We have fabricated sub-micron opto-chemical probes for pH, oxygen and calcium monitoring and demonstrated their
application in intracellular and extracellular monitoring of neurons (cortical neuronal cultures and acute hippocampal
slices). Using these probes, we have measured extracellular pH in the stratum radiatum of the CA1 region of mouse
hippocampus upon stimulation of presynaptic Schaffer collateral axons. Synaptic transmission was monitored using
standard electrophysiological techniques. We find that the local pH transiently changes in response to synaptic
stimulation. In addition, the geometry of the functionalized region on the probe combined with high sensitivity imaging
enables simultaneous monitoring of spatially adjacent but distinct compartments. As proof of concept we impaled
cultured neurons with the probe measured calcium and pH inside as well as directly outside of neurons as we changed
the pH and calcium concentration in the physiological solution in the perfusion chamber. As such these probes can be
used to study the impact of the environment on both cellular and extra-cellular space. Additionally as the chemical
properties of the surrounding medium can be controlled and monitored with high precision, these probes enable
differential measurement of the target parameter referenced to a stable bath. This approach eliminates the uncertainties
associated with non-chemical fluctuations in the fluorescent emission and result in a self-calibrated opto-chemical probe.
We have also demonstrated multifunctional probes that are capable of measuring up to three parameters in the
extracellular space in brain slices.
M. Hossein-Zadeh, J. Delgado, F. Schweizer, and R. Lieberman, "Sub-micron opto-chemical probes for studying living neurons," Proc. SPIE 10051, Neural Imaging and Sensing, 100510G (Presented at SPIE BiOS: January 30, 2017; Published: 8 February 2017); https://doi.org/10.1117/12.2251756.
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