Fast Imaging of Single Molecules and Nanoparticles by Wide-Field Microscopy and Spectrally Resolved Confocal Microscopy

Abstract

The dynamic photophysical behaviour of single Cy5-maleimide molecules and core-shell (CdSe)ZnS quantum dots is compared. To this end a home-built fast and sensitive wide-field microscopy system and a scanning confocal microscope coupled to a spectrograph for spectral imaging are employed. The ability to measure time-resolved spectra of quantum dots is shown to be particularly useful in characterizing single quantum dots. The difference in blinking behaviour of single Cy5-maleimide molecules and (CdSe)ZnS quantum dots can be understood by their physical origin, i.e. the presence of a single 'dark' state in case of Cy5 versus a distribution of 'dark' states in case of (CdSe)ZnS. This intrinsic difference results in higher probabilities to find a quantum dot in a short-lived (<0.02 s) or long-lived (>0.2 s) state than a Cy5-mal molecule. Moreover, from a comparison to data in the literature, it was found that the lifetime of the 'off'-state of the Cy5-mal molecule is longer than for the non derivatized Cy5 molecule.

Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy

“…Analysis of the off-time intervals shows that the probability density of off-time intervals can be described by an inverse power law, i.e., P ( t off ) ∝ t off -(1+α) , in accordance with Kuno et al They reported an excellent agreement between the experimentally observed off-time distribution over nine decades in probability density and five decades in time, using (1 + α) = 1.6 ± 0.1. For our 41 dots, we find an average value of (1 + α) = 1.4 ± 0.2, in correspondence to earlier reported values. , The most probable explanation for the inverse power law behavior is the existence of multiple ionization states and consequently a distribution of recombination rates . Because the process that leads to the off state is assigned to photoionization of the QD, the off-time intervals are related to recombination of the ejected charge carrier with the ionized dot .…”

Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy

“…Analysis of the off-time intervals shows that the probability density of off-time intervals can be described by an inverse power law, i.e., P ( t off ) ∝ t off -(1+α) , in accordance with Kuno et al They reported an excellent agreement between the experimentally observed off-time distribution over nine decades in probability density and five decades in time, using (1 + α) = 1.6 ± 0.1. For our 41 dots, we find an average value of (1 + α) = 1.4 ± 0.2, in correspondence to earlier reported values. , The most probable explanation for the inverse power law behavior is the existence of multiple ionization states and consequently a distribution of recombination rates . Because the process that leads to the off state is assigned to photoionization of the QD, the off-time intervals are related to recombination of the ejected charge carrier with the ionized dot .…”

Alloyed ZnxCd1-xS Nanocrystals with Highly Narrow Luminescence Spectral Width

“…To the best of our knowledge, the observed 14 nm spectral width should be the narrowest one for QDs ensembles at room temperature. This spectral width is similar to the homogeneous line width observed in single dot spectroscopy by phonon-dephasing processes, − which eliminates the effect of inhomogeneous broadening due to size fluctuations at room temperature. It is clear that the inhomogeneous spectral broadening is effectively suppressed in these alloyed nanocrystals ensembles.…”

“…In a continuing effort, we report here the synthesis of ternary wide band gap Zn x Cd 1 - x S nanocrystals with superior optical properties. In particular, we demonstrate the narrowest room-temperature emission spectral width (full width at half-maximum, fwhm) of 14 nm in an ensemble measurement, which is comparable to the homogeneous line width of single CdSe QDs at room temperature. − The obtained high-quality Zn x Cd 1 - x S nanocrystals will be very promising nanomaterials as biological labels and short wavelength optoelectronic devices such as quantum dot lasers, high-density optical recording devices, photovoltaic cells, and displays.…”

Dynamic Monte Carlo Simulations to Model FRET and Photobleaching in Systems with Multiple Donor−Acceptor Interactions

“…Another potential application for the MCSs as described here, might be the simulation of FRET between a semiconductor nanoparticle (quantum dot) and an organic dye . In this case additional de-excitation paths and recombination paths are required to describe the intermittency in the quantum dot emission. − In conclusion, the Monte Carlo simulations proved to be a versatile method to model spatial and temporal fluorescence intensity fluctuations in microscopy with multiple applications in the future.…”

“…30 In this case additional de-excitation paths and recombination paths are required to describe the intermittency in the quantum dot emission. [31][32][33][34] In conclusion, the Monte Carlo simulations proved to be a versatile method to model spatial and temporal fluorescence intensity fluctuations in microscopy with multiple applications in the future.…”

Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy

“…Analysis of the off-time intervals shows that the probability density of off-time intervals can be described by an inverse power law, i.e., P ( t off ) ∝ t off -(1+α) , in accordance with Kuno et al They reported an excellent agreement between the experimentally observed off-time distribution over nine decades in probability density and five decades in time, using (1 + α) = 1.6 ± 0.1. For our 41 dots, we find an average value of (1 + α) = 1.4 ± 0.2, in correspondence to earlier reported values. , The most probable explanation for the inverse power law behavior is the existence of multiple ionization states and consequently a distribution of recombination rates . Because the process that leads to the off state is assigned to photoionization of the QD, the off-time intervals are related to recombination of the ejected charge carrier with the ionized dot .…”

