Sensing via Analyte-Triggered Gelation: Molecular Design and Implementation.

Abstract

Chapter 1 provides an introduction to molecular gels and their applications. Molecular gels are formed through the self-assembly of small molecules and have attracted enormous interests in applications such as drug delivery, tissue engineering, regenerative medicine, environmental remediation and biochemical sensing. Despite all the potential applications, designing gelators remains a challenge because gelation is difficult to predict. This thesis undertakes these challenges by designing new gel-based chemical sensors as well as performing structure-property relationship studies to elucidate the controlling factors in molecular gelation. Chapter 2 describes the design and implementation of a gel-based sensor for nitric oxide. The sensor utilized an oxidation-induced planarization to convert a non-planar precursor into a planar gelator. Solid-state packing suggested that one-dimensional interactions between gelators might be the driving force for gelation.

Chapter 3 describes detailed structure-property relationship studies in molecular gelation on a class of pyridine derivatives. It was found that gelation ability was not correlated to room temperature solubility or the presence of 1D intermolecular interactions. Instead, dissolution parameters were able to distinguish gelators from nongelators. In Chapter 4, we further measured the dissolution parameters on a class of dipeptides and observed a similar trend regardless of molecular framework and solvent system. Chapter 5 describes the design and development of a portable gel-based triacetone triperoxide (TATP) sensor. A H2O2-induced thiol-to-disulfide oxidation was coupled with the solution-to-gel transition in response to the presence of TATP. Further optimizations led to a portable and convenient gel-based TATP sensor. Chapter 6 presents our preliminary efforts on developing a quantitative gel-based sensor by correlating gel properties (e.g., viscosity and modulus) with gelator concentration. A magnetoelastic sensor was identified as a promising quantification tool in gels. Chapter 7 provides a conclusion of the current state for gel-based sensors and an outlook for the field of molecular gels. Notably, our work not only expands the scope of gel-based chemical sensors, but also provides preliminary insights to gelator design with in-depth structure-property relationship studies and makes preliminary effort towards the development of quantitative gel-based sensor.