Condensation Product of 1-Naphthaldehyde and 3-Aminophenol: Fluorescent “on” Probe for Ce3+and “off” Probe for Dichromate (Cr2O72−)

An overview on recent advances of reversible fluorescent probes and their biological applications

Due to the simplicity and low detection limit, fluorescent probes are widely used in both analytical sensing and optical imaging. Compared to conventional fluorescent probes, reversibility endows the reversible fluorescent probe outstanding advantages and special properties, making reversible fluorescent probes with capable of quantitative, repetitive or circulatory. Reversible fluorescent probes can also monitor the concentration dynamics of target analytes in real time, such as metal ions, proteins and enzymes, as well as intracellular redox processes, which have been widely applied in various fields. This review summarized the types and excellent properties of reversible fluorescent probes designed and developed in recent years. It also summarized the applications of reversible fluorescent probe in fluorescence imaging, biological testing, monitoring redox cycles, and proposed the remaining challenges and future development directions of the reversible fluorescent probe. This review provided comprehensive overview of reversible fluorescent probe, which may provide valuable references for the design and fabrication of the reversible fluorescent probe.

Nitrogen and Sulfur Co-doped Carbon Dots as a Turn-Off Fluorescence Probe for the Detection of Cerium and Iron

Carbon dots has becoming one of the most promising fluorescence sensors to determine the trace level of heavy metals in environments because of their advantages in optical properties, response time, and convenient operation procedures. Herein, a novel nitrogen and sulfur co-doped carbon dots (NS-CDs) were prepared though microwave assisted approach using DL-malic acid and allyl thiourea for the first time. Due to the existence of nitrogen and sulfur, the as-prepared NS-CDs exhibited bright blue fluorescence at 430 nm upon 330 nm excitation, with a fluorescence quantum yield of 19.8%. The sensitivity study of NS-CDs against metal ions and organic molecules has approved that the fluorescence could be further quenched by Ce⁴⁺ and Fe³⁺ ions, with the same linear detection ranges varying from 10 to 90 µM. The limits of detection (LOD) were determined as low as 0.75 µM and 0.67 µM for Ce⁴⁺ and Fe³⁺ ions, respectively. The possible quenching mechanism is explained by inner filter effect and static quenching mechanism for Ce⁴⁺ ions, while the quenching effect caused by Fe³⁺ ions is attributed to the inner filter effect, static and dynamic quenching mechanisms. Additionally, the developed sensor was used for the detection of Ce⁴⁺ and Fe³⁺ ions in tap water with satisfactory recoveries. Finally, the designed NS-CDs sensor possesses good biocompatibility against MA104 cells, suggesting the sensor can be potentially applied to detect Ce⁴⁺ and Fe³⁺ ions in environment and biological systems.

A Highly Sensitive and Selective Fluorescent Probe for the Detection of Cerium(III) Using Tridentate Based-Oxazolidine: Experimental and DFT Investigations

A new fluorescent sensor based on oxazolidine derivative, (2-(pyridin-2-yl)oxazolidine-4,4-diyl)dimethanol; TN), was designed and synthesized successfully in high yield (82%) under Schiff base reaction. The structural elucidation of the sensor has been confirmed by Infrared Spectroscopy, Nuclear Magnetic Resonance Spectroscopy, and High Resolution Mass Spectrometry - Electrospray Ionization - Time of Flight. The designed TN sensor exhibited high sensitivity and selectivity towards an aqueous solution of cerium(III) over various metal ions under biologically relevant conditions (100.0 mM HEPES buffer pH 7.4). The limit of detection (LOD) was reported as 54.0 nM. The geometry of tridentate based-oxazolidine (TN) and its coordination of cerium(III) (TN-Ce³⁺) was proven by using the density functional theory (DFT) calculations. The highest occupied molecular orbital - lowest unoccupied molecular orbital energy gap was decreased when TN-Ce³⁺ is formed. The results indicated that TN can be used as a fluorescent probe for high sensitivity and selectivity detection of cerium(III) ions.