Claudine Nì. Allen

Air-Stable Near-Infrared AgInSe2 Nanocrystals

We present the synthesis of air-stable AgInSe2 nanocrystals via thermolysis of an Ag-In-thiolate complex followed by an anion exchange reaction. Evolution of the Ag:In:Se ratio with the reaction time demonstrates progressive incorporation of In(3+) in β-Ag2Se seeds. While their lattice stays in the metastable orthorhombic crystal structure, the final AgInSe2 nanocrystal shape can be spherical, pyramidal, or prismatic depending on reaction conditions. These nanocrystals emit from trap states between 800 and 1300 nm, which is a biologically and technologically important near-infrared range, with a photoluminescence quantum yield up to an order of magnitude of 21%. The appearance of a shoulder within the photoluminescence spectra between 845 and 890 nm is correlated to the presence of prismatic nanocrystals.

Whispering gallery mode sensing with a dual frequency comb probe

Silica microspheres are probed with a dual comb interferometry setup. The impulse responses of these microresonators are measured with a temporal resolution smaller than 400 fs over more than 200 ps. The amplitudes and phases of the impulse responses are interpreted as providing sensing information. The more familiar transmission spectra corresponding to the measured impulse responses are also calculated and shown. Sensing is demonstrated by varying the concentration of isopropanol in de-ionized water surrounding the microsphere and by binding bovine serum albumin on the silanized microsphere surface.

Water-dispersable colloidal quantum dots for the detection of ionizing radiation

Fluorescent CdSe-CdS-Cd0.5Zn0.5S-ZnS core-shell colloidal quantum dots (cQDs) dispersed in aqueous and organic solvents have been prepared and used as scintillators for detecting ionizing radiation. Results demonstrate a linear relationship between emitted luminescence and dose-activity. These results suggest that cQDs alone could be used as liquid scintillators for specific environmental and medical applications.

Telegraphic noise in transport through colloidal quantum dots.

We report measurements of electrical transport through single CdSe/CdS core/shell colloidal quantum dots (cQDs) connected to source and drain contacts. We observe telegraphic switching noise showing few plateaus at room temperature. We model and interpret these results as charge trapping of individual trap states, and therefore we resolve individual charge defects in these high-quality low-strain cQDs. The small number of observed defects quantitatively validates the passivation method based on thick CdS shells nearly lattice-matched to CdSe cores first developed to suppress photoluminescence blinking. Finally, we introduce a figure of merit useful to efficiently distinguish telegraphic noise from noise with a Gaussian distribution.

Morphological control of hybrid polymer-quantum dot solar cells with electron acceptor ligands

We integrate the electro-attractive conjugated molecule tetrafluoro-tetracyano-quinodimethane (F4TCNQ) in the active layer of polymer-CdSe colloidal quantum dot (cQD) solar cells. The addition of this molecule enhances cQD dispersion inside the polymer. In tuning its concentration, we can optimize the active layer morphology for charge separation and transport. A smoother morphology is likely the result of polymer chain adsorption on cQDs via F4TCNQ which increases the steric barrier between cQDs. Our most optimized device has a F4TCNQ:cQDs weight ratio of 0.5% improving the power conversion efficiency by a factor ∼2.3.

Near-infrared emitting AgInTe2 and Zn-Ag-In-Te colloidal nanocrystals

The synthesis of AgInTe2 nanocrystals emitting between 1095 nm and 1160 nm is presented. Evolution of the Ag:In:Te ratio shows progressive incorporation of In3+ in Ag2Te, leading to the formation of orthorhombic AgInTe2. When zinc is added to the synthesis, the photoluminescence quantum yield reaches 3.4 %.

Differentiation Between Analyte Adsorption and Homogenous Index Sensing in WGM Biodetection

We propose new parameters to characterize a whispering gallery mode spectrum, which can be regarded as reliable independent biodetection indicators for an instantaneous microspheres spectrum. With these parameters, since there is no need for spectral comparison to an analyte-free reference, three-dimensional stirring of fluorescent microspheres in fluidic setup is allowed. Through an analysis of fluorescent microspheres in the presence of bacterial spores, we found five insightful quantitative independent parameters for biodetection. Unveiled by this analysis, we demonstrate the possibility to discriminate between analyte presence and homogeneous variation of the solutions refractive index.

