Flexible transistors are the next generation sensing technology, due to multiparametric analysis, reduced complexity, biocompatibility, lightweight with tunable optoelectronic properties. We summarize multitude of applications realized with OFETs.

The successful development of modern gas sensing technologies requires high sensitivity and selectivity coupled to cost effectiveness, which implies the necessity to miniaturize devices while reducing the amount of sensing material. The appealing alternative of integrating nanoparticles of a porous metal–organic framework (MOF) onto capacitive sensors based on interdigitated electrode (IDE) chips is presented. We report the deposition of MIL-96­(Al) MOF thin films via the Langmuir–Blodgett (LB) method on the IDE chips, which allowed the study of their gas/vapor sensing properties. First, sorption studies of several organic vapors like methanol, toluene, chloroform, etc. were conducted on bulk MOF. The sorption data revealed that MIL-96­(Al) presents high affinity toward water and methanol. Later on, ordered LB monolayer films of MIL-96­(Al) particles of ∼200 nm were successfully deposited onto IDE chips with homogeneous coverage of the surface in comparison to conventional thin film fabrication techniques such as drop-casting. The sensing tests showed that MOF LB films were selective for water and methanol, and short response/recovery times were achieved. Finally, chemical vapor deposition (CVD) of a porous thin film of Parylene C (thickness ∼250–300 nm) was performed on top of the MOF LB films to fabricate a thin selective layer. The sensing results showed an increase in the water selectivity and sensitivity, while those of methanol showed a huge decrease. These results prove the feasibility of the LB technique for the fabrication of ordered MOF thin films onto IDE chips using very small MOF quantities.

Organic field effect transistors (OFETs) have been the focus of sensing application research over the last two decades. In comparison to their inorganic counterparts, OFETs have multiple advantages, such as low-cost manufacturing, large area coverage, flexibility and readily tunable electronic material properties. To date, various organic semiconductors (OSCs), both polymers and small molecules, have been extensively researched for the purpose of developing the active channel layers in OFETs, enhancing their sensitivity and selectivity. However, OFET devices still need to be optimized to demonstrate reliable performance at the device level and in sensing applications. This review begins with an introduction of the OFETs with an emphasis on their geometry, materials (OSCs), fabrication process, and data analysis. After this, multiple applications are discussed and the progress regarding sensing elements and precisions is highlighted. In the end, the challenges and possible future directions of OFET arrays in embedded sensing platforms are presented.

MXenes are a promising class of two-dimensional materials with several potential applications, including energy storage, catalysis, electromagnetic interference shielding, transparent electronics, and sensors. Here, we report a novel Mo2CTx MXene sensor for the successful detection of volatile organic compounds (VOCs). The proposed sensor is a chemi-resistive device fabricated on a Si/SiO2 substrate using photolithography. The impact of various MXene process conditions on the performance of the sensor is evaluated. The VOCs toluene, benzene, ethanol, methanol, and acetone are studied at room temperature with varying concentrations. Under optimized conditions, the sensor demonstrates a detection limit of 220 ppb and a sensitivity of 0.0366 Ohm/ppm at a toluene concentration of 140 ppm. It exhibits an excellent selectivity toward toluene against the other VOCs. Ab initio simulations demonstrate selectivity toward toluene in line with the experimental results.

Organic field-effect transistors (OFETs) are emerging as competitive candidates for gas sensing applications due to the ease of their fabrication process combined with the ability to readily fine-tune the properties of organic semiconductors. Nevertheless, some key challenges remain to be addressed, such as material degradation, low sensitivity, and poor selectivity toward toxic gases. Appropriately, a heterojunction combination of different sensing layers with multifunctional capabilities offers great potential to overcome these problems. Here, a novel and highly sensitive receptor layer is proposed encompassing a porous 3D metal–organic framework (MOF) based on isostructural-fluorinated MOFs acting as an NO2 specific preconcentrator, on the surface of a stable and ultrathin PDVT-10 organic semiconductor on an OFET platform. Here, with this proposed combination we have unveiled an unprecedented 700% increase in sensitivity toward NO2 analyte in contrast to the pristine PDVT-10. The resultant combination for this OFET device exhibits a remarkable lowest detection limit of 8.25 ppb, a sensitivity of 680 nA/ppb, and good stability over a period of 6 months under normal laboratory conditions. Further, a negligible response (4.232 nA/%RH) toward humidity in the range of 5%–90% relative humidity was demonstrated using this combination. Markedly, the obtained results support the use of the proposed novel strategy to achieve an excellent sensing performance with an OFET platform.

We report an amorphous indium gallium zinc oxide (IGZO) based toxic gas detection system. The microsystem contains an IGZO thin film transistor (TFT) as a sensing element and exhibits remarkable selectivity and sensitivity to low concentrations of nitrogen dioxide (NO2). In contrast to existing metal oxide based gas sensors, which are active either at high temperature or with light activation, the developed IGZO TFT sensor is operable at room temperature and requires only visible light activation to revive the sensor after exposure to NO2. Furthermore, we demonstrate air-stable sensors with an experimental limit of detection of 100 ppb. This is the first report on metal oxide TFT gas sensors without heating or continuous light activation. Unlike most existing gas sensing systems that take care of identifying the analytes alone, the developed IGZO microsystem not only quantifies NO2 gas concentration but also yields 5-bit digital output. The compact microsystem incorporating readout and analog to digital conversion modules developed using only two TFTs, paves the way for inexpensive toxic gas monitoring systems.

In this work, we present a novel study on the development of an electrochemical biomimetic sensor to detect the ciprofloxacin (CIP) antibiotic.

We present a comparative study of two types of sensor with different transduction techniques but coated with the same sensing material to determine the effect of the transduction mechanism on the sensing performance of sensing a target analyte. For this purpose, interdigitated electrode (IDE)-based capacitors and quartz crystal microbalance (QCM)-based resonators were coated with a zeolitic–imidazolate framework (ZIF-8) metal–organic framework thin films as the sensing material and applied to the sensing of the volatile organic compound acetone. Cyclic immersion in methanolic precursor solutions technique was used for depositing the ZIF-8 thin films. The sensors were exposed to various acetone concentrations ranging from 5.3 to 26.5 vol % in N2 and characterized/compared for their sensitivity, hysteresis, long-term and short-term stability, selectivity, detection limit, and effect of temperature. Furthermore, the IDE substrates were used for resistive transduction and compared using capacitive transduction.