Effect of metal clusters on the swelling of gold-fluorocarbon-polymer composite films

We have investigated the phenomenon of swelling due to acetone diffusion in fluorocarbon polymer films doped with different gold concentrations below the percolation threshold. The presence of the gold clusters in the polymer is shown to improve the mixing between the fluorocarbon polymer and the acetone, which is not a good solvent for this kind of polymers. In order to explain the experimental results the stoichiometry and the morphology of the polymer--metal system have been studied and a modified version of the Flory--Huggins model has been developed

Surface Plasmon Resonance Assay for Label-Free and Selective Detection of Xylella Fastidiosa

Xylella fastidiosa is among the most dangerous plant bacteria worldwide causing a variety of diseases, with huge economic impact on agriculture and environment. A surveillance tool, ensuring the highest possible sensitivity enabling the early detection of X. fastidiosa outbreaks, would be of paramount importance. So far, a variety of plant pathogen biomarkers are studied by means of surface plasmon resonance (SPR). Herein, multiparameter SPR (MP-SPR) is used for the first time to develop a reliable and label-free detection method for X. fastidiosa. The real-time monitoring of the bioaffinity reactions is provided as well. Selectivity is guaranteed by biofunctionalizing the gold transducing interface with polyclonal antibodies for X. fastidiosa and it is assessed by means of a negative control experiment involving the nonbinding Paraburkholderia phytofirmans bacterium strain PsJN. Limit of detection of 105 CFU mL 1 is achieved by transducing the direct interaction between the bacterium and its affinity antibody. Moreover, the binding affinity between polyclonal antibodies and X. fastidiosa bacteria is also evaluated, returning an affinity constant of 3.5   107m 1, comparable with those given in the literature for bacteria detection against affinity antibodies

Sensitive biosensors exploiting the minute changes in the capacitance of protein layers associated to the ligand recognition

Soft matter systems interfaced to an electronic device are presently one of the most challenging research activity that has relevance not only for fundamental studies but also for the development of highly performing bio-sensors. Layers of proteins anchored on solid surfaces have small capacitance that undergoes to only minute changes as the ligand–protein complex is formed. For properly designed systems, the protein layer represents smallest capacitance in a series of capacitors and as such dominates the overall capacitance. When such a protein layer is integrated in a Field Effect Transistor (FET) transduction is remarkably sensitive as the transistor output current is governed by the small changes due to ligand binding. These devices operate in aqueous solutions and are promising as portable sensors for point- of-care applications Two recent achievements will be illustrated: A) the sensitive and quantitative measurement of the weak interactions associated with the binding of neutral enantiomers to Odorant Binding Proteins (OBPs) [1]. immobilized to the gate of a bio-FET. Here the minute change in protein layer capacitance upon binding of S(-)-carvone and R(+)-carvone modulate the response of a water-gated OFET, allowing for chiral differential detection. The FET binding curves modelling provide information on the electrochemical free energies derived from the FET dissociation constants while the electrostatic component is isolated from the threshold voltage shifts. These can be combined with the chemical free energies gathered from the complex formation in solution, overall providing a comprehensive picture of the energy balances for a surface-bound pOBP-carvone complex undergoing chiral interactions. B) Hierarchically organized layers of phospholipids and proteins anchored on the surface of the semiconductor and acting as selective recognition elements independently form the solution ionic strength [2-3]. The charged moieties of the bound proteins along with the counter-ions form a layer that is analogous to an ionic gel. The fixed polyelectrolyte ions generate an electric field that confines the mobile counter-ions in the region of the fixed charges. Eventually a Donnan’s equilibrium is reached and the smallest capacitance in series is associated to the Donnan’s electrical double layer. The molecular recognition process (antigen/antibody in the present case) modify the charge density of the outermost layer and thus its capacitance. This capacitive tuning of the bio-FET response is virtually insensitive to the Debye’s length value and therefore is compatible with use of the transistor as sensor directly in biological fluids at high ionic strength . [1] M.Y. Mulla, E. Tuccori, M. Magliulo, G. Lattanzi, G. Palazzo, K. Persaud, L Torsi Capacitance-modulated transistor detects odorant binding protein chiral interactions Nat. Commun. 2015, 6, 6010 doi: 10.1038/ncomms7010 [2] M. Magliulo, A. Mallardi, M. Yusuf Mulla, S. Cotrone, B.R. Pistillo, P. Favia, I. Vikholm-Lundin, G. Palazzo, L Torsi Electrolyte-Gated Organic Field-Effect Transistor Sensors Based on Supported Biotinylated Phospholipid Bilayer Adv. Mater. 2013, 25, 2090–2094 DOI: 10.1002/adma.201203587 [3]G. Palazzo, D. De Tullio, M. Magliulo, A. Mallardi, F. Intranovo, M.Y. Mulla, P. Favia, I. Vikholm-Lundin, L. Torsi Detection beyond the Debye’s length with an electrolyte gated organic field-effect transistor Adv. Mater. 2015, 27, 911-916. DOI: 10.1002/adma.2014035

