ABSTRACT
Key Laboratory of Pesticide and Chemical Biology (CCNU), Ministry of Education, College of Chemistry, Central China Normal University.
Email: zhangfan@mails.ccnu.edu.cn * Corresponding author: lhbing@mail.ccnu.edu.cn
Smart nanomaterials such as quantum dots (QDs), gold nanoparticles (AuNPs), silver nanoparticles (AgNPs), silica nanoparticles (SiNPs) with unique size-dependent properties in the fi eld of nanotechnology have attracted increasing interest for bioanalytical applications in recent years (Yao et al. 2014). Quantum dots (QDs) as a unique smart semiconductor nanoparticle has become a notable star in the development of optical labels for labelling and sensing and have been broadly applied in fl uorescence assay or imaging for biological and medical researches due to their superior physical and chemical properties (Zrazhevskiy et al. 2010). They were fi rst discovered by Alexey Ekimov in 1981 in a glass matrix and then in colloidal solutions by Louis E. Brus in 1985 (Ekimov and Onushchenko 1982). QDs are semiconductor nanocrystals composed of elements from groups II−VI (e.g., Cd, Zn, Se, and Te) or III−V (e.g., In, P, and As) in the periodic table, for example CdSe, CdTe, HgTe, PbS, PbSe, PbTe, InAs, InP, and GaAs (Klostranec and Chan 2006). They are small enough and range from 2 to 10 nanometers in diameter (physical size smaller than the exciton Bohr radius) to exhibit quantum mechanical properties, such as the quantum-size effect, surface effect, macroscopic quantum tunneling effect and so forth (Alivisatos 2004). These quantum effects would make it invalidate the governing rules at the macroscopic level and generate both high signalto-noise ratio and signal amplifi cation (Bau et al. 2011). Additionally, for their excitons are confi ned in all three spatial dimensions, the electrons are quantized to certain energies, similar to that of a small molecule, thus
giving QDs excellent properties that is not achievable in bulk materials (Alivisatos 1996). With size variable photoluminescence, QDs are promising alternatives to organic dyes for their outstanding optical properties and fl uorescence-based applications. These properties include high quantum yields, long fl uorescence lifetime, large extinction coeffi cients, pronounced photostability, and more importantly, broad absorption with narrow symmetric photoluminescence spectra (full-width at half-maximum ~25-40 nm) spanning the UV to near-infrared region (NIR) (Resch-Genger et al. 2008, Esteve-Turrillas and Abad-Fuentes 2013). All these properties allow the excitation of QDs of various sizes at a common wavelength manifold while imaging, in parallel, the fl uorescence of the different QDs. As a consequence, QDs are suitable for multiplexing analysis and they can be simultaneously excited by a single light source when multiple colors are acquired together (Giepmans et al. 2005).
