Biofunctionalized Two-dimensional MoS₂ Receptors for Rapid Response Modular Electronic SARS-CoV-2 and Influenza A Antigen Sensors

Abstract

Multiplex electronic antigen sensors for detection of SARS-Cov-2 spike glycoproteins or hemagglutinin from Influenza A in liquid samples with characteristics resembling extracted saliva were fabricated using scalable processes with potential for economical mass-production. The sensors utilize the sensitivity and surface chemistry of a two-dimensional MoS2 transducer for attachment of antibody fragments in a conformation favorable for antigen binding. Ultra-thin layers (3 nm) of amorphous MoS2 were directly sputtered over the entire sensor chip at room temperature and laser annealed to create an array of semiconducting 2H-MoS2 active sensor regions between metal contacts. The semiconducting region was functionalized with monoclonal antibody Fab (fragment antigen binding) fragments derived from whole antibodies complementary to either SARS-CoV-2 S1 spike protein or Influenza A hemagglutinin using a papain digestion to cleave the antibodies at the disulfide hinges. The high affinity for the MoS2 transducer surface with some density of sulfur vacancies for the antibody fragment base promoted chemisorption with antigen binding regions oriented for interaction with the sample. The angiostatin converting enzyme 2 (ACE2) receptor protein for the SARS-CoV-2 spike glycoprotein, was tethered to a hexa-histidine (his6) tag at its c-terminus both for purification purposes, as well as a motif for binding to MoS2. This modified protein was also investigated as a bio-recognition element. Electrical resistance measurements of sensors functionalized with antibody fragments and exposed to antigen concentrations ranging from 2-20,000 picograms per milliliter revealed selective responses in the presence of complementary antigens with sensitivity to SARS-CoV-2 or influenza A on the order of pg/mL and comparable to gold-standard diagnostics such as Polymerase Chain Reaction (PCR) analysis. Lack of antigen sensitivity for the larger ACE2 BRE further demonstrates the utility of the engineered antibody fragment/transducer interface in bringing the target antigen closer to the transducer surface for sensitivity required for early detection viral diagnostics.