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.

Sensitive Electrochemical Detection of Microcystin-LR in Water Samples Via Target-Induced Displacement of Aptamer Associated [Ru(NH3)6]3

In this study, we demonstrate the successful development of an electrochemical aptamer-based sensor for point-of-use detection and quantification of the highly potent microcystin-LR (MC-LR) in water. The sensor uses hexaammineruthenium(III) chloride ([Ru(NH₃)₆]³⁺) as redox mediator, because of the ability of the positively charged (3+) molecule to associate with the phosphate backbone of the nucleic acids. We quantitatively measure the target-induced displacement of aptamer associated, or surface confined, [Ru(NH₃)₆]³⁺ in the presence of MC-LR. Upon the addition of MC-LR in the water, surface-confined [Ru(NH₃)₆]³⁺ dissociates, resulting in less faradaic current from the reduction of [Ru(NH₃)₆]³⁺ to [Ru(NH₃)₆]²⁺ Sensing surfaces of highly packed immobilized aptamers were capable of recording decreasing square wave voltammetry (SWV) signals after the addition of MC-LR in buffer. As a result, SWV recorded substantial signal suppression within 15 min of target incubation. The sensor showed a calculated limit of detection (LOD) of 9.2 pM in buffer. The effects of interferents were minimal, except when high concentrations of natural organic matter (NOM) were present. Also, the sensor performed well in drinking water samples. These results indicate a sensor with potential for fast and specific quantitative determination of MC-LR in drinking water samples. A common challenge when developing electrochemical, aptamer-based sensors is the need to optimize the nucleic acid aptamer in order to achieve sensitive signaling. This is particularly important when an aptamer experiences only a small or localized conformational change that provides only a limited electrochemical signal change. This study suggests a strategy to overcome that challenge through the use of a nucleic acid-associated redox label.

Electrochemical Affinity Assays/Sensors: Brief History and Current Status

The advent of electrochemical affinity assays and sensors evolved from pioneering efforts in the 1970s to broaden the field of analytes accessible to the selective and sensitive performance of electrochemical detection. The foundation of electrochemical affinity assays/sensors is the specific capture of an analyte by an affinity element and the subsequent transduction of this event into a measurable signal. This review briefly covers the early development of affinity assays and then focuses on advances in the past decade. During this time, progress on electroactive labels, including the use of nanoparticles, quantum dots, organic and organometallic redox compounds, and enzymes with amplification schemes, has led to significant improvements in sensitivity. The emergence of nanomaterials along with microfabrication and microfluidics technology enabled research pathways that couple the ease of use of electrochemical detection for the development of devices that are more user friendly, disposable, and employable, such as lab-on-a-chip, paper, and wearable sensors.

A Visual Hydrogen Sensor Prototype for Monitoring Magnesium Implant Biodegradation

Alternative metals such as magnesium (Mg) and its alloys have been recently developed for clinical applications such as temporary implants for bone and tissue repair due to their desirable mechanical properties and ability to biodegrade harmlessly in vivo by releasing Mg²⁺, OH^-, and H₂ as biodegradation products. The current methods for monitoring in vivo Mg-alloy biodegradation are either invasive and/or costly, complex, or require large equipment and specially trained personnel, thus making real-time and point-of-care monitoring of Mg-alloy implants problematic. Therefore, innovative methods are critically needed. The objective of this research was to develop a novel, thin, and wearable visual H₂ sensor prototype for noninvasive monitoring of in vivo Mg-implant biodegradation in medical research and clinical settings with a fast response time. In this work, we successfully demonstrate such a prototype composed of resazurin and catalytic bimetallic gold-palladium nanoparticles (Au-Pd NPs) incorporated into a thin agarose/alginate hydrogel matrix that rapidly changes color from blue to pink upon exposure to various levels of H₂ at a constant flow rate. The irreversible redox reactions occurring in the sensor involve H₂, in the presence of Au-Pd NPs, converting resazurin to resorufin. To quantify the sensor color changes, ImageJ software was used to analyze photographs of the sensor taken with a smartphone during H₂ exposure. The sensor concentration range was from pure H₂ down to limits of detection of 6 and 8 μM H₂ (defined via two methods). This range is adequate for the intended application of noninvasively monitoring in vivo Mg-alloy implant biodegradation in animals for medical research and patients in clinical settings.

