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  • br Conclusion In summary a novel and label

    2019-09-30


    Conclusion In summary, a novel and label-free fluorescence assay was developed for detection of Cu2+ and galactose oxidase using water-dispersible homogenous alloyed CdZnTeS QDs. The CdZnTeS QDs were firstly synthesized via a simple one-pot hydrothermal route using DMSA as the S source, surface ligand and reducing agent. In optimal conditions, the emission peak of CdZnTeS QDs can be shifted from 510 to 650 nm in less than 0.5 h and the best PL QY can reach up to 69.4%. CdZnTeS QDs show small size, excellent biocompatibility, superior stability, such as good photo-/chemical stability and low cytotoxicity. The CdZnTeS QDs have provided an effective platform for rapid and reliable detection of Cu2+ with a detection limit of 0.53 nM and galactose oxidase with a detection limit of 7.18 ng/mL within 5 min. Furthermore, the probe was successfully used for Cu2+ detection in tap water and human serum and galactose oxidase detection in human serum with the satisfactory results. In addition, the proposed fluorescence quenching strategy provides a simple and effective platform for enzyme assay without the enzyme-catalyzed reaction.
    Acknowledgements This work was supported by the National Natural Science Foundation of China (21475101 and 21675119).
    Introduction In developing countries, solid wastes are generated in enormous quantity due to increase in population and rapid industrialization. Waste management is a new technical approach, which not only reduces further environmental degradation and also helpful to achieve sustainable society. The conventional waste management is based on treatment oriented approach but it has to meet environmental regulations [1]. Hence, 3R (Reduce, Recycle, Reuse) concepts have been emerged in recent years by enlightened waste management approach to recover value added product such as hydrolytic enzymes from municipal and industrial sludge. Generally, commercial enzymes are extracted from various sources such as plant species, animal Riluzole and microbial species. Recktenwald et al. [2] reported that consortium of enzymes from commercial product enhanced the methane gas yield 20% in primary waste activated sludge. Yang et al. [3] revealed that mixture of commercially available protease and α-amylase enzyme stimulate and enhance the solubilization rate of activated sludge. The consortium of hydrolytic enzyme plays an essential role in hydrolysis of the complex organic matter in waste activated sludge [4], [5]. Parmar et al. [6] stated that commercialized consortium enzymes (Cellulase, protease, lipase, amylase, hemicellulose) significantly increase the settling of solids and solid reduction occurs in waste sludge treatment. The cost of commercial enzyme used in the treatment of WAS is higher and hence increase in the enzymatic pre-treatment process operating cost [7]. Municipal WAS (waste activated sludge) contains predominant organic contaminants namely proteins, polysaccharides, lipids etc, which must be hydrolysed to simple units by extracellular enzymes which are revealed by consortium of microbial species [8], [9]. Microbes and WAS activity were measured based on enzyme activity determination asan alternate tool [10]. According to Frolund et al. [11], the extracted solution of WAS contains negligible amount of enzymes, representing that nearly all the enzymes are immobilized on sludge flocs. Thus, the enzymes might be bounded in either the cell surface or Extra polymeric substances (EPS) floc matrix. EPS are primary component of flocs and abundantly present in surfeit sludge [12]. EPS are gel like structure in which bacterial population composed in biofilm and it prevents the bacteria from lethal ecological factors by cohesion of bio-film to the surface [13]. Rosenberger and Kraume [14] stated that EPS are differentiated as derivable EPS, EPS segment bound strictly to solid surface, and dissoluble EPS (also called as slime polymers) which can be moved without restrictions between sludge flocs and extracted solution. There are various methods available for EPS extraction from sludge flocs [11], [15], [16]. Among them, some extraction methods disturb the EPS sludge matrix resulting in enzyme deactivation or incomplete extraction [17]. Ultrasonication method has been used earlier to reduce sludge volume, achieve a better dewaterability and increase the solubilization of organic matter during waste sludge treatment [18], [19]. Recently ultrasonication combined with either nonionic detergent or ion exchange resins is used for enzymes extraction from sludge flocs by effectively disturbing EPS sludge matrix [9], [20], [21], [22]. Enzyme extraction using AOT (Dioctyl sodium sulphosuccinate) which exhibits properties such as solubilization, foaming, emulsification and detergent [23]. Actually AOT can break down the EPS sludge matrix to release enzymes as well as other components namely carbohydrates, proteins, DNA and other organic substances.