Hybrid MoSe2/P3HT Transistor for Real-Time Ammonia Sensing in Biofluids.

Organic and inorganic hybrid field-effect transistors (FETs), utilizing layered molybdenum diselenide (MoSe2) and an organic semiconductor poly(3-hexylthiophene) (P3HT), are presented for biosensing applications. A new hybrid device structure that combines organic (P3HT) and inorganic (MoSe2) components is showcased for accurate and selective bioanalyte detection in human bodily fluids to overcome 2D-transition metal dichalcogenides (TMDs) nonspecific interactions. This hybrid structure utilizes organic and inorganic semiconductors' high surface-to-volume ratio, carrier transport, and conductivity for biosensing. Ammonia concentrations in saliva and plasma are closely linked to physiological and pathological conditions of the human body. A highly sensitive hybrid FET biosensor detects total ammonia (NH4+ and NH3) from 0.5 µM to 1 mM concentrations, with a detection limit of 0.65 µM in human bodily fluids. The sensor's ammonia specificity in artificial saliva against interfering species is showcased. Furthermore, the fabricated hybrid FET device exhibits a stable and repeatable response to ammonia in both saliva and plasma, achieving a remarkable response level of 2300 at a 1 mM concentration of ammonia, surpassing existing literature by 10-fold. This hybrid FET biosensing platform holds significant promise for developing a precise tool for the real-time monitoring of ammonia concentrations in human biological fluids, offering potential applications in point-of-care diagnostics.

Biocompatible Ionic Liquids in High-Performing Organic Electrochemical Transistors for Ion Detection and Electrophysiological Monitoring.

Organic electrochemical transistors (OECTs) have recently attracted attention due to their high transconductance and low operating voltage, which makes them ideal for a wide range of biosensing applications. Poly-3,4-ethylenedioxythiophene:poly-4-styrenesulfonate (PEDOT:PSS) is a typical material used as the active channel layer in OECTs. Pristine PEDOT:PSS has poor electrical conductivity, and additives are typically introduced to improve its conductivity and OECT performance. However, these additives are mostly either toxic or not proven to be biocompatible. Herein, a biocompatible ionic liquid [MTEOA][MeOSO3] is demonstrated to be an effective additive to enhance the performance of PEDOT:PSS-based OECTs. The influence of [MTEOA][MeOSO3] on the conductivity, morphology, and redox process of PEDOT:PSS is investigated. The PEDOT:PSS/[MTEOA][MeOSO3]-based OECT exhibits high transconductance (22.3 ± 4.5 mS µm-1), high µC* (the product of mobility µ and volumetric capacitance C*) (283.80 ± 29.66 F cm-1 V-1 s-1), fast response time (∼40.57 µs), and excellent switching cyclical stability. Next, the integration of sodium (Na+) and potassium (K+) ion-selective membranes with the OECTs is demonstrated, enabling selective ion detection in the physiological range. In addition, flexible OECTs are designed for electrocardiography (ECG) signal acquisition. These OECTs have shown robust performance against physical deformation and successfully recorded high-quality ECG signals.

Polaron Delocalization Dependence of the Conductivity and the Seebeck Coefficient in Doped Conjugated Polymers.

Conjugated polymers are promising materials for thermoelectrics as they offer good performances at near ambient temperatures. The current focus on polymer thermoelectric research mainly targets a higher power factor (PF; a product of the conductivity and square of the Seebeck coefficient) through improving the charge mobility. This is usually accomplished via structural modification in conjugated polymers using different processing techniques and doping. As a result, the structure-charge transport relationship in conjugated polymers is generally well-established. In contrast, the relationship between the structure and the Seebeck coefficient is poorly understood due to its complex nature. A theoretical framework by David Emin (Phys. Rev. B, 1999, 59, 6205-6210) suggests that the Seebeck coefficient can be enhanced via carrier-induced vibrational softening, whose magnitude is governed by the size of the polaron. In this work, we seek to unravel this relationship in conjugated polymers using a series of highly identical pro-quinoid polymers. These polymers are ideal to test Emin's framework experimentally as the quinoid character and polaron delocalization in these polymers can be well controlled even by small atomic differences (<10 at. % per repeating unit). By increasing the polaron delocalization, that is, the polaron size, we demonstrate that both the conductivity and the Seebeck coefficient (and hence PF) can be increased simultaneously, and the latter is due to the increase in the polaron's vibrational entropy. By using literature data, we also show that this phenomenon can be observed in two closely related diketopyrrolopyrrole-conjugated polymers as well as in p-doped P3HT and PANI systems with an increasing molecular order.

