The Invisible Made Visible

Nanoscale Magnetometry with Fluorescent Nanodiamonds

Revolutionary technology enabling unprecedented visualization of magnetic fields at the molecular level in living systems.

Explore the Science

The Quest to See the Unseeable

Imagine trying to map the intricate magnetic fields of a living cell or visualize the flow of electrical currents in a microchip at the scale of individual molecules. For decades, this was the realm of science fiction.

The Challenge

The magnetic fields produced by single electrons are vanishingly weak and fluctuate rapidly in a watery environment, making them nearly impossible to detect with conventional tools.

The Solution

By harnessing the quantum properties of tiny, fluorescent nanodiamonds and a clever trap that defies the random jitter of nature, scientists are now able to perform nanoscale magnetometry in solution 1 4 .

The Quantum Sensor and The Molecular Cage

Nitrogen-Vacancy Centers

The heart of this technology lies in a tiny atomic defect within a diamond crystal, known as a Nitrogen-Vacancy (NV) center 6 .

How It Works

When you shine a green laser on an NV center, it emits a stable, red fluorescence 1 . The intensity of this red light is directly influenced by magnetic fields through Optically Detected Magnetic Resonance (ODMR) 1 3 .

Key Advantages
  • Biocompatible and non-toxic
  • Can be used inside living cells
  • Extremely sensitive to magnetic fields
  • Photostable (non-blinking)

Anti-Brownian Electrokinetic Trap

To use an FND as a sensitive probe in a liquid, scientists face a fundamental problem: Brownian motion 5 8 .

1. High-Speed Tracking

A laser beam scans in a circle at 40,000 times per second, detecting the nanodiamond's position through fluorescence flicker.

2. Instantaneous Correction

A photon-detecting circuit calculates displacement and applies a precisely tuned electric voltage.

3. Electrokinetic Drift

The voltage induces an electrokinetic force, gently pushing the nanodiamond back toward the center 8 .

A Deep Dive into a Pioneering Experiment

The doctoral thesis "Nanoscale magnetometry with single fluorescent nanodiamonds manipulated in an anti-Brownian electrokinetic trap" by Metin Kayci at EPFL was a landmark demonstration of merging these two technologies 4 .

Methodology: Building the Nano-Lab

  1. The Trap Setup

    A microfluidic chamber integrated with electrodes for the ABEL trap containing a single nanodiamond.

  2. Tracking and Excitation

    The same laser used for trapping also excited the NV centers, causing fluorescence.

  3. Integrating Magnetometry

    An RF antenna delivered microwave frequencies for ODMR spectroscopy.

  4. Scanning the Environment

    The sample stage was moved to map magnetic fields around the trapped particle.

Results and Analysis

Proof of Concept Achieved

The experiment successfully demonstrated that a single, freely-floating nanodiamond could be used as a sensitive magnetometer.

Key Findings:
  • ABEL trap stabilized particles for clean ODMR signals
  • Magnetic field mapping in fluidic environments
  • Non-invasive alternative to atomic force microscopy
  • Ideal for studying soft biological materials

Nanodiamond Magnetometry Performance

Sensitivity

μT/√Hz

10

Spatial Resolution

Nanometers

<50

Trapping Time

Seconds

>10

Biocompatibility

Rating

High

The Scientist's Toolkit

Essential components that make this advanced research possible

Item Function Key Characteristics
Fluorescent Nanodiamonds (FNDs) Primary quantum sensor 6 Contains NV centers; biocompatible; photostable (non-blinking) 1 6
Microfluidic Chamber Platform for trapping and observation 5 Contains electrodes to apply feedback electric fields 5 8
RF Antenna / Microwave Source Manipulates NV center spin state 4 Enables ODMR spectroscopy for magnetic field detection 1 4
Avalanche Photodiode (APD) Detects single photons of fluorescence 5 Provides the high-speed signal for the ABEL trap's feedback loop 5
Surface Functionalization Molecules Allows FNDs to bind to specific targets 6 Can be carboxyl, hydroxyl, or amino groups, or custom biomolecules 6

Beyond the Basics: Enhancing the Toolbox

Machine Learning Integration

Machine learning is now being used to analyze complex ODMR spectra from nanodiamond ensembles, dramatically improving measurement accuracy 3 .

Microwave-Free Techniques

New microwave-free magnetometry techniques use intrinsic fluorescence dips of NV centers, simplifying setup and reducing interference 9 .

A New Era of Nanoscale Exploration

The successful combination of fluorescent nanodiamonds and the ABEL trap represents a significant leap forward in sensing technology.

Neuroscience

Mapping electrical activity of neurons with unprecedented detail 2 4 .

Biomedicine

Tracking individual magnetic nanoparticles inside living cells for drug delivery studies.

Materials Science

Visualizing current flow in microchips and studying magnetic properties of novel materials.

Future Outlook

As methods for fabricating more uniform nanodiamonds advance and trapping technologies become even more precise, the potential of this quantum-enabled toolkit is limitless. We are on the verge of not just understanding but truly seeing the invisible forces that govern the nanoscopic world.

References

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References