Xiaoman Xu

A Ratiometric Fluorescence Universal Platform Based on N, Cu Codoped Carbon Dots to Detect Metabolites Participating in H2O2-Generation Reactions

In this work, a new kind of N, Cu codoped carbon dots (N/Cu-CDs) was prepared via a facile one-pot hydrothermal method by using citric acid monohydrate, copper acetate monohydrate and diethylenetriamine. The prepared N/Cu-CDs with a high quantum yield (50.1%) showed excitation-independent emission at 460 nm. The structure and fluorescence properties of N/Cu-CDs were characterized by high-resolution transmission electron microscopy, fluorescence spectrofluorometer, FT-IR spectrometer, UV-visible spectrophotometer and X-ray photoelectron spectroscopy. N/Cu-CDs were applied to establishing a ratiometric fluorescence probe toward H2O2 based on the inner filter effect (IFE) between N/Cu-CDs and DAP (2,3-diaminophenazine, the oxidative product of o-phenylenediamine (OPD)), and provided a ratiometric fluorescence universal platform for detection of the metabolites participating in H2O2-generation reactions (cholesterol and xanthine). The proposed method was demonstrated to be ultrasensitive and highly selective for cholesterol and xanthine assay with detection limits of 0.03 and 0.10 μM, respectively. The fluorescence probe built was applied to the determination of cholesterol and xanthine in human serum with satisfactory results.

A dual-emissive fluorescent sensor fabricated by encapsulating quantum dots and carbon dots into metal–organic frameworks for the ratiometric detection of Cu2+ in tap water

A novel ratiometric fluorescent (RF) sensor was synthesized via a facile one-pot route by encapsulating quantum dots (QDs) and carbon dots (CDs) having good fluorescence properties into a zeolitic imidazolate framework (ZIF-8, one of the classical metal–organic frameworks). The as-synthesized QDs/CDs@ZIF-8 composite not only possessed the advantages of a RF sensor, but also accumulated target analytes strongly due to the adsorption ability of MOFs. The composite showed good stability and dispersibility in aqueous solution and was further applied to the detection of Cu2+ ions. The QDs/CDs@ZIF-8 composite that is used as a RF sensor exhibited excellent sensitivity and selectivity toward Cu2+. The linear range was 5–100 nM and the LOD was 1.53 nM (3σ/K). The QDs/CDs@ZIF-8 composite could be simply used for detecting Cu2+ in tap water.

Fluorescent zinc(II)-based metal–organic frameworks for nitroaromatics sensing

A new structural metal–organic framework with fluorescence properties, namely Zn4(BTC)2(OH)2(CH3OH)6 (NJMU-001), was synthesized by using 1,3,5-benzenetricarboxylic acid (H3BTC) and zinc nitrate through a solvothermal reaction. In order to obtain good single crystals of NJMU-001, the factors affecting the reaction, such as the reaction temperature, reaction time, solvent and metal salt/ligand molar ratios, were studied. The phase purity of NJMU-001 was investigated via powder X-ray diffraction analysis, elemental analysis and FT-IR spectroscopy. Gas sorption measurements revealed that NJMU-001 was microporous and thermogravimetric analysis indicated that it was thermally stable under 200 °C. Fluorescence study of NJMU-001 in an N,N-dimethylformamide medium showed blue emission at 435 nm upon excitation at 370 nm. This emissive property was used for sensitive sensing of toxic and explosive nitroaromatics by exhibiting fluorescence quenching.

Carbon dots based immunosorbent assay for the determination of GFAP in human serum

Glial fibrillary acidic protein (GFAP) is expressed in the central nervous system and the level of GFAP normally rises with brain injury and astroglial tumors. So, serum GFAP is used as a marker for diagnosing various types of brain damage and astroglial tumors. In this study, a new sensor based on carbon dots (CDs) linked with antibodies to specifically detect GFAP in human serum was developed. Anti-GFAP (Ab1) linked with protein A/G agarose resin (PA/G) as a capture antibody (PA/G-Ab1) and anti-GFAP (Ab2) labeled with CDs as a detection antibody (CDs-Ab2) were prepared firstly. Then the CD-linked antibody immunosorbent assay (CLAISA) method was constructed based on the sandwich conjunction reaction among PA/G-Ab1, GFAP, and CDs-Ab2. CLAISA, using the fluorescence of PA/G-Ab1-GFAP-Ab2-CDs as the direct signal, enabled the proposed immunosensor to detect GFAP sensitively with a linear range of 0.10-8.00 ng ml-1 and a detection limit of 25 pg ml-1. This method was applied to the determination of GFAP in human serum by the standard addition method, and the results showed high accuracy and precision. Considering the easy synthetic process and excellent performance of CLAISA, this method has great potential to be used to monitor GFAP in the clinic.

