Waste to value transformation: Converting Carica papaya seeds into green fluorescent carbon dots for simultaneous selective detection and degradation of tetracycline hydrochloride in water
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Abstract
<p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="first" id="d1056541e117">Rampant
use of antibiotics has resulted in their seepage into groundwater and ultimately
ending up in the food chain, causing antimicrobial resistance. To address this issue,
it is imperative to not only quantitatively detect but eliminate them from water.
An eco-friendly, one-step microwave-induced pyrolysis of waste papaya seeds (PS) with
ethylenediamine (EDA) for just 5min gave green fluorescent nitrogen-doped carbon dots
(PS-CDs), which are capable of detecting and photocatalytically degrading TC. The
fluorescence properties of PS-CDs displayed that it has high sensitivity and selectivity
towards sensing of TC with a detection limit as low as 120 nM. Also, the method gave
satisfactory recovery results when extrapolated to determine TC in spiked milk, orange
juice, tap water, and honey samples. On the other hand, PS-CDs alone potentially function
as an efficient photocatalyst for the degradation of TC. PS-CDs' dual functionality
provides an effectual method for the simultaneous detection and degradation of TC
by a single nanoprobe.
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Tetracyclines were discovered in the 1940s and exhibited activity against a wide range of microorganisms including gram-positive and gram-negative bacteria, chlamydiae, mycoplasmas, rickettsiae, and protozoan parasites. They are inexpensive antibiotics, which have been used extensively in the prophlylaxis and therapy of human and animal infections and also at subtherapeutic levels in animal feed as growth promoters. The first tetracycline-resistant bacterium, Shigella dysenteriae, was isolated in 1953. Tetracycline resistance now occurs in an increasing number of pathogenic, opportunistic, and commensal bacteria. The presence of tetracycline-resistant pathogens limits the use of these agents in treatment of disease. Tetracycline resistance is often due to the acquisition of new genes, which code for energy-dependent efflux of tetracyclines or for a protein that protects bacterial ribosomes from the action of tetracyclines. Many of these genes are associated with mobile plasmids or transposons and can be distinguished from each other using molecular methods including DNA-DNA hybridization with oligonucleotide probes and DNA sequencing. A limited number of bacteria acquire resistance by mutations, which alter the permeability of the outer membrane porins and/or lipopolysaccharides in the outer membrane, change the regulation of innate efflux systems, or alter the 16S rRNA. New tetracycline derivatives are being examined, although their role in treatment is not clear. Changing the use of tetracyclines in human and animal health as well as in food production is needed if we are to continue to use this class of broad-spectrum antimicrobials through the present century.
Carbon dots (CDs), as a new type of carbon-based nanomaterial, have attracted broad research interest for years, because of their diverse physicochemical properties and favorable attributes like good biocompatibility, unique optical properties, low cost, ecofriendliness, abundant functional groups (e.g., amino, hydroxyl, carboxyl), high stability, and electron mobility. In this Outlook, we comprehensively summarize the classification of CDs based on the analysis of their formation mechanism, micro-/nanostructure and property features, and describe their synthetic methods and optical properties including strong absorption, photoluminescence, and phosphorescence. Furthermore, the recent significant advances in diverse applications, including optical (sensor, anticounterfeiting), energy (light-emitting diodes, catalysis, photovoltaics, supercapacitors), and promising biomedicine, are systematically highlighted. Finally, we envisage the key issues to be challenged, future research directions, and perspectives to show a full picture of CDs-based materials.
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