Zhao et al. (ACS Nano 2013) used near-infrared Förster resonance energy transfer (FRET) imaging in tumor-bearing mice to show that quantum-dot-core self-assembled lipidic nanoparticles (SALNPs) rapidly lose their lipid corona after intravenous administration: the vascular lipid-dissociation half-life was about 42 minutes, and corona lipids first became associated with small plasma proteins and later migrated to HDL-sized lipoprotein fractions. That dissociation and trafficking kinetics were quantified for only one formulation (a CdTe/CdSe/CdS/ZnS core with a DSPE-PEG2000 lipid corona); the study proposed that dissociation may influence therapeutic payload delivery, and suggested either screening differently formulated SALNPs for improved stability or deliberately exploiting the exchange to transfer amphiphilic cargo to endogenous lipoprotein carriers. Because its size-fraction (FPLC) data resolve carrier size classes but not molecular identities, the specific plasma proteins or lipoprotein components mediating this rapid lipid exchange — and, likewise, the long-term retention and clearance of the inorganic cores, which were observed to aggregate in phagocytes but not followed long term — remain open questions. Later work resolved parts of this question — notably the drug–carrier compatibility principle, the strong formulation-class dependence of carrier integrity in vivo, and corona proteomics for related lipid nanocarriers — but the in vivo molecular mechanism of lipid-corona exchange and its controllable exploitation remain open, as current (2025–2026) lipid-nanoparticle PEG-shedding studies confirm.

Background

Self-assembled lipidic nanoparticles (SALNPs) are drug-delivery and molecular-imaging constructs in which a hydrophobic core — here a semiconductor quantum dot (QD), a nanocrystal whose emission color is set by its size — is wrapped in a self-assembled monolayer of amphiphilic lipids. The monolayer typically contains PEGylated lipids such as DSPE-PEG2000 (a phospholipid bearing a polyethylene glycol chain of 2000 Da) to stabilize the particle in water and slow its uptake by the mononuclear phagocyte system (MPS), the splenic and hepatic phagocytes that clear foreign particles from blood. Because such a corona is held together by non-covalent forces, its integrity in blood is not guaranteed: plasma is rich in proteins and lipoproteins (the HDL, LDL and VLDL particles that transport lipids and are coated by apolipoproteins), and classical work had already shown that plasma, through its high-density lipoprotein (HDL) fraction, disintegrates small unilamellar liposomes and transfers their phospholipids to lipoproteins (Scherphof and Morselt, 1984).

To observe such processes directly, Zhao and co-workers exploited Förster resonance energy transfer (FRET), the non-radiative transfer of excitation energy from a donor fluorophore to a nearby acceptor within a few nanometers: a 710 nm-emitting CdTe/CdSe/CdS/ZnS core/multi-shell QD served as donor and Cy7-labeled lipids embedded in the corona as acceptors, so that lipid loss from the particle appears as donor dequenching. Near-infrared (NIR) wavelengths were chosen to minimize tissue autofluorescence and absorption. An earlier in vitro study with the same design had already visualized lipid-exchange interactions between the nanoparticle corona and lipoproteins (Skajaa et al., 2010). In the 2013 in vivo study, dual-labeled SALNPs injected intravenously into nude mice bearing HCT116 colon-carcinoma xenografts accumulated in tumors within 30 minutes; intravital microscopy in dorsal window chambers yielded a vascular lipid-dissociation constant of 2.7×10−4 s−12.7\times10^{-4}\,\mathrm{s}^{-1} (half-life about 42 minutes); and fast protein liquid chromatography (FPLC), a size-based chromatographic separation of plasma components, showed that at 2 hours most corona lipids had left the particles and were associated with small plasma proteins (below 5 nm), while by 48 hours they resided mainly in HDL-sized fractions (5–10 nm). The inorganic cores aggregated in tumor and liver phagocytes, while the dissociated lipids trafficked to the kidneys and were partially renally cleared (Zhao et al., 2013).

