Detection Of Low Levels Research Articles

A Review of Analytical Methods and Technologies for Monitoring Per- and Polyfluoroalkyl Substances (PFAS) in Water

Per- and polyfluoroalkyl substances (PFAS) consist of a range of manufactured fluorinated chemicals that are used in a variety of household and waterproofing products, industrial processes, and firefighting foams. In the past few years, there has been increasing concern about PFAS in the environment, since they are difficult to break down through natural processes, are highly persistent in humans, animals, soils and waters, and can travel long distances in surface and groundwater. This has created an increased need for PFAS analysis. Most PFAS monitoring currently takes place using field sampling and chromatographic analytical methods, which are laboratory-based and are very costly when used to monitor PFAS in the environment. Using a semi-systematic literature review approach, a comparative study is conducted in this article on the available analytical methods and sensor technologies that can be used to monitor and detect PFAS in the environment, including chromatographic, instrumentation analysis, and sensor-based methods. This study considered four critical factors for effective and efficient monitoring methods, which include the type of PFAS detected, removing background levels, determining detection limits, and identifying samples. In general, other analytical instruments are used in conjunction with chromatographic techniques for detecting both target and non-target analytes at a lower level of detection (LOD). It is shown that even though some sensor types have a low LOD, they are only useful for detecting targeted PFAS in water samples. However, sensors are an emerging technology that could be developed to enable low-cost, portable methods for the remote detection of PFAS species on-site.

A Novel Validated HS-GC-MS method for the trace level determination of Acetyl chloride as Isopropyl acetate in various anti-cancer drug substances

A novel, simple and precise headspace gas chromatography-mass spectrometry (HS-GC-MS) method was developed and validated for the determination of acetyl chloride (AC) in various anti-cancer drug substances like bendamustine HCl, Ibrutinib, trifluridine and abemaciclib drug substances. In this methodology, AC reacts with isopropyl alcohol and is converted into isopropyl acetate. Hence AC is quantified as Isopropyl acetate. The lower level of detection was achieved on the capillary GC column (DB-624, Fused silica capillary column; 30 m length; 0.32 mm internal diameter, coated with 6% Cyanopropylphenyl and 94% dimethyl polysiloxane stationary phase of 1.8 μm film thickness) with electron impact ionization (EI) technique by GC-MS in selective ion monitoring (SIM) mode. The mass ions were selected for the quantifier is 63 and the qualifier is 87 for isopropyl acetate. The performance of the method was assessed by evaluating the specificity, linearity, sensitivity, precision, accuracy and robustness experiments. The established limit of detection and limit of quantification values for the AC were 0.1 and 0.3 μg/g, respectively. This developed method was found to be linear with a correlation coefficient is greater than 0.999 for all four drug substances. The average recoveries of AC in bendamustine HCl, ibrutinib, trifluridine and abemaciclib were obtained 106.1, 109.0, 97.4 and 101.6%, respectively. The proposed method was validated successfully as per ICH guidelines. Hence, the proposed method can be routinely used for the quantification of AC in various anti-cancer drug substances.

Analytical sensitivity of a method is critical in detection of low-level BRCA1 constitutional epimutation

Recent reports based on a substantial number of cases, warrant need for population-based research to determine implications of constitutional methylation of tumor suppressor genes such as BRCA1 occurring in healthy tissue in the prediction of cancer. However, the detection of the constitutional methylation in DNA extracted from blood has already been shown to be technologically challenging, mainly because epimutations appear to be present in blood at a very low level. The analytical sensitivity required for low-level methylation detection can be provided by NGS, but this technique is still labor and cost-intensive. We assessed if PCR-based MS-HRM and BeadChip microarray technologies, which are standardized and cost-effective technologies for methylation changes screening, provide a sufficient level of analytical sensitivity for constitutional BRCA1 methylation detection in blood samples. The study included whole blood samples from 67 healthy women, 35 with previously confirmed and 32 with no detectable BRCA1 promoter methylation for which we performed both MS-HRM based BRCA1 gene methylation screening and genome wide methylation profiling with EPIC microarray. Our results shown, that low-level BRCA1 methylation can be effectively detected in DNA extracted from blood by PCR-based MS-HRM. At the same time, EPIC microarray does not provide conclusive results to unambiguously determine the presence of BRCA1 constitutional methylation in MS-HRM epimutation positive samples. The analytical sensitivity of MS-HRM is sufficient to detect low level BRCA1 constitutional epimutation in DNA extracted from blood and BeadChip technology-based microarrays appear not to provide that level of analytical sensitivity.

