Monica Cotta | Universidade Estadual de Campinas (original) (raw)

Papers by Monica Cotta

Polymer, 2020

Abstract In the last decade, hyaluronan (HA, polyanion) and chitosan (CHI, polycation) biopolymer... more Abstract In the last decade, hyaluronan (HA, polyanion) and chitosan (CHI, polycation) biopolymers have been assembled by layer-by-layer (LbL) for the synthesis of antibacterial coatings. As electrostatic interactions are the main driving force for the formation of LbL films, pH and ionic strength (IS) are important critical variables of synthesis. In this context, we used surface fractal analysis of HA/CHI films to characterize the growth process for different bilayers obtained with two pH (5 and 3) and IS values (0 and 0.1 M NaCl). Our results showed that the HA/CHI assembling is mainly affected by changes in the pH than IS. Fractal dimension (Df) of pH 5 series presented values ~2.2, indicating that irregularities from the initial random adsorption process are minimized. However, when pH decreased to 3, Df increases up to ~2.5, suggesting a transition to diffusion-limited aggregation.

2019 International Conference on Manipulation, Automation and Robotics at Small Scales (MARSS), 2019

The shape memory alloys (SMAs) have recently been recognized as reliable basement of the technolo... more The shape memory alloys (SMAs) have recently been recognized as reliable basement of the technology of mechanical nanotools with still non determined minimal size. Among them the intermetallic alloy Ti(NiCu) give promising possibilities to create the reconfigurable micro- and nanostructures with shape memory effect (SME) capable to produce mechanical work on nanoscale. In the present report the review of the basic physical phenomena, which provide the possibility for the application of nanostructured SMA Ti(NiCu) for creating of micro and nanotools is given. The preliminary strained layered composites of SMAs are discussed which provide the multiple reversible actuation of a SMA based tool. Fundamental studies devoted to search for minimal size, at which martensitic phase transition and controllable actuation of SMA based tools take place are described. The technology of SMAs treatment by FIB-CVD gives the possibility to create different kinds of micro and nanotools, like nano- twee...

European Polymer Journal, 2018

Hyaluronic acid (HA)/chitosan (CHI) films were assembled by LbL using different conditions of pH ... more Hyaluronic acid (HA)/chitosan (CHI) films were assembled by LbL using different conditions of pH and ionic strength (IS) in order to obtain stable surfaces to avoid the adhesion and proliferation of Pseudomonas aeruginosa and Staphylococcus aureus. The results showed that pH and IS were key synthesis variables for obtaining different features, such as wettability, thickness and the availability of functional groups. The antibacterial effect was more effective against S. aureus with a reduction of approximately 3, 4, and 1.5 log reduction after 4, 8 and 24 hours of culture time, respectively. In the case of P. aeruginosa, the films presented a lower bacterial reduction: 1 log reduction in times evaluated. In conclusion, the results of the antibacterial effect against S. aureus after 24 hours, suggest that the HA/CHI films 2 assembled by LbL can protect several substrates, such as biomedical devices, against bacterial proliferation.

Materials Science and Engineering: C, 2017

In recent years, a common strategy, to obtain more uniform and controlled synthesis of polyelectr... more In recent years, a common strategy, to obtain more uniform and controlled synthesis of polyelectrolytes multilayers (PEMs), relies on a previous polyethylenimine (PEI) coating of the substrate surface. PEI is a synthetic cationic polymer which provides a positive charge distribution on the materials to be covered with PEMs. Despite being an important step, this pre-layer deposition is frequently overlooked and no comprehensive characterizations or deep discussions are reported in literature. In that sense, this work reports on the synthesis of a typical PEI film that works as a precursor for PEMs, and its detailed physicochemical characterization. As many PEMs are produced for antibacterial and biomedical applications, the cytotoxicity of the film was also tested using fibroblasts, and its antibacterial activity was studied using Staphylococcus aureus and Pseudomonas aeruginosa. Our results present the formation of an ultra-thin film of PEI with a thickness around 3.5 nm, and with a significant percent of NH 3 + (35% of the total amount of N) in its chemical structure; NH 3 + is a key chemical group because it is considered an important bacterial killer agent. The film was stable and did not present important cytotoxic effect for fibroblasts up to 7 days, contrary to other reports. Finally, the PEI film showed high antibacterial activity against the S. aureus strain: reductions in cell density were higher than 95% up to 24 h.

AIP Conference Proceedings, 2009

In the last few years, the main Brazihan funding agencies, CNPq and CAPES, have introduced gender... more In the last few years, the main Brazihan funding agencies, CNPq and CAPES, have introduced gender awareness projects. This initiative is a starting point for changing the percentage of women at all career levels in physics, but particularly at the top. The change in the percentage of female researchers at the different levels so far has been quite mild; the most likely reason is that the decision committees consist mostly of male researchers. We show that prejudice is still present in the evaluation process. The average number of publications of the female researchers is 72% higher than for the male researchers at the entrance level, indicating that it is harder for women to enter into the research system.

