pH Calibration Research Articles

A wearable electrochemical sensor for the monitoring of neonicotinoid insecticides, salicylic acid and the pH in plant guttation

Wearable plant sensors can continuously monitor the material absorption and health status of a plant, thereby providing data that can be used to provide precise crop management. Herein, we describe a noninvasive wearable electrochemical sensor designed for monitoring plant guttation that is capable of detecting trace levels of neonicotinoid insecticides, salicylic acid, and pH. The sensor electrodes are prepared using an improved laser-induced graphene (LIG) printing method, with which a single set (six sensors) can be fabricated in only 15.6 s. Leveraging the high surface area and conductivity of LIG, trace-level electrochemical testing for neonicotinoid insecticides, salicylic acid, and pH can be achieved without the need for electrode surface modification. When the sensors are combined with a guttation collection module, the repeated collection of the guttation fluid becomes possible. The sensor weighs only 0.1 g and can be connected to a portable electrochemical workstation and smartphone for real-time on-site data collection. The practical value of the sensor was validated by monitoring the guttation fluid produced by rice, placed under stress through the application of neonicotinoid insecticide, and real-time pH calibration. This noninvasive wearable sensor for monitoring plant guttation enables the real-time detection of target substances, avoids plant stress caused by sensor intrusion, and provides a new direction for the future development of wearable plant sensors.

Biocompatible Re-Containing Block Copolymers for Intracellular pH Mapping in the PLIM Mode.

Monitoring of intracellular pH is of great importance since deviation of this parameter from the "normal" magnitudes can be considered as an indicator of various pathologies. Thus, the development of new efficient and biocompatible sensors suitable for application in biological systems and capable of quantitative pH estimation remains an urgent chemical task. Herein, we report the synthesis of a series of phosphorescent rhenium [Re(NN)(CO)2(PR3)2]+ complexes based on the NN diimine ligands containing pH-responsive carboxylic groups and styrene-containing phosphine ligands. The complexes, which display the highest pH sensitivity, were copolymerized with polyvinylpyrrolidone using the RAFT protocol to impart water solubility and to protect the chromophores from interaction with molecular oxygen. The resulting copolymers show an emission lifetime response onto pH variations in the physiological range. Cellular experiments with Chinese hamster ovary cells (CHO-K1) reveal easy internalization of the probes in cell culture and an approximately uniform distribution in cells, with some preference for location in acidic compartments (late endosomes and lysosomes). Using nigericin to homogenize intra- and extracellular pH, we built a calibration of lifetime versus pH in live CHO-K1 cells. Analysis of the phosphorescence lifetime imaging microscopy (PLIM) data confirms the applicability of the obtained sensors for monitoring the intracellular pH in cell cultures.

Aluminium Interdigitated Electrode with 5.0 μm Gap for Electrolytic Scooting

The goal of the research project is to design, fabricate, and characterize an extremely sensitive biosensor for use in healthcare. Using AutoCAD software, a novel IDE pattern with a 5 μm finger gap was created. Conventional photolithography and regular CMOS technology were used in the fabrication process. A 3D nano profiler, scanning electron microscopy (SEM), high-power microscopy (HPM), and low-power microscopy (LPM) were used to physically characterize the manufactured IDE. Chemical testing was done using several pH buffer solutions, and electrical validation was performed using I-V measurements. The Al IDE was produced, with a tolerance of 0.1 μm between the fabricated IDEs and the design mask. Electrical measurements verified the flawless fabrication of the IDE, and the device's repeatability was validated by the outcomes of comparable IDE samples. For each pH buffer solution, a modest additional volume of 2 μl was used to quantitatively detect slight current fluctuations in the microampere range. Through pH calibration for advanced applications in the realm of chemical sensors using an amperometric method, this research study has verified the chemical behavior of the IDE.

Improvement of the Upper Detection Limit of Ionophore-Based H+-Selective Electrodes: Explanation and Elimination of Apparently Super-Nernstian Responses.

