Nitrogen-doped carbon dots from rhizobium as fluorescence probes for chlortetracycline hydrochloride

Glutathione S-transferase templated copper nanoclusters as a fluorescent probe for turn-on sensing of chlorotetracycline

Hereby, facile-green copper nanoclusters templated by glutathione S-transferase (GST-CuNCs) have been innovatively synthesized via a simple one-pot stirring method at room temperature. The as-prepared nanoclusters exhibited uniform size with satisfactory fluorescence intensity, good stability and low cytotoxicity. Significantly, the fluorescence of the obtained GST-CuNCs could be considerably enhanced by the addition of chlorotetracycline (CTC) rather than other analogues of CTC, which was ascribed to the aggregation-induced enhancement caused by the interaction between CTC and GST. The enhanced fluorescence intensity demonstrated a good linear correlation with the CTC concentration in the range of 30-120 μM (R2 = 0.99517), and the low detection limit was 69.7 nM. Furthermore, the proposed approach showed favorable selectivity and anti-interference toward CTC among prevalent ions and amino acids. Additionally, this nanoprobe was also applied to the quantitative detection of CTC in serum samples with satisfactory outcomes, which demonstrated excellent prospects for practical applications.

A highly selective fluorescent sensor for chlortetracycline based on histidine-templated copper nanoclusters

In this study, histidine-protected copper nanoclusters (Cu NCs@His) were established by using a one-pot method, which histidine and ascorbic acid were applied as the template and reducing agent, respectively. The as-developed Cu NCs@His endued green emission wavelength at 494 nm with the excitation of 378 nm. The Cu NCs@His exhibited green fluorescence under UV light (365 nm). Using Cu NCs@His as a pattern nanosensor, the fluorescent "turn off" mechanism was fabricated for the determination of chlortetracycline in the light of the linear decrease of fluorescence intensities around 494 nm. The chlortetracycline conducted as a quencher, leading to reveal an excellent linear relationship between ln(F₀/F) of Cu NCs@His and chlortetracycline concentrations with the range of 0.5-200 μM, and the detection limit was 0.876 μM. The fluorescence quenching of Cu NCs@His revealed excellent selectivity for chlortetracycline over other potential interfering substances in the human body. This strategy was exhibited to be a convenient sensing platform for the detection of chlortetracycline in real medical samples, which could unfold a brand new and direct system for the sensing of chlortetracycline in real samples.

Wild jujube-based fluorescent carbon dots for highly sensitive determination of oxalic acid

Fluorescent carbon dots (CDs) were synthesized by a one-step hydrothermal treatment of wild jujube and dl-tryptophan. The structure and properties of the CDs were confirmed by transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet visible absorption spectroscopy, fluorescence spectroscopy and so on. The as-prepared CDs exhibit excellent excitation-independent but pH-dependent (4.0-12.0) fluorescent features and emit blue strong fluorescence under 365 nm light. Hg²⁺ can decrease the fluorescence intensity of the CDs through static quenching, while the addition of oxalic acid (OA) recovers it owing to the coordination binding between oxalic acid and Hg²⁺. Based on this, the as-prepared CDs were used as a new "off-on" fluorescent probe for highly sensitive determination of oxalic acid with a wide linear detection range of 0.1-20 mg L^-1 and a low detection limit of 0.057 mg L^-1. Moreover, the fluorescent probe was successfully applied to detect oxalic acid in tomato and cherry tomato samples with satisfactory results.

A novel fluorescence ratio probe based on dual-emission carbon dots for highly selective and sensitive detection of chlortetracycline and cell imaging

The novel dual-emission carbon dots (DECDs) for highly selective and sensitive recognition of chlortetracycline (CTC) and cell imaging were synthesized successfully by one-step synthesis. The obtained DECDs possessed two fluorescence peaks (345 nm and 450 nm) and showed specific response to CTC, resulting in a decrease in fluorescence intensity at 345 nm, a blue shift, and an increase in fluorescence intensity at 450 nm. The obtained DECDs exhibited highly selective response to CTC and not to its analogues, such as tetracycline, doxycycline, and oxytetracycline. Thus, an excellent ratiometric probe for the detection of CTC was fabricated successfully and used for the detection of CTC in real samples with the detection limit (LOD) of 16.45 nM. More importantly, the DECDs were used for quantitative detection of CTC in living cells, which demonstrated excellent biocompatibility and broad prospects in biomedicine application. Finally, the excellent selectivity of DECDs toward CTC was attributed to the FRET mechanism and the formation of complexes.

Hydrogen bonding-mediated assembly of carbon dot@Zr-based metal organic framework as a multifunctional fluorescence sensor for chlortetracycline, pH and temperature detection

Carbon dots@UiO-66(COOH)2 with multifunctional fluorescence responsibilities for chlortetracycline, pH, and temperature detection is prepared via a hydrogen bond-driven solvent-free strategy.

