Bacterioplankton Diversity and Distribution in Relation to Phytoplankton Community Structure in the Ross Sea Surface Waters.

Primary productivity in the Ross Sea region is characterized by intense phytoplankton blooms whose temporal and spatial distribution are driven by changes in environmental conditions as well as interactions with the bacterioplankton community. However, the number of studies reporting the simultaneous diversity of the phytoplankton and bacterioplankton in Antarctic waters are limited. Here, we report data on the bacterial diversity in relation to phytoplankton community structure in the surface waters of the Ross Sea during the Austral summer 2017. Our results show partially overlapping bacterioplankton communities between the stations located in the Terra Nova Bay (TNB) coastal waters and the Ross Sea Open Waters (RSOWs), with a dominance of members belonging to the bacterial phyla Bacteroidetes and Proteobacteria. In the TNB coastal area, microbial communities were characterized by a higher abundance of sequences related to heterotrophic bacterial genera such as Polaribacter spp., together with higher phytoplankton biomass and higher relative abundance of diatoms. On the contrary, the phytoplankton biomass in the RSOW were lower, with relatively higher contribution of haptophytes and a higher abundance of sequences related to oligotrophic and mixothrophic bacterial groups like the Oligotrophic Marine Gammaproteobacteria (OMG) group and SAR11. We show that the rate of diversity change between the two locations is influenced by both abiotic (salinity and the nitrogen to phosphorus ratio) and biotic (phytoplankton community structure) factors. Our data provide new insight into the coexistence of the bacterioplankton and phytoplankton in Antarctic waters, suggesting that specific rather than random interaction contribute to the organic matter cycling in the Southern Ocean.

Organic bioelectronics probing conformational changes in surface confined proteins.

The study of proteins confined on a surface has attracted a great deal of attention due to its relevance in the development of bio-systems for laboratory and clinical settings. In this respect, organic bio-electronic platforms can be used as tools to achieve a deeper understanding of the processes involving protein interfaces. In this work, biotin-binding proteins have been integrated in two different organic thin-film transistor (TFT) configurations to separately address the changes occurring in the protein-ligand complex morphology and dipole moment. This has been achieved by decoupling the output current change upon binding, taken as the transducing signal, into its component figures of merit. In particular, the threshold voltage is related to the protein dipole moment, while the field-effect mobility is associated with conformational changes occurring in the proteins of the layer when ligand binding occurs. Molecular Dynamics simulations on the whole avidin tetramer in presence and absence of ligands were carried out, to evaluate how the tight interactions with the ligand affect the protein dipole moment and the conformation of the loops surrounding the binding pocket. These simulations allow assembling a rather complete picture of the studied interaction processes and support the interpretation of the experimental results.

Label-free C-reactive protein electronic detection with an electrolyte-gated organic field-effect transistor-based immunosensor.

In this contribution, we propose a label-free immunosensor, based on a novel type of electrolyte-gated field-effect transistor (EGOFET), for ultrasensitive detection of the C-reactive protein (CRP). The recognition layer of the biosensor is fabricated by physical adsorption of the anti-CRP monoclonal antibody onto a poly-3-hexyl thiophene (P3HT) organic semiconductor surface. A supplementary nonionic hydrophilic polymer is used as a blocking agent preventing nonspecific interactions and allowing a better orientation of the antibodies immobilized onto the P3HT surface. The whole biomolecule immobilization procedure does not require any pretreatment of the organic semiconductor surface, and the whole functionalization process is completed in less than 30 min. Surface plasmon resonance (SPR) measurements were performed to assess the amount of biomolecules physisorbed onto the P3HT and to evaluate the CRP binding proprieties of the deposited anti-CRP layer. A partial surface coverage of about 23 % of adsorbed antibody molecules was found to most efficiently sense the CRP. The electrical performance of the EGOFET immunosensor was comparable to that of a bare P3HT EGOFET device, and the obtained CRP calibration curve was linear over six orders of magnitude (from 4 pM to 2 µM). The relative standard deviation of the individual calibration points, measured on immunosensors fabricated on different chips, ranged between 1 and 14 %, and a detection limit of 2 pM (220 ng/L) was established. The novel electronic immunosensor is compatible with low-cost fabrication procedures and was successfully employed for the detection of the CRP biomarker in the clinically relevant matrix serum. Graphical abstract Schematic of the EGOFET immunosensor for CRP detection. The anti-CRP monoclonal antibody layer is physisorbed on the P3HT organic semiconductor and the CRP is directly measured by a label-free electronic EGOFET transducer.

