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. 2015 Jul 20;7(4):1759091415592389. doi: 10.1177/1759091415592389

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© The Author(s) 2015

This article is distributed under the terms of the Creative Commons Attribution 3.0 License (http://www.creativecommons.org/licenses/by/3.0/) which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access page (http://www.uk.sagepub.com/aboutus/openaccess.htm).

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Figure 1. — QD surface functionalization ligands or coatings. Structure of compact ligand (CL) coatings CL1, CL2, and CL4 as well as the PEG (DHLA-PEG600-NH₂, n = 12) used in the studies. DHLA-PEG600-NH₂ has an overall positive charge from the amine. CL1 has potential positive charges from the piperazine in addition to negative charge from the carboxyl group. CL2 has one positively charged nitrogen and one negatively charged carboxyl and is probably zwitterionic under physiological conditions. CL4 has one positively charged nitrogen and two negatively charged carboxyls at the terminal end. QD = quantum dot; PEG = polyethylene glycol; DHLA = dihydrolipoic acid.