Alexandra Oliveros

University of South Florida, Tampa, FL, United States

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Publications (12)13.44 Total impact

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    ABSTRACT: We demonstrate the functionalization of n-type (100) and (111) 3C-SiC surfaces with organosilanes. Self-assembled monolayers (SAMs) of amino propyldiethoxymethylsilane (APDEMS) and octadecyltrimethoxysilane (ODTMS) are formed via wet chemical processing techniques. Their structural, chemical, and electrical properties are investigated using static water contact angle measurements, atomic force microscopy, and X-ray photoelectron spectroscopy, revealing that the organic layers are smooth and densely packed. Furthermore, combined contact potential difference and surface photovoltage measurements demonstrate that the heterostructure functionality and surface potential can be tuned by utilizing different organosilane precursor molecules. Molecular dipoles are observed to significantly affect the work functions of the modified surfaces. Furthermore, the magnitude of the surface band bending is reduced following reaction of the hydroxylated surfaces with organosilanes, indicating that partial passivation of electrically active surface states is achieved. Micropatterning of organic layers is demonstrated by lithographically-defined oxidation of organosilane-derived monolayers in an oxygen plasma, followed by visualization of resulting changes of the local wettability, as well as fluorescence microscopy following immobilization of fluorescently labeled BSA protein.
    ACS Applied Materials & Interfaces 01/2013; · 5.90 Impact Factor
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    ABSTRACT: Silicon carbide (SiC) has been around for more than 100 years as an industrial material and has found wide and varied applications because of its unique electrical and thermal properties. In recent years there has been increased attention to SiC as a viable material for biomedical applications. Of particular interest in this review is its potential for application as a biotransducer in biosensors. Among these applications are those where SiC is used as a substrate material, taking advantage of its surface chemical, tribological and electrical properties. In addition, its potential for integration as system on a chip and those applications where SiC is used as an active material make it a suitable substrate for micro-device fabrication. This review highlights the critical properties of SiC for application as a biosensor and reviews recent work reported on using SiC as an active or passive material in biotransducers and biosensors.
    Biomedical Microdevices 01/2013; · 2.72 Impact Factor
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    ABSTRACT: In this article, the biofunctionalization of 6H–SiC (0001) surfaces via self-assembled monolayers (SAMs) has been studied as a means to modify the in vitro biocompatibility of this semiconductor substrate with H4 (human neuroglioma) and PC12 (rat pheochromocytoma) cells. Silanization with aminopropyldiethoxymethylsilane (APDEMS) and aminopropyltriethoxysilane (APTES), which provided moderately hydrophilic surfaces, and alkylation with 1-octadecene that produced hydrophobic surfaces were used to control the 6H–SiC surface chemistry and evaluate changes in cell viability and morphology due to these surface modifications. The morphology of the cells was evaluated with atomic force microscopy. In addition, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were used to quantitatively evaluate the cell viability on the SAM-modified surfaces. In all cases, the cell proliferation was observed to improve with respect to untreated 6H–SiC surfaces, with up to a 2x increase in viability on the 1-octadecene-modified surfaces, up to 6x increase with APDEMS-modified surfaces, and up to 8x increase with APTES-modified surfaces. This proves the potential of SiC as a substrate for medical devices given the possibility to tailor its surface chemistry for specific applications.
    Journal of Materials Research 01/2013; 28(01):78-86. · 1.82 Impact Factor
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    ABSTRACT: Silicon Carbide (SiC), has been shown to be a bio- and hema-compatible substrate that could potentially be used in biosensor applications. The development of a viable biorecognition interface using SiC as the substrate material for bio-detection is described. Surface modification with 3-aminopropyltriethoxysilane (APTES) and immobilization via covalent conjugation of antimyoglobin (anti-Myo) on the modified surfaces is achieved, which are initial steps for immunosensing based devices. Successful formation of APTES layers and antibody immobilization were identified with surface water contact angle (SWCA), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:1643-6.
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    Atomic Force Microscopy Investigations into Biology - From Cell to Protein, 03/2012; , ISBN: 978-953-51-0114-7
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    ABSTRACT: An ever-increasing demand for biocompatible materials provides motivation for the development of advanced materials for challenging applications ranging from disease detection to organ function restoration. Carbon-based materials are considered promising candidates because they combine good biocompatibility with high chemical resistance. In this work we present an initial assessment of the biocompatibility of epitaxial graphene on 6H-SiC(0001). We have analyzed the interaction of HaCaT (human keratinocyte) cells on epitaxial graphene and compared it with that on bare 6H-SiC(0001). We have found that for both graphene and 6H-SiC there is evidence of cell-cell and cell substrate interaction which is normally an indication of the biocompatibility of the material.