DETERMINATION OF CHANGES IN VITAMIN D, FOLIC ACID AND VITAMIN B12 LEVELS IN PATIENTS PRESENTING TO THE EMERGENCY DEPARTMENT AFTER SUICIDAL INTERVENTIONS

ABSTRACT
 
 Introduction: Depression is a psychological and physiological destruction process. In recent years, it has been one of the leading causes of public health problems in our country and in the world. Patients with depressive mood are at a higher risk compared to the normal population in terms of realizing suicidal ideation. Since the first place of application after a suicide attempt is usually the emergency services, the studies carried out in the ED are extremely important in this sense.
 Methods: Data in the study were analyzed using SPSS Data:23.0 (SPSS Inc., Chicago, Illinois, USA). Continuous variables were expressed as mean ± standard deviation (SD). In the evaluation of the data, the significance test of the difference between the two means (Independent t test) was used when the parametric test assumptions were fulfilled, and the Man Whitney U test was used when the parametric test assumptions were not fulfilled.
 Results: In our study, we compared the levels of vitamin D, folic acid and vitamin B12 in patients who applied to the emergency department after a suicide attempt with the normal population. Vitamin D and vitamin B12 levels were found to be significantly lower in the patient group compared to the control group.
 Conclusions: Our current clinical study supports many studies in the literature, with the detection of low levels of vitamin D and vitamin B12 after the examinations of the patient group who came to the emergency room with a depressive episode and the control group.

High voltage response of graphene/4H-SiC UV photodetector with low level detection

A self-powered graphene/silicon carbide (G/4H-SiC) ultraviolet photodetector of a p-i-n like-structure with high voltage response has been fabricated to detect and measure low intensity ultraviolet (UV) radiation. Bilayer graphene sheet grown by chemical vapor deposition (CVD) method was transferred on the top of an epilayer structure of n-/n+ 4 H-SiC. In this structure, two Schottky contacts were formed: one at G/ n- 4H-SiC interface and the other at bulk-4 H-SiC/Cr/Au interface. The photodetector's characteristic measurements revealed low dark current of ∼ 0.58 nA and spectral voltage responsivity of ∼ 0.75 V/W at 300 nm wavelength. Under low level UV illumination of 300 nm wavelength, the photodetector exhibited a leakage current and a photogenerated response voltage of 1.1 nA and 10 mV, respectively. The time-dependent photovoltage measurements displayed a rapid photovoltage response with rise and decay times of ∼74 ns and ∼ 580 ns, respectively. This novel device holds promise for applications requiring sensitive and self-powered UV detection.

Gold-coated tilted fiber Bragg gratings for lead ion sensing.

Surface plasmon resonance sensor based on gold-coated tilted fiber Bragg gratings (SPR-TFBGs) are perfectly suited for fine refractometry. Thanks to the functionalization of the gold layer, they can be used for label-free biosensing. They have been largely used for the specific detection of proteins and cells. In this work, we experimentally demonstrate that they are enough sensitive to detect a very small entity like an environmental pollutant. In this context, we report here a bio-functionalization of the SPR-TFBG with thrombin aptamers for lead ion detection. We used aqueous solutions of lead ions with increasing concentrations from 0.001 ppb to 10 ppb. Based on the affinity bending of Pb2+ ions to the thrombin aptamer, we experimentally demonstrated low detection level of lead ion concentration (0.001 ppb) while the saturation limit is meanly fixed by the physical dimension of the sensor and the binding efficiency.

Electrochemical determination of Vitamin B6 using coral-like MnO2-Pi on Ti3C2Tx MXene

MXenes are 2D nanomaterials that are considered the materials of the future generation due to their high electrical conductivity, good biocompatibility, and ease of functionalization. This research work reports the electrochemical sensing of Vitamin B6 using the Manganese dioxide-inorganic phosphate/MXene brush-coated Carbon fiber paper electrode (MnO2-Pi/MXene/CFP) electrode for the first time. The three-dimensional Ti3C2Tx MXene nanosheets consisting of highly ordered, vertically aligned nanosheets with electrochemically deposited MnO2-Pi are capable of yielding a synergistic effect in combination with high electrochemical performance and large surface area of MnO2-Pi. The reported electrochemical sensor exhibited a wide linear dynamic range (0.06–650 µM) and a low-level detection limit of 0.021 µM. An increase in the anodic peak current confirms the rapid transfer of electrons transfer arising between the Ti3C2Tx MXene and MnO2-Pi. The results attained substantiate that the fabricated sensor has enhanced selectivity, reproducibility, and stability toward the electrochemical determination of Vitamin B6 in real samples.

