Enhanced detection of explosives using organic semiconductors

Abstract

This thesis presents experimental research that aims to develop a novel trace explosive detector using conjugated polymers. New advances include a study of preconcentrator materials to improve sensitivity of the sensors; developing a methodology to make the sensors reusable; and approaches to enhance selective detection.

Sensitivity improvement involves the characterisation of four preconcentration materials PBE, Aflas, PIM-1, and sol-gel for their capacity to absorb, concentrate, and desorb explosives using absorption spectrometry. The results showed that Aflas can absorb explosive molecules from both solution and gas phases, while the retention capacity is poor. PBE showed a strong retention capacity in solution; however, it could not absorb from the gas phase. The sol-gel did not show preconcentration characteristics. PIM-1 showed preconcentration in both phases with high retention capacity, and was successfully applied in a test minefield.

Sensor recycling was investigated using thermal control. The fluorescent polymer Super Yellow (SY) was characterised by exposing it to various explosives at room temperature, resulting in the fluorescence quenching of the SY sensor. An increase in the sensor temperature overcomes the analyte binding interaction, allowing sorbed analytes to diffuse out of the `film, making the SY sensor reusable. The quenching efficiency of the SY sensor and the desorption temperature were also explored to discriminate between analytes.

Further study on selective detection of explosives was conducted using a 2x2 sensor array using four different fluorescent polymers. The sensor array was used with a portable fluorescence lifetime imaging device (which can spatially measure the fluorescence intensity and lifetime) to detect explosive vapours with enhanced selectivity. The responses of the polymers in the array during the flow of analytes and the purging process give insight into the binding interactions of the polymer/analyte pairs, and the responses can distinguish between analytes to serve as a fingerprinting tool for explosives.

Date of Award	10 Jun 2024
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Graham Turnbull (Supervisor)