trans-Endothelial neutrophil migration activates bactericidal function via Piezo1 mechanosensing.

The regulation of polymorphonuclear leukocyte (PMN) function by mechanical forces encountered during their migration across restrictive endothelial cell junctions is not well understood. Using genetic, imaging, microfluidic, and in vivo approaches, we demonstrated that the mechanosensor Piezo1 in PMN plasmalemma induced spike-like Ca2+ signals during trans-endothelial migration. Mechanosensing increased the bactericidal function of PMN entering tissue. Mice in which Piezo1 in PMNs was genetically deleted were defective in clearing bacteria, and their lungs were predisposed to severe infection. Adoptive transfer of Piezo1-activated PMNs into the lungs of Pseudomonas aeruginosa-infected mice or exposing PMNs to defined mechanical forces in microfluidic systems improved bacterial clearance phenotype of PMNs. Piezo1 transduced the mechanical signals activated during transmigration to upregulate nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4, crucial for the increased PMN bactericidal activity. Thus, Piezo1 mechanosensing of increased PMN tension, while traversing the narrow endothelial adherens junctions, is a central mechanism activating the host-defense function of transmigrating PMNs.

Screen-Printed Sensors Modified with Nafion and Mesoporous Carbon for Electrochemical Detection of Lead in Blood.

Lead (Pb) has long been acknowledged as a systemic toxicant, with pronounced health impacts observed even at low exposure levels, particularly in children. Adverse effects include diminished cognitive function, altered behavior, and developmental delays. Consequently, it is imperative to conduct regular monitoring of Blood Lead Levels (BLLs). In this work, we report on an electrochemical sensor based on screen-printed carbon electrode (SPCE) coated with Nafion and mesoporous carbon (MC). The sensor system uses simple sample preparation (acidification and dilution of whole blood), minimal sample volume (a few blood drops, 200 µl), and swift time-to-results (1 h). A limit of quantitation (LOQ) of 0.3 µg dL-1 Pb was achieved in whole blood. To demonstrate the practical utility of our sensor system, we evaluated its performance in the analysis of blood samples collected from children (n = 25). Comparative analysis with the laboratory-based gold standard method of inductively coupled plasma mass spectrometry (ICP-MS) demonstrated approximately 77% accuracy and 94% precision. We anticipate that our approach will serve as a valuable tool for more frequent BLL monitoring, particularly in communities where access to laboratory testing is impractical or expensive.

Microfluidic isolation of breast cancer circulating tumor cells from microvolumes of mouse blood.

Liquid biopsy has shown significant research and clinical implications in cancer. Particularly, the isolation of circulating tumor cells (CTCs) in preclinical studies can provide crucial information about disease progression and therefore may guide treatment decisions. Microfluidic isolation systems have played a considerable role in CTC isolation for cancer studies, disease diagnosis, and prognosis. CTCs are often studied using preclinical animal models such as xenografts or syngeneic models. However, most isolation systems are tested on human cell lines and human blood, whereas less validation studies are done on preclinical samples such as CTCs from mouse models. Here, we demonstrate and evaluate a complete workflow of a sized-based inertial microfluidic device to isolate CTCs from blood using exclusively mouse blood and mouse cancer cell lines. We then incorporate the cytospin, a commonly used method for enumeration of small number of cells in a glass slide to quantify the total cell yield of our workflow.

Three-dimensional lab-on-a-foil device for dielectrophoretic separation of cancer cells.

A simple, low-cost, three-dimensional (3D) lab-on-a-foil microfluidic device for dielectrophoretic separation of circulating tumor cells (CTCs) is designed and constructed. Disposable thin films are cut by xurography and microelectrode array are made with rapid inkjet printing. The multilayer device design allows the studying of spatial movements of CTCs and red blood cells (RBCs) under dielectrophoresis (DEP). A numerical simulation was performed to find the optimum driving frequency of RBCs and the crossover frequency for CTCs. At the optimum frequency, RBCs were lifted 120 µm in z-axis direction by DEP force, and CTCs were not affected due to negligible DEP force. By utilizing the displacement difference, the separation of CTCs (modeled with A549 lung carcinoma cells) from RBCs in z-axis direction was achieved. With the nonuniform electric field at optimized driving frequency, the RBCs were trapped in the cavities above the microchannel, whereas the A549 cells were separated with a high capture rate of 86.3% ± 0.2%. The device opens not only the possibility for 3D high-throughput cell separation but also for future developments in 3D cell manipulation through rapid and low-cost fabrication.

