Accuracy Of pH Measurements Research Articles

Measurement of Human and Bovine Exhaled Breath Condensate pH Using Polyaniline-Modified Flexible Inkjet-Printed Nanocarbon Electrodes.

The collection, processing, and electrochemical analysis of exhaled breath condensate (EBC) from healthy human and animal subjects is reported on. EBC is a biospecimen potentially rich in biomarkers of respiratory disease. The EBC pH was analyzed potentiometrically using a disposable polyaniline (PANI)-modified inkjet-printed (IJP) carbon electrode. Comparison measurements were performed using a commercial screen-printed carbon (SPC) electrode. The PANI-modified electrodes exhibited reproducible and near-Nernstian responses for pH values between 2 and 9 with slopes from -50 to -60 mV/dec. The PANI-modified IJP carbon electrode exhibited a faster response time and superior reproducibility to the modified SPC electrode. In proof-of-concept studies, the healthy human EBC pH was found to be 6.57 ± 0.09 and the healthy bovine EBC pH was 5.9 ± 0.2. All pH determined using the PANI-modified electrodes were in good agreement with the pH determined using a micro glass pH electrode. An RTube device was used to collect EBC from humans while a modified device was used to collect EBC from calves in the field. EBC volumes of 0.5-2 mL for 5-6 min of tidal breathing were collected from healthy animals. The pH of EBC from healthy calves (17 animals) depends on their age from 1 to 9 weeks with values ranging from 5.3 to 7.2. A distinct alkaline shift was observed for many animals around 20 days of age. The bovine EBC pH also depends on the ambient temperature and humidity at the time of collection. The results indicate that the PANI-modified IJP carbon electrodes outperform commercial SPC and provide reproducible and accurate measurement of pH across various biospecimen types.

Fe-Doped SrCoOx FET Sensors for Extreme Alkaline pH Sensing.

The accurate measurement of pH in highly alkaline environments is critical for various industrial applications but remains a complex task. This paper discusses the development of novel Fe-doped SrCoOx-based FET sensors for the detection of extreme alkaline pH levels. Through a comprehensive investigation of the effects of Fe doping on the structure, electrical properties, and sensing performance of SrCoOx, we have identified the optimal doping level that significantly enhances the sensor's performance in highly alkaline conditions. With a Fe doping level of 5 mol %, the sensitivity of the sensor improves to 0.86 lg(Ω)/pH while maintaining the response rate. Further increasing the Fe doping to 10 mol % results in a sensor that demonstrates favorable response time, a suitable pH range, and a linear correlation between lg(R) and pH. The combination of X-ray photoelectron spectroscopy and X-ray diffraction analysis provides insight into the regulation mechanisms of Fe doping on the crystal structure, electronic structure, and oxygen vacancy concentration of SrCoOx. Our findings indicate that Fe doping leads to an increase in oxygen vacancy concentration and a decrease in the energy barrier for oxygen ion migration, which contributes to the improved sensing performance of the Fe-doped SrCoOx sensors. Additionally, the study highlights the influence of oxygen vacancy concentration on the electrical properties of SrCoOx. Precise control over the concentration of oxygen vacancies is crucial for optimizing the sensitivity and response speed of SrCoOx FET sensors under extreme alkalinity conditions.

Accurate pH Monitoring of Highly Concentrated Saline Aqueous Solutions (Seawater-like) with a pH Colorimetric Sensor Array.

A pH colorimetric sensor array (CSA) was prepared on a nitrocellulose membrane and used for accurate pH measurement in highly concentrated saline solutions. The CSAs consisted of sensing spots made of a suitable OrMoSil polymer prepared from organo-fluorinated-silane precursors and/or organosilane with tetraethyl orthosilicate hosting an acid-base indicator. Four CSAs were prepared: D, 1F, 2F, and 3F. In D, a nonfluorinated organosilane was present. From 1F to 3F, the concentration of the fluorinated organosilane increased and improved the pH measurement accuracy in highly saline concentrations. No recalibrations were required, and the analytical signal was stable in time. D, 1F, 2F, and 3F were deposited in triplicate, and they were prepared to work in the seawater pH interval (7.50-8.50). The use of fluorinated precursors led to a lower pH prediction error and tailored the interval of the CSA at more basic pH values so that the inflection points of the sigmoidal calibrations of D, 1F, 2F, and 3F moved from 6.97 to 7.98. The overall pH prediction error was 0.10 pH (1F), 0.02 pH (2F), and 0.04 pH units (3F). The CSAs were stable, reversible, reusable, and independent of salinity (S) between 20 and 40. The performances of the CSA were compared with those of a glass electrode, whose pHNIST values were converted in the pHSWS scale through a conversion equation. Being unaffected by the typical drawback of the glass electrode, the CSAs can be used directly in seawater real samples, and it validated the proposed conversion equation.