    Materials Science Forum 03/2011; 679-680:831-834.
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    ABSTRACT: Crystalline silicon carbide (SiC) and silicon (Si) biocompatibility was evaluated in vitro by directly culturing three skin and connective tissue cell lines, two immortalized neural cell lines, and platelet-rich plasma (PRP) on these semiconducting substrates. The in vivo biocompatibility was then evaluated via implantation of 3C-SiC and Si shanks into a C57/BL6 wild type mouse. The in vivo results, while preliminary, were outstanding with Si being almost completely enveloped with activated microglia and astrocytes, indicating a severe immune system response, while the 3C-SiC film was virtually untouched. The in vitro experiments were performed specifically for the three adopted SiC polytypes, namely 3C-, 4H- and 6H-SiC, and the results were compared to those obtained for Si crystals. Cell proliferation and adhesion quality were studied using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays and fluorescent microscopy. The neural cells were studied via atomic force microscopy (AFM) which was used to quantify filopodia and lamellipodia extensions on the surface of the tested materials. Fluorescent microscopy was used to assess platelet adhesion to the semiconductor surfaces where significantly lower values of platelet adhesion to 3C-SiC was observed compared to Si. The reported results show good indicators that SiC is indeed a more biocompatible substrate than Si. While there were some differences among the degree of biocompatibility of the various SiC polytypes tested, SiC appears to be a highly biocompatible material in vitro that is also somewhat hemocompatible. This extremely intriguing result appears to put SiC into a unique class of materials that is both bio- and hemo-compatible and is, to the best of our knowledge, the only semiconductor with this property. © (2011) Trans Tech Publications,.
    Materials Science Forum, Oslo; Norway; 01/2011
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    ABSTRACT: Crystalline silicon carbide (SiC) and silicon (Si) biocompatibility was evaluated in vitro by directly culruring three skin and connective tissue cell lines, two immortalized neural cell lines, and platelet-rich plasma (PRP) on these semiconducting substrates. The experiments were performed specifically for the three adopted SiC polytypes, namely 3C-, 4H- and 6H-SiC, and the results were compared to those obtained for Si crystals. Cell proliferation and adhesion quality were studied using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide] assays and fluorescent microscopy. For the neural cells studied atomic force microscopy (AFM) was also used to quantify the filopodia and lamellipodia extensions on the surface of the tested materials. Fluorescent microscopy was used to assess platelet adhesion to the semiconductor surfaces where significantly lower values of platelet adhesion to 3C-SiC was observed compared to Si. The reported results show that SiC is indeed a more biocompatible substrate than Si. While there were some differences among the degree of biocompatibility of the various SiC polytypes tested, SiC appears to be a highly biocompatible material in vitro that is also somewhat hemocompatible. This extremely intriguing result appears to put SiC into a unique class of materials that is both bio- and hemo-compatible and is, to the best of our knowledge, the only semiconductor with this property. © 2010 Materials Research Society.
    Materials Research Society symposia proceedings. Materials Research Society 01/2010; 1246:193-198.
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    ABSTRACT: Crystalline silicon carbide (SiC) and silicon (Si) biocompatibility was evaluated in vitro by directly culruring three skin and connective tissue cell lines, two immortalized neural cell lines, and platelet-rich plasma (PRP) on these semiconducting substrates. The experiments were performed specifically for the three adopted SiC polytypes, namely 3C-, 4H- and 6H-SiC, and the results were compared to those obtained for Si crystals. Cell proliferation and adhesion quality were studied using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide] assays and fluorescent microscopy. For the neural cells studied atomic force microscopy (AFM) was also used to quantify the filopodia and lamellipodia extensions on the surface of the tested materials. Fluorescent microscopy was used to assess platelet adhesion to the semiconductor surfaces where significantly lower values of platelet adhesion to 3C-SiC was observed compared to Si. The reported results show that SiC is indeed a more biocompatible substrate than Si. While there were some differences among the degree of biocompatibility of the various SiC polytypes tested, SiC appears to be a highly biocompatible material in vitro that is also somewhat hemocompatible. This extremely intriguing result appears to put SiC into a unique class of materials that is both bio- and hemo-compatible and is, to the best of our knowledge, the only semiconductor with this property. © 2010 Materials Research Society.
