Optimization of Eu3+ Luminescence in DMSO as a Multiparameter Method for Trace Water Detection

A sharp and selective fluorescence paper-based sensor based on inner filter effect for ratiometric detection of four Sudan dyes in food matrix

The addition of Sudan dyes with carcinogenic effects to food threatens human health. Herein, a ratiometric fluorescence strip consisting of core-shell upconversion particles (NaYF4:Yb,Tm@NaYF4:Yb,Er), metal-organic frameworks and dual-template molecularly imprinted polymers was developed to selectively and sensitively detect four Sudan dyes based on inner filter effect (detection time only takes 8 min). The high adsorption capacity of metal-organic frameworks and the greater overlap between the emission of NaYF4:Yb,Tm@NaYF4:Yb,Er and the absorbance of four Sudan dyes enable the signal responses to be more sensitive. The limits of detection in chilli powder samples are as low as 29.87 ng/g, 37.55 ng/g, 47.89 ng/g and 51.02 ng/g, with satisfactory recovery (93.32-103.4%) and minor relative standard deviations (≤4.3%). This method broadens the idea for low-cost and portable detection of multiple illegal additives in complex substrates with high selectivity and sensitivity based on one kind of fluorescent strip.

A fluorene based probe: Synthesis and "turn-on" water sensitivity of the in-situ formed Cu2+ complex: Application in bio-imaging

A new fluorene based probe (FTH) has been evaluated for its photo-physical properties in solution as well as in the aggregated state/viscous environment. Addition of a poor solvent (water) to the solution of the probe in a good (acetonitrile) solvent significantly enhanced the otherwise weak emission due to aggregation induced emission (AIE). The emission enhancement is also related to the increase in viscosity of the solution, leading to the restricted intramolecular rotation of the peripheral (phenyl) groups. Interestingly, the emission behaviour of the non-emissive in-situ formed Cu²⁺ complex is drastically modulated in the presence of water. The solution of the putative Cu²⁺ complex of the probe turns highly emissive (yellow colour) upon addition of a small fraction of water (up to 7.6 wt %), but the yellow emission diminishes upon increasing higher water fraction. We propose that the initially formed Cu²⁺ complex undergoes hydrolysis in the presence of higher water content releasing the free amine possessing the diaryl amino rotors thus rendering the solution non-emissive. Thus the current probe being reported herein discloses its potential to generate trace water sensitive turn-on Cu²⁺ complex. Additionally, the bio-imaging potential of FTH for live cancer cells and its sensitivity towards intracellular presence of Cu²⁺ ions has been demonstrated.

NaCl nanocrystal-encapsulated carbon dots as a solution-based sensor for phosphorescent sensing of trace amounts of water in organic solvents

The phosphorescence of solid-state carbon dots (CDs) has been demonstrated to be susceptible to water molecules. However, solution-based CDs have been rarely exploited for phosphorescence detection of trace amounts of water in organic solvents. Here, we present a straightforward method to embed the CDs into NaCl nanocrystals and show their application for phosphorescence detection of the water content in organic solvents. The phosphorescent CDs inside NaCl nanocrystals were fabricated by hydrothermal treatment of poly(diallyldimethylammonium) (PDDA) polymers and their counter chloride ions (Cl^-) in the presence of NaOH. Because of the interaction with quaternary ammonium surface groups of PDDA-based CDs (PDDA-CDs), the Cl^- ions serve as a nucleation site to trigger NaCl nanocrystal formation. Electron microscopy and spectroscopy techniques demonstrate the embedment of PDDA-CDs into NaCl nanocrystals (PDDA-CDs@NaCl). The PDDA-CDs@NaCl exhibited excitation-independent phosphorescence and excitation-dependent fluorescence in ethanol, methanol, dimethyl sulfoxide, and dimethylformamide. In four different organic solvents, the phosphorescence QYs and lasting times of PDDA-CDs@NaCl range from 23 to 35% and 1.2 to 1.5 s, respectively. Once trace amounts of water are present in an organic solvent, the water-induced dissolution of NaCl nanocrystals switches off the phosphorescence of PDDA-CDs@NaCl. It was found that PDDA-CDs@NaCl was capable of detecting as low as 0.25% v/v water in ethanol and 0.125% v/v water in methanol. The above-discussed results provide fundamental insights regarding the embedment of phosphorescent CDs into a solid matrix as a solution-based sensor.

Local-structure-dependent luminescence in lanthanide-doped inorganic nanocrystals for biological applications

This feature article overviews the recent advances in the local-structure-dependent luminescence in lanthanide-doped inorganic nanocrystals for various biological applications.