Printable Bioelectronics To Investigate Functional Biological Interfaces.

Thin-film transistors can be used as high-performance bioelectronic devices to accomplish tasks such as sensing or controlling the release of biological species as well as transducing the electrical activity of cells or even organs, such as the brain. Organic, graphene, or zinc oxide are used as convenient printable semiconducting layers and can lead to high-performance low-cost bioelectronic sensing devices that are potentially very useful for point-of-care applications. Among others, electrolyte-gated transistors are of interest as they can be operated as capacitance-modulated devices, because of the high capacitance of their charge double layers. Specifically, it is the capacitance of the biolayer, being lowest in a series of capacitors, which controls the output current of the device. Such an occurrence allows for extremely high sensitivity towards very weak interactions. All the aspects governing these processes are reviewed here.

General Approach to the Immobilization of Glycoenzyme Chains Inside Calcium Alginate Beads for Bioassay.

A general method to obtain the efficient entrapment of mixtures of glycoenzymes in calcium alginate hydrogel is proposed in this paper. As a proof of principle, three glycoenzymes acting in series (trehalase, glucose oxidase, and horseradish peroxidase) have been coimmobilized in calcium alginate beads. The release of the enzymes from the hydrogel mesh (leakage) is avoided by exploiting the enzyme's aggregation induced by the concanavalin A. The aggregation process has been monitored by dynamic light scattering technique, while both enzyme encapsulation efficiency and leakage have been quantified spectrophotometrically. Obtained data show an encapsulation efficiency above 95% and a negligible leakage from the beads when enzyme aggregates are larger than 300 nm. Operational stability of "as prepared" beads has been largely improved by a coating of alternated shells of polycation poly(diallyldimethylammonium chloride) and of alginate. As a test for the effectiveness of the overall procedure, analytical bioassays exploiting the enzyme-containing beads have been developed for the optical determination of glucose and trehalose, and limit of detection values of 0.2 and of 40 µM, respectively, have been obtained.

Capacitance-modulated transistor detects odorant binding protein chiral interactions.

Peripheral events in olfaction involve odorant binding proteins (OBPs) whose role in the recognition of different volatile chemicals is yet unclear. Here we report on the sensitive and quantitative measurement of the weak interactions associated with neutral enantiomers differentially binding to OBPs immobilized through a self-assembled monolayer to the gate of an organic bio-electronic transistor. The transduction is remarkably sensitive as the transistor output current is governed by the small capacitance of the protein layer undergoing minute changes as the ligand-protein complex is formed. Accurate determination of the free-energy balances and of the capacitance changes associated with the binding process allows derivation of the free-energy components as well as of the occurrence of conformational events associated with OBP ligand binding. Capacitance-modulated transistors open a new pathway for the study of ultra-weak molecular interactions in surface-bound protein-ligand complexes through an approach that combines bio-chemical and electronic thermodynamic parameters.

Tailoring Functional Interlayers in Organic Field-Effect Transistor Biosensors.

