CONTINUOUSLY EMISSIVE CORE/SHELL NANOPLATELETS

Abstract

The present invention relates to a core/shell nanoplatelet and its use as a fluorophore or a fluorescent agent.

Claims

1-15. (canceled)

16. A population of fluorescent colloidal nanoplatelets, each member of the population comprising an initial nanoplatelet comprising a core including a first semiconductor material or a core/shell including a first semiconductor material/second material and a shell including a second semiconductor material on the surface of the initial nanoplatelet, wherein the thickness of the shell is at least 3 nm and wherein the population exhibits fluorescence quantum efficiency decrease of less than 50% after one hour under light illumination.

17. The population of fluorescent colloidal nanoplatelets according to claim 16, wherein the population exhibits fluorescence quantum efficiency at 100 C. or above that is at least 80% of the fluorescence quantum efficiency of the population at 20 C.

18. The population of fluorescent colloidal nanoplatelets according to claim 16, wherein at least 40% of the nanoplatelets of the population are continuously emissive for a period of at least one minute.

19. The population of fluorescent colloidal nanoplatelets according to claim 16, wherein the shell of the nanoplatelet has a thickness of at least 5 nm.

20. The population of fluorescent colloidal nanoplatelets according to claim 16, wherein the shell of the nanoplatelet has a thickness of at least 6 nm.

21. The population of fluorescent colloidal nanoplatelets according to claim 16, wherein the shell of the nanoplatelet has a thickness of at least 8 nm.

22. The population of fluorescent colloidal nanoplatelets according to claim 16, wherein the shell of the nanoplatelet has a thickness of at least 10 nm.

23. The population of fluorescent colloidal nanoplatelets according to claim 16, wherein the material composing the core and the shell comprises a material M.sub.xE.sub.y wherein: M is selected from group Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, Vb, VIb, VIIb, VIII or mixtures thereof; E is selected from group Va, VIa, VIIa or mixtures thereof; and x and y are independently a decimal number from 0 to 5.

24. The population of fluorescent colloidal nanoplatelets according to claim 16, wherein the material composing the core and the shell comprises a material M.sub.xE.sub.y, wherein: M is Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or a mixture thereof; E is O, S, Se, Te, N, P, As, F, Cl, Br, I, or a mixture thereof; and x and y are independently a decimal number from 0 to 5.

25. A process of growth of a population of fluorescent colloidal nanoplatelets according to claim 16, comprising the steps of injecting the initial colloidal nanoplatelets in a solvent at a temperature ranging from 200 C. to 460 C. and subsequently a precursor of E or M, wherein said precursor of E or M is injected slowly in order to control the shell growth rate; and wherein the precursor of respectively M or E is injected either in the solvent before injection of the initial colloidal nanoplatelets or in the mixture simultaneously with the precursor of respectively E or M, wherein: M is selected from group Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, Vb, VIb, VIIb, VIII or mixtures thereof; E is selected from group Va, VIa, VIIa or mixtures thereof; and x and y are independently a decimal number from 0 to 5.

26. The process according to claim 25, wherein a fraction of the precursor's mixture is mixed with the initial colloidal nanoplatelets before injection in the solvent.

27. A fluorophore comprising a fluorescent colloidal nanoplatelet according to claim 16.

28. A detection system comprising the fluorescent colloidal nanoplatelet according to claim 16.

29. The detection system according to claim 28, wherein the detection system is an affinity assay, fluorescent staining, flow cytometry, nucleic acid sequencing, nucleic acid hybridization, nucleic acid synthesis or amplification, or molecular sorting.

30. An in vivo animal imaging method or an ex vivo live cells imaging method comprising providing the fluorescent colloidal nanoplatelet accord according to claim 16, and applying such fluorescent colloidal nanoplatelet to perform said imaging.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0258] FIG. 1 shows a) an absorption spectrum and b) an emission spectrum of CdSe/CdS core/shell nanoplatelets according to the present invention.

[0259] FIGS. 2A and 2B show TEM images of CdSe/CdS core/shell nanoplatelets with a shell thickness of 1.5 nm according to the present invention.

[0260] FIGS. 3A and 3B show TEM images of CdSe/CdS core/shell nanoplatelets with a shell thickness of 3 nm according to the present invention.