Electrochemical Determination of Manganese in Whole Blood with Indium Tin Oxide Electrode.

In this work, we demonstrate accurate and precise measurement of manganese (Mn) concentration in human whole blood with indium tin oxide (ITO) electrode using square wave stripping voltammetry. While an essential trace metal for human health, elevated levels of Mn due to environmental or occupational exposure have been associated with severe neuromotor dysfunction characterized by parkinsonism and cognitive dysfunction making the monitoring of Mn in whole blood necessary. Pediatric populations are particularly susceptible to Mn given their developing brain and potential long-term impacts on neurodevelopment. The current gold standard for whole blood Mn measurements is by ICP-MS, which is costly and time consuming. The electrochemical detection with ITO working electrode in this work showed a limit of detection of 0.5 µg l-1 and a linear range of 5 to 500 µg l-1, which encompasses the physiological Mn levels in human whole blood (5-18 µg l-1). Our results of Mn measurement in whole blood show an average precision of 96.5% and an average accuracy of 90.3% compared to ICP-MS for both the normal range (5-18 µg l-1) and the elevated levels (>36 µg l-1) that require medical intervention. These results demonstrate the feasibility of Mn measurements in human blood with electrochemical sensors.

Validation of Electrochemical Sensor for Determination of Manganese in Drinking Water.

Manganese (Mn) is an essential nutrient for metabolic functions, yet excessive exposure can lead to neurological disease in adults and neurodevelopmental deficits in children. Drinking water represents one of the routes of excessive Mn exposure. Both natural enrichment from rocks and soil, and man-made contamination can pollute groundwater that supplies drinking water for a substantial fraction of the U.S. population. Conventional methods for Mn monitoring in drinking water are costly and involve a long turn-around time. Recent advancements in electrochemical sensing, however, have led to the development of miniature sensors for Mn determination. These sensors rely on a cathodic stripping voltammetry electroanalytical technique on a miniaturized platinum working electrode. In this study, we validate these electrochemical sensors for the determination of Mn concentrations in drinking water against the standard method using inductively coupled plasma mass spectrometry (ICP-MS). Drinking water samples (n = 78) in the 0.03 ppb to 5.3 ppm range were analyzed. Comparisons with ICP-MS yielded 100% agreement, ∼70% accuracy, and ∼91% precision. We envision the use of our system for rapid and inexpensive point-of-use identification of Mn levels in drinking water, which is especially valuable for frequent monitoring where contamination is present.

Determination of Lead with a Copper-Based Electrochemical Sensor.

This work demonstrates determination of lead (Pb) in surface water samples using a low-cost copper (Cu)-based electrochemical sensor. Heavy metals require careful monitoring due to their toxicity, yet current methods are too complex or bulky for point-of-care (POC) use. Electrochemistry offers a convenient alternative for metal determination, but the traditional electrodes, such as carbon or gold/platinum, are costly and difficult to microfabricate. Our copper-based sensor features a low-cost electrode material-copper-that offers simple fabrication and competitive performance in electrochemical detection. For anodic stripping voltammetry (ASV) of Pb, our sensor shows 21 nM (4.4 ppb) limit of detection, resistance to interfering metals such as cadmium (Cd) and zinc (Zn), and stable response in natural water samples with minimum sample pretreatment. These results suggest this electrochemical sensor is suitable for environmental and potentially biological applications, where accurate and rapid, yet inexpensive, on-site monitoring is necessary.

A high throughput microfluidic platform for size-selective enrichment of cell populations in tissue and blood samples.

Numerous applications in biology and medicine require the efficient and reliable separation of cells for disease diagnosis, genetic analysis, drug screening, and therapeutics. In this work, we demonstrate a novel technology that integrates a passive and an active device to separate, enrich and release cells on-demand from a complex blood sample, or cancer cells derived from a tissue biopsy. We exploit the high throughput (>1 mL min-1), size-based sorting capability of the passive spiral inertial microfluidic (iMF) device to focus particles/cells towards an active lateral cavity acoustic transducer (LCAT) device for size-selective enrichment. We demonstrate that this platform is capable of efficiently (>90%) removing smaller cells, such as RBCs in a blood sample or smaller cancer cells in a heterogeneous cell line, and providing 44 000× enrichment from the remaining sample within 5 min of device operation. Finally, we use this platform for two applications: selective enrichment of the side-population of DU-145 cells from tissue biopsy and isolation of larger monocytes from blood. Our platform integrates the high throughput (processing rate) capacity of spiral iMF with the high selectivity of LCAT, thereby offering a unique route for highly-selective, label-free particle/cell sorting, with potential application in lab-on-chip platforms for liquid biopsy and diagnostics applications.

