Emission transformation in CdSe/ZnS quantum dots conjugated to biomolecules (original) (raw)
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CdSe/ZnS quantum dots with interface states as biosensors
Biosensing and Nanomedicine IV, 2011
The paper presents the brief review of published results as well as the original study of photoluminescence (PL) and Raman scattering of core-shell CdSe/ZnS quantum dots (QDs) with radiative interface states. First commercially available CdSe/ZnS QDs with emission at 525 nm (2.36 eV), 565 nm (2.20 eV), 605 nm (2.05 eV) and 640 nm (1.96 eV) covered by PEG polymer have been compared in nonconjugated states. PL spectra of nonconjugated QDs are characterized by a superposition of PL bands related to exciton emission in CdSe cores and to hot electron-hole emission via high energy states (2.00, 2.20, 2.37, 2.75 and 3.04 eV). The high energy states were studded using QDs of different sizes and at different temperatures. It is shown that these PL bands related to interface states. Then the CdSe/ZnS QDs with the color emission 525nm and 605 nm have been conjugated with bio-molecules-ovarian cancer (OC 125) and anti Interleukin 10 (IL-10) antibodies, respectively. It is revealed that the PL spectrum of bioconjugated QDs has changed dramatically with essential decreasing the hot electron-hole recombination flow via interface states. The variation of PL spectra at the bioconjugation is explained on the base of electrostatic interaction and recharging of QD interface states. The Raman scattering study of nonconjugated and bioconjugated QDs has shown that mentioned antibodies are characterized by the dipole moment that provokes the surface enhance Raman scattering effect in bioconjugated QD samples as well.
Modification of optical properties at bioconjugation of core-shell CdSe/ZnS quantum dots
Journal of Physics: Conference Series, 2010
This paper presents the results of photoluminescence study of core-shell CdSe/ZnS quantum dots (QDs) with radiative interface states in nonconjugated and bioconjugated conditions. PL spectra of nonconjugated QDs are characterized by a superposition of PL bands related to exciton emission in CdSe cores (2.36 eV) and to electron-hole emission via interface states (2.00, 2.75 and 3.04 eV) at the CdSe/ZnS or ZnS/polymer interfaces. The CdSe/ZnS QDs with emission at 525 nm have been conjugated with bio-molecules-mouse ovarian cancer (OC 125) antibodies. It is revealed that PL spectrum of bioconjugated QDs has changed dramatically with essential decreasing of the hot electron-hole recombination flow via interface states. This effect is explained on the base of the model deals with recharging of QD interface states at the bioconjugation with OC125 antibodies. The nature of interface states and their changes at the QD aging process have been discussed as well.
Peculiarities of Raman scattering in bioconjugated CdSe/ZnS quantum dots
Nanotechnology, 2010
The article presents the results of analysis of Raman scattering spectra of non-conjugated and bioconjugated CdSe/ZnS core-shell quantum dots (QDs). Commercial CdSe/ZnS QDs used covered by polymer are characterized by color emission with the maxima at 605-610 nm (2.03-2.05 eV). The bioconjugation process is performed to biomolecules-the antihuman Interleukin 10 (IL10) antibodies (mab). Raman scattering spectra measured at room temperature with excitation by a He-Ne laser line (632.8 nm) demonstrate two groups of peaks: (1) related to the Si substrate at 230-460, 522, 610, 670, 940-1040 cm −1 and (2) to the PEG polymer on the QD surface in the range of 837-3320 cm −1. It is revealed that the CdSe/ZnS QD bioconjugation to the antihuman Interleukin 10 antibodies is accompanied with the dramatic changes in the intensity of the Raman lines of both types: the intensity of the Si related line increases six-or tenfold , but the intensity of the polymer related line decreases tenfold. The models explaining the mentioned effects in Raman scattering spectra have been discussed.
The mechanism of the photoluminescence changes in bio-conjugated CdSe/ZnS quantum dots
Applied Surface Science, 2013
The change of the photoluminescence (PL) and optical characteristics in non-conjugated and conjugated with S6K2 antibody CdSe/ZnS core/shell quantum dots (QDs) during storage in air has been studied by the conventional PL, micro-PL and micro-Raman techniques. The QDs dried on a crystalline Si substrate were kept in the darkness and under illumination. In the PL spectra, the storage resulted in a blue shift of PL peak position, in the increasing of the full width at a half maximum (FWHM) of the PL band and in the decreasing of the PL intensity. In the Raman spectra, the shift of the CdSe LO peak position to the low frequency region and the increasing of its FWHM were observed. The transformations in the PL and optical characteristics correlate with each other and are found to be the largest in bio-conjugated QDs stored under illumination. The increase of the light intensity accelerated the changes occurred during storage. An oxidation of the QD core, which decreases the QD size, is supposed to be responsible for observed transformations. The bio-conjugation is assumed to promote QD oxidation that results in different PL peak position in stored non-conjugated and bio-conjugated QDs. The mechanism of the effect is discussed.
