pH Sensor Research Articles

Rapid Fabrication of Large-Grain Opal Films and Photonic Crystal Hydrogel Sensors by a Filter Paper-Enhanced Evaporation Chip.

Developing a rapid fabrication method for crack-free opal films is a significant challenge with broad applications. We developed a microfluidic platform known as the "filter paper-enhanced evaporation microfluidic chip" (FPEE-chip) for the fabrication of photonic crystal and inverse opal hydrogel (IOPH) films. The chip featured a thin channel formed by bonding double-sided adhesive poly(ethylene terephthalate) with a polymethyl methacrylate cover and a glass substrate. This channel was then filled with nanosphere colloids. The water was guided to evaporate rapidly at the surface of the filter paper, allowing the nanospheres to self-assemble and accumulate within the channel under capillary forces. Experimental results confirmed that the self-assembly method based on the FPEE-chip was a rapid platform for producing high-quality opal, with centimeter-sized opal films achievable in less than an hour. Furthermore, the filter paper altered the stress release mechanism of the opal films during drying, resulting in fewer cracks. This platform was proven capable of producing large-grain, crack-free opal films of up to 30 mm2 in size. We also fabricated crack-free IOPH pH sensors that exhibited color and size responsiveness to pH changes. The coefficient of variation of the gray color distribution for crack-free IOPH ranged from 0.03 to 0.07, which was lower than that of cracked IOPH (ranging from 0.07 to 0.14). Additionally, the grayscale peak value in 1 mm2 of the crack-free IOPH was more than twice that of the cracked IOPH at the same pH. The FPEE-chip demonstrated potential as a candidate for developing vision sensors.

Green synthesis of fluorescent carbon dots from ascorbic acid and their application in sensing and biological imaging

A simple, highly efficient, and environmentally friendly one-step method has been developed to synthesize fluorescent carbon dots (CDs) with the assistance of hydrogen peroxide (H2O2). Here H2O2 acts as a green accelerator to promote the preparation of CDs, while temperature plays a critical role in controlling the entire synthesis process. The prepared CDs demonstrate monodispersion, with an average diameter of ∼6.8 nm, superior stability, and excitation-dependent photoluminescent (PL) behavior. The PL mechanism of the CDs was investigated using time-resolved PL decay, revealing that the PL originates from both the defect state and the intrinsic state of the CDs. Furthermore, the CDs show significant promise as pH sensors and versatile nanothermometry devices, owing to their remarkable sensitivity to both pH and temperature, as demonstrated by the pronounced dependence of their steady-state fluorescence emission spectra. It’s worth noting that temperature and pH sensors present significant reversibility, sensitivity, and linearity. More importantly, the CDs display low cytotoxicity, good biocompatibility, and the ability to enter human breast cancer Bcap-37 cells, making them highly suitable candidates for cellular imaging and labeling.

Air and Water Quality Indexing and Environment Monitoring

The current state of the environment continues to be a pressing global matter resulting from various human activities that release harmful substances posing a threat to living beings. To combat this issue advancements in technology have paved the way for the creation of an Internet of Things (IoT) based Water and Air Quality Monitoring System providing real-time data on environmental conditions. Through web and mobile applications individuals can easily access this system and view graphical representations of water and air quality readings. This innovative system involves sensor nodes strategically placed in different locations collecting field data and evaluating it against the set standards in India. For water monitoring sensors such as the Turbidity Sensor PH Sensor DHT 11 and TDS Sensor are utilized while for air quality the DHT11 sensor MQ-7 sensor and MQ-135 sensor play a crucial role. With this advanced monitoring system timely and accurate information on the state of the environment can be obtained aiding in taking necessary measures to combat pollution

A highly stable membrane-free potentiometric pH sensor with nickel cobalt sulfide as the solid contact layer and ion recognition

In this work, a new NiCo2S4 based H+ ion-selective electrode (ISE) without a polymer membrane was proposed and used to rapidly monitor the pH values of wetland soils in the Yellow River Delta in China. This NiCo2S4-based potentiometric pH sensor without an ion-selective membrane (ISM) exhibited a near-Nernstian response slope (50.9 ± 0.4 mV/dec) and good sensitivity. Furthermore, the developed pH sensors using NiCo2S4 as a solid contact (SC) layer present good reproducibility and the standard deviation of Eo is only 0.75 mV (n = 6). The water layer at the SC/ISM interface of the NiCo2S4-based membrane-free potentiometric pH sensor vanished, thus yielding excellent long-term potential stability (8.6 ± 0.4 μV/h over 264 h). This pH sensor offers a new design strategy for the construction of miniaturized highly stable ISEs without ISM.