Parts per trillion detection of heavy metals in as-is tap water using carbon nanotube microelectrodes

Heavy metal contamination of drinking water is a major global issue. Research reports across the globe show contamination of heavy metals higher than the set standards of the World Health Organization (WHO) and US Environmental Protection Agency (EPA). To our knowledge, no electrochemical sensor for heavy metals with parts per trillion (PPT) limits of detection (LOD) in as-is tap water has been reported or developed. Here, we report a microelectrode that consists of six highly densified carbon nanotube fiber (HD-CNTf) cross sections called rods (diameter ∼69 μm and length ∼40 μm) in a single platform for the ultra-sensitive detection of heavy metals in tap water and simulated drinking water. The HD-CNTf rods microelectrode was evaluated for the individual and simultaneous determination of trace level of heavy metal ions i.e. Cu²⁺, Pb²⁺ and Cd²⁺ in Cincinnati tap water (without supporting electrolyte) and simulated drinking water using square wave stripping voltammetry (SWSV). The microsensor exhibited a broad linear detection range with an excellent limit of detection for individual Cu²⁺, Pb²⁺ and Cd²⁺ of 6.0 nM, (376 ppt), 0.45 nM (92 ppt) and 0.24 nM (27 ppt) in tap water and 0.32 nM (20 ppt), 0.26 nM (55 ppt) and 0.25 nM (28 ppt) in simulated drinking water, respectively. The microelectrode was shown to detect Pb²⁺ ions well below the WHO and EPA limits in a broad range of water quality conditions reported for temperature and conductivity in the range of 5 °C-45 °C and 55 to 600 μS/cm, respectively.

Effects of Experimental Conditions on the Signaling Fidelity of Impedance-Based Nucleic Acid Sensors

Electrochemical impedance spectroscopy (EIS), an extremely sensitive analytical technique, is a widely used signal transduction method for the electrochemical detection of target analytes in a broad range of applications. The use of nucleic acids (aptamers) for sequence-specific or molecular detection in electrochemical biosensor development has been extensive, and the field continues to grow. Although nucleic acid-based sensors using EIS offer exceptional sensitivity, signal fidelity is often linked to the physical and chemical properties of the electrode-solution interface. Little emphasis has been placed on the stability of nucleic acid self-assembled monolayers (SAMs) over repeated voltammetric and impedimetric analyses. We have studied the stability and performance of electrochemical biosensors with mixed SAMs of varying length thiolated nucleic acids and short mercapto alcohols on gold surfaces under repeated electrochemical interrogation. This systematic study demonstrates that signal fidelity is linked to the stability of the SAM layer and nucleic acid structure and the packing density of the nucleic acid on the surface. A decrease in packing density and structural changes of nucleic acids significantly influence the signal change observed with EIS after routine voltammetric analysis. The goal of this article is to improve our understanding of the effect of multiple factors on EIS signal response and to optimize the experimental conditions for development of sensitive and reproducible sensors. Our data demonstrate a need for rigorous control experiments to ensure that the measured change in impedance is unequivocally a result of a specific interaction between the target analyte and nucleic recognition element.

Effect of Lithium and Aluminum on the Mechanical Properties, In Vivo and In Vitro Degradation, and Toxicity of Multiphase Ultrahigh Ductility Mg-Li-Al-Zn Quaternary Alloys for Vascular Stent Application

