Fig. 4: Characterization of single-particle CL emission.

a CL photon detection rate as a function of diameter (full width at half maximum (FWHM) from SE images) for NaHoF₄, NaDyF₄, NaSmF₄, and NaTbF₄ LNPs across the spectral filters matched to their primary emission peaks. Linear fits to the CL signal as a function of diameter are also shown. CL signal from non-emitting control NaGdF₄ LNPs is shown as black dots. b SNR of CL images for NaHoF₄, NaDyF₄, NaTbF₄, and NaSmF₄ LNPs when imaged through their respective spectral filters. The number of single LNPs imaged was 52, 46, 51, and 27, respectively. SNR from control (NaGdF₄) LNPs is shown as gray dots. 56, 36, 31, and 11 NaGdF₄ LNPs were imaged in Ho³⁺, Dy³⁺, Tb³⁺, and Sm³⁺ filters respectively. All LNPs were 18–23 nm in diameter. P-value was <0.001 (***) for all four LNP types in their respective filters. c Representative CL images with different SNRs. d Comparison of the nanocrystal size calculated using TEM (diameter of the circle fitted to nanocrystals) and SE (FWHM of the nanocrystals) images. A TEM image of nanocrystals is also shown. e Comparison of the CL detection rate from NaHoF₄ LNPs shown in (d) and control (NaGdF₄) LNPs. Representative SE and CL images of a NaHoF₄ LNP are also shown. f CL spectra of single LNPs (SE images on the right) and the corresponding ensemble spectra (gray). Scale bars: c 20 nm, d 10 nm, e 20 nm, f 50 nm. In (a) linear fits are of the form \(r={mx}+b\), where \(r\) is CL brightness in photons s⁻¹, \(x\) is the diameter of LNPs in nm, \(m\) is the slope in photons s⁻¹ nm⁻¹ and \(b\) is the y-intercept in photons s⁻¹. The fits are: Ho³⁺ filter: \(r=187x-2607\) (from 165 LNPs), Dy³⁺ filter: \(r=117x-1729\) (from 129 LNPs), Sm³⁺ filter: \(r=51x-770\) (from 28 LNPs), and Tb³⁺ filter: \(r=47x-543\) (from 83 LNPs). Error bars in b show mean and standard deviation. Source data are provided as a Source Data file.