Development of a Colorimetric Polydiacetylene, Solid-Substrate Sensor for SARS-CoV-2 Detection in Human Saliva

The SARS-CoV-2 pandemic caused tremendous loss of life and long-term health effects for many. The virus continues to evolve, and new variants have the potential to cause widespread physical and economic impacts. Long-chain carboxylic acids featuring two conjugated acetylenes midway along the chain easily self-assemble onto various substrates, particularly polyvinylidene fluoride, and then polymerize to form a deep blue film. COVID-19 nucleocapsid or spike protein antibodies can be conjugated to the film, and upon exposure to appropriate trigger proteins, they turn pink or red. Certain additives commonly found in commercial preparations of COVID-19 proteins can trigger false positives. The addition of small amounts of surfactants can increase detector sensitivity, though this must be carefully controlled to avoid false positives. Sensing systems based on both nucleocapsid and ACE2 antibodies can detect authentic samples of the virus in human saliva. The platform is readily adaptable to antibodies from new variants.