Sensors for detecting heavy metals in indoor dust
Small physics departments have been getting rid of their neutron howitzers. They have a bit of plutonium and beryllium in a stainless steel slug in a big tub of paraffin. There are ports filled with stacks of acrylic and that is where you put your filter. Thermal neutrons radio-activate whatever you have and you quickly, because some of the half-lives are very short, stick it in a gamma ray spectrometer with multi-channel scaler (they are throwing those out as well - scored one a while back). Maybe you can snag a setup. Baseless radiation paranoia makes the howitzer hard to get, and keep. However, there are direction on making your own proton accelerator in "The Scientific American Book of Projects for the Amateur Scientist" from 1960 ( the things we used to do in our basements!).

On a more practical level, I would bet the least expensive route is a chemical dip and color test, with filters for specific reaction colors or a simple spectrophotometer. There are filter papers made with the same refractive index as some solvents, so that it vanishes when immersed.