Deformed graphene FET biosensor on textured glass coupled with dielectrophoretic trapping for ultrasensitive detection of GFAP

Numerous efforts have been undertaken to mitigate the Debye screening effect of FET biosensors for achieving higher sensitivity. There are few reports that show sub-femtomolar detection of biomolecules by FET mechanisms but they either suffer from significant background noise or lack robust control. In this aspect, deformed/crumpled graphene has been recently deployed by other researchers for various biomolecule detection like DNA, COVID-19 spike proteins and immunity markers like IL-6 at sub-femtomolar levels. However, the chemical vapor deposition (CVD) approach for graphene fabrication suffers from various surface contamination while the transfer process induces structural defects. In this paper, an alternative fabrication methodology has been proposed where glass substrate has been initially texturized by wet chemical etching through the sacrificial layer of synthesized silver nanoparticles, obtained by annealing of thin silver films leading to solid state dewetting. Graphene has been subsequently deposited by thermal reduction technique from graphene oxide solution. The resulting deformed graphene structure exhibits higher sensor response towards glial fibrillary acidic protein (GFAP) detection with respect to flat graphene owing to the combined effect of reduced Debye screening and higher surface area for receptor immobilization. Additionally, another interesting aspect of the reported work lies in the biomolecule capture by dielectrophoretic (DEP) transport on the crests of the convex surfaces of graphene in a coplanar gated topology structure which has resulted in 10 aM and 28 aM detection limits of GFAP in buffer and undiluted plasma respectively, within 15 min of application of analyte. The detection limit in buffer is almost four decades lower than that documented for GFAP using biosensors which is is expected to pave way for advancing graphene FET based sensors towards ultrasensitive point-of-care diagnosis of GFAP, a biomarker for traumatic brain injury.

Healthcare Monitoring Sensors Based on Organic Transistors: Surface/Interface Strategy and Performance

Organic transistors possess inherent advantages such as flexibility, biocompatibility, customizable chemical structures, solution-processability, and amplifying capabilities, making them highly promising for portable healthcare sensor applications. Through convenient and diverse modifications at the material and device surfaces or interfaces, organic transistors allow for a wide range of sensor applications spanning from chemical and biological to physical sensing. In this comprehensive review, the surface and interface engineering aspect associated with four types of typical healthcare sensors is focused. The device operation principles and sensing mechanisms are systematically analyzed and highlighted, and particularly surface/interface functionalization strategies that contribute to the enhancement of sensing performance are focused. An outlook and perspective on the critical issues and challenges in the field of healthcare sensing using organic transistors are provided as well.

Stretchable conductors for stretchable field-effect transistors and functional circuits

Stretchable electronics have received intense attention due to their broad application prospects in many areas, and can withstand large deformations and form close contact with curved surfaces. Stretchable conductors are vital components of stretchable electronic devices used in wearables, soft robots, and human-machine interactions. Recent advances in stretchable conductors have motivated basic scientific and technological research efforts. Here, we outline and analyse the development of stretchable conductors in transistors and circuits, and examine advances in materials, device engineering, and preparation technologies. We divide the existing approaches to constructing stretchable transistors with stretchable conductors into the following two types: geometric engineering and intrinsic stretchability engineering. Finally, we consider the challenges and outlook in this field for delivering stretchable electronics.

Organic small molecule semiconductor materials for OFET-based biosensors

Biosensors is an advanced detection and monitoring device for the development of biotechnology, and is also a rapid and microanalytical device at the molecular level. Demands for high sensitivity, high flexibility, good biocompatibility, easy chemical modification and low cost offer incentive for exploring new materials to develop the next-generation biosensors. With the vigorous development of organic electronics, the performances of organic devices have been effectively improved, leading to organic semiconductor materials with low cost, good flexibility, easy chemical modification and good biocompatibility for biosensors. Biosensors based on organic field-effect transistors (OFETs) have become one of the most advanced biosensor platforms because of their inherent ability to amplify received signals. Furthermore, OFET-based biosensors have been widely used in the detection of DNA, protein, cell, glucose and other biological substances due to its high sensitivity, fast analysis speed, label-free detection, small size and simple operation. This mini review briefly discusses the organic small molecule semiconductor materials, device configurations, basic principles and application fields of OFETs-based biosensors.

