CdSe/CdS-quantum rods: fluorescent probes for in vivo two-photon laser scanning microscopy

Abstract

CdSe/CdS-Quantum-dots-quantum-rods (QDQRs) with an aspect ratio of ∼ 6 are prepared via the seeded growth method, encapsulated within a shell of crosslinked poly(isoprene)-block-poly(ethylene glycol) (PI-b-PEG) diblock copolymer, and transferred from the organic phase into aqueous media. Their photoluminescence quantum yield (PLQY) of 78% is not compromised by the phase transfer. Within a period of two months the PLQY of QDQRs in aqueous solution at neutral pH decreases only slightly (to ∼ 65%). The two-photon (TP) action cross sections of QDQRs (∼ 10(5) GM) are two orders of magnitude higher than those of CdSe/CdS/ZnS-core/shell/shell quantum dots (QDs, ∼ 10(3) GM) with comparable diameter (∼ 5 nm). After applying PI-b-PEG encapsulated QDQRs onto the small intestinal mucosa of mice in vivo, their strong red fluorescence can easily be observed by two-photon laser scanning microscopy (TPLSM) and clearly distinguished from autofluorescent background. Our results demonstrate that PI-b-PEG encapsulated CdSe/CdS-QDQRs are excellent probes for studying the uptake and fate of nanoparticles by two-photon imaging techniques in vivo.

Excitation wavelength dependence of the photoluminescence quantum yield and decay behavior of CdSe/CdS quantum dot/quantum rods with different aspect ratios

“…QDQRs are applied as fluorescent reporters e.g., in bioanalysis and microscopy, 1,2 and optoelectronic components in photovoltaics, light-emitting diodes (LEDs), and liquid crystal displays (LCDs). [3][4][5][6] Such QDQRs can have different aspect ratios, i.e., different ratios of their length and thickness, and are commonly covered by a coordinatively bound shell of organic ligands controlling their stability and dispersibility.…”

“…[7][8][9] QDQRs can be made water-dispersible following similar strategies as established for spherical QDs, i.e., via ligand exchange or encapsulation with amphiphilic polymers. 1,[10][11][12][13][14] Favorable of QDQRs are their higher molar extinction coefficients and photoluminescence quantum yields (ΦPL) often exceeding those of QDs. 15,16 In addition, their emission is anisotropic or polarized, whereas the photoluminescence (PL) from QDs is isotropic.…”

Quantification of Anisotropy-Related Uncertainties in Relative Photoluminescence Quantum Yield Measurements of Nanomaterials – Semiconductor Quantum Dots and Rods

“…QDRs possess unique photophysical properties, such as size-tunable absorption and emission spectra (dependent on the core diameter), huge absorption cross-sections, and narrow, symmetric emission bands like spherical quantum dots (QDs). [24][25][26][27] In addition, QDRs can have even higher extinction coefficients and brightness compared to QDs. Moreover, most importantly for our study, the emission anisotropy of QDRs depends on their aspect ratios.…”

Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

“…Indeed, measurements of TPA cross sections of various QDs are often performed for a single wavelength only that does not necessarily correspond to the maximum of the TPA band, and the reports lack the confrontation of the obtained values with the quantum yield (QY) of the TPEE, which is a crucial parameter in microscopy imaging applications. Additionally, most of the work have been conducted for cadmium-based QDs, [5][6][7] with inherent cytotoxicity and thus limited applications in biological and biomedical areas. 8 An interesting alternative for II-IV type QDs is less harmful, types III-V semiconductor materials.…”