ELIDIS can also be adapted to a modular version in which the antigen-conjugated strands hybridize with the DNA strands responsible for the strand displacement reaction (Figure ). This modular approach allows the use of more complex recognition elements (i.e., peptide epitopes, proteins, etc.). For example, using this modular version of ELIDIS, we measured two different monoclonal antibodies directly in serum: the anti-MUC (Figure ) antibody and Cetuximab (Figure ). For anti-MUC antibody, we used as antigen a peptide (15 amino acids) excised from the MUC1 protein (MUC peptide). For Cetuximab we used the entire EGFR protein as antigen. The same approach can also be used to detect a bi-specific antibody (Figure ). In this case, we used a bispecific antibody re-engineered to contain one binding site that binds the EGFR protein and the other that targets MUC1 protein. For this target antibody we then used two different antigen-conjugated strands conjugated to EGFR and the MUC peptide (Figure , bottom). For all these modular ELIDIS platforms, we achieved sensitivities and specificities comparable to their non-modular counterpart, with LOD values in the picomolar range (i.e., LOD Anti-MUC Ab = 2 x 10 -12 M; LOD Cetuximab = 1 x 10 -12 M; LOD Bispecific Ab = 4 x 10 -13 M) and average RSD% ˂12% (Figure ). For a better analytical characterization of the developed ELIDIS platform, we compared the analytical performance with that of a commercial ELISA kit. For this purpose, we selected the modular ELIDIS assay for the detection of Cetuximab. ELIDIS provides better sensitivity (LOD of the ELISA kit = 6 x 10 -10 M) with fewer experimental steps and comparable overall assay time (Figure -b, Table ). We also examined the recoveries of spiked blank serum samples for different Cetuximab concentrations (from 10 -12 to 10 -7 M) using ELIDIS platform and the commercial ELISA assay (Figure ). We observe comparable recoveries between ELISA and ELIDIS in the concentration range between 10 -8 and 10 -7 M. It is noteworthy that the ELISA kit does not provide quantitative information below 10 -9 M, whereas ELIDIS remains sensitive even at a concentration of 10 -12 M. ELIDIS can be easily multiplexed and allows simultaneous detection of multiple antibodies in the same sample. To demonstrate this, we rationally designed two different antibody-responsive DNA strand displacement reactions (with different DNA sequences), each of which responding to a specific antibody (anti-Dig and Cetuximab). Thus, each reaction releases a specific GOx-DNA strand in the presence of the target antibody. We then used a disposable electrode that has the same reference and counter electrode but presents two different working electrodes, each modified with a capture probe specific for each GOx-DNA output strand.