[0261] FIGS. 4A and 4B show TEM images of CdSe/CdS core/shell nanoplatelets with a shell thickness of 5.5 nm according to the present invention.

[0262] FIG. 5 shows a) an absorption spectrum and b) an emission spectrum of CdSe/CdZnS core/shell nanoplatelets according to the present invention.

[0263] FIG. 6 shows TEM images of CdSe/CdZnS core/shell nanoplatelets according to the present invention.

[0264] FIG. 7 shows a) an absorption spectrum and b) an emission spectrum of CdSe/ZnS core/shell nanoplatelets according to the present invention.

[0265] FIG. 8 shows TEM images of CdSe/ZnS core/shell nanoplatelets according to the present invention.

[0266] FIG. 9 shows the evolution of the absorption spectrum (black) and the emission spectrum (grey) of CdSe/CdZnS core/shell nanoplatelets according to the present invention after ligand exchange with a hydrosoluble polymer.

[0267] FIG. 10 shows the non-blinking fraction of CdSe/CdS core/shell nanoplatelets with a shell thickness of 3 nm according to the present invention (i.e. the fraction of continuously emissive nanoplatelets).

[0268] FIGS. 11A and 11B show the emission time trace and corresponding normalized fluorescence intensity distribution of a single CdSe/CdS core/shell nanoplatelets with a shell thickness of 3 nm according to the present invention (trace in black and background noise in grey).

[0269] FIG. 12 shows the non-blinking fraction of CdSe/CdS core/shell nanoplatelets with a shell thickness of 5.5 nm according to the present invention (i.e. the fraction of continuously emissive nanoplatelets).

[0270] FIGS. 13A and 13B show the emission time trace and corresponding normalized fluorescence intensity distribution of a single CdSe/CdS core/shell nanoplatelets with a shell thickness of 5.5 nm according to the present invention (trace in black and background noise in grey).

[0271] FIG. 14 shows TEM images of CdSe/CdS core/shell nanoplatelets with a shell thickness of 8.5 nm according to the present invention.

[0272] FIG. 15 shows the non-blinking fraction of CdSe/CdS core/shell nanoplatelets with a shell thickness of 8.5 nm according to the present invention (i.e. the fraction of continuously emissive nanoplatelets).

[0273] FIGS. 16A and 16B show the emission time trace and corresponding normalized fluorescence intensity distribution of a single CdSe/CdS core/shell nanoplatelets with a shell thickness of 8.5 nm according to the present invention (trace in black and background noise in grey).

[0274] FIG. 17 shows the measurement of the normalized fluorescence quantum efficiency coming from film of CdSe/CdZnS nanoplatelets according to the invention, quantum dots of the prior art or CdSe/CdZnS nanoplatelets of the prior art deposed on microscope glass slides. Films are excited using a Hg lamp, and the emitted light is collected with an oil objective (100, NA=1.4) and adapted filters (550 nm short-pass filter for the excitation and 590 nm long-pass filter for the emission).

[0275] FIG. 18 shows the measurement of the normalized fluorescence quantum efficiency coming from CdSe/ZnS nanoplatelets according to the invention, CdSe/CdS/ZnS quantum dots according to the prior art and CdSe/CdZnS nanoplatelets according to the prior art deposed on a glass slide in function of temperature. Films are excited with a laser at 404 nm.

EXAMPLES

Nanoplatelets Cores Preparations

Synthesis of CdSe 460 Nanoplatelets (NPLs)

[0276] 240 mg of Cadmium acetate (Cd(OAc).sub.2) (0.9 mmol), 31 mg of Se 100 mesh, 150L oleic acid (OA) and 15 mL of 1-octadecene (ODE) are introduced in a three neck flask and are degassed under vacuum. The mixture is heated under argon flow at 180 C. for 30 min.

Synthesis of CdSe 510 NPLs

[0277] 170 mg of cadmium myristate (Cd(myr).sub.2) (0.3 mmol), 12 mg of Se 100 mesh and 15 mL of ODE are introduced in a three neck flask and are degassed under vacuum. The mixture is heated under argon flow at 240 C., when the temperature reaches 195 C., 40 mg of Cd(OAc).sub.2 (0.15 mmol) are introduced. The mixture is heated for 10 minutes at 240 C.