The response range of an ion-selective electrode (ISE) has been described by counterion interference at the lower and Donnan failure at the upper detection limit. This approach fails when the potentiometric response at the upper detection limit exhibits an apparently super-Nernstian response, as has been reported repeatedly for H+-selective electrodes. While also observed when samples contain other anions, super-Nernstian responses at low pH are a problem in particular for samples that contain phthalate, a common component of commercial pH calibration solutions. This work shows that coextraction of H+ and a sample anion into the sensing membrane alone does not explain these super-Nernstian responses, even when membrane-internal diffusion potentials are taken into account. Instead, these super-Nernstian responses are explained by the formation of complexes between that anion and at least two protonated ionophore molecules. As demonstrated by experiments and explained with quantitative phase boundary models, the apparently super-Nernstian responses at low pH can be eliminated by restricting the molecular ratio of ionophore and ionic sites. Notably, this conclusion results in recommendations for the optimization of sensing membranes that, in some instances, will conflict with previously reported recommendations from the ionic site theory for the optimization of the lower detection limit. This mechanistic insight is key to maximizing the response range of these ionophore-based ISEs.

Increasing the Sensitivity of pH Glass Electrodes with Constant Potential Coulometry at Zero Current.

It has recently become possible to increase the sensitivity of ion-selective electrodes (ISEs) by imposing a constant cell potential, allowing one to record current spikes with a capacitor placed in series in the circuit. The approach requires a transient current to pass through the measurement cell, which unfortunately may introduce measurement errors and additionally excludes the use of high-impedance indicator electrodes, such as pH glass electrodes. We present here an electronic circuit that overcomes these limitations, where the cell is measured at zero current in combination with a voltage follower, and the current spike and capacitor charging occur entirely within the instrument. The approach avoids the need for a counter electrode, and one may use any electrode useful in potentiometry regardless of its impedance. The characteristics of the circuit were found to approach ideality when evaluated with either an external potential source or an Ag/AgCl electrode. The current may be linearized and extrapolated to further reduce the measurement time. The circuit is further tested with the most common yet very challenging electrode, the pH glass electrode. A precision of 64 μpH was obtained for 0.01 pH change up to 0.05 from a reference solution. Similar pH changes were also measured reliably further away from the reference solution (0.5-0.55) and resulted in a precision of 377 μpH. The limitations of this experimental setup were explored by performing pH calibrations within the measuring range of the probe.

Wireless and battery-free wearable biosensing of riboflavin in sweat for precision nutrition

Nutrition assessment is crucial for dietary guidance and prevention of malnutrition. Recent endeavors in wearable biochemical sensors have enabled real-time, in situ analysis of nutrients in sweat. However, the monitoring of riboflavin, an indispensable vitamin B involved in energy metabolism, remains challenging due to its trace level and variations in the sweat matrix. Herein, we report a wireless, battery-free, and flexible wearable biosensing system for the in situ monitoring of sweat riboflavin. Highly sensitive and selective electrochemical voltammetric detection is realized based on the synergistic effect of electrodeposited reduced graphene oxide (rGO) and platinum nanoparticles (PtNPs) with a low detection limit of 1.2 nM. The fully integrated system is capable of sweat sampling with the microfluidic patch, real-time riboflavin analysis and pH calibration with the flexible electrode array, as well as wirelessly simultaneous near field communication (NFC) energy harvesting and data transmission with the flexible circuit and a smartphone. On-body human sweat analysis demonstrates high accuracy cross-validated with gold-standard measurements, and reveals a strong correlation between sweat and urine riboflavin levels. The proposed wearable platform opens up attractive possibilities for noninvasive nutrient tracking, providing strong potential for personalized dietary guidance towards precision nutrition.

BrGDGT lipids in cold regions reflect summer soil temperature and seasonal soil water chemistry

The distribution of brGDGT lipids produced by soil bacteria has been used to reconstruct temperatures in marine and terrestrial settings as far back as the Cretaceous period. However, modern calibrations of this proxy have primarily relied on air rather than in situ soil temperatures, which can differ by more than 10 °C. Furthermore, the influence of other parameters such as temperature seasonality and soil chemistry on brGDGT lipids is not fully understood. We measured brGDGT distributions, in situ soil temperatures, pH, soil water content, and electrical conductivity on soils from the Eastern Canadian Arctic and Iceland. We compiled our results with those of published soil brGDGT studies that also provide in situ soil temperatures and ancilliary measurements and generated global temperature and pH calibrations from the resulting dataset. Soil temperatures outperformed air temperatures in these calibrations, with mean summer soil temperature providing the highest-performing fit among the 10 tested soil temperature parameters. When applied to a loess/paleosol sequence from the Chinese Loess Plateau, these new calibrations produced paleotemperature and paleo-pH histories consistent with the results of previous studies, encouraging the application of our new calibrations on a broader scale. We also detected 7-methyl and IIIa’’ brGDGT isomers in our Eastern Canadian Arctic and Iceland soils, which have been shown in lakes to relate to salinity and anoxia, respectively. While neither correlated with bulk soil properties such as conductivity, soil water content, or pH, these brGDGT isomers did correlate with seasonality and winter soil temperature. We hypothesize that these compounds are generated in winter by bacteria in habitable niches of more saline, sometimes anoxic liquid water in the otherwise frozen soil matrix. Finally, we report the presence of overly branched GDGTs with m/z = 1064 and suggest that these heptamethylated tetraethers should be investigated as a potential tool for improving brGDGT calibrations. Overall, our results expand our understanding of the seasonality of brGDGT production, especially at high latitudes, and provide in situ soil temperature and pH calibrations for global use.

