Inverse-opal conducting polymer monoliths in microfluidic channels

Inverse opal monolithic flow-through structures of polyaniline (PANI) were achieved in microfluidic channels for lab-on-a-chip (LOC) applications. In order to achieve the uniformly porous monolith, polystyrene (PS) colloidal crystal (CC) templates were fabricated in channel. An inverse opal PANI structure was achieved on-chip, through a two-step process involving the electrochemical growth of PANI and subsequent removal of the template. The effect of electropolymerisation on these structures is discussed. It was found that growth time is critical in achieving an ordered structure with well-defined flow-through pores. This is significant in order to fabricate optimal porous PANI structures that maximise surface area of the monolith and also provide well-defined flow profiles through the micro-channel

Characterisation and optimisation of electrochemically addressable templated polyaniline structures

The application of intrinsically conducting polymers (ICPs) for lab-on-chip applications has shown recent success with many research groups reporting novel methods to incorporate and control ICP materials in lab-on-chip platforms. Chemical and electrochemical polymerisation have been used to successfully incorporate ICP materials within microfluidic platforms. However, fabrication of 3D ordered flow-through ICP structures has remained a limitation in this research area to date. This work describes how fabricating a reproducible ICP templating method within the confines of a microfluidic channel consisting of a polystyrene (PS) sphere colloidal crystal (CC) provides a viable solution to this issue. The capillary force packing method developed as part of this thesis offers for the first time a quick and reliable method for the uniform fabrication of unimodal and bimodal CC templates in channel. This is in contrast to other methods such as drop casting, spin coating and dip-drawing which were designed for CC fabrication on planar substrates. Here, 3D ordered CC structures were fabricated exclusively within the µchannel which were ordered along the length, width and depth of the cuboid channel and CC thickness was dictated solely by µchannel depth. This is in contrast to other CC fabrication methods were volume fraction (VFS/L) dictates CC thickness. Subsequently, the CCs were utilised to template ICP materials, namely polyaniline (PANI), in a microfluidic channel, where PANI was grown via electrochemical polymerisation. It was shown that control of the electrochemical polymerisation time was critical not only to the depth of the resulting inverse opal PANI, but also to the intrinsic morphology and flow-through nature of the material. This research demonstrated the fabrication of significantly deeper PANI inverse opal structures than had been previously reported, due to the new CC templating method employed which could be achieve over a wide range of channel depths (e.g. 50 – 180 µm). Although, this increased channel depth resulted in an inherent inhomogeneity through the depth of the final electrochemically polymerised inverse opal structure due to a current density gradient. To overcome this inhomogenity, an investigation of chemical polymerisation of PANI was undertaken. Prior to CC template formation, aniline monomer was adsorbed onto the PS spheres in solution and subsequently packed in channel. After CC formation of aniline coated PS spheres, chemical polymerisation of the surface-confined aniline was carried out and templated PANI/PS opal structures were achieved. This chemical polymerisation method resulted in a 3D ordered, flow-through PANI/PS opal structures with homogeneous PANI coverage housed within a sealed microfluidic channel. By incorporation of a working electrode along the µchannel, the PANI structure was also electrochemically addressable maintaining the potential for lab-on-chip applications such sensing or separation. Finally the effect of dopant type on hydrophobicity of PANI films was investigated. Fabrication of PANI films was achieved on gold-sputtered working electrodes using HCl or Sodium dodecyl sulphate (SDS) as dopant. The PANI films were characterised by comparison of their water contact angle (WCA), morphology and surface roughness. It was found that SDS-doped PANI films displayed an ultra-hydrophobic WCA when doped, which upon dedoping became hydrophilic. In contrast, HCl-doped PANI films displayed hydrophilic surface chemistry with little variation upon doping/dedoping. When comparing surface roughness, SDS-doped PANI films displayed an order of magnitude higher roughness to that of the HCl-doped films, likely due to the soft templating effect of SDS during polymerisation. In summary this thesis presents new research into ICP structures that can be utilised to develop new applications in miniaturised platforms such as lab-on-chip. The benefits of the methods developed are the flow through nature and electrochemical addressability of the final ICP materials. In conjunction the templating method developed in this thesis offers a fabrication route for homogeneous 3D ordered ICP materials which are reproducibly templated in channel. The CC fabricated in this thesis offer a unique and versatile template for microfluidic applications where increased order or surface area is a requirement such as sensing and separation

