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Electrodeposited amorphous hydrated iridium oxide (IrOx) is a promising material for pH sensing due to its high sensitivity and the ease of fabrication. However, durability and variability continue to restrict the sensors effectiveness. Variation in probe films can be seen in both performance and fabrication, but it has been found that performance variation can be controlled with potentiostatic conditioning (PC). To make proper use of this technique, the morphological and chemical changes affecting the conditioning process must be understood. Here, a thorough study of this material, after undergoing PC in a pH-sensing-relevant potential regime, was conducted by voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Fitting of XPS data was performed, guided by raw trends in survey scans, core orbitals, and valence spectra, both XPS and UPS. The findings indicate that the PC process can repeatably control and conform performance and surface bonding to desired calibrations and distributions, respectively; PC was able to reduce sensitivity and offset ranges to as low as ±0.7 mV/pH and ±0.008 V, respectively, and repeat bonding distributions over ~2 months of sample preparation. Both Ir/O atomic ratios (shifting from 4:1 to over 4.5:1) and fitted components assigned hydroxide or oxide states based on the literature (low-voltage spectra being almost entirely with suggested hydroxide components, and high-voltage spectra almost entirely with suggested oxide components) trend across the polarization range. Self-consistent valence, core orbital, and survey quantitative trends point to a likely mechanism of ligand conversion from hydroxide to oxide, suggesting that the conditioning process enforces specific state mixtures that include both theoretical Ir(III) and Ir(IV) species, and raising the conditioning potential alters the surface species from an assumed mixture of Ir species to more oxidized Ir species.

This review covers data on the role of reduced extracellular pH (acidosis) in tumor tissue in the development of tumorigenesis. The following processes characterizing the malignant phenotype of the tumor are considered: (1) protease activation causing destruction of the intercellular matrix and disruption of intercellular interactions, which makes invasion and metastasis possible; (2) genome instability; (3) inhibition of the antitumor immune response; (4) activation of exosome synthesis, which plays an important role in intercellular communications and is involved in the formation of "premetastasis niches"; and (5) P-glycoprotein activation and a number of other processes associated with the formation of the malignant tumor phenotype. It is concluded that acidosis plays a leading role in the realization of these malignant tumor properties. The role of pH-sensors in transmitting information about the pH value of the extracellular environment (its acidity) inside the cell is described. The possibility of the leading role of acidosis at the earliest stages of tumor process in overcoming the regulatory action of surrounding normal cells is also described. The therapeutic effect of many antitumor drugs depends on the pH value of the medium in which they act. In this regard, the role of acidosis in the action of various preparations for chemotherapy and the possibility of influencing tumor acidosis in order to enhance the antitumor activity of substances are further discussed. [ABSTRACT FROM AUTHOR]

Measuring pH in oxidizing solutions is a crucial issue in areas such as aquaculture, water treatment, industrial chemistry, and environmental analysis. For this purpose, a low-cost potentiometric flexible sensor using a polymer film as a pH-sensitive material has been developed in this study. The sensor consists in a polyaniline film electrodeposited from a sulfuric acid solution on a gold electrode previously deposited on a flexible polyimide substrate. The resulting polyaniline-based pH sensors showed an interesting performance detection in aqueous solution, leading to sensitive (73.4 mV per unit pH) and reproducible (standard deviation of 1.75) responses over the entire pH range from 3 to 8. On the contrary, they were inoperative in the presence of oxidizing hypochlorite ions. Thus, other polyaniline films were electrodeposited in the presence of cetyltrimethylammonium bromide or Tritonx100 surfactant in an attempt to improve the sensing performance of the pH sensors in oxidizing solutions. The pH sensors based on polyaniline and Tritonx100 surfactant were then found to be sensitive (62.3 mV per unit pH) and reproducible (standard deviation of 1.52) in aqueous solutions containing hypochlorite ions. All polyaniline films were also characterized by profilometry and electronic microscopy to correlate the physicochemical features with the performance of the sensors. [ABSTRACT FROM AUTHOR]

Metal oxide ion-gated transistors (MOIGTs) have garnered significant attention within the sensing domain due to their potential for achieving heightened sensitivity while consuming minimal energy across diverse scenarios. By harnessing the advantageous combination of metal oxides' high carrier mobility and facile surface customization, coupled with the potent signal amplification capabilities of ion-gated transistors, MOIGTs offer a promising avenue for discerning biomolecules, overseeing chemical reactions, pH levels, as well as facilitating gas or light determination. Over the past few decades, the MOIGT field has made remarkable strides in refining device physics, enhancing material properties, showcasing robust sensing capabilities, and broadening its application spectrum. These advancements have simultaneously unveiled new challenges and opportunities, necessitating interdisciplinary expertise to fully unlock the commercial potential of MOIGTs. In this comprehensive review, we offer a snapshot of this swiftly evolving technology, delve into its current applications, and provide insightful recommendations for future directions in the coming decade. [ABSTRACT FROM AUTHOR]

Due to the distinctive optical, mechanical and electrical characteristics, silicon nanowire (SilNW), one of the one dimensional nanostructures, has become a potential sensing nanomaterial. SilNWs have drawn interest in high-sensitive sensor fabrication, primarily because of their large surface-volume ratios, which significantly enhanced the detection limit to femtomolar concentrations and also provided high sensitivity. Due to its high charge sensitivity, SilNW FET-based sensors had been employed extensively for sensing various chemical as well as biological species. In this work, the sensing performance and applications of different SilNW biosensors, gas sensors, chemical and metal ion sensors were studied. In this study, we have also elaborated the most current developments as well as the sensing performance of various SilNW-based Covid-19 sensors. [ABSTRACT FROM AUTHOR]

This work presents the pH sensing ability of a fluorescent indolin‐3‐imine derivative. Protonation of the weakly basic imine (pKa=8.3 of its conjugate acid) results in a significant red‐shift of the absorption band. The fluorophore acts as a photobase, with a basicity increase of approximately 6 units upon photoexcitation. This behavior promotes excited state proton transfer from weak acids such as protic solvents. The characteristics of the fluorophore enable sensing of water fractions in organic solvents and differentiation between methanol, ethanol, and longer chain alcohols. Initial cell studies indicated the future potential of indolin‐3‐imines as fluorophores for bioimaging applications. [ABSTRACT FROM AUTHOR]