Surface composition of mixed self-assembled monolayers on Au by infrared attenuated total reflection spectroscopy

Abstract Self-assembled monolayers (SAMs) of N-(2-hydroxyethyl)-3-mercaptopropanamide (NMPA) were synthesized directly on the surface of electron-beam evaporated Au films, starting from 3-mercaptopropionic acid (3MPA) via ethyl-3-(3-dimethylamino-propyl)carbodiimide/N-hydroxysulfosuccinimide sodium salt (EDC/NHSS) coupling with ethanolamine hydrochloride. The influence on the reaction yield of the acidity of EDC/NHSS solutions (pH = 5.6 or 4.8) was assessed by exploiting the high surface sensitivity of infrared attenuated total reflection spectroscopy. The light-matter interaction was modeled in the framework of a matrix formalism considering the complete multi-layer sample structure. A comparison between the relative intensity of the main absorption bands, associated with amide I and carbonyl stretching of carboxylic acid or amide II vibrations, with a calibration curve obtained from the measurement of mixed 3MPA/NMPA SAMs, show that the more acid solution is 16% more efficient. This is mostly due to the higher protonation of the 3MPA

A general approach to the encapsulation of glycoenzymes chains inside calcium alginate gel beads

In this work an enzyme encapsulation general approach, based on the use of calcium alginate hydrogels, is reported. Alginate gels are biodegradable and low cost and have been found to provide a good matrix for the entrapment of sensitive biomolecules. Alginate is an anionic polymer whose gelation occurs by an exchange of sodium ions from the polymer chains with multivalent cations, resulting in the formation of a three dimensional gel network. For gelation alginate is dripped into a calcium chloride solution. The cations diffuse from the continuous phase to the interior of the alginate droplets and form a gelled matrix. By means of this “external gelation method” beads with a diameter of few millimeters can be obtained (see figure 1). The entrapment of enzymes in alginate beads suffers some disadvantages, like as low enzyme loading efficiency with reduction of the immobilization yields and reusability, related to the enzyme leakage from the large beads pores (cut off of about 100 kDa). Please click Additional Files below to see the full abstract

Soft matter films interfaced to electronic devices: capacitance-modulated field effect transistors integrating protein layers

Soft matter systems interfaced to an electronic device are presently one of the most challenging research activity that has relevance not only for fundamental studies but also for the development of highly performing bio-sensors. Layers of proteins anchored on solid surfaces have small capacitance that undergoes to only minute changes as the ligand–protein complex is formed. For properly designed systems, the protein layer represents smallest capacitance in a series of capacitors and as such dominates the overall capacitance. When such a protein layer is integrated in a Field Effect Transistor (FET) transduction is remarkably sensitive as the transistor output current is governed by the small changes due to ligand binding. These devices operate in aqueous solutions and are promising as portable sensors for point-of-care applications Two recent achievements will be illustrated: A) the sensitive and quantitative measurement of the weak interactions associated with the binding of neutral enantiomers to Odorant Binding Proteins (OBPs) [1]. immobilized to the gate of a bio-FET. Here the minute change in protein layer capacitance upon binding of S(-)-carvone and R(+)-carvone modulate the response of a water-gated OFET, allowing for chiral differential detection. The FET binding curves modelling provide information on the electrochemical free energies derived from the FET dissociation constants while the electrostatic component is isolated from the threshold voltage shifts. These can be combined with the chemical free energies gathered from the complex formation in solution, overall providing a comprehensive picture of the energy balances for a surface-bound pOBP-carvone complex undergoing chiral interactions. B) Hierarchically organized layers of phospholipids and proteins anchored on the surface of the semiconductor and acting as selective recognition elements independently form the solution ionic strength [2-3]. The charged moieties of the bound proteins along with the counter-ions form a layer that is analogous to an ionic gel. The fixed polyelectrolyte ions generate an electric field that confines the mobile counter-ions in the region of the fixed charges. Eventually a Donnan’s equilibrium is reached and the smallest capacitance in series is associated to the Donnan’s electrical double layer. The molecular recognition process (antigen/antibody in the present case) modify the charge density of the outermost layer and thus its capacitance. This capacitive tuning of the bio-FET response is virtually insensitive to the Debye’s length value and therefore is compatible with use of the transistor as sensor directly in biological fluids at high ionic strength . [1] M.Y. Mulla, E. Tuccori, M. Magliulo, G. Lattanzi, G. Palazzo, K. Persaud, L Torsi Capacitance-modulated transistor detects odorant binding protein chiral interactions Nat. Commun. 2015, 6, 6010 doi: 10.1038/ncomms7010 [2] M. Magliulo, A. Mallardi, M. Yusuf Mulla, S. Cotrone, B.R. Pistillo, P. Favia, I. Vikholm-Lundin, G. Palazzo, L Torsi Electrolyte-Gated Organic Field-Effect Transistor Sensors Based on Supported Biotinylated Phospholipid Bilayer Adv. Mater. 2013, 25, 2090–2094 DOI: 10.1002/adma.201203587 [3] G. Palazzo, D. De Tullio, M. Magliulo, A. Mallardi, F. Intranuovo, M.Y. Mulla, P. Favia, I. Vikholm-Lundin, L. Torsi Detection beyond the Debye’s length with an electrolyte gated organic field-effect transistor Adv. Mater. 2015, 27, 911-916. DOI: 10.1002/adma.201403541