The paper's own discussion delimits part of the open question: the reported dissociation behavior is valid only for the particular SALNP type studied; the consequences for payload delivery are proposed but unquantified; and prevention or exploitation of the exchange is only proposed. Because its FPLC data resolve carrier size classes but not molecular identities, the identity of the molecular carriers executing the exchange — and, likewise, the long-term fate of the cores, which were observed to aggregate in phagocytes but not followed long term — are open directions inferred from the study's data rather than explicitly delimited by it. Follow-up literature has since mapped parts of this space: in vitro lipid-exchange kinetics and activation energies on QD micelles (Zhao et al., 2014); low-affinity binding of individual plasma proteins to lipid-coated QDs measured by fluorescence correlation spectroscopy (FCS), a single-molecule technique that infers binding from diffusion statistics (Klapper et al., 2015); in vivo protein coronas on clinically used liposomes (Hadjidemetriou et al., 2015); quantitative integrity measurements of other self-assembled carriers in living animals (Bouchaala et al., 2016; Sun et al., 2018; Tao et al., 2020; Zhang et al., 2022); the drug–carrier compatibility principle for in vivo release (Zhao et al., 2016); a review of FRET approaches to nanomedicine biofate (Chen et al., 2019); and, in the mRNA-vaccine era, serum-induced PEG-lipid shedding from lipid nanoparticles (LNPs) and its dependence on PEG-lipid anchor chemistry (Niederkofler et al., 2025; Lu et al., 2026). What no study has yet delivered is the in vivo molecular identification of the exchange mediators, the formulation dependence of in vivo dissociation beyond the single formulation studied, or a strategy to prevent or exploit the exchange on this platform.

Problem Statement

The problem, as delimited and proposed by Zhao et al. (ACS Nano 2013), is to understand and control the in vivo lipid-corona exchange of self-assembled lipid-coated nanoparticles, taking the quantum-dot-core SALNP as the reference system. It comprises four jointly supporting parts serving one common objective — making the in vivo stability and payload fate of this carrier class rationally designable:

(1) Mediators: identify the specific plasma proteins or lipoprotein components that mediate the initial rapid lipid exchange between the SALNP corona and blood components after intravenous administration, and characterize the kinetics of the observed time-dependent migration of corona lipids from association with small plasma proteins (below roughly 5 nm) to HDL-sized carriers (5–10 nm). This direction is inferred from the source's FPLC size-fraction data, which resolve carrier size classes but not molecular identities.

(2) Generality: determine how the in vivo dissociation and component-trafficking kinetics depend on formulation parameters — core composition, lipid chemistry, PEG density, corona composition, and payload — beyond the single CdTe/CdSe/CdS/ZnS-core, DSPE-PEG2000-corona formulation originally studied, whose findings the source explicitly delimits as "valid only for the particular type of SALNPs studied".

(3) Functional consequences: quantify how in vivo dissociation affects therapeutic payload delivery efficiency (including cargo such as cholesterol-conjugated siRNAs — small interfering RNAs — or amphiphilic drugs that is intended to remain corona-associated), and establish the long-term retention and clearance behavior of the inorganic cores, whose aggregation and phagocytic sequestration the source observed but did not follow long term.

(4) Control: develop formulation or ligand strategies that either improve in vivo corona stability — following the source's suggestion to screen differently formulated SALNPs for compositions with improved stability — or exploit the exchange phenomenon, as the source proposes, to transfer amphiphilic agents from the carrier to endogenous lipoprotein carriers for delivery.

The four directions above are alternative, jointly supporting parts of the one common objective rather than a conjunctive checklist. The five parameters of Part 2 — core composition, lipid chemistry, PEG density, corona composition, and payload — describe the scope of the formulation space to be probed rather than a joint requirement, so a systematic dependence on one parameter may be established with the others held fixed; the two goals of Part 3 (payload-delivery consequence and long-term core retention/clearance) and the two components of Part 1 (identification of the mediating plasma proteins or lipoprotein components, and characterization of the migration kinetics) are likewise independent of each other.

