flavonoid-based fluorescent probe AF is reported for successful discrimination of HSA from BSA. The sensing performances of probe, including sensing dynamic, sensitivity and selectivity, have been carefully studied. Moreover, sensing mechanism was elucidated by Job's plot, displacement experiment, and molecular docking, suggesting that the specific response to HSA originated from the albumin-induced restricted intramolecular rotation (RIR) of probe. This work may provide a simple way for designing of novel probes for HSA with high selectivity. [ABSTRACT FROM AUTHOR]