Biointerface Strategies for COVID-19 Spike Protein Detection: A Surface Engineering Approach

Rapid diagnosis or health monitoring biosensors have been developed with the advent of technology. Silicon and metal oxides are used as the base material for these biosensors as a point-of-care unit. However, surface modification is needed to introduce functional groups for anchoring the bioreceptor. This study aims to explore the differences in the spike protein binding efficiency directly on the bare amine self-assembled monolayers (SAMs) and further cross-linked with the N-ethyl-N'-(3-(dimethylamino)propyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) and glutaraldehyde (GA). The specificity of binding was improvised by attaching a primary antibody to the modified surfaces. The functional groups, morphology, and wettability of the engineered surface were characterized using various analytical techniques. As depicted by fluorescence imaging, the spike protein was explicitly bound to the designed surfaces, while albumin was a negative control. The surface roughness after the attachment of spike protein varied as 13.64 nm (amine) > 3.81 nm (glutaraldehyde) > 1.91 nm (EDC-NHS). The EDC-NHS modified surface showed a higher and uniform surface coverage with the lowest roughness among all of the surfaces. The maximum N/C ratio, calculated from XPS data, was 0.16 for the EDC-NHS surface, i.e., twice that of the bare amine surface. The wettability of the EDC-NHS surface after protein binding was also found unaltered compared to the other two chemistries employed. The EDC-NHS surface resulted in a contact angle (CA) of ∼57°, which is close to that of the native spike protein (CA = 58°). While CA significantly reduced to 49° and 39° in the case of amine and glutaraldehyde surfaces, respectively. Most importantly, the EDC-NHS surface retained the native-like structure of the spike protein, which is crucial for the accurate sensing of infections and other related biomedical applications.