Bare and Polymer-Coated Indium Tin Oxide as Working Electrodes for Manganese Cathodic Stripping Voltammetry.

Though an essential metal in the body, manganese (Mn) has a number of health implications when found in excess that are magnified by chronic exposure. These health complications include neurotoxicity, memory loss, infertility in males, and development of a neurologic psychiatric disorder, manganism. Thus, trace detection in environmental samples is increasingly important. Few electrode materials are able to reach the negative reductive potential of Mn required for anodic stripping voltammetry (ASV), so cathodic stripping voltammetry (CSV) has been shown to be a viable alternative. We demonstrate Mn CSV using an indium tin oxide (ITO) working electrode both bare and coated with a sulfonated charge selective polymer film, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-sulfonate (SSEBS). ITO itself proved to be an excellent electrode material for Mn CSV, achieving a calculated detection limit of 5 nM (0.3 ppb) with a deposition time of 3 min. Coating the ITO with the SSEBS polymer was found to increase the sensitivity and lower the detection limit to 1 nM (0.06 ppb). This polymer modified electrode offers excellent selectivity for Mn as no interferences were observed from other metal ions tested (Zn(2+), Cd(2+), Pb(2+), In(3+), Sb(3+), Al(3+), Ba(2+), Co(2+), Cu(2+), Ni(3+), Bi(3+), and Sn(2+)) except Fe(2+), which was found to interfere with the analytical signal for Mn(2+) at a ratio 20:1 (Fe(2+)/Mn(2+)). The applicability of this procedure to the analysis of tap, river, and pond water samples was demonstrated. This simple, sensitive analytical method using ITO and SSEBS-ITO could be applied to a number of electroactive transition metals detectable by CSV.

Microfluidic manufacture of rt-PA -loaded echogenic liposomes.

Echogenic liposomes (ELIP), loaded with recombinant tissue-type plasminogen activator (rt-PA) and microbubbles that act as cavitation nuclei, are under development for ultrasound-mediated thrombolysis. Conventional manufacturing techniques produce a polydisperse rt-PA-loaded ELIP population with only a small percentage of particles containing microbubbles. Further, a polydisperse population of rt-PA-loaded ELIP has a broadband frequency response with complex bubble dynamics when exposed to pulsed ultrasound. In this work, a microfluidic flow-focusing device was used to generate monodisperse rt-PA-loaded ELIP (µtELIP) loaded with a perfluorocarbon gas. The rt-PA associated with the µtELIP was encapsulated within the lipid shell as well as intercalated within the lipid shell. The µtELIP had a mean diameter of 5 µm, a resonance frequency of 2.2 MHz, and were found to be stable for at least 30 min in 0.5 % bovine serum albumin. Additionally, 35 % of µtELIP particles were estimated to contain microbubbles, an order of magnitude higher than that reported previously for batch-produced rt-PA-loaded ELIP. These findings emphasize the advantages offered by microfluidic techniques for improving the encapsulation efficiency of both rt-PA and perflurocarbon microbubbles within echogenic liposomes.

Cloud Point Extraction for Electroanalysis: Anodic Stripping Voltammetry of Cadmium.