Flexible sensors enable the gathering of information from nonplanar surfaces, which facilitates huge data collection tasks. Monitoring of pH levels in industrial wastewater is one example. For this purpose, stable, reliable flexible pH sensors are required to monitor pH in pipes or containers. Carbon nanotube field‐effect transistors (CNT‐FETs) are attractive transducers for flexible sensors because of their multiple functionalities, such as good electrical properties and mechanical flexibility. However, semiconducting single‐walled carbon nanotubes (s‐SWNTs) must be separated from metallic SWNTs of high purity for channel materials to be used in CNT‐FETs. Herein, a simple method to sort s‐SWNTs in an aqueous system using only dispersion and centrifugation is developed. This sorting method is much less expensive than other techniques, such as density gradient ultracentrifugation, agarose‐gel chromatography, or selective sorting by conjugated polymers. These sorted s‐SWNTs result in high‐performance CNT‐FETs with electrical hysteresis reduced to almost zero and improved bias stability. This method demonstrates the importance of the solubility parameter between polymers and water for CNT‐FET hysteresis. The resulting carbon nanotubes also have high uniformity of characteristics, making them valuable as transducers for flexible sensors. Furthermore, real‐time pH monitoring using ion‐sensitive, field‐effect transistors (ISFETs) based on CNT‐FET is demonstrated. [ABSTRACT FROM AUTHOR]

The main goal of our research is to synthesize a novel nano Zn+2 complex with the 8-(2-(dansyl chloride)azo)adenine (LA) ligand as a pH sensor because of its advantageous properties. The molecular formulas of the ligand and Zn+2 -LA complex were confirmed by studying the elemental analyses (C.H.N.), spectral methods, XRD, and thermal analyses (TGA). The molar ratio of ZnZn+2 -LA was studied as a ratio (1:2) (M:L). Through the survey in FT-IR and UV-Vis spectra, it was found that the complex has a tetrahedral geometry shape with a dark purple color λmax (552 nm), obtained from a single molecule. The optimum concentration is 0.3 mM, pH = 5.5, and time = 0-3 hours, which in the studies followed Lambert-Beer’s law. Linearity ranged from 0.025 to 0.4 mM for the Zn+2 -LA complex, with a linear correlation coefficient of 0.9963. The detection limit was 0.0219 μg/mL, and the limit of quantification was 0.0663 μg/mL. LA could be used as a titration indicator of sodium hydroxide (NaOH) by oxalic acid (H2C2O4) with a maximum concentration of 0.1 M of H2C2O4. Finally, the characteristic fluorescence peaks of the solutions were identified at 462 nm and 554 nm for the ligand LA and its complex respectively, which were dependent on pH = 5.5 and at 1 minute. The type of emission fluorescence is π*→ n transition. [ABSTRACT FROM AUTHOR]

Measuring pH in oxidizing solutions is a crucial issue in areas such as aquaculture, water treatment, industrial chemistry, and environmental analysis. For this purpose, a low-cost potentiometric flexible sensor using a polymer film as a pH-sensitive material has been developed in this study. The sensor consists in a polyaniline film electrodeposited from a sulfuric acid solution on a gold electrode previously deposited on a flexible polyimide substrate. The resulting polyaniline-based pH sensors showed an interesting performance detection in aqueous solution, leading to sensitive (73.4 mV per unit pH) and reproducible (standard deviation of 1.75) responses over the entire pH range from 3 to 8. On the contrary, they were inoperative in the presence of oxidizing hypochlorite ions. Thus, other polyaniline films were electrodeposited in the presence of cetyltrimethylammonium bromide or Tritonx100 surfactant in an attempt to improve the sensing performance of the pH sensors in oxidizing solutions. The pH sensors based on polyaniline and Tritonx100 surfactant were then found to be sensitive (62.3 mV per unit pH) and reproducible (standard deviation of 1.52) in aqueous solutions containing hypochlorite ions. All polyaniline films were also characterized by profilometry and electronic microscopy to correlate the physicochemical features with the performance of the sensors.

Abstract Ammonia and ammonium play an essential role in the metabolism of almost all living organisms. Despite their importance for human health as well as plant growth, knowledge about passive NH3/NH4+ membrane permeabilities is scarce. Large unilamellar vesicles (LUVs), a popular model membrane system, have the potential to be a game changer. However, despite a variety of environmental sensitive dyes awaiting encapsulation into membrane vesicles, a pH sensor for the acidic pH region is currently missing. This gap is filled by introducing conjugated Oregon Green (OG) which can be encapsulated into lipid‐ or polymer‐based vesicles. This allows the quantification of proton or weak base permeabilities across the vesicular membrane and functionally characterizes pH sensitive membrane proteins at an acidic pH as low as pH 4.0. Furthermore, the expanded pH range enables simultaneous estimation of ion permeabilities without the use of membrane potential uncouplers due to an increased ion sensitivity. The utility of the sensor is demonstrated by quantifying passive NH3, NH4+, and Cl− permeabilities through vastly different lipid and polymer membranes. Moreover, its performance is benchmarked against carboxyfluorescein, an established pH‐sensor in the neutral pH‐range.

Wearable pH sensors for sweat analysis have garnered significant scientific attention for the detection of early signs of many physiological diseases. In this study, a MoS2‐polyaniline (PANI) modified screen‐printed carbon electrode (SPCE) is fabricated and used as a sweat biosensor. The exfoliated MoS2 nanosheets are drop casted over an SPCE and are functionalized by a conducting polymer, polyaniline (PANI) via the electropolymerization technique. The as‐fabricated biosensor exhibits high super‐Nernstian sensitivity of −70.4 ± 1.7 mV pH−1 in the linear range of pH 4 to 8 of 0.1 m standard phosphate buffer solution (PBS), with outstanding reproducibility. The sensor exhibits excellent selectivity against the common sweat ions including Na+, Cl−, K+, and NH4+ with tremendous long‐term stability over 180 min from pH 4 to 6. The enhanced active surface area and better electrical conductivity as a consequence of the synergistic effect between MoS2 and PANI are correlated with the boosted performance of the as‐produced biosensor. The feasibility of the sensor is further examined using an artificial sweat specimen and the successful detection confirms the potential of the biosensor for a real‐time noninvasive, skin attachable, and flexible wearable pH sensor. [ABSTRACT FROM AUTHOR]