This review aims to provide an update on the development involving dielectric/organic semiconductor (OSC) interfaces for the realization of biofunctional organic field-effect transistors (OFETs). Specific focus is given on biointerfaces and recent technological approaches where biological materials serve as interlayers in back-gated OFETs for biosensing applications. Initially, to better understand the effects produced by the presence of biomolecules deposited at the dielectric/OSC interfacial region, the tuning of the dielectric surface properties by means of self-assembled monolayers is discussed. Afterward, emphasis is given to the modification of solid-state dielectric surfaces, in particular inorganic dielectrics, with biological molecules such as peptides and proteins. Special attention is paid on how the presence of an interlayer of biomolecules and bioreceptors underneath the OSC impacts on the charge transport and sensing performance of the device. Moreover, naturally occurring materials, such as carbohydrates and DNA, used directly as bulk gating materials in OFETs are reviewed. The role of metal contact/OSC interface in the overall performance of OFET-based sensors is also discussed.

Detection beyond Debye's length with an electrolyte-gated organic field-effect transistor.

Electrolyte-gated organic field-effect transistors are successfully used as biosensors to detect binding events occurring at distances from the transistor electronic channel that are much larger than the Debye length in highly concentrated solutions. The sensing mechanism is mainly capacitive and is due to the formation of Donnan's equilibria within the protein layer, leading to an extra capacitance (CDON) in series to the gating system.

Bio-sorbable, liquid electrolyte gated thin-film transistor based on a solution-processed zinc oxide layer.

Among the metal oxide semiconductors, ZnO has been widely investigated as a channel material in thin-film transistors (TFTs) due to its excellent electrical properties, optical transparency and simple fabrication via solution-processed techniques. Herein, we report a solution-processable ZnO-based thin-film transistor gated through a liquid electrolyte with an ionic strength comparable to that of a physiological fluid. The surface morphology and chemical composition of the ZnO films upon exposure to water and phosphate-buffered saline (PBS) are discussed in terms of the operation stability and electrical performance of the ZnO TFT devices. The improved device characteristics upon exposure to PBS are associated with the enhancement of the oxygen vacancies in the ZnO lattice due to Na(+) doping. Moreover, the dissolution kinetics of the ZnO thin film in a liquid electrolyte opens the possible applicability of these devices as an active element in "transient" implantable systems.

A comparative study of the gas sensing behavior in P3HT- and PBTTT-based OTFTs: the influence of film morphology and contact electrode position.

Bottom- and top-contact organic thin film transistors (OTFTs) were fabricated, using poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C16) as p-type channel semiconductors. Four different types of OTFTs were fabricated and investigated as gas sensors against three volatile organic compounds, with different associated dipole moments. The OTFT-based sensor responses were evaluated with static and transient current measurements. A comparison between the different architectures and the relative organic semiconductor was made.

Electronic transduction of proton translocations in nanoassembled lamellae of bacteriorhodopsin.

An organic field-effect transistor (OFET) integrating bacteriorhodopsin (bR) nanoassembled lamellae is proposed for an in-depth study of the proton translocation processes occurring as the bioelectronic device is exposed either to light or to low concentrations of general anesthetic vapors. The study involves the morphological, structural, electrical, and spectroscopic characterizations necessary to assess the functional properties of the device as well as the bR biological activity once integrated into the functional biointerlayer (FBI)-OFET structure. The electronic transduction of the protons phototranslocation is shown as a current increase in the p-type channel only when the device is irradiated with photons known to trigger the bR photocycle, while Raman spectroscopy reveals an associated C═C isomer switch. Notably, higher energy photons bring the cis isomer back to its trans form, switching the proton pumping process off. The investigation is extended also to the study of a PM FBI-OFET exposed to volatile general anesthetics such as halothane. In this case an electronic current increase is seen upon exposure to low, clinically relevant, concentrations of anesthetics, while no evidence of isomer-switching is observed. The study of the direct electronic detection of the two different externally triggered proton translocation effects allows gathering insights into the underpinning of different bR molecular switching processes.

Plain poly(acrylic acid) gated organic field-effect transistors on a flexible substrate.

We report on the use of a polyanionic proton conductor, poly(acrylic acid), to gate a poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene]-based organic field-effect transistor (OFET). A planar configuration of the OFET is evaluated, and the electrical performance and implementation on a flexible substrate are discussed.