Miniaturized fluorescence pH sensor with assembly free ball lens on a tapered multimode optical fiber.

In biochemistry, the absence of a compact, assembly-free pH sensor with high sensitivity and signal-to-noise ratio has been a persistent hurdle in achieving accurate pH measurements in real time, particularly in complex liquid environments. This manuscript introduces what we believe to be a novel solution in the form of a miniaturized pH sensor utilizing an assembly-free ball lens on a tapered multimode optical fiber (TMMF), offering the potential to revolutionize pH sensing in biochemical applications. A multimode optical fiber (MMF) was subjected to tapering processes, leading to the creation of an ultra-thin needle-like structure with a cross-sectional diameter of about 12.5 µm and a taper length of 3 mm. Subsequently, a ball lens possessing a diameter of 20 µm was fabricated at the apex of the taper. The resultant structure was coated utilizing the dip-coating technique, involving a composite mixture of epoxy and pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF), thereby ensconcing the tapered ball lens with dye molecules for pH sensing. This study encompassed the fabrication and evaluation of six distinct fiber structures, incorporating the cleaved endface, the convex lens, and the ball lens structures to compare light focal lengths and propagation intensities. Computational simulations and numerical analyses were conducted to elucidate the encompassing light focal distances across the full array of lens configurations. The efficacy of the proposed pH sensor was subsequently assessed through its deployment within a complex liquid medium spanning a pH spectrum ranging from 6 to 8. Real-time data acquisition was performed with a fast response time of 0.5 seconds. A comparative analysis with a pH sensor predicated upon a single TMMF embedded with the fluorescent dye underscored the substantial signal enhancement achieved by the proposed system twice the fluorescence signal magnitude. The proposed assembly-free miniaturized pH sensor not only substantiates enhanced signal collection efficiency but also decisively addresses the persistent challenges of poor signal-to-noise ratio encountered within contemporary miniaturized pH probes.

Fabrication of High-Performance pH Sensor Based on NiO/Mxene/PANI Modified Sensing Platform

Accurate pH measurement is a fundamental cornerstone in various scientific and industrial processes, playing a pivotal role in ensuring the quality and efficiency of countless applications. There is a significant demand for pH sensors with versatile applications across various sectors, including agriculture, healthcare, food processing, textiles, leather, wet laboratories, and environmental remediation [1-3]. In this study, we embark on a journey of innovation and precision, focusing on the development of a cutting-edge pH sensor. Our research endeavors to address the critical need for enhanced pH sensing capabilities through a meticulously designed sensing platform, combining the unique attributes of nickel oxide (NiO) nanoparticles (NPs), polyaniline (PANI), and MXene, all ingeniously integrated onto a nickel foam (NF) electrode. The fabrication process involved a series of steps, including the synthesis of NiO NPs via the sol-gel method, following by mixing NiO and MXene, followed by further mixing with PANI and electrodeposited onto the nickel foam electrode. Fig 1 represents the fabrication process of NF electrodes with NiO/MXene/PANI composites.The performance of the electrode was evaluated using cyclic voltammetry (CV) across various buffer solutions where NiO-PANI-MXene modified NF electrode, pt wire, and Ag/AgCl electrode were used as a working electrode, counter electrode, and reference electrode respectively. MXene are layered materials composed of transition metal carbides, nitrides, or carbonitrides. What makes MXene attractive for pH sensing is its surface functionalization, that often includes hydroxyl (-OH) and oxygen (-O) groups. These groups are responsive to variations in hydronium ion (H₃O⁺) concentration. In acidic solutions with high H₃O⁺ concentrations, these groups undergo protonation, modifying MXene's electrical properties, and affecting conductivity and potential. This alteration forms the basis for MXene's pH sensing ability, detectable through methods like open circuit potential (OCP), where changes in current at specific voltages correlate with pH levels, enabling precise pH measurements. To characterize the composites, various analytical techniques were employed. SEM-EDX, TEM and XRD were used for comprehensive structural analysis. In parallel, cyclic voltammetry (CV), amperometry, and OCP were employed to monitor shifts in potential corresponding to different pH levels within the buffer solution. The results revealed that the NiO/MXene/PANI sensor exhibited remarkable sensitivity over the pH range from 3 to 11. The pH sensor exhibits a sensitivity of 46.00 mV/pH (R2 = 0.99) and maintains consistent performance within the physiological pH range spanning from 3 to 11. This prototype currently undergoing testing alongside a commercially available pH meter using real samples, such as orange and a baking powder etc. solution. The durability and repeatability assessments have yielded encouraging outcomes. Thus, the presented NiO/MXene/PANI based pH sensor represents a significant advancement in pHsensing technology, offering improved sensitivity and stability. The incorporation of MXene within the sensing platform holds a promise for the future developments of solid-state pH sensors.Reference Jamal, T. K. Dey, T. Nasrin, A. Khosla, & K. M. Razeeb, 2022, Journal of The Electrochemical Society, 169(5), 057517.Islam, H. Shao, M. M. R. Badal, K. M. Razeeb, & M. Jamal, 2021, PloS one, 16 (3), e0248142.V. Mun’delanji, and E. Tamiya, 2015, Nanobiosensors and nanobioanalyses: A Review(pp. 3-20). Tokyo, Japan: Springer. Fig. 1. Fabrication process of NiO/MXene/PANI modified nickel foam electrode. Figure 1

