A large-Stokes-shift fluorescent probe for Zn2+ based on AIE, and application in live cell imaging.

A fluorescence-enhanced sensor based on aggregation-induced emission (AIE) was synthesized using a di(2-picolyl)amine (DPA) group as a highly selective metal chelating agent for Zn2+. The combination of the probe and Zn2+ was achieved in an environment where the volume fraction of water was 90%, giving the probe good biocompatibility, and a large Stokes shift (100 nm) occurred after Zn2+ was combined with the probe. The obvious color change makes the probe visible to the naked eye, and gives it a high signal-to-noise ratio, and high contrast, and minimizes self-absorption. Because of the high selectivity of the DPA group to Zn2+, the sensitivity of the probe to detect Zn2+ has been improved. The mechanism of the formation of complexes between the probe and Zn2+ was confirmed by nuclear magnetic resonance spectroscopy (NMR), high-resolution mass spectrometry (HRMS), and particle size distribution. Under the optimal experimental conditions, the linear fluorescence reaction of Zn2+ was good, between 0.2 and 18 µM, and the detection limit was 1.3 × 10-7 M. The low toxicity and excellent membrane permeability of the probe in living cells enable it to be efficiently applied for Zn2+ imaging in cells. Graphical abstract.

A novel ratiometric sensor prepared based aggregation-induced emission for ultrafast detection of SO2 derivatives in food samples and living cells.

As one of the gaseous signaling molecules, aberrant levels of SO2 are usually associated with many diseases. it is of great significance to develop sensitive methods for detection SO2 on real. In this paper, a D-π-A near-infrared aggregation-induced fluorescent probe (DPA-CN) was built using diphenylamino-4-benzaldehyde and malononitrile for sensing SO2. The DPA-CN exhibit AIE characterization that can quickly recognize SO2 via the Michael addition mechanism. The DPA-CN displayed emission blue drift from 650 nm to 560 nm after adding SO2, thereby realizing rapid and sensitive colorimetric detection of SO2. The mechanism for recognition of SO2 was verified via magnetic resonance imaging (1H NMR), electrospray ionization mass spectrometry (ESI-MS), scanning electron microscopy (SEM) and dynamic light scattering (DLS). The DPA-CN realized rapid and sensitive recognition of SO2 with high specificity in 10 s within the concentration range of 0-100 µM. The limit of detection (LOD) is as low as 0.31 µM. Owing to its high sensitivity and low toxicity, the DPA-CN can be applied in monitoring of SO2 in living cells and food analysis. Furthermore, the DPA-CN was used to prepare a visible and ultrafast semiquantitative paper-based SO2 sensor with low cost and easy operation.

A design of red emission CDs-based aptasensor for sensitive detection of insulin via fluorescence resonance energy transfer.

We successfully designed an aptasensor based on the red emission carbon dots (R-CDs) and effectively detected insulin (INS) via fluorescence resonance energy transfer (FRET). In the process, the aptamer (apt) labeled with R-CDs (R-CDs@apt) was used as fluorescence donor and graphene oxide (GO) was used as fluorescence receptor. The successful detection due to the aptamer sequence has a certain affinity for Go and INS, while the affinity for INS is stronger than that of GO. When INS is not added to the detection system, the aptamer is adsorbed onto the surface of GO, shortening the distance between R-CDs@apt and GO, resulting in FRET and the quenching of fluorescence of R-CDs@apt. When INS was added to the detection system, the aptamer selectively bound INS and separated from the adsorption of GO, FRET gradually disappeared and the fluorescence of R-CDs@apt/GO/INS system was restored. By comparing the changes of fluorescence intensity before and after adding INS, the detection of INS was implemented. The aptasensor has a good linear curve with the detection limit of as low as 1.1 nM when the concentration of INS reached 1.3-150 nM. This method has excellent selectivity and anti-interference. Therefore, it is a potential method for detecting substances in biological fluids.

A novel AIE active NIR fluorophore based triphenylamine for sensing of Hg2+ and CN- and its multiple application.

New strategies still need to be proposed that can be used to sense and remove toxic environmental pollutants in a sensing system. In this research, a novel NIR fluorescence sensor 1 was designed and prepared with aggregation induced emission (AIE) property. The fluorescence intensity of the sensor 1 in DMSO/H2O mixed solvent was changed along with the proportion of water. The sensor 1 can be successfully used for real-time detection and removal of Hg2+ in 20% DMSO aqueous solution with high selectivity, quick response and so on. Furthermore it can be efficiently reused and recycled without any loss through Na2S. In addition, the sensor 1 displayed high sensitivity and selectivity to cyanide ions in 1% DMSO aqueous solution with the presence of other interference anions. The sensing mechanism for Hg2+ and cyanide ion was evaluated by 1H NMR spectra, Mass spectrometry. The sensor 1 exhibited low cytotoxicity for biological applications, which was used as an outstanding fluorescent transducer for detection of cyanide ion in living cells. Based on the visible fluorescence change for the sensor 1 to cyanide ion, the measurement was performed for food materials containing cyanide, such as potato, cassava powder and almond. This research provides perspective potential in solving the problem of other pollution and stimulating new thinking for designing of the novel fluorescence materials.

