CMOS based Electrostatically-Formed Nanowire (EFN) sensor is based on a silicon nanowire field-effect transistor (FET) with a nanowire that is electrostatically formed and controlled by post fabrication. The EFN-FET is composed of doped silicon region surrounded by three gates: bottom gate and two lateral junction gates. Appropriate biasing at the gates induces depletion regions at the gate-silicon interfaces and an un-depleted silicon region which is electrostatically shaped into a wire of several nm in diameter is now available for conduction. Target gas molecules get adsorbed on the SiO₂ surface and via field-effect modifies the current conduction through the nanowire. Further, surface functionalization of these EFN sensors by metal nanoparticles could be an effective approach to achieve selectivity towards gases. For example, Pd nanoparticles (1 nm) decorated EFN (Pd-EFN) sensor shows promising results towards hydrogen gas. It shows excellent sensor responses at all concentrations ranging from 0.2 to 2.56% with quick response and recovery times. Also, the responses are linear over the entire concentration range and shows good repeatability. A low detection limit of 200 ppm (with a sensor response of 500%) is achieved which is much lower than the lower explosive limit of hydrogen gas which is 4%. The sensor retains good performances even in humid conditions with 80% RH. The sensor performances can further be tuned through application of different gate biases. A comparison of the performance metrics with the state of the art hydrogen sensors show that Pd-EFN proves to be a promising hydrogen sensor.

We evaluated the minimum concentration and minimum size of magnetic particles (MPs) within which modern ultra-sensitive magnetic field sensors (MFS) can detect them. Calculations showed that magnetite MPs with specific magnetization with characteristic sizes of ≥50 nm and a concentration of CV ~ 0.1 vol.% Can be detected at a distance l ≤ 0.1 mm using MFS with a magnetic field resolution of SB ≥1nT. However, at such a close distance it is impossible to non-invasively approach the biological object of study. On the other hand, the same MPs are easily detected at l ≤ 30 mm using supersensitive MFS based on the phenomena of superconductivity (SQUID) or superconductivity and spintronics (combined MFS (CMFS)). These sensors require cryogenic operating temperatures (4–77 K), and SB ~ 10–100 fT are realized in them. Note that superparamagnetic particles or carbon nanotubes (CNTs) can also be non-invasively detected by SQUID or CMFS sensors, assuming that their concentration in the material is CV ≥ 0.0000001 vol.%. It is believed that CNTs may contain catalytic iron particles or encapsulated magnetic nanoparticles in nanotubes. Thus, modern supersensitive magnetic field sensors with SB ≤ 100 fT make it possible to detect MPs in nanoscale, submicron, and micron sizes in biological objects. They can be used for non-invasive control of organs, implants, prostheses and drug carriers in the necessary parts of the body. Particularly important is the non-invasive control of CNTs in functional biocompatible nanomaterials, which have good prospects for widespread use in medical practice.

Pyroelectric infrared sensors are often based on lead-containing materials, which are harmful to the environment and subject of governmental restrictions. Ferroelectric Hf_1−xZr_xO₂ thin films offer an environmentally friendly alternative. Additionally, CMOS integration allows for integrated sensor circuits, allowing for scalable and cost-effective applications. In this work, we demonstrate the deposition of pyroelectric thin films on area-enhanced structured substrates via thermal atomic layer deposition. Scanning electron microscopy indicates a conformal deposition of the pyroelectric film in the holes with a diameter of 500 nm and a depth of 8 μm. By using TiN electrodes and photolithography, capacitor structures are formed, which are contacted via the electrically conductive substrate. Ferroelectric hysteresis measurements indicate sizable remanent polarization of up to 331 μC cm⁻², which corresponds to an area increase of up to 15 by the nanostructured substrate. For pyroelectric analysis, a sinusoidal temperature oscillation is applied to the sample. Simultaneously, the pyroelectric current is monitored. By assessing the phase of the measured current profile, the pyroelectric origin of the signal is confirmed. The devices show sizable pyroelectric coefficients of −475 μC m⁻² K⁻¹, which is larger than that of lead zirconate titanate (PZT). Based on the experimental evidence, we propose Hf_1−xZr_xO₂ as a promising material for future pyroelectric applications.

Systematic optimization of surface engineering (dimensionality) indeed plays a crucial role for achieving efficient vapor sensing performance. Among various semiconducting metal oxides, owing to some of its unique features and advantages, ZnO has attracted worldwide researchers for application in various fields including chemical sensors. Concomitant optimization of the surface attributes (varying different dimensions) of ZnO became a sensation for the entire research family. Moreover, the small thickness and extremely large surface of exfoliated 2D nanosheets render the gas sensing material as an ideal candidate, for achieving strong coupling with different gas molecules. However, temperature is a crucial factor in the field of chemical sensing. Recently, graphene-based gas sensors have attracted attention due to their variety of structures, unique sensing performances and room temperature working conditions. In this work, highly sensitive and fast responsive low temperature (60 ºC) based ethanol sensor, based on RGO/2D ZnO nanosheets hybrid structure, is reported. After detailed characterizations, vapor sensing potentiality of such sensor was tested for the detection of ethanol. The ethanol sensor offered the response magnitude of 89% (100 ppm concentration) with response and recovery time of 12 s/29 s respectively. Due to excessively high number of active sites for VOC interaction, with high yield synthesis process and appreciably high carrier mobility, paved the path for developing future generation, miniaturized and flexible (wearable) vapor sensor devices meeting the multidimensional requirements for traditional and upcoming (health/medical sector) applications. Underlying mechanistic framework for vapor sensing, through such hybrid junction, was explained with the Energy Band Diagram.

We developed a highly sensitive acetone bio-sniffer (gas-phase biosensor) based on an enzyme reductive reaction to monitor breath acetone concentration. The acetone bio-sniffer device was constructed by attaching a flow-cell with nicotinamide adenine dinucleotide (NADH)-dependent secondary alcohol dehydrogenase (S-ADH) immobilized membrane onto a fiber-optic NADH measurement system. This system utilizes an ultraviolet light emitting diode as an excitation light source. Acetone vapor was measured as fluorescence of NADH consumption by the enzymatic reaction of S-ADH. A phosphate buffer that contained oxidized NADH was circulated into the flow-cell to rinse the products and the excessive substrates from the optode; thus, the bio-sniffer enables real-time monitoring of acetone vapor concentration. A photomultiplier tube detects the change in the fluorescence emitted from NADH.

The relationship between fluorescence intensity and acetone concentration was identified from 20 ppb to 5300 ppb. This encompasses the range of concentration of acetone vapor found in breath of healthy people and of those suffering from disorders of carbohydrate metabolism. Then, the acetone bio-sniffer was used to monitor exhaled breath acetone concentration change before and after meal. When the sensing region was exposed to exhaled breath, fluorescence intensity decreased and reached to saturation immediately. Then it returned to the initial state upon cessation of the exhaled breath flow. We anticipate its future use as a non-invasive analytical tool for assessment of lipid metabolism in exercise, fasting and diabetes mellitus.