Nanoparticle synthesis
Core–shell-type β-NaYF4-based nanoparticles have been ready following a modified thermal decomposition protocol beforehand utilized in our laboratory26. For the core synthesis, 2 mmol of whole lanthanide acetates (Ln = Y3+, Yb3+, Er3+ or Tm3+, proportioned based on the specified doping ratios) have been combined with 18.25 ml of oleic acid and 20 ml of octadecene in a 250-ml three-neck flask. The combination was degassed below a vacuum at 110 °C for 1 h to take away residual moisture. Subsequently, 6.25 mmol of sodium oleate, 10 mmol of ammonium fluoride, 1.9 mmol of oleylamine (no oleylamine for 3+) and eight.75 ml of octadecene have been added, and the combination was stirred below a vacuum at 25 °C for 1 h. The response was then heated to 310 °C below a nitrogen stream and maintained for 50 min earlier than being quickly cooled. The ensuing core nanocrystals have been precipitated utilizing ethanol and centrifuged at 5,000g for five min. The pellet was additional washed with hexane and ethanol combination (1:1.5 quantity ration) adopted by one other spherical of centrifugation at 5,000g for five min. Lastly, the pellet was redispersed in 50 ml of hexane.
For shell progress, 2.4 ml of the core nanoparticle dispersion was combined with 4 ml of oleic acid and 6 ml of octadecene, and hexane was eliminated below a vacuum at 70 °C for 30 min. The answer was then heated to 290 °C below a nitrogen stream. Shell precursors (beforehand ready) have been added in three sequential injections at 15-min intervals as follows: (1) 0.50 ml of Y/Gd precursor; (2) 0.25 ml of sodium trifluoroacetate (NaTFA) answer and 0.40 ml of Y/Gd precursor; (3) 0.35 ml of NaTFA and 0.85 ml of Y/Gd precursor. After the ultimate injection, the response was held at 290 °C for 17 min after which quenched to room temperature. The nanoparticles have been purified by ethanol–hexane washing, as completed above. For the Tm3+ and Er3+ sequence of UCNP cores with totally different concentrations of Yb3+ and dopants, solely the primary three injection steps have been used. The purified core–shell nanoparticles have been dispersed in 5 ml of hexane. For nanoparticles with a better shell thickness, we elevated the injection rounds to get the specified shell thickness26.
The Y/Gd precursor was ready by heating 2 mmol of yttrium acetate and 0.5 mmol of gadolinium acetate in 10 ml of oleic acid and 15 ml of octadecene below a vacuum at 110 °C for 15 min. The combination was then heated to 160 °C for 30 min below a nitrogen stream and subsequently cooled to room temperature. The NaTFA answer was obtained by dissolving 6 mmol of NaTFA in 15 ml of oleic acid below a vacuum at 50 °C till absolutely dissolved.
Floor functionalization
For floor modification, 1 ml of as-prepared core–shell nanoparticles was dried below a vacuum and combined with 150 mg of poly(maleic anhydride-alt-1-octadecene) (PMAO) dissolved in 10 ml of chloroform64. The response was stirred for 1.5 h at room temperature, after which chloroform was eliminated below a vacuum. The particles have been redispersed by sonication in 10 ml of 100-mM NaF answer containing 150 mg of 4-(dimethylamino) pyridine and centrifuged at 32,000g for two h. The precipitate was washed as soon as with NaF answer to take away extra reagents and dispersed in 3 ml of 1× PBS supplemented with 100 mM of NaF.
For HaloTag ligand conjugation, 1.5 ml of PMAO-coated nanoparticles was combined with 6 µl of 350-mM methyl-PEG-amine (MA(PEG)24-NH2) and eight µl of 8-mM HaloTag ligand-PEG-amine below stirring. Then, 30 mg of EDC dissolved in 100 µl of 1× PBS was added, and the response proceeded for two h. One other 30 mg of EDC and 6 µl of 350-mM MA(PEG)24-NH2 have been then added and reacted for two h. The ensuing ligand-conjugated nanoparticles have been centrifuged at 20,000g for two h. The supernatant containing principally monodispersed-ligand-conjugated nanoparticles was then concentrated and washed utilizing an Amicon 100-kDa centrifugal filter.