Towards a Point-of-Care (POC) Diagnostic Platform for the Multiplex Electrochemiluminescent (ECL) Sensing of Mild Traumatic Brain Injury (mTBI) Biomarkers

Globally, 70 million people are annually affected by TBI. A significant proportion of all TBI cases are actually mild TBI (concussion, 70-85%), which is considerably more difficult to diagnose due to the absence of apparent symptoms. Current clinical practice of diagnosing mTBI largely resides on the patients' history, clinical aspects, and CT and MRI neuroimaging observations. The latter methods are costly, time-consuming, and not amenable for decentralized or accident site measurements. As an alternative (and/or complementary), mTBI diagnostics can be performed by detection of mTBI biomarkers from patients' blood. Herein, we proposed two strategies for the detection of three mTBI-relevant biomarkers (GFAP, h-FABP, and S100β), in standard solutions and in human serum samples by using an electrochemiluminescence (ECL) immunoassay on (i) a commercial ECL platform in 96-well plate format, and (ii) a "POC-friendly" platform with disposable screen-printed carbon electrodes (SPCE) and a portable ECL reader. We further demonstrated a proof-of-concept for integrating three individually developed mTBI assays ("singleplex") into a three-plex ("multiplex") assay on a single SPCE using a spatially resolved ECL approach. The presented methodology demonstrates feasibility and a first step towards the development of a rapid POC multiplex diagnostic system for the detection of a mTBI biomarker panel on a single SPCE.

Detection of Glial Fibrillary Acidic Protein in Patient Plasma Using On-Chip Graphene Field-Effect Biosensors, in Comparison with ELISA and Single-Molecule Array

Glial fibrillary acidic protein (GFAP) is a discriminative blood biomarker for many neurological diseases, such as traumatic brain injury. Detection of GFAP in buffer solutions using biosensors has been demonstrated, but accurate quantification of GFAP in patient samples has not been reported, yet in urgent need. Herein, we demonstrate a robust on-chip graphene field-effect transistor (GFET) biosensing method for sensitive and ultrafast detection of GFAP in patient plasma. Patients with moderate–severe traumatic brain injuries, defined by the Mayo classification, are recruited to provide plasma samples. The binding of target GFAP with the specific antibodies that are conjugated on a monolayer GFET device triggers the shift of its Dirac point, and this signal change is correlated with the GFAP concentration in the patient plasma. The limit of detection (LOD) values of 20 fg/mL (400 aM) in buffer solution and 231 fg/mL (4 fM) in patient plasma have been achieved using this approach. In parallel, for the first time, we compare our results to the state-of-the-art single-molecule array (Simoa) technology and the classic enzyme-linked immunosorbent assay (ELISA) for reference. The GFET biosensor shows competitive LOD to Simoa (1.18 pg/mL) and faster sample-to-result time (<15 min), and also it is cheaper and more user-friendly. In comparison to ELISA, GFET offers advantages of total detection time, detection sensitivity, and simplicity. This GFET biosensing platform holds high promise for the point-of-care diagnosis and monitoring of traumatic brain injury in GP surgeries and patient homes.

The Current State of Traumatic Brain Injury Biomarker Measurement Methods

Traumatic brain injury (TBI) is associated with high rates of morbidity and mortality partially due to the limited tools available for diagnosis and classification. Measuring panels of protein biomarkers released into the bloodstream after injury has been proposed to diagnose TBI, inform treatment decisions, and monitor the progression of the injury. Being able to measure these protein biomarkers at the point-of-care would enable assessment of TBIs from the point-of-injury to the patient's hospital bedside. In this review, we provide a detailed discussion of devices reported in the academic literature and available on the market that have been designed to measure TBI protein biomarkers in various biofluids and contexts. We also assess the challenges associated with TBI biomarker measurement devices and suggest future research directions to encourage translation of these devices to clinical use.

