Development of biofunctional and biocompatible surfaces for biodiagnostic applications utilising plasma enhanced chemical vapour deposition

Plasma enhanced chemical vapour deposition was investigated for the deposition of biofunctional thin films onto surfaces in the fabrication of biomedical diagnostic devices. Two major aspects of the deposited films were assessed for their applicability in new diagnostic systems. The first relates to the functionality of the surface. The functionality of the surface relates to the ability of specific surface functional groups to be deposited stably and in a manner that will allow for biomolecular adhesion. Biomolecular adhesion is an important feature of surfaces requiring immobilisation of a detection agent, especially in liquid throughput devices. A comprehensive characterisation of the films developed herein was carried out. Following on from work previously undertaken by members of our research group, the films developed have shown a high degree of stability of the density of surface functional groups after exposure to aqueous conditions similar to those employed by liquid throughput devices. I found that the densities of these surface groups are superior to films created through liquid chemical deposition. Processes developed as part of this work were tailored for optimal manufacturability, e.g. the removal of heating apparatus required by the aminopropyltriethoxysilane monomer by installing a complimentary tetraethyl orthosilicate and allylamine process. Secondly, I investigated surface wettability and developed a novel process for surface wettability control using atetraethyl orthosilicate and acrylic acid film stack. The plasma polymerised acrylic acid film was employed to react with the underlying organosilicon matrix, causing a shift in the surface characteristics. The polymeric acrylic acid network was shown to have a wearing effect on the organosilicon, catalysed by environmental water vapour. This process was subsequently controlled for the purpose of wettability control of the surface. As the underlying organosilicon layer is reduced, the increasingly oxygen rich interface becomes more hydrophilic, giving specific and stable control over the surfaces‟ water contact angle. As the fluidic interaction with a surface is generally of high importance in microfluidics, control of this provides a method of improving the workability of novel fluidic systems with materials that previously showed unfavourable characteristics

Characteristic of silicon doped diamond like carbon thin films on surface properties and human serum albumin adsorption

Diamond-like carbon (DLC) coatings are useful for creating biocompatible surfaces for medical implants. DLC and silicon doped DLC have been synthesised using plasma enhanced chemical vapour deposition (PECVD). The effects of surface morphology on the interaction of human serum albumin (HSA) with doped and undoped DLC films have been investigated using a range of surface analysis techniques using Raman spectroscopy and atomic force microscopy (AFM). Raman spectra of doped DLC show that silicon doped DLC reduces the growth range of the ID/IG ratio, with a significant red-shift of the G peak position. Following exposure to protein, for undoped DLC the peaks at 1664 cm−1 and around 1241 cm−1 can be attributed to amide I and III, respectively, with an increase in the surface morphology of the surfaces giving some indication of the protein structure on the surfaces. Results indicate that HSA exhibit the majority of β-sheet during the adsorption on the surfaces. The results showed that the silicon incorporation DLC tends to increase of surface roughness and the adsorbed level of HSA is higher with higher levels of silicon doping of the DLC. Therefore, doping DLC may provide a method of controlling the adsorption of protein

Physicochemical and biological activity analysis of low-density polyethylene substrate modified by multi-layer coatings based on DLC structures, obtained using RF CVD method

In this paper, the surface properties and selected mechanical and biological properties of various multi-layer systems based on diamond-like carbon structure deposited on low-density polyethylene (LDPE) substrate were studied. Plasma etching and layers deposition (incl. DLC, N-DLC, Si-DLC) were carried out using the RF CVD (radio frequency chemical vapor deposition) method. In particular, polyethylene with deposited N-DLC and DLC layers in one process was characterized by a surface hardness ca. seven times (up to ca. 2.3 GPa) higher than the unmodified substrate. Additionally, its surface roughness was determined to be almost two times higher than the respective plasma-untreated polymer. It is noteworthy that plasma-modified LDPE showed no significant cytotoxicity in vitro. Thus, based on the current research results, it is concluded that a multilayer system (based on DLC coatings) obtained using plasma treatment of the LDPE surface can be proposed as a prospective solution for improving mechanical properties while maintaining biocompatibility

Synthesis of plasmonic gold nanoparticles on soft materials for biomedical applications