Herein, a miniaturized wireless sensing vaginal ring for the in situ continuous monitoring of vaginal pH and real-time transmission of the pH data to a smartphone is reported, aimed at the diagnosis and management of bacterial vaginosis, a common condition frequently and adversely affecting women. The sensing vaginal ring consists of a bioresorbable pH fluorescence sensor placed on top of a polydimethylsiloxane ring encapsulating a miniaturized driving/readout optoelectronic circuit, data acquisition system, wireless transceiver, and power supply. The pH sensor consists of a micrometer-thick porous silica scaffold conformably coated with a nanometer-thick polymer multilayer stack and is intended to be replaced after 4 days. The sensor fully dissolves in biocompatible by-products eliminating waste management issues; conversely, the ring embedding the circuit is reusable with new sensors. The pH sensor, as well as the sensing vaginal ring, show excellent performance in the continuous measurement of pH in vaginal fluid and can monitor the pH level over the physio-pathological range of 3-7.5 with high linearity, accuracy, and reliability, transmitting the data to a smartphone in real time. The proposed technology can be immediately translated to other diseases, among which wound healing, intragastric activity, and cancer progression, where continuous monitoring of pH is required, as well as to other markers/analytes by engineering the polymer stack with suitable receptors, such as aptamers and other molecular probes. [ABSTRACT FROM AUTHOR]

The crevice corrosion of the 7075-T651 aluminium alloy was investigated using in situ electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves (PC), and H+ sensors in acidic NaCl solution with different contents of NaNO3. In the solution without NaNO3, the pH in the crevice increased rapidly and gradually reached a relatively stable status. The corrosion of the aluminium alloy in the crevice was inhibited and crevice corrosion could not be initiated. In the solution with NaNO3, the pH increased rapidly at the initial immersion period and then decreased gradually. The corrosion of the aluminium alloy inside the crevice could be enhanced and the corrosion of the aluminium alloy outside crevice could be inhibited. This triggered crevice corrosion in the solution with NaNO3. The inhibited corrosion outside the crevice can be attributed to the improved passive film of the specimen outside the crevice by nitrate. The accumulated secondary products of ammonia inside the crevice led to selective dissolution of copper, which triggered the nucleation of pitting corrosion and promoted the corrosion of the specimen inside the crevice. [ABSTRACT FROM AUTHOR]

Abstract Wearable pH sensors for sweat analysis have garnered significant scientific attention for the detection of early signs of many physiological diseases. In this study, a MoS2‐polyaniline (PANI) modified screen‐printed carbon electrode (SPCE) is fabricated and used as a sweat biosensor. The exfoliated MoS2 nanosheets are drop casted over an SPCE and are functionalized by a conducting polymer, polyaniline (PANI) via the electropolymerization technique. The as‐fabricated biosensor exhibits high super‐Nernstian sensitivity of −70.4 ± 1.7 mV pH−1 in the linear range of pH 4 to 8 of 0.1 m standard phosphate buffer solution (PBS), with outstanding reproducibility. The sensor exhibits excellent selectivity against the common sweat ions including Na+, Cl−, K+, and NH4+ with tremendous long‐term stability over 180 min from pH 4 to 6. The enhanced active surface area and better electrical conductivity as a consequence of the synergistic effect between MoS2 and PANI are correlated with the boosted performance of the as‐produced biosensor. The feasibility of the sensor is further examined using an artificial sweat specimen and the successful detection confirms the potential of the biosensor for a real‐time noninvasive, skin attachable, and flexible wearable pH sensor.

Abstract It is vital to acquire real‐time pH signals with high resolution as pH variation can reflect important information regarding health status and physiological environment. Field‐effect transistor (FET)‐based biosensors (bio‐FETs), a kind of potentiometric sensor, are being rapidly developed for pH detection due to their advantages of high sensitivity, low temperature dependence, and high portability. More importantly, the high scalability of bio‐FETs renders them applicable for achieving high spatial resolution in pH sensing. In this review paper, the design, operation principle, and critical characteristics of the FET‐based pH sensor are introduced. Then, the recent progress in pH mapping with FET sensor arrays, including static array where a sensor pixel is directly addressed by wiring, and active‐matrix array where a sensor pixel is accessed by additional switching FETs, is presented. Last, typical examples of pH sensor arrays in biomedical applications, such as health monitoring and DNA sequencing and elongation are presented.

Electrodeposited amorphous hydrated iridium oxide (IrOx) is a promising material for pH sensing due to its high sensitivity and the ease of fabrication. However, durability and variability continue to restrict the sensor’s effectiveness. Variation in probe films can be seen in both performance and fabrication, but it has been found that performance variation can be controlled with potentiostatic conditioning (PC). To make proper use of this technique, the morphological and chemical changes affecting the conditioning process must be understood. Here, a thorough study of this material, after undergoing PC in a pH-sensing-relevant potential regime, was conducted by voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Fitting of XPS data was performed, guided by raw trends in survey scans, core orbitals, and valence spectra, both XPS and UPS. The findings indicate that the PC process can repeatably control and conform performance and surface bonding to desired calibrations and distributions, respectively; PC was able to reduce sensitivity and offset ranges to as low as ±0.7 mV/pH and ±0.008 V, respectively, and repeat bonding distributions over ~2 months of sample preparation. Both Ir/O atomic ratios (shifting from 4:1 to over 4.5:1) and fitted components assigned hydroxide or oxide states based on the literature (low-voltage spectra being almost entirely with suggested hydroxide components, and high-voltage spectra almost entirely with suggested oxide components) trend across the polarization range. Self-consistent valence, core orbital, and survey quantitative trends point to a likely mechanism of ligand conversion from hydroxide to oxide, suggesting that the conditioning process enforces specific state mixtures that include both theoretical Ir(III) and Ir(IV) species, and raising the conditioning potential alters the surface species from an assumed mixture of Ir species to more oxidized Ir species.