In Vitro Comparative Cytotoxicity Study of Aminated Polystyrene, Zinc Oxide and Silver Nanoparticles on a Cervical Cancer Cell Line

Nanoparticles use in nano-biotechnology applications have increased significantly with Aminated polystyrene amine (AmPs NP), Zinc oxide (ZnO NP), and Silver (Ag NP) nanoparticles utilized in wide variety of consumer products. This has presented a number of concerns due to their increased exposure risks and associated toxicity on living systems. Changes in the structural and physicochemical properties of nanoparticles can lead to changes in biological activities. This study investigates, compares, and contrasts the potential toxicity of AmPs, ZnO and Ag NPs on an in vitro model (HeLa cells) and assesses the associated mechanism for their corresponding cytotoxicity relative to the surface material. It was noted that NPs exposure attributed to the reduction in cell viability and high-level induction of oxidative stress. All three test particles were noted to induce ROS to varying degrees which is irrespective of the attached surface group. Cell cycle analysis indicated a G2/M phase cell arrest, with the corresponding reduction in G0/G1 and S phase cells resulting in caspase-mediated apoptotic cell death. These findings suggest that all three NPs resulted in the decrease in cell viability, increase intracellular ROS production, induce cell cycle arrest at the G2/M phase and finally result in cell death by caspase-mediated apoptosis, which is irrespective of their differences in physiochemical properties and attached surface groups

Liposomal Encapsulation of Silver Nanoparticles Enhances Cytotoxicity and Causes Induction of Reactive Oxygen Species‐ Independent Apoptosis

Silver nanoparticles (AgNP) are one of the most widely investigated metallic NPs due to their promising antibacterial activities. In recent years, AgNP research has shifted beyond antimicrobial use to potential applications in the medical arena. This shift coupled with the extensive commercial applications of AgNP will further increase human exposure and the subsequent risk of adverse effects that may result from repeated exposures and inefficient delivery, meaning research into improved AgNP delivery is of paramount importance. In this study, AgNP were encapsulated in a natural biosurfactant, dipalmitoylphosphatidylcholine, in an attempt to enhance the intracellular delivery and simultaneously mediate the associated cytotoxicity of the AgNP. It was noted that because of the encapsulation, liposomal AgNP (Lipo-AgNP) at 0.625g ml(-1) induced significant cell death in THP1 cell lines a notably lower dose than that of the uncoated AgNP induced cytotoxicity. The induced cytotoxicity was shown to result in an increased level of DNA fragmentation resulting in a cell cycle interruption at the S phase. It was shown that the predominate form of cell death upon exposure to both uncoated AgNP and Lipo-AgNP was apoptosis. However, a reactive oxygen species-independent activation of the executioner caspases 3/7 occurred when exposed to the Lipo-AgNP. These findings showed that encapsulation of AgNP enhance AgNP cytotoxicity and mediates a reactive oxygen species-independent induction of apoptosis

Carbon Nanomaterials and their application to Electrochemical Sensors: A review

Carbon has long been applied as an electrochemical sensing interface owing to its unique electrochemical properties. Moreover, recent advances in material design and synthesis, particularly nanomaterials, has produced robust electrochemical sensing systems that display superior analytical performance. Carbon nanotubes (CNTs) are one of the most extensively studied nanostructures because of their unique properties. In terms of electroanalysis, the ability of CNTs to augment the electrochemical reactivity of important biomolecules and promote electron transfer reactions of proteins is of particular interest. The remarkable sensitivity of CNTs to changes in surface conductivity due to the presence of adsorbates permits their application as highly sensitive nanoscale sensors. CNT-modified electrodes have also demonstrated their utility as anchors for biomolecules such as nucleic acids, and their ability to diminish surface fouling effects. Consequently, CNTs are highly attractive to researchers as a basis for many electrochemical sensors. Similarly, synthetic diamonds electrochemical properties, such as superior chemical inertness and biocompatibility, make it desirable both for (bio) chemical sensing and as the electrochemical interface for biological systems. This is highlighted by the recent development of multiple electrochemical diamond-based biosensors and bio interfaces

Production of polystyrene spheres for use as a templating material for polyaniline monolith structures.

