From nanotech to living sensors:
Unraveling the spin physics of biosensing at the nanoscale
Speaker: Prof. Clarice D. Aiello
Recap editor: Jingtian Hu
Introduction: Without us realizing it, quantum physics is already playing a key role in our everyday technology such as the semiconductors in our smartphones. Emerging applications such as quantum communications and quantum computing are taking the field to another level. However, have you heard of quantum biology? For quite a long time, quantum mechanics – a theory that describes the world at the scale of atoms or smaller – has very limited overlap with biological systems. One major reason is that the living organisms exhibit complex, dynamic environment noises that almost prohibit the extraction of subatomic information. Also, the properties of cells and tissues so far can mostly be predicted without quantum mechanics by classical molecular cell biology and biochemistry theories.
Last Saturday, Prof. Clarice D. Aiello shared with the Martlets her pioneer research in exploring quantum phenomena in biology. Her team is making exciting discoveries on how spins – a microscopic fundamental quantum property – of an electron have profound effects on macroscopic animal behaviors such as the migration of birds with their inteaction with magnetic fields. Despite of the existing unknowns and uncertainties in the fields, this emerging research field has tremendous possibilities in life science ranging from fundamental biology to therapeutics and behavior science.
Ultrasensitive magnetometry by a nitrogen vacancy: The quantized spin state of an electron produces a magnetic moment that can be used to probe external magnetic fields. However, probing the spin-states of a single electron is challenging because (1) electrons in most materials either form an electron sea or are bound tightly to the nuclei of atoms and (2) the spin coherence time, which decides how long the quantum information (like magnetic fields) can be kept, is short at room temperature. Prof. Aiello tackles the challenge by creating a nitrogen-vacancy center on the surface of a diamond by replacing two carbon atoms with a nitrogen atom and a vacancy site. This surface defect contains has a single unpaired electron whose spin state has a long coherence time (millisecond scale) and can be probed by optical spectroscopy. Prof. Aiello is interested in using these nitrogen-vacancy centers to study biological processes that can be regulated by weak magnetic fields.
Animal behaviors modulated quantum-mechanically: Birds can migrate over thousands of miles without a compass or a GPS and rarely get lost. Their navigation sense can be disrupted by external magnetic fields and is thus believed to rely on the magnetic field of the Earth. However, scientists could not identify any magnets (such as iron oxide) that can function as a compass in these animals. Prof. Aiello and her colleagues are approaching the problem differently with focuses on bio-molecules such as cryptochrome, a light-sensitive protein in the retina that sustain spin states. Upon light illumination, this protein can produce spin-correlated radical pairs, which transduce magnetic signals into unique patterns of neuron firing to realize vision-based magnetic sensing. Also, the quantum responses of other macromolecules are potentially critical for deciding the outcomes of biochemical reactions based on the magnetic field. Prof. Aiello is leading the research in elucidating the mechanisms of these quantum biological processes. In particular, the magnetic field of the Earth is extremely weak and beyond the sensitivity predicted for the spin-correlated radical pairs and how biological systems achieved this extraordinary sensitivity is still an open question.