N-doped carbon dots as a fluorescent probe for the sensitive and facile detection of carbamazepine based on the inner filter effect

A sensitive and facile method for the detection of carbamazepine (CBZ) was established based on the inner filter effect (IFE). In this IFE system, blue-emitting carbon dots (CDs) were used as a fluorophore and CBZ was a capable absorber, competitively absorbing the excitation light of the CDs. As a result, the fluorescence of the CDs could be quenched effectively by CBZ due to the inner filter effect. The interaction between the CDs and CBZ was studied, and we found that the absorption spectrum of CBZ overlapped with the excitation spectrum of the CDs. The excitation of the CDs was significantly weakened due to competitive absorption, resulting in the fluorescence quenching of the CDs. Under the optimum conditions, the fluorescence quenching efficiency versus the concentration of CBZ from 10–90 μg mL−1 gave a linear response, and the limit of detection (3σ/K) was 1.93 μg mL−1. The method was successfully applied to the detection of CBZ in tablet and human urine samples. The present method is simple, economical, and friendly to the environment, showing potential utility in practice.

Carbon dots coated with molecularly imprinted polymers: A facile bioprobe for fluorescent determination of caffeic acid

A new and sensitive method for fluorescent determination of caffeic acid (CA) was proposed based on silane-functionazed carbon dots coated with molecularly imprinted polymers (CDs@MIPs). CDs@MIPs were prepared by using CA as the templates on the surface of silane-functionazed carbon dots(CDs) with a sol-gel process. The as-prepared CDs@MIPs were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and fluorescence spectroscopy. The CDs@MIPs exhibited distinguished selectivity and high binding affinity to CA templates, and also showed good reusability. Under optimal conditions, the fluorescence intensity of CDs@MIPs decreased linearly with the increase of CA in the range of 0.5-200 μM. The limit of detection was 0.11 μM (3σ/K). Finally, the proposed method was successfully applied to the detection of CA in human plasma. The result indicates that the method built has promising potential for monitoring CA concentration in clinic.

One-Pot Synthesis of a Magnetic, Ratiometric Fluorescent Nanoprobe by Encapsulating Fe3O4 Magnetic Nanoparticles and Dual-Emissive Rhodamine B Modified Carbon Dots in Metal–Organic Framework for Enhanced HClO Sensing

In this work, a new magnetic, ratiometric fluorescent nanoprobe has been designed and fabricated by encapsulating Fe3O4 magnetic nanoparticles (MNPs) and dual-emissive carbon dots into the cavities of metal-organic frameworks (MOFs). This one-pot method combined hybrid characteristics of MOFs with multiple properties of the encapsulated functional materials. The MOF-based nanoprobe possessed the advantages of MOFs (strong adsorption ability, accumulating the analytes), Fe3O4 MNPs (magnetic separation), and ratiometric sensors (eliminating the variabilities caused by the instability of the instruments and environment). The MOF-based nanoprobe was dispersible and stable in aqueous solution, and the nanoprobe was applied to HClO sensing. This work will provide a promising strategy for design and synthesis of novel MOF-based composite materials.

Determination of Verapamil HCl in Pharmaceutical Preparations by a Fluorescent Nano Probe Based on CdTe/CdS/ZnS Quantum Dots

An analytical technique based on fluorescence quenching of CdTe/CdS/ZnS quantum dots (QDs) was developed to quantify verapamil in commercially available preparations. Various reaction parameters were optimized and the method developed was validated. One way analysis of variance (ANOVA) and post hoc tests at a 5% significance level were performed to justify the significance of the variation in observations. The linear range of the verapamil concentration was 0.25–5 µg/mL while the limit of detection was 20 µg/mL. Recovery and relative standard deviations were not more than ±10% of the actual amount and <5.9%, respectively. Foreign materials, common metal ions and pharmaceutical excipients of dosage forms caused little interference. To verify the application of the analytical method, the quantity of verapamil in commercially available dosage forms was measured. Verapamil content in the tablets and injections was not more than ±10% of the stated amount and it conformed to the specifications of both the British and the United States pharmacopoeias. In the case of statistical analysis, p-value was <0.05 in almost all levels of all parameters except for the optimized level of system. It can be concluded from the results that the designed method is simple, reliable, cost effective, selective, rapid and sensitive enough to be used for quantitative measurement of the verapamil HCl in dosage forms for quality control purposes.