Estimation of Tritium Concentration in the Rain- and Groundwater in the Dry River of Hafr Al Batin, Saudi Arabia

Natural tritium is widely dispersed in the environment, leading to human exposure to tritium through water ingestion, inhalation of tritium gas, and absorption through the skin. High levels of tritium in the environment can pose significant health risks due to the potential carcinogenic effects of tritium. Therefore, this study aims to estimate the tritium concentration in spiked water, rainwater, and groundwater by a liquid scintillation counter (LSC). Due to the lower detection levels of the LSC, an enrichment process of tritium ten- to thirtyfold was carried out using the electrolysis process. The enriched water was then analyzed to estimate the tritium concentration. Five reference samples were prepared by diluting a standard with known concentrations (spiked sample) to verify the precision of the measurement technique. The estimated tritium levels of the rainwater and the groundwater were within the 0.3 to 3.5 tritium units (TU) range. A comparatively higher tritium concentration was estimated for the shallow wells in the lower valley of the monitored areas. However, relatively lower concentrations were detected for wells located in the hillside areas. These findings will assist regulatory authorities in formulating strategies to ensure public safety by mitigating human exposure to tritium.

DiffReplication - An Energy-Aware Fault Tolerance Model for Silent Error Detection and Mitigation in Heterogeneous Extreme-scale Computing Environment

At extreme scale, the frequency of silent errors – a class of errors that remain undetected by low-level error detection mechanisms – increases significantly with the computational complexity of the application and the scale of the computing infrastructure. As hardware and software advances are made to usher in the next scientific era of computing, developing new approaches to mitigate the impact of silent errors remains a challenging problem. In this work, we propose an energy-aware fault-tolerance model, referred to diffReplication to overcome silent errors. In the proposed model, the main process is associated with one replica that executes at the same rate as the main process, and one diffReplica that is executed at a fraction of the main process' execution rate. If the main and its replica reach consensus at the end of a computation phase, the state of the diffReplica is updated and computation is resumed. If the synchronization attempt results in a disagreement, however, the diffReplica increases its execution speed to complete the computation and quickly reach the synchronization barrier. Assuming a single error over any given synchronization interval, a majority voting is used to reach consensus and tolerate silent errors. To further enhance its performance, diffReplication is augmented with speculative execution, whereby the main or its fast replica is selected to continue execution without waiting for the diffReplica. The selection process is based on the previous behaviour of the main and its replica. A performance analysis study is carried out to assess the performance of diffReplication, in terms of the energy saving and time-to-completion reduction achieved by the diffReplication scheme. The experiment shows that speculative execution reduces the time to completion with additional energy, and dynamic decision-making balances the energy consumption and time to completion. 

3D Printing for Cancer Diagnosis: What Unique Advantages Are Gained?

Cancer is a complex disease with global significance, necessitating continuous advancements in diagnostics and treatment. 3D printing technology has emerged as a revolutionary tool in cancer diagnostics, offering immense potential in detection and monitoring. Traditional diagnostic methods have limitations in providing molecular and genetic tumor information that is crucial for personalized treatment decisions. Biomarkers have become invaluable in cancer diagnostics, but their detection often requires specialized facilities and resources. 3D printing technology enables the fabrication of customized sensor arrays, enhancing the detection of multiple biomarkers specific to different types of cancer. These 3D-printed arrays offer improved sensitivity, allowing the detection of low levels of biomarkers, even in complex samples. Moreover, their specificity can be fine-tuned, reducing false-positive and false-negative results. The streamlined and cost-effective fabrication process of 3D printing makes these sensor arrays accessible, potentially improving cancer diagnostics on a global scale. By harnessing 3D printing, researchers and clinicians can enhance early detection, monitor treatment response, and improve patient outcomes. The integration of 3D printing in cancer diagnostics holds significant promise for the future of personalized cancer care.

