Recombinant antibodies comprising anti-human immunoglobulin g-invertase fusion proteins and methods of using the same

A method of diagnosing an infection of a pathogen in a subject in need thereof, comprising:

• a) contacting a sample of the subject with at least one polypeptide of the pathogen under conditions sufficient for an antibody to the at least one polypeptide of the pathogen to bind the at least one polypeptide of the pathogen to produce a bound antibody;
• b) contacting the bound antibody with at least one recombinant antibody fusion protein to produce a binding complex, wherein the at least one recombinant antibody fusion protein is capable of binding to a human IgG and has a catalytic activity of converting at least one substrate into at least one detectable product;
• c) contacting the binding complex with the at least one substrate under conditions sufficient to convert the at least one substrate into the at least one detectable product;
• and
• d) detecting the presence or absence of the at least one detectable product in the sample of the subject, wherein detecting the presence of the at least one detectable product in the sample indicates that the subject has an infection of the pathogen,
• optionally wherein the method further comprises obtaining the sample from the subject, optionally wherein the sample is an oral fluid, nasal fluid, saliva, blood, plasma, or serum, and optionally wherein the pathogen comprises a severe acute respiratory syndrome coronavirus-2 (SARS-COV-2).