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Concentration-dependent photoluminescence carbon dots (CDs) have been successfully synthesized through the one-step hydrothermal treatment of o-phthalic acid and ethylenediamine. The CDs possessed higher fluorescence quantum yield, up to 39.22%, exhibiting distinguished optical property, water solubility, and stability. The CDs that emit strong blue-green fluorescence can visually identify and determine tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC). TC quenched the fluorescence of CDs at 500 nm owing to the inner filter effect; OTC behaved similarly, but the emission wavelength of CDs was red-shifted to 515 nm. Inversely, once CTC was introduced to CDs solution, the fluorescence increased and the emission peak was blue-shifted to 450 nm. Bandgap transition and electrostatic interaction were proposed to be the mechanisms for the detection of OTC and CTC by CDs. Wide linear relationships were established for TC, OTC, and CTC with the limits of detection to be 50 nM, 36 nM, and 373 nM, respectively. Furthermore, the nanoscale probe constructed by this system has been applied to detect tetracyclines (TCs) in complex samples with satisfying recoveries (93.2-114%) and was designed as a portable test strip sensor for visually on-site TCs of honey sample screening. Accordingly, the preparation process of the nano fluorescent probe is simple and environmentally friendly, and the probe has a specific recognition ability for tetracyclines. The synthesized CDs in this work provide a new orientation for fast, effective, and visual real-time detection of tetracycline in actual samples.

In this paper, a FRET (Forster resonance energy transfer) based fluorescence method was developed for the quickly detection of ochratoxin A (OTA) in agricultural products (e.g., flour and beer). A highly fluorescent nitrogen doped carbon dots (CD) were served as energy donor, the DNA and MCH (6-mercapto-1-hexanol) modified Ag nanoparticles were served as energy acceptor in the FRET system. OTA can be detected in a concentration range between 10 and 5000 nM, the limit of detection is 8.7 nM. This method has three advantages: (1) an enhanced fluorescent intensity can be acquired by utilizing the nitrogen doped CD synthesized by one-step approach without sophisticated modification of nanoparticles; (2) OTA detection was accomplished quickly (less than 30 min) by using MCH as assistant molecule; (3) an extended OTA detection linear range was acquired, which may facilitate the OTA detection in real agricultural samples, and is helpful for solving food safety problems., (Copyright © 2018 Elsevier B.V. All rights reserved.)

[Display omitted] • CQD/Dex/PVA nanocomposites are prepared by low-cost green technique. • Glucose sensing by "switch-OFF" fluorescence mechanism. • Highly selective for sensing of glucose in presence of interfering sugars. • Very low detection limit of 61.1 μM. • Glucose contents in human blood serums are compared with commercial glucometer. Herein, carbon quantum dot (CQD) doped dextran/polyvinyl alcohol (PVA) (CQD/Dex/PVA) nanocomposites are synthesized for in vivo detection of glucose by non-enzymatic "switch-OFF" fluorescence mechanism in real human blood serums. Highly functional, dispersible and stable CQD is obtained from aloe vera by carbonization and a facile solution mixing technique is adopted for the preparation of CQD/Dex/PVA nanocomposites. It is noticed that hydrogen bonding between –OH group of glucose and that of the dextran and PVA quenches the fluorescence intensity of the nanocomposite. The synthesized CQD/Dex/PVA nanocomposite is highly selective for sensing of glucose in presence of other interfering sugars which proves its suitability to be implemented in complex biological environment. This biosensing technique exhibits linear range from 0.27 mM to 1.72 mM, R2 = 0.986 and a low detection limit of 61.1 μM. The measurements of glucose content in twelve real human blood serums are done and compared with commercial glucometer with satisfactory recoveries. Considering the high selectivity, sensitivity and accuracy, this "switch-OFF" fluorescence method holds promising application in diabetes management. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-sensitive and highly selective label-free fluorescent aptasensor was developed for the rapid detection of Hg(II), using water soluble cysteamine-capped CdTe/ZnS quantum dots (cysteamine@CdTe/ZnS QDs) as an luminescent probe and a single strain DNA aptamer designed to specifically bind to Hg(II) ions. Negative charge aptamers could aggregate the cationic cysteamine@CdTe/ZnS core/shell quantum dots, so the fluorescence quenching occurred. When Hg(II) ions, as a target, were added to the quantum dots solution, the aptamers with thymine (T)-rich sequences were selectively bound to the mercury ions. This is due to the powerful affinity of Hg(II) ions to the T bases of the DNA aptamer. It leads to the formation of an Hg (II)-bridged T base pair and the aptamers rearrangement into a hairpin-like structure. In the presence of Hg(II), de-aggregation of the quantum dots was occurs, so the fluorescence intensity was gradually increased with enhancing its concentration. Hg(II) could be measured in the range of 5.0 × 10 −10 to 1.0 × 10 −6 mol L −1 with a low limit of detection, 8.0 × 10 −11 mol L −1 . The fabricated fluorescent aptasensor also demonstrated excellent selectivity for Hg(II) detection, this principal was investigated by theoretical and experimental methods so it was applied lucratively for the determination of Hg(II) in real water and waste water samples. [ABSTRACT FROM AUTHOR]

Wang, L. and Shi, Y., 2019. Determination of heavy metal ions in seawater by water-soluble quantum dot fluorescence probe. In: Li, L.; Wan, X.; and Huang, X. (eds.), Recent Developments in Practices and Research on Coastal Regions: Transportation, Environment and Economy. Journal of Coastal Research, Special Issue No. 98, pp. 146–150. Coconut Creek (Florida), ISSN 0749-0208. In recent years, many analytical methods have been applied to the detection of toxic metal ions. However, the interference caused by a matrix will make the measurement method less precise, and some drugs are difficult to determine. We must find a highly sensitive analytical method; only in this way can we effectively monitor the content of heavy metal ions. Quantum dot (QD) technology is an interdisciplinary technology with high sensitivity. The photoluminescence properties of QDs are closely related to their surface modification. Many metal ions can significantly affect the optical properties of QDs through different mechanisms of action. QDs with wide excitation, narrow emission, and high-fluorescence quantum yield have broad application prospects in the field of fluorescence imaging in biological analysis. At present, the application of QDs to detect metal ions in complex substrates is a promising method. The difficulty of using QDs to detect heavy metals lies in how to improve their anti-interference performance in complex substrates. [ABSTRACT FROM AUTHOR]