Dendritic excitations govern back-propagation via a spike-rate accelerometer
Optical constraints on two-photon voltage imaging
- Voltage changes are smaller than calcium (most popular functional imaging method in fluorescence microscopy) over a very thin membrane, and they’re super fast, requiring kHz sampling rates
- "Compared with 1P excitation, 2P excitation requires ∼10^4-fold more illumination power per cell to produce similar photon count rates"
- At depths of 300 um you can image just ~12 (!) neurons with GEVIs before running into heating limits
Simultaneous, cortex-wide dynamics of up to 1 million neurons reveal unbounded scaling of dimensionality with neuron number
- 1M neuron GCaMP dataset recorded at ~2 Hz (Ca imaging commonly done at 30 Hz). I think this is the largest 2p functional dataset.
- Downsampling the 10 Hz dataset to 2 Hz resulted in 40% fewer reliable dimensions
A fluorescent-protein spin qubit
A method to read out spin-state and measure nanoscale magnetic fields, like nitrogen-vacancy (NV) centers but with proteins!
- Excite YFP with blue light
- Some of the excited electrons cross into T1
- Zero-field splitting: T1 sublevels separate out (due to proximity of the two electrons in triplet state)
- Pulse of 912 nm light excites electron into T2 (T2 predicted by modeling, could also say Tn here?)
- Electron relaxes back to S1 and fluoresces
- Spin state read out with optically-activated delayed fluorescence (OADF) — the efficiency (read out as the delay) of T2 → S1 depends on what spin sublevel it was in before the 912 nm pulse
- To measure B:
- First do a sweep of microwaves to figure out what drove flips to spin sublevels → optically-detected magnetic resonance (ODMR) read out with OADF
- Then in the presence of a magnetic field, you do a frequency sweep of microwaves until you detect the OADF signal again. A magnetic field moves these sublevels further apart (Zeeman effect)
- You can use the difference between the initial signal and the one in the presence of B to measure B
Quantum Spin Resonance in Engineered Magneto-Sensitive Fluorescent Proteins Enables Multi-Modal Sensing in Living Cells
- MagLOV excited with light, creating a spin-correlated radical pair (SCRP), which the authors think is a triplet
- B field separates energy levels: Zeeman splitting
- This causes a reduction in fluorescence because paths to recombine and move back to singlet then fluorescence are reduced now that the triplet states are spread out
- The stronger the B field, the more the sublevels separate and the less fluorescence from recombination because only the T0 sublevel can recombine into a singlet (in the absence of B the triplet sublevels can mix with singlet and recombine)
- RF that matches the difference between triplet states leads to increase in fluorescence via restoring mixing
- The size of B determines which RF frequency generates fluorescence → this is how you measure B
Magnetic resonance control of reaction yields through genetically-encoded protein:flavin spin-correlated radicals in a live animal
- Similar to the above paper but using mScarlet + a flavin cofactor / in C. elegans