Alloyed ZnxCd1-xS Nanocrystals with Highly Narrow Luminescence Spectral Width

“…To the best of our knowledge, the observed 14 nm spectral width should be the narrowest one for QDs ensembles at room temperature. This spectral width is similar to the homogeneous line width observed in single dot spectroscopy by phonon-dephasing processes, − which eliminates the effect of inhomogeneous broadening due to size fluctuations at room temperature. It is clear that the inhomogeneous spectral broadening is effectively suppressed in these alloyed nanocrystals ensembles.…”

“…In a continuing effort, we report here the synthesis of ternary wide band gap Zn x Cd 1 - x S nanocrystals with superior optical properties. In particular, we demonstrate the narrowest room-temperature emission spectral width (full width at half-maximum, fwhm) of 14 nm in an ensemble measurement, which is comparable to the homogeneous line width of single CdSe QDs at room temperature. − The obtained high-quality Zn x Cd 1 - x S nanocrystals will be very promising nanomaterials as biological labels and short wavelength optoelectronic devices such as quantum dot lasers, high-density optical recording devices, photovoltaic cells, and displays.…”

Dynamic Monte Carlo Simulations to Model FRET and Photobleaching in Systems with Multiple Donor−Acceptor Interactions

“…Another potential application for the MCSs as described here, might be the simulation of FRET between a semiconductor nanoparticle (quantum dot) and an organic dye . In this case additional de-excitation paths and recombination paths are required to describe the intermittency in the quantum dot emission. − In conclusion, the Monte Carlo simulations proved to be a versatile method to model spatial and temporal fluorescence intensity fluctuations in microscopy with multiple applications in the future.…”

“…30 In this case additional de-excitation paths and recombination paths are required to describe the intermittency in the quantum dot emission. [31][32][33][34] In conclusion, the Monte Carlo simulations proved to be a versatile method to model spatial and temporal fluorescence intensity fluctuations in microscopy with multiple applications in the future.…”

Photooxidation and Photobleaching of Single CdSe/ZnS Quantum Dots Probed by Room-Temperature Time-Resolved Spectroscopy

“…Analysis of the off-time intervals shows that the probability density of off-time intervals can be described by an inverse power law, i.e., P ( t off ) ∝ t off -(1+α) , in accordance with Kuno et al They reported an excellent agreement between the experimentally observed off-time distribution over nine decades in probability density and five decades in time, using (1 + α) = 1.6 ± 0.1. For our 41 dots, we find an average value of (1 + α) = 1.4 ± 0.2, in correspondence to earlier reported values. , The most probable explanation for the inverse power law behavior is the existence of multiple ionization states and consequently a distribution of recombination rates . Because the process that leads to the off state is assigned to photoionization of the QD, the off-time intervals are related to recombination of the ejected charge carrier with the ionized dot .…”

Alloyed ZnxCd1-xS Nanocrystals with Highly Narrow Luminescence Spectral Width

“…To the best of our knowledge, the observed 14 nm spectral width should be the narrowest one for QDs ensembles at room temperature. This spectral width is similar to the homogeneous line width observed in single dot spectroscopy by phonon-dephasing processes, − which eliminates the effect of inhomogeneous broadening due to size fluctuations at room temperature. It is clear that the inhomogeneous spectral broadening is effectively suppressed in these alloyed nanocrystals ensembles.…”

“…In a continuing effort, we report here the synthesis of ternary wide band gap Zn x Cd 1 - x S nanocrystals with superior optical properties. In particular, we demonstrate the narrowest room-temperature emission spectral width (full width at half-maximum, fwhm) of 14 nm in an ensemble measurement, which is comparable to the homogeneous line width of single CdSe QDs at room temperature. − The obtained high-quality Zn x Cd 1 - x S nanocrystals will be very promising nanomaterials as biological labels and short wavelength optoelectronic devices such as quantum dot lasers, high-density optical recording devices, photovoltaic cells, and displays.…”

Dynamic Monte Carlo Simulations to Model FRET and Photobleaching in Systems with Multiple Donor−Acceptor Interactions

“…Another potential application for the MCSs as described here, might be the simulation of FRET between a semiconductor nanoparticle (quantum dot) and an organic dye . In this case additional de-excitation paths and recombination paths are required to describe the intermittency in the quantum dot emission. − In conclusion, the Monte Carlo simulations proved to be a versatile method to model spatial and temporal fluorescence intensity fluctuations in microscopy with multiple applications in the future.…”

“…30 In this case additional de-excitation paths and recombination paths are required to describe the intermittency in the quantum dot emission. [31][32][33][34] In conclusion, the Monte Carlo simulations proved to be a versatile method to model spatial and temporal fluorescence intensity fluctuations in microscopy with multiple applications in the future.…”