Lossy-mode-resonance sensor based on perovskite nanomaterial with high sensitivity

Lossy-mode-resonance (LMR) is a surface plasmon resonance (SPR)-analogue optical phenomenon, which is sensitive to the surrounding environment variations and can be considered as an important detection signal in biochemical sensors. Compared with the SPR sensor which can only operate under transverse magnetic (TM)-polarized light, the LMR sensor shows a more excellent application prospect and can operate in both TM- and transverse electric (TE)-polarized light. In this work, a CH₃NH₃PbBr₃-based LMR configuration is proposed to apply in optical sensors. When the incident light is in TM mode, the preferred way to improve the performance of the LMR sensor is optimizing the thickness of the matching layer, and the highest sensitivity of 11382 refractive index unit (RIU^-1) is achieved, which is more than 200 times larger than that of the conventional Au-based SPR sensor; when the incident light is in TE mode, it is more advantageous to improve the properties of LMR sensor by optimizing the thickness of CH₃NH₃PbBr₃ layer, and a high sensitivity of 21697 RIU^-1 is obtained. With such high sensitivity, we believe that the CH₃NH₃PbBr₃-based LMR sensor will find potential applications in biology, medicine, chemistry and other fields.

Extended gate-type organic transistor functionalized by molecularly imprinted polymer for taurine detection

Molecularly imprinted polymers (MIPs) are a fascinating technology for the sensitive and selective detection of target molecules. However, in most situations, the need for complicated and expensive analytical devices for reading the responses of MIPs greatly limits their applications. For exploring low-cost and easy-to-use applications of MIPs, herein we have developed a MIP-modified extended-gate type organic field-effect transistor (MIP-OFET). Taurine was selected as a demonstrative analyte due to its biological roles and utility as a nutrient. We explored the rational design of the novel MIP with the aid of density functional theory and wave function calculations and characterized the electrochemically synthesized MIP using differential pulse voltammetry and electrochemical impedance spectroscopy. The mechanism of taurine detection by the MIP-OFET can be explained by the changes in the surface potential of the MIP-functionalized extended-gate electrode accompanied with the capture of taurine. The detection limit of taurine in complete aqueous media was estimated to be 0.33 μM, which was lower or comparable to those calculated by high-performance liquid chromatography. Furthermore, taurine in a commercial drink without any extraction was also successfully detected using the fabricated MIP-OFET. This study would broaden the scope of the applications of MIP-OFETS as chemical sensors for on-site detection of various daily nutrients.

Low-Voltage, Dual-Gate Organic Transistors with High Sensitivity and Stability toward Electrostatic Biosensing

High levels of performance and stability have been demonstrated for conjugated polymer thin-film transistors in recent years, making them promising materials for flexible electronic circuits and displays. For sensing applications, however, most research efforts have been focusing on electrochemical sensing devices. Here we demonstrate a highly stable biosensing platform using polymer transistors based on the dual-gate mechanism. In this architecture a sensing signal is transduced and amplified by the capacitive coupling between a low-k bottom dielectric and a high-k ionic elastomer top dielectric that is in contact with an analyte solution. The new design exhibits a high signal amplification, high stability under bias stress in various aqueous environments, and low signal drift. Our platform, furthermore, while responding expectedly to charged analytes such as the protein bovine serum albumin, is insensitive to changes of salt concentration of the analyte solution. These features make this platform a potentially suitable tool for a variety of biosensing applications.

