Co-reporter:Daoli Zhao, David Siebold, Noe T. Alvarez, Vesselin N. Shanov, and William R. Heineman
Analytical Chemistry September 19, 2017 Volume 89(Issue 18) pp:9654-9654
Publication Date(Web):August 17, 2017
DOI:10.1021/acs.analchem.6b04724
In this work, all three electrodes in an electrochemical cell were fabricated based on carbon nanotube (CNT) thread. CNT thread partially insulated with a thin polystyrene coating to define the microelectrode area was used as the working electrode; bare CNT thread was used as the auxiliary electrode; and a micro quasi-reference electrode was fabricated by electroplating CNT thread with Ag and then anodizing it in chloride solution to form a layer of AgCl. The Ag|AgCl coated CNT thread electrode provided a stable potential comparable to the conventional liquid-junction type Ag|AgCl reference electrode. The CNT thread auxiliary electrode provided a stable current, which is comparable to a Pt wire auxiliary electrode. This all-CNT thread three electrode cell has been evaluated as a microsensor for the simultaneous determination of trace levels of heavy metal ions by anodic stripping voltammetry (ASV). Hg2+, Cu2+, and Pb2+ were used as a representative system for this study. The calculated detection limits (based on the 3σ method) with a 120 s deposition time are 1.05, 0.53, and 0.57 nM for Hg2+, Cu2+, and Pb2+, respectively. These electrodes significantly reduce the dimensions of the conventional three electrode electrochemical cell to the microscale.
Co-reporter:Shirmir D. Branch, Amanda M. Lines, John Lynch, Job M. Bello, William R. Heineman, and Samuel A. Bryan
Analytical Chemistry July 18, 2017 Volume 89(Issue 14) pp:7324-7324
Publication Date(Web):June 12, 2017
DOI:10.1021/acs.analchem.7b00258
A novel microfabricated optically transparent thin-film electrode chip for fluorescence and absorption spectroelectrochemistry has been developed. The working electrode was composed of indium tin oxide (ITO); the quasi-reference and auxiliary electrodes were composed of platinum. The stability of the platinum quasi-reference electrode was improved by coating it with a planar, solid state Ag/AgCl layer. The Ag/AgCl reference was characterized with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cyclic voltammetry measurements showed that the electrode chip was comparable to a standard electrochemical cell. Randles-Sevcik analysis of 10 mM K3[Fe(CN)6] in 0.1 M KCl using the electrode chip gave a diffusion coefficient of 1.59 × 10–6 cm2/s, in comparison to the value of 2.38 × 10–6 cm2/s using a standard electrochemical cell. By using the electrode chip in an optically transparent thin-layer electrode (OTTLE), the absorption based spectroelectrochemical modulation of [Fe(CN)6]3–/4– was demonstrated, as well as the fluorescence based modulation of [Ru(bpy)3]2+/3+. For the fluorescence spectroelectrochemical determination of [Ru(bpy)3]2+, a detection limit of 36 nM was observed.
Co-reporter:Daoli Zhao, Tingting Wang, Keaton Nahan, Xuefei Guo, ... William R. Heineman
Acta Biomaterialia 2017 Volume 50(Volume 50) pp:
Publication Date(Web):1 March 2017
DOI:10.1016/j.actbio.2017.01.024
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 significanceBiodegradable 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 1 month. 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.Download high-res image (132KB)Download full-size image
Co-reporter:Cory A. Rusinek, Adam Bange, Mercedes Warren, Wenjing Kang, Keaton Nahan, Ian Papautsky, and William R. Heineman
Analytical Chemistry 2016 Volume 88(Issue 8) pp:4221
Publication Date(Web):March 16, 2016
DOI:10.1021/acs.analchem.5b03381
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 (Zn2+, Cd2+, Pb2+, In3+, Sb3+, Al3+, Ba2+, Co2+, Cu2+, Ni3+, Bi3+, and Sn2+) except Fe2+, which was found to interfere with the analytical signal for Mn2+ at a ratio 20:1 (Fe2+/Mn2+). 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.
Co-reporter:Daoli Zhao, Tingting Wang, Julia Kuhlmann, Zhongyun Dong, Shuna Chen, Madhura Joshi, Pravahan Salunke, Vesselin N. Shanov, Daeho Hong, Prashant N. Kumta, William R. Heineman
Acta Biomaterialia 2016 Volume 36() pp:361-368
Publication Date(Web):May 2016
DOI:10.1016/j.actbio.2016.03.039
Abstract
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 (30–400 μM) permeating through the skin with a response time of about 30 s. 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 30 s.
Co-reporter:Daoli Zhao, Tingting Wang, William Hoagland, David Benson, Zhongyun Dong, Shuna Chen, Da-Tren Chou, Daeho Hong, Jingyao Wu, Prashant N. Kumta, William R. Heineman
Acta Biomaterialia 2016 Volume 45() pp:399-409
Publication Date(Web):November 2016
DOI:10.1016/j.actbio.2016.08.049
Abstract
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.