Magnesium alloys are the most widely studied biodegradable metals for biodegradable vascular stent application. Two major issues with current magnesium alloy based stents are their low ductility and fast corrosion rates. Several studies have validated that introduction of Li into the magnesium alloys will significantly improve the ductility while alloying with Al will improve the corrosion resistance and strength. In the present study, we studied the effects of alloying different amounts of Li and Al on the Mg-Li-Al-Zn (LAZ) quaternary alloy system. Rods were made from four different LAZ alloys, namely, LAZ611, LAZ631, LAZ911, and LAZ931 following melting, casting, and then extrusion. Systematic assessment of mechanical properties, in vitro corrosion, cytotoxicity, and in vivo degradation including local and systemic toxicity conducted demonstrated the beneficial effects of Li and Al on the mechanical properties. Our results specifically suggest that alloying with Li significantly improved the ductility while Al enhanced the strength of the LAZ alloys. Four of the LAZ alloys exhibited different corrosion rates in Hank's balanced salt solution depending on the chemical composition. Indirect in vitro cytotoxicity tests also showed lower cytotoxicity for the alloys exhibiting higher corrosion resistance. In vivo corrosion rates in the mouse subcutaneous model showed different corrosion rates compared to the in vitro tests. Nevertheless, all of the four LAZ alloys displayed no local and systemic toxicity based on the histology analysis. This research study, therefore, demonstrated the benefits of using Li and Al as alloying elements in LAZ alloys and the potential use of LAZ alloys for vascular stent application.

Electroosmotic flow driven microfluidic device for bacteria isolation using magnetic microbeads

The presence of bacterial pathogens in water can lead to severe complications such as infection and food poisoning. This research proposes a point-of-care electroosmotic flow driven microfluidic device for rapid isolation and detection of E. coli in buffered solution (phosphate buffered saline solution). Fluorescent E. coli bound to magnetic microbeads were driven through the microfluidic device using both constant forward flow and periodic flow switching at concentrations ranging from 2 × 105 to 4 × 107 bacteria/mL. A calibration curve of fluorescent intensity as a function of bacteria concentration was created using both constant and switching flow, showing an increase in captured fluorescent pixel count as concentration increases. In addition, the use of the flow switching resulted in a significant increase in the capture efficiency of E. coli, with capture efficiencies up to 83% ± 8% as compared to the constant flow capture efficiencies (up to 39% ± 11%), with a sample size of 3 µL. These results demonstrate the improved performance associated with the use of the electroosmotic flow switching system in a point-of-care bacterial detection assay.

A Comprehensive Review: Development of Electrochemical Biosensors for Detection of Cyanotoxins in Freshwater

Cyanobacteria harmful algal blooms are increasing in frequency and cyanotoxins have become an environmental and public concern in the U.S. and worldwide. In this Review, the majority of reported studies and developments of electrochemical affinity biosensors for cyanotoxins are critically reviewed and discussed. Essential background information about cyanobacterial toxins and electrochemical biosensors is combined with the rapidly moving development of electrochemical biosensors for these toxins. Current issues and future challenges for the development of useful electrochemical biosensors for cyanotoxin detection that meet the demands for applications in field freshwater samples are discussed. The major aspects of the entire review article in a prescribed sequence include (i) the state-of-the-art knowledge of the toxicity of cyanotoxins, (ii) important harmful algal bloom events, (iii) advisories, guidelines, and regulations, (iv) conventional analytical methods for determination of cyanotoxins, (v) electrochemical transduction, (vi) recognition receptors, (vii) reported electrochemical biosensors for cyanotoxins, (viii) summary of analytical performance, and (ix) recent advances and future trends. Discussion includes electrochemical techniques and devices, biomolecules with high affinity, numerous array designs, various detection approaches, and research strategies in tailoring the properties of the transducer-biomolecule interface. Scientific and engineering aspects are presented in depth. This review aims to serve as a valuable source to scientists and engineers entering the interdisciplinary field of electrochemical biosensors for detection of cyanotoxins in freshwaters.