References

  1. Yiming Zhao, Inge van Rooy, Sjoerd Hak, Francois Fay, Jun Tang, Catharina de Lange Davies, Mihaela Skobe, Edward Allen Fisher, Aurelian Radu, Zahi A. Fayad, Celso de Mello Donegá, Andries Meijerink, Willem J. M. Mulder. Near-Infrared Fluorescence Energy Transfer Imaging of Nanoparticle Accumulation and Dissociation Kinetics in Tumor-Bearing Mice. ACS Nano 2013, 7(11), 10362–10370. DOI: 10.1021/nn404782p, https://doi.org/10.1021/nn404782p
  2. G. Scherphof, H. Morselt. On the size-dependent disintegration of small unilamellar phosphatidylcholine vesicles in rat plasma. Evidence of complete loss of vesicle structure. Biochemical Journal 1984, 221(2), 423–429. DOI: 10.1042/bj2210423, https://doi.org/10.1042/bj2210423
  3. Torjus Skajaa, Yiming Zhao, Dave J. van den Heuvel, Hans C. Gerritsen, David P. Cormode, Rolf Koole, Matti M. van Schooneveld, Jan Andries Post, Edward A. Fisher, Zahi A. Fayad, Celso de Mello Donega, Andries Meijerink, Willem J. M. Mulder. Quantum Dot and Cy5.5 Labeled Nanoparticles to Investigate Lipoprotein Biointeractions via Förster Resonance Energy Transfer. Nano Letters 2010, 10(12), 5131–5138. DOI: 10.1021/nl1037903, https://doi.org/10.1021/nl1037903
  4. Yiming Zhao, Philipp Schapotschnikow, Torjus Skajaa, Thijs J. H. Vlugt, Willem J. M. Mulder, Celso de Mello Donegá, Andries Meijerink. Probing Lipid Coating Dynamics of Quantum Dot Core Micelles via Förster Resonance Energy Transfer. Small 2014, 10(6), 1163–1170. DOI: 10.1002/smll.201301962, https://doi.org/10.1002/smll.201301962
  5. Yvonne Klapper, Pauline Maffre, Li Shang, Kristina N. Ekdahl, Bo Nilsson, Simon Hettler, Manuel Dries, Dagmar Gerthsen, G. Ulrich Nienhaus. Low affinity binding of plasma proteins to lipid-coated quantum dots as observed by in situ fluorescence correlation spectroscopy. Nanoscale 2015, 7(22), 9980–9984. DOI: 10.1039/c5nr01694k, https://doi.org/10.1039/c5nr01694k
  6. Marilena Hadjidemetriou, Zahraa Al-Ahmady, Mariarosa Mazza, Richard F. Collins, Kenneth Dawson, Kostas Kostarelos. In Vivo Biomolecule Corona around Blood-Circulating, Clinically Used and Antibody-Targeted Lipid Bilayer Nanoscale Vesicles. ACS Nano 2015, 9(8), 8142–8156. DOI: 10.1021/acsnano.5b03300, https://doi.org/10.1021/acsnano.5b03300
  7. Redouane Bouchaala, Luc Mercier, Bohdan Andreiuk, Yves Mély, Thierry Vandamme, Nicolas Anton, Jacky G. Goetz, Andrey S. Klymchenko. Integrity of lipid nanocarriers in bloodstream and tumor quantified by near-infrared ratiometric FRET imaging in living mice. Journal of Controlled Release 2016, 236, 57–67. DOI: 10.1016/j.jconrel.2016.06.027, https://doi.org/10.1016/j.jconrel.2016.06.027
  8. Yiming Zhao, François Fay, Sjoerd Hak, Jose Manuel Perez-Aguilar, Brenda L. Sanchez-Gaytan, Brandon Goode, Raphaël Duivenvoorden, Catharina de Lange Davies, Astrid Bjørkøy, Harel Weinstein, Zahi A. Fayad, Carlos Pérez-Medina, Willem J. M. Mulder. Augmenting drug–carrier compatibility improves tumour nanotherapy efficacy. Nature Communications 2016, 7, 11221. DOI: 10.1038/ncomms11221, https://doi.org/10.1038/ncomms11221
  9. Sofie Snipstad, Sjoerd Hak, Habib Baghirov, Einar Sulheim, Ýrr Mørch, Sylvie Lélu, Eva von Haartman, Marcus Bäck, K. Peter R. Nilsson, Andrey S. Klymchenko, Catharina de Lange Davies, Andreas K. O. Åslund. Labeling nanoparticles: Dye leakage and altered cellular uptake. Cytometry Part A 2017, 91(8), 760–766. DOI: 10.1002/cyto.a.22853, https://doi.org/10.1002/cyto.a.22853
  10. Xuanrong Sun, Guowei Wang, Hao Zhang, Shiqi Hu, Xin Liu, Jianbin Tang, Youqing Shen. The Blood Clearance Kinetics and Pathway of Polymeric Micelles in Cancer Drug Delivery. ACS Nano 2018, 12(6), 6179–6192. DOI: 10.1021/acsnano.8b02830, https://doi.org/10.1021/acsnano.8b02830