The HaloTag-PEG-amine conjugate was ready in two sequential reactions55. In step one, 150 µl of 10-mM HaloTag Ligand Constructing Blocks Amine (O4) dissolved in anhydrous DMF was mixed with 15 µl of 100-mM succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate and 1 µl of triethylamine. The response combination was incubated in a single day at 37 °C to permit for the formation of a maleimide-activated intermediate. Subsequently, 10 µl of 150-mM SH-PEG-NH2 in anhydrous DMF was added, and the response was continued for 10 h at room temperature. The ultimate product was saved at −20 °C till additional use.
Electron microscopy measurement
TEM was used to characterize the morphology and dimension distribution of the synthesized nanoparticles. The TEM photographs have been acquired on an FEI Tecnai G2 Spirit Twin microscope operated at an accelerating voltage of 120 kV. A number of micrographs have been collected for every pattern to make sure statistical accuracy. The particle dimension distributions of each core and core–shell samples have been obtained by measuring the projected space of at the least 700 particular person nanoparticles and changing it to the corresponding equal diameter. The imply particle diameter and normal deviation have been then calculated, and the distinction between the core and core–shell imply diameters was used to estimate the shell thickness. Consultant TEM photographs and the corresponding dimension histograms for core and core–shell nanoparticles are proven in Supplementary Figs. 2, 3, 5 and 6, whereas Supplementary Fig. 10 presents the consultant photographs and dimension distributions of HaloTag-ligand-conjugated nanoparticles.
For correlative measurements, SEM was carried out on the identical FOV beforehand imaged optically. The UCNP samples have been ready on an ibidi gridded glass coverslip with a 50-µm grid. A 50-µl aliquot of poly-L-lysine answer (0.1% w/v in water) was first utilized to the coverslip and rinsed after 1 min to type a layer that promotes nanoparticle attachment and minimizes lateral motion. The nanoparticle dispersion was then added and unbound or loosely adsorbed particles have been eliminated by washing with hexane. After drying, optical imaging was carried out, and the grid coordinates of the imaged areas have been recorded for correlation. The identical slide was then coated with a skinny Au–Pd alloy (~3–4 nm in thickness) layer by sputtering to arrange it for SEM measurement. SEM imaging was performed utilizing a ZEISS Gemini 450 microscope geared up with an in-lens secondary electron detector.
Structural and chemical characterization
For the structural characterization of the optimized U-STORM probes, we carried out X-ray diffraction measurements. First, the samples have been concentrated by evaporating 600 µl of every UCNP dispersion to dryness adopted by redispersion in 50 µl of hexane. The ensuing concentrated answer was then drop forged onto cleaned glass slides and air dried to type uniform skinny movies. X-ray diffraction measurements have been carried out utilizing a PANalytical X’Pert diffractometer geared up with a Cu Kα1 radiation supply (λ = 1.54056 Å). Knowledge have been collected within the Bragg–Brentano geometry utilizing a 2θ–ω scan configuration. The obtained diffraction patterns have been in contrast with the reference knowledge from the Worldwide Centre for Diffraction Knowledge. All samples exhibited attribute peaks similar to the hexagonal β-phase NaYF4 crystal construction, confirming profitable synthesis (Supplementary Fig. 1)
The fundamental compositions and dopant ratios of the optimized U-STORM probes have been decided by inductively coupled plasma (ICP) optical emission spectroscopy. Roughly 5 mg of every dried nanoparticle pattern was used, assuming an natural mass fraction of ~50%. Every pattern was dissolved in 3% (v/v) aqueous nitric acid ready from ICP-grade reagents to yield a ultimate focus of 10 mg ml−1. The calibration requirements for particular person lanthanide components have been obtained from Agilent and used to generate normal curves for quantitative evaluation. The measured elemental concentrations (ppm) have been transformed to relative molar percentages to find out the lanthanide composition of every pattern (Supplementary Desk 4). The reported values characterize the general stoichiometry of the nanoparticles and don’t distinguish between the core and shell compositions.
