ISFET and fiber optic sensor technologies: in vivo experience for critical care monitoring

Dual-Gate Organic Thin-Film Transistor and Multiplexer Chips for the Next Generation of Flexible EG-ISFET Sensor Chips

Ion-sensitive field-effect transistors (ISFETs) are used as elementary devices to build many types of chemical sensors and biosensors. Organic thin-film transistor (OTFT) ISFETs use either small molecules or polymers as semiconductors together with an additive manufacturing process of much lower cost than standard silicon sensors and have the additional advantage of being environmentally friendly. OTFT ISFETs' drawbacks include limited sensitivity and higher variability. In this paper, we propose a novel design technique for integrating extended-gate OTFT ISFETs (OTFT EG-ISFETs) together with dual-gate OTFT multiplexers (MUXs) made in the same process. The achieved results show that our OTFT ISFET sensors are of the state of the art of the literature. Our microsystem architecture enables switching between the different ISFETs implemented in the chip. In the case of sensors with the same gain, we have a fault-tolerant architecture since we are able to replace the faulty sensor with a fault-free one on the chip. For a chip including sensors with different gains, an external processor can select the sensor with the required sensitivity.

Advances in Optical Sensors for Persistent Organic Pollutant Environmental Monitoring

Optical chemical sensors are widely applied in many fields of modern analytical practice, due to their simplicity in preparation and signal acquisition, low costs, and fast response time. Moreover, the construction of most modern optical sensors requires neither wire connections with the detector nor sophisticated and energy-consuming hardware, enabling wireless sensor development for a fast, in-field and online analysis. In this review, the last five years of progress (from 2017 to 2021) in the field of optical chemical sensors development for persistent organic pollutants (POPs) is provided. The operating mechanisms, the transduction principles and the types of sensing materials employed in single selective optical sensors and in multisensory systems are reviewed. The selected examples of optical sensors applications are reported to demonstrate the benefits and drawbacks of optical chemical sensor use for POPs assessment.

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Electrostatically Governed Debye Screening Length at the Solution-Solid Interface for Biosensing Applications

Biosensors based on field-effect devices (bioFETs) offer numerous advantages over current technologies and therefore have attracted immense research over the decades. However, short Debye screening length in highly ionic physiological solutions remains the main obstacle for bioFET realization. This challenge becomes considerably more acute at the electrolyte-oxide interface of the sensing area due to high ion concentration induced by the charged amphoteric sites, which prohibits any attempt to employ the field-effect mechanism to "sense" any charged biomolecules. In this work, we present an electrostatic approach by which the double layer (DL) excess ion concentration is removed, thus forcing the DL ion concentration to match the bulk concentration, which subsequently forces bulk screening length at the DL, thereby "exposing" target biomolecules to the underlying bioFET. To this end, we employ local tunable surface electric fields, introduced to the DL using surface passivated-metal electrodes. We examine numerically and analytically the effect of these electric fields on the DL ion distribution. We also numerically demonstrate the feasibility of the proposed approach for a fully depleted silicon-on-insulator based bioFET and show how the threshold voltage shift induced by the presence of target molecules increases by almost two orders of magnitude upon the removal of the surface excess ion population.

Ion Aggregation and R3N+-C(R)-H···NR3 Hydrogen Bonding in a Fluorous Phase

Potentiometric selectivities show that in fluorous ion-selective electrode membranes the tetrabutylammonium ion binds to fluorophilic proton ionophores. For the ionophore bis[3-(perfluorooctyl)propyl](2,2,2-trifluoroethyl)amine, this type of interaction is confirmed by the effect of the ionophore on the ionic conductivity of perfluoro(perhydrophenanthrene) solutions of a fluorophilic NBu₄⁺ salt. In this system, ion pairs, triple ions, and higher ionic aggregates dominate over single ions, and the ionophore increases the conductivity by favoring the formation of ion aggregates with a net charge. These observations are consistent with the formation of R₃N⁺-C(R)-H···NR₃ type hydrogen bonds between the nitrogen atom of the ionophore and the hydrogen atoms in the α position to the positively charged quaternary ammonium center of NBu₄⁺. Similar interactions were observed in a number of crystalline phases. To date, observations of C-H···N type hydrogen bonds in liquid phases have been very few, and solution-phase N⁺-C-H···N type hydrogen bonds have not been reported previously. Interestingly, no interactions between NBu₄⁺ and the more basic ionophore tridodecylamine were observed in conventional plasticized poly(vinyl chloride) membranes doped with the ionophore tridodecylamine, emphasizing the uniquely low polarity of fluorous phases.

Electrochemical processes and mechanistic aspects of field-effect sensors for biomolecules

Electronic biosensing is a leading technology for determining concentrations of biomolecules. In some cases, the presence of an analyte molecule induces a measured change in current flow, while in other cases, a new potential difference is established. In the particular case of a field effect biosensor, the potential difference is monitored as a change in conductance elsewhere in the device, such as across a film of an underlying semiconductor. Often, the mechanisms that lead to these responses are not specifically determined. Because improved understanding of these mechanisms will lead to improved performance, it is important to highlight those studies where various mechanistic possibilities are investigated. This review explores a range of possible mechanistic contributions to field-effect biosensor signals. First, we define the field-effect biosensor and the chemical interactions that lead to the field effect, followed by a section on theoretical and mechanistic background. We then discuss materials used in field-effect biosensors and approaches to improving signals from field-effect biosensors. We specifically cover the biomolecule interactions that produce local electric fields, structures and processes at interfaces between bioanalyte solutions and electronic materials, semiconductors used in biochemical sensors, dielectric layers used in top-gated sensors, and mechanisms for converting the surface voltage change to higher signal/noise outputs in circuits.

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.

Recent trends in potentiometric sensor arrays--a review

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed.