Quantum dot and carbon dot polymer nanocomposites for latent fingermark detection

Author: Jessirie Dilag

Dilag, Jessirie, 2014 Quantum dot and carbon dot polymer nanocomposites for latent fingermark detection, Flinders University, School of Chemical and Physical Sciences

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Abstract

Over the last decade interest in fluorescent nanoparticles for forensic applications has greatly increased. This thesis describes the synthesis of fluorescent nanoparticles with polymer grafted from their surface for latent fingermark detection. This allows for essential colour contrast for fingermark visualisation and subsequent person identification. In the first part of the thesis cadmium sulfide (CdS) quantum dots (QDs) were synthesised. These QDs have size tuneable fluorescence, which was investigated using theoretical calculations of band gap energies measured by UV-visible spectrophotometry. Once synthesised a chain transfer agent (CTA) was immobilised onto the QD surface using a Steglich esterification method. Subsequently reversible addition fragmentation chain transfer (RAFT) polymerisation (a controlled polymerisation technique), was used to graft dimethylacrylamide (DMA) from the surface of the QDs via the CTA on its surface. This gave a CdS/p(DMA) nanocomposite, which was water soluble. Aqueous solutions of CdS/p(DMA) were then applied as a solution reagent to successfully detect latent fingermarks deposited on non-porous substrates. The fluorescently developed fingermarks were visualised and photographed using a Polilight® (UV = 350 nm). The RAFT process was versatile in that different monomers could be used, and hence different polymers with suitable physical attributes were synthesised. Random copolymers of DMA with methyl methacrylate (MMA) and styrene (Sty) were then grafted from the CdS QDs to give CdS/p(DMA-co-MMA) and CdS/p(DMA-co-Sty). This ultimately led to the synthesis of fluorescent powders that could be dusted onto the latent fingermarks for detection. The powders were found to give better ridge definition than the solution form. Despite protection of the CdS QDs in the core of the polymers synthesised, there was always a residual concern for the use of the heavy metal, Cd, in the synthesis of these and other conventional QDs. Over the past decade years, research into nanocarbons has grown exponentially, with our interest particularly focused on using fluorescent carbon nanoparticles (C-dots) for this thesis. C-dots, in literature, have been reported as non-toxic, biocompatible, alternatives to conventional QDs. C-dots were synthesised via thermal oxidation of activated charcoal (AC) in nitric acid. They were inexpensive to synthesise. Their optical properties were visually comparable to the CdS QDs, and emission intensities were found to be defined by working pH (acidity/basicity). We applied the same polymerisation techniques (RAFT) to synthesise C-dot/polymer nanocomposites to successfully detect latent fingermarks that were deposited on non-porous materials. Visually, these were comparable to the QD/polymer nanocomposites previously synthesised and applied successfully to the detection latent fingermark on non-porous surfaces. Lastly, the RAFT process was further exploited - by which the active end group (given by the RAFT agent) of the polymer was modified in a straightforward manner. Divinyl sulfone (DVS) modified magnetic beads were attached to CdS and C-dot polymer nanocomposites via a one-pot aminolysis/thiol-ene click reaction. This resulted in a magnetic fluorescent CdS QD or C-dot polymer powder that could potentially be used as a type of “Magna Powder” in latent fingermark detection.

Keywords: quantum dot,carbon dot,polymer,nanocomposite,forensic science,fingermark,fingerprint,raft polymerisation
Subject: Nanotechnology thesis

Thesis type: Doctor of Philosophy
Completed: 2014
School: School of Chemical and Physical Sciences
Supervisor: Professor Amanda Ellis