Simultaneous chronoamperometry and piezoelectric microgravimetry determination of nitroaromatic explosives using molecularly imprinted thiophene polymers.

Thin films of conducting molecularly imprinted polymers (MIPs) were prepared for simultaneous chronoamperometry (CA) and piezoelectric microgravimetry (PM) determination of several explosive nitroaromatic compounds (NTs) including 2,4,6-trinitrophenol (TNP), 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitrobenzene (TNB), and 2,4-dinitrotoluene (DNT). For that, the bis(2,2'-bithienyl)-(4-aminophenyl)methane 1 functional monomer allowing for π-π stacking recognition of the NTs was designed and synthesized. Both theoretical DFT calculations at the M062X/3-21G* level and experimental fluorescence titrations indicated the 1:1 stoichiometry of the 1 and NT prepolymerization complexes formed in solutions. The NT-templated MIP (MIP-NT) films were deposited by potentiodynamic electropolymerization on the Au-coated quartz crystal resonators (Au-QCRs) from solutions of 1 and each of the NT templates at the 1-to-NT mole ratio of 1:1. For sensing application, the NTs were extracted from the MIP-NT films. Completeness of the extraction was confirmed by the presence and absence before and after extraction, respectively, of both the XPS peak of the N 1s electrons of the NT nitro groups and the DPV peak of electroreduction of the NTs for the MIP-NT. Ultimately, the recognition signal was transduced to the analytical signal of simultaneous changes of CA cathodic current and PM resonant frequency. The limit of detection (LOD) for NTs was in the range of hundreds and tens micromolar for CA and PM, respectively. Moreover, selectivity with respect to common interferences of the chemosensors was in the range 2.1-4.8, as determined by molecular cross-imprinting.