Alexander Ohlinger et al. at the Ludwig Maximilian Universitiy in Munich have constructed a highly sensitive sound collecting device using a gold nanoparticle confined in an optical trap. This trap acts like a pair of tweezers for sound waves traveling in a liquid medium. Apparently this nanoparticle setup can detect sounds down to -60dB. The lowest sound a human can hear is around 0dB. The loudest we hear without pain is 120dB. To give you an idea of these numbers, according to WorsleySchool.net, a human whisper is about 20dB. A power saw is about 110dB.
It's hard to imagine -60dB, but I hope they are able to do this. I'd love to hear what a bacterium sounds like as it's shuffling around the miasma.