Orbital CO2 reconstruction using boron isotopes during the late Pleistocene, an assessment of accuracy

Abstract. Boron isotopes in planktonic foraminifera are a widely used proxy to determine ancient surface seawater pH and by extension atmospheric CO2 concentration and climate forcing on geological timescales. Yet, to reconstruct absolute values for pH and CO2, we require a δ11Bforam-borate to pH calibration and independent determinations of ocean temperature, salinity, a second carbonate parameter, and the boron isotope composition of seawater. Although δ11B-derived records of atmospheric CO2 have been shown to perform well against ice-core-based CO2 reconstructions, these tests have been performed at only a few locations and with limited temporal resolution. Here we present two highly resolved CO2 records for the late Pleistocene from Ocean Drilling Program (ODP) Sites 999 and 871. Our δ11B-derived CO2 record shows a very good agreement with the ice core CO2 record with an average offset of 13±46 (2σ) and an RMSE of 26 ppm, with minor short-lived overestimations of CO2 (of up to ∼50 ppm) occurring during some glacial onsets. We explore potential drivers of this disagreement and conclude that partial dissolution of foraminifera has a minimal effect on the CO2 offset. We also observe that the general agreement between δ11B-derived and ice core CO2 is improved by optimising the δ11Bforam-borate calibration. Despite these minor issues, a strong linear relationship between relative change in climate forcing from CO2 (from ice core data) and pH change (from δ11B) exists over the late Pleistocene, confirming that pH change is a robust proxy of climate forcing over relatively short (<1 million year) intervals. Overall, these findings demonstrate that the boron isotope proxy is a reliable indicator of CO2 beyond the reach of the ice cores and can help improve determinations of climate sensitivity for ancient time intervals.

Diel Variation in Phytoplankton Biomass Driven by Hydrological Factors at Three Coastal Monitoring Buoy Stations in the Taiwan Strait

To investigate the diurnal variation in phytoplankton biomass and its regulating factors during the diurnal cycle, we conducted in situ observations in June 2018 at three buoy stations, including Douwei Buoy Station, Minjiang Estuary Buoy Station, and Huangqi Buoy Station on the western side of the Taiwan Strait. The calibration of buoy sensor data, including temperature, salinity, dissolved oxygen, pH, chlorophyll, and phycoerythrin, was conducted simultaneously. In addition, water sampling was conducted to measure chlorophyll a and phycoerythrin concentrations at hourly time intervals. The results showed that the 24 h cumulative chlorophyll a concentration order for the buoys was Minjiang Estuary (10.280 μg/L) > Huangqi (7.411 μg/L) > Douwei (4.124 μg/L). The Minjiang Estuary had a lower nighttime biomass proportion than Douwei and Huangqi. The diurnal variation in phytoplankton was jointly regulated by water masses, tides, and light. There were three response patterns, including the “light trumps tidal influences” pattern at Douwei, the “Low-tide, High-biomass” pattern at Minjiang Estuary, and the “High-tide, High-biomass” pattern at Huangqi. The prediction of algal blooms and hypoxia using buoy monitoring needs to be based on seasonal water mass background and tidal influence.

Fe Single-Atom Nanozyme-Modified Wearable Hydrogel Patch for Precise Analysis of Uric Acid at Rest.

Resting sweat analysis could provide unique insight into the metabolic levels of physiological and pathological states. However, the low secretion rate of resting sweat and the low concentration of metabolic molecules pose challenges for the development of noninvasive wearable sensors. Here, we demonstrated a wearable patch for the precise analysis of uric acid at rest. Fe single-atom nanozymes (FeSAs) with excellent electrocatalytic activity were used to develop a sensor for selective catalysis of uric acid (UA, 1-425 μM), and the catalytic mechanism of UA was later explored by density functional theory. In addition, polyaniline was integrated into the wearable patch for pH detection; thus, accurate analysis of sweat UA molecules can be achieved by pH calibration. Then, we explored the possibility of collecting resting sweat with different ratios of agarose hydrogels to reduce the sweat accumulation time. Finally, the possibility of a wearable patch for accurate UA detection in volunteer sweat samples was experimentally verified. We believe that our work provides novel insights and ideas for the analysis of resting sweat using wearable devices, further driving advancements in the field of personalized medicine.

