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 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

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

Correction: Printable and flexible electronics: from TFTs to bioelectronic devices

Correction for 'Printable and flexible electronics: from TFTs to bioelectronic devices' by M. Magliulo et al., J. Mater. Chem. C, 2015, 3, 12347–12363

Correction: Printed, cost-effective and stable poly(3-hexylthiophene) electrolyte-gated field-effect transistors

Correction for 'Printed, cost-effective and stable poly(3-hexylthiophene) electrolyte-gated field-effect transistors' by Davide Blasi et al., J. Mater. Chem. C, 2020, DOI: 10.1039/d0tc03342a

About the amplification factors in organic bioelectronic sensors

A systematic comparison between electrochemical and organic bioelectronic sensors reveals a unified rational description for a transistor amplified detection

Enhanced stability of organic field-effect transistor biosensors bearing electrosynthesized ZnO nanoparticles

Herein electrosynthesized ZnO nanoparticles (ZnO NPs) agents to largely improve functional bio-interlayer organic field-effect transistor (FBI-OFET) biosensors stability are investigated. For a proof-of-principle, streptavidin (SA) was chosen as the capturing biomolecule to sense biotin and poly-3-hexylthiophene (P3HT) served as channel material. The ZnO NPs were prepared and integrated into the FBI-OFET architecture by means of a straightforward and versatile procedure. To this end, ZnO NPs were mixed with an SA solution and the resulting aqueous suspension was readily spin-coated onto the SiO2gate dielectric. The P3HT film was spin-coated on the SA-ZnO NPs layer afterwards with the whole fabrication procedure taking no more than 30 min. The FBI-OFET biosensors bearing the ZnO NPs exhibited a shelf life exceeding one year, while the bare ones failed to work after few weeks. Moreover, the ZnO NPs enabled a two orders of magnitude increase in field-effect mobility while the already proven very good sensing performances were retained. The electrical and XPS characterization of the ZnO NPs based functional bio-interlayer provided information about the role of the nanostructured oxide on the improved device stability and a plausible mechanism for this occurrence is derived accordingly