Biosynthesized Quantum Dot for Facile and Ultrasensitive Electrochemical and Electrochemiluminescence Immunoassay

Nanomaterials are commonly utilized for amplified immunoassay of biomarkers. However, traditional nanomaterial-based immunoassay usually requires a time-consuming and labor-intensive nanoparticle modification and conjugation process, which impedes their practical applications. Here, a new immunoassay method based on biosynthesized nanomaterials is developed with versatile functions for facile and ultrasensitive detection of cancer biomarker. In this method, the utilized biosynthesized quantum dots (BQDs) allow convenient antibody conjugation and electrode modification, and demonstrate excellent electrochemical and electrochemiluminescent responses. The differential pulse voltammetric, faradaic impedance spectroscopy, and electrochemiluminescent measurements with the BQD-modified electrode show detection limits at picomolar levels as well as good specificity toward human prostate-specific antigen detection. The inherent recognization capability as well as the inherent electrochemical and electrochemiluminescence features thus enable BQDs as good candidates for facile immunosensors with high sensitivity. Such a biosynthesized nanomaterial-based approach opens up the possibility of using innovative designs for nanoparticle-based assays, and developing reliable and practical methods for early disease diagnosis.

On-the-Spot Detection and Speciation of Cannabinoids Using Organic Thin-Film Transistors

Quality control is imperative for Cannabis since the primary cannabinoids, Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD), elicit very different pharmacological effects. THC/CBD ratios are currently determined by techniques not readily accessible by consumers or dispensaries and which are impractical for use in the field by law-enforcement agencies. CuPc- and F₁₆-CuPc-based organic thin-film transistors have been combined with a cannabinoid-sensitive chromophore for the detection and differentiation of THC and CBD. The combined use of these well-characterized and inexpensive p- and n-type materials afforded the determination of the CBD/THC ratio from rapid plant extracts, with results indistinguishable from high-pressure liquid chromatography. Analysis of the prepyrolyzed sample accurately predicted postpyrolysis THC/CBD, which ultimately influences the psychotropic and medicinal effects of the specific plant. The devices were also capable of vapor-phase sensing, producing a unique electrical output for THC and CBD relative to other potentially interfering vaporized organic products. The analysis of complex medicinal plant extracts and vapors, normally reserved for advanced analytical infrastructure, can be achieved with ease, at low cost, and on the spot, using organic thin-film transistors.

Chirality Discrimination at the Single Molecule Level by Using a Cationic Supermolecule Quasi-Gated Organic Field Effect Transistor

Achieving rapid and highly sensitive small molecule chiral discrimination is a great challenge in modern-day analytical sciences. Herein, an organic field effect transistors (OFET) is developed by employing an imidazolium 3,5-dimethylphenylcabamoylated-β-cyclodextrin (Im⁺-Ph-β-CD) as both the recognition unit and a quasi gate, which induces a secondary accumulation channel of electrons in the n-type transistor to achieve the signal transduction and amplification via field effect. The charge of the imidazolium group is partially shielded due to its self-inclusion in the CD cavity, and this shielding effect is reduced at varying degrees in the existence of isomers due to the competitive inclusion. Consequently, the different weak intermolecular interactions related to the target-induced CD-enantiomer complexation with different geometry and stabilization energy for each isomer can be transformed to electronic signals based on the variety of Im⁺-Ph-β-CD's effective charge rather than the intrinsic charge of analytes, hence leading to chiral differentiation, and the hydrogen-bonding network of Im⁺-Ph-β-CD membrane further magnifies the signal. This working strategy even allows chiral discrimination of electrically neutral analytes. The as-prepared sensor affords rapid and real-time discrimination to small molecule enantiomers at single molecule level with a limit of detection of 8.1 × 10^-19 M in a 200 μL volume (about 100 small molecules). Moreover, we prove the great potential of the chiral organic field effect transistor in quantitative analysis of commercial medicines.

P and N type copper phthalocyanines as effective semiconductors in organic thin-film transistor based DNA biosensors at elevated temperatures