Cancer microenvironment exhibits lower pH compared to healthy tissues, a characteristic which can be exploited using a pH-responsive needle to increase the accuracy of cancer biopsy. A needle, coated with pH-responsive polyaniline (PANI) nanoparticles (PANI-needle), is developed for the minimally invasive and quantitative pH analysis of tissue based on ratiometric photoacoustic (PA) imaging. The ratiometric PA signal from the PANI-needle within the 850–700 nm wavelength range shows a linear response as pH changes from 7.5 to 6.5. Owing to the high surface area of nanostructured PANI, the PA signal of PANI-needle exhibits a fast and reversible response of less than a few seconds. In a tissue-mimicking hydrogel phantom composed of two regions with different pH, PA ratios of PANI-needle successfully differentiate the local pH. The PANI-needle coupled with ultrasound-guided PA imaging is a promising technology for detection of malignant tissue through quantitative pH analysis during needle biopsy.

A novel 3 × 4 colorimetric sensing platform, named the chemometric-assisted litmus test (CLT), has been developed by covalently anchoring commercial pH indicators to ethylene vinyl alcohol (EVOH). The proposed device can be exploited for pH determinations in a wide range from 1 to 13 and in specific narrow ranges, achieving sufficient accuracy and errors below 0.5 pH units. The experimental procedure is simple, quick and reliable; equilibration is reached in less than 2 h, CLT pictures are acquired by a camera, and data treatment is performed applying chemometric techniques such as principal component analysis (PCA) and partial least square regression (PLS) to RGB indices. [ABSTRACT FROM AUTHOR]

pH is a tightly regulated physiological parameter that is often altered in diseased states like cancer. The development of biosensors that can be used to non-invasively image pH with hyperpolarized (HP) magnetic resonance spectroscopic imaging has therefore recently gained tremendous interest. However, most of the known HP-sensors have only individually and not comprehensively been analyzed for their biocompatibility, their pH sensitivity under physiological conditions, and the effects of chemical derivatization on their logarithmic acid dissociation constant (pKa). Proteinogenic amino acids are biocompatible, can be hyperpolarized and have at least two pH sensitive moieties. However, they do not exhibit a pH sensitivity in the physiologically relevant pH range. Here, we developed a systematic approach to tailor the pKa of molecules using modifications of carbon chain length and derivatization rendering these molecules interesting for pH biosensing. Notably, we identified several derivatives such as [1-13C]serine amide and [1-13C]-2,3-diaminopropionic acid as novel pH sensors. They bear several spin-1/2 nuclei (13C, 15N, 31P) with high sensitivity up to 4.8 ppm/pH and we show that 13C spins can be hyperpolarized with dissolution dynamic polarization (DNP). Our findings elucidate the molecular mechanisms of chemical shift pH sensors that might help to design tailored probes for specific pH in vivo imaging applications.

The detection of intracellular pH is crucial for elucidating the pathological process of cancers, as well as for medical diagnostic applications. Here, we developed an aggregation‐induced emission active pH‐responsive fluorescent probe (TPE‐DCP) for sensitively detecting cell pH changes. The probe shows obvious pH‐sensing properties at ~615 nm, with a pKa value of 6.82 and a good linear pH response ranging from 8.5 to 4.5. TPE‐DCP holds advantages such as excellent anti‐interference performance, good photostability, and low cytotoxicity, and has been successfully used to image intracellular pH changes in cells. [ABSTRACT FROM AUTHOR]

An optical fiber surface plasmon resonance (SPR) sensor, leveraging hyperbolic metamaterials (HMMs) and pH-sensitive hydrogels, has been devised for pH detection in perspiration. Dispersion-tunable HMMs enable the sensor to transcend the inherent structural constraints of an optical fiber and enhance its refractive index (RI) sensitivity. pH-sensitive hydrogels exhibit diverse swelling behaviors due to varying ionization degrees of carboxyl groups under different solution pH conditions, leading to a notable RI change. The sensor achieves a high RI sensitivity of 6963.64 nm RIU -1 and remarkable pH sensitivity of -64.04 and -30.63 nm pH -1 within the pH ranges of 2.7 to 4.7 and 4.7 to 7.5, respectively. Compared to the sensitivity of three other constituents in perspiration, namely, urea, sodium chloride, and glucose, the sensor demonstrates exceptional pH selectivity. Additionally, it maintains good stability during operation and after prolonged storage. It is believed that the sensor has potential in health monitoring, medical diagnosis, disease treatment, etc.

In recent years thanks to the Internet of Things (IoT), the demand for the development of miniaturized and wearable sensors has skyrocketed. Among them, novel sensors for wearable medical devices are mostly needed. The aim of this review is to summarize the advancements in this field from current points of view, focusing on sensors embedded into textile fabrics. Indeed, they are portable, lightweight, and the best candidates for monitoring biometric parameters. The possibility of integrating chemical sensors into textiles has opened new markets in smart clothing. Many examples of these systems are represented by color-changing materials due to their capability of altering optical properties, including absorption, reflectance, and scattering, in response to different external stimuli (temperature, humidity, pH, or chemicals). With the goal of smart health monitoring, nanosized sol–gel precursors, bringing coupling agents into their chemical structure, were used to modify halochromic dyestuffs, both minimizing leaching from the treated surfaces and increasing photostability for the development of stimuli-responsive sensors. The literature about the sensing properties of functionalized halochromic azo dyestuffs applied to textile fabrics is reviewed to understand their potential for achieving remote monitoring of health parameters. Finally, challenges and future perspectives are discussed to envisage the developed strategies for the next generation of functionalized halochromic dyestuffs with biocompatible and real-time stimuli-responsive capabilities. [ABSTRACT FROM AUTHOR]

The sulfuric acid attack is a common form of degradation of reinforced concrete in contact with industrial wastewater, mine water, acid rain, or in sewage treatment stations. In this work, new pH-sensitive IrOx electrodes were developed for monitoring the pH inside mortar or concrete. To test their ability, the pH sensors were embedded in mortar samples at different depths and the samples were exposed to sulfuric acid solution. In another set of experiments, iron wires were placed at the same depths inside similar mortar samples and their corrosion was monitored as the acid attacked the mortar. Severe acid attack led to cement dissolution and formation of gypsum. The new pH sensors succeeded in measuring the pH changes inside the mortars. The pH gradient, from the high acid environment to the high alkaline mortar interior, occurred in a narrow region. Corrosion of the iron electrodes started only when the acidic solution was in their close vicinity. [ABSTRACT FROM AUTHOR]

