# Nanometer-Precision Tracking of Adipocyte Dynamics via Single Lipid Droplet Whispering-Gallery Optical Resonances

## TL;DR

A new biophotonic technique uses light to track tiny fat droplets in living cells with extreme precision, revealing cell behavior and metabolism in real time.

## Contribution

This is the first application of whispering-gallery-mode resonances in live adipocytes for nanometer-scale tracking of lipid droplet dynamics.

## Key findings

- The technique achieves nanometer-scale precision in measuring lipid droplet size and deformation in real time.
- It detects early signs of cell viability loss before conventional assays can.
- The method reveals adipocyte heterogeneity and lipolytic responses to drugs like forskolin and isoproterenol.

## Abstract

Biophotonicsand
more recently, biointegrated
photonicsoffer
transformative tools for probing cellular processes with unprecedented
precision. Among these, whispering-gallery-mode (WGM) resonators (optical
microcavities formed in spherical structures) have emerged as powerful
biosensors and intracellular barcodes. Lipid droplets (LDs), with
their high refractive index and intrinsic spherical geometry, are
ideal candidates for supporting intracellular lasing. Although lasing
in LDs has been previously demonstrated, it has not yet been harnessed
to study live-cell biology. Here, we report the first use of WGM resonances
in LDs of live primary adipocytes, employing a continuous-wave (CW)
laser at powers below the biological damage threshold. By measuring
these resonances, we achieved nanometer-scale precision in size estimation,
enabling real-time observation of rapid LD dynamics and deformations
on the minute scalefar beyond the spatiotemporal resolution
of conventional microscopy. We systematically characterized this photonic
sensing approach, demonstrating its ability to resolve adipocyte heterogeneity,
monitor lipolytic responses to forskolin and isoproterenol, and detect
early signs of cell viability losswell before conventional
assays. This proof-of-concept establishes intracellular LD WGM resonances
as a robust platform for investigating live single-cell metabolism.
The technique enables rapid, cost-effective assessment of adipocyte
function, reveals cell-to-cell variability obscured by bulk assays,
and lays the foundation for high-throughput analysis of metabolism-
and obesity-related diseases at both the cellular and tissue levels.