Detection of tannic acid exploiting carbon dots enhanced hydrogen peroxide/potassium ferricyanide chemiluminescence

Development of water-dispersible Dy(III)-based organic framework as a fluorescent and electrochemical probe for quantitative detection of tannic acid in real alcoholic and fruit beverages

Tannic acid (TA) is a water-soluble polyphenol and used in beverages, medical fields as clarifying and additive agents. In daily life, TA is unavoidable, and excessive consumption of tannin containing foods can harm health. Thus, rapid and sensitive quantification is highly necessary. Herein, an eco-friendly fluorometric and electrochemical sensing of TA was developed based on a dysprosium(III)-metal-organic framework (Dy(III)-MOF). An aqueous dispersion of Dy(III)-MOF exhibits strong dual emissions at 479 and 572 nm with an excitation at 272 nm, due to the 4f-4f electronic transition and "antenna effect". Chromophore site of the functional ligand, and Dy(III) ion could potentially serve as a sensing probe for TA via quenching (fluorescence). The fluorometric sensor worked well in a wide linear range concentrations from 0.02 to 25 μM with a limit of detection (LOD) of 0.0053 μM. Secondly, the cyclic voltammetric of TA at Dy(III)-MOF modified screen-printed carbon electrode (SPCE) has been investigated. The Dy(III)-MOF/SPCE showed an anodic peak signal at +0.22 V with a five-fold stronger current than the control electrode surface. Under optimized sensing parameters, the Dy(III)-MOF/SPCE delivered wide linear concentrations from 0.01 to 200 μM with a LOD of 0.0023 μM (S/N = 3). Accessibility of real practical samples in alcoholic and juice-based beverages were quantified, resulting in superior recovery rates (98.13-99.53%), F-test, and t-test confirmed high reliability (<95% confidence level (n = 3)). Finally, practicability result of the electrochemical method was validated by fluorometric with a relative standard deviation (RSD) of 0.18-0.46 ± 0.17% (n = 3). The designed probe has proven to be a key candidate for the accurate analysis of TA in beverage samples to ensure food quality.

High-loading Cu single-atom nanozymes supported by carbon nitride with peroxidase-like activity for the colorimetric detection of tannic acid

The design of nanozymes with high metal atom loading is of great significance to improve enzyme activity and is also the key to furthering the construction of highly sensitive colorimetric sensors. In this work, a colorimetric sensor for the quantitative analysis of tannic acid (TA) was developed based on two-dimensional carbon nanosheet carbon nitride (CN)-supported Cu single-atom nanozymes (Cu/CN). Cu/CN was synthesized by supramolecular preorganization and calcination, with an ultrathin nanosheet structure and a high density of Cu active sites, with a Cu loading of up to 14.3 wt%. Benefiting from the above characteristics, Cu/CN exhibits peroxidase-mimicking activity and excellent catalytic performance. Therefore, a colorimetric sensor was constructed for the fast and sensitive quantitative analysis of TA with good linearity in the range of 0.09-3.2 μM and a low detection limit of 30 nM. Furthermore, the sensor was successfully applied to the analysis of TA in tea samples of different varieties. This work sheds new light on the design of nanozymes with a high density of active sites and the analysis of TA in real environments.

A Review on Carbon Dots: Synthesis, Characterization and Its Application in Optical Sensor for Environmental Monitoring

The development of carbon dots (CDs), either using green or chemical precursors, has inevitably led to their wide range application, from bioimaging to optoelectronic devices. The reported precursors and properties of these CDs have opened new opportunities for the future development of high-quality CDs and applications. Green precursors were classified into fruits, vegetables, flowers, leaves, seeds, stem, crop residues, fungi/bacteria species, and waste products, while the chemical precursors were classified into acid reagents and non-acid reagents. This paper quickly reviews ten years of the synthesis of CDs using green and chemical precursors. The application of CDs as sensing materials in optical sensor techniques for environmental monitoring, including the detection of heavy metal ions, phenol, pesticides, and nitroaromatic explosives, was also discussed in this review. This profound review will offer knowledge for the upcoming community of researchers interested in synthesizing high-quality CDs for various applications.

Fabrication of fluorescence sensor based on molecularly imprinted polymer on amine-modified carbon quantum dots for fast and highly sensitive and selective detection of tannic acid in food samples

Developing a rapid and accurate method for tannic acid (TA) detection and measurement is necessary due to its extensive applications in the food industry. In this work, a fluorescence sensor with a low limit of detection was synthesized for TA for the first time. First, amine-modified carbon quantum dots (a-CQDs) with high-quantum yield were synthesized by the hydrothermal method. A layer of molecularly imprinted polymer (MIP) was then placed on a-CQDs by the surface printing method to increase the sensor selectivity. The mechanism of TA detection by the prepared a-CQDs/MIPs was quenching the fluorescence intensity of a-CQDs in the presence of TA due to the transfer of electrons from the TA to the a-CQDs. The linear range of the sensor response was at the TA concentration of 1-200 nmol L^-1 and its detection limit was 0.6 nmol L^-1 under optimal conditions. Finally, the sensor was used to measure TA in grape juice, green tea, and black tea samples using the recovery method. Recovery values between 97.4 and 103.6% and RSDs less than 3.8% indicated the high potential of the prepared sensor for TA analysis in complex food samples.

Photochromism and photomagnetism in three cyano-bridged 3d-4f heterobimetallic viologen frameworks

The incorporation of photochromic moieties into coordination polymers is of particular interest because it can endow them with various switching functions such as electrical conductivity, luminescence, and magnetism. In this context, a viologen ligand as a photochromic moiety was incorporated into 3d-4f heterobimetallic hexacyanoferrates, resulting in three novel 3-D photochromic complexes with different metal cations, namely {[Ln(BCEbpy) M(CN)₆ (H₂O)₄]·2H₂O}_n (denoted as CoDy, CoEu, and FeDy, Ln = Dy, Eu; M = Fe, Co, H₂BCEbpy·2Br = N,N'-bis(carboxymethyl)-4,4'-bipyridinium dibromide). And the photoresponsive mechanism has been well discussed based on the solid UV-vis, IR, ESR, photoluminescence, and magnetism data. Moreover, accompanying the photochromic process, these unique complexes exhibit different photomagnetic behaviors upon UV-vis irradiation at RT because of the different ferromagnetic coupling interactions between photogenerated radicals and lanthanide cations.