  11. Zahraa S. Al-Ahmady, Marilena Hadjidemetriou, James Gubbins, Kostas Kostarelos. Formation of protein corona in vivo affects drug release from temperature-sensitive liposomes. Journal of Controlled Release 2018, 276, 157–167. DOI: 10.1016/j.jconrel.2018.02.038, https://doi.org/10.1016/j.jconrel.2018.02.038
  12. Tongkai Chen, Bing He, Jingsong Tao, Yuan He, Hailiang Deng, Xueqing Wang, Ying Zheng. Application of Förster Resonance Energy Transfer (FRET) technique to elucidate intracellular and In Vivo biofate of nanomedicines. Advanced Drug Delivery Reviews 2019, 143, 177–205. DOI: 10.1016/j.addr.2019.04.009, https://doi.org/10.1016/j.addr.2019.04.009
  13. Kaylin M. McMahon, Andrea E. Calvert, Irina S. Dementieva, Saber Hussain, John T. Wilkins, C. Shad Thaxton. Interparticle Molecular Exchange of Surface Chemical Components of Native High-Density Lipoproteins to Complementary Nanoparticle Scaffolds. ACS Sensors 2020, 5(10), 3019–3024. DOI: 10.1021/acssensors.0c01117, https://doi.org/10.1021/acssensors.0c01117
  14. Jinsong Tao, Zhengjie Wei, Yuan He, Xingyang Yan, Simon Ming-Yuen Lee, Xueqing Wang, Wei Ge, Ying Zheng. Toward understanding the prolonged circulation and elimination mechanism of crosslinked polymeric micelles in zebrafish model. Biomaterials 2020, 256, 120180. DOI: 10.1016/j.biomaterials.2020.120180, https://doi.org/10.1016/j.biomaterials.2020.120180
  15. Hao Zhang, Zhenyu He, Chaopeng Fu, Pan Pan, Yifeng Zhu, Meng Xu, Shengwei Deng, Guoqing Ying, Youqing Shen. Dissociation of polymeric micelle under hemodynamic shearing. Nano Today 2022, 45, 101517. DOI: 10.1016/j.nantod.2022.101517, https://doi.org/10.1016/j.nantod.2022.101517
  16. Chang Xu, Haoru Zhu, Kai Wang, Haitao Hu, Xuyong Wei, Dongdong Xu, Jing Zhang, Yanpeng Liu, Jun Chen, Youqing Shen, Nasha Qiu, Xiao Xu. Oral Celastrol Micelles Forming High-Density Lipoprotein Corona Targeting Hepatocytes for MASLD Treatment. Advanced Science 2025, 12(45), e00854. DOI: 10.1002/advs.202500854, https://doi.org/10.1002/advs.202500854
  17. Simon Niederkofler, Petteri Parkkila, Nima Aliakbarinodehi, Nima Sasanian, Gustav Emilsson, David Ulkoski, Celso J.O. Ferreira, Nicole Stéphanie Galenkamp, Bruno F.B. Silva, Dan Lundberg, Yujia Jing, Lennart Lindfors, Björn Agnarsson, Fredrik Höök. Effects of Serum Incubation on Lipid Nanoparticle PEG Shedding, mRNA Retention, and Membrane Interactions. ACS Applied Materials & Interfaces 2025, 17(47), 64219–64231. DOI: 10.1021/acsami.5c17052, https://doi.org/10.1021/acsami.5c17052
  18. Chuan-En Lu, Kai Liu, Audrey Gallud, Viktoriia Meklesh, Lisbeth Thorup Ravnkilde, Juna Santos, Filipa Dias Louro, Tasso Miliotis, Marco A. Alfonzo-Mendez, Joanna Rejman, Luca Panariello, Hanna M.G. Barriga, Molly M. Stevens, Fredrik Höök, Marianna Yanez Arteta, Johan Ulander, Suzy Jones, Alan Sabirsh. The Impact of Polyethylene Glycol Lipid Anchors on the Physicochemical Properties, Protein Corona, Function, and Biodistribution of Lipid Nanoparticles. ACS Nano 2026, 20(12), 9875–9890. DOI: 10.1021/acsnano.5c19757, https://doi.org/10.1021/acsnano.5c19757
  19. Babak Borhan, Amanda M. Murray, Amir Ata Saei, Bahareh Ghaffari, James E. Jackson, Naseeha Mohammed, Michael J. Mitchell, Hojatollah Vali, Kathryn A. Whitehead, Morteza Mahmoudi. Influence of protein aggregates, extracellular vesicles, and lipoprotein fusion on ionizable lipid nanoparticles protein corona analysis. Nature Communications 2026, 17, 5261. DOI: 10.1038/s41467-026-74240-4, https://doi.org/10.1038/s41467-026-74240-4