Quantification of biomarkers present in dried physiological samples

A method, comprising:

• i) eluting a dried sample of physiological fluid in a diluent to form a liquid sample, wherein the physiological fluid obtained is from a human subject, and wherein the diluent comprises one or more immunoglobulins, a detergent, urea, and one or more blocking agents;
• ii) contacting at least a portion of the liquid sample with a first capture antibody capable of binding tau protein (Tau);
• iii) contacting the mixture of step ii) with a plurality of detectable agents, wherein the plurality of detectable agents comprises a first detectable agent comprising a biotinylated first detection antibody capable of binding Tau, and wherein the contacting comprises the formation of an immunocomplex of first capture antibody-Tau-first detection antibody;
• iv) washing the mixture of step iii);
• v) contacting the combination of step iv) with a streptavidin-bound label, wherein the streptavidin-bound label interacts with a biotin of the biotinylated first detection antibody of the immunocomplex;
• vi) washing the mixture of step v);
• vii) generating a detectable signal from the streptavidin-bound label of step vi);
• viii) detecting the detectable signal of step vii), wherein the limit of detection (LOD) for Tau is less than about 250 pg/mL and/or the limit of quantitation (LOQ) for Tau is less than about 250 pg/mL;
• and
• ix) obtaining a concentration of the Tau in the liquid sample based upon the detectable signal.