Is there a spec for the nominal sensitivity of Bruker's DMASP cantilevers for sensing? As in the charge or current per meter of applied force or displacement to the cantilever tip, as opposed to the displacement of the tip per applied voltage?

As phrased, this is a bit of a difficult question. When you deflect
the DMASP piezo, it will create a charge (not a voltage). The equations
that relate the conjugate variables of cantilver: angle, deflection,
piezo volume, and piezo charge to applied: bending moment, Uniform load
(both usually 0 for SPM), Tip Load, and Piezo Voltage are well described
in the paper by Smits:

From this you can calculate the generated charge, and then convert
that to a voltage depending on the circuitry you attach to accomplish
the measurement.

For your experiment, your best approach is to make a charge sensor (infinite input impedance).

If you use a voltage sensor, the voltage, and decay, you measure will
be proportional to the input resistance and capacitance of your sensor.
You will essentially get the derivative of your signal (as the
generated charge is depleted by the measurement amplifier).

A way to get around this is to measure the change in capacitance of
the piezo (rather than the voltage or charge). You can find several
papers where people have used the DMASP in this type of self sensing
mode. The basic concept is a “capacitive” Wheatstone bridge.

The following paper show different options for doing this, and from it you can get an idea of the deflection sensitivity of the DMASP.

As phrased, this is a bit of a difficult question. When you deflect
the DMASP piezo, it will create a charge (not a voltage). The equations
that relate the conjugate variables of cantilver: angle, deflection,
piezo volume, and piezo charge to applied: bending moment, Uniform load
(both usually 0 for SPM), Tip Load, and Piezo Voltage are well described
in the paper by Smits:

From this you can calculate the generated charge, and then convert
that to a voltage depending on the circuitry you attach to accomplish
the measurement.

For your experiment, your best approach is to make a charge sensor (infinite input impedance).

If you use a voltage sensor, the voltage, and decay, you measure will
be proportional to the input resistance and capacitance of your sensor.
You will essentially get the derivative of your signal (as the
generated charge is depleted by the measurement amplifier).

A way to get around this is to measure the change in capacitance of
the piezo (rather than the voltage or charge). You can find several
papers where people have used the DMASP in this type of self sensing
mode. The basic concept is a “capacitive” Wheatstone bridge.

The following paper show different options for doing this, and from it you can get an idea of the deflection sensitivity of the DMASP.