Coating of CdSe quantum dots by biopolymer: synthesis and optical Properties

Colloidal semiconductor quantum dots (QDs) have attained great attention because of their broad excitation wavelength, tunable emission wavelength, bright fluorescence (FL), andhigh stability against photobleaching and chemicals [1]. This feature makes them very attractive for various biologicalapplications such as optical sensing, tracing, and imaging of biomolecules. For most biological applications of QDs, their aqueous solubility is indispensable. Water-soluble QDs have been typically prepared either by surface modification of hydrophobic QDs synthesized in organic solution or directlyin aqueous solution [2]. The surface modification of hydrophobic QDs is achieved typically by adopting one of thetwo strategies. The first strategy is to form a hydrophilic surface shell, using amphiphilic polymers, around their hydrophobic ligand shell. Regrettably, it results in much largerparticles with poorer size dispersion because of thick surface shell formation and difficulty in precise control of shellthickness; hence, limiting their wide applications. The second strategy is to perform the so-called ligand exchange that replaces hydrophobic ligands with hydrophilic ones [3]. In thiswork, we introduce a new way to prepared high FL intensity of water soluble CdSe QDs by coating their surface by polyacrylamide grafted onto Collgen (Collgen-g-PAAm) biopolymers