Many health-related diagnostics are expensive, time consuming and invasive. Organic thin film transistor (OTFT) based devices show promise to enable rapid, low cost diagnostics that are an important aspect to enabling increased access and availability to healthcare. Here, we describe OTFTs based upon two structurally similar P (copper phthalocyanine – CuPc) and N (hexdecafluoro copper phthalocyanine – F₁₆-CuPc) type semiconductor materials, and demonstrate their potential for use as both temperature and DNA sensors. Bottom gate bottom contact (BGBC) OTFTs with either CuPc or F₁₆-CuPc semiconducting layers were characterized within a temperature range of 25 °C to 90 °C in both air and under vacuum. CuPc devices showed small positive shifts in threshold voltage (V_T) in air and significant linear increases in mobility with increasing temperature. F₁₆-CuPc devices showed large negative shifts in V_T in air and linear increases in mobility under the same conditions. Similar OTFTs were exposed to DNA in different hybridization states and both series of devices showed positive V_T increases upon DNA exposure, with a larger response to single stranded DNA. The N-type F₁₆-CuPc devices showed a much greater sensing response than the P-type CuPc. These findings illustrate the use of these materials, especially the N-type semiconductor, as both temperature and DNA sensors and further elucidate the mechanism of DNA sensing in OTFTs.

This study illustrates the use of an N-type semiconductor, in both temperature and DNA sensors and further elucidates the mechanism of DNA sensing in OTFTs.

Impedance Spectroscopic Detection of Binding and Reactions in Acid-Labile Dielectric Polymers for Biosensor Applications

We synthesized previously unreported copolymers with cleavable acid-labile side chains for use as electrochemical sensing layers in order to demonstrate a novel architecture for a one-step immunosensor. This one-step system is in contrast to most antigen-capture signal amplification methods that involve complicated secondary labeling techniques, or require the addition of redox probes to achieve a sensing response. A series of novel copolymers composed of various trityl-containing monomers were synthesized and characterized to determine their dielectric properties. Results indicate that the thin films of these polymers are stable in water, but some begin to degrade under acidic conditions or upon antigen binding, causing observable changes in the phase angle.

Electronic Cortisol Detection Using an Antibody-Embedded Polymer Coupled to a Field-Effect Transistor

A field-effect transistor-based cortisol sensor was demonstrated in physiological conditions. An antibody-embedded polymer on the remote gate was proposed to overcome the Debye length issue (λ_D). The sensing membrane was made by linking poly(styrene- co-methacrylic acid) (PSMA) with anticortisol before coating the modified polymer on the remote gate. The embedded receptor in the polymer showed sensitivity from 10 fg/mL to 10 ng/mL for cortisol and a limit of detection (LOD) of 1 pg/mL in 1× PBS where λ_D is 0.2 nm. A LOD of 1 ng/mL was shown in lightly buffered artificial sweat. Finally, a sandwich ELISA confirmed the antibody binding activity of antibody-embedded PSMA.

Blood biomarkers for evaluation of perinatal encephalopathy: state of the art

PURPOSE OF REVIEW

The rapid progress in biomarker science is on the threshold of significantly changing clinical care for infants in the neonatal ICU. Infants with neonatal brain injuries will likely be the first group whose management is dramatically altered with point-of-care, rapidly available brain biomarker analysis. Providing an interim update on progress in this area is the purpose of this review.

RECENT FINDINGS

Highlighted findings from the past 18 months of publications on biomarkers in neonatal brain injury include; Specific nonbrain markers of cardiac health and global asphyxia continue to provide information on brain injury after hypoxic-ischemic encephalopathy (HIE). Prediction of injury in the piglet hypoxia-ischemia model is improved with the use of a combination score of plasma metabolites. In a neonatal piglet model of perinatal hypoxia-ischemia, a systemic proinflammatory surge of cytokines has been identified after rewarming from therapeutic hypothermia. New biomarkers identified recently include osteopontin, activin A, neutrophil gelatinase-associated lipocalin, secretoneurin, Tau and neurofilament light protein. Brain-based biomarkers differ in their ability to predict short-term in-hospital outcomes and long-term neurologic deficits.

SUMMARY

Neonatal brain biomarker research is currently in its very early development with major advances still to be made.

