Chemical sensors based on swellable molecularly imprinted polymer microspheres in a hydrogel
A novel design of chemical sensors based on swellable molecularly imprinted polymer microspheres is presented. These sensors were successfully used to measure norephedrine and theophylline in water and in buffer at neutral pH. A new method was developed for preparing swellable norephedrine templated poly (N-isopropylacrylamide-acrylic acid) (poly NIPA-AAc) particles by suspension polymerization in a perfluorocarbon solvent using ultrasonic emulsion technique. The particles were crosslinked with 5% of N, N'-methlene-bis-acylamide (MBA) using 20% fluorinated surfactant as a stabilizer. The resulting particles were around 6 mum in diameter. HYPAN and poly (vinyl alcohol) (PVA) hydrogels were used to make hydrogel membranes containing norephedrine templated poly NIPA-AAc particles. The PVA membrane has higher response at high temperature. The phase transition of poly NIPA-AAc is affected by heating rate and pH. The sensor responds to norephedrine in water with high sensitivity (1.0 x 10-7 M) and specificity. The response time is ∼5 minutes. A dispersion polymerization method was developed to prepare swellable theophylline (THO) templated poly(N-isopropylacrylamide-methacrylic acid) (poly NIPA-MAA) microspheres in acetonitrile with 5% MBA as the crosslinker. MAA was used as a functional monomer to form recognition sites with the template during polymerization. Poly (styrene-co-acrylonitrile) (20% w/w) was used as a stabilizer resulting in uniform, spherical microspheres with diameter ∼1.0 mum. The percentages of NIPA and crosslinker are critical variables affecting polymer properties including the magnitude of swelling and shrinking, sensitivity, and selectivity. The response of PVA membranes containing templated microspheres in water and buffer were investigated. These microspheres were successfully used for theophylline sensing in water and phosphate buffer with high sensitivity (1.0 x 10-8 M) and selectivity (no response to caffeine up to 1.0 x 10-3 M). Poly (NIPA-N-t-butylacrylamide-MAA) (poly NIPA-NTBA-MAA) and poly (N-n-propylacrylamide-MAA) (poly NNPA-MAA) microspheres were prepared by the same method. The resulting microspheres were uniform, spherical, and ∼1.0 mum in diameter. The lower transition temperatures (12 and 15°C) of these polymers enable them to be used at room temperature. They were sensitive to theophylline concentration as low as 1.0 x 10-7 M and did not respond to caffeine as high as 1.0 x 10-3 M.
Networked Digital Library of Theses and Dissertations