Dual-channel fluorescent signal readout strategy for cysteine sensing

Visualization of cysteine in AD mouse with a high-quantum yield NIR fluorescent probe

Alzheimer's disease (AD) has gradually received enthusiastic attention with the aging process, and studying its biological relevance is expected. Excitingly, fluorescence probes were considered to be powerful tools for exploring biological correlations. Therefore, a highly selective near-infrared (NIR) fluorescent probe (DCM-Cl-Acr) for imaging cysteine (Cys) in AD was designed and synthesized. Through structural optimization, the probe exhibited high fluorescence quantum yield and low detection limit (20 nM) towards Cys. Meanwhile, based on the high selectivity and high sensitivity response exhibited by the probe to Cys, it was successfully applied to visualize endogenous and exogenous Cys in living cells and zebrafish, and showed good discrimination from homocysteine (Hcy) and glutathione (GSH). Further, the correlation between AD and Cys concentration was clarified by imaging studies in hippocampus tissue of AD mouse, and the abnormal accumulation of Cys in the hippocampus of AD brain was demonstrated.

Current Progress of Ratiometric Fluorescence Sensors Based on Carbon Dots in Foodborne Contaminant Detection

Carbon dots (CDs) are widely used in the detection of foodborne contaminants because of their biocompatibility, photoluminescence stability, and ease of chemical modification. In order to solve the interference problem of complexity in food matrices, the development of ratiometric fluorescence sensors shows great prospects. In this review, the progress of ratiometric fluorescence sensors based on CDs in foodborne contaminant detection in recent years will be summarized, focusing on the functionalized modification of CDs, the fluorescence sensing mechanism, the types of ratiometric fluorescence sensors, and the application of portable devices. In addition, the outlook on the development of the field will be presented, with the development of smartphone applications and related software helping to better enable the on-site detection of foodborne contaminants to ensure food safety and human health.

Ratiometric fluorescence assay based on carbon dots and Cu2+-catalyzed oxidation of O-phenylenediamine for the effective detection of deferasirox

The monitoring of deferasirox (DEF) has important clinical roles in patients who need iron excretion. However, analytical methods with practicability and simplicity are limited. Moreover, ratiometric fluorescence strategies based on Förster resonance energy transfer (FRET) from carbon dots (CDs) as a donor are rarely reported as a drug monitor. In this work, CDs with an appropriate emitting wavelength at 480 nm and excitation around 370 nm were prepared by hydrothermal approach and HCl post-treatment. O-Phenylenediamine (OPD) can be oxidized by Cu²⁺ to produce yellow fluorescent 2,3-diaminophenazine (oxOPD) in the system of Cu²⁺ and OPD (Cu–OPD). Correspondingly, a remarkable FRET from CDs to oxOPD in the system of CDs, Cu²⁺ and OPD (CDs–Cu–OPD) was fabricated with the quenching illustration of CDs, but emitting property of oxOPD. Attributed to the chelation ability of DEF on Cu²⁺, the inhibitory effects of DEF on the Cu²⁺-triggered oxidative capability reduced the FRET system by the decreased oxOPD. Thus, the recovered CDs at F₄₈₀ and decreased oxOPD at F₅₆₀ were found through a ratiometric mode by the addition of DEF in CDs–Cu–OPD for the DEF assay. The FRET behavior of CDs and oxOPD in CDs–Cu–OPD was proved clearly through the calculation of the association constant, binding constant, number of binding sites, and the distance between the donor and acceptor. Furthermore, this ratiometric method exhibited promising analytical performance for DEF with the application in real samples. The implementation of this work expands the application field of CDs and OPD oxidation in drug monitoring, and even other biological analyses through ratiometric strategy.

CDs with appropriate emission property interacted with Cu²⁺-catalyzed oxidation of OPD to form a ratiometric fluorescence strategy for deferasirox (DEF) detection.