Large-field microscopy setup
Large-field imaging was carried out on a custom-built microscope geared up with two diode lasers, as described beforehand: a 976-nm fibre-coupled laser (Thorlabs, BL976-PAG900) and a 638-nm free-space laser (Cobolt, 06-MLD)26. The 976-nm NIR excitation beam was mirrored by a 950-nm dichroic mirror into an upright Nikon ×60 oil-immersion goal (numerical aperture, 1.49), onto which the pattern was mounted. A motorized mirror allowed the excitation beam to be displaced laterally on the again focal airplane of the target, enabling fast switching between epifluorescence and whole inside reflection fluorescence (TIRF) illumination modes (Mad Metropolis Labs, TIRF Module). For all of the measurements, the samples have been illuminated within the epifluorescence mode with an influence density of ~20 kW cm−2. Fluorescence emission was collected via the identical goal, handed via the 950-nm dichroic mirror and centered by a 400-mm tube lens via a 950-nm short-pass filter. The emission beam then handed via an iris aperture and right into a light-tight detection field, the place it was spectrally divided into 4 channels utilizing dichroic mirrors at 510, 610 and 705 nm. Every channel was collimated with a 255-mm lens and recombined utilizing a symmetric set of dichroics (Supplementary Fig. 13). The emission was lastly centered by a 300-mm lens, leading to a calibrated picture scale of 100 nm per pixel. The 4 spectrally separated photographs have been directed to occupy distinct quadrants on the digital camera detector (Andor Solis iXon Extremely 897 electron-multiplying charge-coupled system), with the iris adjusted to stop crosstalk between channels. For single-colour imaging, solely the blue or NIR or purple emission channels similar to the UCNPs have been recorded, whereas for multicolour super-resolution imaging, each blue and purple channels have been acquired concurrently. The 638-nm laser was directed right into a micromirror meeting positioned under the again port of the target at an angle producing whole inside reflection on the pattern interface (Mad Metropolis Labs, RM21 MicroMirror TIRF, MCL TIRF Lock module). The mirrored beam was captured by the micromirrors and centered on a quadrant photodetector. When axial drift (z) happens throughout TIRF illumination, the mirrored beam angle modifications, resulting in a shift in illumination within the quadrants of the photodiode. This shift could be calibrated to replicate the axial drift and used afterwards to actively monitor and proper axial (z) drift, making certain steady focus throughout prolonged imaging classes. All lenses have been sourced from Thorlabs and are AB coated. Dichroics have been sourced from Semrock (AVR optics). The microscope stage and emission-path optomechanics have been sourced from Mad Metropolis Labs. Mirror mounts have been sourced from Newport Company, and all different optic components have been sourced from Thorlabs.
Cell tradition
U2OS human osteosarcoma cells (HTB-96, ATCC) have been maintained in Dulbecco’s modified Eagle’s medium (DMEM; Life Applied sciences) supplemented with 10% fetal bovine serum (Sigma-Aldrich) and 1× penicillin–streptomycin (Life Applied sciences). Cells have been cultured at 37 °C in a humidified incubator below 5% CO2. Cultures have been routinely screened for mycoplasma contamination to make sure cell-line integrity.
Plasmid development and lentivirus transduction
To generate HaloTag7-EGFR (HaloTag-EGFR) fusion constructs, the HaloTag7 coding sequence was cloned in-frame with EGFR right into a pSin lentiviral expression vector55. Lentiviral particles have been produced by the transient transfection of HEK293T packaging cells utilizing Lipofectamine 3000 (Life Applied sciences) in an Opti-MEM medium (Life Applied sciences), following the producer’s protocol. The medium was changed with a normal progress medium after 6 h, and viral supernatants have been collected and filtered at 48 h and 72 h post-transfection. For steady expression, U2OS cells at 60%–70% confluency have been incubated with the viral supernatant for 4 h, adopted by restoration in a whole medium and subsequent choice with 1 µg ml−1 of puromycin (Life Applied sciences) for 3–5 days. The ensuing U2OS-HaloTag-EGFR cell line was maintained below puromycin choice for downstream labelling and imaging experiments.