3D printed Fabry-Perot acoustic probe with a glass horn tube

Sensing an incoming acoustic signal is typically associated with absorbing the energy, perturbing the measurement and therefore causing a deformation of the sensing elements, which is mainly related to the acoustic wave pressure. Here, we demonstrated a fiber-tip based Fabry-Perot (FP) acoustic probe sensor, which was directly printed on an optical fiber tip by a two-photon 3D printing technique and assembled by a glass horn structure, which can improve the sensitivity. It showed that the sensor has a −3 dB bandwidth of 366.05 kHz at the first resonant frequency of 467.84 kHz. A low noise-limited minimum detectable pressure level of 4.71 mPa/Hz1/2@100 kHz is obtained. Due to the acoustic wave focusing property of the horn structure, the detected signal intensity can be amplified by 4 times as the sensor located at the bottom position. It demonstrates that 3D printed micro acoustic devices could be used for weak acoustic wave detection in the applications of partial discharge, photoacoustic imaging and non-destructive detection.

Matched or moved? Asymmetry in high- and low-level visual processing of motion events

AbstractConsensus on the extent to which cross-linguistic differences affect event cognition is currently absent. This is partly because cognitive influences of language have rarely been examined within speakers of different languages in tasks that manipulate the level of visual processing. This study presents a novel combination of a high-level approach upregulating the involvement of language, namely self-paced sentence-video verification, and a low-level visual detection method without language use, namely breaking continuous flash suppression (b-CFS) (Yang et al., 2014). The results point to cross-linguistic effects on event cognition by revealing variations in visual processing patterns of manner and path by English versus Mandarin Chinese speakers. Language specificity was found on both levels of processing. An asymmetry in response speed across tasks highlights an important difference between facilitation of detecting contrasts when recruitment of verbal labels is automatic, versus facilitation of verifying correspondences when labels are overt.

Electrochemical Detection of Furaltadone Antibiotic Drug by the Rare Earth Metal Tungstate Decorated Screen Printed Carbon Electrode

Furaltadone (FLD) is an antibiotic drug that is widely treated for coccidiosis, intestinal infection, and turkey blackhead. Moreover, excessive use of FLD may have some negative consequences for humans and domestic animals. Therefore, practical, sensitive, selective, and facile detection of FLD is still needed. In this exploration, a Eu2(WO4)3-nanoparticles-modified screen-printed carbon electrode was developed for the low-level detection of FLD. Hydrothermal techniques were used effectively to prepare the Eu2(WO4)3 complex. Scanning electron microscopy and X-ray diffraction investigations were used to confirm the Eu2(WO4)3. The results revealed that the Eu2(WO4)3 was well formed, crystalline, and uniformly distributed. Furthermore, the electrochemical behavior of the SPCE/Eu2(WO4) electrode was examined by differential pulse voltammetry and cyclic voltammetry studies. The SPCE/Eu2(WO4) electrode demonstrated improved electrocatalytic activity in the detection of FLD with a detection limit of 97 µM (S/N = 3), linear range of 10 nM to 300 µM, and sensitivity of 2.1335 µA µM−1 cm−2. The SPCE/Eu2(WO4) electrode detected FLD in the presence of 500-fold excess concentrations of other interfering pollutant ions. The practical feasibility of the SPCE/Eu2(WO4) electrode was tested on different antibiotic medicines and showed adequate recovery. Moreover, the SPCE/Eu2(WO4) electrode shows appreciable repeatability, high stability, and reproducibility.

Low level detection of acetone vapor by improvised design of high “Q” tunable frequency Helmholtz photoacoustic cell using UV, mid- IR and THz sources

The paper reports the designing and fabrication aspects of a high “Q = 492.3” Helmholtz photoacoustic (PA) cell employed for the trace level detection of acetone, a biomarker by using 266 nm- UV, Mid-IR (5.4–10.6 micron) and 0.11 Terahertz (THz) sources. The designed Helmholtz PA cell is made of Aluminum and possesses a natural frequency tunable between 1.4 to 4.4 kHz range using a movable piston arrangement of the microphone sensor. Numerous types of disorders, including diabetes, asthma, lung cancer, etc., can be diagnosed using the acetone concentration obtained through breath analysis. The comparative study is related to the response of different types of excitation mechanisms contributed by electronics, vibrational and rotational modes of acetone. The low-level detection (LoD) limit for acetone is of the order of 5.06 & 7.92 ppbV, and 15.3 pptV, respectively, in UV, Mid-IR, and THz region. This study contributes to the development of a highly sensitive, non-invasive acetone detection and quantification modality.

