Intellectual merit: This is a collaborative project between researchers at Indiana University (IU) and Kansas State University (KSU). We have addressed the following two fundamental issues that are critical in developing nanoporous films and membranes for highly efficient detection and separation of environmentally relevant anions. This collaborative project has led to five publications in peer-reviewed journals with two more papers in preparation.

(1) We have shown that nanoporous films fabricated from a polymer consisting of two immiscible polymer chains (diblock copolymer) provides a means to fabricate high-porosity nanoporous films. Our diblock copolymers are based on polystyrene (PS) and poly(ethylene oxide) (PEO) segments that are connected through a photosensitive group cleavable by UV light. They form cylinder-shaped PEO nanostructures as a result of microphase separation of the two immiscible polymer chains. Nanoporous thin films can be prepared by spin-casting thin diblock copolymer films on substrates, annealing the films under humidified benzene vapor to induce the microphase separation, followed by the UV irradiation and subsequent washing with methanol to remove the cylindrical PEO nanostructures.The major challenge is to align the cylindrical PEO nanostructures perpendicularly to the electrode surface as vertically oriented nanopores are desirable for efficient capture and detection of target anions at the electrode-supported nanoporous films. We have found that functionalization of electrode surfaces with a self-assembled monolayer provides a robust way to obtain thin diblock copolymer films comprising vertically oriented cylindrical PEO nanostructures.  After removing the nanostructures, we obtained high porosity films that exhibit high accessibility of electroactive species toward the underlying electrode through the resulting nanopores.  We have successfully demonstrated that the surfaces of the nanoscale pores and underlying electrode can be chemically functionalized to obtain nanospaces with tailored environments.  We have also shown that the performance of electrochemical DNA detection can be improved by use of nanoporous film-coated electrodes as platforms of stem-loop DNA probes, possibly owing to the nanopore-induced manipulation of the dynamics of the probes.

(2) We have designed functional molecules that change their electrochemical properties upon binding to target anions for selective capture/release and detection of environmentally relevant anions such as chloride and phosphate ions. Through systematic spectroscopic and electrochemical measurements, we have quantitatively assessed the contribution of electrostatic interactions on anion binding, which provides important guidelines for designing anion receptors with controlled selectivity and affinity.

Broader Impacts: (1) Three graduate students including one female have been working on the project. The female student at IU took on leadership roles in student-run associations on campus at IU, including the Student Chapter of the Materials Research Society and Women in Organic Chemistry.  (2) The PI and collaborator PI at KSU co-organized a special symposium at Pittcon 2020 on “Supramolecular Chemistry for Sensing, Sequestration and Separation” to advertise the state-of-the-art in supramolecular research to analytical chemists.  (3) The co-PI and collaborator PI at KSU developed a new course on Polymer Synthesis and Characterization. In the course, four graduate students at KSU were trained on diblock copolymer synthesis via controlled radical polymerization and their characterization methods including FTIR external reflection spectroscopy, NMR, ellipsometry, size-exclusion chromatography, and atomic force microscopy.  

Last Modified: 11/28/2022
Modified by: Yi Yi