AIP Conference Proceedings, 2005

Scientific reports, Jan 20, 2015

Microorganism pathogenicity strongly relies on the generation of multicellular assemblies, called... more Microorganism pathogenicity strongly relies on the generation of multicellular assemblies, called biofilms. Understanding their organization can unveil vulnerabilities leading to potential treatments; spatially and temporally-resolved comprehensive experimental characterization can provide new details of biofilm formation, and possibly new targets for disease control. Here, biofilm formation of economically important phytopathogen Xylella fastidiosa was analyzed at single-cell resolution using nanometer-resolution spectro-microscopy techniques, addressing the role of different types of extracellular polymeric substances (EPS) at each stage of the entire bacterial life cycle. Single cell adhesion is caused by unspecific electrostatic interactions through proteins at the cell polar region, where EPS accumulation is required for more firmly-attached, irreversibly adhered cells. Subsequently, bacteria form clusters, which are embedded in secreted loosely-bound EPS, and bridged by up to ...

MRS Proceedings, 2005

ABSTRACTWe have recently shown that spatial ordering for epitaxially grown InP dots can be obtain... more ABSTRACTWe have recently shown that spatial ordering for epitaxially grown InP dots can be obtained using the periodic stress field of compositional modulation on the InGaP buffer layer. The aim of this present work is to study the growth of films of GaP by Chemical Beam Epitaxy (CBE), with in-situ monitoring by Reflection High Energy Electron Diffraction (RHEED), on layers of unstressed and stressed GaAs. Complementary, we have studied the role of a buried InP dot array on GaP nucleation in order to obtain three-dimensional structures. In both cases, the topographical characteristics of the samples were investigated by Atomic Force Microscopy (AFM) in non-contact mode. Thus vertically-coupled quantum dots of different materials have been obtained keeping the in-place spatial ordering originated from the composition modulation.

Physical Review B, 2000

We have observed changes in the morphology of InP films grown in epiready and processed substrate... more We have observed changes in the morphology of InP films grown in epiready and processed substrates. These changes are attributed to selective InP growth in areas in the submicron range due to the presence of C-based selective micromasks. Analyzing the behavior of the height-height correlation function, we show that both the roughness exponent and the correlation length changes depending on the area in which growth is taking place. For small area surfaces the correlation length increases and the roughness exponent decreases, indicating enhanced adatom relaxation due to the presence of the borders of the finite growing areas. Nonlinear terms should be included in continuum models in order to explain the observed results.

PLoS ONE, 2013

The phytopathogen Xylella fastidiosa grows as a biofilm causing vascular occlusion and consequent... more The phytopathogen Xylella fastidiosa grows as a biofilm causing vascular occlusion and consequently nutrient and water stress in different plant hosts by adhesion on xylem vessel surfaces composed of cellulose, hemicellulose, pectin and proteins. Understanding the factors which influence bacterial adhesion and biofilm development is a key issue in identifying mechanisms for preventing biofilm formation in infected plants. In this study, we show that X. fastidiosa biofilm development and architecture correlate well with physicochemical surface properties after interaction with the culture medium. Different biotic and abiotic substrates such as silicon (Si) and derivatized cellulose films were studied. Both biofilms and substrates were characterized at the micro-and nanoscale, which corresponds to the actual bacterial cell and membrane/ protein length scales, respectively. Our experimental results clearly indicate that the presence of surfaces with different chemical composition affect X. fastidiosa behavior from the point of view of gene expression and adhesion functionality. Bacterial adhesion is facilitated on more hydrophilic surfaces with higher surface potentials; XadA1 adhesin reveals different strengths of interaction on these surfaces. Nonetheless, despite different architectural biofilm geometries and rates of development, the colonization process occurs on all investigated surfaces. Our results univocally support the hypothesis that different adhesion mechanisms are active along the biofilm life cycle representing an adaptation mechanism for variations on the specific xylem vessel composition, which the bacterium encounters within the infected plant.

Physical Review Letters, 2011

We have performed a detailed study of the lattice distortions of InP wurtzite nanowires containin... more We have performed a detailed study of the lattice distortions of InP wurtzite nanowires containing an axial screw dislocation. Eshelby predicted that this kind of system should show a crystal rotation due to the dislocation induced torque. We have measured the twisting rate and the dislocation Burgers vector on individual wires, revealing that nanowires with a 10-nm radius have a twist up to 100% larger than estimated from elasticity theory. The strain induced by the deformation has a Mexican-hat-like geometry, which may create a tube-like potential well for carriers.

Physical Review B, 2010

We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanow... more We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on "ab initio" calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, respectively, which are in good agreement with the experimental results.

