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A metamaterial composed of diamond-shaped (70 m X 35 m) copper patches was designed and used to detect nanoparticles with 0.75-1.1 terahertz transmission spectroscopy. Deoxyribonucleic acid (DNA) bases adenine, thymine, cytosine, and guanine were detected and identified. Cytosine showed 1.7 dB higher absorption around 0.975 THz than the other bases. SARS-CoV-2 infected saliva showed different spectrum and -10 dB higher absorption than uninfected saliva over 0.75-1.1 THz. Other nanoparticles consisting of 100-500 nm antimony, carbon black, zeolite aluminosilicate molecular sieves), Terfenol-D (Tb0.3 Dy0.7Fe2), Cu2S, Ag2S, dust collected from bench tops, 10-100 m size diamond particles, red polystyrene beads, iron particles and graphene sheets were also tested. Sensor sensitivity for uninfected saliva was 0.3 dB/ng and for infected saliva was 0.8 dB/ng. The metamaterial surface studied here enables detection of airborne particles larger than 10 m in diameter. 

Sensors with 60 nm gap junctions coated with aptamers that bind with S1 and S2 spiking proteins of the SARS-CoV-2 virus were developed. Sensor impedance changes with virus enabling rapid (~1 min), point-of-care detection. Exosomes and other nanoparticles in the saliva produce false positive signals but do not bind with aptamers and are easily removed to achieve 6% false positivity rates. A positive sensor voltage is used to attract the negatively charged SARS-CoV-2 virus to the junction and reduce sensor false negativity rates to below 7%. The limit of detection of the sensor is ~1000 viruses and can be altered by changing sensor’s lateral dimension and its transduction noise level.