Wavelength encoded analytical imaging and fiber optic sensing with pH sensitive CdTe quantum dots

Abstract

CdTe quantum dots (QDs), capped with mercaptopropionic acid (MPA), were synthesized and the variation of their fluorescence properties (steady state and lifetime) with pH was assessed in solution and when immobilized in a sol-gel host. Three different sizes of CdTe QDs with excited state lifetimes ranging from 42 to 48 ns and with emission maximum at 540 nm (QD(540)), 580 nm (QD(580)) and 625 nm (QD(625)) were selected. The solution pH affects the maximum emission wavelength (shifts to higher wavelengths of 23, 24 and 27 nm for QD(540), QD(580) and QD(625), respectively), the excited state lifetime and the fluorescence intensity in a reversible way. Linearization of the maximum emission wavelength variation with the pH allows the estimation of an apparent ionization constant (pK(a)) for each QD: 6.5+/-0.1 (QD(540)), 6.1+/-0.5 (QD(580)) and 5.4+/-0.3 (QD(625)). The variation of the QDs fluorescence properties was further explored using confocal laser scanning microscopy allowing the implementation of a new calibration method for pH imaging in solution. QDs were successfully immobilized on the tip of an optical fiber by dip-coating using sol-gel procedure. The immobilized QDs showed a similar pH behaviour to the one observed in solution and an apparent lifetime of 80, 68 and 99 ns, respectively. The proposed QDs based methodology can be successfully used to monitor pH using wavelength encoded data in imaging and fiber optic sensing applications.

Development of Biocompatible and Proton-Resistant Quantum Dots Assembled on Gelatin Nanospheres

“…Thus, PE may minimize the surface nonradiative recombination and increase confinement of charge carrier, which can lead to a higher band gap energy, and a higher quantum yields (QY). 31,32 The pH Effects on Photostability. The photoquenching of luminescence at low pH value limits the application of QDs in bioimaging in vitro and in vivo, 31,35 for some important physiological cells normally live in low pH values (<7), including endosomes and lysosomes inside cells (pH 5−6.5) and some tumor cells (pH 6−6.9).…”

“…Acid etching results in the changes of nanocrystal semiconductive structures, and lead to the decreases of the PL intensity and lifetime of QDs. 32 Here, the negatively changed PSS layer may neutralize the surrounding protons in acidic conditions, and, therefore, resist the potential proton effect on the PL photostability of the core−shell QDs-GNs. In addition, the immobilization of QDs on GNs prevents negative-changed QDs from aggregations caused by the addition of protons.…”

Synthesis and Analytical Applications of Quantum Dots Coated with Different Generations of DAB Dendrimers

“…These variations are a consequence of the change of the quantum confinement of the QDs as consequence of the ionization of the carboxylic groups of MPA and amine groups of DAB capping the CdS QDs (Gonçalves et al, 2009;Leitão et al, 2008). The variation of the fluorescence properties (intensity and wavelength at the maximum of the emission spectra) of DAB-G 5 -CdS with the pH was expected because QDs capped with ionisable ligands are quite promising pH sensors (Maule et al, 2010 QDs is attached to DAB other applications can be designed taking into consideration the unique properties of dendrimers.…”

Synthesis of nitric oxide probes with fluorescence lifetime sensitivity

“…10, 11 Additional benefits of fluorescence lifetime includes contrast enhancement through alleviation of some of the typical problems associated with intensities including scattering, 12 sample turbidity, and autofluorescence. 13-15 Recently, several papers describing lifetime sensitive probes based on cyanine dyes, 16, 17 quantum dots 18, 19 and fluorescent proteins 20 have been published.…”