The instantaneous isolation of green fluorescent colloidal quantum dots of iron selenide capped with biocompatible oleic acid is reported in this study. These iron-containing quantum dots also serve as a safe alternative to the conventionally used metal-chalcogenide systems in which the heavy metal component is usually toxic. The isolated colored colloidal solutions exhibited intense green fluorescence on exposure to ultraviolet light, which was also confirmed by photoluminescence spectroscopy. The isolated product was subjected to dynamic light scattering and transmission electron microscopy, and the particles were found to exhibit spherical morphology with an average diameter of 6–8？nm, confirming the isolation of quantum dots. The isolated iron selenide quantum dots have promising potential towards bioimaging and sensing, due to the biocompatible coating of oleic acid and iron, which also allows possibility of further chemical derivatization. 1. Introduction Quantum dots (QDs) have emerged as one of the most fascinating systems in the new millennium. They have garnered widespread interest amongst a multitude of research groups as they exhibit higher extinction coefficients, higher quantum yields, less photobleaching, broad absorption, and narrow emissions, which can be tuned with size [1, 2]. Due to these properties they are used in infrared photodetectors, solid state lasers, photovoltaics, QD-LEDs, medical imaging, targeting, therapy, and sensing [3–6]. The other major advantage of QDs is that they can be functionalized with a variety of molecules like antibodies, aptamers, proteins, DNA, and so forth, to enable specificity for early and rapid detection [7, 8]. Moreover in comparison to organic fluorophores which display high photobleaching and low extinction coefficients, QDs are definitely the more suitable alternatives. The impressive investigations on these systems in almost every discipline are reflected in the work being carried out globally. In addition to the important aspect of discovering novel materials; attempts are constantly being made, to explore new routes of synthesis and functionalization. Several specific quantum dot systems have been fabricated with an aim towards targeting special applications. Most of the synthesized systems fall under the category of metal chalcogenides, and typically synthesized are the II-VI systems [9]. They include cations of zinc, cadmium, and mercury, combined with anionic oxygen, sulphur, selenium, or tellurium that exhibit a high degree of photoluminescence due to the presence of a direct band gap
References
[1]
L. Spanhel, M. Haase, H. Weller, and A. Henglein, “Photochemistry of colloidal semiconductors. 20. Surface modification and stability of strong luminescing CdS particles,” Journal of the American Chemical Society, vol. 109, no. 19, pp. 5649–5655, 1987.
[2]
A. P. Alivisatos, “Semiconductor clusters, nanocrystals, and quantum dots,” Science, vol. 271, no. 5251, pp. 933–937, 1996.
[3]
M. Grundmann, “Present status of quantum dot lasers,” Physica E, vol. 5, no. 3, pp. 167–184, 1999.
[4]
T. J. Bukowski and J. H. Simmons, “Quantum dot research: current state and future prospects,” Critical Reviews in Solid State and Materials Sciences, vol. 27, no. 3-4, pp. 119–142, 2002.
[5]
A. M. Smith, X. Gao, and S. Nie, “Quantum dot nanocrystals for in vivo molecular and cellular imaging,” Photochemistry and Photobiology, vol. 80, no. 3, pp. 377–385, 2004.
[6]
B. Debasis, L. Qian, T.-K. Tseng, and P. H. Holloway, “Quantum dots and their multimodal applications: a review,” Materials, vol. 3, pp. 2260–2345, 2010.
[7]
S. Dwarakanath, J. G. Bruno, A. Shastry et al., “Quantum dot-antibody and aptamer conjugates shift fluorescence upon binding bacteria,” Biochemical and Biophysical Research Communications, vol. 325, no. 3, pp. 739–743, 2004.
[8]
V. Bagalkot, L. Zhang, E. Levy-Nissenbaum et al., “Quantum dot-aptamer conjugates for synchronous cancer imaging, therapy, and sensing of drug delivery based on Bi-fluorescence resonance energy transfer,” Nano Letters, vol. 7, no. 10, pp. 3065–3070, 2007.
[9]
J. G. Brennan, T. Siegrist, P. J. Carroll et al., “Bulk and nanostructure group II-VI compounds from molecular organometallic precursors,” Chemistry of Materials, vol. 2, no. 4, pp. 403–409, 1990.
[10]
J. Zhang, X. G. Chen, L. Huang, J. T. Han, and X. F. Zhang, “Self-assembled polymeric nanoparticles based on oleic acid-grafted chitosan oligosaccharide: biocompatibility, protein adsorption and cellular uptake,” Journal of Materials Science, pp. 1–9, 2012.
[11]
M. Akhtar, J. Akhtar, M. A. Malik, F. Tuna, M. Helliwell, and P. O'Brien, “Deposition of iron selenide nanocrystals and thin films from tris(N,N-diethyl-N[prime or minute]-naphthoylselenoureato)iron(iii),” Journal of Materials Chemistry, vol. 22, pp. 14970–14975, 2012.
[12]
R. Koole, W. J. M. Mulder, M. M. van Schooneveld, G. J. Strijkers, A. Meijerink, and K. Nicolay, “Magnetic quantum dots for multimodal imaging,” Wiley Interdisciplinary Reviewsy, vol. 1, no. 5, pp. 475–491, 2009.
[13]
A. Hoshino, K. Fujioka, T. Oku et al., “Physicochemical properties and cellular toxicity of nanocrystal quantum dots depend on their surface modification,” Nano Letters, vol. 4, no. 11, pp. 2163–2169, 2004.
[14]
T. Pradeep, Nano: The Essentials, McGraw-Hill, 2008.
[15]
C. De Mello Donegá, P. Liljeroth, and D. Vanmaekelbergh, “Physicochemical evaluation of the hot-injection method, a synthesis route for monodisperse nanocrystals,” Small, vol. 1, no. 12, pp. 1152–1162, 2005.
[16]
D. V. Talapin, A. L. Rogach, A. Kornowski, M. Haase, and H. Weller, “Highly luminescent monodisperse CdSe and CdSe/ZnS nanocrystals synthesized in a hexadecylamine-trioctylphosphine oxide-trioctylphospine mixture,” Nano Letters, vol. 1, no. 4, pp. 207–211, 2001.
[17]
Ventra, Introduction to Nanoscale Science and Technology, Springer, New York, NY, USA, 2004.
[18]
C. E. M. Campos, J. C. De Lima, T. A. Grandi, K. D. Machado, and P. S. Pizani, “Structural studies of iron selenides prepared by mechanical alloying,” Solid State Communications, vol. 123, no. 3-4, pp. 179–184, 2002.
[19]
Schmidt, Hydrazine and Its Derivatives: Preparation, Properties, Applications, John Wiley & Sons, New York, NY, USA, 2nd edition, 2001.