A quencher-free 2-aminopurine modified hairpin aptasensor for ultrasensitive detection of Ochratoxin A.

A sensitive, efficient and quencher-free fluorescence aptasensor to detect Ochratoxin A (OTA) based on aptamer, 2-aminopurine (2AP) labeled Oligonucleotide sequence, as well as exonuclease I (Exo I) activity was developed. In which the aptamer specific to OTA was modified into a hairpin structure, and 8 bases at the 3' ends are exposed (H); also, 2AP is embedded in the oligonucleotide complementary to the 8 bases (2AP-probe).The detection principle based on 2AP-probe could be bonded to its complementary sequence and quenches the fluorescence of 2AP; The aptamer has a stronger affinity for the target than its complementary sequence; Exo I can dissociate single-stranded DNA and has little effect on double-stranded DNA as well as folded DNA. In the absence of OTA, the fluorescence of 2AP is quenched due to the complementary pairing of H and 2AP-probe; in the presence of OTA, H selective binding target is detached from 2AP-probe, and the fluorescence of 2AP is slightly restored. Moreover, when the Exo I is added to the detection system, 2AP-probe is dissociated by the Exo I to release the free 2AP, and the fluorescence of the system is further enhanced thereby realizing the detection of OTA. The detection limit of the aptasensor was low as 0.03 nM with a linear range of 0.5-100 nM. Moreover, the aptasensor has good selectivity and practicability and also has good potential in realizing the detection of toxic and harmful substances in food complex matrices.

An AIE active pyrene based fluorescent probe for selective sensing Hg2+ and imaging in live cells.

A novel fluorescence probe pyrene based derivatives (1) with aggregation induced emission (AIE) properties was synthesized by an easy procedure. The probe 1 was characterized by UV-vis, Fluorescent, NMR, MS, SEM etc. It displayed high sensitivity and selectivity to Hg2+ compared with other metal ions in H2O/DMF solvent and the detection limit was 4.2 × 10-7 M. Upon addition of Hg2+, the 1 - Hg2+ compound was formed with the formation of 2:1. More importantly, the probe exhibited very low cytotoxicity and strong fluorescence emission in live cells. This showed that the probe had potential applications for detection of Hg2+ in environment and biosystems.

An active fluorescent probe based on aggregation-induced emission for intracellular bioimaging of Zn2+ and tracking of interactions with single-stranded DNA.

A novel dual-sensing fluorescence probe L was designed and synthesized for highly selective and sensitive detection of Zn2+ and DNA. The probe L achieved a detection limit of 3.8 nM for Zn2+, which is lower than the acceptable level of Zn2+ in living cells. The probe L displayed high selectivity toward Zn2+ over other interference metal ions and amino acids. Moreover, the probe L displayed low cytotoxicity and good cell permeability, indicating its potential for detecting and bio-imaging of Zn2+. In addition, the probe L-Zn2+ exhibited enhanced fluorescence signal for DNA detection through the metal-coordination interaction between Zn2+ and DNA. The enhanced signal is higher than that of the classical ethidium bromide probe. The experiments in aqueous media verified the feasibility of applying probe L in real samples.

Linear Schiff-base fluorescence probe with aggregation-induced emission characteristics for Al3+ detection and its application in live cell imaging.

A simple Schiff-base derivative with salicylaldehyde moieties as fluorescent probe 1 was reported by aggregation-induced emission (AIE) characterization for the detection of metal ions. Spectral analysis revealed that probe 1 was highly selective and sensitive to Al3+. The probe 1 was also subject to minimal interference from other common competitive metal ions. The detection limit of Al3+ was 0.4 µM, which is considerably lower than the World Health Organization standard (7.41 µM), and the acceptable level of Al3+ (1.85 µM) in drinking water. The Job's plot and the results of 1H-NMR and FT-IR analyses indicated that the binding stoichiometry ratio of probe 1 to Al3+ was 1:2. Probe 1 demonstrated a fluorescence-enhanced response upon binding with Al3+ based on AIE characterization. This response was due to the restricted molecular rotation and increased rigidity of the molecular assembly. Probe 1 exhibited good biocompatibility, and Al3+ was detected in live cells. Therefore, probe 1 is a promising fluorescence probe for Al3+ detection in the environment.