We here report the synthesis and characterization of three new molecules based on an unprecedented anthra [2,3- d ]imidazole unit. The new heterocycle was unexpectedly formed while attempting to obtain 2,3-diacetamidoanthracene by reducing the corresponding anthraquinone molecules by sodium borohydride. The same reaction was successfully performed using two further different 2,3-diamidoanthraquinone derivatives, thus confirming its generality. The chemical identity of the novel molecules was also proved by realizing single crystals suitable for XRD diffraction and solving the crystalline structure of one of the prepared systems. All the molecules are strong blue emitters in ethanol, with fluorescence quantum yields around 0.40. Because of the acid-base properties of anthraimidazole ring, the optical response was investigated at different pH values. While slight differences were observed in acidic conditions, in the alkaline pH range we observed a dramatic change of the fluorescence spectra in a narrow pH range (from 11 to 13), with the color of the emission turning from blue to green. This feature makes the new class of derivatives here reported very promising as pH sensors working in strongly alkaline conditions. [Display omitted] • The serendipitous synthesis of new molecules containing an unprecedented anthra [2,3- d ]imidazole heterocycle is reported. • The novel molecules are blue emitters in ethanol solution with a Φ PL of 0.40. • Emission behaviour is pH dependent and a dramatic change in color emission is observed in strongly alkaline conditions. • The structures of the neutral and protonated forms of the anthra [2,3- d ]imidazole derivative have been solved by SC-XRD. [ABSTRACT FROM AUTHOR]

ABSTRAK Besaran fisika dapat berpengaruh baik secara langsung maupun tidak langsung terhadap keberlangsungan hidup makhluk hidup baik di darat maupun di air, termasuk pada budidaya ikan lele. Jika kualitas air selalu berubah-ubah atau tidak stabil, maka dapat berpengaruh buruk terhadap kondisi ikan seperti stres, sakit atau kematian jika tidak dapat beradaptasi terhadap perubahan yang terjadi. Suhu dan pH air merupakan dasar selain dari beberapa parameter lainnya yang digunakan untuk menjaga kualitas air kolam agar tetap sehat. Termometer dan pH meter dalam penggunaannya harus melakukan pengukuran langsung ke lokasi untuk mengetahui nilai pH dan suhu dari air kolam. Sehingga diperlukan alat monitoring pH dan suhu dengan pemanfaatan IoT yang dapat memberikan efisiensi waktu dalam melakukan pemantauan kualitas air kolam secara real time tanpa harus datang langsung ke lokasi untuk mengefisiensi waktu. Sensor yang digunakan adalah sensor pH dan sensor DS18B20. Serta menggunakan NodeMCU ESP8266 yang merupakan mikrokontroler yang telah dilengkapi oleh module WiFi ESP8266 di dalamnya. Hasil pengujian sensor pH dengan besar nilai R square = 0,909, sedangkan pada sensor suhu menghasilkan nilai R square = 0,911. Ini menunjukkan bahwa kedua sensor memiliki tingkat kevalidan alat adalah sangat valid. Kata kunci— monitoring, pH, suhu, sensor pH, sensor DS18B20 ABSTRACT Physical quantities effect things survive either in the land or water, such catfish cultivation. Unstable water quality change can impact the fish condition, such as being sick, stressed or died. Those conditions happen when the fishes can not adopt with the condition change. Water’s temperature and pH are the basic part is used to keep catfish pool water quality. Thermometer and pH meter had to be tested in the real location to analyse the pool’s water pH and termperature condition. pH and temperature monitoring tool based on IoT is needed to give efficient time in controlling water quality. Sensors used is pH and DS18B20 sensors. NodeMCU ESP8266 is used as microcontroller by WiFi ESP8266 module help. The R squere of pH sensors testing result is for 0,909. Beside, the R squere of temperature sensor is for 0,911. The result shows that both sensors have a very good validity score. Keywords— monitoring, pH, temperature, pH sensors, DS18B20

Surface functionalization of metallic nanoparticles (NPs) with external groups can be engineered to fabricate sensors that are responsive to various stimuli like temperature, pH, and numerous ions. Herein, we report the synthesis of gold nanoparticles (GNPs) functionalized with 3-mercaptopropionic acid (GNPs-MPA) and the doping of these nanoparticles into hydrogel materials using the breathing-in/breathing-out (BI-BO) method. MPA has a carboxyl group that becomes protonated and, thus, ionized at a pH below its pKa (4.32); hence, the GNPs-MPA solutions and gels were mostly pH-responsive in the range of 3–5. Optical properties were assessed through ultraviolet-visible (UV-Vis) spectroscopy, namely: transmission and absorption, and the parameters used to quantify the pH changes were the full width at half maximum (FWHM) and position of surface plasmon resonance (SPR). The solutions and gels gradually changed their colors from red to indigo with pH decrementation from 5 to 3, respectively. Furthermore, the solutions' and doped gels' highest FWHM sensitivities towards pH variations were 20 nm and 55 nm, respectively, while the SPR's position sensitivities were 18 nm and 10 nm, respectively. Also, transmission and scanning electron microscopy showed synchronized dispersion and aggregation of NPs with pH change in both solution and gel forms. The gel exhibited excellent repeatability and reversibility properties, and its response time was instantaneous, which makes its deployment as a colorimetric pH-triggered sensor practical. To the best of our knowledge, this is the first study that has incorporated GNPs into hydrogels utilizing the BI-BO method and demonstrated the pH-dependent optical and colorimetric properties of the developed nanocomposites. [ABSTRACT FROM AUTHOR]

In this article, organic and polymeric materials, printing technology, and sensing principles are investigated toward a reliable printed wearable pH sensor realized on textiles. A literature study and experimental work of three different organic and polymeric material‐based pH sensors and their corresponding measurement methods are systematically made. Initially, the three different sensors, a conductometric PEDOT:PSS sensor, a voltametric carbon‐alizarin sensor, and a potentiometric graphene/polyaniline (PANI) sensor are selected based on specific established criteria and are reproduced on foils for a feasibility study. Mass production and feasibility for fabrication on textile substrates are also the objectives of this work, and lead to the deployment of printing and coating techniques for the sensor fabrication. These three sensors are printed on flexible foils and tested and verified for sensor performances. Based on the experimental results and literature study, a conclusive comparison between the sensing principles regarding device fabrication, functionality, and wearability is performed. As per this analysis, a potentiometric PANI sensor is printed on a textile substrate and tested for a buffer solution of pH ranging from 4 to 9.5. The potentiometric PANI sensor shows a sensitivity of 45 mV pH−1 with linear sensor responses and repeatable characteristics. [ABSTRACT FROM AUTHOR]

Miniaturized electrolyte–insulator–semiconductor capacitors (EISCAPs) with ultrathin gate insulators have been studied in terms of their pH‐sensitive sensor characteristics: three different EISCAP systems consisting of Al–p‐Si–Ta2O5(5 nm), Al–p‐Si–Si3N4(1 or 2 nm)–Ta2O5 (5 nm), and Al–p‐Si–SiO2(3.6 nm)–Ta2O5(5 nm) layer structures are characterized in buffer solution with different pH values by means of capacitance–voltage and constant capacitance method. The SiO2 and Si3N4 gate insulators are deposited by rapid thermal oxidation and rapid thermal nitridation, respectively, whereas the Ta2O5 film is prepared by atomic layer deposition. All EISCAP systems have a clear pH response, favoring the stacked gate insulators SiO2–Ta2O5 when considering the overall sensor characteristics, while the Si3N4(1 nm)–Ta2O5 stack delivers the largest accumulation capacitance (due to the lower equivalent oxide thickness) and a higher steepness in the slope of the capacitance–voltage curve among the studied stacked gate insulator systems. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) is an abundant metal oxide, widely used in food industry, cosmetics, medicine, water treatment and electronic devices. TiO2 is of interest for next-generation indium-free thin-film transistors and ion-gated transistors due to its tunable optoelectronic properties, ambient stability, and solution processability. In this work, we fabricated TiO2 films using a wet chemical approach and demonstrated their transistor behavior with room temperature ionic liquids and aqueous electrolytes. In addition, we demonstrated the pH sensing behavior of the TiO2 IGTs with a sensitivity of ~48 mV/pH. Furthermore, we demonstrated a low temperature (120°C), solution processed TiO2-based IGTs on flexible polyethylene terephthalate (PET) substrates, which were stable under moderate tensile bending. [ABSTRACT FROM AUTHOR]

Over the last few decades, a large number of pH sensitive materials with new compositions and structures have been proposed. Solid state sensors based on organic, inorganic and composite materials are actively investigated, with an increasing interest in the performance offered by nano-scale materials. Our review provides a thorough, up-to-date knowledge of a wide range of pH measurement methods and related sensing materials, firstly by introducing well established materials and methods for pH sensing and then, by covering recent developments in inorganic, organic and nano-engineered devices. The main sensor parameters, including sensitivity, stability, response time and testing conditions are reported. Given the importance of pH sensing in environmental applications, in particular seawater monitoring, sensors tested in seawater are highlighted and discussed. [ABSTRACT FROM AUTHOR]

Responsive polymers are considered smart materials since they undergo physical or structural changes in response to external stimuli like pH or temperature. While those polymers have been conventionally used in catalysis, textile/coating industries, drug/gene delivery, and tissue engineering; more recent research is focused on the application as a sensor. In many cases, external stimuli like pH or temperature are detected by converting the transition behavior of responsive polymers into an easily visible output signal. In this review article, we have summed up previously reported literature under the giver persuasion, mostly between the years 2010–2020 to highlight the recent developments in the promising role of responsive polymers as a smart sensor to detect either single stimuli like temperature/pH, or dual-stimuli by combining more than one responsive block like temperature and pH. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) is an abundant metal oxide, widely used in food industry, cosmetics, medicine, water treatment and electronic devices. TiO2 is of interest for next-generation indium-free thin-film transistors and ion-gated transistors due to its tunable optoelectronic properties, ambient stability, and solution processability. In this work, we fabricated TiO2 films using a wet chemical approach and demonstrated their transistor behavior with room temperature ionic liquids and aqueous electrolytes. In addition, we demonstrated the pH sensing behavior of the TiO2 IGTs with a sensitivity of ∼48 mV/pH. Furthermore, we demonstrated a low temperature (120°C), solution processed TiO2-based IGTs on flexible polyethylene terephthalate (PET) substrates, which were stable under moderate tensile bending.

A novel 3 × 4 colorimetric sensing platform, named the chemometric-assisted litmus test (CLT), has been developed by covalently anchoring commercial pH indicators to ethylene vinyl alcohol (EVOH). The proposed device can be exploited for pH determinations in a wide range from 1 to 13 and in specific narrow ranges, achieving sufficient accuracy and errors below 0.5 pH units. The experimental procedure is simple, quick and reliable; equilibration is reached in less than 2 h, CLT pictures are acquired by a camera, and data treatment is performed applying chemometric techniques such as principal component analysis (PCA) and partial least square regression (PLS) to RGB indices.

