To synthesize of QDs using chemical

To synthesize of QDs using chemical, physical and biological rotes several methods have been reported. Each method has advantages and disadvantages regarding things such as cost, scalability, size distribution, photoluminescence, quantum yield etc. which are very common. Therefore, researchers focused towards the formulation of such a method which eliminates not all but most of these disadvantages for the efficient synthesis of quantum dots as they have potential applications in many fields. QDs are generally synthesized by different chemical and physical methods but most of these methods are complex, hazardous, expensive and time consuming. The biological synthesis is the alternative way to overcome these problems due to its eco-friendliness and it also has tremendous potential to generate different size and shape of QDs. Fig. Different methods for synthesis of QDs There are mainly two approaches for QDs synthesis which can be classified according to their assembly. Top-down approach In top-down approach a nanoscale objects creates using bulk material (Tolaymat et al., 2010). Top-down is a process that starts from a large pieces and subsequently uses finer and finer tools for creating correspondingly smaller structures. In top down approach, the electron beam lithography, reactive-ion etching, wet chemical etching methods used. The main disadvantages of this process are the structural imperfections by patterning and addition of impurities into the QDs. Bottom-up approach in bottom-up approach smaller components of atomic or molecular dimensions self-assemble together, according to a natural physical principle or an externally applied driving force, to give rise to a larger and more organized system (Swihart, 2003). In bottom up approach a number of different self-assembly techniques (bottom-up) have been used to synthesize the QDs, which are subdivided into wet-chemical and vapor-phase methods. Hot-solution decomposition, microemulsion, competitive reaction chemistry, solgel, sonic waves or microwaves, electrochemistry are types of wet-chemical methods. Self-assembly of nanostructures in material grown by sputtering, liquid metal ion sources, aggregation of gaseous monomers, molecular beam epitaxy (MBE) are vapor-phase methods. Chemical method For the synthesis of QDs many chemical methods have been used such as precipitation chemical reduction, microemulsion (colloidal), electrochemical, microwave-assisted and hydrothermal, sovothermal and sol-gel method. In generation of QDs, the redox reaction mainly involved for the colloidal dispersion in organic solvent and water. In chemical methods the characteristics of QDs are mainly depending upon temperature as such there is no distinct boundary among the different chemical methods. To enhance the rate of reaction the higher temperature is required. The reducing agents such as sodium citrate, N, N- dimethylformamide, polyols and other reducing agents are mainly involve in chemical reactions and to avoid the formation of agglomeration in the reaction the capping or stabilizing agents such as polyvinyl pyrolidine, sodium dodecyl sulphate (SDS) are used. The major limitation of chemical methods is during the synthesis of QDs the utilization of toxic chemicals, heavy metals is used therefore it cannot be use for the medical applications. Arul et al., 2011 discloses preparation of uniform and well-dispersed cerium dioxide quantum dots via precipitation method by dissolving cerium ammonium nitrate at 80C water bath with a vigorous stirring. The pH of the solution was increased to 11 by adding ammonia to obtain cerium hydroxide precipitates. The resultant powder was dried at 90C for an overnight and further calcinated at 600C to yield precipitate that can be dispersed in hexane to obtain transparent colloidal solution (Arul et al., 2011). Prabhash and Nair in 2016 used the chemical reduction method for synthesis of copper quantum dots (CuQDs) and tailoring of its band gap. In the reaction chlorides added as precursors and CTAB (cetyltrimethylammonium bromide) citric acid added as surfactant. CuQDs with size 3 – 10 nm were observed under