TiO2 Nano Flowers Based EGFET Sensor for pH Sensing

Preparation and application of a Cu-doped antimony electrode to improve the performance of pH measurement in seawater

Antimony-based electrodes are widely used in various fields for pH detection due to their low cost. However, their application in the marine environment is significantly hampered by the significant potential drift observed in seawater pH measurements. This study focuses on enhancing the stability of a pure antimony electrode by doping various amounts of copper without compromising its pH response. A series of electrochemical tests demonstrated that the fabricated alloy electrodes exhibited excellent pH response characteristics, including sensitivity, ion selectivity, response time, reversibility, and temperature coefficients. Moreover, the alloy electrodes were more resistant to corrosion than the pure antimony electrode, thereby guaranteeing the stability. Notably, the alloy electrodes containing 63 at% and 70 at% antimony exhibited superior electrochemical characteristics. The surface analysis elucidated that the alloy electrode had reduced oxidation, surface cracks and antimony peeling compared to the pure antimony electrode. Furthermore, the prepared alloy electrodes exhibited excellent pH response and stability in simulated high-salinity seawater and real seawater. The above results highlight that doping cheap copper into antimony can improve the electrode stability by enhancing the corrosion resistance and slowing down the oxidation rate, thus enabling reliable long-time operation in a relatively stable state. These findings provide experimental support for developing novel pH electrodes based on non-noble metals for use in challenging environments such as seawater.

Advances in pH Sensing: From Traditional Approaches to Next-Generation Sensors in Biological Contexts

pH has been considered one of the paramount factors in bodily functions because most cellular tasks exclusively rely on precise pH values. In this context, the current techniques for pH sensing provide us with the futuristic insight to further design therapeutic and diagnostic tools. Thus, pH-sensing (electrochemically and optically) is rapidly evolving toward exciting new applications and expanding researchers' interests in many chemical contexts, especially in biomedical applications. The adaptation of cutting-edge technology is subsequently producing the modest form of these biosensors as wearable devices, which are providing us the opportunity to target the real-time collection of vital parameters, including pH for improved healthcare systems. The motif of this review is to provide insight into trending tech-based systems employed in real-time or in-vivo pH-responsive monitoring. Herein, we briefly go through the pH regulation in the human body to help the beginners and scientific community with quick background knowledge, recent advances in the field, and pH detection in real-time biological applications. In the end, we summarize our review by providing an outlook; challenges that need to be addressed, and prospective integration of various pH in vivo platforms with modern electronics that can open new avenues of cutting-edge techniques for disease diagnostics and prevention.

Performance Improvement of a ZnGa2O4 Extended-Gate Field-Effect Transistor pH Sensor

ZnGa2O4 sensing films were prepared using an RF magnetron sputtering system and connected to a commercial metal oxide semiconductor field-effect transistor (MOSFET) as the extended-gate field-effect transistor (EGFET) to detect pH values. Experimental parameters were adjusted by varying the oxygen flow rate in the process chamber to produce ZnGa2O4 sensing films with different oxygen ratios. These films were then treated in a furnace tube at an annealing temperature of 700 °C. The sensitivity and linearity of the constant current mode and the constant voltage mode were measured and analyzed in the pH range of 2-12. Under the deposition conditions with an oxygen ratio of 6%, the sensitivity reached 23.14 mV/pH and 33.49 μA/pH, with corresponding linearity values of 92.1 and 96.15%, respectively. Finally, the sensing performance of the ZnGa2O4 EGFET pH sensor with and without annealing processes was analyzed and compared.

