Facile fabrication of boron and nitrogen co-doped carbon dots for "ON-OFF-ON" fluorescence sensing of Al3+ and F- ions in water samples

Water contamination with harmful ions has grown to be a significant environmental issue on a global scale. Therefore, the fabrication of simple, cost-effective, and reliable sensors is essential for identifying these ions. Herein, co-doping of carbon dots with new caffeine and H3BO3-derived boron (B) and nitrogen (N) was performed (BN@CDs). The as-prepared BN@CDs probe was used for the tandem fluorescence sensing of Al3+ and F- based on "ON-OFF-ON" switches. The BN@CDs nanoswitch has a high quantum yield of 44.8% with λexc. and λem. of 360 nm and 440 nm, respectively. The probe exhibited good stability with different pH, ionic-strengths, and irradiation times. The fluorescence emission of BN@CDs was decreased as the Al3+ concentration was increased with a linear range of 0.03-90 μM and a limit of detection (S/N = 3) equal to 9.0 nM. Addition of F- restored the BN@CDs emission as F- ions form a strong and stable complex with Al3+ ions [Al(OH)3F]-. Therefore, the ratio response (F/F°) was raised by raising the F- ion concentration to the range of 0.18-80 μM with a detection limit (S/N = 3) of 50.0 nM. The BN@CDs sensor exhibits some advantages over other reported methods in terms of simplicity, high quantum yield, and low detection limit. Importantly, the sensor was successfully applied to determine Al3+ and F- in various ecological water specimens with accepted results.

Orange Pomace-Derived Fluorescent Carbon Quantum Dots: Detection of Dual Analytes in the Nanomolar Range

Green-emissive carbon quantum dots (CQDs) with exclusive chemosensing aspects were synthesized from orange pomace as a biomass-based precursor via a facile microwave method without using any chemicals. The synthesis of highly fluorescent CQDs with inherent nitrogen was confirmed through X-ray diffraction, X-ray photoelectron, Fourier transform infrared, Raman, and transmission electron microscopic techniques. The average size of the synthesized CQDs was found to be 7.5 nm. These fabricated CQDs displayed excellent photostability, water solubility, and outstanding fluorescent quantum yield, i.e., 54.26%. The synthesized CQDs showed promising results for the detection of Cr⁶⁺ ions and 4-nitrophenol (4-NP). The sensitivity of CQDs toward Cr⁶⁺ and 4-NP was found up to the nanomolar range with the limit of detection values of 59.6 and 14 nM, respectively. Several analytical performances were thoroughly studied for high precision of dual analytes of the proposed nanosensor. Various photophysical parameters of CQDs (quenching efficiency, binding constant, etc.) were analyzed in the presence of dual analytes to gain more insights into the sensing mechanism. The synthesized CQDs exhibited fluorescence quenching toward incrementing the quencher concentration, which was rationalized by the inner filter effect through time-correlated single-photon counting measurements. The CQDs fabricated in the current work exhibited a lower detection limit and a wide linear range through the simple, eco-friendly, and rapid detection of Cr⁶⁺ and 4-NP ions. To evaluate the feasibility of the detection approach, real sample analysis was conducted, demonstrating satisfactory recovery rates and relative standard deviations toward the developed probes. This research paves the way for developing CQDs with superior characteristics utilizing orange pomace (biowaste precursor).

Waste to value transformation: Converting Carica papaya seeds into green fluorescent carbon dots for simultaneous selective detection and degradation of tetracycline hydrochloride in water

Rampant use of antibiotics has resulted in their seepage into groundwater and ultimately ending up in the food chain, causing antimicrobial resistance. To address this issue, it is imperative to not only quantitatively detect but eliminate them from water. An eco-friendly, one-step microwave-induced pyrolysis of waste papaya seeds (PS) with ethylenediamine (EDA) for just 5min gave green fluorescent nitrogen-doped carbon dots (PS-CDs), which are capable of detecting and photocatalytically degrading TC. The fluorescence properties of PS-CDs displayed that it has high sensitivity and selectivity towards sensing of TC with a detection limit as low as 120 nM. Also, the method gave satisfactory recovery results when extrapolated to determine TC in spiked milk, orange juice, tap water, and honey samples. On the other hand, PS-CDs alone potentially function as an efficient photocatalyst for the degradation of TC. PS-CDs' dual functionality provides an effectual method for the simultaneous detection and degradation of TC by a single nanoprobe.

Sophorajaponica L. flower mediated carbon dots with nitrogen and sulfur co-doped as a sensitive fluorescent probe for amoxicillin detection

This article first reported the green synthesis of N, S co-doped fluorescent carbon dots (N, S-CDs-Sop) and sought to establish the fluorescence detection system for amoxicillin (AMX). By using Sophorajaponica L. flower as the green precursor and dl-homocystine as the co-dopant, N, S-CDs-Sop were successfully prepared via a one-pot hydrothermal method, exhibiting good water solubility and excellent photoluminescence. It was revealed that the surface of N, S-CDs-Sop was abundant in amino, hydroxyl and carboxyl groups after being characterized by a variety of techniques. When Fe³⁺ was added, Fe³⁺ could be complexed with N, S-CDs-Sop to from N, S-CDs-Sop-Fe³⁺ chelation leading to a significant static quenching of fluorescence. However, when N, S-CDs-Sop, Fe³⁺ and AMX coexisted, AMX would coordinate with Fe³⁺ and form the strong chelate due to the favorable chemical structure, resulting in the rapid fluorescence recovery. Such a fast, simple and sensitive fluorescence "off-on" strategy with a low LOD and a relatively wide range was successfully applied to the detection of AMX, which is closely correlated with human health.