HRTEM. The CuQDs coated with citric acid showed the energy band gap shift from 3.67 eV to 4.27 eV. And the CuQDs coated with CTAB showed the energy band gap shift from4.17 eV to 4.52 eV (Prabhash and Nair, 2016). Physical method For the synthesis of QDs many work have been done by physical method. Physical method involves lithography, ball milling method molecular beam epitaxy (MBE), laser ablation, ultrasonication, radiolysis, vaporization etc. The physical approach of synthesis possess many advantage with respect to the chemical synthesis as the solvent contamination is not observed in the films produced, in addition to this, the films shows uniform distribution of nanoparticles throughout the nanofilm. The cost of instrument and larger space and high energy requirement for set-up of all the experimental conditions are the major limitations of these methods. The main disadvantages of these methods are the production of defection formation, even damage to the bulk of the crystal itself, poor interface quality, size nonuniformity. Bertino and colleagues in 2007 used ultraviolet and x-ray lithography method for the synthesis of highly luminescent semiconductor quantum dots. The aqueous solution of a group II metal ion with either of 2-mercaptoethanol, thioacetamide or selenourea chalcogenide precursor was replaced with the pore-filling silica hydrogel solvent. In exposed region the chalcogenide precursor was photodissociated and chalcogenide nanoparticles were formed. The appropriate type of radiation was used to obtain the patterns. In the precursor solution the thioglycerol and citrate capping agents were added o controlled the mean size of QDs. Due to the photoactivation 30 of QY increased. This technique wont be used for large scale production as 50 polydispersity was observed (Bertino et al., 2007). In 1997 Tsuzuki and HYPERLINK https//www.researchgate.net/profile/Paul_Mccormick3 Mccormick used mechanochemical reaction for the synthesis of CdS quantum dots (CdS QDs). 0957-4484/18/31/315603UV-VIS absorption spectroscopy, transmission electron microscopy, X-ray diffraction techniques were used for characterization of synthesized QDs. The 8 nm CdS QDs were formed due to the solid-state displacement reaction CdCl2 Na2S -( CdS 2NaCl induced by mechanical milling. The grinding media size was changed to maintain the particle size below 8 nm. By decreasing the size of CdS QDs the blue shift was also observed (Tsuzuki and HYPERLINK https//www.researchgate.net/profile/Paul_Mccormick3 Mccormick, 1997). . Biological method To synthesize the QDs various chemical, physical and biological methods have been used. Although, physical and chemical methods are more popular in the synthesis of QDs, the use of toxic chemicals greatly limits their process of synthesis and biomedical applications (Pantidos and Horsfall, 2014). However, all together these methods are energy and capital intensive and later on these processes needs synthetic additives or capping agents. Therefore, researcher turns towards the biological route for the QDs synthesis (Faghri and Slouti, 2011). In last few decades the huge developments is observed in the field of green chemistry and scientists too are opting for the greener option for the synthesis of QDs. The biological methods overdue all the disadvantages of chemical methods and provide an alternative for the same. Using natural reducing, capping and stabilizing agents the desired characteristics of the QDs can be achieved. In literature there are many reports for the synthesis of QDs using organisms (Microorganisms and biological systems such as plants) which can deploy the use of enzyme and other natural precursors for the bioreduction and formation of QDs. The biological synthesis of QDs offers numerous benefits of ecofriendliness and compatibility for pharmaceutical and other biological applications as they do not use toxic chemicals for the synthesis protocol. Microorganisms for the synthesis of QDs Biogenic methods for synthesis of QDs employing either biological microorganisms or plant extracts have emerged as a simple and viable alternative to physical methods and chemical methods. Microorganisms