Nano-Brush Structure for Rapid Label-Free Differentiation of Alzheimer's Disease Stages and Direct Capture of Neuron-Derived Exosomes from Human Blood Plasma

The measurement of the neurofilament light chain (NFL) in human blood plasma/serum is a promising liquid biopsy for Alzheimer's disease (AD) diagnosis, offering advantages over conventional neuroimaging techniques recommended in clinical guidelines. Here, a controllable nano-brush structure comprising upstanding silicon nanowires coated with indium tin oxide was employed as the sensing substrate. This nano-brush structure was modified with an NFL antibody (NFLAb) via silane coupling and then further connected as the extended gate in a field-effect transistor (EGFET). Notable signal differences emerged within a 2 min timeframe, enabling the label-free differentiation in human blood plasmas among four distinct cohorts: healthy controls, subjective cognitive decline, mild cognitive impairment, and dementia due to AD. Our study indicates that achieving a surface roughness exceeding 400 nm on the modified nano-brush structure enables the effective electrical sensing in our EGFETs. These distinct electrical responses measured via the NFLAb-modified nano-brush EGFETs can be attributed to the combined effects of the captured NFLs and NFL-specific neuron-derived exosomes (NDEs) found in dementia patients, as confirmed by electron spectroscopy for chemical analysis, atomic force microscopy, and scanning electron microscopy. Finally, the potential of quantitatively detecting NDEs on the NFLAb-modified nano-brush structure was demonstrated using spiked solutions containing NFL-specific NDEs from IMR-32 neuroblast cells, wherein concentration-dependent changes were observed in the EGFETs output signal. Our findings show that the NFLAb-modified nano-brush EGFET enables rapid, label-free differentiation between healthy individuals and patients at varying stages of AD.

Modification of Liquid Separation Membranes Using Multidimensional Nanomaterials: Revealing the Roles of Dimension Based on Classical Titanium Dioxide

Membrane technology has become increasingly popular and important for separation processes in industries, as well as for desalination and wastewater treatment. Over the last decade, the merger of nanotechnology and membrane technology in the development of nanocomposite membranes has emerged as a rapidly expanding research area. The key motivation driving the development of nanocomposite membranes is the pursuit of high-performance liquid separation membranes that can address the bottlenecks of conventionally used polymeric membranes. Nanostructured materials in the form of zero to three-dimensions exhibit unique dimension-dependent morphology and topology that have triggered considerable attention in various fields. While the surface hydrophilicity, antibacterial, and photocatalytic properties of TiO₂ are particularly attractive for liquid separation membranes, the geometry-dependent properties of the nanocomposite membrane can be further fine-tuned by selecting the nanostructures with the right dimension. This review aims to provide an overview and comments on the state-of-the-art modifications of liquid separation membrane using TiO₂ as a classical example of multidimensional nanomaterials. The performances of TiO₂-incorporated nanocomposite membranes are discussed with attention placed on the special features rendered by their structures and dimensions. The innovations and breakthroughs made in the synthesis and modifications of structure-controlled TiO₂ and its composites have enabled fascinating and advantageous properties for the development of high-performance nanocomposite membranes for liquid separation.

Polymorphic control in titanium dioxide particles

The hydrolysis-condensation reaction of TiO₂ was adapted to the phase inversion temperature (PIT)-nano-emulsion method as a low energy approach to gain control over the size and phase purity of the resulting metal oxide particles. Three different PIT-nano-emulsion syntheses were designed, each one intended to isolate high purity rutile, anatase, and brookite phase particles. Three different emulsion systems were prepared, with a pH of either strongly acidic (H₂O : HNO₃, pH ∼0.5), moderately acidic (H₂O : isopropanol, pH ∼4.5), or alkaline (H₂O : NaOH, pH ∼12). PIT-nano-emulsion syntheses of the amorphous TiO₂ particles were conducted under these conditions, resulting in average particle diameter distributions of ∼140 d nm (strongly acidic), ∼60 d nm (moderately acidic), and ∼460 d nm (alkaline). Different thermal treatments were performed on the amorphous particles obtained from the PIT-nano-emulsion syntheses. Raman spectroscopy and powder X-ray diffraction (PXRD) were employed to corroborate that the thermally treated particles under H₂O : HNO₃ (at 850 °C), H₂O : NaOH (at 400 °C), and H₂O : isopropanol (at 200 °C) yielded highly-pure rutile, anatase, and brookite phases, respectively. Herein, an experimental approach based on the PIT-nano-emulsion method is demonstrated to synthesize phase-controlled TiO₂ particles with high purity employing fewer toxic compounds, reducing the quantity of starting materials, and with a minimum energy input, particularly for the almost elusive brookite phase.