Co-reporter:Daoli Zhao, Tingting Wang, William R. Heineman
TrAC Trends in Analytical Chemistry 2016 Volume 79() pp:269-275
Publication Date(Web):May 2016
DOI:10.1016/j.trac.2016.01.015
•H2 detection techniques are essential for H2 medicine.•H2 sensors can monitor biodegradation of Mg alloys being developed for repair of broken bones.•Electrochemical methods for H2 detection have attracted more attention in bioanalytical applications.•Optical sensors for H2 detection in bioanalysis are simple, effective and visual.•Color indicator sensors for H2 detection have been used for screening hydrogen-producing microorganisms.H2 sensors have been receiving more attention, especially with the development of H2 medicine and biodegradable alloys that produce H2. The H2 sensors discussed in this review are primarily the electrochemical, chemochromic metal oxide, and color indicator sensors. This review focuses on the bioanalytical application of these existing H2 sensors. The performance parameters of these sensors are reviewed to aid in identifying and selecting appropriate sensors for practical applications.
Co-reporter:Cory A. Rusinek, Adam Bange, Ian Papautsky, and William R. Heineman
Analytical Chemistry 2015 Volume 87(Issue 12) pp:6133
Publication Date(Web):May 21, 2015
DOI:10.1021/acs.analchem.5b00701
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 (Cd2+) 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 Cd2+ to form an extractable ion pair. This offers good selectivity for Cd2+ 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 Cd2+ 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.
Co-reporter:Daoli Zhao, Tingting Wang, Daewoo Han, Cory Rusinek, Andrew J. Steckl, and William R. Heineman
Analytical Chemistry 2015 Volume 87(Issue 18) pp:9315
Publication Date(Web):August 10, 2015
DOI:10.1021/acs.analchem.5b02017
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). Pb2+ and Cd2+ were used as a representative system for this initial study. Well-defined stripping voltammograms were obtained when Pb2+ and Cd2+ 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 Pb2+ and Cd2+, respectively.
Co-reporter:Tingting Wang, Daoli Zhao, Noe Alvarez, Vesselin N. Shanov, and William R. Heineman
Analytical Chemistry 2015 Volume 87(Issue 19) pp:9687
Publication Date(Web):August 20, 2015
DOI:10.1021/acs.analchem.5b01784
Carbon nanotube (CNT) film was evaluated as an optically transparent electrode (OTE) for thin layer spectroelectrochemistry. Chemically inert CNT arrays were synthesized by chemical vapor deposition (CVD) using thin films of Fe and Co as catalysts. Vertically aligned CNT arrays were drawn onto a quartz slide to form CNT films that constituted the OTE. Adequate conductivity and transparency make this material a good OTE for spectroelectrochemistry. These properties could be varied by the number of layers of CNTs used to form the OTE. Detection in the UV/near UV region down to 200 nm can be achieved using these transparent CNT films on quartz. The OTE was characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, UV–visible spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and thin layer spectroelectrochemistry. Ferricyanide, tris(2,2′-bipyridine) ruthenium(II) chloride, and cytochrome c were used as representative redox probes for thin layer spectroelectrochemistry using the CNT film OTE, and the results correlated well with their known properties. Direct electron transfer of cytochrome c was achieved on the CNT film electrode.
Co-reporter:Tingting Wang, Daoli Zhao, Xuefei Guo, Jaime Correa, Bill L. Riehl, and William R. Heineman
Analytical Chemistry 2014 Volume 86(Issue 9) pp:4354
Publication Date(Web):March 27, 2014
DOI:10.1021/ac500163f
A Nafion film loaded with novel catalyst-free multiwalled carbon nanotubes (MWCNTs) was used to modify a glassy carbon (GC) electrode to detect trace concentrations of metal ions, with europium ion (Eu3+) as a model. The interaction between the sidewalls of MWCNTs and the hydrophobic backbone of Nafion allows the MWCNTs to be dispersed in Nafion, which was then coated as a thin film on the GC electrode surface. The electrochemical response to Eu3+ was found to be ∼10 times improved by MWCNT concentrations between 0.5 and 2 mg/mL, which effectively expanded the electrode surface into the Nafion film and thereby reduced the diffusion distance of Eu3+ to the electrode surface. At low MWCNT concentrations of 0.25 and 0.5 mg/mL, no significant improvement in signal was obtained compared with Nafion alone. Scanning electron microscopy and electrochemical impedance spectroscopy were used to characterize the structure of the MWCNT–Nafion film, followed by electrochemical characterization with Eu3+ via cyclic voltammetry and preconcentration voltammetry. Under the optimized conditions, a linear range of 1–100 nM with a calculated detection limit of 0.37 nM (signal/noise = 3) was obtained for determination of Eu3+ by Osteryoung square-wave voltammetry after a preconcentration time of 480 s.