Super-Nernstian pH detection using out-of-equilibrium body potential in silicon on insulator ISFET sensors: Proof-of-concept and optimization paths

In this work, we demonstrate pH sensing using the out-of-equilibrium body potential (VB) monitored in silicon-on-insulator (SOI) double-gate “ISFET-like” devices with deposited metal contacts. Similar to the behavior of a dual-gate ISFET, in this study, the conductive channel induced by the back-gate voltage at the silicon/buried oxide (Si/BOX) interface is modulated by the charges to-be-sensed that are intentionally placed on the top silicon oxide layer SiO2 covering the Si film. The detection of the surface charge modulation was evidenced by monitoring in real-time the out-of-equilibrium body potential, while the classic shift in the drain current served as control experiment and for benchmarking. These first experiments demonstrate the successful implementation of this new pH detection paradigm, with super-Nernstian sensitivity. To provide optimization options for the body-potential sensing, TCAD simulations of the pH sensors were performed in a 2D structure and illustrated the possibility to further enhance the device sensitivity with an optimized architecture. Moreover, the pH-induced shift occurs at very high applied gate biases for the drain current, contrary to the body potential, which implies a sensor with lower power consumption when VB is used as reading method. Thus, body potential monitoring provides a promising reading method to reach the required low-power consumption regime of the tomorrow’s sensing devices.

Green Synthesis of Various Heteroatom‐doped Carbon Quantum Dots from Urine, Whey, and Their Mixture: The Optimization of Synthesis and Potential Applications

AbstractThe employment of biomass waste for the fabrication of carbon quantum dots (CQDs), as a novel fluorescent material with high photoluminescence (PL) activity, has gained intense interest for the last decade. However, the fabrication of CQD from biomass waste encounters challenges including low fluorescence yield, reproducibility, and stability. Therefore, the novel, simple, flexible fabrication routes for CQDs using biomass waste as a precursor are still essential for practical applications. In this study, we reported the employment of human urine (U), sour whey (W), and their mixture (U/W) as precursors for the hydrothermal green synthesis approach. For all cases, CQDs with an excitation‐dependent emission nature were obtained with a quantum yield (QY) value of 48 %, 28 %, and 39 % for U, W, and U/W, respectively. For each case, doping of various heteroatoms such as N, P, S, etc., in the structure of CQDs contributed PL characteristics with high QY, reasonably low cytotoxicity, and, robust pH and storage stability which indicate their high potential in various biomedical applications such as bioimaging and pH sensors. This study proves the utilization of human urine and whey as the precursors for the fabrication of CQDs through a low‐cost, flexible, and eco‐friendly green synthesis procedure.

Super-Nernstian model based on acid doped polyaniline pH sensor

A polyaniline pH sensor with super-Nernstian sensitivity (>59.12 mV/pH) was obtained through acid doping. After preparing polyaniline sensor by potentiostatic electropolymerization, the electrochemical property of sensor can be modulated by adjusting acid doping formulas. The result shows that when using doping solution containing 2.2 g/L sodium dihydrogen phosphate and 5 g/L sodium chloride at pH = 6, the polyaniline sensor exhibits a linear super-Nernstian behavior (−69.31 ± 1.66 mV/pH) in PBS buffer (pH 5.00 ∼ 9.00). We observed that the surface of electrode has a three-dimensional network structure which can greatly increase the surface area of the sensing film, thus improving the conductivity and the sensitivity of the senor. The mechanism of acid doping is revealed: phosphate and polyaniline form salt, which makes polyaniline change from insulator to metal state and improves the conductivity. This is one important reason for its super-Nernstian behavior. In order to better understand this behavior, a new super-Nernstian model is established. The parameter 1/r > 1 is introduced to represent the acid doping index of the sensor, which directly affects the sensitivity of the film. According to the formula, super-Nernstian behavior of pH sensor can be mathematically modeled. This investigation yields a consistently stable super-Nernstian pH sensor while providing enhanced insights into its super-Nernstian characteristics and underlying mechanisms.

