Development of a fluorescent m icrowave‐assisted synthesized carbon dots/Cu 2+ probe for rapid detection of tea polyphenols

An optical and visual multi-mode sensing platform base on nitrogen, sulfur, boron co-doped carbon dots for rapid and simple determination of ferric ions in water

Abnormal iron ions levels may lead to some diseases and serious environmental pollution. Herein, optical and visual detection strategies of Fe3+ in water based on co-doped carbon dots (CDs) were established in the present study. Firstly, a one-pot synthetic strategy for the preparation of the N, S, B co-doped CDs with a home microwave oven was developed. Secondly, the optical properties, chemical structures, and morphology of CDs were further characterized by fluorescence spectroscopy, Uv-vis absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscope. Finally, the results indicated that the fluorescence of the co-doped CDs was quenched by ferric ions via the static mechanism and the aggregation of CDs, accompanied by the increased red color. The multi-mode sensing strategies of Fe3+ with fluorescence photometer, UV-visible spectrophotometer, portable colorimeter and smartphone had the advantages of good selectivity, excellent stability and high sensitivity. Fluorophotometry based on co-doped CDs was a powerful probe platform for measuring lower concentrations of Fe3+ due to its higher sensitivity, better linear relationship, lower limit of detection (0.27 μM) and limit of quantitation (0.91 μM). In addition, the visual detection methods with a portable colorimeter and smartphone had been proven to be very suitable for rapid and simple sensing of higher concentrations of Fe3+. Moreover, the co-doped CDs utilized for Fe3+ probes in tap water and boiler water obtained satisfactory results. Consequently, the efficient, versatile optical and visual multi-mode sensing platform could be extended to apply such a visual analysis of ferric ions in the biological, chemical and other fields.

A fluorescence aptasensor based on carbon quantum dots and magnetic Fe3O4 nanoparticles for highly sensitive detection of 17β-estradiol

Trace amounts of 17β-estradiol (E2) in food and the environment poses a threat to human health, which has created the demand for sensitive analytical methods to detect E2. In this study, a novel fluorescent aptasensor was developed for sensitive detection of E2 based on double-chain hybridization between carbon quantum dots-labelled with E2 aptamer (CQDs-aptamer) and Fe₃O₄ nanoparticles modified by complementary DNA (Fe₃O₄-cDNA). Under the optimal conditions, the aptasensor displayed a good linear range of 10^-11-10^-6 M for E2 with the coefficient of determination (R²) of 0.996, and a low detection limit of 3.48 × 10^-12 M was obtained. Besides, the aptasensor showed high selectivity and good reproducibility for E2 detection, which was successfully applied to the sensitive detection of E2 in milk as compared with tap water and lake water with satisfactory recoveries from 85.21% to 114.80%, suggesting the great significance of this aptasensor for detecting food contaminants in the food industry.

A fluorescence biosensor based on single-stranded DNA and carbon quantum dots for acrylamide detection

As a potential carcinogen produced in food thermal processing, acrylamide (AM) can cause irreversible harm to human health. For the detection of AM in food products, a simple fluorescent biosensor based on single-stranded DNA (ssDNA) and carbon quantum dots (CQDs) was developed. Reduced fluorescence intensity of CQDs at 445 nm (excitation at 350 nm) was induced by the attachment of ssDNA. In the presence of AM, ssDNA was preferentially bound to AM by hydrogen bonding and the degree of fluorescence reduction was smaller than that without AM. Under optimized conditions, results showed that the sensing approach for detecting AM had a low detection limit of 2.41 × 10^-8 M in the standard solution, and a linear relationship ranging from 5 × 10^-3 to 1 × 10^-7 M with the determination coefficient (R²) of 0.9895 was obtained. Furthermore, a good recovery percentage (91.36-98.11%) in bread crust showed the potential for practical applications of this proposed biosensor.