Cadmium free quantum dots: Principal attractions, properties, and applications

For the past thirty years, interest on semiconductor nanocrystals from versatile systems of II–VI Quantum Dots (QDs) has been actively grown depending upon their application to light-emitting diodes (Gaponik in Mater Chem 10: 2163–2166, 2000 [1]), lasers (Artemyev et al. in Nano Lett 1:309–314, 2001 [2]), and biomedical research (Bruchez et al. in Science 281:2013–2016, 1998 [3]; Chan and Nie in Science 281:2016–2018, 1998 [4]; Michalet et al. in Science 307:538– 544, 2005 [5]). However, the presence of highly toxic cadmium limits the application range particularly in the lighting and biological fields. To lessen the toxicity issue, various approaches were developed, such as overcoating the toxic core by non-toxic ZnS shell preventing the leakage of cadmium ions (Chou and Chan in Nat Nanotechnol 7(7):416–417, 2012 [6]; Ghaderi et al. in J Drug Targeting 19:475– 486, 2011 [7]; Winnik and Maysinger in Acc Chem Res 46:672–680, 2012 [8]). Despite this action, II–VI QDs still remain unsafe due to initiated response to UV irradiation- or oxidation-resulted cadmium release through oxidized surface sites (Derfus et al. in Nano Lett 4:11–18, 2004 [9]). Therefore, the research focus was shifted to so-called cadmium free QDs, such as ZnSe, InP, and CuInS₂.