Cloud point extraction (CPE) is a well-established technique for the preconcentration of hydrophobic species from water without the use of organic solvents. Subsequent analysis is then typically performed via atomic absorption spectroscopy (AAS), UV-vis spectroscopy, or high performance liquid chromatography (HPLC). However, the suitability of CPE for electroanalytical methods such as stripping voltammetry has not been reported. We demonstrate the use of CPE for electroanalysis using the determination of cadmium (Cd(2+)) by anodic stripping voltammetry (ASV). Rather than using the chelating agents which are commonly used in CPE to form a hydrophobic, extractable metal complex, we used iodide and sulfuric acid to neutralize the charge on Cd(2+) to form an extractable ion pair. This offers good selectivity for Cd(2+) as no interferences were observed from other heavy metal ions. Triton X-114 was chosen as the surfactant for the extraction because its cloud point temperature is near room temperature (22-25 °C). Bare glassy carbon (GC), bismuth-coated glassy carbon (Bi-GC), and mercury-coated glassy carbon (Hg-GC) electrodes were compared for the CPE-ASV. A detection limit for Cd(2+) of 1.7 nM (0.2 ppb) was obtained with the Hg-GC electrode. ASV with CPE gave a 20x decrease (4.0 ppb) in the detection limit compared to ASV without CPE. The suitability of this procedure for the analysis of tap and river water samples was demonstrated. This simple, versatile, environmentally friendly, and cost-effective extraction method is potentially applicable to a wide variety of transition metals and organic compounds that are amenable to detection by electroanalytical methods.

Disposable copper-based electrochemical sensor for anodic stripping voltammetry.

In this work, we report the first copper-based point-of-care sensor for electrochemical measurements demonstrated by zinc determination in blood serum. Heavy metals require careful monitoring, yet current methods are too complex for a point-of-care system. Electrochemistry offers a simple approach to metal detection on the microscale, but traditional carbon, gold (Au), or platinum (Pt) electrodes are difficult or expensive to microfabricate, preventing widespread use. Our sensor features a new low-cost electrode material, copper, which offers simple fabrication and compatibility with microfabrication and PCB processing, while maintaining competitive performance in electrochemical detection. Anodic stripping voltammetry of zinc using our new copper-based sensors exhibited a 140 nM (9.0 ppb) limit of detection (calculated) and sensitivity greater than 1 µA/µM in the acetate buffer. The sensor was also able to determine zinc in a bovine serum extract, and the results were verified with independent sensor measurements. These results demonstrate the advantageous qualities of this lab-on-a-chip electrochemical sensor for clinical applications, which include a small sample volume (µL scale), reduced cost, short response time, and high accuracy at low concentrations of analyte.

Copper-based electrochemical sensor with palladium electrode for cathodic stripping voltammetry of manganese.

In this work, we report on the development of a palladium-based, microfabricated point-of-care electrochemical sensor for the determination of manganese using square wave cathodic stripping voltammetry. Heavy metals require careful monitoring, yet current methods are too complex for a point-of-care system. Voltammetry offers an attractive approach to metal detection on the microscale, but traditional carbon, gold, or platinum electrodes are difficult or expensive to microfabricate, preventing widespread use. Our sensor uses palladium working and auxiliary electrodes and integrates them with a copper-based reference electrode for simple fabrication and compatibility with microfabrication and printed circuit board processing, while maintaining competitive performance in electrochemical detection. Copper electrodes were prepared on glass substrate using a combination of microfabrication procedures followed by electrodeposition of palladium. The disposable sensor system was formed by bonding a poly(dimethylsiloxane) (PDMS) well to the glass substrate. Cathodic stripping voltammetry of manganese using our new disposable palladium-based sensors exhibited 334 nM (18.3 ppb) limit of detection in borate buffer. The sensor was used to demonstrate manganese determination in natural water samples from a pond in Burnet Woods, located in Cincinnati, OH, and the Ohio River.

Improving Reproducibility of Lab-on-a-Chip Sensor with Bismuth Working Electrode for Determining Zn in Serum by Anodic Stripping Voltammetry.

This work reports on the continuing development of a lab-on-a-chip electrochemical sensor for determination of zinc in blood serum using square wave anodic stripping voltammetry. The microscale sensor consists of a three electrode system, including an environmentally friendly bismuth working electrode, an integrated silver/silver chloride reference electrode, and a gold auxiliary electrode. The sensor demonstrates a linear response in 0.1 M acetate buffer at pH 6 for zinc concentrations in the 1-30 µM range. By optimizing bismuth film deposition and better control of the fabrication process, repeatability of the sensor was improved, reducing variability from 42% to <2%. Through optimization of electrolyte and stripping voltammetry parameters, limit of detection was greatly improved to 60 nM. The optimized sensor was also able to measure zinc in the extracted blood serum. Ultimately, with integrated sample preparation, the sensor will permit rapid (min) measurements of zinc from a sub-mL sample (a few drops of blood) for clinical applications.

Deciphering fibroblast-induced drug resistance in non-small cell lung carcinoma through patient-derived organoids in agarose microwells.

