An outlook on the potential of Si nanocrystals as luminescent probes for bioimaging
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Mauro Falconieria) ENEA, C.R. Casaccia, I-00123 Rome, Italy
Enrico Trave Department of Molecular Sciences and Nanosystems, Ca’ Foscari University, Dorsoduro 2137, I-30123 Venezia, Italy
Alice Panariti and Ilaria Rivolta Department of Health Science, University of Milano-Bicocca, 4820900 Monza, Monza and Brianza, Italy (Received 30 May 2012; accepted 10 August 2012)
Silicon nanocrystals (Si-nc) present several plus points as advanced fluorescent biomarkers but suffer from difficulties met in controlling their intrinsic photoluminescence (PL). Here, we first consider the reasons for this difficulty, showing results that support an interface defect-related origin of the PL. Attainment of a controlled PL emission would then require tuning of defects in the capping oxide, a hard and yet unaddressed task. Alternatively, we demonstrate the possible use of Si-nc as antennas, or sensitizers, of a luminescent rare-earth ion in an engineered fluorophore. In this approach the relatively high and broadband optical absorption of Si-nc was exploited, keeping the advantages of a near-infrared inorganic light emitter. Another fundamental part of the assessment of Si-nc for bioimaging is their biocompatibility. Here, we report toxicity tests based on the lactate dehydrogenase release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays on epithelial cells and fibroblasts, confirming that Si-nc in concentration suitable for luminescent labeling do not affect significantly the cells viability.
I. INTRODUCTION
Recent advances in biological and biomedical research are pushing the scientific community toward the development of new techniques to visualize cellular compartments and structures and to investigate cellular processes.1 One of the main techniques used in cell biology is fluorescence labeling; progress in this field is, however, limited by some inherent characteristics of currently used organic dyes, like the tendency to photooxidation and blinking.2 More recently, semiconductor nanocrystals (the so-called quantum dots, QD) were largely investigated as biomarkers being more robust toward photobleaching than organic fluorophores and offering size-controllable tunability of the emission wave lengths for multicolor labeling.3,4 Unfortunately, the most popular II–IV QDs, like CdS and CdSe, contain toxic elements that hamper their application in biology and medicine.5 Among the materials that could overcome this limitation, luminescent Si nanocrystals (Si-nc) appear as the ideal candidates (especially for in vivo bioimaging) being inert, nontoxic, and apt to surface chemical functionalization and bioconjugation. Moreover, Si is abundant in nature, economical, and widely investia)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.295 J. Mater. Res., Vol. 28, No. 2, Jan 28, 2013
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gated for a large variety of other applications ranging from photonics to photovoltaics and optoelectronics.6 Unlike bulk Si, which is not a good
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