A system for measuring the membrane potential of a neuron is disclosed. The system comprises one or more photoacoustic ion indicators, each comprising a metal chelating agent linked to a chromophore molecule. The metal chelating agent is configured to selectively bind to one of sodium ions, calcium ions, and potassium ions. The system further comprises a photoacoustic probe including a laser configured to emit a light signal to the chromophore and an ultrasound transducer configured to receive a photoacoustic signal in response to the light signal. The system further comprises a processor configured to receive the photoacoustic signal from the ultrasound transducer, determine a quantity of photoacoustic ion indicators exhibiting the shift, and calculate a membrane potential of the neuron based on quantity of photoacoustic ion indicators exhibiting the shift.
PHOTOACOUSTIC ION INDICATORS