Dielectric resonating microspheres for biosensing: An optical approach to a biological problem

Detecting and identifying biomolecules or microorganisms in aqueous solutions are often a complex task requiring precious amounts of time. Decreasing this time while reducing costs and minimizing complexity is crucial for several applications in the life sciences and other fields and is the subject of extensive work by biologists and biomedical engineers around the world. Optical sensors, more specifically dielectric microspheres, have been proposed as suitable sensors for viruses, bacteria, and other biological analytes. This paper reviews initial key publications as well as the latest progress regarding such microspheres and their potential use as biological sensors. We cover recent work on fluorescent microspheres and their integration in microfluidic devices, while addressing the limitations and practical requirements of such biodiagnostics. Our aim in this paper is to appeal to both biologists and physicists, even if new to this field. We conclude by briefly suggesting ways of integrating dielectric microspheres and biosensing into college and university courses in both physics and in biology.Detecting and identifying biomolecules or microorganisms in aqueous solutions are often a complex task requiring precious amounts of time. Decreasing this time while reducing costs and minimizing complexity is crucial for several applications in the life sciences and other fields and is the subject of extensive work by biologists and biomedical engineers around the world. Optical sensors, more specifically dielectric microspheres, have been proposed as suitable sensors for viruses, bacteria, and other biological analytes. This paper reviews initial key publications as well as the latest progress regarding such microspheres and their potential use as biological sensors. We cover recent work on fluorescent microspheres and their integration in microfluidic devices, while addressing the limitations and practical requirements of such biodiagnostics. Our aim in this paper is to appeal to both biologists and physicists, even if new to this field. We conclude by briefly suggesting ways of integrating dielectric ...

Robust shell passivation of CdSe colloidal quantum dots to stabilize radioluminescence emission

Systematic characterization of semiconductor colloidal quantum dots (cQDs) response to ionizing radiation must be performed to use them in radiation detection. In this study, the robustness of multi-shell (MS) and core/shell (CS) cQDs was investigated under irradiation. Radioluminescence (RL) measurements with kV and MV photon beams revealed a better resistance of MS cQDs to ionizing radiation, with their spectra fluctuating by barely ∼ 1 nm. A systematic signal recovery between subsequent irradiations was noticed for MS cQDs only. A beam energy dependence of the RL stability was detected between kV and MV energies. At the same point of dose cumulated, the RL signal loss for the kV beams was observed to be ∼6-7% smaller than that of the MV beam, for both types of cQDs. These results demonstrate that MS cQDs are better candidates as ionizing radiation sensors than CS cQDs, especially in the kV energy range.

Characterization of a binary system composed of luminescent quantum dots for liquid scintillation

Scintillation dosimetry has evolved towards utilizing 3D liquid dosimeters to perform quality assurance verification of complex treatment configuration for photon, electron and proton beams. However, most of the fluorophores utilized in these dosimeters are alike and present limitations. This study aims to establish the profile of CdSe colloidal quantum dots (cQDs) that were given the role of the fluorophore in a binary liquid scintillation system. We chose to investigate the cQDs because of their wide absorption spectrum, the tunability of their absorption and emission spectra with respect to their size and composition, and their ability to function as an effective energy transfer intermediate. The scintillation intensity and spectral response of three organic solvent-based liquid cQD dispersions have been investigated upon irradiation with kV and MV photon beams. The solvents used to disperse the cQDs were hexane, toluene and linear alkylbenzene. The scintillation efficiency of the cQD dispersions has proven to be dependent on the nature of the solvent, the alkylbenzene cQD liquid dispersion having the brightest light emission of the three solutions, for an equivalent deposited dose in the scintillator. Its light output was found to reach a tenth of the light intensity of a commercial liquid scintillator, Ultima Gold, irradiated under the same conditions. This cQD dispersion also demonstrated a remarkable energy transfer to the cQDs, only 5% of its intensity being due to Cherenkov light production in the solvent. Overall, these results indicate that the alkylbenzene cQD liquid dispersion could be the best choice for a potential cQD-based liquid scintillator.