Fingerprinting Chemical Analytes with Water-Soluble Conjugated Polymer-Based Fluorescent Sensor Arrays

Over the past decades, conjugated polymers (CPs) have been applied to electronic and photonic devices, expanding this field in material chemistry. One recent area of interest on CPs comprises their application in the development of chemical sensors. That considered, the focus of this work was on the construction of water-soluble conjugated polymer-based chemical tongues and their application in sensing. Initially, four water-soluble poly(para-phenyleneethynylene)s (PPEs) were prepared, two of which reported for the first time on the basis of this work. The two novel PPEs are negatively charged, posses benzylic side chains, and react sensitively towards 2,4-dinitrotoluene and 2,4,6-trinitrotoluene. Twelve different nitro-aromatics were successfully discriminated by a small sensor array consisting of either the two novel PPEs or additional two neutral PPEs, using linear discriminant analysis to treat the data. A sensor array based on a combination of positively charged water-soluble PPEs, or green fluorescent protein (GFP), and three metal ions (Fe2+, Co2+, and Cu2+) at different pH values was also reported for the first time. The array discriminates all of the 20 natural amino acids in water. The sensitivity of the array was dramatically improved by addition of further sensor elements, and an optimized eight-member sensor array that discriminates all of the 20 amino acids with 100% accuracy was created. The results show great coherence upon grouping the amino acids according to their type: hydrophobic, polar and aromatic. Finally, two types of hypothesis-free sensor arrays, consisting of either three cationic PPEs or the same PPEs complexed with cucurbituril[8] (CB[8]) have been constructed. The PPE-CB[8] array discriminates tea-based amino acids and methylxanthine alkaloids (caffeine, theophylline and theobromine) through a displacement mechanism, while for the PPE-alone array, only caffeine, theobromine and theophylline elicited relevant fluorescence response. Both the PPE and PPE/CB[8] arrays effectivelly generated discriminating patterns for teas on the basis of differential fluorescence quenching, and allowed the differentiation of teas by brand, price, quality grades, and geographic origins. All together, the results herein obtained represent a significant contribution to the development of the field of chemical sensors based on CPs.