Tumor pH Imaging Using Chemical Exchange Saturation Transfer (CEST)-MRI.

Magnetic resonance imaging (MRI) is a noninvasive imaging technique that allows for physiological and functional studies of the tumor microenvironment. Within MRI, the emerging field of chemical exchange saturation transfer (CEST) has been largely exploited for assessing a salient feature of all solid tumors, extracellular acidosis. Iopamidol-based tumor pH imaging has been demonstrated to provide accurate and high spatial resolution extracellular tumor pH maps to elucidate tumor aggressiveness and for assessing response to therapy, with a high potential for clinical translation. Here, we describe the overall setup and steps for measuring tumor extracellular pH of tumor models in mice by exploiting MRI-CEST pH imaging with a preclinical MRI scanner following the administration of iopamidol. We address issues of pH calibration curve setup, animal handling, pH-responsive contrast agent injection, acquisition protocol, and image processing for accurate quantification and visualization of tumor acidosis.

A Novel Method for Understanding the Mixing Mechanisms to Enable Sustainable Manufacturing of Bioinspired Silica.

Bioinspired silica (BIS) has received unmatched attention in recent times owing to its green synthesis, which offers a scalable, sustainable, and economical method to produce high-value silica for a wide range of applications, including catalysis, environmental remediation, biomedical, and energy storage. To scale-up BIS synthesis, it is critically important to understand how mixing affects the reaction at different scales. In particular, successful scale-up can be achieved if mixing time is measured, modeled, and kept constant across different production scales. To this end, a new image analysis technique was developed using pH, as one of the key parameters, to monitor the reaction and the mixing. Specifically, the technique involved image analysis of color (pH) change using a custom-written algorithm to produce a detailed pH map. The degree of mixing and mixing time were determined from this analysis for different impeller speeds and feed injection locations. Cross validation of the mean pH of selected frames with measurements using a pH calibration demonstrated the reliability of the image processing technique. The results suggest that the bioinspired silica formation is controlled by meso- and, to a lesser extent, micromixing. Based on the new data from this investigation, a mixing time correlation is developed as a function of Reynolds number-the first of a kind for green nanomaterials. Further, we correlated the effects of mixing conditions on the reaction and the product. These results provide valuable insights into the scale-up to enable sustainable manufacturing of BIS and other nanomaterials.

Noninvasive assessment of renal dynamics and pH in a unilateral ureter obstruction model using DCE MR-CEST urography.

To assess the potential of DCE MR CEST urography for assessing renal function in mice with unilateral ureter obstruction (UUO) by simultaneous pH and renal uptake/clearance measurements following injection of iopamidol. The right ureter of nine mice was obstructed via suture ligation. The animals were imaged at day 1, 2, and 3 post-obstruction on an 11.7T MRI scanner. Ninety-six sets of saturated CEST images at 4.3 and 5.5ppm were collected. Renal pH values were obtained by calculating the signal ratio for these two frequencies and using a pH calibration curve. Renal time activity curves were measured as a percentage change in the post-injection CEST signal at 4.3ppm relative to the average pre-injection signal. For the healthy mice, the time activity curves of both kidneys were nearly identical and displayed rapid excretion of contrast. For the UUO mice, the dynamic CEST curves for the obstructed kidneys displayed prolonged time to peak (TTP) values and delayed contrast excretion compared with the contralateral (CL) kidneys. Renal pH maps of the healthy animals showed similar acidic values for both kidneys (pH6.65 ± 0.04 vs 6.67 ± 0.02), whereas in the obstructed kidneys there was a significant increase in pH values compared with the CL kidneys (pH6.67 ± 0.08 vs 6.79 ± 0.11 in CL and UUO kidneys, respectively). Our findings indicate that DCE-MR-CEST urography can detect changes in renal uptake/excretion and pH homeostasis and distinguish between obstructed and unobstructed kidney as early as 1 day after UUO.