Patient-derived organoids (PDOs) serve as invaluable 3D tumor models, retaining the histological complexity and genetic heterogeneity found in primary tumors. However, the limitation of small sample volumes and the lack of tailored platforms have hindered the research using PDOs. Within the tumor microenvironment, cancer-associated fibroblasts play a pivotal role in influencing drug sensitivity. In this study, we introduce an agarose microwell platform designed for PDO-based tumor and tumor microenvironment models, enabling rapid drug screening and resistance studies with small sample volumes. These microwells, constructed using 3D printing molds, feature a U-shaped bottom and 200 µm diameter. We successfully generated co-culture spheroids of non-small cell lung carcinoma (NSCLC) cells, including NCI-H358 or A549, and NSCLC PDOs F231 or F671 with fibroblast cell line, WI-38. Our results demonstrate the production of uniformly-sized spheroids (coefficient of variation <30%), high viability (>80% after 1 week), and fibroblast-induced drug resistance. The PDOs maintained their viability (>81% after 2 weeks) and continued to proliferate. Notably, when exposed to adagrasib, a KRASG12C inhibitor, we observed reduced cytotoxicity in KRASG12C-mutant spheroids when co-cultured with fibroblasts or their supernatant. The fibroblast supernatant sustained proliferative signals in tumor models. Taking into account the physical features, viability, and drug resistance acquired through supernatants from the fibroblasts, our platform emerges as a suitable platform for in vitro tumor modeling and the evaluation of drug efficacy using patient-derived tissues.

Manganese in residential drinking water from a community-initiated case study in Massachusetts.

BACKGROUND: Manganese (Mn) is a metal commonly found in drinking water, but the level that is safe for consumption is unknown. In the United States (U.S.), Mn is not regulated in drinking water and data on water Mn concentrations are temporally and spatially sparse. OBJECTIVE: Examine temporal and spatial variability of Mn concentrations in repeated tap water samples in a case study of Holliston, Massachusetts (MA), U.S., where drinking water is pumped from shallow aquifers that are vulnerable to Mn contamination. METHODS: We collected 79 residential tap water samples from 21 households between September 2018 and December 2019. Mn concentrations were measured using inductively coupled plasma mass spectrometry. We calculated descriptive statistics and percent of samples exceeding aesthetic (secondary maximum containment level; SMCL) and lifetime health advisory (LHA) guidelines of 50 µg/L and 300 µg/L, respectively. We compared these concentrations to concurrent and historic water Mn concentrations from publicly available data across MA. RESULTS: The median Mn concentration in Holliston residential tap water was 2.3 µg/L and levels were highly variable (range: 0.03-5,301.8 µg/L). Mn concentrations exceeded the SMCL and LHA in 14% and 12% of samples, respectively. Based on publicly available data across MA from 1994-2022, median Mn concentration was 17.0 µg/L (N = 37,210; range: 1-159,000 µg/L). On average 40% of samples each year exceeded the SMCL and 9% exceeded the LHA. Samples from publicly available data were not evenly distributed between MA towns or across sampling years. IMPACT STATEMENT: This study is one of the first to examine Mn concentrations in drinking water both spatially and temporally in the U.S. Findings suggest that concentrations of Mn in drinking water frequently exceed current guidelines and occur at concentrations shown to be associated with adverse health outcomes, especially for vulnerable and susceptible subpopulations like children. Future studies that comprehensively examine exposure to Mn in drinking water and its associations with children's health are needed to protect public health.

Next generation microfluidics: fulfilling the promise of lab-on-a-chip technologies.

Microfluidic lab-on-a-chip technologies enable the analysis and manipulation of small fluid volumes and particles at small scales and the control of fluid flow and transport processes at the microscale, leading to the development of new methods to address a broad range of scientific and medical challenges. Microfluidic and lab-on-a-chip technologies have made a noteworthy impact in basic, preclinical, and clinical research, especially in hematology and vascular biology due to the inherent ability of microfluidics to mimic physiologic flow conditions in blood vessels and capillaries. With the potential to significantly impact translational research and clinical diagnostics, technical issues and incentive mismatches have stymied microfluidics from fulfilling this promise. We describe how accessibility, usability, and manufacturability of microfluidic technologies should be improved and how a shift in mindset and incentives within the field is also needed to address these issues. In this report, we discuss the state of the microfluidic field regarding current limitations and propose future directions and new approaches for the field to advance microfluidic technologies closer to translation and clinical use. While our report focuses on using blood as the prototypical biofluid sample, the proposed ideas and research directions can be extrapolated to other areas of hematology, oncology, biology, and medicine.

