Morphology of Poly(styrene- co-butadiene) Random Copolymer Thin Films and Nanostructures on a Graphite Surface

Molecularly Imprinted Polymer Nanoparticles Enable Rapid, Reliable, and Robust Point-of-Care Thermal Detection of SARS-CoV-2

Rapid antigen tests are currently used for population screening of COVID-19. However, they lack sensitivity and utilize antibodies as receptors, which can only function in narrow temperature and pH ranges. Consequently, molecularly imprinted polymer nanoparticles (nanoMIPs) are synthetized with a fast (2 h) and scalable process using merely a tiny SARS-CoV-2 fragment (∼10 amino acids). The nanoMIPs rival the affinity of SARS-CoV-2 antibodies under standard testing conditions and surpass them at elevated temperatures or in acidic media. Therefore, nanoMIP sensors possess clear advantages over antibody-based assays as they can function in various challenging media. A thermal assay is developed with nanoMIPs electrografted onto screen-printed electrodes to accurately quantify SARS-CoV-2 antigens. Heat transfer-based measurements demonstrate superior detection limits compared to commercial rapid antigen tests and most antigen tests from the literature for both the alpha (∼9.9 fg mL-1) and delta (∼6.1 fg mL-1) variants of the spike protein. A prototype assay is developed, which can rapidly (∼15 min) validate clinical patient samples with excellent sensitivity and specificity. The straightforward epitope imprinting method and high robustness of nanoMIPs produce a SARS-CoV-2 sensor with significant commercial potential for population screening, in addition to the possibility of measurements in diagnostically challenging environments.

Thin Polymer Film Force Spectroscopy: Single Chain Pull-out and Desorption

Atomic force microscopy (AFM) was utilized to investigate the force associated with chain pull-out and single chain desorption of poly(styrene-co-butadiene) random copolymer thin films on mica, silicon, and graphite substrates. Chain pull-out events were common and produced a force of 20-25 pN. The polymer desorption force was strongest on the graphite substrate and weakest on the mica, which agreed with the calculated work of adhesion for each system and the substrate hydrophobicity. Furthermore, it was demonstrated that there was a systematic order to when each of these phenomena occurred during the tip retraction from the surface, which provided information about the structure of the thin films.