Is there a material which can be applied to a surface that will block liquids but is dissolved by blood?
The idea is to use the liquid to close a circuit, but only if blood is present.
I'm wondering if there is something I can coat on the circuit to act as a barrier preventing other liquids from reaching the circuit, but that would react to the chemical components of blood by dissolving, allowing the blood to reach and close the circuit.
One application might be in a bandage, to detect if a wound has reopened. The number of liquids in that context is pretty limited. A limited number of false positive edge cases is also acceptable