The pH measurement of cement-based materials: Effect of leaching time, leaching technique and water-to-solid ratio

Corrosion of steel is an electrochemical process that is affected by pH and potential difference. The pH of concrete may change due to physical, chemical, and biological influence over time. Therefore, it is important to measure and monitor the pH of reinforced concrete as a structural health monitoring parameter related to durability. Ex-situ leaching (ESL) method is commonly applied to produce the equilibrated aqueous solutions for the pH measurement of cement-based materials. However, there are limited studies about the effect of leaching time, leaching technique and water-to-solid (w/s) ratio when applying this method. This may lead to underestimation of pH and unnecessary prolonged leaching time. The solution temperature compensated pH value was used during analysis of the data. By testing on the OPC mortar with cement-to-sand ratio of 1:3 and water-to-cement ratio of 0.55, the optimum w/s ratio and minimum leaching time are 2 and 5 min, respectively. The minimum quantity for solid per sample shall not be less than 5.0 g. The findings of this research will contribute to a more accurate pH measurement and may play a part in regulating a standard for cement-based materials.

A Multichannel Electrochemical Sensor Interface IC for Bioreactor Monitoring.

This research article introduces a novel integrated circuit (IC) designed for bioreactor applications catering to multichannel electrochemical sensing. The proposed IC comprises 2x potentiometric, 2x potentiostat, 2x ISFET channels and 1x temperature channel. The potentiostat channel utilizes a current conveyor-based architecture with a programmable mirroring ratio, enabling an extensive measurement range of 114 dB. The potentiometric channel incorporates a customized electrostatic discharge (ESD) protection circuit to achieve ultra-low input leakage in the picoampere range, while the ISFET channel employs a constant-voltage, constant-current topology for accurate pH measurement. Combined with the die temperature sensor, this IC is well-suited for monitoring bioreactions in real-time. Additionally, all channels can be time-multiplexed to a reconfigurable analog backend, facilitating the conversion of input signals into digital codes. The prototype of the IC is fabricated using 0.18 μm standard CMOS technology, and each channel is experimentally characterized. The interface IC demonstrates a peak power consumption of 22 μW.

Binary RuO2-CuO Electrodes Outperform RuO2 Electrodes in Measuring the pH in Food Samples.

Glass electrodes are the only type of pH-sensitive electrodes currently used in the food industry. While widely used, they have several disadvantages, especially in the areas of brittleness and price. Ruthenium(IV) oxide (RuO2) pH electrodes are a well-known alternative to conventional glass electrodes, providing improved durability and lower price. Nevertheless, partial substitution of RuO2 with cupric oxide (CuO) would further lower the price and reduce the toxicity of the electrode. In this paper, we present the applicability of RuO2-CuO electrodes for pH measurement in food samples. The electrodes were fabricated by screen printing and covered with a protective Nafion membrane. In the experiments with food samples, the RuO2-CuO electrodes outperformed RuO2 electrodes in measuring the pH with an almost twofold higher rate of accurate measurements. The utilization of CuO for the fabrication of pH electrodes allowed the accurate measurement of pH in a larger variety of food samples without compromising the response time.

