Susana Palma

Effects of phase transfer ligands on monodisperse iron oxide magnetic nanoparticles

Oleic acid coated iron oxide nanoparticles synthesized by thermal decomposition in organic medium are highly monodisperse but at the same time are unsuitable for biological applications. Ligand-exchange reactions are useful to make their surface hydrophilic. However, these could alter some structural and magnetic properties of the modified particles. Here we present a comprehensive study and comparison of the effects of employing either citric acid (CA) or meso-2,3-dimercaptosuccinic acid (DMSA) ligand-exchange protocols for phase transfer of monodisperse hydrophobic iron oxide nanoparticles produced by thermal decomposition of Fe(acac)3 in benzyl ether. We show the excellent hydrodynamic size distribution and colloidal stability of the hydrophilic particles obtained by the two protocols and confirm that there is a certain degree of oxidation caused by the ligand-exchange. CA revealed to be more aggressive towards the iron oxide surface than DMSA and greatly reduced the saturation magnetization values and initial susceptibility of the resulting particles compared to the native ones. Besides being milder and more straightforward to perform, the DMSA ligand exchange protocol produces MNP chemically more versatile for further functionalization possibilities. This versatility is shown through the covalent linkage of gum Arabic onto MNP-DMSA using carboxyl and thiol based chemical routes and yielding particles with comparable properties.

AAL+: Continuous Institutional and Home Care Through Wireless Biosignal Monitoring Systems

This chapter describes the research and development of AAL+, a new tool for continuous short-to-medium and long range patient monitoring. The system has two versions, each targeted at a different environment and at subjects with different needs: (a) AAL+ Institutional, for patients that live in healthcare institutions such as assisted living facilities, with delicate needs in terms of medical assistance and monitoring; and (b) AAL+ Home, for individuals that live in their homes, maintaining some independence and physical capabilities. In the next sections we describe the particular characteristics of each version as well as the development, test and deployment scenarios, in close collaboration with partners from the clinical field and end-users. Currently, the system is in a late prototype stage and was tested in a real environment at two healthcare institutions: an assisted living residence and a public hospital Users’ reactions show that this system brings advantages which extend to institutions, caregivers and end-users, and translate into faster assistance, higher efficiency of the services and new intervention models.

Covalent coupling of gum arabic onto superparamagnetic iron oxide nanoparticles for MRI cell labeling: physicochemical and in vitro characterization

Gum arabic (GA) is a hydrophilic composite polysaccharide derived from exudates of Acacia senegal and Acacia seyal trees. It is biocompatible, possesses emulsifying and stabilizing properties and has been explored as coating agent of nanomaterials for biomedical applications, namely magnetic nanoparticles (MNPs). Previous studies focused on the adsorption of GA onto MNPs produced by co-precipitation methods. In this work, MNPs produced by a thermal decomposition method, known to produce uniform particles with better crystalline properties, were used for the covalent coupling of GA through its free amine groups, which increases the stability of the coating layer. The MNPs were produced by thermal decomposition of Fe(acac)3 in organic solvent and, after ligand-exchange with meso-2,3-dimercaptosuccinic acid (DMSA), GA coating was achieved by the establishment of a covalent bond between DMSA and GA moieties. Clusters of several magnetic cores entrapped in a shell of GA were obtained, with good colloidal stability and promising magnetic relaxation properties (r2 /r1 ratio of 350). HCT116 colorectal carcinoma cell line was used for in vitro cytotoxicity evaluation and cell-labeling efficiency studies. We show that, upon administration at the respective IC50 , GA coating enhances MNP cellular uptake by 19 times compared to particles bearing only DMSA moieties. Accordingly, in vitro MR images of cells incubated with increasing concentrations of GA-coated MNP present dose-dependent contrast enhancement. The obtained results suggest that the GA magnetic nanosystem could be used as a MRI contrast agent for cell-labeling applications.

Tilapia fish microbial spoilage monitored by a single optical gas sensor

As consumption of fish and fish-based foods increases, non-destructive monitoring of fish freshness also becomes more prominent. Fish products are very perishable and prone to microbiological growth, not always easily detected by organoleptic evaluation. The analysis of the headspace of fish specimens through gas sensing is an interesting approach to monitor fish freshness. Here we report a gas sensing method for monitoring Tilapia fish spoilage based on the application of a single gas sensitive gel material coupled to an optical electronic nose. The optical signals of the sensor and the extent of bacterial growth were followed over time, and results indicated good correlation between the two determinations, which suggests the potential application of this simple and low cost system for Tilapia fish freshness monitoring.