Analysis of Magnetic Microbead Capture With and Without Bacteria in a Microfluidic Device Under Different Flow Scenarios

Efficient detection of pathogens is essential for the development of a reliable point-of-care diagnostic device. Magnetophoretic separation, a technique used in microfluidic platforms, utilizes magnetic microbeads (mMBs) coated with specific antigens to bind and remove targeted biomolecules using an external magnetic field. In order to assure reliability and accuracy in the device, the efficient capture of these mMBs is extremely important. The aim of this study was to analyze the effect of an electroosmotic flow (EOF) switching device on the capture efficiency (CE) of mMBs in a microfluidic device and demonstrate viability of bacteria capture. This analysis was performed at microbead concentrations of 2 × 106 beads/mL and 4 × 106 beads/mL, EOF voltages of 650 V and 750 V, and under constant flow and switching flow protocols. Images were taken using an inverted fluorescent microscope and the pixel count was analyzed to determine to fluorescent intensity. A capture zone was used to distinguish which beads were captured versus uncaptured. Under the steady-state flow protocol, CE was determined to range from 31% to 42%, while the switching flow protocol exhibited a CE of 71–85%. The relative percentage increase due to the utilization of the switching protocol was determined to be around two times the CE, with p < 0.05 for all cases. Initial testing using bacteria-bead complexes was also performed in which these complexes were captured under the constant flow protocol to create a calibration curve based on fluorescent pixel count. The calibration curve was linear on a log-log plot, with R2-value of 0.96. The significant increase in CE highlights the effectiveness of flow switching for magnetophoretic separation in microfluidic devices and prove its viability in bacterial analysis.

In Situ Spectroscopic Analysis and Quantification of [Tc(CO)3]+ in Hanford Tank Waste

The quantitative conversion of nonpertechnetate [Tc(CO)₃]⁺ species in nuclear waste storage tank 241-AN-102 at the Hanford Site is demonstrated. A waste sample containing the [Tc(CO)₃]⁺ species is added to a developer solution that rapidly converts the nonemissive species into a luminescent complex, which is detected spectroscopically. This method was first demonstrated using a [Tc(CO)₃]⁺ sample of nonwaste containing matrix to determine a detection limit (LOD), resulting in a [Tc(CO)₃]⁺ LOD of 2.20 × 10^-7 M, very near the LOD of the independently synthesized standard (2.10 × 10^-7 M). The method was then used to detect [Tc(CO)₃]⁺ in a simulated waste using the standard addition method, resulting in a [Tc(CO)₃]⁺ concentration of 1.89 × 10^-5 M (within 27.7% of the concentration determined by β liquid scintillation counting). Three samples from 241-AN-102 were tested by the standard addition method: (1) a 5 M Na adjusted fraction, (2) a fraction depleted of ¹³⁷Cs, and (3) an acid-stripped eluate. The concentrations of [Tc(CO)₃]⁺ in these fractions were determined to be 9.90 × 10^-6 M (1), 0 M (2), and 2.46 × 10^-6 M (3), respectively. The concentration of [Tc(CO)₃]⁺ in the as-received AN-102 tank waste supernatant was determined to be 1.84 × 10^-5 M.

In vivo quantification of hydrogen gas concentration in bone marrow surrounding magnesium fracture fixation hardware using an electrochemical hydrogen gas sensor

Magnesium (Mg) medical devices are currently being marketed for orthopedic applications and have a complex degradation process which includes the evolution of hydrogen gas (H₂). The effect of H₂ exposure on relevant cell types has not been studied; and the concentration surrounding degrading Mg devices has not been quantified to enable such mechanistic studies. A simple and effective method to measure the concentration of H₂ in varying microenvironments surrounding Mg implants is the first step to understanding the biological impact of H₂ on these cells. Here, the in vivo measurement of H₂ surrounding fracture fixation devices implanted in vivo is demonstrated. An electrochemical H₂ microsensor detected increased levels of H₂ at three anatomical sites with a response time of about 30 s. The sensor showed the H₂ concentration in the bone marrow at 1 week post-implantation (1460 ± 320 µM) to be much higher than measured in the subcutaneous tissue (550 ± 210 µM) and at the skin surface (120 ± 50 µM). Additionally, the H₂ concentrations measured in the bone marrow exceeded the concentration in a H₂ saturated water solution (∼800 µM). These results suggest that H₂ emanating from Mg implants in bone during degradation pass through the bone marrow and become at least partially trapped because of slow permeation through the bone. This study is the first to identify H₂ concentrations in the bone marrow environment and will enable in vitro experiments to be executed at clinically relevant H₂ concentrations to explore possible biological effects of H₂ exposure.