Dual-Responsive and Reusable Optical Sensors Based on 2,3-Diaminoquinoxalines for Acidity Measurements in Low-pH Aqueous Solutions.

This work is focused on the age-old challenge of developing optical sensors for acidity measurements in low-pH aqueous solutions (pH < 5). We prepared halochromic (3-aminopropyl)amino-substituted quinoxalines QC1 and QC8 possessing different hydrophilic-lipophilic balance (HLB) and investigated them as molecular components of pH sensors. Embedding the hydrophilic quinoxaline QC1 into the agarose matrix by sol-gel process allows for fabrication of pH responsive polymers and paper test strips. The emissive films thus obtained can be used for a semi-quantitative dual-color visualization of pH in aqueous solution. Being exposed to acidic solutions with pH in the range of 1-5, they rapidly give different color changes when the analysis is performed in daylight or under irradiation at 365 nm. Compared with classical non-emissive pH indicators, these dual-responsive pH sensors allow for an increase in the accuracy of pH measurements, particularly in complex environmental samples. pH indicators for quantitative analysis can be prepared by the immobilization of amphiphilic quinoxaline QC8 using Langmuir-Blodgett (LB) and Langmuir-Schäfer (LS) techniques. Compound QC8 possessing two long alkyl chains (n-C8H17) forms stable Langmuir monolayers at the air-water interface, and these monolayers can be successfully transferred onto hydrophilic quartz and hydrophobic polyvinylchlorid (PVC) substrates using LB and LS techniques, respectively. The 30-layer films thus obtained are emissive, reveal excellent stability, and can be used as dual-responsive pH indicators for quantitative measurements in real-world samples with pH in the range of 1-3. The films can be regenerated by immersing them in basic aqueous solution (pH = 11) and can be reused at least five times.

Measuring Protons with Photons: A Hand-Held, Spectrophotometric pH Analyzer for Ocean Acidification Research, Community Science and Education.

Ocean Acidification (OA) is negatively affecting the physiological processes of marine organisms, altering biogeochemical cycles, and changing chemical equilibria throughout the world’s oceans. It is difficult to measure pH broadly, in large part because accurate pH measurement technology is expensive, bulky, and requires technical training. Here, we present the development and evaluation of a hand-held, affordable, field-durable, and easy-to-use pH instrument, named the pHyter, which is controlled through a smartphone app. We determine the accuracy of pH measurements using the pHyter by comparison with benchtop spectrophotometric seawater pH measurements, measurement of a certified pH standard, and comparison with a proven in situ instrument, the iSAMI-pH. These results show a pHyter pH measurement accuracy of ±0.046 pH or better, which is on par with interlaboratory seawater pH measurement comparison experiments. We also demonstrate the pHyter’s ability to conduct both temporal and spatial studies of coastal ecosystems by presenting data from a coral reef and a bay, in which the pHyter was used from a kayak. These studies showcase the instrument’s portability, applicability, and potential to be used for community science, STEM education, and outreach, with the goal of empowering people around the world to measure pH in their own backyards.

Interaction of the Fungal Metabolite Harzianic Acid with Rare-Earth Cations (Pr3+, Eu3+, Ho3+, Tm3+).

Rare-earth elements (REEs) are in all respect a class of new contaminants that may have toxic effects on organisms and microorganisms and information on their interactions with natural ligands should be of value to predict and control their diffusion in natural environments. In the current study, we investigate interactions of tripositive cations of praseodymium, europium, holmium, and thulium with harzianic acid (H2L), a secondary metabolite produced by selected strains of fungi belonging to the Trichoderma genus. We applied the same techniques and workflow previously employed in an analogous study concerning lanthanum, neodymium, samarium, and gadolinium tripositive cations. Therefore, in the current study, HPLC-ESI-HRMS experiments, circular dichroism (CD), and UV-Vis spectrophotometric absorption data, as well as accurate pH measurements, were applied to characterize bonding interactions between harzianic acid and Pr3+, Eu3+, Ho3+, and Tm3+ cations. Problems connected to the low solubility of harzianic acid in water were overcome by employing a 0.1 M NaClO4/(CH3OH + H2O 50/50 w/w) mixed solvent. For Pr3+, Ho3+, and Tm3+, only the mono complexes PrL+, HoL+, and TmL+ were detected and their formation constant determined. Eu3+ forms almost exclusively the bis complex for which the corresponding formation constant is reported; under our experimental conditions, the mono complex EuL+ is irrelevant. Combining the results of the present and previous studies, a picture of interactions of harzianic acid with rare-earth cations extending over 8 of the 17 REEs can be composed. In order to complement chemical information with toxicological information, a battery of bioassays was applied to evaluate the effects of praseodymium, europium, holmium, and thulium tripositive cations on a suite of bioindicators including Aliivibrio fischeri (Gram-negative bacterium), Raphidocelis subcapitata (green alga), and Daphnia magna (microcrustacean), and median effective concentration (EC50) values of Pr3+, Eu3+, Ho3+, and Tm3+ for the tested species were assessed.

