> ## Content Index
> Fetch the complete content index at: https://research-pop.com/llms.txt
> Use this file to discover other available public pages before exploring further.

# ETH Zurich and Empa team use single-particle FRET to map the ligand shell of perovskite quantum dots
- URL: https://research-pop.com/shanghai-jiao-tong-university-led-team-stabilizes-efficient-perovskite-modules-with-a-self-passivated-composite-oxide-buffer-2/
- Published: 2026-09-21T15:27:37.000Z
- Updated: 2026-09-21T15:27:37.000Z
- Author: ResearchPOP
- Tags: Materials Science

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-21-at-17.08.57.png)

Source: [https://advanced.onlinelibrary.wiley.com/doi/10.1002/adma.75051](https://advanced.onlinelibrary.wiley.com/doi/10.1002/adma.75051?ref=research-pop.com)

## At a glance

The inorganic core of a colloidal quantum dot can be imaged at atomic resolution, yet the soft and disordered organic ligands surrounding it remain difficult to see directly. These ligands still shape almost every stage of a quantum dot's life, from synthesis and stabilization to light emission, electronic coupling and interactions with photocatalytic reactants.

Researchers at ETH Zurich and Empa combined single-particle photoluminescence spectroscopy with single-molecule Förster resonance energy transfer, or FRET, to turn a dye-tagged ligand into a molecular ruler for the shell of individual CsPbBr₃ perovskite quantum dots. Across about 200 quantum-dot–dye pairs, the inferred donor–acceptor distances spanned roughly 3.5–8 nm. Measurements with several probes on the same particle showed that local differences within one quantum dot can account for the heterogeneity observed across the sample.

Changing the chemistry of the surrounding ligand tails shifted the average dye-to-surface separation from about 0.25 to 1.02 nm. Atomistic modelling produced a comparable range and led the authors to identify local ligand coverage as a primary source of the measured variation. The work provides an experimental way to examine organic quantum-dot surfaces one particle and one molecular probe at a time.

## Background

Colloidal quantum dots are solution-grown semiconductor nanocrystals used in light emission, detection, imaging, sensing, quantum photonics and catalysis. Their inorganic cores receive much of the attention, but organic ligands form the material's first interface with solvents, neighbouring particles, device layers and reactants. They protect the core and passivate defects while also controlling particle spacing, electronic transport and access to the surface.

Vibrational spectroscopy and nuclear magnetic resonance can reveal ligand bonding and average conformations, but they generally average over many particles. Electron microscopy resolves the inorganic core of a single dot, while the low-contrast organic shell remains largely invisible. The unresolved issue is not only what an average ligand shell looks like, but also whether different regions of the same particle provide distinct molecular environments.

FRET offers a route to distance information. Energy transfer between an emissive donor and an acceptor dye depends steeply on their separation, approximately following an inverse-sixth-power relationship. If a dye is attached to the end of a surface-bound ligand, changes in emission intensity and excited-state lifetime can report where that molecular probe sits relative to the quantum dot.

## Research question

The study examines whether a dye-labelled ligand can be introduced into a quantum-dot shell while retaining a clear FRET signal, whether the observed heterogeneity arises mainly between different particles or within individual particles, and whether the method responds predictably when the chemistry of the native ligand tail changes.

The authors combine CsPbBr₃ perovskite quantum dots with a clickable phosphoethanolamine-based probe, single-particle time-resolved photoluminescence and atomistic modelling. This approach allows them to move from confirming energy transfer to extracting distances, comparing several local environments on one particle and relating those measurements to ligand chemistry and coverage.

## Inside the study

The measurement begins with the contrast between a readily imaged inorganic core and a difficult-to-see organic shell. Molecular-dynamics modelling shows that ligands attached to the same CsPbBr₃ surface can bend, extend and interpenetrate in different ways. The researchers place a dye at the tail of a surface-bound ligand, so that the quantum dot acts as the FRET donor and the dye as the acceptor. Stronger transfer indicates a shorter donor–acceptor separation, while weaker transfer points to a more extended configuration.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-21-at-17.09.02-1.png)

To construct the probe, the team prepared a precursor ligand, L1, containing a phosphoethanolamine group for surface coordination, an aliphatic spacer and a terminal strained alkyne. Copper-free click chemistry joins an azide-functionalized BODIPY dye to this ligand to produce L2\. The dye absorption overlaps with the emission of CsPbBr₃, providing the spectral conditions needed for energy transfer.

A small fraction of the native ligands was replaced by L2 through spontaneous ligand exchange. When the resulting quantum dots were excited at 355 nm, the spectra contained quantum-dot emission near 511 nm and dye emission near 555 nm. The quantum-dot lifetime shortened, while the time-resolved dye signal displayed a rise associated with indirect excitation. Together, these measurements show that the probe enters the ligand shell and participates in FRET.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-21-at-17.09.07-1.png)

The researchers then excited individual quantum dots with a 405 nm pulsed laser and recorded photons in separate donor and acceptor channels. Dye photobleaching provided an internal check on the assignment. When an acceptor stopped emitting, its photon count fell while the quantum-dot emission and donor lifetime increased. These anticorrelated intensity changes and the recovery of the donor lifetime identify energy transfer within an individual quantum-dot–dye pair.