Entirely Biodegradable Wireless pH Sensor with Split‐Ring Resonators for Soil pH Monitoring

AbstractThis paper describes a wireless and battery‐free soil pH sensor made entirely of degradable materials. Soil pH monitoring is significant for precision agriculture and environmental conservation because soil health can be estimated by measuring soil pH. Soil pH can be measured by collecting soil samples and analyzing them in a laboratory environment or by inserting an electrode‐type sensor into the soil and measuring soil pH on site. However, neither method is suitable for wide‐area soil pH sensing for precision agriculture or environmental conservation. Herein, a fully biodegradable wireless pH sensor is presented that can be dispersed to outdoor environment to detect soil acidity. The sensor is operated wirelessly through split‐ring resonators (SRRs) that consist of patterned octacalcium phosphate (OCP)‐coated magnesium (Mg) on a poly‐lactic acid (PLA) sheet. At acidic soil pH, the degradation of each SRR results in a change in the electromagnetic response of the sensor. The operation of the sensor in six different types of acidic soils is demonstrated to distinguish the acidic soil wirelessly. It is expected that the biodegradable sensor can be applied to low‐cost, easy‐to‐use, and environmentally friendly monitoring of soil pH.

Role of Histidine 310 in Amydetes vivianii firefly luciferase pH and metal sensitivities and improvement of its color tuning properties.

Firefly luciferases emit yellow-green light and are pH-sensitive, changing the bioluminescence color to red in the presence of heavy metals, acidic pH and high temperatures. These pH and metal-sensitivities have been recently harnessed for intracellular pH indication and toxic metal biosensing. However, whereas the structure of the pH sensor and the metal binding site, which consists mainly of two salt bridges that close the active site (E311/R337 and H310/E354), has been identified, the specific role of residue H310 in pH and metal sensing is still under debate. The Amydetes vivianii firefly luciferase has one of the lowest pH sensitivities among the group of pH-sensitive firefly luciferases, displaying high bioluminescent activity and special spectral selectivity for cadmium and mercury, which makes it a promising analytical reagent. Using site-directed mutagenesis, we have investigated in detail the role of residue H310 on pH and metal sensitivity in this luciferase. Negatively charged residues at position 310 increase the pH sensitivity and metal sensitivity; H310G considerably increases the size of the cavity, severely impacting the activity, H310R closes the cavity, and H310F considerably decreases both pH and metal sensitivities. However, no substitution completely abolished pH and metal sensitivities. The results indicate that the presence of negatively charged and basic side chains at position 310 is important for pH sensitivity and metals coordination, but not essential, indicating that the remaining side chains of E311 and E354 may still coordinate some metals in this site. Furthermore, a metal binding site search predicted that H310 mutations decrease the affinity mainly for Zn, Ni and Hg but less for Cd, and revealed the possible existence of additional binding sites for Zn, Ni and Hg.

Development of Microcontroller Based Water Quality Monitoring and Water Level Control Device

Access to clean and safe water is not only a fundamental human right but also a vital requirement for electronics industries, chemicals industries, pharmaceuticals, food and beverage production, fisheries and aquatic farming. This project addresses the pressing issue of water quality monitoring and efficient water usage within the context of these industries. The study's identification of problem areas for water quality can lead to more efficient interventions and solutions to safeguard the environment, and prevent waterborne diseases. This paper presents the design and implementation of microcontroller-based system for monitoring water quality and water level in the thank, the water in the thank is refilled when it goes beyond a set threshold with the aid of an automatic switch control. The system is a hybrid of 3 subsystems: a Water Level Checker, a Water Quality Monitoring System and an Automatic Switch control system. The Water level checker consists of Ultrasonic sensors. The Water Quality Monitoring system consists of pH sensors, TDS (Total Dissolved Solids) sensors and Turbidity sensors. The continuous (Analog) data from the water quality sensors used would be outputted via an LCD (Liquid Crystal Display). The Automatic Switch control system consists of 5v Relay modules and a 12v Pump that would automatically switch ON/OFF depending on the level of water in the tank. The values of EC (Electrical Conductivity) and TDS spike drastically to the introduction of salt from as low as 138 -906 for TDS and 0.34 – 2.04 for EC, signifying increase in water capacity of electrical conductivity. Temperature rise in the afternoon also increases TDS values from 142 for clean water to 920 for the salty water while it ranges from 138 for clean water to 906 for salt water at both morning and evening time. Pumping aspects of the system are triggered when water level in the thank falls below 10% and trips off when water level goes above 95% as programmed in the control unit. The developed system marks a significant achievement in water management and automation technology. integration of quality monitoring sensors has enabled real-time evaluation of water parameters that holds potential for applications in environmental monitoring, ensuring safe drinking water, and safeguarding aquatic ecosystems. The automated switch control mechanism responds dynamically to water levels, enabling the system to trigger actions such as pump activation or filling processes based on predefined thresholds.