such as bacteria, yeast and fungi play an important role in remediation of toxic metals through reduction of the metal ions, these were considered as interesting nanofactories (Slocik et al., 2004 Krumov et al., 2009). Bacteria play a crucial role in a metal biochemical cycling and mineral formation in surface and subsurface environments. In presence of high concentration and even toxic metal ions, bacteria harbor numerous detoxifications (Gadd, 2009). Few reports are available on the use of microorganisms for the synthesis of QDs. HYPERLINK https//www.ncbi.nlm.nih.gov/pubmed/termHolmes20JD5BAuthor5Dcauthortruecauthor_uid9274006 Holmes JD and colleagues in 1997 used Klebsiella pneumonia and biotransformed the cadmium ions into photoactive, a-sized CdS particles. In batch culture the particle kinetics formation was observed by electronic absorption spectroscopy (EAS), electron microscopy (EM), energy-dispersive X-ray analysis. On outer cell of Klebsiella pneumonia approximately 5 nm in diameter of CdS particles were observed by electron microscopy and these particles were increased in stationary phase to 200 nm size. The synthesized CdS particles were found 3-4 of total cell biomass. The smaller 4 nm Q-particles were aggregated to form 200nm particles. In the presence of zinc, lead silver, mercury and copper ions the metal sulfide particles were not formed in K. pneumoniae batch cultures. 48.6 cadmium and 0.04 zinc particles were formed when zinc and cadmium ions were added to the growth medium. Similarly, Only CdS particles were formed when lead and cadmium ions present during growth. The mechanism revealed that CdS formation was not based on only cadmium induced release of hydrogen sulfide (Holmes et al., 1997). In 2002, HYPERLINK https//pubs.acs.org/author/Ahmad2CAbsar Absar Ahmad reported synthesis of Q-state CdS nanoparticles using fungus, Fusarium oxysporum and aqueous CdSO4 solution. The sulfate reductase enzymes of Fusarium oxysporum converted the sulfate ions to sulfide ions which reacted with aqueous Cd2 ions to form CdS nanoparticles. The enzymatic pathway of fungi developed a rational biosynthesis strategy for synthesis of nanoparticles (Ahmad et al., 2002). HYPERLINK https//www.ncbi.nlm.nih.gov/pubmed/termKowshik20M5BAuthor5Dcauthortruecauthor_uid12115128 Kowshik M 2002 reported the intracellular synthesis of CdS nanoparticles by reaction carried out of Schizosaccharomyces pombe with 1 mM cadmium in solution. The absorbance peak appeared at 305 nm. The size of the synthesized CdS nanoparticles were found to be 1-1.5 nm with Wurtzite (Cd(16)S(20))-type hexagonal lattice structure. When the synthesized CdS heterojunction with poly (p-phenylenevinylene) was considered as ideal diode as it exhibited 75 mA/cm(2) current at 10 V when forward biased and approximately 15 V in the reverse biased mode (Kowshik et al., 2002). Sweeney and colleagues in 2004 reported the intracellular synthesis of cadmium sulfide (CdS) nanocrystals in E. coli. The E. coli was incubated with sodium sulfide and cadmium chloride. The 2-5 nm a wurtzite crystal were formed. They also highlighted different physiological and genetic parameters which enhanced the formation of cadmium sulfide (CdS) in E. coli cells. In logarithmic phase of E. coli the CdS nanocrystal biosynthesis increased about 20-fold compared to late logarithmic phase (Sweeney et al., 2004). Shuhong et at., 2005 used marine diatoms, Nitzschia frustulum for synthesis of silicon oxide / germanium oxide nanocomposite. By two-stage cultivation process the germanium was incorporated into living diatom cell mass. XRD and TEM with EDS techniques were used for characterization of synthesized nanocomposite. After addition of germanium to biogenic oxide,a clear blueshift was observed. The photoluminescence observed due to self-trapped exciton affected by quantum confinement effect in this nanocomposite (Shuhong et at., 2005). Bai et al, in 2006 synthesized zinc sulfide (ZnS) nanoparticles by immobilized Rhodobacter sphaeroides. The UV-vis optical absorption and photoluminescence spectra, transmission electron microscopy, energy dispersive analyses of X-rays, X-ray diffraction