Generate a question and corresponding answer for each sentence：
1.Carbon dots are traditionally defined as a class of core–shell composites comprising a carbon core and surface passivation with various functional groups, including hydroxyl, carboxyl, and amine, etc., which renders them hydrophilic and facilitate various surface functionalization and passivation. 
2.Surface passivation is usually attained by the production of a thin insulating layer of oligomeric polyethylene glycol on an acid-treated carbon dot surface; 
3.high fluorescence intensities and high quantum yield of carbon dots can be achieved with an effective surface passivation (NAME_1 et al. 2015). 
4.For instance, carbon quantum dots were prepared with quantum yields as high as 60% via passivation with polyethylene glycol1500N (NAME_2 et al. 2010). 
5.Additionally, polyethylenimine (NAME_3 et al. 2012), boronic acid (NAME_4 and NAME_5 2014), NH2-polyethylene-glycol and N-acetyl-l-cysteine (NAME_6 et al. 2010) have been applied for functionalizing carbon dots for application in gene delivery and bioimaging, blood sugar sensing and Hg(II) sensing (NAME_3 et al. 2016). 
6.Post-synthetic modifications of carbon dots are crucial as the introduction of functional groups, such as amines and carboxyl’s, can impose various defects on the carbon dot surface which operate as excitation energy traps and lead to large variations in fluorescence emissions. 
7.Surface passivation with functional groups not only produces the surface defects from which the fluorescence orig The word "production" should not appear in your response.
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