Peptoid-Based Biosensors

Detection of viral pathogens is an essential part of the health care system, enabling medical providers to identify disease and prescribe appropriate treatments. Current detection methods like PCR and ELISA can be slow, expensive, and occasionally unable to provide the necessary sensitivity and specificity, particularly for cross-reacting species. Electrochemical sensors enhanced with peptoid-functionalized nanoparticles are an alternative diagnostic platform that offers rapid, direct detection of pathogens. These sensors function by registering a change in current associated with the binding of a target analyte; peptoid-functionalized nanoparticle coatings may increase the specificity and speed of these interactions. Gold nanoparticles (AuNPs) provide additional biocompatibility essential to biological molecule detection. Preparation of modified AuNPs involves the exchange of citrate stabilizing molecules for thiol-containing peptoids capable of imparting desired functionality. The surface modification of AuNPs is complicated by the tendency of nanoparticles to aggregate upon dislocation of the citrate layer, which imparts electrostatic stabilization. Several peptoids of varying size and sequence were found to promote AuNP aggregation, visible due to a shift in solution color from pink to blue or clear. Gold nanoparticle aggregation after peptoid introduction was found to be dependent on nanoparticle size, solvent, solution pH, and the inclusion of biological blocking buffers. Temperature, exposure to light, and mixing had minimal impact on functionalization kinetics and resultant aggregation. A successful gold nanoparticle functionalization method was developed by implementing an intermediate Tween monolayer, which provided steric stabilization after peptoid displacement of citrate stabilizing ions. Once bound on AuNPs, biological molecules often undergo changes to secondary or tertiary structure due to the nanoparticle surface curvature. Green fluorescent protein (GFP) was therefore used as a proof-of-concept to demonstrate functionality of the AuNP-bound peptoid. Fluorescence measurements indicated potential binding of GFP to the modified AuNPs, albeit at low levels. Further testing is needed to clarify this interaction.