In this work we studied the interaction between CdSe/ZnS core-shell quantum dots (QDs) and bovine serum albumin (BSA) protein, and the temperature effects on the structural and spectroscopic properties of both, individual QDs and protein and their bioconjugates (QDs@BSA), by fluorescence and UV-vis spectroscopy. The recorded UV-vis data and the calculated rate of BSA fluorescence quenching by the QDs demonstrated that the interaction between them leads to the formation of QDs@BSA complex. Moreover we show that, compared to the monotonically decrease of the non-conjugated QDs fluorescence intensity, the temperature dependence of the QDs@BSA emission has a much more complex behavior, highly sensitive to the conformational changes of the protein.
Semiconductors, 2009
The photoluminescence and photoluminescence excitation spectra, the X ray diffraction pat terns, and the effect of conjugation with biomolecules upon these characteristics are studied for silanized CdSe/ZnS quantum dots. Along with the band of annihilating excitons in the quantum dots, the lumines cence spectra exhibit emission associated with defects. It is established that the emission spectrum of defects involves at least two components. It is shown that the defects are located mainly at the small sized quantum dots; the defects responsible for the long wavelength component are located mainly at the quantum dots larger in size than the quantum dots, at which the defects responsible for the short wavelength component are located. It is found that conjugation with biomolecules induces not only the blue shift of the excitonic band, but transformation of the emission spectra of defects and an increase in the contribution of defects to the luminescence spectrum as well. The changes observed in the emission spectrum of defects are attributed to the formation of certain emission centers. It is shown that, when conjugated with biomolecules, the quan tum dots experience increasing compression strains. This effect is responsible for the blue shift of the lumi nescence band of the quantum dots.
Raman scattering study in bio-conjugated core-shell CdSe/ZnS quantum dots
Journal of Non-Crystalline Solids, 2008
We studied the effect on Raman scattering spectra of bio-molecule conjugation with core/shell CdSe/ZnS quantum dots. It is found that in some cases the conjugation leads to noticeable variation of these spectra, so that the detection of bio molecules could be done more accurately. An explanation of the effect is proposed.
Bioconjugate Chemistry, 2008
Chemical modification of the surface of CdSe/ZnS quantum dots (QDs) with small molecules or functional ligands often alters the characteristics of these particles. For instance, dopamine conjugation quenches the fluorescence of the QDs, which is a property that can be exploited for sensing applications if the conjugates are taken up into living cells. However, different sizes and/or preparations of mercaptocarboxylic acid solubilized QDs show very different properties when incubated with cells. It is unknown what physical parameters determine a QDs ability to interact with a cell surface, be endocytosed, escape from endosomes, and/or enter the nucleus. In this study, we examine the surface chemistry of QD-dopamine conjugates and present an optimized method for tracking the attachment of small biomolecules to the surface. It is found that the fluorescence intensity, surface charge, colloidal stability, and biological interactions of the QDs vary as a function of the density of dopamine on the surface. Successful targeting of QD-dopamine to dopamine receptor positive PC12 cells correlates with greater homogeneity of particle thiol layer, and a minimum number of ligands required for specific association can be estimated. These results will enable users to develop methods for screening QD conjugates for biological activity before proceeding to experiments with cell lines and animals.
Applied Physics Letters, 2011
We report changes in the photophysical properties of core-shell type CdSe/ZnS quantum dots ͑QDs͒ under optical irradiation. QDs either in aqueous solution or immobilized in a silica sol gel matrix have been excited at different wavelengths and fluxes. Illumination of the sample with 140 fs 700 nm Ti:sapphire laser pulses of the peak power of the order of 4 GW/ cm 2 caused gradual increase in the luminescence lifetime from an initial value of 3.5 increasing to 4.5 ns and an increase in luminescence intensity by ϳ8%. Using about 16 GW/ cm 2 peak power resulted in a shortening of the luminescence lifetime to 3 ns and a decrease in intensity by ϳ75%. Both photobrightening and photodarkening were fully reversible. We discuss the kinetics of photobrightening and photodarkening and investigate the suitability of QDs as luminescence lifetime sensors with tunable parameters.
Micro-Raman and micro-photoluminescence study of bio-conjugated core–shell CdSe/ZnS nanocrystals
Physica B: Condensed Matter, 2014
The micro-Raman and micro-photoluminescence spectra of non-conjugated and conjugated with antibody against S6K2 commercial CdSe/ZnS quantum dots (QDs) were investigated under different excitation wavelengths and at different temperatures. In the photoluminescence (PL) spectra, the additional PL band shifted on 0.6-0.65 eV to higher energies from the CdSe/ZnS QD exciton PL band is revealed. The relative intensity of this band is found to be several times larger in bio-conjugated QDs, than in the non-conjugated ones. The characteristics of both PL bands (the PL intensity, spectral position and half-width of the PL band) vary similarly under continuous laser light irradiation, storage of the QD samples in the atmospheric ambience as well as during the temperature change. In the Raman spectra recorded under excitation resonant with the high-energy PL band, the additional Raman peaks at about 300 cm À 1 and 600 cm À 1 , which are close to the frequency of LO and 2LO phonons of bulk CdS, are found. It is proposed that alloyed QDs with chemical composition close to CdS are responsible for the additional high-energy PL band. The possible reasons for the formation of the alloyed QDs are discussed.