Fluorescent nanoparticles based on AIE fluorogens for bioimaging.

Fluorescent nanoparticles (FNPs) have recently attracted increasing attention in the biomedical field because of their unique optical properties, easy fabrication and outstanding performance in imaging. Compared with conventional molecular probes including small organic dyes and fluorescent proteins, FNPs based on aggregation-induced emission (AIE) fluorogens have shown significant advantages in tunable emission and brightness, good biocompatibility, superb photo- and physical stability, potential biodegradability and facile surface functionalization. In this review, we summarize the latest advances in the development of fluorescent nanoparticles based on AIE fluorogens including polymer nanoparticles and silica nanoparticles over the past few years, and the various biomedical applications based on these fluorescent nanoparticles are also elaborated.

PbI2-Based Dipping-Controlled Material Conversion for Compact Layer Free Perovskite Solar Cells.

A two-step sequential deposition method has been extensively employed to prepare the CH3NH3PbI3 active layer from the PbI2 precursor in perovskite solar cells (PSCs). The variation of the photovoltaic performance of PSCs made by this method was always attributed to different dipping times that induce complete/incomplete conversion of PbI2 into CH3NH3PbI3. To solve this issue, we employed a solvent vapor annealing (SVA) method to prepare PbI2 crystallites with large grain size for preparation of high quality perovskite. With this method, the increased PbI2 dipping time in CH3NH3I solution was found to reduce the photovoltaic performance of resulting PSCs without a significant change in PbI2/CH3NH3PbI3 contents in the perovskite films. We attribute this abnormal reduction of the photovoltaic performance to intercalation/deintercalation of the PbI2 core with a CH3NH3PbI3 shell, which causes the doping effect on both the PbI2 and CH3NH3PbI3 crystal lattices and the formation of a CH3NH3PbI3 capping layer on the surface, as revealed by UV-vis absorption, X-ray diffraction, FT-IR, and scanning electron microscope measurements. Based on our findings, a multistep dipping-drying process was employed as an alternative method to improve the crystalline quality. The method achieved power conversion efficiency up to 11.4% for the compact layer free PSC sharing a simple device structure of ITO/perovskite/spiro-OMeTAD/Ag.

High-efficiency aqueous-solution-processed hybrid solar cells based on P3HT dots and CdTe nanocrystals.

Without using any environmentally hazardous organic solution, we fabricated hybrid solar cells (HSCs) based on the aqueous-solution-processed poly(3-hexylthiophene) (P3HT) dots and CdTe nanocrystals (NCs). As a novel aqueous donor material, the P3HT dots are prepared through a reprecipitation method and present an average diameter of 2.09 nm. When the P3HT dots are mixed with the aqueous CdTe NCs, the dependence of the device performance on the donor-acceptor ratio shows that the optimized ratio is 1:24. Specifically, the dependence of the device performance on the active-layer thermal annealing conditions is investigated. As a result, the optimized annealing temperature is 265 °C, and the incorporation of P3HT dots as donor materials successfully reduced the annealing time from 1 h to 10 min. In addition, the transmission electron microscopy and atomic force microscopy measurements demonstrate that the size of the CdTe NCs increased as the annealing time increased, and the annealing process facilitates the formation of a smoother interpenetrating network in the active layer. Therefore, charge separation and transport in the P3HT dots:CdTe NCs layer are more efficient. Eventually, the P3HT dots:CdTe NCs solar cells achieved 4.32% power conversion efficiency. The polymer dots and CdTe NCs based aqueous-solution-processed HSCs provide an effective way to avoid a long-time thermal annealing process of the P3HT dots:CdTe NCs layer and largely broaden the donor materials for aqueous HSCs.

Tetraphenylpyrazine-based AIEgens: facile preparation and tunable light emission.

Research on aggregation-induced emission (AIE) has been a hot topic. Due to enthusiastic efforts by many researchers, hundreds of AIE luminogens (AIEgens) have been generated which were mainly based on archetypal silole, tetraphenylethene, distyrylanthracene, triphenylethene, and tetraphenyl-1,4-butadiene, etc. To enlarge the family of AIEgens and to enrich their functions, new AIEgens are in high demand. In this work, we report a new kind of AIEgen based on tetraphenylpyrazine (TPP), which could be readily prepared under mild reaction conditions. Furthermore, we show that the TPP derivatives possess a good thermal stability and their emission could be fine-tuned by varying the substituents on their phenyl rings. It is anticipated that TPP derivatives could serve as a new type of widely utilized AIEgen, based on their facile preparation, good thermo-, photo- and chemostabilities, and efficient emission.

Highly sensitive determination of ssDNA and real-time sensing of nuclease activity and inhibition based on the controlled self-assembly of a 9,10-distyrylanthracene probe.

We report here a fluorescent biosensor for highly sensitive determination of single-stranded DNA (ssDNA) with remarkable fluorescence enhancement and label-free sensing of S1 nuclease activity and inhibition in real time based on ssDNA-controlled self-assembly of a 9,10-distyrylanthracene (DSA) probe with the aggregation-induced emission (AIE) property, thereby avoiding a sophisticated fabrication process and aggregation-caused quenching (ACQ) effect. Compared with previous technologies, this assay has some advantages. First, since the DSA probe can be synthesized through a simple and effective synthetic route and the sensing technology adopts the unlabelled ssDNA, this biosensor shows advantages of simplicity and cost efficiency. Besides, for the determination of ssDNA, S1 nuclease, and inhibitor, the DSA-based probe provides high sensitivity and a good linear relationship due to the AIE property. As a result, we determined the DNA 24-mer concentration as low as 150 pM, and we are able to detect ssDNA lengths with a linear range from 6mer to 24mer (R = 0.998) as well as DNA 24-mer concentrations with a linear range from 0 to 200 nM (R = 0.998) and S1 nuclease concentrations with a linear range from 6 to 32 U ml(-1) (R = 0.995), respectively. Moreover, the fluorescent intensity with various concentrations of S1 nuclease becomes highly discriminating after 3-16 min. Thus, it is possible to detect nuclease activity within 3-16 min, which demonstrates another advantage of a quick response of the present biosensor system.