Fluorescence chemosensor for anion recognition, solvatochromism and protein binding studies based on Schiff- base derivative

A new salicylidene-based chemosensor (E)-N1-(2-hydroxy-3-methoxy-5-nitrobenzylidene)-N2-phenylbenzene-1,2-diamine (MNP) has been developed by condensation of 3-methoxy-5-nitrosalicylaldehyde with N-phenyl-o-phenylenediamine and analysed using FT-IR, 1H-NMR and ESI-MS spectral techniques. The photophysical properties of MNP, including solvatochromism were investigated and the colour changed from bright yellow to red in the presence of water. This MNP specifically detects only Cu2+ with "turn-off" and a colour turned from light yellow to violet in CH3CN/H2O (9/1, v/v) mixture.The optimized geometry of the MNP-Cu complex was analyzed using DFT methods and the results is confirm the formation of the MNP-Cu complex. Besides, the F− and H2PO4−anions are preferentially sensed by the MNP in comparison to other anions, leading a "turn-off" and the colour change from light yellow to dark yellow in the THF medium.From the pH sensor data, the fluorescence intensity increased at pH 4.0 due to protonation of the -OH group. The interaction of the MNP with protein molecules (BSA, HSA) was investigated using absorption and emission spectral methods. The investigation computed values of the binding constant and the Stern-Volmer quenching constant demonstrated that the MNP had a far stronger affinity for BSA than for HSA. The interaction of the MNP with protein molecules was confirmed using docking studies.

The development of an IoT-based automated temperature and pH monitoring system to enhance the management of gourami fish ponds

This research aims to develop an Internet of Things (IoT)-based automated system for monitoring temperature and pH in the context of gourami fish farming. Gourami fish ponds are often situated in various environments with significant variations in environmental conditions. The system is designed to enable pond owners to remotely monitor real-time water temperature and pH, which are key factors in maintaining optimal water quality and fish health. The temperature sensor used is the DS18B20, while the pH sensor used is the E210C. The ESP32 platform is employed due to its integrated Wi-Fi capabilities. Monitoring displays are accessible on an LCD, personal computer (PC), and smartphone. This research involves the calibration and validation of temperature and pH sensors to ensure accurate measurements. The average standard deviation value for the temperature sensor is 0.092, and for the pH sensor, it is 0.031. The average accuracy of the temperature sensor is 98.60%, while the pH sensor has an average accuracy of 98.41%. The results demonstrate that IoT-based temperature and pH monitoring allow for in-depth data analysis of environmental conditions and long-term trend analysis in pond management.

Development of Ag2O–TeO2-based glass and glass/stainless steel reference electrodes for pH sensors

Glass pH sensors are unsuitable for in vivo biomedical, clinical, or food applications because of the brittleness of glass, the difficulty in measuring small volumes and complicated matrix, and the necessity of calibration. Enamel structures such as glass/stainless steel (SUS) may substitute glass-based pH electrodes. This study developed new reference electrodes for pH sensors using ternary Ag2O–TeO2-MaOb (M = B, Ge, and P) glass and glass/SUS. The effect of the partial replacement of TeO2 in Ag2O–TeO2 glasses with B2O3, GeO2, and P2O5 on the pH sensitivity was investigated. (1) The effect of the partial replacement on the pH 4–9 sensitivity, which is defined as 100% for the ideal working electrode and 0% for the ideal reference electrode estimated from pH potential, became prominent in the order of GeO2, B2O3, and P2O5 in glass electrodes. Ag2O–TeO2–B2O3 glasses showed the lowest pH 7–9 sensitivity of 1% among the present electrodes. Ag2O–TeO2–P2O5 glasses showed the lowest pH 4–9 sensitivities of 24–33% among the present electrodes. (2) 25Ag2O･55TeO2･20P2O5/SUS showed a very low pH 4–9 sensitivity of 5% in glass/SUS electrodes. In this case, AgP2 may be responsible for the low pH 4–9 sensitivity because only AgP2 was detected from XRD measurements, and a small particle on the surface was observed in AFM observations. On the other hand, the crystallization of the glass matrix of 25Ag2O･55TeO2･20P2O5/SUS was suppressed by adding P2O5. Thus, 25Ag2O･55TeO2･20P2O5/SUS is a candidate for a robust KCl-leakless reference electrode for pH sensors.

