On-chip Attoampere Measuring Circuit for Ultimate Molecular Biosensing

We present a CMOS charge preamplifier with a novel reset network based on tunneling and/or hot-electron, that introduces virtually no leakage (< 1 aA) and no noise (< 20 aA / √Hz). We demonstrate that this key component unlocks the full potential of a capacitive transimpedance amplifier, allowing charge measurements within a very wide time window (< 20 minutes) or resolving attoamperes with an averaging time of a few seconds, allowing for ultimate electronic biosensing. To preserve the performace of the preamplifier in operative conditions against the presence of leakage currents that may degrade the reading, we demonstrate the effectiveness of appropriate cleaning and treatment of the chip's surface. We show that passivation of the chip's surface with hexamethyldisilazane (HMDS) reduces surface leakage currents by three orders of magnitude, down to the attoampere level. This extreme current resolution places the proposed circuit scheme at the core of any advanced bioapplication where extremely small levels of currents should be detected.