Organic field-effect transistor sensors: a tutorial review.

The functioning principles of electronic sensors based on organic semiconductor field-effect transistors (OFETs) are presented. The focus is on biological sensors but also chemical ones are reviewed to address general features. The field-induced electronic transport and the chemical and biological interactions for the sensing, each occurring at the relevant functional interface, are separately introduced. Once these key learning points have been acquired, the combined picture for the FET electronic sensing is proposed. The perspective use of such devices in point-of-care is introduced, after some basics on analytical biosensing systems are provided as well. This tutorial review includes also a necessary overview of the OFET sensing structures, but the focus will be on electronic rather than electrochemical detection. The differences among the structures are highlighted along with the implications on the performance level in terms of key analytical figures of merit such as: repeatability, sensitivity and selectivity.

Chiral sensor devices for differentiation of enantiomers.

Differentiation of enantiomers remains one of the most attractive and important research areas in analytical chemistry due to its impact on pharmaceutical, chemical, biotechnology, and food industries. For a long time chiral separation techniques, such as high performance liquid chromatography (HPLC), gas chromatography (GC), and capillary electrophoresis (CE), have represented the gold standard for the separation and determination of enantiomers. These techniques, besides being time consuming and expensive, are also not suitable for real time analysis. Therefore, the development of fast and reliable chiral sensors remains a challenge to achieve on-line analysis of enantiomers in both gas and liquid samples. The scope of this chapter is to provide an overview on the basic functioning principles, as well as on the performance level, of solid-state sensing devices for enantiomers differentiation. Particular attention is paid to work providing a set of analytical figures of merit (sensitivity, repeatability, reproducibility, limit-of-detection, etc.) as well as to studies involving miniaturized (or miniaturizable) analytical devices that can deliver real-time, on-line, and label-free information on chiral compounds.

A new point-of-care portable immunosensor for non-invasive assessment of oro-ileal transit time by oral fluid tauroursodeoxycholate measurement after its oral load.

A non-invasive test for oro-ileal transit time (OITT) evaluation was developed, based on the measurement of tauroursodeoxycholic acid (TUDCA) oral fluid concentration profile after its oral administration. Exploiting the fact that TUDCA is actively absorbed only in the ileum, OITT is measured as the time corresponding to TUDCA maximum oral fluid concentration (tmax). To measure oral fluid TUDCA concentration in a point-of-care setting, an ultrasensitive portable immunosensor was developed, based on a competitive chemiluminescent enzyme immunoassay (CL-EIA), using immobilized anti-TUDCA antibody and an ursodeoxycholic acid (UDCA)-peroxidase conjugate as tracer, detected by enhanced chemiluminescence employing a portable charge-coupled device (CCD)-based device. The test was validated in 24 healthy subjects before and after treatment with Loperamide, a drug that increases OITT. The developed CL-EIA was accurate and precise, with a LLOQ of 50 pmol L(-1). The measured OITT for healthy subjects (291 ± 50 min) was fairly well correlated with OITT values obtained by measuring TUDCA in serum (r=0.89). An increased OITT was observed in all the studied subjects after Loperamide treatment. The CL immunosensor can be employed directly in gastroenterology and paediatric units and it can thus represent a new non-invasive simple test for OITT evaluation in a point-of-care setting, with improved diagnostic utility.

Electrolyte-gated organic field-effect transistor sensors based on supported biotinylated phospholipid bilayer.

Anchored, biotinylated phospholipids forming the capturing layers in an electrolyte-gated organic field-effect transistor (EGOFET) allow label-free electronic specific detection at a concentration level of 10 nM in a high ionic strength solution. The sensing mechanism is based on a clear capacitive effect across the PL layers involving the charges of the target molecules.

Part per trillion label-free electronic bioanalytical detection.

