Fluorescent detection of tartrazine based on the supramolecular self-assembly of cationic perylene diimide

Preparation and utilization of carbon dots as a nanoprobe for sensitive detection of tartrazine and palladium (II)

We prepared novel green, eco-friendly carbon dots as a dual-channel probe for highly sensitive and selective detection of tartrazine (Trz) and palladium(II) (Pd(II)) involving, respectively, FRET and electron transfer mechanisms. Furthermore, the successful utilization of the carbon dots for detecting Trz and Pd(II) in actual samples implies its potential application prospects in analysis.

Exciton Delocalization and Polarizability in Perylenetetracarboxylic Diimide Probed Using Electroabsorption and Fluorescence Spectroscopies

Perylenetetracarboxylic diimide (PTCDI) is an n-type organic semiconductor molecule that has been widely utilized in numerous applications such as photocatalysis and field-effect transistors. Polarizability and dipole moment, which are inherent properties of molecules, are important parameters that determine their responses to external electric and optical fields, physical properties, and reactivity. These parameters are fundamentally important for the design of innovative materials. In this study, the effects of external electric fields on absorption and fluorescence spectra were investigated to obtain the PTCDI parameters. The PTCDI substituted by an octyl group (N,N'-Dioctyl-3,4,9,10-perylenedicarboximide) dispersed in a polymethyl methacrylate (PMMA) matrix was studied in this work. The features of vibronic progression in the absorption spectrum were analogous to those observed in solution. The red shift of the absorption band caused by the Stark effect was mainly observed in the presence of an external electric field. Changes in parameters such as the dipole moment and polarizability between the ground and the Franck-Condon excited states of the PTCDI monomer were determined. The fluorescence spectrum shows a contribution from a broad fluorescence band at wavelengths longer than the monomer fluorescence band. This broad fluorescence is ascribed to the excimer-like fluorescence of PTCDI. The effects of the electric field on the fluorescence spectrum, known as the Stark fluorescence or electrofluorescence spectrum, were measured. Fluorescence quenching is observed in the presence of an external electric field. The change in the polarizability of the monomer fluorescence band is in good agreement with that of the electroabsorption spectrum. A larger change in the polarizability was observed for the excimer-like fluorescence band than that for the monomer band. This result is consistent with exciton delocalization between PTCDI molecules in the excimer-like state.

Carbon dots derived from expired drugs based ratiometric fluorescent sensor for horseradish peroxidase in fruits and vegetables and screening inhibitors

Household storage of pharmaceuticals to extract raw materials synthesized from carbon points facilitates the utilization of solid waste resources. A novel ratiometric fluorescence sensing technique was developed to ascertain the presence of horseradish peroxidase (HRP) in fruits and vegetables. The method employed a fluorescent probe, synthesized from expired amoxicillin (referred to as carbon dots, or A-CDs), serving as a reference fluorophore. Additionally, 2,3-diaminophenazine (DAP) was utilized as a specific response signal. DAP resulted from a catalytic reaction system involving phenylenediamine and hydrogen peroxide under the catalysis of HRP. The fluorescence intensity corresponding to DAP at 562 nm exhibited a substantial increase, simultaneous with the fluorescence quenching of A-CDs at 450 nm. The ratiometric fluorescence nanosensors displayed a broad linear range and high sensitivity for the detection of HRP. Across the concentration range 0.01 to 6 U L-1, the fluorescence intensity ratio between DAP and A-CDs demonstrated a proportional increase with rising HRP concentration, achieving an impressive detection limit of 0.002 U L-1. The recovery of HRP in fruit and vegetable samples ranged from 96.1 to 103%, with an RSD value of less than 3.8%. The proposed method facilitated the screening of inhibitors of HRP enzyme activity, contributing to the preservation of freshness in fruits and vegetables.