Carboxylic Acid enriched nanospheres of semiconductor nanorods for cell imaging.

During the past decades, nanomaterials such as noblemetal, lanthanide-doped, magnetic, luminescent SiO2, [9,10] and semiconductor nanomaterials have been extensively investigated and used in the development of sensitive and selective detection and imaging in biological and medical fields. Owing to their novel optical properties, semiconductor nanocrystals are of great interest to many fields such as field-effect transistors, waveguides, nanolasers, photovoltaics, electronics, and biolabels. Specific applications, for example, biolabels, require these nanocrystals to be not only highly luminescent but also water-soluble. Up to now, lots of facile methods have been developed for the preparation of semiconductor nanoparticles and nanorods; however, most of them are mainly based on the decomposition of organometallic precursors in hydrophobic solvents. Also, these as-prepared nanocrystals are hydrophobic, which is inconvenient for bioapplications. It is still a challenge to synthesize monodisperse semiconductor nanorods by using common inorganic salts such as nitrates as precursors. Furthermore, the surface modification of hydrophobic nanocrystals is another challenge. In this work, we have developed a facile strategy for the preparation of CdS and ZnS:Mn nanorods with nitrates as precursors. By simply modifying the solvothermal conditions, the sizes of the as-prepared nanorods were desirably tuned. Then, the hydrophobic short nanorods were encapsulated to form amphiphilic polymer coated nanospheres with a facile ultrasonication strategy. With an abundance of carboxylic acid groups in the polymer coating on the outer face, these colloidal nanospheres are water-soluble and bioconjugatable. These luminescent nanospheres were also used as biolabels in cell fluorescence imaging, as reported herein. The synthesis was conducted in oleylamine with nitrates as precursors. At 160 8C, colloidal CdS and ZnS nanorods were grown in an oleylamine solution of nitrates (1 mmol) and thioacetamide (1.2 mmol). Figure 1 shows the TEM images of the semiconductor nanorods prepared in oleylamine by solvothermal processing for 12 h (or 24 h) at 160 8C.