Azurin-TiO2 hybrid nanostructure field effect transistor for efficient ultraviolet detection.

Hybrid semiconductor nanostructures have attracted tremendous response due to their unique properties and applications in nano-optoelectronics and sensors. Here, we fabricated a back-gated transistor based on 300 nm channel of the Azurin-TiO2 hybrid nanostructure, whose enhanced performance is attributed to the synergetic effect of the metal oxide and azurin. Surface potential mapping under the dark and light condition using Kelvin probe force microscopy, gives the perfect correlation of band gap estimation for Azurin, TiO2 and Azurin-TiO2 nanostructures. The extracted parameters of the transistor exhibit the majority carrier mobility of 2.26 cm2 V-1 s-1, Schottky barrier height of 133.56 meV and low off current (6 × 10-10 A). The photodetector showed the high spectral response of 8.7 × 105 A W-1 and detectivity of 6.4 × 1014 Jones for 260 nm wavelength, at an applied gate bias of 5 V. The short carrier transit time (3 µs) and large recombination time (0.4 s) with multiple recirculations of photo generated carries facilitate the high gain of 2.6 × 106. A significant rejection ratio (R 260/R 530) of 56.2 at V GS = 5 V and the linear dynamic range of 45.75 dB for 260 nm wavelength is achieved. The obtained rise and fall time of the photodetector is 0.52 s, and 0.65 s, respectively. This study suggests the applicability of Azurin-TiO2 hybrid nanostructures with high performance for the biocompatible optoelectronic devices.

Vancomycin functionalized WO3 thin film-based impedance sensor for efficient capture and highly selective detection of Gram-positive bacteria.

In this study, we report a facile, reusable, and highly sensitive label-free impedance sensor for discriminating Gram-positive and Gram-negative bacteria. The impedance sensor was fabricated using gold interdigitated electrodes onto a tungsten oxide thin film. X-Ray diffraction confirmed the formation of polycrystalline tungsten oxide. Field emission scanning electron microscopy and atomic force microscopy revealed that tungsten oxide has a porous structure. Tungsten oxide was functionalized with vancomycin, a glycopeptide antibiotic known to have a specific interaction with the peptidoglycan layer of Gram-positive bacteria. Fourier transform infrared microscopy and scanning electron microscopy were employed to test the morphological coating of vancomycin on interdigitated electrodes/tungsten oxide sensor. The functionalized tungsten oxide sensor was highly efficient in the capture of Gram-positive bacteria. The impedance measurement was also sensitive to differentiate between viable and non-viable Gram-positive bacteria. Limit of detection 102 colony forming unit/ml, linear dynamic range 102-107 colony forming unit/ml under physiological conditions and reusable nature of this vancomycin coated impedance sensor provide a label-free strategy for quick, sensitive and highly selective detection of Gram-positive bacteria.

S-Layer Protein for Resistive Switching and Flexible Nonvolatile Memory Device.

In this work, a flexible resistive switching memory device consisting of S-layer protein (Slp) is demonstrated for the first time. This novel device (Al/Slp/indium tin oxide/polyethylene terephthalte) based on a simple and easy fabrication method is capable of bistable switching to low resistive state (LRS) and high resistive state (HRS). This device exhibits bistable memory behavior with stability and a long retention time (>4 × 103 s), being stable up to a 500 cycle endurance test and with significant HRS/LRS ratio. The device possesses consistent switching performance for more than 100 times bending, corresponding to desired applicability for biocompatible wearable electronics. The memory mechanism is attributed to a trapping/de-trapping process in S-layer protein. These promising results of the flexible memory device could find a way in the wearable storage applications like smart bands and sports equipments' sensors.