Dispersion-aggregation-dispersion colorimetric detection for mercury ions based on an assembly of gold nanoparticles and carbon nanodots.

Mercury is a common heavy metal element in natural systems and is highly toxic to the human body. Herein, a novel colorimetric detection of Hg2+ ions is proposed based on the aggregation of gold nanoparticles (AuNPs) induced by carbon quantum dots (CDs) with the assistance of glutathione (GSH). In this sensing system, the AuNP/CDs composite forms through Au-N bonds. Simultaneously, the color of the solution turns from wine red to blue. The well-dispersed AuNPs can be restored after the addition of GSH, because GSH competes with CDs to bind onto the surface of AuNPs and protect AuNPs from aggregation. In the presence of Hg2+ ions, GSH can chelate with Hg2+ to form a complex, which subsequently enables CDs to facilitate the aggregation of the AuNPs again. Therefore, according to the red-to-blue color change, a colorimetric sensor is established for the sensitive and selective detection of Hg2+ with a detection limit of 7.5 nM. Moreover, this sensor is successfully used to detect Hg2+ spiked in environmental water. This very simple and cost-effective strategy will promote the development of a colorimetric sensor for the determination of other metal ions in biological and environmental fields.

A donor-π-acceptor aggregation-induced emission compound serving as a portable fluorescent sensor for detection and differentiation of methanol and ethanol in the gas phase.

The design strategy of aggregation-induced emission (AIE) fluorophores with donor-π-acceptor (D-π-A) conjugation structure has greatly contributed to the development of luminescent materials and devices, including volatile organic compounds (VOCs) sensors. In this work, a D-π-A fluorophore DEBAB was synthesized, showing both AIE and intramolecular charge transfer (ICT) properties as confirmed by spectroscopic data and quantum chemical calculations. Furthermore, there is notable emission-enhancement when DEBAB is exposed to small-molecule alcohols, such as methanol and ethanol. Based on this phenomenon, a portable film sensor was fabricated, capable of detecting methanol and ethanol in gas phase, with detection limit (DL) as low as 8.02 ppm. Our systematic investigation suggests that hydrogen-bonding may be formed between DEBAB and alcohols, intensifying the AIE efficacy while influencing the ICT process. This working mechanism is supported by density functional theory (DFT) calculations including electrostatic potential mapping and molecular total energy. In addition, a sensor array was fabricated on a cellulose paper strip, showing different levels of emission changing in response to alcohols. Thus the detection and differentiation of methanol and ethanol are enabled.

Strategy for optical data encryption and decryption using a D-A type stimuli-responsive AIE material.

In this study, we report a new donor-acceptor (D-A) type stimuli-responsive material, (E)-4-(((9-ethyl-9H-carbazol-2-yl)methylene)amino)benzoic acid (C1), which possesses both aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) natures. It glows green photoluminescence which changes into yellow color in response to mechanical stimuli, and fumigation in volatile organic compounds (VOCs) can switch the emission back to the initial state with high reversibility. In addition, the C1 film glows yellow-orange light, but turns into blue emission under continuous fumigation in ethyl acetate vapor. However the vapochromism behaves different when the C1 film is smeared: The emission of the smeared film is similar to the unsmeared but changes into cyan color after fumigation. The differences in vapochromism between smeared and unsmeared film can be easily distinguished by naked eyes. As revealed by SEM, the as-prepared film undergoes a morphology change from ill-shaped particles to microspheres in response to organic vapor, while the smeared film with scratched surface changes into dendritic patterns. According to the morphology study, the vapochromic luminescence can be ascribed to the physical adsorption of ethyl acetate vapor and the resulting change in the ICT process. In light of the unique vapochromism of C1, a new encryption-decryption technique for data recording was developed. Information can be recorded on the C1 film by mechanical writing and simultaneously concealed. It can be only accessed via fumigation in organic vapor, demonstrating a reliable steganography technology.