Transforming waste into value: pomelo-peel-based nitrogen-doped carbon dots for the highly selective detection of tetracycline

Highly efficient and sensitive detection of tetracycline in environmental water: Insights into the synergistic mechanism of biomass-derived carbon dots and N-methyl pyrrolidone solvent

The tetracycline (TC) residue in water environment has caused serious public safety issue. Thus, efficient sensing of TC is highly desirable for environmental protection. Herein, biomass-derived nitrogen-doped carbon dots (N-CDs) synthesized from natural Ophiopogon japonicus f. nanus (O. japonicus) were used for TC detection. The unique solvent synergism efficiently enhanced detection sensitivity, and the detailed sensing mechanism was deeply investigated. The blue fluorescence of N-CDs was quenched by TC via static quenching and inner filter effect. Moreover, the enhancement of green fluorescence from deprotonated TC was firstly proposed and sufficiently verified. The solvent effect of N-methyl pyrrolidone (NMP) and the fluorescence resonance energy transfer (FRET) with N-CDs achieved an instantaneous enhancement of the green emission by 64-fold. Accordingly, a ratiometric fluorescence method was constructed for rapid and sensitive sensing of TC with a low detection limit of 6.3 nM within 60 s. The synergistic effect of N-CDs and solvent assistance significantly improved the sensitivity by 7-fold compared to that in water. Remarkably, the biomass-derived N-CDs displayed low cost, good solubility, and desired stability. The deep insights into the synergism with solvent can provide prospects for the utilization of biomass-based materials and broaden the development of advanced sensors with promising applications.

A dual-mode ratiometric probe using europium-doped cyclen-functional carbon dots for fluorescent and point-of-care detection of tetracycline

The overuse of tetracycline (TC) has led to the accumulation of antibiotic residues in drinking water and animal products, which can consequently lead to bacteria resistance and chronic disease in humans. Urgently addressing the need for a rapid, user-friendly, and point-of-care test for TC detection. In this work, we use cyclen and citric acid to synthesise carbon dots (CDs) with a unique ring-shaped structure on their surface and combine them with europium (Eu3+) to form an Eu-CDs fluorescent probe. In the presence of TC in aqueous systems, the Eu-CDs probe emits two distinctive fluorescent signals: the stable blue emission from cyclen-modified CDs and the red emission from Eu3+,showing a proportional increase with TC concentration. The developed Eu-CDs probe demonstrates accurate and selective detection capabilities for TC class antibiotics among various interfering factors. The Eu-CDs probe exhibits excellent linearity within the concentration range of 0.04-2.4 µM and achieves an impressive detection limit of 2.7 nM. Moreover, point-of-care Eu-CDs test strips are designed, allowing convenient on-site TC analysis through the detection of a colour change from blue to red under a portable UV light. The results highlight the effectiveness of the proposed dual-mode ratiometric fluorescent Eu-CDs probe and test strips, offering a practical point-of-care testing strategy for real-world TC detection applications.

A paper-based ratiometric fluorescence sensor based on carbon dots modified with Eu3+ for the selective detection of tetracycline in seafood aquaculture water

Paper-based ratiometric fluorescence sensors are normally prepared using two or more types of fluorescent materials on a paper chip for simple, low-cost and fast detection. However, the choice of multi-step and one-step modifications on the paper chip affects the analytical performance. Herein, a novel paper-based dual-emission ratiometric fluorescence sensor was designed for the selective detection of tetracycline (TC). Carbon dots (CDs) modified with Eu3+ were combined with a sealed paper-based microfluidic chip by two methods: one-step grafting of CDs-Eu3+ on paper and step-by-step grafting of CDs and Eu3+ on paper. The analytical performance was studied and optimized respectively. The red fluorescence of Eu3+ at 450 nm is enhanced and the blue fluorescence of CDs at 617 nm is quenched by energy transfer in the presence of TC. Under optimal conditions, TC is selectively determined in the linear range from 0.1 μM to 100 μM with a detection limit of 0.03 μM by the step-by-step grafting method. In addition, the sealed paper chip could effectively prevent pollution and volatilization from the reagent. This technique has been used to analyze TC in seafood aquaculture water with satisfactory results.

Efficient Electrochemiluminescence Sensing in Microfluidic Biosensors: A Review

Microfluidic devices are capable of handling 10-9 L to 10-18 L of fluids by incorporating tiny channels with dimensions of ten to hundreds of micrometers, and they can be fabricated using a wide range of materials including glass, silicon, polymers, paper, and cloth for tailored sensing applications. Microfluidic biosensors integrated with detection methods such as electrochemiluminescence (ECL) can be used for the diagnosis and prognosis of diseases. Coupled with ECL, these tandem devices are capable of sensing biomarkers at nanomolar to picomolar concentrations, reproducibly. Measurement at this low level of concentration makes microfluidic electrochemiluminescence (MF-ECL) devices ideal for biomarker detection in the context of early warning systems for diseases such as myocardial infarction, cancer, and others. However, the technology relies on the nature and inherent characteristics of an efficient luminophore. The luminophore typically undergoes a redox process to generate excited species which emit energy in the form of light upon relaxation to lower energy states. Therefore, in biosensor design the efficiency of the luminophore is critical. This review is focused on the integration of microfluidic devices with biosensors and using electrochemiluminescence as a detection method. We highlight the dual role of carbon quantum dots as a luminophore and co-reactant in electrochemiluminescence analysis, drawing on their unique properties that include large specific surface area, easy functionalization, and unique luminescent properties.