Two birds with one stone: Visual colorful assessment of dipicolinic acid and Cu2+ by Ln-MOF hybrid attapulgite nano-probe

The poor solubility of Ln-MOF fluorescent nano-probe in water significantly limited their practical application. At the same time, the determination of target analytes is mostly carried out in buffer solution, but the preparation of buffer solution and pH calibration often bring inconvenience to the test. In this work, a bifunctional fluorescent nano-probe (ATP@Eu:Tb-MOF) was constructed at room temperature through one-step method using inorganic nanoclays ATP and Ln-MOF, which recognized anthrax biomarker DPA and Cu2+ in commercially pure drinking water. This nano-probe achieved visual detection of DPA with ultra-high sensitivity (LOD-DPA = 8.82 nM), excellent selectivity to DPA isomers and high reliability in the detection of DPA released by Bacillus subtilis. In addition, the probe can also selectively detect Cu2+ through the “turn-off” pathway with a high sensitivity (LOD-Cu2+ = 6.94 nM). Intelligent visual monitoring was realized by fast reading and analyzing the RGB values of the color changing images of the paper-based nano-probe using smartphone color scanning APP. Furthermore, thin-film-based luminescent nanoprobe can also make excellent visual color assessment of DPA and Cu2+, and advanced logic gate circuit analytical devices were also designed.

Robust Dual Optical Sensor for pH and Dissolved Oxygen

As part of moving our optical pH and dissolved oxygen (DO) optical chemosensors toward industrial applications, we decided to explore a many-sensors-in-one principle. It was tested if physical segregation of the optical sensor components in a single sensor polymer could remove cross-talk and quenching. It was found that a design concept with an oxygen-responsive dye in polymer nanoparticles and a pH-responsive dye in an organically modified siloxane polymer resulted in a robust pH/O2 dual optical sensor. Individually, the O2-sensitive nanoparticles, a known component for optical DO sensing, and the pH sensor are operational. Thus, it was decided to test if nanoparticles enclosed within the pH-sensitive responsive sol-gel (i) could work together if segregated and (ii) could operate with a single intensity signal that is without a reference signal; developments within industrial optical sensor technology indicate that this should be feasible. The prototype optode produced in this work was shown to have a negligible drift over 60 h, bulk diffusion-limited DO response, and independent response to pH and O2. On the individual optode, pH calibration was found to show the expected sigmoidal shape and pKa, while the complexity of the calibration function for the DO signal was significant. While the engineering of the sensor device, optics, and hardware are not robust enough to attempt generic sensor calibration, it was decided to demonstrate the design concept in simple fermentation experiments. We conclude that the dual sensor design with the physical segregation of components is viable.

The distribution of intact polar lipid-derived branched tetraethers along a freshwater-seawater pH gradient in coastal East China Sea

In view of the application of microbial branched tetraether lipids (i.e., brGDGTs) in terrestrial pH reconstructions, their potential as seawater pH proxy is investigated from the Yangtze River Estuary (YRE) to the shelf region in the East China Sea (ECS). BrGDGTs occurring as ‘fossil’ core and in ‘living’ intact polar lipids (CL-brGDGTs and IPL-brGDGTs, respectively) in surface sediments are separately analyzed. The results show that riverine IPL-brGDGTs are rapidly lost at the transition from the YRE to the marine settings and sedimentary IPL-brGDGTs are predominantly produced in situ in brackish water environments. Among environmental parameters, surface water pH is a determinant factor controlling the cyclization of IPL-brGDGTs, with higher cyclization at higher pH. Hereby, two IPL-brGDGTs-based seawater pH calibrations are established in the brackish seawater environment in this study: surface pH = 7.28 + 1.08 × #Ringstetra (n = 18, r2 = 0.87, RMSE = 0.05, p < 0.01) and surface pH = 7.13 + 3.82 × f(Ic) + 4.29 × f(IIb') + 4.21 × f(IIIa) (n = 18, r2 = 0.90, RMSE = 0.04, p < 0.01), which are different from those established in terrestrial environments. This is the first work demonstrating that in situ produced microbial brGDGTs can trace seawater pH change in marine environment, which makes it promising to apply brGDGTs for seawater pH reconstructions in marine settings where the terrestrial inputs are negligible.

MOrange2, a Genetically Encoded, pH Sensitive Fluorescent Protein, is an Alternative to BCECF-AM to Measure Intracellular pH to Determine NHE3 and DRA Activity.

