Quantum Dots Encapsulated with Amphiphilic Polysaccharides as Bacteria Detecting Probes
Date Issued
2010
Date
2010
Author(s)
Hsu, Jui-Fu
Abstract
Quantum dot (QD) has better sensitivity and stability compared with traditional organic dye and fluorescent protein. It has special advantages in science and technology. In the biomedical field, QD has been increasingly used in fluorescent labeling of biological molecules, DNA identification and disease diagnosis. In this study, we first used sodium periodate (NaIO4) to oxidize chitosan for the formation of aldehyde chitosan. Then, alkyl chains were bonded to aldehyde chitosan to form amphiphilic chitosan which has both hydrophobic and hydrophilic features. In addition, alkyl amines were grafted with propylene glycol alginate (PGA) by reacting with propylene glycol groups in the presence of sodium hydroxide. The alkylated PGA also has amphiphilic characteristics. These two amphiphilic polysaccharides could make LumidotTM QDs converted from the organic phase into aqueous phase dispersion by hydrophobic interaction. Our results showed that LumidotTM QDs capped with chitosan conjugated with 1-hexadecylamine revealed much better quantum yield than the ones made by amphiphilic PGA. This is probably due to the merit of positively charged chitosan resulting in robust electrostatic interaction on the surface of LumidotTM QDs. Although aldehyde chitosan has only 14% of aldehyde GlcN grafted with 1-hexadecylamine, yet it is sufficient to encapsulate LumidotTM QDs. This study also attempted to prepare CdSe/ZnS QDs. It was suitable for yellow and longer wavelength fluorescence QDs by reaction time control of the nuclear layer (CdSe). CdSe/ZnS QDs were encapsulated by amphiphilic chitosan dispersed in 0.1 M MES-NaOH buffer. If pH is higher than 6, the dispersion of particles clearly becomes unstable. However, the stability can be maintained if pH is less than 5.3. Since QDs encapsulated with amphiphilic chitosan have positive charges, they can attach to negatively charged bacterial surface by electrostatic attraction, or by EDC coupling to cell membrane’s proteins with carboxyl groups. In this study, QDs were tried to label on E. coli for detecting the amount of bacteria in suspension. Although the experiment did not succeed, if QD synthesis and the method of QD-bacteria association can be improved, it remains worthwhile for further exploring.
Subjects
quantum dots
amphiphilic polysaccharide
chitosan
propylene glycol alginate
E. coli
Type
thesis
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