You must carefully choose insulation and apply guarding potentials, and you must use an amplifier with picoampere input-bias currents.
必须谨慎选择绝缘方法和使用保护电位，必须使用输入偏置电流为微微安级的放大器。
2
The leakage of the 1n3595 diode is generally less than one picoampere even with 1mv of forward bias, so the circuit won't interfere with measurements of 10pa or more.