Detection of aspartame via microsphere-patterned and molecularly imprinted polymer arrays

A colloidal sphere-patterned polyterthiophene thin film sensor with high binding affinity and selectivity toward aspartame was fabricated using a technique combining molecular imprinting and colloidal sphere lithography. The successful imprinting of aspartame into electropolymerized molecularly imprinted polymer generated artificial recognition sites capable of rebinding aspartame into the microporous film, which was sensitively detected using quartz crystal microbalance measurements. The resulting sensor exhibited a good linear response after exposure to aspartame concentrations ranging from 12.5 μM to 200 μM and a detection limit of ~31 μM. It also demonstrated a high selectivity toward aspartame as compared to other peptide-based analogs including alanine-phenylalanine (Ala-Phe), alanine-glutamine (Ala-Gln), glycylglycine (Gly-Gly), and arginylglycylaspartic acid (RGD). The formation of the highly ordered and micropatterned surface was induced and monitored in situ by electrochemical quartz crystal microbalance and atomic force microscopy. Analyte imprinting and removal were characterized using X-ray photoelectron spectroscopy. Based on molecular modeling (semi-empirical AM1 quantum calculations), the formation of a stable pre-polymerization complex due to the strong hydrogen bonding interactions between the terthiophene monomer and aspartame played a key role in the effective aspartame imprinting and detection.