Optimization of a paper-based ELISA for a human performance biomarker.

Monitoring aspects of human performance during various activities has recently become a highly investigated research area. Many new commercial products are available now to monitor human physical activity or responses while performing activities ranging from playing sports, to driving, and even sleeping. However, monitoring cognitive performance biomarkers, such as neuropeptides, is still an emerging field due to the complicated sample collection and processing, as well as the need for a clinical lab to perform analysis. Enzyme-linked immunosorbent assays (ELISAs) provide specific detection of biomolecules with high sensitivity (picomolar concentrations). Even with the advantage of high sensitivity, most ELISAs need to be performed in a laboratory setting and require around 6 h to complete. Transitioning this assay to a platform where it reduces cost, shortens assay time, and is able to be performed outside a lab is invaluable. Recently developed paper diagnostics provide an inexpensive platform on which to perform ELISAs; however, the major limiting factor for moving out of the laboratory environment is the measurement and analysis instrumentation. Using something as simple as a digital camera or camera-enabled Windows- or Android-based tablets, we are able to image paper-based ELISAs (P-ELISAs), perform image analysis, and produce response curves with high correlation to target biomolecule concentration in the 10 pM range. Neuropeptide Y detection was performed. Additionally, silver enhancement of Au NPs conjugated with IgG antibodies showed a concentration-dependent response to IgG, thus eliminating the need for an enzyme-substrate system. Automated image analysis and quantification of antigen concentrations are able to be performed on Windows- and Android-based mobile platforms.

Single Cell Analysis of Inertial Migration by Circulating Tumor Cells and Clusters.

Single-cell analysis provides a wealth of information regarding the molecular landscape of the tumor cells responding to extracellular stimulations, which has greatly advanced the research in cancer biology. In this work, we adapt such a concept for the analysis of inertial migration of cells and clusters, which is promising for cancer liquid biopsy, by isolation and detection of circulating tumor cells (CTCs) and CTC clusters. Using high-speed camera tracking live individual tumor cells and cell clusters, the behavior of inertial migration was profiled in unprecedented detail. We found that inertial migration is heterogeneous spatially, depending on the initial cross-sectional location. The lateral migration velocity peaks at about 25% of the channel width away from the sidewalls for both single cells and clusters. More importantly, while the doublets of the cell clusters migrate significantly faster than single cells (~two times faster), cell triplets unexpectedly have similar migration velocities to doublets, which seemingly disagrees with the size-dependent nature of inertial migration. Further analysis indicates that the cluster shape or format (for example, triplets can be in string format or triangle format) plays a significant role in the migration of more complex cell clusters. We found that the migration velocity of a string triplet is statistically comparable to that of a single cell while the triangle triplets can migrate slightly faster than doublets, suggesting that size-based sorting of cells and clusters can be challenging depending on the cluster format. Undoubtedly, these new findings need to be considered in the translation of inertial microfluidic technology for CTC cluster detection.

Determination of Mercury with a Miniature Sensor for Point-of-care Testing.

In developing countries, subsistence gold mining entails mixing metallic mercury with crushed sediments to extract gold. In this approach, the gold-mercury amalgam is heated to evaporate mercury and obtain gold. Thus, the highly volatile mercury can be absorbed through inhalation, resulting in adverse health effects. Urinalysis can be used to detect mercury, which is excreted in urine and feces, and correlate exposure with toxic effects. The current gold standard analytical methods are based on fluorescence or inductively coupled plasma mass spectrometry methods, but are expensive, time consuming, and are not easily accessible in countries where testing is needed. In this work, we report on a miniature electrochemical sensor that can rapidly detect mercury in urine at levels well below the US Biological Exposure Index (BEI) limit of 50 ppb (µg/L). The sensor is based on a thin-film gold electrode and anodic stripping voltammetry electroanalytical approach. The sensor successfully detected mercury at trace levels in urine, with a limit of detection of ~15 ppb Hg in the linear range of 20-80 ppb. With the low-cost disposable sensors and portable instrumentation, it is well suited for point-of-care applications.