Our group is currently developing in-field detection systems alongside the Australian Federal Police Forensic Services utilising molecularly imprinted polymers as the recognition elements. This review looks at MIP synthesis and our perceptions of future directions from an Australian and forensic perspective.

Synthesis of trans-aconitic acid molecularly imprinted polymers in [bmim][BF4] and [bmim][PF6] under photochemical (5 degrees C, AIBN) and thermal (60 degrees C, AIBN) conditions gave polymer micro-spheres (<200 nm), under bulk and precipitation polymerisation conditions, and higher selectivity indices (100% improvement) relative to the more traditional precipitation polymerisation (CH3CN, high solvent volumes) approach.

Xanthates ([1-(O-ethylxanthyl)ethyl]benzene (CTA1) and [1-(O-trifluoroethylxanthyl)ethyl]benzene (CTA2)) have the capacity to control the molecular weight distribution in emulsion polymerizations to produce very small nanoparticles below 20 nm. We form stable translucent polystyrene latexes using surfactant (sodium dodecyl sulfate, SDS) and a small amount of pentanol as cosurfactant. The high CTA concentration results in a greater retardation in rate until consumption of all the RAFT agent. With an increase in CTA1 the particle size decreases from 38 to 8 nm and the particle number concentration N c increases from 2 Â 10 18 to 2 Â 10 20 particles/L. Although an increase in N c should in principle lead to a faster rate of polymerization, we observe a greater retardation in rate with increasing CTA. The higher C tr,RAFT of CTA2 results in a greater initial retardation until consumption of all the RAFT agent and particle diameters lower than 5 nm and at high concentrations of CTA2 diameters that are not measurable. Kinetic simulations solving the Smith-Ewart equations explain the anomaly between R • (formed from the fragmentation of the R group from the RAFT agent) acting to nucleate micelles and terminate radicals within particles. The small and mobile R • radicals can exit particles, re-enter micelles or other particles, re-exit until they either nucleate micelles, or terminate with propagating polymeric chains. This process of exit and re-entry is similar to limit 3 in a conventional emulsion polymerization. The higher micelle nucleation rate through initiation within micelles by R • radicals results in smaller and a greater number of particles. Exit is the dominant mechanism for greater nucleation and retardation.

Caffeine templated molecularly imprinted polymers (MIPs) have been prepared using identical polymer formulations by thermal and microwave induced initiation, and the binding performance of the systems compared using solid phase extraction (SPE). While the binding capacity of MIP (Microwave) was found to be lower than MIP (Thermal) , MIP (Microwave) recorded a higher imprinting factor (IF) due to comparatively low levels of non-specific binding. Selectivity against theophylline in cross-reactivity studies was also found to be greater for MIP (Microwave) . While large time savings are achievable through the use of microwave irradiation conditions, physical analysis of the polymers (surface area analysis, thermal gravimetric analysis and differential scanning calorimetry) reveals that the different polymerisation methods lead to differences in both polymer structure and performance.

The selectivity and rebinding capacity of molecularly imprinted polymers selective for propranolol (1) using the room temperature ionic liquids [BMIM][BF4], [BMIM][PF6], [HMIM][PF6] and [OMIM][PF6] and CHCl3 were examined. The observed IF (imprinting factor) values for MIPBF4, MIPPF6 and MIPCHCl3 were 1.0, 1.98 and 4.64, respectively. The longer chain HMIM and OMIM systems returned lower IF values of 1.1 and 2.3, respectively. MIPPF6 also showed a 25% binding capacity reduction vs. MIPCHCl3 (5 μmol g(−1)vs. 7 μmol g(−1) respectively). MIPCHCl3 and MIPPF6 differed in terms of BET surface area (306 m(2) g(−1)vs. 185 m(2) g(−1)), pore size (1.10 and 2.19 nm vs. 0.97 and 7.06 nm), the relative number of pores (Type A: 10.4 vs. 7.5%; Type B: 8.5 vs. 3.0%), and surface zeta potential (−37.9 mV vs. −20.3 mV). The MIP specificity for 1 was examined by selective rebinding studies with caffeine (2) and ephedrine (3). MIPPF6 rebound higher quantities of 2 than MIPCHCl3, but this was largely due to non-specific binding. Both MIPCHCl3 and MIPPF6 showed a higher affinity for 3 than for 2. Reduction in the Room Temperature Ionic Liquid (RTIL) porogen volume had little impact on the polymer morphology, but did result in a modest decrease in IF from 2.6 to 2.3 and in the binding capacity (30% to 19%). MIPCHCl3 retained the highest template specificity on rebinding from CHCl3 (IF = 4.6) dropping to IF = 0.6 in MeOH/[BMIM][PF6]. The MIPCHCl3 binding capacity remained constant using CHCl3, CH2Cl2 and MeOH (46–52%), dropped to 6% on addition of [BMIM][PF6] and increased to 83% in H2O (but at the expense of specificity with IFH2O = 1.4). MIPPF6 rebinding from MeOH saw an increase in specific rebinding to IF = 4.9 and also an increase in binding capacity to 48% when rebinding 1 from MeOH and to 42% and 45% with H2O and CH2Cl2, respectively, although in the latter case the increased capacity was at the cost of specificity with IFCH2Cl2 = 1.2. Overall the MIPPF6 capacity and specificity were enhanced on addition of MeOH.