This paper presents a novel chemical sensor that combines an organic, floating gate field‐effect transistor and a functional graphene electrode, aimed at realizing the basic building block for novel biomedical sensor systems. A non‐covalent functionalization of graphene with sensing peptides bearing a pyrene moiety is described as a way to provide graphene with chemical responsivity without affecting its electronic and optical features. Given the special properties of the materials and technologies used, and the intrinsic multi‐modality of the active device, it is possible to develop a complete range of chemosensing devices by varying the chemical specificity of the immobilized receptor. The devices are fully flexible, highly transparent, and can be completely fabricated into large areas using cost‐effective and industrially relevant techniques. A complete electrical characterization of the fabricated devices is reported, and their successful use as pH sensors is described as a representative example for demonstrating their sensing capability. [ABSTRACT FROM AUTHOR]

Field‐effect transistors (FETs) with nanoscale channels have emerged as excellent platforms for constructing high‐sensitivity biosensors. However, in typical FET‐based biosensors, the electronic perturbation at channel/electrolyte interfaces results in poor stability and severe signal drifts, making long‐term continuous measurements quite challenging. To address this issue, here the dielectric/semiconductor interface is tailored by depositing an ultrathin layer of Al2O3 (≈7 nm in thickness) on In2O3 FETs via solution‐based processes. The results show that the Al2O3 dielectric layers effectively passivate the In2O3 channel and endow the device with low operation voltage (0.05 V), high sensitivity (61.9 mV pH−1), and low current drift (0.35 mV h−1) upon long‐term and continuous pH monitoring. This work paves the way to real‐time biosensing with high sensitivity, excellent stability, and low power consumption. [ABSTRACT FROM AUTHOR]

It is necessary and important to develop a simple, accurate, stable, and low-cost quality detection sensor for ensuring the quality of the fish. This paper aims to develop a flexible wireless pH sensor system to detect the freshness of fish. The pH sensor system consists of an indium tin oxide (ITO) electrode, an Ag/AgCl reference electrode, a computing adder, and a wireless communication module. The operational amplifier addition circuit raises the overall potential signal collected by the pH electrode and sends it to the wireless reader from the sensor tag. The sensitivity of the pH electrode is −50.974 mV/pH, and other properties of the electrode, such as reproducibility and response times, are excellent. This paper uses a flexible wireless pH sensor system to continuously monitor fish meat stored at 28 °C for 36 h. The experimental results show that the pH of the fish tissue solution changes with the quality of the fish, and the flexible wireless pH sensor system can achieve accuracy, convenience, and long-term wireless food quality inspection.

Pyranine (HPTS) is a remarkably interesting pH‐sensitive dye that has been used for plenty of applications. Its high quantum yield and extremely sensitive ratiometric fluorescence against pH change makes it a very favorable for pH‐sensing applications and the development of pH nano‐/microsensors. However, its strong negative charge and lack of easily modifiable functional groups makes it difficult to use with charged substrates such as silica. This study reports a methodology for noncovalent HPTS immobilization on silica microparticles that considers the retention of pH sensitivity as well as the long‐term stability of the pH microsensors. The study emphasizes the importance of surface charge for governing the sensitivity of the immobilized HPTS dye molecules on silica microparticles. The importance of the immobilization methodology, which preserves the sensitivity and stability of the microsensors, is also assessed. [ABSTRACT FROM AUTHOR]

Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)applications. Multimodal imaging as well as simultaneous control and monitoring of intracellular movements profit from the combination of these functionalities. Accordingly, several methods have been developed for the synthesis of magnetic fluorescent particles. The majority of these methods, however, require complex modification and purification steps and result in a low yield of particles. Here, we describe a straightforward and scalable method for the magnetic modification of cellulose-based fluorescent particles. The method is based on the use of microwave-synthesized magnetite nanoparticles prepared from ferrous sulfate at high pH. Magnetic modification did not change the pH sensitivity or the optical properties of the fluorescent particles, and allowed them to be manipulated by external magnetic field. Our results demonstrate the possibility of large scale, easy production of bifunctional particles. We anticipate that our method can be expanded to include other types of particles or functionalities relevant for biomedical applications. [ABSTRACT FROM AUTHOR]

The development of the electronic tongue (e-tongue) significantly relies on the monitoring of taste-inducing molecules and ions in solutions. One of the five primary flavors, sourness, has a direct correlation with pH measurement, making it essential for food assessment. However, real-time food evaluation is constrained by the high cost and limited portability of conventional taste sensors. Ti 3 C 2 MXene is remarkable in the field of two-dimensional (2D) materials for its abundance of functional groups and metallic conductivity. These characteristics contribute to its enormous potential as a material for the fabrication of taste sensors with high sensitivity. This study presents the fabrication and application of reliable and reversible pH sensors based on 2D Ti 3 C 2 MXene for the first time. By integrating a microfluidic channel with interdigitated electrodes (IDEs) and a Nafion layer, the sensors exhibit high selectivity for real-time detection of hydronium ions with the MXene channel. Differentiating soft drinks and evaluating the fermentation of Kimchi are demonstrated. Our work on a low-cost, high-performance MXene-based sensor will pave the way for the future of e-tongue development. • The reliable measurements of ions are effectively conducted by microfluidic channel. • MXene-based pH sensor exhibits high selectivity and sensitivity to pH variation. • The real-time pH monitoring was demonstrated by high performance MXene-based pH sensor. [ABSTRACT FROM AUTHOR]

In recent years thanks to the Internet of Things (IoT), the demand for the development of miniaturized and wearable sensors has skyrocketed. Among them, novel sensors for wearable medical devices are mostly needed. The aim of this review is to summarize the advancements in this field from current points of view, focusing on sensors embedded into textile fabrics. Indeed, they are portable, lightweight, and the best candidates for monitoring biometric parameters. The possibility of integrating chemical sensors into textiles has opened new markets in smart clothing. Many examples of these systems are represented by color-changing materials due to their capability of altering optical properties, including absorption, reflectance, and scattering, in response to different external stimuli (temperature, humidity, pH, or chemicals). With the goal of smart health monitoring, nanosized sol–gel precursors, bringing coupling agents into their chemical structure, were used to modify halochromic dyestuffs, both minimizing leaching from the treated surfaces and increasing photostability for the development of stimuli-responsive sensors. The literature about the sensing properties of functionalized halochromic azo dyestuffs applied to textile fabrics is reviewed to understand their potential for achieving remote monitoring of health parameters. Finally, challenges and future perspectives are discussed to envisage the developed strategies for the next generation of functionalized halochromic dyestuffs with biocompatible and real-time stimuli-responsive capabilities.

The sulfuric acid attack is a common form of degradation of reinforced concrete in contact with industrial wastewater, mine water, acid rain, or in sewage treatment stations. In this work, new pH-sensitive IrOx electrodes were developed for monitoring the pH inside mortar or concrete. To test their ability, the pH sensors were embedded in mortar samples at different depths and the samples were exposed to sulfuric acid solution. In another set of experiments, iron wires were placed at the same depths inside similar mortar samples and their corrosion was monitored as the acid attacked the mortar. Severe acid attack led to cement dissolution and formation of gypsum. The new pH sensors succeeded in measuring the pH changes inside the mortars. The pH gradient, from the high acid environment to the high alkaline mortar interior, occurred in a narrow region. Corrosion of the iron electrodes started only when the acidic solution was in their close vicinity.