techniques were used for analysis of synthesized ZnS nanoparticles. The average 8 nm size ZnS nanoparticles were observed but also reported that at different culture time the the ZnS diameter varied (Bai et al., in 2006) Kumar et al., 2007 reported the synthesis of CdSe quantum dots using the fungus, Fusarium oxysporum. The Fusarium oxysporum was incubated with SeCl4 and CdCl2 at room temperature (Kumar et al., 2007). Prasad and Jha in 2010 reported Lactobacillus sp. and Sachharomyces cerevisiae mediated low cost green synthesis of CdS nanoparticles. The synthesis was carried out at room temperature. UV-vis spectroscopy, transmission electron microscopy, XRD was used for characterization of QDs. In UV-vis spectroscopy analysis the peaks were observed at 369nm and 393 respectively for yeast and Lactobacillus assisted synthesis of CdS nanoparticles. The optical band gap was estimated from absorbance spectra. The size of synthesized CdS nanoparticles was found to be 2.5-5.5nm (Prasad and Jha, 2010). HYPERLINK https//www.ncbi.nlm.nih.gov/pubmed/termBao20H5BAuthor5Dcauthortruecauthor_uid20350621 Bao H in 2010 reported the Escherichia coli based synthesis of cadmium telluride (CdTe) quantum dots (QDs). The size-tunable optical properties of the synthesized cadmium telluride (CdTe) quantum dots (QDs) were confirmed X-ray diffraction and transmission electron microscopy Ultraviolet-visible, photoluminescence spectroscopy. The synthesized CdTe QDs showed good crystallinity and fluorescence emission from 488 to 551 nm. The Fourier transform infrared spectroscopy, zeta potential and hydrodynamic size analysis confirmed a surface protein capping layer. 2 M CdTeQDs the 92.9 viability of cells was observed in an environment. The bacterial morphology, growth and CdTe QDs in Luria-Bertani medium containing E. coli-secreted proteins were analysed it was observed that extracellular synthesis was directly relied on the E. coli-secreted proteins. The mechanism of protein-assisted biosynthesis of QDs was also proposed (Bao et al., 2010). In 2010, Bao H used yeast cells for synthesis of biocompatible cadmium telluride (CdTe) quantum dots (QDs). The synthesis of CdTeQDs was confirmed by Ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL) spectroscopy. The fluorescence emission was observed from 490 to 560 nm. The XRD analysis confirmed the cubic zinc blende structure with good crystallinity. The synthesized (2-3.6 nm) CdTe QDs were capped by protein hence found water soluble and biocompatible (Bao et al., 2010). The CdS nanoparticles were synthesized using Brevibacterium casei SRKP2. Electron microscopy and XRD were used to characterization of synthesized CdS nanoparticles. The 10-30nm size CdS nanoparticles were observed. The synthesis was monitored at different parameters i.e. growth of the organism, concentration of CdCl(2) and Na(2)S, time and pH. The highest emission was observed at pH 9. The synthesized CdS nanoparticles were immobilized with polyhydroxybutyrate (PHB) and it was found that the fluorescence emission was not affected (Pandian et al., 2011). Mi C in 2011 synthesized CdS quantum dots (CdSQDs) in genetically engineered Escherichia coli (E. coli). The foreign genes encoding a CdS binding peptide was incorporated in Escherichia coli (E. coli).The synthesized were separated by freezing-thawing and lysis of cells and purification was done using anion-exchange resin. The synthesized CdSQDs were characterized by X-ray spectroscopy, X-ray diffraction, High-resolution transmission electron microscopy, luminescence spectroscopy. The synthesis of CdSQDs was observed at different parameters such as bacteria incubation time, reaction times on QD growth, effects of reactant concentrations (Mi et al., 2011). HYPERLINK https//www.ncbi.nlm.nih.gov/pubmed/termSyed20A5BAuthor5Dcauthortruecauthor_uid23357677 Syed A in 2013 used fungus Fusarium oxysporum for synthesis of highly fluorescent CdTe quantum dots. The Fusarium oxysporum was incubated with a mixture of TeCl4 and CdCl2 at ambient conditions. Ultraviolet-visible (UV-Vis) spectroscopy, Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Fourier Transformed Infrared Spectroscopy (FTIR) analysis, Photoluminescence (PL) and X-ray Photoelectron spectroscopy (XPS) techniques were used for characterization of synthesized CdTe quantum dots. The synthesized CdTe quantum dots were showed the antibacterial activity against Gram positive and Gram negative bacteria (Syed et al., 2013). In 2013, Malarkodi C reported Serratia nematodiphila reduced the cadmium sulphate solution and synthesized cadmium sulfide nanoparticles (CdSNPs). In UV-Vis spectrophotometer analysis, the absorption peak was appeared at 420nm. In SEM and EDX analysis it was observed that the average size of CdS nanoparticles was 12nm and morphology was spherical. In colloidal solution the CdS nanoparticles were controlled and reduced by protein containing amine group. The synthesized CdS nanoparticles exhibited good bactericidal activity against Klebsiella planticola and Bacillus subtilis (Malarkodi et al., 2013). It was reported that Escherichia coli cells were used for the synthesis of cadmium selenide quantum dots (CdSeQDs). The process was optimized at different parameters such as Escherichia coli cells growth, concentration of inorganic reactants, co-incubation duration of reaction. The optical properties of synthesized CdSeQDs were analysed by inverted fluorescence microscope, Ultraviolet-visible and photoluminescence spectroscopy. The TEM was used to find out size distribution of the nanocrystals extracted from cells and in vivo the location of nanocrystals foci. The FTIR analysis confirmed the protein capping layer around the CdSeQDs which reduces the cytotoxicity (Yan et al., 2014). In 2015, Mariya Borovava developed an easily reproducible, efficient and eco-friendly method for the synthesis of cadmium sulphide quantum dots using HYPERLINK mailtoMariya Borovaya developed a easily reproducible, efficient and eco-friendly method or the synthesis of cadmium sulphide quantum dots using Pleurotus ostreatus (Jacq.) P. Kumm. Department of Genomics and Molecular Biotechnology, Institute of Food Biotechnology and Genomics, National Academy of Sciences of Ukraine, Kyiv, [email protected] View further author information mycelium of the basidiomycete fungus Pleurotus ostreatus. The stable luminescent CdS nanocrystals were synthesized by incubating P. ostreatus mycelium with inorganic sodium sulphide and cadmium sulphate. Spherical shaped 4 to 5nm in size CdS QDs were observed in TEM analysis. The wurtzite crystalline structure was confirmed by electron diffraction pattern. The UV-Vis spectrometry absorption peak observed at 453 nm and emission peak was appeared at 462 nm (Borovaya et al., 2015). View further author information The future economy in biomanufacturing can be achieved by natures unique ability of scalable manufacturing and cost effective solution with reduced impact on environment. To extrinsic control on crystallite size in the quantum confinement range during biosynthesis of CdS nanocrystals the Stenotrophomonas maltophilia and E.coli bacterial strain was engineered. At ambient pressure and temperatures the engineered Stenotrophomonas maltophilia and E.coli yields water-soluble, extracellular quantum dots. The synthesized CdSQDs had size-dependent band gap and photoluminescent properties (Yang et al., 2015). The cadmium and tellurite resistant Antarctic bacteria were isolated and characterized. These cadmium and tellurite resistant Antarctic bacteria were exposed to oxidizing heavy metals for the synthesis of CdS and CdTe QDs. Cells grown at different metal concentration and temperature and observed the difference in biosynthesis. In periplasmic space of cells the nanometric electron-dense elements and structures were observed. At different time the fluorescence emission from green to red were observed. Electron microscopy analysis of treated cells revealed nanometric electron-dense elements and structures resembling membrane vesicles mostly associated to periplasmic space (Plaza et al., 2016). Munusamy et al. 2016 synthesized CeO2 nanoparticles (CeO2 NPs) using fungus Curvularia lanata and investigate to antibacterial activity. UV-visible spectroscopy, TEM, PL, FTIR, Raman spectroscopy, XRD, TG/DTA tools were used