Plasmonic metal nanomaterials are usually supported by rigid substrates, typically made of silicon or glass. Recently, there has been growing interest in developing soft plasmonic devices. Such devices are low weight, low cost, exhibit elevated flexibility and improved mechanical properties. Moreover, they maintain the features of conventional nano-optic structures, such as the ability to enhance the local electromagnetic field. On account of these characteristics, they show promise as efficient biosensors in biological, medical, and bio-engineering applications. Here, we demonstrate the fabrication of soft polydimethylsiloxane (PDMS) plasmonic devices. Using a combination of techniques, including electroless deposition, we patterned thin membranes of PDMS with arrays of gold nanoparticle clusters. Resulting devices show regular patterns of gold nanoparticles extending over several hundreds of microns and are moderately hydrophilic, with a contact angle of about 80°. At the nanoscale, scanning electron and atomic force microscopy of samples reveal an average particle size of ∼50 nm. The nanoscopic size of the particles, along with their random distribution in a cluster, promotes the enhancement of electromagnetic fields, evidenced by numerical simulations and experiments. Mechanical characterization and the stress-strain relationship indicate that the device has a stiffness of 2.8 MPa. In biological immunoassay tests, the device correctly identified and detected anti-human immunoglobulins G (IgG) in solution with a concentration of 25 μg/ml

Synthesis of Tailored Perfluoro Unsaturated Monomers for Potential Applications in Proton Exchange Membrane Preparation

The aim of the present work is the synthesis and characterization of new perfluorinated monomers bearing, similarly to Nafion®, acidic groups for proton transport for potential and future applications in proton exchange membrane (PEM) fuel cells. To this end, we focused our attention on the synthesis of various molecules with (i) sufficient volatility to be used in vacuum polymerization techniques (e.g., PECVD)), (ii) sulfonic, phosphonic, or carboxylic acid functionalities for proton transport capacity of the resulting membrane, (iii) both aliphatic and aromatic perfluorinated tags to diversify the membrane polarity with respect to Nafion®, and (iv) a double bond to facilitate the polymerization under vacuum giving a preferential way for the chain growth of the polymer. A retrosynthetic approach persuaded us to attempt three main synthetic strategies: (a) organometallic Heck-type cross-coupling, (b) nucleophilic displacement, and (c) Wittig–Horner reaction (carbanion approach). Preliminary results on the plasma deposition of a polymeric film are also presented. The variation of plasma conditions allowed us to point out that the film prepared in the mildest settings (20 W) shows the maximum monomer retention in its structure. In this condition, plasma polymerization likely occurs mainly by rupture of the bond in the monomer molecule