NHE3 (Na+/H+ exchanger3) and SLC26A3 (Cl-/HCO3- exchanger, DRA) are the major components of the intestinal neutral NaCl absorptive process and based on the intestinal segment, contribute to HCO3- absorption and HCO3- secretion. NHE3 and DRA are highly regulated by changes in second messengers, cAMP, cGMP and Ca2+. Precise and convenient measurement of exchanger activity is necessary to allow rapid study of physiologic and pharmacologic functions. Some epithelial cells are difficult to load with AM ester dyes and loading may not be uniform. The use of a genetically modified fluorescent protein, mOrange2 was explored as an intracellular pH sensor protein to measure exchange activity of NHE3 and DRA. The model used was FRT cells stably expressing NHE3 or DRA with intracellular pH measured by changes of mOrange2 fluorescence intensity. Intracellular pH was monitored using a) Isolated single clones of FRT/mOrange2/HA-NHE3 cells studied in a confocal microscope with time-lapse live cell imaging under basal conditions and when NHE3 was inhibited by exposure to forskolin and stimulated by dexamethasone, b) coverslip grown FRT/mOrange2 cells expressing NHE3 or DRA using a computerized fluorometer with a perfused cuvette with standardization of the mOrange2 absorption and emission signal using K+/Nigericin as an internal standard in each experiment. A similar rate of intracellular alkalization by Na+ addition in cells expressing NHE3 and by Cl- removal in cells expressing DRA was found in mOrange2 expressing cells compared to the same cells loaded with BCECF-AM, both using the same pH calibration with K+/Nigericin. Using mOrange2 as the pH sensor, NHE3 basal activity was quantitated and shown to be inhibited by forskolin and stimulated by dexamethasone, and DRA was oppositely shown to be stimulated by forskolin, responses similar to results found using BCECF-AM. This study demonstrates that mOrange2 protein can be an effective alternate to BCECF-AM in measuring intracellular pH (preferred setting Ex520nm, Em 563nm) as affected by NHE3 and DRA activity, with the advantage, compared to AM ester dyes, that genetic expression can provide uniform expression of the pH sensor.

IOT based Vertical Farming using PH calibration and controlling

IOT based Vertical Farming using PH calibration and controlling

Janus Hydrogel Microbeads for Glucose Sensing with pH Calibration.

We present fluorescent Janus hydrogel microbeads for continuous glucose sensing with pH calibration. The Janus hydrogel microbeads, that consist of fluorescent glucose and pH sensors, were fabricated with a UV-assisted centrifugal microfluidic device. The microbead can calibrate the pH values of its surroundings and enables accurate measurements of glucose within various pH conditions. As a proof of concept, we succeeded in obtaining the accurate value of glucose concentration in a body-fluid-like sample solution. We believe that our fluorescent microbeads, with pH calibration capability, could be applied to fully implantable sensors for continuous glucose monitoring.

Development of global temperature and pH calibrations based on bacterial 3-hydroxy fatty acids in soils

Abstract. Gram-negative bacteria produce specific membrane lipids, i.e. 3-hydroxy fatty acids with 10 to 18 C atoms. They have been recently proposed as temperature and pH proxies in terrestrial settings. Nevertheless, the existing correlations between pH or temperature and indices derived from 3-OH FA distribution are based on a small soil dataset (ca. 70 samples) and only applicable regionally. The aim of this study was to investigate the applicability of 3-OH FAs as mean annual air temperature (MAAT) and pH proxies at the global level. This was achieved using an extended soil dataset of 168 topsoils distributed worldwide, covering a wide range of temperatures (5 to 30 ∘C) and pH (3 to 8). The response of 3-OH FAs to temperature and pH was compared to that of established branched glycerol dialkyl glycerol tetraether (GDGT)-based proxies (MBT'5Me/CBT). Strong linear relationships between 3-OH-FA-derived indices (RAN15, RAN17 and RIAN) and MAAT or pH could only be obtained locally for some of the individual transects. This suggests that these indices cannot be used as palaeoproxies at the global scale using simple linear regression models, in contrast with the MBT'5Me and CBT. However, strong global correlations between 3-OH FA relative abundances and MAAT or pH were shown by using other algorithms (multiple linear regression, k-NN and random forest models). The applicability of the three aforementioned models for palaeotemperature reconstruction was tested and compared with the MAAT record from a Chinese speleothem. The calibration based on the random forest model appeared to be the most robust. It generally showed similar trends with previously available records and highlighted known climatic events poorly visible when using local 3-OH FA calibrations. Altogether, these results demonstrate the potential of 3-OH FAs as palaeoproxies in terrestrial settings.