Analyte Sensitive Ultrasound Contrast Agents Based On Molecularly Imprinted Nanogel Sensors.

摘要

Recently developed ultrasound contrast agents provide traditional ultrasound techniques with highly localized contrast within samples depending on contrast agent concentration. Contrast agents resonate at characteristic frequencies, allowing background signals in backscatter collected from samples to be easily removed through filtration, leaving only resonance from contrast agents remaining. The goal of this thesis was to develop analyte sensitive contrast agents based on molecularly imprinted poly(N-isopropylacrylamide) (pNIPA) nanogel polymers. Molecularly imprinted pNIPA was synthesized in presence of target analyte theophylline. Ultrasonic analysis of pNIPA behavior in the presence of varying theophylline concentration revealed amplitude changes at various frequencies. Analysis of chemically similar caffeine demonstrated ultrasonic changes at different frequencies.;Solutions containing increasing amounts of theophylline in the 8.4 to 167 muM range with 1% by weight molecularly imprinted pNIPA in water were analysed ultrasonically. Concentration models displayed very high linearity (r2 coefficient exceeding 0.99). Additional concentration models were constructed in a matrix of solutions containing both the imprinted analyte theophylline, and interferant caffeine. Regression models for the two analytes demonstrated good linearity in the micromolar range (r2 of 0.98 for theophylline, 0.87 for caffeine) using different subsets of frequencies for each analyte.;A tighter binding arrangement between analyte and pNIPA was achieved through synthesis of molecularly imprinted pNIPA in the collapsed phase. This increased analyte sensitivity and linear range to nanomolar concentrations. Quantification assays were carried out on a dopamine oxidation product, (5-6-dihydroxyindole, DHI), from 16.7 to 163 nM. High linearity was obtained (r2 correlation coefficient exceeding 0.99). The experiment was repeated in a presence of albumin, a biologically relevant interferant, with good agreement between actual and estimated concentration.;Multi-analyte quantification was improved by combining two differently imprinted pNIPA nanogels to form multiplexed nanogels. Simultaneous quantification assays were carried out for theophylline (8.4 to 49 uM) and DHI (48.8 to 176 nM). Good linearity between estimated and actual concentrations were obtained (r2 of 0.99 for DHI, 0.96 for theophylline).;Determination of a larger analyte, tobacco mosaic virus (TMV), was also carried out. Concentration models in the 9 to 140 ppb range showed excellent linearity (correlation coefficients exceeding 0.99). The process was repeated in presence of another virus, tomato bushy stunt virus (TBSV), acting as an interferant. Similar linearity was obtained.;Critical points of the ultrasound quantification system based on molecularly imprinted nanogels are summarized in the Conclusion chapter. Improvements focusing on obtaining stronger ultrasonic signals in aforementioned analyses are discussed in the Future Works section.