STATEMENT OF SIGNIFICANCE

An electrochemical H₂ sensor was used to monitor the degradation of a Mg fracture fixation system in a lapine ulna fracture model. Interestingly, the H₂ concentration in the bone marrow is 82% higher than H₂ saturated water solution. This suggests H₂ generated in situ is trapped in the bone marrow and bone is less permeable than the surrounding tissues. The detectable H₂ at the rabbit skin also demonstrates a H₂ sensor's ability to monitor the degradation process under thin layers of tissue. H₂ sensing shows promise as a tool for monitoring the degradation of Mg alloy in vivo and creating in vitro test beds to more mechanistically evaluate the effects of varying H₂ concentrations on cell types relevant to osteogenesis.

In Situ Quantification of [Re(CO)3]+ by Fluorescence Spectroscopy in Simulated Hanford Tank Waste

A pretreatment protocol is presented that allows for the quantitative conversion and subsequent in situ spectroscopic analysis of [Re(CO)₃]⁺ species in simulated Hanford tank waste. In this test case, the nonradioactive metal rhenium is substituted for technetium (Tc-99), a weak beta emitter, to demonstrate proof of concept for a method to measure a nonpertechnetate form of technetium in Hanford tank waste. The protocol encompasses adding a simulated waste sample containing the nonemissive [Re(CO)₃]⁺ species to a developer solution that enables the rapid, quantitative conversion of the nonemissive species to a luminescent species which can then be detected spectroscopically. The [Re(CO)₃]⁺ species concentration in an alkaline, simulated Hanford tank waste supernatant can be quantified by the standard addition method. In a test case, the [Re(CO)₃]⁺ species was measured to be at a concentration of 38.9 μM, which was a difference of 2.01% from the actual concentration of 39.7 μM.

In Vitro and in Vivo Evaluation of Multiphase Ultrahigh Ductility Mg-Li-Zn Alloys for Cardiovascular Stent Application

Magnesium alloys have been extensively studied as a novel biodegradable metallic material for cardiovascular stent application. However, the ductility limitation of magnesium alloy has been a key issue for biodegradable stents applications. In this study, two different multiphase ultrahigh ductility Mg-Li-Zn alloys, LZ61 and LZ91, are fabricated in the form of extruded rods and evaluated both in vitro and in vivo. The microstructure, mechanical properties and in vitro degradation are evaluated as well as in vitro cytotoxicity. The in vivo degradation, tissue response, and systematic toxicity are evaluated in a mouse subcutaneous model. Measurements show that LZ61 and LZ91 exhibit more than 40% elongation at fracture without significantly compromising the strength. Both in vitro and in vivo degradation showed low degradation rates for LZ61 but high degradation rate for the LZ91 alloy. Excellent biocompatibility is observed both in vivo and in vitro for LZ61 and LZ91. In summary, this study successfully demonstrates that the ultraductility multiphase Mg-Li-Zn alloy has the potential to be used for stent applications. Compared to LZ91, the LZ61 alloy shows better balance of mechanical properties, corrosion resistance, and biocompatibility, indicating its promise for cardiovascular stent applications.

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.

In vivo characterization of magnesium alloy biodegradation using electrochemical H2 monitoring, ICP-MS, and XPS