Synthesis of CdSe 550 NPLs

[0278] 170 mg of Cd(myr).sub.2 (0.3 mmol) and 15 mL of ODE are introduced in a three neck flask and are degassed under vacuum. The mixture is heated under argon flow at 250 C. and 1 mL of a dispersion of Se 100 mesh sonicated in ODE (0.1M) are quickly injected. After 30 seconds, 80 mg of Cd(OAc).sub.2 (0.3 mmol) are introduced. The mixture is heated for 10 minutes at 250 C.

Synthesis of CdTe 428 NPLs

[0279] A three neck flask is charged with 130 mg of cadmium proprionate (Cd(prop).sub.2) (0.5 mmol), 80 L of OA (0.25 mmol), and 10 mL of ODE, and the mixture is stirred and degassed under vacuum at 95 C. for 2 h. The mixture under argon is heated at 180 C. and 100 L of a solution of 1 M Te dissolved in trioctylphosphine (TOP-Te) diluted in 0.5 mL of ODE are swiftly added. The reaction is heated for 20 min at the same temperature.

[0280] When 428 NPLs are prepared using Cd(OAc).sub.2, TOP-Te 1 M is injected between 120 and 140 C.

Synthesis of CdTe 500 NPLs

[0281] A three-neck flask is charged with 130 mg of Cd(prop).sub.2 (0.5 mmol), 80 L of OA (0.25 mmol), and 10 mL of ODE, and the mixture is stirred and degassed under vacuum at 95 C. for 2 h. The mixture under argon is heated at 210 C., and 100 L of a solution of 1 M TOP-Te diluted in 0.5 mL of ODE is swiftly added. The reaction is heated for 30 min at the same temperature.

[0282] When Cd(OAc)2 was used as cadmium precursor, TOP-Te is injected between 170 and 190 C.

Synthesis of CdTe 556 NPLs

[0283] 133 mg of Cd(OAc).sub.2 (0.5 mmol), 255 L of OA (0.8 mmol), and 25 mL of ODE are charged into a three-neck flask, and the mixture is stirred and degassed under vacuum at 95 C. for 2 h. The flask is filled with argon and the temperature is increased to 215 C. Then, 0.05 mmol of stoichiometric TOP-Te (2.24 M) diluted in 2.5 mL ODE is injected with a syringe pump at a constant rate over 15 min. When the addition is completed, the reaction is heated for 15 min.

Synthesis of CdS 375 NPLs

[0284] In a three neck flask 160 mg of Cd(OAc).sub.2 (0.6 mmol), 190 L (0.6 mmol) of OA, 1.5 mL of sulfur dissolved in 1-octadecene (S-ODE) 0.1M and 13.5 mL of ODE are introduced and degassed under vacuum for 30 minutes. Then the mixture is heated at 180 C. under Argon flow for 30 minutes.

Synthesis of CdS 407 NPLs

[0285] In a three neck flask 160 mg of Cd(OAc).sub.2 (0.6 mmol), 190 L (0.6 mmol) of OA, 1.5 mL of S-ODE 0.1M and 13.5 mL of octadecene are introduced and degassed under vacuum for 30 minutes. Then the mixture is heated at 260 C. under Argon flow for 1 minute.

Synthesis of Core/Shell (Crown) CdSe/CdS NPLs

[0286] In a three neck flask, 320 mg of Cd(OAc).sub.2 (1.2 mmol), 380 L of OA (1.51 mmol) and 8 mL of octadecene are degassed under vacuum at 65 C. for 30 minutes. Then CdSe nanoplatelets cores in 4 mL of ODE are introduced under Argon. The reaction is heated at 210 C. and 0.3 mmol of S-ODE 0.05M are added drop wise. After injection, the reaction is heated at 210 C. for 10 minutes.

Synthesis of Core/Shell (Crown) CdSe/CdTe NPLs

[0287] In a three neck flask, CdSe nanoplatelets cores in 6 mL of ODE are introduced with 238 L of OA (0.75 mmol) and 130 mg of Cd(prop).sub.2. The mixture is degassed under vacuum for 30 minutes then, under argon, the reaction is heated at 235 C. and 50 L of TOP-Te IM in 1 mL of ODE is added drop wise. After the addition, the reaction is heated at 235 C. for 15 minutes.

