Synthesis of sulfur-rich nitrogen dots from a single source precursor and its application in dual-mode sensing

Novel fluorescent probes based on sulfur and nitrogen co-doped carbon dots for determination of three N-substituted phenothiazine derivatives in dosage forms

In the current work, sulfur and nitrogen co-doped carbon dots (S,N-CDs) as simple, sensitive, and selective turn-off fluorescent nanosensors were utilized for analysis of three phenothiazine derivatives, including acetophenazine (APZ), chlorpromazine (CPH), and promethazine (PZH). S,N-CDs were synthesized through a green one-pot microwave-assisted technique using widely available precursors (thiourea and ascorbic acid). HRTEM, EDX, FTIR spectroscopy, UV-Vis absorption spectroscopy, and fluorescence spectroscopy were used to characterize the as-synthesized CDs. When excited at 330 nm, the carbon dots produced a maximum emission peak at 410 nm. The cited drugs statically quenched the S,N-CDs fluorescence as revealed by the Stern-Volmer equation. The current method represents the first spectrofluorimetric approach for the determination of the studied drugs without the need for chemical derivatization or harsh reaction conditions. The importance of the proposed work is magnified as the cited drugs do not have any fluorescent properties. The fluorescence of the developed sensor exhibited a linear response to APZ, CPH, and PZH in the concentration ranges of 5.0-100.0, 10.0-100.0, and 10.0-200.0 μM with detection limits of 1.53, 1.66, and 2.47 μM, respectively. The developed fluorescent probes have the advantages of rapidity and selectivity for APZ, CPH, and PZH analysis in tablets with acceptable % recoveries of (98.06-101.66 %). Evaluation of the method's greenness was performed using the Complementary Green Analytical Procedure Index (ComplexGAPI) and Analytical GREEnness metric (AGREE) metrics, indicating that the method is environmentally friendly. Validation of the proposed method was performed according to ICHQ2 (R1) guidelines.

Measurement of mercury with highly selective fluorescent chemoprobe by carbon dots and silver nanoparticles

This work describes a novel fluorescent chemoprobe that uses carbon dots and silver nanoparticles (AgNPs) to monitor mercury ions in aqueous samples attributed to the principle of inner filter effect. The fluorescent response signal of the carbon dots is diminished by AgNPs, attributed to inner filter effect, and is restored with the addition of Hg²⁺. The fluorescent chemoprobe was specific over the range from 0.01 to 2.5 μM and a high sensitivity of 3.6 nM. The chemoprobe was validated using real local aqueous samples, and the spike recoveries of 97.4%-103% were excellent and satisfied. The data indicated that the developed fluorescent chemoprobe was sensitive, selective, stable and reliable. This fluorescent chemoprobe provides a sensitive tool with broad prospects for mercury detection in aqueous samples and the work will offer ideas for designing and constructing novel fluorescent probes.

Multicolor nitrogen dots for rapid detection of thiram and chlorpyrifos in fruit and vegetable samples

The development of sensitive fluorescence sensors and efficient preparation of samples is a challenge in the detection of pesticides in complex samples. In this study, multicolor nitrogen dots (M-Ndots) were synthesised via microwave irradiation at 140 °C for 10 min with 5-amino-1H-tetrazole and p-phenylenediamine as precursors, which have a high fluorescence quantum yield of up to 31%. Furthermore, the M-Ndots were employed as fluorescence sensors for pesticide detection by being combined with a gas membrane separation device, to eliminate the interference from the complex sample matrix. In this process, the M-Ndots were used for sensing thiram and chlorpyrifos through their affinities to Cu²⁺ and Fe³⁺, respectively. Because thiram could decompose into volatile CS₂, its derivate was sensed using the fluorescence of M-Ndots via a complexation reaction with Cu²⁺. Chlorpyrifos, due to its volatility, can reduce the Fe³⁺ ion by inhibiting the activity of acetylcholinesterase, which produces H₂O₂ to oxidise Fe²⁺. In a real application, the time consumption for 96 samples was less than 30 min in one run of the gas membrane separation device. The recoveries for thiram and chlorpyrifos ranged from 90.0% to 115.0%, and the analytical results were validated using LC-MS/MS methods, with relative errors ranging from -7.4% to 10.1%.

RNA-responsive fluorescent carbon dots for fast and wash-free nucleolus imaging

RNA as a carrier of genetic information plays a critical role in various physiological processes. RNA-rich nucleolus is usually employed as an important biomarker for many malignant diseases. Herein, RNA-responsive fluorescent carbon dots (CDs) were synthesized by a simple microwave method. Due to the presence of cationic benzothiazolium groups in the CDs, a "turn-on" fluorescence signal was achieved between CDs and RNA. The CDs exhibit excellent RNA selectivity and a good linear relationship with a detection limit of 0.62 μg/mL. The small particle size, polarity sensitivity and RNA response behavior of CDs realized fast and wash-free nucleolus imaging effectively. Overall, these CDs provide a powerful potential tool for monitoring cell nucleus activity and elucidating RNA dynamics.

Coumarin Thiourea-Based Fluorescent Turn-on Hg2+ Probe That Can Be Utilized in a Broad pH Range 1-11

A novel coumarin-thiourea conjugate was synthesized facilely. It served as a fluorescent turn-on chemosensor for selective detection of Hg²⁺ ion over other common competitive metal ions including Li⁺, Na⁺, K⁺, Ag⁺, Cu²⁺, Fe²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺, Ca²⁺, Mg²⁺, Al³⁺, Cr³⁺ and Fe³⁺ ions based on the Hg²⁺-promoted desulfurization and cyclization reactions. Addition of Hg²⁺ ion to the sensor solution in 2:8 EtOH/H₂O induced a hypsochromic shift of the UV-Vis absorption band from 360 nm to 340 nm accompanying distinct enhancement in the absorption intensity while addition of other metal ions failed to bring about substantial change in the absorption spectra. Addition of Hg²⁺ to the sensor solution also caused marked increase in the fluorescence emission intensity and most common competitive metal ions did not interfere with the selective sensing of Hg²⁺ ion by the sensor. The detection limit of Hg²⁺ ion by the probe was calculated to be 1.46 × 10^-7 M and the probe could be utilized for selective detection of Hg²⁺ ion by fluorescence turn-on mode over a broad pH range of 1-11.