Over the past forty years, in terms of performanceespeciallyThe rapid development of nanotechnology based on nanomaterials has penetrated into various industries. At present, the two major scientific challenges facing nanotechnology are: 1) nanomaterials or nanostructures due tonano effectHowever, the excellent performance assigned to it is always difficult to fully exert; 2) The stability of nanomaterials in long-term applications. Quantum dots (QDs) are crystalline nanoparticles that exhibit size dependent properties due to the quantum confinement effect of electronic states, and possess fluorescent dyes and fluorescent proteinsQDs, with their high brightness and excellent photochemical stability, are currently ideal markers for highly sensitive single-molecule detection. However, QDs have high surface energy, are prone to non-specific adsorption, and have poor colloidal stability. Polymer coated quantum dots (QDs) fluorescent nanospheres (FNs) not only compensate for these shortcomings, but also improve the sensitivity of biomedical detection.

Recently, Professor Pang Daiwen from Nankai University visitedJournal of the American Chemical Society（JACS, IF=16.38）Publish important academic achievements in magazines,In response to the problem of low photoluminescence quantum yield (PLQY) of FNs (even when using QDs with almost 100% PLQY to prepare FNs, the PLQY cannot exceed 65%, and the high brightness advantage of QDs cannot be fully utilized), research is conducted and a control strategy is developed in an attempt to achieve a breakthrough.

The Pang Daiwen team discovered that the reason for the decrease in PLQY during the preparation of FNs by free radical polymerization is:

Figure 1. a.¹H NMR spectra, where * represent the chemical shift signal of caped ligands; b. Normalized electron paramagnetic resonance (EPR) spectra, using DMPO as a spin-rapping agent; c. Illustration of the influence of free radicals (R•) on the capped ligands.

From the nuclear magnetic resonance spectrum, it can be seen that after embedding QDs in the sphere, the coordination signal of oleic acid is still retained, the carbon carbon double bond signal is significantly weakened, and the coordination signal of thiol group almost disappears. Combined with the electron spin resonance spectrum, the double bond on oleic acid is triggered by free radicals and reacts with styrene to graft polystyrene. Further combined with mass spectrometry analysis, products from various stages of chain transfer reaction were detected where thiol ligands were gradually oxidized and eventually shed. Therefore, oleic acid has stronger coordination stability during free radical polymerization, and it is necessary to exchange thiol ligands with it.

Figure 3. a, b. XPS spectrum of QD micelles (M2) treated by KPS; c. PLQY of extracted QDs and their FNs developed with different concentration KPS; d.TEM images of FNs evolved with increasing concentration KPS (mg/mL), all scale bars are 50 nm; e. Illustration of the formation procedure of FNs.

Although QDs coordinated with pure oleic acid, the free radicals generated by initiator decomposition can still oxidize the ZnS confined shell of QDs, resulting in defects that cause non radiative transitions. By precisely controlling the concentration of the initiator, the PLQY of FNs can be improved to a certain extent while forming nanospheres, but it is still lower than that of the original QDs. This is because during the polymerization process, the compatibility between oleic acid ligands and (poly) styrene is poor, resulting in their aggregation within the sphere, and the energy transfer/self absorption generated makes it difficult for QDs to fully utilize their high brightness.

Figure 4. Characterization of cross-linked FNs (cFNs) with different mass ratio between DVB and St + DVB: a. TEM images of cFNs with different mass ratio, scale bars: 100 nm; b. PLQY; c. Normalized femtosecond transient absorption kinetics decay profiles detected at 400 nm of QDs, FNs, and cFNs; d. Time-resolved fluorescence spectra of QDs (t₁= 22.4 ns, 85.2%; t₂= 77.6 ns, 14.8%), FNs (t₁= 4.1 ns, 23.8%; t₂= 16.0 ns, 62.9%; t₃= 79.0 ns, 13.3%) and cFNs (t₁= 18.2 ns, 85.5%; t₂= 65.1 ns, 14.5%); e. Illustration of the formation procedure of cFNs.

The research team is working on DLS andNanoflowWhen accurate data could not be provided, the NanoCoulter particle size analyzer was used to obtain characterization data highly consistent with TEM, and the article was successfully published. Congratulations!