Synthesis of CdSeS alloyed NPLs

[0288] 170 mg of Cd(myr).sub.2 (0.3 mmol) and 15 mL of ODE are introduced in a three neck flask and are degassed under vacuum. The mixture is heated under argon flow at 250 C. and 1 mL of a dispersion of Se 100 mesh sonicated in S-ODE and ODE (total concentration of selenium and sulfur 0.1M) are quickly injected. After 30 seconds, 120 mg of Cd(OAc).sub.2 (0.45 mmol) are introduced. The mixture is heated for 10 minutes at 250 C.

Shells Growth

[0289] CdS Shell Growth with Octanethiol

[0290] In a three neck flask, 15 mL of trioctylamine (TOA) are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 300 C. under Argon and 5 mL of core nanoplatelets in ODE are swiftly injected followed by the injection of 7 mL of 0.1 M octanethiol solution in ODE and 7 mL of 0.1M Cd(OA).sub.2 in ODE with syringe pumps at a constant rate over 90 min. After the addition, the reaction is heated at 300 C. for 90 minutes.

CdS Shell Growth with Butanethiol

[0291] In a three neck flask, 15 mL of trioctylamine (TOA) are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 300 C. under Argon and 5 mL of core nanoplatelets in ODE are swiftly injected followed by the injection of 7 mL of 0.1 M butanethiol solution in ODE and 7 mL of 0.1M Cd(OA).sub.2 in ODE with syringe pumps at a constant rate over 90 min. After the addition, the reaction is heated at 300 C. for 90 minutes.

ZnS Shell Growth with Octanethiol

[0292] In a three neck flask, 15 mL of trioctylamine are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 300 C. under Argon and 5 mL of core nanoplatelets in octadecene are swiftly injected followed by the injection of 7 mL of 0.1 M octanethiol solution in octadecene and 7 mL of 0.1M zinc oleate (Zn(OA).sub.2) in octadecene with syringe pumps at a constant rate over 90 min. After the addition, the reaction is heated at 300 C. for 90 minutes.

ZnS Shell Growth with Butanethiol

[0293] In a three neck flask, 15 mL of trioctylamine are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 300 C. under Argon and 5 mL of core nanoplatelets in octadecene are swiftly injected followed by the injection of 7 mL of 0.1 M butanethiol solution in octadecene and 7 mL of 0.1M zinc oleate (Zn(OA).sub.2) in octadecene with syringe pumps at a constant rate over 90 min. After the addition, the reaction is heated at 300 C. for 90 minutes.

CdZnS Gradient Shell Growth with Octanethiol

[0294] In a three neck flask, 15 mL of trioctylamine are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 300 C. under Argon and 5 mL of core nanoplatelets in octadecene are swiftly injected followed by the injection of 7 mL of 0.1 M octanethiol solution in octadecene with syringe pumps at a constant rate and 3.5 mL of 0.1M Cd(OA).sub.2 in octadecene and 3.5 mL of 0.1M Zn(OA).sub.2 in octadecene with syringe pumps at variables rates over 90 min. After the addition, the reaction is heated at 300 C. for 90 minutes.

CdZnS Gradient Shell Growth with Butanethiol

[0295] In a three neck flask, 15 mL of trioctylamine are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 300 C. under Argon and 5 mL of core nanoplatelets in octadecene are swiftly injected followed by the injection of 7 mL of 0.1 M butanethiol solution in octadecene with syringe pumps at a constant rate and 3.5 mL of 0.1M Cd(OA).sub.2 in octadecene and 3.5 mL of 0.1M Zn(OA).sub.2 in octadecene with syringe pumps at variables rates over 90 min. After the addition, the reaction is heated at 300 C. for 90 minutes.

CdxZn1-xS Alloys Shell Growth with Octanethiol

[0296] In a three neck flask, 15 mL of trioctylamine are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 300 C. under Argon and 5 mL of core nanoplatelets in octadecene are swiftly injected followed by the injection of 7 mL of 0.1 M octanethiol solution in octadecene, 3.5 mL of 0.1M Cd(OA).sub.2 in octadecene and 3.5 mL of 0.1M Zn(OA).sub.2 in octadecene with syringe pumps at a constant rate over 90 min. After the addition, the reaction is heated at 300 C. for 90 minutes.

