Exploring signal transduction mechanisms in molecularly imprinted polymers for forensic applications

by Timothy Kirkman

Institution: University of Newcastle
Degree: PhD
Year: 2014
Keywords: polymer; molecular imprinting; drugs; conductive polymer; gold nanoparticles; nanoparticles; ephedrine; epinephrine; adrenaline; sensor; signal transduction
Record ID: 1055183
Full text PDF: http://hdl.handle.net/1959.13/1055291


Research Doctorate - Doctor of Philosophy (PhD) This work explores the potential of two signal transduction mechanisms for molecularly imprinted polymers (MIPs) primarily for the detection of (-)-ephedrine (EPD). Firstly, gold nanoparticles were utilised resulting in a surface plasmon resonance based detection mechanism. Poly(acrylic acid-co-N’-isopropylacrylamide-co-N,N’-methylenebisacrylamide) (PAA-IPA-MBA), a conventional cross-linked MIP film, and poly(acrylic acid-co-acrylonitrile-co-methyl methacrylate) (PAA-AN-MMA), a phase-inversed 2D MIP film, were investigated. Gold nanoparticles were prepared and embedded into these polymers, with the resulting MIP systems demonstrating good selectivity and specificity for EPD. Spectroscopic detection studies based on hypsochromic shift in the wavelength of maximum absorbance in the surface plasmon resonance (SPR) of the embedded gold nanoparticles were performed. While SPR response was not observed for PAA-IPA-MBA, PAA-AN-MMA MIP films exhibited prominent shifts of up to 15nm after as little as 10 minutes of EPD sorption. Wavelengths shift observed in the non-imprinted PAA-AN-MMA after EPD sorption was minimal (≤8 nm) signifying MIP selectivity and significantly reduced (≤5 nm) in the presence of template analogues signifying MIP specificity. To the best of our knowledge, this is the first time SPR signal has been observed in 2D MIP films. Secondly, a composite of molecularly imprinted and poly(3,4 ethylenedioxythiophene): polystyrenesulfonic acid (PEDOT:PSS) conductive polymer (CP) was developed for the detection of EPD. 3-Methylthienyl methacrylate (MTMA) was successfully used as a dual purpose monomer to link between the CP (via its thiophene moiety) and MIP (via its vinylic group) components of the composite. Composite particles of PEDOT:PSS and cross-linked MIP of acrylic acid and methylenebisacrylamide afforded the highest level of MIP binding (0.91μmol/mg after 2 hours) and selectivity (imprinting factor of 27 obtained after 10 minutes stabilising to 11 after 2 hours). While this CP-MIP composite particles lost its selectivity when embedded into a PEDOT:PSS conductive matrix (to allow electrochemical detection) due to significant non-selective interaction between EPD and the PSS in excess, we have demonstrated, for the first time, the potential of a CP-MIP composite for electrochemical sensing given the right conditions and matrix. The design and formulation of all MIPs investigated in this study are supported by interaction studies between monomers and analytes (template and competing analogues) using semi-empirical molecular modelling and NMR spectroscopy.