A Functional Bio-Interlayer Organic Field-Effect Transistor (FBI-OFET) sensor, embedding a streptavidin protein capturing layer, capable of performing label-free selective electronic detection of biotin at 3 part per trillion (mass fraction) or 15 pM, is proposed here. The response shows a logarithmic dependence spanning over 5 orders of magnitude of analyte concentration. The optimization of the FBI analytical performances is achieved by depositing the capturing layer through a controllable Layer-by-Layer (LbL) assembly, while an easy processable spin-coating deposition is proposed for potential low-cost production of equally highly performing sensors. Furthermore, a Langmuirian adsorption based model allows rationalizing the analyte binding process to the capturing layer. The FBI-OFET device is shown to operate also with an antibody interlayer as well as with an ad hoc designed microfluidic system. These occurrences, along with the proven extremely high sensitivity and selectivity, open to FBI-OFETs consideration as disposable electronic strip-tests for assays in biological fluids requiring very low detection limits.

Volatile general anesthetic sensing with organic field-effect transistors integrating phospholipid membranes.

The detailed action mechanism of volatile general anesthetics is still unknown despite their effect has been clinically exploited for more than a century. Long ago it was also assessed that the potency of an anesthetic molecule well correlates with its lipophilicity and phospholipids were eventually identified as mediators. As yet, the direct effect of volatile anesthetics at physiological relevant concentrations on membranes is still under scrutiny. Organic field-effect transistors (OFETs) integrating a phospholipid (PL) functional bio inter-layer (FBI) are here proposed for the electronic detection of archetypal volatile anesthetic molecules such as diethyl ether and halothane. This technology allows to directly interface a PL layer to an electronic transistor channel, and directly probe subtle changes occurring in the bio-layer. Repeatable responses of PL FBI-OFET to anesthetics are produced in a concentration range that reaches few percent, namely the clinically relevant regime. The PL FBI-OFET is also shown to deliver a comparably weaker response to a non-anesthetic volatile molecule such as acetone.

Interfacial electronic effects in functional biolayers integrated into organic field-effect transistors.

Biosystems integration into an organic field-effect transistor (OFET) structure is achieved by spin coating phospholipid or protein layers between the gate dielectric and the organic semiconductor. An architecture directly interfacing supported biological layers to the OFET channel is proposed and, strikingly, both the electronic properties and the biointerlayer functionality are fully retained. The platform bench tests involved OFETs integrating phospholipids and bacteriorhodopsin exposed to 1-5% anesthetic doses that reveal drug-induced changes in the lipid membrane. This result challenges the current anesthetic action model relying on the so far provided evidence that doses much higher than clinically relevant ones (2.4%) do not alter lipid bilayers' structure significantly. Furthermore, a streptavidin embedding OFET shows label-free biotin electronic detection at 10 parts-per-trillion concentration level, reaching state-of-the-art fluorescent assay performances. These examples show how the proposed bioelectronic platform, besides resulting in extremely performing biosensors, can open insights into biologically relevant phenomena involving membrane weak interfacial modifications.

Microcantilevers and organic transistors: two promising classes of label-free biosensing devices which can be integrated in electronic circuits.

Most of the success of electronic devices fabricated to actively interact with a biological environment relies on the proper choice of materials and efficient engineering of surfaces and interfaces. Organic materials have proved to be among the best candidates for this aim owing to many properties, such as the synthesis tunability, processing, softness and self-assembling ability, which allow them to form surfaces that are compatible with biological tissues. This review reports some research results obtained in the development of devices which exploit organic materials' properties in order to detect biologically significant molecules as well as to trigger/capture signals from the biological environment. Among the many investigated sensing devices, organic field-effect transistors (OFETs), organic electrochemical transistors (OECTs) and microcantilevers (MCLs) have been chosen. The main factors motivating this choice are their label-free detection approach, which is particularly important when addressing complex biological processes, as well as the possibility to integrate them in an electronic circuit. Particular attention is paid to the design and realization of biocompatible surfaces which can be employed in the recognition of pertinent molecules as well as to the research of new materials, both natural and inspired by nature, as a first approach to environmentally friendly electronics.