Overview of recent developments in organic thin-film transistor sensor technology

Bio and chemical sensing represents one of the most attractive applications of organic electronics and of Organic Thin Film Transistors (OTFTs) in particular. The implementation of miniaturized portable systems for the detection of chemical analytes as well as of biological species, is still a challenge for the sensors’ community. In this respect OTFTs appear as a new class of sensors able, in principle, to overcome some of the commercial sensors drawbacks. As far as volatile analytes are concerned, commercially available sensing systems, such as metal oxide based chemi-resistors, offer great stability but rather poor selectivity. In spite of the improved selectivity offered by organic chemi-resistors the reliability of such devices is not yet satisfactorily proven. On the other hand, complex odors recognition, but also explosives or pathogen bacteria detection are currently being addressed by sensor array systems, called “e-noses”, that try to mimic the mammalian olfactory system. Even though potentially very effective, this technology has not yet reached the performance level required by the market mostly because miniaturization and cost effective production issues. OTFT sensors can offer the advantage of room temperature operation and deliver high repeatable responses. Beside, they show very good selectivity properties. In fact, they implement organic active layers, which behave as sensing layers as well. This improves OTFTs sensitivity towards different chemical and biological analytes as organic materials can be properly chemically tailored to achieve differential detection and potentially even discrimination of biological species. In addition to this, OTFTs are also able to offer the unique advantages of a multi-parametric response and a gate bias enhanced sensitivity. Recently thin dielectric low-voltage OTFTs have also been demonstrated. Their implementation in low power consumption devices has attracted the attention of the organic electronic community. But such low power transistors have also a great potential in sensing applications specifically those performed in a liquid environment. In fact, low-voltage OTFTs have been recently demonstrated to deliver reliable responses even when operated in water for hundreds of measurement cycles. This open new perspectives in the field of cheap, low-power and mass-produced aqueous sensors

Assessment of gold bio-functionalization for wide-interface biosensing platforms

The continuous improvement of the technical potential of bioelectronic devices for biosensing applications will provide clinicians with a reliable tool for biomarker quantification down to the single molecule. Eventually, physicians will be able to identify the very moment at which the illness state begins, with a terrific impact on the quality of life along with a reduction of health care expenses. However, in clinical practice, to gather enough information to formulate a diagnosis, multiple biomarkers are normally quantified from the same biological sample simultaneously. Therefore, it is critically important to translate lab-based bioelectronic devices based on electrolyte gated thin-film transistor technology into a cost-effective portable multiplexing array prototype. In this perspective, the assessment of cost-effective manufacturability represents a crucial step, with specific regard to the optimization of the bio-functionalization protocol of the transistor gate module. Hence, we have assessed, using surface plasmon resonance technique, a sustainable and reliable cost-effective process to successfully bio-functionalize a gold surface, suitable as gate electrode for wide-field bioelectronic sensors. The bio-functionalization process herein investigated allows to reduce the biorecognition element concentration to one-tenth, drastically impacting the manufacturing costs while retaining high analytical performance