Representative particles showed intensity-based FRET efficiencies from about 15% to 85%. Lifetime measurements were used to determine efficiencies for about 200 single-donor, single-acceptor pairs. Converting those values into distance produced a broad distribution from 3.5 to 8 nm. Transmission electron microscopy gave an average particle radius of 4.1(3) nm. Many probes lie close to the inorganic surface, but the full distribution shows that their configurations are not uniform.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-21-at-17.09.10-1.png)

Particles carrying several probes allowed the team to compare different molecular environments on the same quantum dot. In one example, three successive acceptor-photobleaching steps revealed FRET efficiencies ranging from 0.18 to 0.64, equivalent to a distance span of 1.7 nm. On another particle, two probes both had efficiencies close to 0.7 and differed in distance by only 0.3 nm.

The wider analysis included about 40 dots with multiple acceptors and about 60 with a single acceptor. The mean difference in FRET efficiency was 0.20 ± 0.04 within particles and 0.209 ± 0.007 between particles. Expressed as distance differences, the corresponding values were 0.81 ± 0.22 and 0.71 ± 0.03 nm. The absence of a significant distinction between these comparisons supports the authors' conclusion that local variation within individual dots can account for the heterogeneity seen across the sample.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-21-at-17.09.17-1.png)

The team next prepared CsPbBr₃ quantum dots with a library of phosphoethanolamine-based ligands bearing branched or linear aliphatic, polystyrene and polyether tails. They introduced the same L2 probe into each shell. Every ligand family produced a broad distance distribution, but the average dye-to-surface separation changed with the surrounding chemistry.

C8C12, C12C16 and polystyrene tails favoured configurations in which the polar dye remained near the perovskite surface. Linear C14 and PEG750 tails placed it farther away on average. Across the ligand library, the mean surface separation ranged from approximately 0.25 to 1.02 nm. The probe could thus distinguish both local disorder and shifts associated with the chemistry of the host ligand environment.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-21-at-17.09.23-1.png)

Atomistic modelling helped connect these measurements with the local structure of the shell. The authors placed L2 on a CsBr-terminated CsPbBr₃ surface with no native ligands, 50% C14-PEA coverage or 50% PEG750-PEA coverage. Molecular-dynamics trajectories at 300 K and potential-energy scans gave calculated dye-to-surface distances of 0.23–1.40 nm, comparable with the experimental range of 0.25 ± 0.14 to 1.02 ± 0.15 nm.

Without neighbouring ligands, the polar dye tends to approach the inorganic surface. Higher local coverage pushes it outward, while the surrounding tail chemistry changes its preferred configuration. The authors identify local ligand coverage as a primary source of heterogeneity, potentially through ligand patches or facet-dependent binding. They also retain other possible contributions, including reversible surface coordination, placement at a facet, edge or corner, and conformational disorder of L2 itself.

![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/09/Screenshot-2026-09-21-at-17.09.28-1.png)

## Takeaways and outlook

The study brings single-molecule FRET, a method widely used as a molecular ruler, to the organic surface of colloidal quantum dots. A clickable dye-labelled ligand, single-particle photon counting and lifetime analysis convert an otherwise difficult-to-image shell into a distribution of measurable distances. Atomistic simulations then connect those distances with the local molecular environment.

The resulting picture is not a uniform brush of ligands surrounding an identical core. Quantum dots from the same batch and capped with the same native chemistry can contain locally different environments on each particle. Changing the ligand tail also shifts the probe's average position. These local environments matter for surface passivation and particle coupling in optoelectronics, as well as for the access of reactants to a quantum-dot surface in photocatalysis.

The current experiments provide a structural snapshot. The authors point to the nanosecond time resolution available to single-molecule FRET as a possible route towards following ligand dynamics and connecting local molecular motion with collective material function.

## About the researchers

Leon G. Feld (ETH Zurich and Empa) is the first author. Gabriele Rainò and Maksym V. Kovalenko (ETH Zurich and Empa) are the corresponding authors.

The other authors are Oleksandr Kolomiiets, Noah A. Shahin, Sebastian Sabisch and Amrutha Rajan, all affiliated with ETH Zurich and Empa.

## Original research

Leon G. Feld; Oleksandr Kolomiiets; Noah A. Shahin; Sebastian Sabisch; Amrutha Rajan; Gabriele Rainò; Maksym V. Kovalenko. “Single-Particle FRET Probes Heterogeneity in the Ligand Shell of Colloidal Perovskite Quantum Dots.” *Advanced Materials* (2026), e75051\. DOI: [10.1002/adma.75051](https://doi.org/10.1002/adma.75051?ref=research-pop.com). Published online 18 September 2026.

---

## Research POP Notes

This article reflects the independent interpretation of the Research POP team and does not represent the views of the authors, their institutions or the journal. If you identify any inaccuracies or have concerns regarding the content, figures or attribution, please contact us at [team.researchpop@gmail.com](mailto:team.researchpop@gmail.com). We will review the matter promptly and make corrections or remove the relevant material where appropriate.