Development of carbon nanostructures from non-conventional resources

Carbon nanostructures (CNSs) perpetuate the scientific interest over decades due to their remarkable properties and emerging technological applications. The development of sustainable technologies for the synthesis of CNSs from natural resources grabbed immense research attention aiming to implement these high-end materials in wide range of nano electronic devices through safe and environmentally friendly routes. Even though a number of top down and bottom up approaches have been developed for the production of CNSs, most of them either aided by catalysts or involved solvent assisted multi-step process that considerably increase the cost of production and hinders the realization of low cost CNSs based commercial devices. In addition, vast majority of these techniques use high pure petroleum derived hydrocarbon gas precursors that are non-renewable and expensive. Hence, it is imperative to develop scalable techniques that can derive high quality CNSs directly on arbitrary substrates from naturally derived carbon feed stocks. This work aims to develop an environmentally benign plasma enhanced chemical vapor deposition technique for fabricating CNSs from Citrus sinensis essential oil, a bio renewable precursor, and explored the potential of these nanostructures for gas sensing application. C. sinensis essential oil, obtained through cold extraction of orange peels is a rich source of non-synthetic hydrocarbon compounds principally limonene. Inherently volatile in nature, C. sinensis essential oil can serve as an ideal candidate material compatible to plasma enhanced chemical vapor deposition. This thesis investigated the fabrication of vertically-oriented graphene nanostructures from C.sinensis essential oil through radio frequency plasma enhanced chemical vapor deposition process, the fundamental properties, extend to which the process parameters influenced the structure and morphological features, and the suitability of the developed vertical graphene arrays for gas sensing applications. Special attention is paid to probe deep into the morphological evolution with the help of a set of advanced analytical characterization methods and multi-parameter model simulations. In the first phase, C.sinensis vapors were subjected to low RF power glow discharge that resulted in the formation of plasma polymer thin films, and the material properties were studied as a function of input RF energy. The fundamental properties of plasma polymer thin films fabricated at different RF power level (10−75 W) were characterized with variable angle spectroscopic ellipsometry, UV-visible spectroscopy, Fourier transform infrared spectroscopy X-ray photoelectron spectroscopy and atomic force microscopy. Optical characterization showed that independent of deposition power films exhibited good transparency (~90 %) in the visible region and a refractive index of 1.55 at 500nm. The optical band gap measured around 3.60 eV and falls within the insulating region. The atomic force microscopic (AFM) images revealed that the surface is pinhole-free and smooth at nanoscale, with average surface roughness dependent on the deposition power. Film hardness increased from 0.50 GPa to 0.78 GPa as applied power increased from 10 to 75 W. In the second phase, experiments were modified by redesigning the experimental set up in order to eliminate hydrogen from the deposits leaving only crystalline carbon. The RF power deliberately kept high, substrate temperature was raised and hydrogen gas fed into the reactor in controlled manner. A sequence of experiments were carried out by systematically changing the process parameters such as in put RF power (300-500W), hydrogen flow rate (10-50 sccm) and deposition duration (2-8 min) and analysed the structural and morphological evolution of the resulted vertical graphene nanostructure. The structure-property correlation of vertical graphene arrays with the plasma process parameters was performed. The Raman spectra ascertained the formation of less defected multilayered graphene nanostructures and scanning electron microscopic images provided the primary evidences of morphological evolution. The potential of the novel analytical techniques such as Hough transformations, fractal dimension distributions and Minkowski connectivity for the analysis of graphene array morphology was then successfully demonstrated. Worth noting that, these advanced techniques displayed significant changes and revealed the complex morphological transformation of C. sinensis derived vertical graphene subjected to change in process conditions. Precisely, vertical graphene nanowalls obtained at 300 and 500W presented a narrow height distribution profile but much wider array formed at 400 W. Fourier and Hough transformation spectra showed a prominent change with an increase in power, thus highlighted change in the morphology with the density of nanoflakes. Similarly, 2D FFT transform spectra of vertical graphene samples also presented notable changes with increasing hydrogen flux. The most narrow height distributions, well-shaped Hough transformation spectra and distribution of fractal dimensions obtained for structures formed at 20 and 50 sccm of hydrogen flow rate. In addition to this, the principal characteristics of thus fabricated vertical graphene such as flake length (Lvg) and flake half width (Wvg) are theoretically modelled by an ad hoc model based on a large number of interaction elemental processes and correlated with the experimental results. The combination of the experimental and simulation results ensured important insights and deeper understanding of the processes that govern formation of the vertical graphene morphology.Vertical graphene nanostructures having superior structural and morphological properties were successfully fabricated at an input RF energy of 500W, hydrogen flow rate of 30 sccm and deposition duration of 6 minutes. The third phase presented an in-depth study of the properties of C.sinensis oil derived graphene over a set of conducting (copper and nickel) and insulating substrates (silicon and quartz). The SEM images of thus fabricated graphene patterns showed the unique feature of vertically interconnected and non-agglomerated carbon nanowall structures having maze-like and petal-like networks. Moreover, the normalized height distribution function and 2-D FFT spectra analysis ascertained that vertical graphene formed on silicon substrates displayed the most uniform distribution. X-ray photoelectron spectroscopy spotted only the presence of carbon and the transmission electron microscopic studies revealed the formation of unique onion-like closed loops. The 3-D nanoporous structure of C.sinensis oil derived graphene showed high hydrophobicity and measured a water contact angle of 129°. The surface energy studies were performed using Neumann model, Owens-Wendt-Kaelble approach and van Oss- Chaudhury-Good relation and estimated within the range 35‒41 mJ/m². Finally, plasma reformed vertical graphene from C. sinensis was integrated into a sensor device prototype to evaluate the performance in gas sensing. The chemiresistive type sensor exhibited sensing activity towards acetone. In summary, this thesis has identified a viable renewable resource and successfully developed a process that transform them into vertical graphene nanostructures. Furthermore, the fabricated graphene was integrated to real world devices and evaluated the performance. The outcomes of this investigation add knowledge base to the state-of-the-art of green chemistry approach for the synthesis of vertical graphene carbon nanostructures

Fully Biodegradable Temperature Sensors with High Mechanical Stability and Low Thermal Mass

In this work we have successfully designed, fabricated and extensively characterized a flexible and stretchable temperature sensor that biodegrade in the environment. The design is based on a ultrathin resistance temperature detector (RTD). The core material used is Magnesium, which is transient and biocompatible material. It has been encapsulated from both sides with a transparent and degradable elastomer. It shows high mechanical stability and a transient time of two month