Fabrication of surface molecularly imprinted electrochemical sensor for the sensitive quantification of chlortetracycline with ionic liquid and MWCNT improving performance

Chlortetracycline (CTC) is a widely used broad-spectrum antibiotic, its residue likely occurs in the environment and foods, bringing some negative effects to human health. Hence the detection and quantification of CTC in environmental and food samples is relevant. Herein, a novel electrochemical sensor based on surface molecularly imprinted polymer (SMIP) was constructed for the quantitative detection of CTC. The SMIP was synthesized by using ionic liquid (IL) functionalized MWCNT (MWCNT-IL) as supporter, 1-carboxymethyl-3-vinylimidazolium bromide (IL₁) as functional monomer, CTC as template, ethylene glycol dimethyl acrylate as crosslinker, and azobisisobutyronitrile as initiator. The obtained composite IL₁-SMIP exhibited high adsorption capacity for CTC and the imprinting factor was ca. 4.1. It was found that IL played an important role in improving the property of SMIP, which was also evaluated by DFT-based calculation. The resulting sensor IL₁-SMIP/MWCNT-IL/GCE showed high selectivity, sensitivity and reproducibility. CTC could be quantified from 0.4 μM to 55 μM with a detection limit of 0.08 μM (S/N = 3) under the optimized conditions. The practical applicability of the sensor was demonstrated successfully by determining CTC in real samples.

Preparation of yellow-emitting carbon dots and their bifunctional detection of tetracyclines and Al3+ in food and living cells

A novel bifunctional carbon dot (CD)-based sensing platform was constructed for detection of tetracyclines (TCs) and Al³⁺. The fluorescence CDs were fabricated by hydrothermal method using phenylenediamine (p-PD) and ethylenebis(oxyethylenenitrilo) tetraacetic acid (EGTA) as precursors. The obtained prepared CDs show bright yellow fluorescence (y-CDs, E_X = 400 nm and Em = 556 nm), high fluorescence quantum yield (QY = 21.55 ± 0.06%), and preferable optical stability. TCs can directly quench the fluorescence of y-CDs based on static quenching characteristics and a small internal filtration effect (IEF). By adding Al³⁺ to the y-CDs + TCs system, the fluorescence is partly recovered because TCs escape from the surface of the y-CDs and form a more stable chelate with Al³⁺. The sensing platform displays good selectivity and high sensitivity to TCs and Al³⁺ with low detection limits of 0.057-0.23 μM and 0.091 μM, respectively. Importantly, this sensing platform has enabled the detection of TCs and Al³⁺ in milk samples with satisfactory recoveries and RSDs, confirming the reliability and feasibility of this method. Combining with low toxicity and preferable biocompatibility, the y-CDs are extended to cellular imaging and detection of CTC and Al³⁺ in A549 cells.

Ratiometric fluorescence and smartphone dual-mode detection of glutathione using carbon dots coupled with Ag+-triggered oxidation of o-phenylenediamine

Developing ratiometric fluorescence and smartphone dual-mode bioanalysis methods is important but challenging. A ratiometric fluorescence method for determining glutathione (GSH) using carbon dots (CDs) and Ag⁺-triggered o-phenylenediamine (OPD) oxidation is described here. Ag⁺oxidizes OPD to give 2,3-diaminophenazine (oxOPD), which effectively quenches CD fluorescence at 436 nm through the inner filter effect and causes a new emission peak at 561 nm. GSH chelates with Ag⁺and prevents the Ag⁺oxidizing OPD and therefore effectively preserves CD emission at 436 nm (blue) and allows only weak oxOPD fluorescence at 561 nm (orange) to occur. The oxOPD to CD fluorescence intensity ratio decreased linearly as the GSH concentration increased in the range 0-150 nM, and the detection limit was 15 nM. The ratiometric fluorescence probe lit with an ultraviolet lamp clearly changed color from orange to blue as the GSH concentration increased. An image was acquired using a smartphone camera and converted into digital values. The blue and red channel ratio was calculated and used to quantify GSH. The method therefore allows dual-mode detection of GSH.

Nitrogen-doped carbon dots derived from hawthorn for the rapid determination of chlortetracycline in pork samples

In recent years, the methods for rapidly detecting antibiotics using the unique fluorescent properties of carbon dots have attracted increasing attentions. The purpose of this study is to prepare carbon dots by hawthorn and establish a rapid fluorescence sensor for the detection of chlortetracycline in pork samples. An environmentally friendly nitrogen-doped carbon dots (N-CDs) with hawthorn powder as the carbon source and diethylenetriamine (DETA) as the nitrogen source was synthesized by one-pot hydrothermal process. The preparation conditions of the N-CDs were optimized. Subsequently, the characteristics of the N-CDs were elucidated by fluorescence, UV absorption, transmission electron microscope, fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The N-CDs showed a quantum yield of 22.96%, emission at 447 nm at the maximum excitation wavelength of 370 nm and an average particle diameter of 3.17 nm. Meanwhile, the factors affecting the fluorescence intensity of the N-CDs were studied. Moreover, the fluorescence quenching method for detecting chlortetracycline in pork was established and optimized. Under the best experimental conditions, the linear range (R² = 0.9992) was developed over 0.4-20 μg mL^-1 with a detection limit of 0.073 ± 0.005 μg mL^-1 (S/N = 3). Chlortetracycline in pork samples had been successfully detected with good recoveries of 93.62%-103.18%, which suggested that the study provided a new approach for the detection of chlortetracycline in pork.