Determination of l-theanine in tea water using fluorescence-visualized paper-based sensors based on CdTe quantum dots/corn carbon dots and nano-porphyrin with chemometrics

Fluorescent-based nanosensors for selective detection of a wide range of biological macromolecules: A comprehensive review

Thanks to their unique attributes, such as good sensitivity, selectivity, high surface-to-volume ratio, and versatile optical and electronic properties, fluorescent-based bioprobes have been used to create highly sensitive nanobiosensors to detect various biological and chemical agents. These sensors are superior to other analytical instrumentation techniques like gas chromatography, high-performance liquid chromatography, and capillary electrophoresis for being biodegradable, eco-friendly, and more economical, operational, and cost-effective. Moreover, several reports have also highlighted their application in the early detection of biomarkers associated with drug-induced organ damage such as liver, kidney, or lungs. In the present work, we comprehensively overviewed the electrochemical sensors that employ nanomaterials (nanoparticles/colloids or quantum dots, carbon dots, or nanoscaled metal-organic frameworks, etc.) to detect a variety of biological macromolecules based on fluorescent emission spectra. In addition, the most important mechanisms and methods to sense amino acids, protein, peptides, enzymes, carbohydrates, neurotransmitters, nucleic acids, vitamins, ions, metals, and electrolytes, blood gases, drugs (i.e., anti-inflammatory agents and antibiotics), toxins, alkaloids, antioxidants, cancer biomarkers, urinary metabolites (i.e., urea, uric acid, and creatinine), and pathogenic microorganisms were outlined and compared in terms of their selectivity and sensitivity. Altogether, the small dimensions and capability of these nanosensors for sensitive, label-free, real-time sensing of chemical, biological, and pharmaceutical agents could be used in array-based screening and in-vitro or in-vivo diagnostics. Although fluorescent nanoprobes are widely applied in determining biological macromolecules, unfortunately, they present many challenges and limitations. Efforts must be made to minimize such limitations in utilizing such nanobiosensors with an emphasis on their commercial developments. We believe that the current review can foster the wider incorporation of nanomedicine and will be of particular interest to researchers working on fluorescence technology, material chemistry, coordination polymers, and related research areas.

Foliar application of glycinebetaine and Zn fertilizer improves both the apparent and functional qualities of albino tea [Camellia sinensis (L.) O. Kuntze]

With Zn deficiency increasing in the global population, functional plant food (including tea) can help to fill the nutrition gap that the main crops cannot meet. Glycinebetaine (GB), an important bioactive substance with a wide range of natural sources, has received limited attention towards its effects on Zn biofortification and the quality of tea. The Zn enrichment and metabolite responses of albino tea [cv. White leaf No. 1 (WL-1)] to the foliar application of GB, Zn, and their combination (Zn + GB) were investigated in a field experiment. The result indicated that the 100-buds weight, total N, Zn, Thea, and total amino acid content in the young leaves of WL-1 with Zn2 + GB2 treatment were significantly increased, whereas the Chla contents were decreased (p < 0.05). The total catechins and CAF contents of Zn2 + GB2 treatment were lower than those of other treatments, with significance (p < 0.05). Multivariate analysis and general quantitative analysis returned complementary results, revealing that Zn2 + GB2 treatment was better for the apparent and functional quality of WL-1. The more theanine and Zn, limited chlorophyll, catechin, and caffeine contributed to the quality improvement, as well as to maintaining the leaf albinistic characteristics, inhibiting astringency and bitterness, exerting flavor and umami, and improving the ultimate beneficial functions. The combined application of Zn and GB is a promising practice for Zn biofortification and for the quality improvement of tea, with spraying 750 L ha^-1 of 2.0 g L^-1 Zn fertilizer and 3.2 g L^-1 GB mixture recommended.

Paper-based electrochemiluminescence device for the rapid estimation of trimethylamine in fish via the quenching effect of thioglycolic acid-capped cadmium selenide quantum dots

A paper-based electrochemiluminescence device (µPAD-ECL) for the estimation of trimethylamine (TMA) concentration in fish was developed using tris(2,2'-bipyridyl)ruthenium(II) complex coupled with water soluble thioglycolic acid-capped CdSe quantum dots on the inkjet-printed paper-based device. The quenching effect of tertiary amines on the ECL intensity was found to be sensitive and concentration dependent. This effect allows the measurement of TMA at low concentrations. Under the optimal conditions, the linear concentration range was exhibited from 1 × 10^-12 to 1 × 10^-7 M and a detection limit of 2.09 × 10^-13 M, with relative standard deviation of 1.97 %. The applicability of µPAD-ECL is demonstrated by the rapid estimation of trimethylamine concentration in fish tissue, and could be used as a method for screening the total amount of tertiary amines in fishery products in remote communities. The results obtained using the paper-based devices agreed well with those obtained applying high performance liquid chromatography with benzoyl derivatization, at a confidence level of 95%.

Visual paper-based sensor for the highly sensitive detection of caffeine in food and biological matrix based on CdTe-nano ZnTPyP combined with chemometrics

Caffeine naturally occurs in tea and cocoa, which is also used as an additive in beverages and has pharmacological effects such as refreshing, antidepressant, and digestion promotion, but excessive caffeine can cause harm to the human body. In this work, based on the specific response between nano zinc 5, 10, 15, 20-tetra(4-pyridyl)-21H-23H-porphine (nano ZnTPyP)-CdTe quantum dots (QDs) and caffeine, combined with chemometrics, a visual paper-based sensor was constructed for rapid and on-site detection of caffeine. The fluorescence of QDs can be quenched by nano ZnTPyP. When caffeine is added to the system, it can pull nano ZnTPyP off the surface of the QDs to achieve fluorescence recovery through electrostatic attraction and nitrogen/zinc coordination. The detection range is 5 × 10^-11~3 × 10^-9 mol L^-1, and the detection limit is 1.53 × 10^-11 mol L^-1 (R² = 0.9990) (S/N = 3). The paper-based sensor constructed exhibits good results in real samples, such as tea water, cell culture fluid, newborn bovine serum, and human plasma. Therefore, the sensor is expected to be applied to the rapid instrument-free detection of caffeine in food and biological samples.Graphical abstract.