Nanotechnology, 2011

We performed a detailed investigation of the structural and optical properties of multi-layers of... more We performed a detailed investigation of the structural and optical properties of multi-layers of InP/GaAs quantum dots, which present a type II interface arrangement. Transmission electronic microscopy analysis has revealed relatively large dots that coalesce forming so-called quantum posts when the GaAs layer between the InP layers is thin. We observed that the structural properties and morphology affect the resulting radiative lifetime of the carriers in our systems. The carrier lifetimes are relatively long, as expected for type II systems, as compared to those observed for single layer InP/GaAs quantum dots. The interface intermixing effect has been pointed out as a limiting factor for obtaining an effective spatial separation of electrons and holes in the case of single layer InP/GaAs quantum-dot samples. In the present case this effect seems to be less critical due to the particular carrier wavefunction distribution along the structures.

Journal of Applied Physics, 2011

We present a low-temperature (73 K) study of the optical properties of multi-layer type II InP/ G... more We present a low-temperature (73 K) study of the optical properties of multi-layer type II InP/ GaAs self-assembled quantum dots by means of surface photovoltage (SPV) spectroscopy, taking advantage of its high sensitivity and contactless nature. The samples contain 10 periods of InP quantum dot planes separated by 5 nm GaAs spacers. The SPV amplitude spectra reveal two major broad peaks, situated at low and high energies, respectively. These features are analyzed taking into account the type II character of the structure, the quantum coupling effects, the spectral behavior of the SPV phase, and the photoluminescence spectra. As a result they have been attributed to optical transitions in the quantum dots and the wetting layers, respectively. The main mechanism for carrier separation in the SPV generation process is clarified via the analysis of the SPV phase spectra. The influence of the substrate absorption on the SPV spectra is discussed in details. V

Journal of Applied Physics, 2007

We investigate the formation of compositional modulation and atomic ordering in InGaP films. Such... more We investigate the formation of compositional modulation and atomic ordering in InGaP films. Such bulk properties-as well as surface morphologies-present a strong dependence on growth parameters, mainly the V/III ratio. Our results indicate the importance of surface diffusion and, particularly, surface reconstruction for these processes. Most importantly from the application point of view, we show that the compositional modulation is not necessarily coupled to the surface instabilities, so that smooth InGaP films with periodic compositional variation could be obtained. This opens a new route for the generation of templates for quantum dot positioning and three-dimensional arrays of nanostructures.

Journal of controlled release : official journal of the Controlled Release Society, Jan 30, 2012

The low efficiency of gene transfer is a recurrent problem in DNA vaccine development and gene th... more The low efficiency of gene transfer is a recurrent problem in DNA vaccine development and gene therapy studies using non-viral vectors such as plasmid DNA (pDNA). This is mainly due to the fact that during their traffic to the target cell's nuclei, plasmid vectors must overcome a series of physical, enzymatic and diffusional barriers. The main objective of this work is the development of recombinant proteins specifically designed for pDNA delivery, which take advantage of molecular motors like dynein, for the transport of cargos from the periphery to the centrosome of mammalian cells. A DNA binding sequence was fused to the N-terminus of the recombinant human dynein light chain LC8. Expression studies indicated that the fusion protein was correctly expressed in soluble form using E. coli BL21(DE3) strain. As expected, gel permeation assays found the purified protein mainly present as dimers, the functional oligomeric state of LC8. Gel retardation assays and atomic force microsc...

Biosensors and Bioelectronics, 2012

The development of highly-sensitive and label-free operating semiconductor-based, biomaterial det... more The development of highly-sensitive and label-free operating semiconductor-based, biomaterial detecting sensors has important applications in areas such as environmental science, biomedical research and medical diagnostics. In the present study, we developed an Indium Phosphide (InP) semiconductor-based resistive biosensor using the change of its electronic properties upon biomaterial adsorption as sensing element. To detect biomaterial at low concentrations, the procedure of functionalization and covalent biomolecule immobilization was also optimized to guarantee high molecule density and high reproducibility which are prerequisite for reliable results. The characterization, such as biomolecular conjugation efficiency, detection concentration limits, receptor:ligand specificity and concentration detection range was analyzed by using three different biological systems: i) synthetic dsDNA and two phytopathogenic diseases, ii) the severe CB-form of Citrus Tristeza Virus (CTV) and iii) Xylella fastidiosa, both causing great economic loss worldwide. The experimental results show a sensitivity of 1 pM for specific ssDNA detection and about 2 nM for the specific detection of surface proteins of CTV and X. fastidiosa phytopathogens. A brief comparison with other semiconductor based biosensors and other methodological approaches is discussed and confirms the high sensitivity and reproducibility of our InP based biosensor which could be suitable for reliable early infection diagnosis in environmental and life sciences.

Applied Physics Letters, 2003

Applied Physics Letters, 1995