Group III–V material alloys such as gallium nitride (GaN) with piezoelectric and pyroelectric properties are used for designing advanced devices suitable for harsh surroundings such as high temperature and acidic ambience. In the present paper, we introduce a unified model using InAlGaN quaternary alloy in the barrier layer to analyze the performance of pH sensors based on high electron-mobility transistors (HEMTs) Our model is used to accurately calculate the threshold voltage, the sheet charge concentration and thus the drain current, in response to changes in the pH values of the electrolyte put in the gate area of the InAlGaN/GaN heterostructure based sensor. We have taken three devices for our studies with varying In mole fraction from 0% to 16% and Al mole fraction from 23% to 74%. The sensitivity of a HEMT based pH sensor depends on its transconductance. The maximum transconductance values of the InAlGaN/GaN devices were found to be much higher than those of the AlGaN/GaN HEMT devices. A theoretical sensitivity of 1.3 mA/pH was achieved for the quaternary structures. Our model shows good agreement with the experimental data available in literature, presenting less than 1.2% root mean square error in almost all the devices. We observe that HEMTs based on the InAlGaN/GaN structures have better sensitivity than the AlGaN/GaN structures in pH sensing applications. Our findings may be used in designing quaternary HEMT based novel pH sensors. [ABSTRACT FROM AUTHOR]

A fluorescent chromophore and a pH-sensitive heterocycle were integrated within a single covalent skeleton to generate four molecular switches with ratiometric fluorescence response. Upon acidification, the pH-sensitive heterocycle opens to shift bathochromically the absorption and emission bands of the fluorescent chromophore. As a result, an equilibrium between two species with resolved fluorescence is established with fast kinetics in aqueous environments. The relative amounts of the two interconverting forms and their relative emission intensities change with pH, providing the opportunity to probe this parameter ratiometrically with fluorescence measurements. Specifically, the resolved emissions of the two species can be collected in separate detection channels of the same microscope to map their ratio across a labeled sample and reconstruct its pH distribution ratiometrically with spatial resolution at the micrometer level. Additionally, the sensitivity of these molecular switches varies with the nature of the heterocyclic ring and with its substituents, allowing the possibility of regulating their response to a given pH range of interest with the aid of chemical synthesis. Thus, a family of valuable fluorescent probes for ratiometric pH sensing in a diversity of samples can emerge from the unique combination of structural and photophysical properties designed into our innovative molecular switches.

Wearable sensors reflect the real–time physiological information and health status of individuals by continuously monitoring biochemical markers in biological fluids, including sweat, tears and saliva, and are a key technology to realize portable personalized medicine. Flexible electrochemical pH sensors can play a significant role in health since the pH level affects most biochemical reactions in the human body. pH indicators can be used for the diagnosis and treatment of diseases as well as the monitoring of biological processes. The performances and applications of wearable pH sensors depend significantly on the properties of the pH–sensitive materials used. At present, existing pH–sensitive materials are mainly based on polyaniline (PANI), hydrogen ionophores (HIs) and metal oxides (MOx). In this review, we will discuss the recent progress in wearable pH sensors based on these sensitive materials. Finally, a viewpoint for state–of–the–art wearable pH sensors and a discussion of their existing challenges are presented.

Surface functionalization of metallic nanoparticles (NPs) with external groups can be engineered to fabricate sensors that are responsive to various stimuli like temperature, pH, and numerous ions. Herein, we report the synthesis of gold nanoparticles (GNPs) functionalized with 3-mercaptopropionic acid (GNPs-MPA) and the doping of these nanoparticles into hydrogel materials using the breathing-in/breathing-out (BI-BO) method. MPA has a carboxyl group that becomes protonated and, thus, ionized at a pH below its pKa (4.32); hence, the GNPs-MPA solutions and gels were mostly pH-responsive in the range of 3–5. Optical properties were assessed through ultraviolet-visible (UV-Vis) spectroscopy, namely: transmission and absorption, and the parameters used to quantify the pH changes were the full width at half maximum (FWHM) and position of surface plasmon resonance (SPR). The solutions and gels gradually changed their colors from red to indigo with pH decrementation from 5 to 3, respectively. Furthermore, the solutions’ and doped gels’ highest FWHM sensitivities towards pH variations were 20 nm and 55 nm, respectively, while the SPR’s position sensitivities were 18 nm and 10 nm, respectively. Also, transmission and scanning electron microscopy showed synchronized dispersion and aggregation of NPs with pH change in both solution and gel forms. The gel exhibited excellent repeatability and reversibility properties, and its response time was instantaneous, which makes its deployment as a colorimetric pH-triggered sensor practical. To the best of our knowledge, this is the first study that has incorporated GNPs into hydrogels utilizing the BI-BO method and demonstrated the pH-dependent optical and colorimetric properties of the developed nanocomposites.

We report on a stable and sensitive biochemical sensor based on amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with a versatile extended-gate electrode used as the sensing membrane. The extended-gate allows the active transistor channel not to be exposed to the ionic analyte and the gate surface may be modified with chemicals or affinity reagents without affecting the operation of the active sensor. The extended-gate a-IGZO TFT was able to detect the pH levels of various solutions based on protonation and deprotonation at the surface of the indium-tin-oxide (ITO) extended-gate electrode achieving a pH dependent threshold voltage shift of 22.8 mV/pH. Highly sensitive and specific protein sensing was achieved for both electrical polarities according to pH values of solutions using the biotin-streptavidin interaction. The extended-gate TFT sensor demonstrated a detection limit for streptavidin down to 10 fM, using the biotin-streptavidin binding on the extended-gate surface. It was also possible to detect changes in the streptavidin concentration in real-time with specificity and repeatability. Since the extended-gate can be easily replaced without affecting the performance of the a-IGZO TFT, this sensor configuration may be utilized for future multifunctional biomolecular sensing and analysis. [ABSTRACT FROM AUTHOR]