Surface plasmon resonance sensors using molecularly imprinted polymers for sorbent assay of theophylline, caffeine, and xanthine

A sensory system based on the optical phenomenon of surface plasmon resonance (SPR), which employs either photothermal deflection spectroscopy (PDS) or a photodiode array (PDA) for detection, was developed to use molecularly imprinted (MI) polymethacrylic acid -ethylene glycol dimethacrylates (PMAA-EDMA) as the sensing element. The MI polymers were first processed by Soxhlet extraction to remove the print molecules (theophylline, caffeine, and xanthine), yielding the specific anti-polymers. Each anti-polymer was layered over a silver film to serve as the analysis surface for the molecularly imprinted sorbent assay (MIA) of one target drugs. This surface was exposed for 60 min to an aqueous standard drug solution, dried in air, and the uptake of the print molecule into the anti- polymer was monitored by shifts in the SPR angle θ(r) (and hence the SPR- PDS signal measured at constant θ). The linear dynamic range of the MIA was found to extend up to 6 mg/mL, with a concentration detection limit estimated at 0.4 mg/mL for theophylline in aqueous solution. A cross-reactivity study of the anti-theophylline and anti-caffein