Highly Sensitive and Selective Sol-Gel Spin-Coated Composite TiO2-PANI Thin Films for EGFET-pH Sensor

A highly selective and sensitive EGFET-pH sensor based on composite TiO2-PANI had been developed in this work. A sol-gel titanium dioxide (TiO2) and the composite of TiO2 with semiconducting polyaniline (PANI) were deposited using a simple spin-coating method on an indium tin oxide (ITO) substrate. The films have been explored as a sensing electrode (SE) of extended gate field-effect transistor (EGFET) for pH applications in the range of pH 2 to 12. The pH sensitivities between TiO2, TiO2-PANI bilayer composite, and TiO2-PANI composite thin films were discussed. Among these, the TiO2-PANI composite thin film showed a super-Nernstian behavior with high sensitivity of 66.1 mV/pH and linearity of 0.9931; good repeatability with a standard deviation of 0.49%; a low hysteresis value of 3 mV; and drift rates of 4.96, 5.54, and 3.32 mV/h in pH 4, 7, and 10, respectively, for 6 h. Upon applying the TiO2-PANI composite as the SE for nitrate measurement, low sensitivity of 12.9 mV/dec was obtained, indicating that this film is a highly selective sensing electrode as a pH sensor. The surface morphology and crystallinity of the thin films were also discussed.

Fabrication of a Mesoporous Multimetallic Oxide-based Ion-Sensitive Field Effect Transistor for pH Sensing

Sensitive and reliable noninvasive sensors are in demand to cope with an increasing need for robust working conditions and fast results. One of the leading potential technologies is field-effect transistor (FET)-based sensors to improve response time, sensitivity, and stability. Here, a sol-gel method fabricates an ion-sensitive field-effect transistor with a high current and output sensitivity for electrochemical sensing, solving binary device design, component regulating, and long-term stability, while maintaining the promoted sensitivity. Metal oxide-based devices with single and binary contents are fabricated and characterized for monitoring pH changes, with performance fitted to a Nernst-Poisson model. After detecting the performance, the result was compared with devices in different components and ratios to obtain excellent performance and high stability. In addition, these extended gate FETs with multimetallic oxide promise efficiency and stability optimization in terms of a flexible component design, demonstrating the feasibility of the novel sol-gel fabrication method to achieve efficient and reliable FET sensors.

Fabrication and Characterization of In0.9Ga0.1O EGFET pH Sensors

In this study, the In0.9Ga0.1O sensing membrane were deposited by using the RF magnetron sputtering at room temperature and combined with commercial MOSFETs as the extended gate field effect transistor (EGFET) pH sensors. The sensing performance of the In0.9Ga0.1O EGFET pH sensors were measured and analyzed in the pH value of range between 2 to 12. In the saturation region, the pH current sensitivity calculated from the linear relationship between the IDS and pH value was approximately 56.64 μA/pH corresponding to the linearity of 97.8%. In the linear region, the pH voltage sensitivity exhibited high sensitivity and linearity of 43.7 mV/pH and 96.3%, respectively. The In0.9Ga0.1O EGFET pH sensors were successfully fabricated and exhibited great linearity. The analyzed results indicated that the In0.9Ga0.1O was a robust material as a promising sensing membrane and effectively used for pH sensing detection application.

Sensitive pH measurement using EGFET pH-microsensor based on ZnO nanowire functionalized carbon-fibers

Herein, we report the fabrication of zinc oxide nanowire (ZnO NW) coated carbon fiber (CF) ultra-microelectrodes (UME). ZnO NWs were grown on commercial multifilament CFs through hydrothermal process in a teflon-lined autoclave at 90 °C for 4 h. X-ray diffraction (XRD), Raman and scanning electron microscopy characterizations showed that crystalline and well oriented NW structures were successfully obtained. The fabrication of the pH sensitive UME was carried out by a novel approach which allowed controlling the protruding length of the modified CF surface. The UME was then integrated with a metal-oxide-semiconductor field effect transistor (MOSFET) for the construction of an EGFET pH-microsensor. The present pH microsensor is expected to be useful for localized pH measurement in small volumes such single cell analysis.