Soft, environmentally degradable microfluidic devices for measurement of sweat rate and total sweat loss and for colorimetric analysis of sweat biomarkers

AbstractAdvanced capabilities in noninvasive, in situ monitoring of parameters related to sweat serve as the basis for obtaining real‐time insights into human physiological state, health, and performance. Although recently reported classes of soft, skin‐interfaced microfluidic systems support powerful functions in this context, most are designed as single‐use disposables. As a result, associated waste streams have the potential to create adverse environmental impacts. Here, we introduce materials and fabrication techniques that bypass these concerns through biodegradable microfluidic systems with a full range of features, including measurement of sweat rate and total loss, and colorimetric analysis of biomarkers. The key components fully degrade through the enzymatic action of microorganisms in natural soil environments, or in industrial compost facilities, to yield end products with beneficial uses as fertilizers and species to improve soil health. Detailed characterization of the constituent materials, the fabrication procedures, the assembly processes, and the completed devices reveal a set of essential performance parameters that are comparable to, or even better than, those of non‐degradable counterparts. Human subject studies illustrate the ability of these devices to acquire accurate measurements of sweat loss, sweat rate, pH, and chloride concentration during physical activities and thermal exposures.image

Cost-Effective and Portable Instrumentation to Enable Accurate pH Measurements for Global Industry 4.0 and Vertical Farming Applications

Global Vertical Farming (VF) applications with characteristic Industry 4.0 connectivity will become more and more relevant as the challenges of food supply continue to increase worldwide. In this work, a cost-effective and portable instrument that enables accurate pH measurements for VF applications is presented. We demonstrate that by performing a well-designed calibration of the sensor, a near Nernstian response, 57.56 [mV/pH], ensues. The system is compared to a ten-fold more expensive laboratory gold standard, and is shown to be accurate in determining the pH of substances in the 2–14 range. The instrument yields precise pH results with an average absolute deviation of 0.06 pH units and a standard deviation of 0.03 pH units. The performance of the instrument is ADC-limited, with a minimum detectable value of 0.028 pH units, and a typical absolute accuracy of ±0.062 pH units. By meticulously designing bias and amplification circuitry of the signal conditioning stage, and by optimizing the signal acquisition section of the instrument, a (minimum) four-fold improvement in performance is expected.

A novel two-channel ratio fluorescent probe for monitoring intracellular pH fluctuations

Accurate measurement of pH is of great significance in the research of biology and medicine sciences. Cell is the basic unit of living organism and the proper pH of cytoplasm and organelles such as lysosome is the precondition to maintain its function. Alteration of pH may impair the normal process of cells and lead to occurrence of diseases. Sensitively sensing the pH of cytoplasm and organelles is of great value for biomedical research. Due to the complexity of biological microenvironment, it is still challenging to simultaneously detect the pH changes of cytoplasm and lysosome. Here, we reported a ratiometric pH probe with NIR fluorescence termed as PCHC, which realized sensitive cytoplasmic and lysosome pH detection. The probe was prepared by connecting coumarin with dicyanmethylene-4H-pyran via amidation reaction, and displays large Stoke-shift, good biosafety and pH selectivity. After entering the cell, the probe shows blue in cytoplasm and NIR fluorescence in lysosome due to respective pH. The ratio of blue and NIR fluorescence signal can be served as indicator to monitor pH change of cytoplasm and lysosome simultaneously, which has potential application for investigation of pH alteration related diseases.

Novel Self-Calibrating Amperometric and Ratiometric Electrochemical Nanotip Microsensor for pH Measurement in Rat Brain.

