Integration of a polymerisable fluorescent urea-nitrobenzoxadiazole monomer 1 into a few-nanometre thin molecularly imprinted polymer (MIP) shell coated onto a 300 nm silica core with the tetrabutylammonium salt of N-carbobenzyloxy-L-phenylalanine (Cbz- or Z-ʟ-Phe) as the imprinted template yields core/shell MIP nanoparticles that respond to the designated analyte with a strong fluorescence increase in the visible spectral range. The system shows promising imprinting and enantioselectivity factors of 3.6 and 1.9 when benzylmethylacrylate (BMA) is used as co-monomer and ethylene glycol dimethacrylate (EDMA) as cross-linker. A second, naphthalimide-based fluorescent urea 2 is employed in the preparation of MIP thin-films and monolithic polymers for separation techniques. Spectroscopic and chromatographic studies of the MIPs with the analytes Z-ʟ-Phe, Z-ʟ-glutamic acid (Z-ʟ-Glu) and penicilin G (PenG) revealed the (enantio)selective discrimination behaviour of these materials.
A 2,3-diaminophenazine bis-urea fluorescent probe monomer (1) was developed. It responds to phenylphosphate and phosphorylated amino acids in a ratiometric fashion with enhanced fluorescence accompanied by the development of a redshifted emission band arising from an excited-state proton transfer (ESPT) process in the hydrogen-bonded probe/analyte complex. The two urea groups of 1 form a cleft-like binding pocket (Kb>10^10 L^2 mol^-2 for 1:2 complex). Imprinting of 1 in presence of ethyl ester- and fluorenylmethyloxycarbonyl (Fmoc)-protected phosphorylated tyrosine (Fmoc-pTyr-OEt) as the template, methacrylamide as co-monomer, and ethyleneglycol dimethacrylate as crosslinker gave few-nanometer-thick molecularly imprinted polymer (MIP) shells on silica core microparticles with excellent selectivity for the template in a buffered biphasic assay. The supramolecular recognition Features were established by spectroscopic and NMR studies. Rational screening of comonomers and cross-linkers allowed to single out the best performing MIP components, giving significant imprinting factors (IF>3.5) while retaining ESPT emission and the ratiometric response in the thin polymer shell. Combination of the bead-based detection scheme with the phase-transfer assay dramatically improved the IF to 15.9, allowing sensitive determination of the analyte directly in aqueous media.