# Super-Resolution Microscopy of Neuronal Synapses with Small Quantum Dots and Advanced Imaging Tools

> **NIH NIH R01** · UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN · 2020 · $315,712

## Abstract

Abstract
The ability to measure the molecular mechanisms of neuronal communication at the nanometer spatial scale
will have enormous impact in both basic bioscience and in future clinical neuroscience. In particular, AMPA-
and NMDA-type glutamate receptors (AMPARs/NMDARs, known as iGluRs) are involved in neuron-to-neuron
communication across synapses, where these receptors contribute to learning and memory, and when
dysregulated, to neurodegenerative diseases including Alzheimer's, Parkinson's and complications from
strokes. A critical mechanistic event is the transport of iGluRs into and out of synapses (or parts of synapses)
in a dynamic process called synaptic plasticity. A revolution is underway because of the recent ability to
resolve these events at the nanometer-scale using fluorescence super-resolution microscopy (FSRM).
However significant inherent problems with this technology have led to confounding results and misinformation.
The biggest problem has been with the fluorescent probes used to image receptors: conventional organic
fluorescent probes last only a few seconds; commercial (and big) quantum dots (bQDs), despite their
exceptional brightness and photostability, are over 20 nm in diameter and are too large to fit inside the synaptic
cleft where iGluRs are active. We recently overcame this problem through an R21, which enabled us to
develop small quantum dots (sQDs) that are <10 nm in diameter. They specifically label iGluRs in the synaptic
cleft, which is just ~20-30 nm wide. The sQDs do this with tremendous brightness and stability, resulting in
FSRM images in 3-dimensions with 100 ms time-resolution for greater than 2 minutes of continuous excitation.
In contrast, bQD-labeled AMPARs are predominantly stuck in the extra-synaptic space because steric
hindrance prevents them from going inside. We have recently extended these findings with a newer sQD that
is completely stable, and with small organic fluorophores that we now show are stable enough, on live neurons
(which previously had been too photolabile for such measurements.) Our findings, some of which have been
published in 3 papers resulting from our R21 grant, may have tremendous implications for basic science and
health: the surface mobility and trafficking of iGluRs, which depend on the ease of diffusion inside and outside
of synapses, regulates synaptic efficacy. Here we wish to understand the distribution and dynamics of iGluRs,
both within the synapses and between synapses, using our new sQDs and other new photoactivatable
fluorescent proteins and some organic fluorophores. For this, a number of new advances in optics, probe
design, and care with receptor monovalency are necessary. After these technical problems are solved (which
will be useful to answer many different biological questions), we will validate the biology that we have
observed, and to apply these to proof-of-principle experiments involved in two key biological questions: 1) In
what way do receptors move ...

## Key facts

- **NIH application ID:** 9975253
- **Project number:** 5R01NS100019-04
- **Recipient organization:** UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN
- **Principal Investigator:** Hee Jung Chung
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $315,712
- **Award type:** 5
- **Project period:** 2017-07-01 → 2021-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9975253

## Citation

> US National Institutes of Health, RePORTER application 9975253, Super-Resolution Microscopy of Neuronal Synapses with Small Quantum Dots and Advanced Imaging Tools (5R01NS100019-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9975253. Licensed CC0.

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