EGFR labelling and cell imaging with U-STORM workflow
For live-cell labelling, cells have been first blocked with 1% (w/v) casein answer (Sigma) ready in DMEM for five min to reduce non-specific binding. Subsequently, the nanoparticle combination containing 5 nM of each blue- and red-emitting HaloTag-ligand-conjugated U-STORM probes dispersed in 1% casein and DMEM have been added, and the cells have been incubated at 37 °C in 5% CO2 for five min. After that, unbound nanoparticles have been eliminated by washing with 1% casein and DMEM. For EGFR activation with EGF, we added 100-nM EGF in DMEM post-washing and incubated for five min. Subsequent, we fastened the cells utilizing 4% paraformaldehyde answer (Electron Microscopy Sciences) for 15 min at room temperature. The samples have been then washed with 1× PBS 3 times earlier than imaging. After that, an optimized focus of PMAO-coated non-blinking UCNPs dispersed in 1× PBS answer was added to the system and used as fiducial markers for drift correction. For U-STORM imaging on the cell pattern, an acquisition charge of 300 ms per body was used with an excitation energy of ~20 kW cm−2. Each blue and purple channels have been recorded concurrently with a single excitation with out utilizing any imaging buffers or exterior modulations. The focal airplane was positioned on the basal membrane of the cell and maintained all through every imaging session.
U-STORM evaluation
All of the STORM movies have been recorded utilizing the Andor Solis software program (iXon Extremely, Solis model: 4.31.30024.0) with a 300 electron-multiplying achieve and 300-ms publicity time. After producing a stack of .tiff recordsdata from the video, the localizations of the particles current within the ON state are carried out utilizing the MATLAB software program SLIMfast2 (ref. 65). The localization parameters have been saved fixed between movies and situations (Supplementary Desk 3), besides the ‘Depth Threshold’ parameter that was modified on a case-by case foundation to account for various background ranges and keep away from any crosstalk. After accumulating the localizations from all of the particles from all of the frames, the following step was to carry out drift correction. For drift correction, we used our brilliant non-blinking co-doped UCNPs, which emit photons in each blue and purple channels as fiducial markers. First, we measured the drift for every body from all of the markers current within the FOV. Subsequent, we calculate the typical drift per body by taking a mean of the drifts related to every marker. Then, we subtract this common drift from the uncooked localization dataset to acquire the drift-corrected localization clusters (Supplementary Fig. 14).
Picture registration between the blue and purple channels was carried out utilizing the localization centroids of fiducial markers. A world affine transformation matrix was first generated by analysing the positions of a number of fiducial markers positioned close to the measured FOV66. After making use of this international correction, a neighborhood affine transformation matrix was constructed utilizing fiducial markers throughout the identical FOV to refine the alignment between channels. Following drift correction and picture registration, particular person localization clusters have been recognized utilizing the density-based spatial clustering of purposes with noise (DBSCAN) algorithm applied in MATLAB. Every detected cluster was then fitted with a 2D Gaussian mannequin to find out its centroid place. In circumstances the place two clusters have been in shut proximity and partially overlapped, depth thresholding was utilized to separate localizations similar to totally different depth regimes, permitting impartial localization and centroid extraction for every emitter.
Blinking evaluation
Blinking parameters, together with obligation cycle, PPS values, ON–OFF dwell occasions and statistical growing older, have been calculated from the depth–time traces of single UCNPs. A threshold depth was utilized to separate ON and OFF occasions. The edge was usually chosen as an depth worth increased than the imply of the low-intensity distribution, similar to roughly three to 4 occasions its normal deviation. Any depth above this threshold depth worth is taken into account as an ON occasion. For probes that exhibited pure blinking, the OFF states matched the background sign. In circumstances the place flickering occurred and the lowest-intensity stage didn’t coincide with the background, the lowest-intensity state was handled because the OFF state, and the brink was decided accordingly. After ON and OFF occasions have been recognized, the obligation cycle was computed because the fraction of the full acquisition time spent within the ON state. The PPS values have been obtained by changing electron-multiplying charge-coupled system counts to photon numbers utilizing the calibration issue, adopted by calculating the typical variety of photons emitted per second throughout ON occasions.
Statistics and reproducibility
No statistical methodology was used to predetermine the pattern dimension. No knowledge have been excluded from the analyses. The experiments weren’t randomized. The investigators weren’t blinded to allocation throughout experiments and consequence evaluation.
Reporting abstract
Additional data on analysis design is offered within the Nature Portfolio Reporting Abstract linked to this text.