Air-gap sacrificial materials by initiated chemical vapor deposition

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2007.Includes bibliographical references (leaves 81-83).P(neopentyl methacrylate-co-ethylene glycol dimethacrylate) copolymer, abbreviated as P(npMAco-EGDA), was selected as the potential air-gap sacrificial material among possible combination of twenty monomers and four crosslinkers. P(npMA-co-EGDA) was deposited onto substrates using initiated chemical vapor deposition (iCVD) technique. Spectroscopic data showed the effective incorporation of both components in the copolymer and the integrity of repeating units were retained. The onset temperature of decomposition of P(npMA-co-EGDA) copolymer could be tuned between 290-3500C by varying the composition of the copolymer. The removal rate of polymer was calculated based on interferometry signal-time curve. The activation energy was determined by fitting the rate of decomposition with logistic model and found to be 162.7+8kJ/mole, which was similar to published data. Flash pyrolysis gas chromatography mass spectroscopy analysis showed that the products of thermal decomposition are monomers, rearranged small molecules and low oligomers. The modulus and the hardness were in the range of 3.9 to 5.5 GPa and 0.38 to 0.75 GPa, respectively, and were higher than those of linear poly(methyl methacrylate) (PMMA). Air-gap structures were constructed in the following scheme: P(npMA-co-EGDA) was deposited on the substrate by iCVD, followed by spincasting PMMA electron beam resist and scanning electron beam lithography to implement patterns on the resist. Reactive ion etching (RIE) was then applied to simultaneously etch the PMMA resist and P(npMA-co-EGDA) sacrificial material away in a controlled manner, leaving the patterned sacrificial material on the substrate.(cont.) A layer of porous silica was deposited to cover the substrate and the patterned sacrificial material by plasma-enhanced chemical vapor deposition (PECVD) at 2500C and the sample was thermally annealed to allow the decomposed fragments to diffuse through the overlayer of silica. Using the scheme described above, it was possible to construct air-gap structures with feature size of 200nm and feature height of 1 00nm.by Long Hua Lee.S.M

The functionalization of carbon nanosheets

Carbon nanosheets are a novel two-dimensional nanostructure made up of 2-20 graphene atomic planes oriented with their in-plane axis perpendicular to the growth substrate. Previous efforts in developing nanosheet technology have focused on the characterization of the system and their development as an electron source due to the high atomic enhancement factor (beta) and low turn on field. Further investigation of nanosheets as high surface area electrodes revealed poor wetting by polymeric material and extreme hydrophobic behavior.;Because nanosheet technology has promise as a high surface area electrode material, this thesis research has focused on three areas of interest: the enhancement of nanosheets through chemical modification, the incorporation of the nanosheets into a polymeric composite and the delivery of a proof of concept measurement. We have successfully introduced defects into the graphene lattice of the nanosheet system via an acid treatment. Inspection of these defects by x-ray absorption near-edge spectroscopy (XANES) shows the introduction of two features in the spectra assigned to C=O pi* and C-O sigma* transitions. Thermal desorption spectroscopy (TDS) was used to identify the oxygen containing groups created during the functionalization as carboxylic and hydroxyl functional groups. These groups were identified through the combination of carboxylic, hydroxyl, anhydride and lactone peaks in the CO2, CO and H 2O TDS spectra. Deconvolution of the TDS spectra using 1st and 2nd order Polanyi-Wigner equations enables the calculation of desorption energy values for individual features and for the estimation of the number of atoms desorbing from the surface during a particular event. Identification of the exact nature of the functional groups was attempted through high resolution x-ray photoelectron spectroscopy (XPS) of the C(1s) and O(1s) peaks. Though the pairing of sub-peaks with specific functionalities of the system was not possible due to the complexities of the spectra, the trends observed in the data support the data gathered via the XANES and TDS experiments.;Also, a procedure for the classification of defect density and exact functionality was outlined. Deconvolution of the TDS spectra using 1 st and 2nd order Polanyi-Wigner equations enabled the calculation of desorption energy values for individual features and for the estimation of the number of atoms desorbing from the surface during a particular event. This information along with the changing sub-peak areas from dedicated and calibrated XPS system would allow for not only a more accurate estimation of defect density, but also for the identification of sub-peaks in the C(1s) and O(1s) spectra.;Finally, photoluminescence measurements of poly[2-methoxy-5-(2\u27-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and MEH-PPV/nanosheet systems showed a quenching of three orders of magnitude for the MEH-PPV/nanosheet system suggesting that nanosheets are a viable option for excition separation in organic photovoltaics

Exploring general chemistry students' metacognitive monitoring on examinations

Includes bibliographical references.2016 Fall.To view the abstract, please see the full text of the document