Hydroponics Monitoring and Control System

This paper presents the design and construction of a hydroponics monitoring system that can collect parameters of hydroponic systems, such as temperature, water limit, pH level, and nutrient levels. The monitoring system was developed using an ESP32 microcontroller and several sensors, including total dissolved solids (TDS), pH, water level, and temperature sensors. The ESP32 microcontroller gathers and processes data from the sensors to automatically activate the water or salt pump and drain the necessary materials into the hydroponic system's plant basin. The user can then view the hydroponic parameters through the Blynk application on a smart phone. The user can also activate the pumps for water, nutrients, or salt using the application's interface on a smart phone, or the ESP32 microcontroller can activate them automatically if the parameter values deviate from the required values

Unlocking the potential of 2D nanomaterials for sustainable intelligent packaging

The demand for high food safety standards, spoilage prevention, and the minimization of food waste has spurred extensive investigation into intelligent food packaging. Within this field, considerable attention has been directed towards two-dimensional (2D) nanomaterials owing to their exceptionally thin layered configuration and diverse physicochemical, electrical, optical, and thermal properties. These attributes render 2D nanomaterials highly suitable for enhancing sensing capabilities in intelligent packaging systems. This review delves into the forefront of research concerning the utilization of 2D nanomaterials in intelligent packaging applications. It provides a comprehensive survey of intelligent food packaging concepts and explores various 2D materials, including graphene-based materials, MXene, and silicate clay, investigated for their potential in intelligent packaging systems. Additionally, the review interprets the structure, properties, and utilization of 2D materials in diverse biosensing systems encompassing gas, moisture, pH, and bacteria sensors, indicators, or wireless tags. Moreover, it examines the influence of 2D materials on the mechanical, optical, thermal, barrier, and bioactive properties of smart packaging, while also deliberating on their respective advantages and limitations. By combining these foundational elements, this study offers a distinctive and thorough contribution to the domain of food packaging, laying the groundwork for the future development of sustainable and high-performance packaging materials.

Development of a reverse transcription loop-mediated isothermal amplification assay with novel quantitative pH biosensor readout method for SARS-CoV-2 detection.

Reverse transcription loop-mediated isothermal amplification (RT-LAMP) is a molecular amplification method that can detect SARS-CoV-2 in a shorter time than the current gold-standard molecular diagnostic reverse transcription-polymerase chain reaction (RT-PCR). However, previously developed RT-LAMP assays have mostly relied on highly subjective visual colorimetric interpretation. In this study, an RT-LAMP assay was developed with quantitative measurement of reaction pH using a novel portable pH biosensor compared to qualitative colorimetric interpretation and gel electrophoresis, with 57 clinical COVID-19 samples used for validation of the test. The LoD of the assay is 103 copies/μL. The highest sensitivity was found in the qualitative methods (93.75%), while the highest specificity and likelihood ratio was found in the pH sensor (87.5% and 6.72). On the sensor measurement, a significant difference (p < 0.0001) was observed between the average pH of the RT-PCR (+) COVID-19 (6.15 ± 0.27), while the average pH of the RT-PCR (-) samples (6.72 ± 0.22). Correlation analysis revealed a strong correlation (r = 0.78, p < 0.0001) between the Ct values obtained from RT-PCR with the biosensor pH readout. RT-LAMP with the quantitative pH sensor readout method has the potential to be further developed as an objective molecular assay for rapid and simple detection of SARS-CoV-2.

SERS Microsensors for the Study of pH Regulation in Cystic Fibrosis Patient-Derived Airway Cultures.

