The present invention provides a method of testing the integrity of a microporous membrane using a colloid solution containing metal particles or metal compound particles that can accurately determine the integrity of a virus removal membrane formed of hydrophilized synthetic polymer that has been subjected to protein solution filtration, and to provide a method of producing the colloid solution. The quantum dots are formed on the surfaces normal to each other, whereby the polarization dependency can be eliminated as described above. Then, when the user repeats the misunderstood utterance, the rejection reference can be used to eliminate the incorrect recognition result as a potential subsequent recognition result. The head has an outer periphery, and a bottom surface extending outwardly from the shaft toward the outer periphery.