    Materials Research Society Symposium; 01/2010
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    ABSTRACT: Brain machine interface (BMI) devices offer a platform that can be used to assist people with extreme disabilities, such as amyotrophic lateral sclerosis (ALS) and Parkinson's disease. Silicon (Si) has been the material of choice used for the manufacture of BMI devices due to its mechanical strength, its electrical properties and multiple fabrication techniques; however, chronically implanted BMI devices have usually failed within months of implantation due to biocompatibility issues and the fact that Si does not withstand the harsh environment of the body. Single crystal cubic silicon carbide (3C-SiC) and nanocrystalline diamond (NCD) are semiconductor materials that have previously shown good biocompatibility with skin and bone cells. Like Si, these materials have excellent physical characteristics, good electrical properties, but unlike Si, they are chemically inert. We have performed a study to evaluate the general biocompatibility levels of all of these materials through the use of in vitro techniques. H4 human neuroglioma and PC12 rat pheochromocytoma cell lines were used for the study, and polystyrene (PSt) and amorphous glass were used as controls or for morphological comparison. MTT [3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide] assays were performed to determine general cell viability with each substrate and atomic force microscopy (AFM) was used to quantify the general cell morphology on the substrate surface along with the substrate permissiveness to lamellipodia extension. 3C-SiC was the only substrate tested to have good viability and superior lamellipodia permissiveness with both cell lines, while NCD showed a good level of viability with the neural H4 line but a poor viability with the PC12 line and lower permissiveness than 3C-SiC. Explanations pertaining to the performance of each substrate with both cell lines are presented and discussed along with future work that must be performed to further evaluate specific cell reactions on these substrates.
    Journal of Molecular Recognition 08/2009; 22(5):380-8. · 3.01 Impact Factor
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    ABSTRACT: Brain machine interface (BMI) technology has been demonstrated to be a therapeutic solution for assisting people suffering from damage to the central nervous system (CNS), but BMI devices using implantable neural prosthetics have experienced difficulties in that they are recognized by glial cells as being foreign material, which leads to an immune response cascade process called gliosis. One material, cubic silicon carbide (3C-SiC), may provide an excellent solution for the generation of an implantable neural prosthetic interface component of a BMI system. We have recently reported on the biocompatibility of 3C-SiC with immortalized cells, and have extended this work by demonstrating neural cell action potential instigation via an electrode type device. Biocompatibility assessment of 3C-SiC was accomplished using in vitro methodology. 96 hour MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays were performed to determine neural cell viability. Atomic force microscopy (AFM) was used to quantify attached cell morphology and determine lamellipodia/ filopodia interaction with the surface of the semiconductor. It was seen that neurons show excellent viability, cell morphology, and good lamellipodia/ filopodia permissiveness when interacting with 3C-SiC. A neuronal activation device (NAD), based on the planar Michigan microelectrode probe, was constructed from 3C-SiC with the goal of activating an action potential within a neuron. In order to illicit an action potential, neurons were seeded on the NAD device and then they were subjected to a biphasic square pulse signal. Successful action potential activation was recorded through the use of Rhod-2, a Ca2+ sensitive fluorescent dye. Based on these results, 3C-SiC may be an excellent material platform for neural prosthetics.
    MRS Proceedings. 12/2008; 1236.
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    ABSTRACT: The biocompatibility of 6H-SiC (0001) surfaces was increased by more than a factor of six through the covalent grafting of NH2 terminated self-assembled monolayers (SAM) using APDEMS and APTES molecules. Surface functionalization began with a hydroxyl, OH, surface termination. The study included two NH2 terminated surfaces obtained through silanization with APDEMS (aminopropyldiethoxymethylsilane) and APTES (aminopropyltriethoxysilane) molecules (hydrophilic surfaces) and a CH3 terminated surface produced via alkylation with 1-octadecene (hydrophobic surface). H4 human neuroglioma and PC12 rat pheochromocytoma cells were seeded on the functionalized surfaces and the cell morphology was evaluated with atomic force microscopy (AFM). In addition, 96 hour MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays were employed to evaluate the cell viability on the SAM modified samples. The biocompatibility was enhanced with a 2 fold (171-240%) increase with 1-octadecene, 3-6 fold (320-670%) increase with APDEMS and 5-8 fold (476-850%) increase with APTES with respect to untreated 6H-SiC surfaces.
    MRS Proceedings. 12/2008; 1235.