for analysis of synthesized CeO2 NPs. The absorption peak was appeared at 298.35 nm in UV-visible spectrum and 5 to 20nm spherical shaped CeO2 NPs were observed in TEM analysis. The cubic structure was confirmed by XRD, A clear zone of inhibition was observed against gram negative and gram positive bacteria in antibacterial analysis (Munusamy et al. 2016). Plant for the synthesis of QDs The synthesis of QDs using plant shows high potential as compared to microorganisms. The plant contains a tremendous variety of biomolecules which can acts as a reducing and capping agent during synthesis of quantum dots and hence the rate of reduction and stabilization increases (Kavitha et al., 2013). Plants provide a biological synthesis route of several QDs which is more eco-friendly and allows a controlled synthesis with well-defined characteristics. Some specific plant parts such as leaves, roots, fruits, latex, seeds or whole plants are used for the synthesis of QDs. The plants are easily available and safe to handle Are the main advantages of phytosynthesized QDs and have potential use in biomedical applications. In literature few reports are available on plant based synthesis of QDs. The current expansion and execution of new technologies have led to the beginning of new era, the non-rebellion which unfolds role of plants in green synthesis of nanoparticles which seem to have drawn quite an unarguable attention with a view of synthesizing stable nanoparticles. It is advantageous to employ the plants towards synthesis of nanoparticles as compared to microbes with the presence of extensive variability of biomolecules in plants such as alkaloids, terpenoids, phenol, flavonoids, tannins, quinines etc. can act as capping and reducing agent and thus, increases the rate of reduction and stabilization of nanoparticles (Kavitha et al., 2013). The main mechanism considered for the process is plant assisted reduction due to phytochemicals. Again the plants are easily available and safe to handle, therefore phytosynthesized nanoparticles have the great biomedical applications. Some specific plant parts, such as leaves, roots, fruits, latex, seeds or whole plants are used for the synthesis of nanoparticles (Singh et al., 2014). HYPERLINK https//www.ncbi.nlm.nih.gov/pubmed/termBorovaya20MN5BAuthor5Dcauthortruecauthor_uid26088983Mariya N Borovaya in 2014 developed efficient and eco-friendly method for synthesis of CdS QDs using hairy root culture of Linaria maroccana L. Linaria root extract incubated with sodium sulfide and inorganic cadmium sulphate. In UV-Vis spectrometry analysis the absorption peaks were observed at 362nm, 398nm and 464nm, and the emission peaks were observed at 425, 462, 500nm. 5 to 7 nm spherical shaped CdS QDs were observed in Transmission electron Microscopy and wurtzite crystalline structure was confirmed by Electron diffraction pattern. In applications of bioscience, medicine and chemical research these CdS QDs have great potential (Borovaya et al., 2014). Mariselvam et al., 201 4 used aqueous root extract of plant Rubia cardifolia for the synthesis of copper quantum dots (CuQDs). UV-Visible spectrophotometer, AFM, SEM, TEM, and fluorescence microscopy techniques used for characterization of synthesized CuQDs. The CuQDs found as 22.68 nm in size and spherical with rough surfaced. It gives green fluorescence under AFM. The synthesized CuQDs showed antibacterial activity against pathogenic bacteria such as Plesiomonas shigelloides, Shigella spp., Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Streptococcus aureus by diameter of inhibition zone measurement and colony forming capability assay (Mariselvam et al., 2014). The plant leaf extract of Neem (Azadirachta indica) and Fenugreek (Trigonella foenum-graecum) used for synthesis of graphene quantum dots (GQDs) by hydrothermal method. The reaction was carried out at 300C for 8 hours in water without passivizing, organic solvent and reducing agent.The size of the GQDs were analyzed using High resolution transmission electron microscope and found that the average size of 5nm for synthesized GQDs from Neem (N-GQDs) and 7 nm for synthesized GQDs from Fenugreek (F-GQDs). The high quantum yield was observed in N-GQDs (41.2) compared to F-GQDs (38.9). GQDs used the red-green-blue (RGB) color mixing method to develop a white light converting cap (Roy et al., 2014). Yue et al 2014 used apple juice as raw material in hydrothermal method for synthesis of fluorescent carbon quantum dots. The fluorescence of CQDs quenched by Hg2 with high specificity based on this phenomena for detection of Hg2 a sensitive sensor was constructed with the detection limit 2.3 Nm(s/n3) (Yue et al., 2014). Du et al in 2015 refluxed the extraction of orange pericarp using hydrothermal method for the synthesis of fluorescent carbon quantum dots (CQDs). To control the particle size and quantum yield the time and temperature was adjusted. By using this green synthesis approach the uniform morphology and size of CQDs were obtained (Du et al., 2015). In 2015, G. Bhuvaneswari used chemical precipitation method with green material for synthesis of cadmium sulphide quantum dots (CdSQDs). The papaya peel extract was used as a capping agent. To study size, morphology, distribution and crystallinity the High Resolution Transmission Electron Microscopy (HRTEM) and X-ray diffraction pattern (XRD) characterization techniques were used. The cubic phase CdSQDs with 2.7 nm average size were obtained. The formation of CdSQDs was confirmed as blue shift was observed in UV-Vis spectroscopy analysis (Bhuvaneswari et al., 2015). In 2015, Kalavakunta et al used a aegle marmelos fruit extract in precipitation method for synthesis of Zinc oxysulfide quantum dots (ZOS QDs). The UV-visible spectroscopy, transmission electron microscopy, X-ray diffraction, photoluminescence spectroscopy, energy dispersive X-ray spectroscopy and vibrating sample magnetometry techniques were used for the characterization of the synthesized ZOS QDs. The band gap decreased to 3.46 eV as 16 oxygen was incorporated in ZnS crystal as observed in EDX analysis. The room temperature ferromagnetism (RTF) was observed in ZOS QDs vibrating sample magnetometer analysis. The ZOS QDs showed the good cell viability with HeLa cells (Kalavakunta et al., 2015). In 2015, Arumugam and colleagues used Gloriosa superba L. leaf extract for the synthesis of In 2017, Singh and colleagues used Eclipta albaleaf extract as aHYPERLINK https//www.sciencedirect.com/topics/materials-science/reducing-agents o Learn more about Reducing agentsreducing agent and zinc acetate as a precursor for the synthesis of zinc oxide quantum dots (ZnO QDs). The optimum condition for synthesis of ZnOQDs was 5mM zinc acetate, 7ml leaf extract, pH 7, 40C temperature and incubated for 75 min. In UV-Vis spectroscopy analysis the peak was appeared at 324 nm. Spherical 6nm size ZnSQDs were observed in HYPERLINK https//www.sciencedirect.com/topics/materials-science/transmission-electron-microscopy o Learn more about Transmission Electron Microscopytransmission electron microscopy (TEM) and its crystalline nature was revealed in selected areaHYPERLINK https//www.sciencedirect.com/topics/materials-science/electron-diffraction o Learn more about Electron Diffractionelectron diffraction(SAED) analysis. The synthesized ZnO QDs were also showed antimicrobial activity against E.colicells (Singh et al., 2017). In 2018 HYPERLINK https//pubs.acs.org/author/Shivaji2CKavithaKavitha Shivaji synthesized 25 nm particle size CdS QDs using Camellia sinensis tea leaf extract. These synthesized CdS QDs explored in different applications e.g. bioimaging, antibacterial activity and apoptosis off lung cancer cells. The fluorescence emission and flow cytometry analysis were carried out to understand the role of CdS QDs in bioimaging and cytotoxicity effect in A549 cells. The concentration-dependent fluorescence emission of CdS QDs recorded at 670 nm at 410 nm excitation wavelength. The growth of lung cancer cells inhibited as the CdS QDs arrested in S phase of A549 cell cycle. The different types of bacterial growth were inhibited by CdS QDs due to its antibacterial activity (Kavitha et al., 2018). tr7Ib)JuLqGv3Jw,JJyho_JyhuiO5Hj1mmrCCAL ZCt)dMb [email protected] 3lfl
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