Study of polydiacetylene-based colorimetric chemosensors and development of oligonucleotide-chemosensor conjugate as a dual analytes responsive detection platform

Abstract

Chapter Ⅰ. Development of polydiacetylene-based colorimetric chemosensors for detection of heptanal and Ca2+.

Chemosensors consist of two common parts which are a signaling part and a receptor part. Among many types of signaling processes applied in chemosensors, colorimetric signaling based on the change of color has received attention because of the simple detection by the naked eye. The polydiacetylene (PDA) is one of the attractive colorimetric signal transducers, that ene-yne backbone of the conjugated polymer shows a distinct blue color, and the conformational perturbation of the PDA backbone by external stimuli is followed by the blue-to-red color transition. Based on the unique structure and activity relationship, the introduction of numerous receptors facilitated the development of various PDA-based chemosensors and in this study, two receptors were designed for the detection of heptanal and Ca2+. Aldehydes with long alkyl chains such as heptanal are important biomarkers, but chemosensors for the detection of the aldehydes have been rarely reported. Herein, a chemosensor based on hydroxylamine-functionalized PDA was developed for the selective detection of heptanal, which contains a long alkyl chain. The hydroxylamine group of PDA reacts with the aldehyde group of heptanal, while hydrophobic interactions between the alkyl chains of PDA and heptanal occur simultaneously. As a result, the synergistic interactions allowed for the selective detection of heptanal over formaldehyde and acetaldehyde, which do not contain long alkyl chains. In addition, the developed PDA-based chemosensor was applied to determine heptanal in serum samples. Ca2+ is an important metal ion in serum that can be used as a biomarker for malignant tumors and hyperparathyroidism. Therefore, some probes based on mono-species ligands for detection of Ca2+ in serum have been developed, but often suffer from poor selectivity for the target ion over Mg2+, Cu2+, and Zn2+. Thus, co-functionalization with phosphate and carboxylate on PDA was proposed to selectively detect calcium ions in serum, inspired by biologically abundant phosphate–calcium ion and carboxylate– calcium ion binding. Although each ligand also interacts with other metal ions, the cooperative effect through the introduction of mixed ligands facilitated the selective detection of calcium ions over major interference in many calcium ion probes. The sensor system exhibited highly sensitive detection of calcium ions and the detection method was employed to determine the concentration of calcium ions in various serums.

Chapter Ⅱ. Development of oligonucleotide-chemosensor conjugate as a dual analytes responsive detection platform.

Physiological processes, which occur in a complex biological environment, accompany a change of multiple elements and so it makes important detect the molecules simultaneously. Because of the confused data interpretation anticipated when using two other probes for simultaneous detection, a dual responsive probe, which can detect two analytes in one probe, has been regarded desirably for simultaneous detection. The dual responsive probe operating as a logic gate is the most ideal in a subclass where an absence of analytes and the presence of each or both analytes exhibit four different emissions. Due to the complicated conditions for the achievement of the ideal case, most of the reported probes were confined to a simple linkage between two individual detection probes based on the small molecule chemosensor, which has the examples for the detection of various targets and easy connection methods. Oligonucleotide-based detection platform also has been well-known as a versatile biosensor to detect various analytes through a hybridization probe and an aptamer probe. In addition, the chemical modification of oligonucleotide with fluorophore or quencher for the signal transduction was well established, allowing the application of these modification methods to various molecular connections. Therefore, some dual responsive probes were suggested based on the oligonucleotide probes like the small molecule chemosensors. Despite these shared properties between small molecule- and oligonucleotide-based probes such as various detection examples and easy chemical modification, the fundamental difference in the receptor composition derived from abiotic and biotic molecules makes its own domains involving the kind of targets, modifications, and the process for probe preparation. Thus, we expected that the oligonucleotide-chemosensor conjugates can expand the detectable targets and applicable scaffold as a novel dual responsive detection platform. As proof of the concept, two other oligonucleotide probe-chemosensor conjugates were introduced for the detection of ATP and ZIP1 mRNA with Zn2+, respectively. For the simultaneous detection of ATP and Zn2+ which were the key biomarkers related to diabetes in a secretary granule of the pancreatic beta cell, an aptamer probe for ATP detection and Zn2+ chemosensor was readily conjugated, and it was confirmed that the conjugate can be applied to discriminate four different cases that involve the absence of targets, and presence of each or both targets. And, for the simultaneous detection of ZIP1 mRNA and Zn2+ that can offer clues about transformation to malignancy in prostate cells, the hybridization probe for ZIP1 mRNA detection and Zn2+ detection chemosensor were simply conjugated and the conjugate showed a property to determine the four distinct cases according to the existence of ZIP1 mRNA and Zn2+.