CdxZn1-xS Alloys Shell Growth with Butanethiol

[0297] In a three neck flask, 15 mL of trioctylamine are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 300 C. under Argon and 5 mL of core nanoplatelets in octadecene are swiftly injected followed by the injection of 7 mL of 0.1 M butanethiol solution in octadecene, (x)*3.5 mL of 0.1M Cd(OA).sub.2 in octadecene and (1x)*3.5 mL of 0.1M Zn(OA).sub.2 in octadecene with syringe pumps at a constant rate over 90 min. After the addition, the reaction is heated at 300 C. for 90 minutes.

CdZnS Shell Growth (Manufactured According to the Prior Art: Ambient Temperature Mahler et al. JACS. 2012, 134(45), 18591-18598)

[0298] 1 mL of CdSe 510 NPLs in hexane is diluted in 4 mL of chloroform, then 100 mg of thioacetamide (TAA) and 1 mL of octylamine are added in the flask and the mixture is sonicated until complete dissolution of the TAA (about 5 min). The color of the solution changed from yellow to orange during this time. 350 L of a solution of Cd(NO3)2 0.2 M in ethanol and 150 L of a solution of Zn(N03)2 0.2 M in ethanol are then added to the flask. The reaction was allowed to proceed for 2 h at 65 C. After synthesis, the core/shell platelets were isolated from the secondary nucleation by precipitation with a few drops of ethanol and suspended in 5 mL of chloroform. Then 100 L of Zn(NO3)2 0.2 M in ethanol is added to the nanoplatelets solution. They aggregate steadily and are resuspended by adding 200 L oleic acid.

ZnS Alternative Shell Growth

[0299] In a three neck flask, 15 mL of trioctylamine are introduced and degassed under vacuum at 100 C. Then the reaction mixture is heated at 310 C. under Argon and 5 mL of core nanoplatelets in octadecene mixed with 50 L of precursors mixture are swiftly injected followed by the injection of 2 mL of 0.1M zinc oleate (Zn(OA).sub.2) and octanethiol solution in octadecene with syringe pump at a constant rate over 80 min.

Effect of Ligand Exchange on Quantum Yield

[0300] Ligand Exchange Procedure (1-dodecanethiol)

[0301] Ligand exchange with 1-dodecanthiol have been done by treating 1 mL of core/shell nanoplatelets solution with 200 L of 1-dodecanethiol. Then the solution is left without stirring at 65 C. overnight. After, the exchanged nanoplatelets are washed by two successive precipitations by EtOH and resuspension in hexane (Table 1).

TABLE-US-00001 TABLE 1 Sample Native NPLs After ligand exchange.sup.1 NPLs CdSe/CdZnS 75% 69% NPLs CdSe/CdS/ZnS 72% 65% NPLs CdSe/ZnS 74% 72% NPLs CdSe/CdZnS of the prior art 58% 10% .sup.1Exchanged with 1-dodecanethiol.

Ligand Exchange Procedure (Polymerized Ligands)

[0302] 1 mg of Core/shell nanoplatelets in hexane are precipitated with ethanol and centrifuged. The supernatant is removed and the nanoplatelets are dispersed in 200 L of 3-mercaptopropionic acid (MPA). The mixture is sonicated to obtain a homogenous dispersion. The nanoplatelets dispersion is stored at 60 C. for 2 hours. Then the nanoplatelets are centrifuged and the MPA phase is discarded. The nanoplatelets are dispersed in DMF under sonication and 2 mg of potassium tert-butoxide are added and nanoplatelets dispersion is sonicated. The mixture is centrifuged and the DMF phase is discarded. The precipitated nanoplatelets are washed with ethanol and the nanoplatelets are dispersed in sodium tetraborate buffer. 200 L of aqueous solution of polymerized ligands, previously reduced 30 min with NaBH.sub.4, are added to nanoplatelets dispersion. The solution is stored at 60 C. overnight. The excess of free ligand and reagents are removed by Vivaspin. The evolution of the absorption spectrum and the emission spectrum of CdSe/CdZnS core/shell nanoplatelets after ligand exchange with a hydrosoluble polymer are for example shown in FIG. 9. In addition, Table 2 exhibits the percentage (%) of Quantum yield on NPLs exchanged with polymerized ligands the following day and after 2 months.

