The authors describe the synthesis of a two-dimensional organic-inorganic perovskite of the type NH3(CH2)10NH3)PbBr4 by a fast precipitation method. The resulting powder under photoecitation at 270 nm exhibits yellow luminescence (peaking at 550 nm) in DMSO/water mixtures if the ratio is bigger than 4/6. On addition of Hg(II) and a rhodamine spirolactam, ring opening occurs and colorimetric and fluorescent responses can be seen. Specifically, the emission at 550 nm gradually decreases and a new emission peak appears at 585 nm (corresponding to the emission peak of RBEA-Hg(II) complex) while the color of the solution gradually turns to pink under visible light. The emission peak of the modified perovskite overlaps the 585 nm absorption of rhodamine B, and this results in a FRET effect whose Förster radius (donor-acceptor distance) is calculated from decay time data to be 10.4 Å. Based on these findings, a FRET-based assay for Hg(II) was worked that has a 2.4 μM detection limit.

•Methods for synthesis of “OFF–ON” fluorescein fluorescent probes.•Sensing mechanisms and sensor design using fluorescein.•Sensing applications and properties to various analytes.Fluorescein derivatives are important fluorescent probes which can be used for detection and optical imaging. Fluorescein derivatives are usually constructed by introducing aldehyde groups or esterified onto fluorescein xanthene ring and benzene moiety. Typically, the research direction of connecting amino groups with fluorescein monoaldehyde is in hot. Because of their high activity, these derivatives can be complexed with the analytes to produce changes of colors and the increase or decrease of fluorescence intensity. This article reviewed fluorescein probes in the past two years according to classification of different analytes including metal ions, anions, small molecules and biological macromolecules. The synthesis methods, optical properties, possible mechanisms and applications of fluorescein probes are summarized. This article provides a reference for the screening of fluorescein probes with high sensitivity and biological detection and can propel their further applications in sensing and detection of analytes.Fluorescein is an important class of fluorescent probes. This article reviewed fluorescein fluorescent probes in the past two years according to classification of different analytes including metal ions, anions, small molecules and biological macromolecules. The synthesis method, optical properties, possible mechanisms and applications of “OFF–ON” fluorescein fluorescent probes were summarized in here.Download high-res image (128KB)Download full-size image

•Facile preparation of carbon nanodots/WO3 nanocomposite with high photocatalytic activity were designed.•A novel photocatalytic assay of degrading methylene blue by carbon nanodots/WO3 was performed.•Carbon nanodots/WO3 showed excellent stability which could be recycled for the photocatalytic degradation of methylene blue.Herein we designed a simple and effective method for synthesizing carbon nanodots/tungsten trioxide nanocomposite with high photocatalytic activity. The as-prepared carbon nanodots/ tungsten trioxide has strong photoabsorption under visible light irradiation. Then, carbon nanodots/tungsten trioxide was successfully applied to the degradation of methylene blue. The photodegradation efficiency of methylene blue can be reached as high as 100% after 0.5 h visible light illumination. In addition, carbon nanodots/tungsten trioxide could also be used to degrade rhodamine B and methyl orange. Most importantly, the photocatalytic activity of carbon nanodots/tungsten trioxide did not exhibit obvious changes after five cycles. The results indicate that carbon nanodots/tungsten trioxide has potential applications in the degradation of organic pollutants in industrial waste water.

Ratiometric fluorescent probes allow the simultaneous measurement of two fluorescence signals at different wavelengths followed by calculation of their intensity ratio, which can provide more precise measurement results than intensity-based fluorescent probes. Excitation energy transfer is widely used in the design of ratiometric fluorescent probes. Rhodamine is a convenient platform for the construction of “OFF–ON” ratiometric chemosensors. Rhodamine-based ratiometric fluorescent probes based on the excitation energy transfer mechanism can be constructed by conjugated or non-conjugated connections with other chromophores. In this review, we summarized the recent advances regarding rhodamine-based ratiometric fluorescent probes based on excitation energy transfer. We reviewed these probes according to the classification of “through-space” and “through-bond” probes; we focused on the contributions of different donor fluorophores and the types of connections between the energy donors and acceptors.