Brain pH has been proven to be a key factor in maintaining normal brain function. The relationship between local pH fluctuation and brain disease has not been extensively studied due to lack of the accurate in situ analysis technology. Herein, we have for the first time proposed a voltammetric pH sensor by measuring the ratio of current signals instead of the previously reported potential based on the Nernst equation. Single-walled carbon nanotubes (CNT) were first self-assembled on the electrode surface of a carbon-fiber nanotip electrode (CFNE). Then, poly-o-phenylenediamine (PoPD) molecules were deposited as pH-responsive molecules through in situ electrochemical polymerization. The compact CFNE/CNT/PoPD exhibited a good redox process with the on-off-on ratiometric electrochemical response to pH ranging from 4.5 to 8.2, providing self-correction for in situ pH detection. Thus, the proposed sensor enabled the accurate measurement of pH with excellent selectivity even in the presence of proteins or electroactive species. In addition, the sensor showed high repeatability, reproducibility, and reversibility in measuring pH and even demonstrated good stability when it was exposed to air for 5 months. Finally, we successfully detected the fluctuation of pH in rat brains with cerebral ischemia and rat whole blood. Overall, this research not only provides a good tool for the detection of rat brain pH but also provides a new strategy for further designing nanosensors for intracellular or subcellular pH.

Fabrication and Characterization of Iridium Oxide pH Microelectrodes Based on Sputter Deposition Method.

pH value plays an important role in many fields such as chemistry and biology; therefore, rapid and accurate pH measurement is very important. Because of its advantages in preparation, wide test range, rapid response, and good biocompatibility, iridium oxide material has received more and more attention. In this paper, we present a method for preparing iridium oxide pH microelectrodes based on the sputter deposition method. The sputtering parameters of iridium oxide are also studied and optimized. Open-circuit potential tests show that microelectrodes exhibit near-Nernstian pH response with good linearity (about 60 mV/pH), fast response, high stability (a slight periodic fluctuation of potential change <2.5 mV in 24 h), and good reversibility in the pH range of 1.00–13.00.

Green Synthetic Fluorescent Carbon Quantum Dot as pH Sensor Applied to Real Water Samples Determination

Willow, a common tree species, is mainly distributed in temperate regions of the Northern Hemisphere. Catkins are the seeds of willow. In addition to propagating new willows, it is of great significance to study its application in other areas. Carbon quantum dots (CQDs) have attracted extensive attention owing to their excellent luminescence properties, low toxicity and water solubility. The use of CQDs for accurate measurement of pH is of great significance in environmental, medical and other fields. Based on this, blue-emission fluorescent CQDs with 4.93% quantum yield (Q.Y.) are prepared via natural product catkins as the only raw material by one-step hydrothermal method. The prepared CQDs exhibit excellent water solubility, narrow particle size distribution, excitation-dependent photoluminescence properties and sensitive pH response behavior. The fluorescence intensity of CQDs has a good linear relationship with pH in the range of 6–12, and the correlation coefficient is 0.994. In addition, the CQDs have good stability, and the response to pH displays excellent reversibility, which can be developed as a pH sensor to quantitatively monitor the pH values in real water samples. Thereby, the potential practical application is promising.

Development of a high‐throughput method for examining bacterial supernatant pH using ratiometric UV‐VIS spectrophotometry