Crosslinked fish scale gelatin/alginate dialdehyde functional films incorporated with carbon dots derived from pomelo peel waste for active food packaging

A multifunctional and environmentally friendly composite film was developed by incorporating pomelo peel-derived carbon dots (PCDs) into a fish scale gelatin (FSG)/alginate dialdehyde (ADA) biopolymer matrix. ADA was used to reinforce the physicomechanical properties of the FSG film via Schiff base crosslinking. PCDs with strong antioxidant and antimicrobial activities were synthesized via a hydrothermal method. The effect of various PCDs content on the surface morphological, physicochemical, and functional characteristics of the composite films was investigated. The results showed that the introduction of PCDs into the FSG/ADA matrix effectively reinforced the mechanical performance, enhanced the water vapor and water resistance, increased UV-light blocking, conferred fluorescence properties, and improved the thermal properties of the composite films. Under 3 wt% PCDs content, the FSG/ADA/PCDs-3 % composite film not only presented significant antioxidant capacity with a radical scavenging rate of 91.71 % for DPPH and approximately 100 % for ABTS, but also exhibited excellent antimicrobial ability against bacteria and fungi. Results of a preservation experiment showed that the prepared FSG/ADA/PCDs-3 % film preserved the physiological qualities of strawberries post-harvest and extended their shelf-life to 7 days at room temperature. Overall, the fabricated FSG/ADA/PCDs composite films are promising for use in eco-friendly active food packaging.

Upcycling Waste: Citrus limon Peel-Derived Carbon Quantum Dots for Sensitive Detection of Tetracycline in the Nanomolar Range

In this work, a sustainable method was developed for the production of water-soluble carbon quantum dots employing a green approach. The synthetic protocol was employed using the microwave pyrolysis technique, while lemon peel served as a carbon precursor. Fabrication of highly fluorescent lemon-peel-derived CQDs (LP-CQDs) having inherent nitrogen functionality was validated by X-ray photoelectron spectroscopy, FTIR, X-ray diffraction, Raman spectroscopic analysis, and TEM techniques. The average particle size of fabricated LP-CQDs was 4.46 nm. LP-CQDs yielded a remarkable quantum yield of 49.5%, which displayed excellent salinity, photostability, storage time, conditions, and pH stability. LP-CQDs displayed encouraging results for tetracycline (TC) detection using a PL turn-off approach. The sensitivity of LP-CQDs toward TC was seen in a nanomolar range having a detection limit of 50.4 nM. Method validation was comprehensively studied to ensure the precision of the nanosensor. A complete analysis of different photophysical parameters of LP-CQDs was performed with TC to gain a deeper understanding of the sensing mechanism. Fabricated LP-CQDs showed fluorescence quenching toward TC, elucidated by the inner filter effect (IFE) mechanism. The synthesized nanoprobe demonstrated a lesser detection limit with a broad linear range, enabling facile, cheap, environmentally friendly, and fast detection of TC. Practicality of the detection method was assessed through analysis of real samples, resulting in satisfactory recovery percentage and relative standard deviation with respect to the developed probes. Furthermore, LP-CQDs were used as fluorescent inks and to fabricate paper-based fluorescent strips. This study lays the door for the sensing platform of LP-CQDs toward detection of TC, which may impact the potential role of environmental sustainability.

The synthesis of N-doped carbon dots for visual differentiating and detection of tetracyclines

N-doped carbon dots (N-CDs) were synthesized from L-glutamine and triethanolamine using a one-step hydrothermal method. The N-CDs emitting blue fluorescence had selective responses to tetracyclines (TCs) and could be used as a fluorescent probe to realize the quantitative detection and qualitative analysis of TCs. A method for the determination of TCs using the N-CDs in actual samples was successfully established. The recovery rate was maintained at 97.50-105.60%, and the relative standard deviation (RSD) was less than 3%. In addition, TCs can be visually distinguished using filter paper by the different fluorescence colours (light green, dark blue, and yellow-green) of the N-CDs/TCs system under ultraviolet light. This study provides a relatively simple method to detect and identify TCs.

Recent progress of carbon dot fluorescent probes for tetracycline detection

We made a detailed discussion about TCs and CDs, including the synthetic methods, doping strategies and promising prospects.