This NSF Small Business Innovation Research Phase II project is to synthesize cadmium-free, water-soluble, and multicolor quantum dots (QDs) by chemical doping. The project will focus on the synthesis of high quality doped ZnSe QDs using a newly developed phosphine-free approach. From these cadmium free doped derivatives with high quality blue, green, and red emissione will be produced. Then the doped core/shell QDs will be processed to make them water-soluble and biocompatible through proprietary methods for biomedical applications.
Successful development of the proposed techniques will result in a new generation of biolabels and make significant advances in biomedical applications of such cadmium-free doped QDs. The "green" nature of the production methods, mineral precursors, natural surfactants, non-toxic and nonvolatile solvents and cadmium free QDs, will assist to maintain a sustainable environment, in addition to delivering high performance end products to the public.
As the popularity of quantum dots soars, the concern about their toxicity rises. There is an urgent need to study Cd-free quantum dots and their applications. However the lack of the availability of high quality Cd-free quantum dots has been the bottleneck in this field. Through this NSF SBIR project, Ocean NanoTech has developed and scaled up the production of fluorescent cadmium free core/shell quantum dots. These QDs are very stable and have high emission efficiency in the emission range of 560-830 nm. For biological applications, these organic soluble QDs were converted to water soluble nanocrystals through Ocean’s proprietary coating method, which makes water soluble QDs compact for in vitro and in vivo applications. The transmission electronic microscope (TEM), dynamic light scatting (DLS), electrophoresis gel, and fluorescent spectrometry were used for characterization of these QDs in term of their emission efficiency, stability, particle size and non-specific binding. Antibody conjugated Cd-free QDs were applied to stain tumor cell and tissue for target-specific imaging. We also demonstrated that the Cd-free QDs were excellent contrast agent for fluorescent lifetime microscopy. Ocean Nanotech also applied these QDs in the fabrication of light-emitting diodes(LEDs). The emergence of solution-processed QD based light emitting diodes has recently offered great prospects for developing low-cost, efficient, bright, and large area colorful displays compatible with flexible substrates. The band-edge electroluminescence (EL) of QDs of cadmium compounds, i.e., Cd(S,Se,Te), exhibits size tunable spectral emission and narrow bandwidth (FWHM ∼ 25–40 nm), allowing for the design and fabrication of color-saturated red, green and blue (RGB) QDLEDs with simple device configurations and high spectral purities that outperform those of liquid crystal displays and organic light emitting diodes. As promising as the solution-processed QDLEDs are, a serious drawback of the present colloidal QDLED technology is its dependence on heavy-metal cations, such as cadmium, lead, and mercury. The regulatory acceptance of these nanocrystal materials containing heavy-metal constituents could potentially hinder the ultimate research transformation and commercialization of the QDLED technology. Toward this end, intensive research studies have been conducted to develop colloidal QDLEDs free of cadmium, lead, and mercury compositions. To date, all the approaches have fundamental limitations to the luminescence spectral control, quantum yield and effectiveness of QDLEDs In the past several years, Ocean NanoTech, with its collaborators, has been published more than 10 publications in Cd based QDLEDs (Nature, Photonics, 2007, NanoLetter 2007, ACS Nano2009). After we synthesized high quality CIS QDs, we applied them in the fabrication of QDLEDs. The high brightness of QDLEDS fabricated with heavy metal-free QDs was achieved in first time. The emission colors were yellow, orange and red. We also used CIS QDs fabricated white LEDs for lighting application. The excellent results have been published in NanoLetter (2011, 11, 329) and Advanced materials (2011, 23 3553). Above results show that CIS based Cd-free QDs are very promising nanomaterials for photovoltaic, lighting, display and biomedical applications. The further development of Cd-free quantum dots will benefit the environment and human health. Ocean NanoTech continues to improve the quality and safety of the nanomaterials With the support of this project, we were able to train more than ten undergraduate students. They are equipped with some basic knowledge and skills in nanoparticles and their applications. The undergraduate students are interested in nanomaterial science and greatly encouraged towards a career in science and engineering. Other than the undergraduate students, we were also able to train 10 graduate students or postdocs from our collaborators' research groups. The training was focused on a deeper understanding of Cd-free quantum dots from the synthesis to their applications.