Polystyrene (PS) spheres are potentially useful as a reproducible, sacrificial templating material for monolith columns once they can be utilised to create a uniform microstructured packing which enables a higher monolith batch to batch reproducibility. To achieve PS spheres which can meet these requirements, their synthesis was optimised. Parameters investigated included variation of reactant concentrations, along with optimisation of reaction conditions temperature, agitation speed and nitrogen flow during aeration. Temperature and agitati on played vital roles in the size and homogeneity of the synthesised PS spheres. Temperature affected the equilibrium concentration of monomer in the aqueous phase. When reaction temperature was increased, sphere size reduced and as reaction temperature decreased sphere size increased. A similar trend was seen when agitation speed was varied. At higher agitation speed average PS sphere size decreased as the rate of polymerisation increased. At lower agitation speed the average PS sphere size increased as the rate of polymerisation decreased. Ensuring fluctuations in both temperature and agitation were kept to a minimum was key to maintaining reproducibility. Any fluctuation above ~10% in either temperature or agitation speed affected standard deviation irreversibly. The facile dissolution of the PS spheres was also investigated. If the spheres produced could not be dissolved, their use as a sacrificial templating material would not be possible. By decreasing the original concentration of cross-linker, dissolution increased dramaticall

Inverse-opal conducting polymer monoliths in micro-fluidic channels.

Inverse opal monolithic flow-through structures of polyaniline (PANI) were achieved in microfluidic channels for lab-on-a-chip (LOC) applications. In order to achieve the uniformly porous monolith, polystyrene (PS) colloidal crystal (CC) templates were fabricated in channel. An inverse opal PANI structure was achieved on-chip, through a two-step process involving the electrochemical growth of PANI and subsequent removal of the template. The effect of electropolymerisation on these structures is discussed. It was found that growth time is critical in achieving an ordered structure with well-defined flow-through pores. This is significant in order to fabricate optimal porous PANI structures that maximise surface area of the monolith and also provide well-defined flow profiles through the micro-channel

Utilising 3D binary colloidal crystals to customise macropore and mesopore morphology and porosity

Current approaches to fabricate hierarchically porous (macroporous-mesoporous) monolithic materials for HPLC include using silica and thermally- or UV-initiated organic polymer. Silica monolith preparation is usually carried out using a sol–gel process to induce a hierarchical pore structure. Polymer monoliths, which contain primarily macropores have emerged as complimentary stationary phases to silica monoliths. It has proven difficult to date to prepare polymer monoliths in a single-step that possess a hierarchical pore structure, i.e. large through-pores, to enable flow at low back pressure, and a multiplicity of mesopores to increase surface area. 3D binary colloidal crystals may be formed by packing uniform spheres, followed by filling the interstitial space with a fluid that is subsequently converted into a solid skeleton. Upon removal of the spheres, a solid skeleton is created in the former interstitial spaces and interconnected voids where the spheres were originally located. By virtue of creating the solid skeleton, smaller pores (small macropores, mesopores, or micropores) can naturally be formed, e.g. as occurs during silica monolith fabrication. Further control of the skeleton architecture can be obtained when a secondary template is employed, e.g. ionic and nonionic surfactants, block copolymers, small colloids, etc. Micro-and nano-structuring using sacrificial templating approaches can induce both macropores and mesopores into polymer monoliths that can increase surface area by several orders of magnitude in a highly controlled fashion

Development of 3-dimensional nanostructured unimodal and bimodal polystyrene templates

The aim of this project is to construct a reproducible nanostructured polystyrene (PS) sphere colloid. The polystyrene colloidal crystal must incorporate both macro-sized (μm) and nano-sized (nm) spheres to further advance the potential applications of such templates. However the preparation of bimodal structures with a repeatable macropore-mesopore structure is not a straight forward process. Multiple methods were explored in the construction of unimodal and bimodal colloid crystal templates. Areas of interested such as variation in sphere size, up to two orders of magnitude between macro and nano-sized were investigated, along with determination of the rate at which each PS sphere size packed by capillary forces. Two methods have been singled out sequential deposition and co-deposition. Sequential deposition utilised two separate solutions one containing nano-sized PS spheres, the second macro-sized. During packing the glass chip is transferred between the macro and nano solutions before predetermined times. It was found that while packing sequentially formation of a nano-sized unimodal colloid was preferable. This was due to a faster rate of capillary force packing for the nano-sized PS spheres when compared to the macro-sized. The second method utilised was co-deposition. In this method a solution of both macro and nano-sized PS spheres was homogenised and packed for a period of twelve hours. To date co-deposition has shown the most promise as a reliable method to produce bimodal colloidal crystal