TABLE-US-00002 TABLE 2 Native After ligand 2 months after ligand Sample NPLs exchange.sup.1 exchange.sup.2 NPLs of the prior art 20% 7% N.A. NPLs CdSe/CdZnS 75% 69% 62% NPLs CdSe/ZnS 68% 65% 60% .sup.1Exchanged with polymerized ligands. .sup.2Stored at 4 C. in the dark in a concentration of 10 M.

Layered Material Preparation:

[0303] A solution of CdSeZnS nanoplatelets is first precipitated in air free glove box by addition of ethanol. After centrifugation the formed pellet is redispersed in chloroform solution. Meanwhile a solution at 30% in weight of Poly(maleic anhydride-alt-octadecene) (MW=40 kg.Math.mol.sup.1) in chloroform is prepared. Then the nanoplatelets solution is mixed with the polymer solution in a 1:1 volume ratio and the solution is further stirred. On an O.sub.2 insulating substrate (glass or PET) the solution nanoplatelets-polymer mixture is brushed and let dried for 30 min. Then UV polymerizable oligomer made of 99% of lauryl methacrylate and 1% of benzophenone is deposited on the top of the nanoplatelets film. A top substrate (same as the bottom substrate) is deposited on the system. The film is the polymerized under UV for 4 min. The layered material is then glued thanks to a PMMA solution dissolved in chloroform on a 455 nm LED from Avigo technology. The LED is operated under a constant current ranging from 1 mA to 500 mA.

[0304] Ensemble Measurements:

[0305] The nanoplatelets in hexane solution are diluted in a mixture of 90% hexane/10% octane and deposited by drop-casting on a glass substrate. The sample is visualized using an inverted fluorescent microscope. An area of the sample containing several nanoplatelets is excited using a Hg lamp, and the emitted light is collected with an oil objective (100, NA=1.4) and adapted filters (550 nm short-pass filter for the excitation and 590 nm long-pass filter for the emission). The emitted light of the sample can be observed on a CCD camera (Cascade 512B, Roper Scientific) or directly through the microscope eyepiece with the naked eyes. A movie of the illuminated field containing at least 100 nanoplatelets is recorded for 1 minute at 33 Hz frame rate. Using home-made software, the fluorescence intensity time traces of the emitting nanoplatelets are extracted as well as the noise of the background. By fixing an off threshold at 3 times the noise, the time of the first off event is computed for each time trace. Plotting the number of nanoplatelets which never went off over time give access to the global Non-blinking fraction of nanoplatelets over time.

[0306] Single Particle Measurements:

[0307] The fluorescence intensity emission of unique nanoplatelets are recorded on a confocal microscope (Microtime 200, Picoquant) and a Hanbury Brown and Twist setup based on two avalanche photodiodes (SPAD PDM, MPD, time resolution 50 ps). The photodetection signal is recorded by a HydraHarp 400 module (Picoquant). In this configuration, the studied nanocrystal is excited with a pulsed diode emitting at 405 nm. To obtain a single nanoplatelet spectrum, a part or the totality of the collected photons is sent to an Andor shamrock 750 spectrometer. The dispersion system is a prism, and the detector is a CCD camera (Cascade 512B, Roper Scientific). Typical time traces of single nanoplatelets are obtained by integrating the number of photons collected over 10 ms.

Photobleaching Measurements in Air

[0308] The nanoplatelets or quantum dots in hexane solution are diluted in a mixture of 90% hexane/10% octane and deposited by drop-casting on a glass substrate. The sample is visualized using an inverted fluorescent microscope. An area of the sample containing nanoplatelets or quantum dots as a concentration still allowing distinguishing single nanocrystals is excited using a Hg lamp, and the emitted light is collected with an oil objective (100, NA=1.4) and adapted filters (550 nm short-pass filter for the excitation and 590 nm long-pass filter for the emission). The emitted light of the sample can be observed on a CCD camera (Cascade 512B, Roper Scientific). An image of the illuminated field is taken every minute and the mean intensity of the film is normalized with the initial intensity, allowing to plot the mean intensity variations over time (see FIG. 17).

Fluorescence Stability Versus Temperature Measurement

[0309] The layered material preparation is described above. The layered material is heated via a hot plate at the desired temperature ranging from 20 C. to 200 C. and the fluorescence is measured using an optical fiber spectrometer (Ocean-optics usb 2000) under excitation with a laser at 404 nm. The measurements are taken after temperature stabilization (see FIG. 18).