Acidification of the airway surface liquid in the respiratory system could play a role in the pathology of Cystic Fibrosis, but its low volume and proximity to the airway epithelium make it a challenging biological environment in which to noninvasively collect pH measurements. To address this challenge, we explored surface enhanced Raman scattering microsensors (SERS-MS), with a 4-mercaptobenzoic acid (MBA) pH reporter molecule, as pH sensors for the airway surface liquid of patient-derived in vitro models of the human airway. Using air-liquid interface (ALI) cultures to model the respiratory epithelium, we show that SERS-MS facilitates the optical measurement of trans-epithelial pH gradients between the airway surface liquid and the basolateral culture medium. SERS-MS also enabled the successful quantification of pH changes in the airway surface liquid following stimulation of the Cystic Fibrosis transmembrane conductance regulator (CFTR, the apical ion channel that is dysfunctional in Cystic Fibrosis airways). Finally, the influence of CFTR mutations on baseline airway surface liquid pH was explored by using SERS-MS to measure the pH in ALIs grown from Cystic Fibrosis and non-Cystic Fibrosis donors.

Temperature-compensated high-sensitivity refractive index, liquid level and PH sensing realization enabled by a small-period microfiber long period grating cascaded with microfiber Bragg grating

Conventional reported optical fiber sensors could not have both good temperature-compensated characteristic and high PH sensing sensitivity. In this study, we proposed and fabricated a small-period microfiber long period grating (SP-mFLPG) cascaded with a line-by-line microfiber Bragg grating (mFBG) by using femtosecond (fs) laser directly writing technique for high-sensitivity temperature-compensated sensing refractive index(RI), liquid level(LL), PH value. To be the different from traditional LPG devices, the temperature sensitivities of SP-mFLPG was measured as −8.61 pm/℃ owing to the strong coupling occurred between the fundamental mode of TE11 mode and the higher-order mode of TE111, which could be compensated with the mFBG device with a temperature sensitivity of 7.85 pm/℃. On the basis of this temperature-insensitive sensing strategy, our proposed SP-mFLPG sensor can sense RI, LL and pH with high sensitivities of 866.343 nm/RIU, 7.224 nm/mm, −5.70 nm/PH, respectively. Our obtained PH sensitivity is much higher than numerous reported state-of-the-art optical fiber PH sensors. Thus, our proposed optical microfiber device can be found potential applications in real-time measuring some important biochemical reaction procedures.

A film composed of PEDOT:PSS/PVA as a sensitive medium for pH sensor in optical fiber

In this work, a pH sensitive transducer element attached to a multimode optical fiber section is proposed. The sensitive element is a PEDOT:PSS/PVA composite film that exhibited sensitivity at low pH values in the range of 1–7 pH. The addition of PVA was important for the adhesion process to the optical fiber surface. The morphology of the PEDOT:PSS polymers allowed characterization at pH stimuli that were based on the optical power transmission generated from the interaction of the light propagating in the optical fiber core and the optical fiber section coated with the sensitive film. A sensitivity of −0.05 dB/pH and a linear fit R2 of 0.93 was obtained, the response time was 3 s, while the sensor recovery time was 50 s maintaining stability higher than 10 min.

CO2 exposure drives a rapid pH response in live adult Drosophila.

CO2 anesthesia is the most common method for immobilizing Drosophila for research purposes. But CO2 exposure has consequences-it can impact fertility, behavior, morphogenesis, and cytoskeletal dynamics. In this respect, Drosophila is an outstanding model for studying the impact of CO2 exposure on tissues. In this study we explored the response of intracellular pH (pHi) to a one-minute CO2 pulse using a genetically encoded, ubiquitously expressed pH sensor, tpHusion, to monitor pHi within a live, intact, whole fly. We compared wild-type flies to flies lacking Imaginal disc growth factors (Idgfs), which are chitinase-like proteins that facilitate developmental processes and the innate immune response. Morphogenetic and cytoskeletal defects in Idgf-null flies are enhanced after CO2 exposure. We found that pHi drops sharply within seconds of the beginning of a CO2 pulse and recovers over several minutes. The initial profile was nearly identical in control and Idgf-null flies but diverged as the pHi returned to normal. This study demonstrates the feasibility of monitoring pH in live adult Drosophila. Studies exploring pH homeostasis are important for understanding human pathologies associated with pH dysregulation.