Biosensor development for low-level acetaldehyde gas detection using mesoporous carbon electrode printed on a porous polyimide film

Acetaldehyde, which is an intermediate product of alcohol metabolism, is known to induce symptoms, including alcohol flushing, vomiting, and headaches in humans. Therefore, real-time monitoring of acetaldehyde levels is crucial to mitigating these health issues. However, current methods for detecting low-concentration gases necessitate the use of complex measurement equipment. In this study, we developed a low-cost, low-detection-limit, enzyme-based electrochemical biosensor for acetaldehyde gas detection that does not require sophisticated equipment. The sensor was constructed by screen-printing electrodes onto a porous polyimide film, using grafted MgO-templated carbon (GMgOC) as working electrode material, carbon for the counter electrode, and silver/silver chloride for the reference electrode. Pyrroloquinoline-quinone-dependent aldehyde dehydrogenase was immobilized on the working electrode, and a chamber was attached to the electrode chip and filled with 1-methoxy-5-methylphenazinium methyl sulfate solution. The sensor can be used to measure acetaldehyde gas concentrations from 0.02 to 0.1 ppm, making it suitable for monitoring human skin gas. This low detection limit was achieved by delivering the analyte through the porous polyimide film on which the electrodes were printed and accumulating acetaldehyde in the mesoporous GMgOC of the working electrode. This mechanism suggests that this sensor design can be adapted to develop other low-detection limit gas sensors, such as those for screening skin gas biomarkers.

Wearable microneedle-based colorimetric and fluorescence sensing for transdermal diagnostics

Interstitial fluid is a readily accessible source of biomarkers for various diseases, providing a less invasive and more convenient option than traditional blood or tissue sampling methods. Microneedle-based point-of-care testing devices have gained significant interest due to their potential for direct detection of target analytes in ISF, accomplished through minimally invasive penetration of the stratum corneum. Thus, microneedle-based devices can be considered as adhesive tools for diagnostic sensing and therapeutic drug administration. Microneedle-based colorimetric and fluorescence sensing has the potential to revolutionize disease diagnosis and monitoring, offering a rapid, highly sensitive, specific, and cost-effective alternative to traditional methods. These devices enable the detection of low levels of biomarkers in the collected fluid, which is particularly important in situations requiring prompt diagnosis and treatment. This review covers the types of microneedles and their fabrication methods, the detection principles of microneedle-based colorimetric and fluorescence sensing, as well as their key applications, advantages, and limitations. Additionally, the review explores ways to overcome current limitations and improve the performance, as well as future perspectives for the development of microneedle-based devices.

Divergent adaptive immune responses define two types of long COVID.

The role of adaptive immune responses in long COVID remains poorly understood, with contrasting hypotheses suggesting either an insufficient antiviral response or an excessive immune response associated with inflammatory damage. To address this issue, we set to characterize humoral and CD4+ T cell responses in long COVID patients prior to SARS-CoV-2 vaccination. Long COVID patients who were seropositive (LC+, n=28) or seronegative (LC-, n=23) by spike ELISA assay were recruited based on (i) an initial SARS-CoV-2 infection documented by PCR or the conjunction of three major signs of COVID-19 and (ii) the persistence or resurgence of at least 3 symptoms for over 3 months. They were compared to COVID patients with resolved symptoms (RE, n=29) and uninfected control individuals (HD, n=29). The spectrum of persistent symptoms proved similar in both long COVID groups, with a trend for a higher number of symptoms in the seronegative group (median=6 vs 4.5; P=0.01). The use a highly sensitive S-flow assay enabled the detection of low levels of SARS-CoV-2 spike-specific IgG in 22.7% of ELISA-seronegative long COVID (LC-) patients. In contrast, spike-specific IgG levels were uniformly high in the LC+ and RE groups. Multiplexed antibody analyses to 30 different viral antigens showed that LC- patients had defective antibody responses to all SARS-CoV-2 proteins tested but had in most cases preserved responses to other viruses. A sensitive primary T cell line assay revealed low but detectable SARS-CoV-2-specific CD4 responses in 39.1% of LC- patients, while response frequencies were high in the LC+ and RE groups. Correlation analyses showed overall strong associations between humoral and cellular responses, with exceptions in the LC- group. These findings provide evidence for two major types of antiviral immune responses in long COVID. Seropositive patients showed coordinated cellular and humoral responses at least as high as those of recovered patients. In contrast, ELISA-seronegative long COVID patients showed overall low antiviral responses, with detectable specific CD4+ T cells and/or antibodies in close to half of patients (52.2%). These divergent findings in patients sharing a comparable spectrum of persistent symptoms raise the possibility of multiple etiologies in long COVID.