Label-Free Direct Electrical Detection of a Histidine-Rich Protein with Sub-Femtomolar Sensitivity using an Organic Field-Effect Transistor

There is a growing interest in achieving sensor systems to enable on-site testing of biomarkers. Herein, a new strategy for highly sensitive protein detection at sub-femtomolar levels without any labelling has been demonstrated by using an organic field-effect transistor (OFET). An artificial histidine-rich protein receptor (NiII-nitrilotriacetic acid complex, NiII-nta) functionalizes a detection portion (i.e. an extended-gate electrode) of the fabricated OFET device. The OFET responds electrically and selectively to a target analyte (bovine serum albumin), meaning that the binding processes at the NiII-nta on the extended-gate electrode for the analyte affect the field-effect properties of the device. Our results demonstrate that the combination of the OFET with the artificial receptor is an ideal approach for label-free and immune-free protein detection.

UV-Ozone Interfacial Modification in Organic Transistors for High-Sensitivity NO2 Detection

A new type of nitrogen dioxide (NO₂ ) gas sensor based on copper phthalocyanine (CuPc) thin film transistors (TFTs) with a simple, low-cost UV-ozone (UVO)-treated polymeric gate dielectric is reported here. The NO₂ sensitivity of these TFTs with the dielectric surface UVO treatment is ≈400× greater for [NO₂ ] = 30 ppm than for those without UVO treatment. Importantly, the sensitivity is ≈50× greater for [NO₂ ] = 1 ppm with the UVO-treated TFTs, and a limit of detection of ≈400 ppb is achieved with this sensing platform. The morphology, microstructure, and chemical composition of the gate dielectric and CuPc films are analyzed by atomic force microscopy, grazing incident X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, revealing that the enhanced sensing performance originates from UVO-derived hydroxylated species on the dielectric surface and not from chemical reactions between NO₂ and the dielectric/semiconductor components. This work demonstrates that dielectric/semiconductor interface engineering is essential for readily manufacturable high-performance TFT-based gas sensors.

Extended Solution Gate OFET-based Biosensor for Label-free Glial Fibrillary Acidic Protein Detection with Polyethylene Glycol-Containing Bioreceptor Layer

A novel organic field effect transistor (OFET) -based biosensor is described for label-free glial fibrillary acidic protein (GFAP) detection. We report the first use of an extended solution gate structure where the sensing area and the organic semiconductor are separated, and a reference electrode is not needed. Different molecular weight polyethylene glycols (PEGs) are mixed into the bio-receptor layer to help extend the Debye screening length. The drain current change was significantly increased with the help of higher molecular weight PEGs, as they are known to reduce the dielectric constant. We also investigated the sensing performance under different gate voltage (V_g). The sensitivity increased after we decreased V_g from -5 V to -2 V, because the lower V_g is much closer to the OFET threshold voltage and the influence of attached negatively charged proteins become more apparent. Finally, the selectivity experiments toward different interferents were performed. The stability and selectivity are promising for clinical applications.

Orthogonal Ambipolar Semiconductor Nanostructures for Complementary Logic Gates

We report orthogonal ambipolar semiconductors that exhibit hole and electron transport in perpendicular directions based on aligned films of nanocrystalline "shish-kebabs" containing poly(3-hexylthiophene) (P3HT) and N,N'-di-n-octyl-3,4,9,10-perylenetetracarboxylic diimide (PDI) as p- and n-type components, respectively. Polarized optical microscopy, scanning electron microscopy, and X-ray diffraction measurements reveal a high degree of in-plane alignment. Relying on the orientation of interdigitated electrodes to enable efficient charge transport from either the respective p- or n-channel materials, we demonstrate semiconductor films with high anisotropy in the sign of charge carriers. Films of these aligned crystalline semiconductors were used to fabricate complementary inverter devices, which exhibited good switching behavior and a high noise margin of 80% of 1/2 Vdd. Moreover, complementary "NAND" and "NOR" logic gates were fabricated and found to exhibit excellent voltage transfer characteristics and low static power consumption. The ability to optimize the performance of these devices, simply by adjusting the solution concentrations of P3HT and PDI, makes this a simple and versatile method for preparing ambipolar organic semiconductor devices and high-performance logic gates. Further, we demonstrate that this method can also be applied to mixtures of PDI with another conjugated polymer, poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene]) (PBTTT), with better hole transport characteristics than P3HT, opening the door to orthogonal ambipolar semiconductors with higher performance.