A simple one-step hydrothermal method was designed to synthesize fluorescent carbon nanodots (CNDs). The resulting CNDs exhibited excellent properties such as good solubility, superior photo-stability and low toxicity. Significantly, the CNDs were found to be an effective fluorescence sensing platform for turn-on detection of glutathione (GSH). The initial fluorescence of CNDs was quenched through an electron transfer process in the presence of dopamine, while the quenched fluorescence was enhanced with the further addition of GSH. Moreover, it showed a good linear relationship between GSH concentration and the relative fluorescence intensity of the system. Significantly, this sensing platform successfully detected GSH in biological fluids, indicating its potential applications in the field of biology.

Carbon dots (CDs), a new class of fluorescent materials, have recently attracted considerable research interest. CDs have overcome some defects of traditional nanomaterial. In addition to their small size and optical properties, CDs have the excellent advantages of good biocompatibility and are easy to achieve surface functionalization. Since this discovery, CDs can be widely used in the field of biochemical sensing and environmental testing. This article reviews the progress in the research and development of CDs on their syntheses, applications for the fluorescence detection and possible mechanisms. Finally, we have an outlook of the research trends and future prospects of CDs.

•Highly fluorescent quantum yield carbon dots were prepared.•Carbon dots fluorescence was selectively quenched by quercetin.•Carbon dots acted as sensitive and selective nanoprobes for quercetin determination in aqueous solution.•No interference from other flavonoids and phenolic compounds was observed.The organosilane-functionalized carbon dots (SiCDs) were synthesized using citric acid with N-(b-aminoethyl)-g-aminopropyl methyldimethoxy silane (AEAPMS). The as-synthesized SiCDs were characterized by IR, TEM, XPS, NMR and fluorescence. The SiCDs showed a strong emission at 455 nm with excitation at 365 nm. The SiCDs exhibited analytical potential as sensing probes for quercetin (QCT) determination. pH effect, temperature effect, interferences, and analytical performance of the method were investigated. It suggested that SiCDs exhibited high sensitivity and selectivity toward QCT: the linear ranges of SiCDs were estimated to be 0–40 μM while the limit of detection (LOD) was calculated to be 79 nM.

Fluorogenic methods in conjunction with suitable probes have emerged as preferable modalities for the monitoring and measurement of trace metal ions. The number of new Zn2+-responsive fluorescent chemosensors has increased substantially in recent years, as a consequence of biologically and environmental importance of zinc ions, comprising organic fluorophore derivatives, biological functional materials and so on. In this review, we highlight recent advances made in the development of Zn2+ fluorescent sensors. This paper focuses on reviewing sensor molecules based on organic fluorophore derivatives, involving quinoline, BODIPY, coumarin, and so forth. On the basis of current research results, novel fluorescent chemosensors for zinc ions derived from organic fluorophores will be synthesized to increase the sensitivity, water solubility, and bio-compatibility of the sensor for in vivo analysis.

•Amphiphilic carbon dots were obtained by simply modifying hydrophobic carbon dots.•Amphiphilic carbon dots/morin-Al3+ was used as a selective turn-on probe for Al3+.•The method was employed to intracellular imaging Al3+ in living cells.In this paper, a simple and effective method was designed to synthesize hydrophobic carbon dots. Subsequently, amphiphilic fluorescent carbon dots (A-CDs) were synthesized by further surface modification. The result A-CDs show excellent optical properties with a quantum yield of 16.9%. It was interestingly found that morin (MR) and its fluorescent metal-ion complex (MR-Al3+) can successfully coordinate on the surface of A-CDs, the emission of A-CDs completely overlapped the absorption peak of MR-Al3+. Thus, the prepared A-CDs can be used as an effective fluorescent probe for Al3+ based on a fluorescence resonance energy transfer process. The sensing platform can realize real-time detection of Al3+ within 0.5 min. The fluorescence signals of the system were linearly correlated with the concentration of Al3+ over a range of 8–20 μM, with a detection limit of 0.113 μM. The method was also successfully applied to image the distribution of Al3+ in Human Umbilical Vein Endothelial Cells.