Sensing of viral antigens has become a critical tool in combating infectious diseases. Current sensing techniques have a tradeoff between sensitivity and time of detection; with 10-30 min of detection time at a relatively low sensitivity and 6-12 h of detection at a high (picomolar) sensitivity. In this research, uniquely nanoengineered interfaces are demonstrated on 3D electrodes that enable the detection of spike antigens of SARS-CoV-2 and their variants in seconds at femtomolar concentrations with excellent specificity, thus, overcoming this tradeoff. The 3D electrodes, manufactured using a high-resolution aerosol jet 3D nanoprinter, consist of a microelectrode array of sintered gold nanoparticles coated with graphene and antibodies specific to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike antigens. An impedance-based sensing modality is employed to sense several pseudoviruses of SARS-CoV-2 variants of concern (VOCs). This device is sensitive to most of the pseudoviruses of SARS-CoV-2 VOCs. A high sensitivity of 100 fm, along with a low limit-of-detection of 9.2 fm within a test range of 0.1-1000 pm, and a detection time of 43 s are shown. This work illustrates that effective nano-bioengineering of interfaces can be used to create an ultrafast and ultrasensitive healthcare diagnostic tool for combating emerging infections.