Re: Is it possible to detect a living thing via their emission spectra?

Yes I believe it is possible.

Of course the distance from the sensing (which you didn't specify) would be an important element; currently we already can sense living things via their emission spectra, IF the sensors are close enough. Of lot of that sensing is first order EM fields, not free EM radiation.

You probably meant of an appreciable distance.
In that case, the sensitivity, discrimination and low frequency detection capabilities of the sensor will be most important.

But yes, bioelectric processes do emit EM radiation, it is only a matter of technology to detect it.