Organic thin-film transistors fabricated using a slot-die-coating process and related sensing applications

We herein present the results of a study involving the fabrication of semiconductor thin films for organic thin-film transistors composed of a small molecular TIPS-PEN composite blended with a polymer binder of PaMS, i.e., TIPS-PEN:PaMS.

A High-Capacitance Salt-Free Dielectric for Self-Healable, Printable, and Flexible Organic Field Effect Transistors and Chemical Sensor

Printable and flexible electronics attract sustained attention for their low cost, easy scale up, and potential application in wearable and implantable sensors. However, they are susceptible to scratching, rupture, or other damage from bending or stretching due to their "soft" nature compared to their rigid counterparts (Si-based electronics), leading to loss of functionality. Self-healing capability is highly desirable for these "soft" electronic devices. Here, a versatile self-healing polymer blend dielectric is developed with no added salts and it is integrated into organic field transistors (OFETs) as a gate insulator material. This polymer blend exhibits an unusually high thin film capacitance (1400 nF cm -2 at 120 nm thickness and 20-100 Hz). Furthermore, it shows pronounced electrical and mechanical self-healing behavior, can serve as the gate dielectric for organic semiconductors, and can even induce healing of the conductivity of a layer coated above it together with the process of healing itself. Based on these attractive properties, we developed a self-healable, low-voltage operable, printed, and flexible OFET for the first time, showing promise for vapor sensing as well as conventional OFET applications.

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.

Toward organic electronics with properties inspired by biological tissue

The carbon framework common to both organic semiconductors and biological structures suggests that these two classes of materials should be easily integrated.

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.

Electrical signaling of enzyme-linked immunosorbent assays with an ion-sensitive field-effect transistor

Optical laboratory-based immunoassays, such as enzyme-linked immunosorbent assay (ELISA) give a high sensitivity and specificity of various fatal diseases. However, these assays are no longer efficient in on-spot diagnostics of wide-spreading and contagious infections. At this point in time, portable and handhold devices play a pivotal role in infectious diseases with quick diagnostics at or near the site of the disease propagation. In this paper, we demonstrated a novel electrical immunoassay of ELISA that was not based on optical signaling but on electrical signaling. This was done by combining an ion-sensitive field-effect transistor (ISFET) with ELISA. By harnessing the catalytic reaction of alkaline phosphatase that precipitated silver particles, we effectively overcame the chronic Debye screening length issue of the ISFET. Ultimately, small signal ranging from 1 pg/mL to 10 ng/mL was immensely amplified with the ALP label, regardless of buffer conditions. The sensor platform herein surpassed a sensing capability of conventional ELISA that is considered to have a LOD on the order of ~1 ng/mL. The results were compared with those of horseradish peroxidase label, which is generally used for optical analyses in ELISA. Our newly developed ISFET-based portable sensor holds a large potential for point-of-care tools in a variety of diseases, without being limited by the need for expensive equipment such as spectrophotometers.

Performance enhancement of capacitive-coupling dual-gate ion-sensitive field-effect transistor in ultra-thin-body

Recently, thin-film transistor based-ISFETs with the dual-gate (DG) structures have been proposed, in order to beat the Nernst response of the standard ISFET, utilizing diverse organic or inorganic materials. The immutable Nernst response can be dramatically transformed to an ultra-sensing margin, with the capacitive-coupling arisen from the DG structure. In order to advance this platform, we here embedded the ultra-thin body (UTB) into the DG ISFET. The UTB of 4.3 nm serves to not only increase its sensitivity, but also to strongly suppress the leakage components, leading to a better stability of the DG ISFET. In addition, we first provide a comprehensive analysis of the body thickness effects especially how the thick body can render the degradation in the device performance, such as sensitivity and stability. The UTB DG ISFET will allow the ISFET-based biosensor platform to continue enhancement into the next decade.