The effect of widely different corrosion rates of Mg alloys on four parameters of interest for in vivo characterization was evaluated: (1) the effectiveness of transdermal H₂ measurements with an electrochemical sensor for noninvasively monitoring biodegradation compared to the standard techniques of in vivo X-ray imaging and weight loss measurement of explanted samples, (2) the chemical compositions of the corrosion layers of the explanted samples by XPS, (3) the effect on animal organs by histology, and (4) the accumulation of corrosion by-products in multiple organs by ICP-MS. The in vivo biodegradation of three magnesium alloys chosen for their widely varying corrosion rates - ZJ41 (fast), WKX41 (intermediate) and AZ31 (slow) - were evaluated in a subcutaneous implant mouse model. Measuring H₂ with an electrochemical H₂ sensor is a simple and effective method to monitor the biodegradation process in vivo by sensing H₂ transdermally above magnesium alloys implanted subcutaneously in mice. The correlation of H₂ levels and biodegradation rate measured by weight loss shows that this non-invasive method is fast, reliable and accurate. Analysis of the insoluble biodegradation products on the explanted alloys by XPS showed all of them to consist primarily of Mg(OH)₂, MgO, MgCO₃ and Mg₃(PO₄)₂ with ZJ41 also having ZnO. The accumulation of magnesium and zinc were measured in 9 different organs by ICP-MS. Histological and ICP-MS studies reveal that there is no significant accumulation of magnesium in these organs for all three alloys; however, zinc accumulation in intestine, kidney and lung for the faster biodegrading alloy ZJ41 was observed. Although zinc accumulates in these three organs, no toxicity response was observed in the histological study. ICP-MS also shows higher levels of magnesium and zinc in the skull than in the other organs.

STATEMENT OF SIGNIFICANCE

Biodegradable devices based on magnesium and its alloys are promising because they gradually dissolve and thereby avoid the need for subsequent removal by surgery if complications arise. In vivo biodegradation rate is one of the crucial parameters for the development of these alloys. Promising alloys are first evaluated in vivo by being implanted subcutaneously in mice for 1month. Here, we evaluated several magnesium alloys with widely varying corrosion rates in vivo using multiple characterization techniques. Since the alloys biodegrade by reacting with water forming H₂ gas, we used a recently demonstrated, simple, fast and noninvasive method to monitor the biodegradation process by just pressing the tip of a H₂ sensor against the skin above the implant. The analysis of 9 organs (intestine, kidney, spleen, lung, heart, liver, skin, brain and skull) for accumulation of Mg and Zn revealed no significant accumulation of magnesium in these organs. Zinc accumulation in intestine, kidney and lung was observed for the faster corroding implant ZJ41. The surfaces of explanted alloys were analyzed to determine the composition of the insoluble biodegradation products. The results suggest that these tested alloys are potential candidates for biodegradable implant applications.

Determination of manganese by cathodic stripping voltammetry on a microfabricated platinum thin-film electrode

In this work, we report on the determination of trace manganese (Mn) using cathodic stripping voltammetry (CSV) using a microfabricated sensor with a Pt thin-film working electrode. While an essential trace metal for human health, prolonged exposure to Mn tends to gradually impair our neurological system. The potential sources of Mn exposure make it necessary to monitor the concentration in various sample matrices. Previous work by us and others suggested CSV as an effective method for measuring trace Mn. The analytical performance metrics were characterized and optimized, leading to a calculated limit of detection (LOD) of 16.3 nM (0.9 ppb) in pH 5.5, 0.2 M acetate buffer. Further, we successfully validated Mn determination in surface water with ~90% accuracy and >97% precision as compared with ICP-MS "gold standard" measurement. Ultimately, with stable, accurate and precise electrochemical performance, this Pt sensor permits rapid monitoring of Mn in environmental samples, and could potentially be used for point-of-use measurements if coupled with portable instrumentation.

Visual H2 sensor for monitoring biodegradation of magnesium implants in vivo

A visual sensor for H₂ was used to transdermally monitor H₂ that originated from biodegrading magnesium (Mg) alloys implanted subcutaneously in mice. The visual sensor consisted of a thin film of H₂-sensitive material (MoO₃ and Pd catalyst) coated on a flexible plastic sheet that was pressed against the mouse skin directly above the implant. Although the H₂ levels permeating through the skin during the degradation process were very low, the sensor changed color to give a three dimensional (3D) visualization of H₂ permeation. The correlation between the visual sensor response and measurements made with an electrochemical H₂ microsensor on several magnesium alloys demonstrates that the visual sensor has the capability to monitor in real-time the dissolution rate of implants in vivo. This detection method is noninvasive, easy to implement, effective and potentially low cost compared to electrochemical detection.