Deep Learning Applications Based on WISE Infrared Data: Classification of Stars, Galaxies and Quasars

The Wide-field Infrared Survey Explorer (WISE) has detected hundreds of millions of sources over the entire sky. However, classifying them reliably is a great challenge due to degeneracies in WISE multicolor space and low detection levels in its two longest-wavelength bandpasses. In this paper, the deep learning classification network, IICnet (Infrared Image Classification network), is designed to classify sources from WISE images to achieve a more accurate classification goal. IICnet shows good ability on the feature extraction of the WISE sources. Experiments demonstrate that the classification results of IICnet are superior to some other methods; it has obtained 96.2% accuracy for galaxies, 97.9% accuracy for quasars, and 96.4% accuracy for stars, and the Area Under Curve of the IICnet classifier can reach more than 99%. In addition, the superiority of IICnet in processing infrared images has been demonstrated in the comparisons with VGG16, GoogleNet, ResNet34, MobileNet, EfficientNetV2, and RepVGG-fewer parameters and faster inference. The above proves that IICnet is an effective method to classify infrared sources.

Treatment factors associated with viral suppression among adolescents on antiretroviral therapy in Kenya

Background: There are approximately 99,159 adolescents living with human immunodeficiency virus in Kenya, with a viral suppression rate of 67%, according to the Joint United Nations Program on HIV/AIDS in 2021 [1] . There are limited studies in Kenya on factors associated with viral load suppression among adolescents. The objectives of this study were to determine the treatment factors associated with viral suppression among adolescents on antiretroviral therapy. Methods: A retrospective cross-sectional analysis of 38,503 HIV-infected adolescents receiving antiretroviral therapy for at least 6 months with a documented viral load result. The data was from routinely collected HIV program data in Kenya that is submitted from comprehensive care centers with electronic medical records to the National Aids and STI Control Program (NASCOP) for the period of January 2018–December 2022. Results: The study population was 38503 HIV-infected adolescents (10–19 years) on antiretroviral therapy. The viral suppression was at 81.2%., higher than the 2021 UNAIDS estimate of 67%. low detectable levels were 88%, low level viremia was 12%, high-risk LLV was 38%, and suspected treatment failure as 62%. Virological suppression with integrase strand transfer inhibitors based regimens – Abacavir and Tenofovir was 81.6% and 86.4%, respectively. The suppression with protease inhibitors based regimens was 70% (highest) and 56.4% (Lowest) Conclusion: The viral suppression among adolescents on antiretroviral therapy was 81.2% lower than the UNAIDS 95/95/95 global target but higher than the 2021 UNAIDS estimate of 67%. There is a need to interrogate the viral suppression in adolescents on protease inhibitors.

Dynamic Behavior of Cortisol and Cortisol Metabolites in Human Eccrine Sweat

The simultaneous measurement of cortisol with its downstream metabolites in human eccrine sweat is a sensitive approach to capture minute-to-minute stress responses. This study investigates exercise stress induced time dependent dynamic changes in cortisol, cortisone and downstream inactive cortisol metabolites in human eccrine sweat using a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Cortisol and metabolite production (change in concentration over time) was measured in sweat at different time points during an administered exercise stress session with four healthy volunteers. Biomarker production plots were found to be highly individualized and sensitive to stress interventions such as exercise, and corresponded with stress response measures such as increases in heart rate. The LC-MS/MS method yielded baseline resolution between cortisol and cortisol metabolites with lower levels of detection and quantitation for each compound below 1 partper-billion (ppb). Cortisol and cortisol metabolites were found at concentrations ranging from 1 – 25 ppb in human eccrine sweat. They were also found to be stable in sweat with respect to temperature (37 C for up to 5 hours), pH (3-9) and freeze/thaw cycles (up to 4) This indicates that changes in these biomarker concentrations and their rate of production are due to stress-related physiological enzyme activation, rather than passive degradation in sweat. The physiological status of enzyme activation is thus captured and preserved in human eccrine sweat samples. This is advantageous for the development of wearable devices and methodologies which can assess human health, stress, wellbeing and performance.