Machine learning for the meta-analyses of microbial pathogens’ volatile signatures

Non-invasive and fast diagnostic tools based on volatolomics hold great promise in the control of infectious diseases. However, the tools to identify microbial volatile organic compounds (VOCs) discriminating between human pathogens are still missing. Artificial intelligence is increasingly recognised as an essential tool in health sciences. Machine learning algorithms based in support vector machines and features selection tools were here applied to find sets of microbial VOCs with pathogen-discrimination power. Studies reporting VOCs emitted by human microbial pathogens published between 1977 and 2016 were used as source data. A set of 18 VOCs is sufficient to predict the identity of 11 microbial pathogens with high accuracy (77%), and precision (62–100%). There is one set of VOCs associated with each of the 11 pathogens which can predict the presence of that pathogen in a sample with high accuracy and precision (86–90%). The implemented pathogen classification methodology supports future database updates to include new pathogen-VOC data, which will enrich the classifiers. The sets of VOCs identified potentiate the improvement of the selectivity of non-invasive infection diagnostics using artificial olfaction devices.

Scalable and Easy-to-use System Architecture for Electronic Noses

The purpose of this work was the development of a scalable and easy-to-use electronic noses (E-noses) system architecture for volatile organic compounds sensing, towards the final goal of using several E-noses acquiring large datasets at the same time. In order to accomplish this, each E-nose system is comprised by a delivery system, a detection system and a data acquisition and control system. In order to increase the scalability, the data is stored in a database common to all E-noses. Furthermore, the system was designed so it would only require five simple steps to setup a new E-nose if needed, since the only parameter that needs to be changed is the ID of the new E-nose. The user interacts with a node using an interface, allowing for the control and visualization of the experiment. At this stage, there are three different E-nose prototypes working with this architecture in a laboratory environment.

Design and Evolution of an Opto-electronic Device for VOCs Detection

Electronic noses (E-noses) are devices capable of detecting and identifying Volatile Organic Compounds (VOCs) in a simple and fast method. In this work, we present the development process of an opto-electronic device based on sensing films that have unique stimuli-responsive properties, altering their optical and electrical properties, when interacting with VOCs. This interaction results in optical and electrical signals that can be collected, and further processed and analysed. Two versions of the device were designed and assembled. E-nose V1 is an optical device, and E-nose V2 is a hybrid opto-electronic device. Both E-noses architectures include a delivery system, a detection chamber, and a transduction system. After the validation of the E-nose V1 prototype, the E-nose V2 was implemented, resulting in an easy-to-handle, miniaturized and stable device. Results from E-nose V2 indicated optical signals reproducibility, and the possibility of coupling the electrical signals to the optical response for VOCs sensing.

Author Correction: Machine learning for the meta-analyses of microbial pathogens’ volatile signatures

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

An affinity triggered MRI nanoprobe for pH-dependent cell labeling

The pH-sensitive affinity pair composed by neutravidin and iminobiotin was used to develop a multilayered Magnetic Resonance Imaging (MRI) nanoprobe responsive to the acidic pH of tumor microenvironment. The multilayer system was assembled on meso-2,3-dimercaptosuccinic acid-coated iron oxide magnetic nanoparticles (MNP), which convey negative MRI contrast enhancement properties to the nanoprobe. The outer stealth PEG-layer is altered in acidic media due to the disruption of interactions between neutravidin–iminobiotin. As a consequence, the positively charged inner layer is exposed and enhances interactions with cells. The nanoprobe uptake by HCT116 cells cultured in vitro under acidic conditions had a 2-fold increase compared to the uptake at physiological pH. The uptake difference is particularly clear in T2-weighted MRI phantoms of cells incubated with the nanoprobes at both pH conditions. This work sets the proof-of-concept of a MNP-based MRI nanoprobe targeting acidic tumor microenvironment through the use of a specific bio-recognition interaction that is pH-sensitive. This tumor targeting strategy is potentially applicable to the generality of tumors since the typical hypoxic conditions and high glycolysis rate in cancer cells create an acidic environment common to the majority of cancer types.