Background Bacterial supernatant pH measurements are highly relevant to downstream applications, such as organoid or cell line treatment, mass spectrometry, and metabolic analysis. Although high-throughput systems have been implemented for examining bacterial growth, high-throughput systems for measuring bacterial supernatant pH are lacking. The traditional method for measuring the solution pH of bacterial supernatants uses pH meters and electrodes. However, this method is not compatible with high throughput approaches which employ microplate readers. While fluorescent dyes can be used to measure solution pH, bacterial media is highly auto-fluorescent, making this system incompatible for microbial analysis. To overcome these limitations, we have developed a simple, high-throughput assay to measure bacterial supernatant pH using ratiometric UV-VIS spectrophotometry and phenol red, the pH indicator dye contained in the medium DMEM. Phenol red exhibits a gradual transition from yellow to fuchsia from acid to basic solution pH, respectively. The aim of this study was to develop a high-throughput and accessible method to monitor pH changes in multiple samples using a standard microplate reader. Methods & Results As a proof of concept, we prepared a series of solutions with pHs that ranged from 3 to 10 in DMEM and DMEM containing a fully defined bacterial media, termed ZMBI, at a ratio 3:1. UV-VIS spectral analysis of phenol red from 350-750 nm confirmed the reported wavelengths for the isosbestic point - a specific wavelength at which the total absorbance of an indicator dye remains consistent – and the wavelength of maximum absorption (λmax) to be 470 and 560 nm, respectively. Calibration curves generated by the ratio of these two wavelengths (560 nm/470 nm) revealed a sigmodal curve, which could be fit by a four-parameter logistics curve. To test the ability of this system to correctly calculate pH, commensal gut microbes Lactobacillus reuteri and Escherichia coli were grownin ZMBI overnight anaerobically and aerobically, respectively. A comparison between standard pH electrode analysis and our newly developed wavelength analysis revealed similar calculated pHs. To generate a high-throughput system, L. reuteri and E. coli were grown in 1 mL of ZMBI in DeepWell microplates overnight. To examine bacterial growth, 100 µL of culture was transferred to flat bottomed 96-well microplates and optical density was measured at OD600nm. For pH analysis, a 200-µL volume of culture was transferred to round bottomed 96-well plates, centrifuged and cell-free supernatant was blended with ZMBI at a 3:1 ratio. Back calculated solution pH values using the sigmodal calibration curve yielded similar results to the pH electrode values. Conclusions We have successfully employed DMEM's phenol-red dye, which is well suited for a colorimetric assay, to study bacterial supernatant pH. This method allows for rapid and accurate pH measurement which can be easily be applied to multiple organisms and adapted to several downstream applications.

Measurement of the Intestinal pH in Mice under Various Conditions Reveals Alkalization Induced by Antibiotics.

The intestinal pH can greatly influence the stability and absorption of oral drugs. Therefore, knowledge of intestinal pH is necessary to understand the conditions for drug delivery. This has previously been measured in humans and rats. However, information on intestinal pH in mice is insufficient despite these animals being used often in preclinical testing. In this study, 72 female ICR mice housed in SPF (specific pathogen-free) conditions were separated into nine groups to determine the intestinal pH under conditions that might cause pH fluctuations, including high-protein diet, ageing, proton pump inhibitor (PPI) treatment, several antibiotic treatment regimens and germ-free mice. pH was measured in samples collected from the ileum, cecum and colon, and compared to control animals. An electrode, 3 mm in diameter, enabled accurate pH measurements with a small amount of gastrointestinal content. Consequently, the pH values in the cecum and colon were increased by high-protein diet, and the pH in the ileum was decreased by PPI. Drastic alkalization was induced by antibiotics, especially in the cecum and colon. The alkalized pH values in germ-free mice suggested that the reduction in the intestinal bacteria caused by antibiotics led to alkalization. Alkalization of the intestinal pH caused by antibiotic treatment was verified in mice. We need further investigations in clinical settings to check whether the same phenomena occur in patients.

Accurate pH and O2 Measurements from Spray Underwater Gliders

AbstractThe California Current System is thought to be particularly vulnerable to ocean acidification, yet pH remains chronically undersampled along this coast, limiting our ability to assess the impacts of ocean acidification. To address this observational gap, we integrated the Deep-Sea-DuraFET, a solid-state pH sensor, onto a Spray underwater glider. Over the course of a year starting in April 2019, we conducted seven missions in central California that spanned 161 glider days and &gt;1600 dives to a maximum depth of 1000 m. The sensor accuracy was estimated to be ± 0.01 based on comparisons to discrete samples taken alongside the glider (n = 105), and the precision was ±0.0016. CO2 partial pressure, dissolved inorganic carbon, and aragonite saturation state could be estimated from the pH data with uncertainty better than ± 2.5%, ± 8 μmol kg−1, and ± 2%, respectively. The sensor was stable to ±0.01 for the first 9 months but exhibited a drift of 0.015 during the last mission. The drift was correctable using a piecewise linear regression based on a reference pH field at 450 m estimated from published global empirical algorithms. These algorithms require accurate O2 as inputs; thus, protocols for a simple predeployment air calibration that achieved accuracy of better than 1% were implemented. The glider observations revealed upwelling of undersaturated waters with respect to aragonite to within 5 m below the surface near Monterey Bay. These observations highlight the importance of persistent observations through autonomous platforms in highly dynamic coastal environments.