An inorganic nanoparticle is provided (step A) having the size of the aggregate of the protein misfolding disease. Free amino groups or free carboxyl groups are formed (step B) on the surface of the nanoparticle (for functionalizing the nanoparticle surface into an amine- or carboxy-functionalized nanoparticle. Maleinimido spacer carboxylic acid is bound to the free amino groups in step (B). Or, free carboxyl groups in step (B) are converted into NHS esters. Monomers of the protein aggregate are bound i) to the maleinimido spacer carboxylic acids by way of a sulfhydryl group at the free end of the monomers, or ii) to the NHS esters by way of the amino group at the free end of the monomer. A standard is provided for use in the detection of protein aggregates occurring with protein misfolding diseases.