STATEMENT OF SIGNIFICANCE

Biodegradable Mg implants offer advantages over permanent implants such as stainless steel that are used for broken bone repair. Mg alloys gradually dissolve, avoiding the need for removal by a later surgery if complications arise. Here we report a visual H₂ sensor that can be used in the research laboratory to monitor the corrosion process in vivo during animal testing of different Mg alloys. The sensor consists of a plastic sheet with a thin coating that changes color in the presence of H₂ gas. The sensor is easily used by taping it on the skin over the Mg implant. The color change gives a map of the H₂ level permeating from the degrading Mg through the skin above it. This low cost, simple method of monitoring the dissolution of biodegradable implants would greatly facilitate the development of the biodegradable materials, especially in animal studies where in vivo biodegradation is tested.

In vivo monitoring the biodegradation of magnesium alloys with an electrochemical H2 sensor

Monitoring the biodegradation process of magnesium and its alloys in vivo is challenging. Currently, this process is monitored by micro-CT and X-ray imaging in vivo, which require large and costly instrumentation. Here we report a simple and effective methodology to monitor the biodegradation process in vivo by sensing H2 transdermally above a magnesium sample implanted subcutaneously in a mouse. An electrochemical H2 microsensor was used to measure the biodegradation product H2 at the surface of the skin for two magnesium alloys (ZK40 and AZ31) and one high purity magnesium single crystal (Mg8H). The sensor was able to easily detect low levels of H2 (30-400μM) permeating through the skin with a response time of about 30s. H2 levels were correlated with the biodegradation rate as determined from weight loss measurements of the implants. This new method is noninvasive, fast and requires no major equipment.

STATEMENT OF SIGNIFICANCE

Biomedical devices such as plates and screws used for broken bone repair are being developed out of biodegradable magnesium alloys that gradually dissolve when no longer needed. This avoids subsequent removal by surgery, which may be necessary if complications arise. A rapid, non-invasive means for monitoring the biodegradation process in vivo is needed for animal testing and point of care (POC) evaluation of patients. Here we report a novel, simple, fast, and noninvasive method to monitor the biodegradation of magnesium in vivo by measuring the biodegradation product H2 with an electrochemical H2 sensor. Since H2 rapidly permeates through biological tissue, measurements are made by simply pressing the sensor tip against the skin above the implant; the response is within 30s.

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.

Electrospun carbon nanofiber modified electrodes for stripping voltammetry

Electrospun polyacrylonitrile (PAN) based carbon nanofibers (CNFs) have attracted intense attention due to their easy processing, high carbon yield, and robust mechanical properties. In this work, a CNF modified glassy carbon (GC) electrode that was coated with Nafion polymer was evaluated as a new electrode material for the simultaneous determination of trace levels of heavy metal ions by anodic stripping voltammetry (ASV). Pb(2+) and Cd(2+) were used as a representative system for this initial study. Well-defined stripping voltammograms were obtained when Pb(2+) and Cd(2+) were determined individually and then simultaneously in a mixture. Compared to a bare GC electrode, the CNF/Nafion modified GC (CNF/Nafion/GC) electrode improved the sensitivity for lead detection by 8-fold. The interface properties of the CNF/Nafion/GC were characterized by electrochemical impedance spectroscopy (EIS), which showed the importance of the ratio of CNF/Nafion on electrode performance. Under optimized conditions, the detection limits are 0.9 and 1.5 nM for Pb(2+) and Cd(2+), respectively.

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.

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.

Lab-on-a-Chip Sensor with Evaporated Bismuth Film Electrode for Anodic Stripping Voltammetry of Zinc

In this work, we report on the development of a lab-on-a-chip electrochemical sensor that uses an evaporated bismuth electrode to detect zinc using square wave anodic stripping voltammetry. The microscale electrochemical cell consists of a bismuth working electrode, an integrated silver/silver chloride reference electrode, and a gold auxiliary electrode. The sensor demonstrated linear response in 0.1 M acetate buffer at pH 6 with zinc concentrations ranging from 1 μM to 30 μM and a calculated detection limit of 60 nM. The sensor was also able to successfully detect zinc in a bovine serum extract and the results were verified with independent AAS 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.