Proteins as quantum sensors inside living cells
Context
For decades, fluorescent proteins such as Green Fluorescent Protein (GFP) and its variants have been used as biological “glow tags” to track molecules inside cells. Now, two studies published in Nature (2026) show that certain fluorescent proteins can be engineered to behave as quantum sensors — detecting magnetic fields and radio waves from inside living cells.
This marks a shift from solid-state quantum devices (like diamond sensors) to genetically encoded biological quantum sensors.
Why this is a breakthrough
Traditionally:
Most quantum sensors are made from solid materials (e.g., diamond nitrogen-vacancy centers).
They are highly sensitive but:
Difficult to insert into cells
Hard to position at specific subcellular locations
In contrast:
Proteins can be encoded in DNA.
Cells can produce them naturally.
They can be fused to other proteins for precise targeting.
They operate inside warm, dynamic biological environments — once thought too “noisy” for quantum effects.
The quantum mechanism: Radical pairs and spin
When a fluorescent protein absorbs light:
An electron jumps to a higher-energy state.
It usually returns quickly, emitting light (fluorescence).
But in some proteins:
The excited electron forms a radical pair with a nearby molecule.
Each radical has an unpaired electron.
Their electron spins become temporarily linked (quantum correlated).
Weak magnetic fields can alter spin interactions.
This changes how much light the protein emits.
Thus, magnetic fields → alter electron spin → change fluorescence.
This is the basis of the sensing mechanism.
Study 1: EYFP as a quantum sensor (University of Chicago)
Researchers worked with a variant of enhanced yellow fluorescent protein (EYFP).
Key findings:
EYFP has a metastable triplet state.
Electron spins could be:
Initialised using laser pulses
Manipulated with microwave fields
Read out optically
This completes the full cycle required of a qubit (quantum bit).
Importantly:
Optically detected magnetic resonance (ODMR) was observed:
In human kidney cells (low temperature)
In Escherichia coli at room temperature
This proves quantum behaviour survives in biological conditions.
Study 2: MagLOV proteins (University of Oxford)
The Oxford team engineered a plant light-sensing protein (based on AsLOV2) into a magneto-sensitive fluorescent protein family called MagLOV.
Through genetic mutation and selection, they improved:
Magnetic sensitivity
Stability
Light tolerance
Genetic compatibility
Key result:
MagLOV exhibited optically detected magnetic resonance inside living bacterial cells at room temperature.
Radio waves at specific frequencies changed fluorescence predictably.
This directly reveals electron spin behaviour in living cells.
Why sensing inside cells matters
Many biological processes involve subtle electronic and magnetic effects:
Enzyme reactions involving metal ions
Short-lived free radicals
Electron transfer in respiration
Photosynthesis
Until now, studying these inside living cells was nearly impossible.
Protein-based quantum sensors:
Can be targeted to specific proteins or organelles.
Allow nanoscale measurements of:
Magnetic fields
Electric fields
Temperature
Chemical environment
Beyond sensing: Improved imaging
The MagLOV team also demonstrated:
1. Lock-in detection
Magnetic field switched on/off.
Fluorescence signal separated from background noise.
Enhances weak signals.
2. Magnetic spatial localisation
Using magnetic field gradients.
Determined 3D positions of expressing cells.
Conceptually similar to MRI principles, but genetically encoded.
Current limitations
Lower sensitivity than solid-state diamond sensors
Shorter coherence times
Photobleaching under prolonged illumination
However, fluorescent proteins themselves took decades to mature into standard tools. Similar optimisation may close the gap.
Conceptual significance
This work:
Challenges the idea that biology destroys quantum states.
Bridges quantum physics and molecular biology.
Opens the field of hybrid quantum-biological technologies.
In future, such sensors could:
Track protein shape changes in real time.
Monitor drug binding events.
Reveal biochemical reaction dynamics inside living cells.
Enable nanoscale biophysical diagnostics.
Prelims Practice MCQs
Q. With reference to protein-based quantum sensors, consider the following statements:
They rely on electron spin dynamics within fluorescent proteins.
They require ultra-cold laboratory conditions to function.
They can be genetically encoded within living cells.
Which of the statements given above is/are correct?
A. 1 and 3 only
B. 2 only
C. 1 only
D. 1, 2 and 3
Answer: A
Explanation:
Statement 1 is correct: These sensors operate via electron spin states and radical pair mechanisms.
Statement 2 is incorrect: A key breakthrough is that they function in living cells at room temperature.
Statement 3 is correct: They are encoded via DNA and produced by cells.
Q. Optically detected magnetic resonance (ODMR), recently demonstrated in engineered fluorescent proteins, refers to:
A. Detection of nuclear magnetic resonance using X-rays
B. Measuring magnetic fields by observing changes in fluorescence under microwave radiation
C. Use of ultrasound to detect protein vibrations
D. Conversion of light directly into electrical current
Answer: B
Explanation:
In ODMR, electron spin states are manipulated using microwaves and read out optically through changes in fluorescence intensity. This confirms quantum spin control in biological systems.