Co-reporter:Amos Doepke, Julia Kuhlmann, Xuefei Guo, Robert T. Voorhees, William R. Heineman
Acta Biomaterialia 2013 Volume 9(Issue 11) pp:9211-9219
Publication Date(Web):November 2013
DOI:10.1016/j.actbio.2013.07.011
Abstract
Understanding Mg corrosion is important to the development of biomedical implants made from Mg alloys. Mg corrodes readily in aqueous environments, producing H2, OH− and Mg2+. The rate of formation of these corrosion products is especially important in biomedical applications where they can affect cells and tissue near the implant. We have developed a corrosion characterization system (CCS) that allows realtime monitoring of the solution soluble corrosion products OH−, Mg2+, and H2 during immersion tests commonly used to study the corrosion of Mg materials. Instrumentation was developed to allow the system to also record electrochemical impedance spectra simultaneously in the same solution to monitor changes in the Mg samples. We demonstrated application of the CCS by observing the corrosion of Mg (99.9%) in three different corrosion solutions: NaCl, HEPES buffer, and HEPES buffer with NaCl at 37 °C for 48 h. The solution concentrations of the corrosion products measured by sensors correlated with the results using standard weight loss measurements to obtain corrosion rates. This novel approach gives a better understanding of the dynamics of the corrosion process in realtime during immersion tests, rather than just providing a corrosion rate at the end of the test, and goes well beyond the immersion tests that are commonly used to study the corrosion of Mg materials. The system has the potential to be useful in systematically testing and comparing the corrosion behavior of different Mg alloys, as well as protective coatings.
Co-reporter:Cynthia A. Schroll, Sayandev Chatterjee, Tatiana G. Levitskaia, William R. Heineman, and Samuel A. Bryan
Analytical Chemistry 2013 Volume 85(Issue 20) pp:9924
Publication Date(Web):September 9, 2013
DOI:10.1021/ac402518p
The electrochemical and spectroelectrochemical behavior of europium(III) chloride in a molten salt eutectic, 3LiCl–2KCl, over a temperature range of 643–1123 K using differential pulse voltammetry, cyclic voltammetry, potential step chronoabsorptometry, and thin-layer spectroelectrochemistry is reported. The electrochemical reaction was determined to be the one-electron reduction of Eu3+ to Eu2+ at all temperatures. The redox potential of Eu3+/2+ shifts to more positive potentials, and the diffusion coefficient for Eu3+ increases as temperature increases. The results for the number of electrons transferred, redox potential, and diffusion coefficient are in good agreement between the electrochemical and spectroelectrochemical techniques. This research extends our ability to develop a spectroelectrochemical sensor for lanthanides and actinides into molten salt media.
Co-reporter:Tingting Wang, Kevin T. Schlueter, Bill L. Riehl, Jay M. Johnson, and William R. Heineman
Analytical Chemistry 2013 Volume 85(Issue 20) pp:9486
Publication Date(Web):September 3, 2013
DOI:10.1021/ac400987u
A novel method for the detection of nitrate was developed using simplified nitrate reductase (SNaR) that was produced by genetic recombination techniques. The SNaR consists of the fragments of the Mo–molybdopterin (MO–MPT) binding site and nitrate reduction active site and has high activity for nitrate reduction. The method is based on a unique combination of the enzyme-catalyzed reduction of nitrate to nitrite by thin-layer coulometry followed by spectroscopic measurement of the colored product generated from the reaction of nitrite with Griess reagents. Coulometric reduction of nitrate to nitrite used methyl viologen (MV2+) as the electron transfer mediator for SNaR and controlled potential coulometry in an indium tin oxide (ITO) thin-layer electrochemical cell. Absorbance at 540 nm was proportional to the concentration of nitrate in the sample with a linear range of 1–160 μM and a sensitivity of 8000 AU M–1. The method required less than 60 μL of sample. Detection of nitrate could also be performed by measuring the charge associated with coulometry. However, the spectroscopic procedure gave superior performance because of interference from the large background charge associated with coulometry. Results for the determination of nitrate concentration in several natural water samples using this device with spectroscopic detection are in good agreement with analysis done with a standard method.
Co-reporter:Rebecca E. Barlag;H. Brian Halsall
Analytical and Bioanalytical Chemistry 2013 Volume 405( Issue 11) pp:3541-3547
Publication Date(Web):2013 April
DOI:10.1007/s00216-012-6488-3
The effect of a perfluorocarbon emulsion oxygen therapeutic (PEOT) on the detection of the drugs theophylline and phenytoin was explored using a commercial enzyme multiplied immunoassay technique (EMIT®). The EMIT technique is based on the enzymatic production of NADH, which is typically detected in serum samples spectrophotometrically. Here, amperometry using the rotating disk electrode on a single drop of solution is demonstrated to detect theophylline and phenytoin in the presence of PEOT. In the study, 2,6-dichloroindophenol (DCIP) added to the immunoassay mixture is reduced by the NADH to DCIPH2. Oxidation of DCIPH2 is monitored electrochemically at +200 mV using a glassy carbon rotating disk electrode. Slopes of amperograms are proportional to the concentration of drug in the immunoassay sample. This technique yields excellent quantitative data in the therapeutic range for both drugs in 2–20 % PEOT.
Co-reporter:Hideki Kuramitz, H. Brian Halsall and William R. Heineman
Analytical Methods 2012 vol. 4(Issue 6) pp:1783-1789
Publication Date(Web):04 May 2012
DOI:10.1039/C2AY05738G
A paramagnetic microbead-based enzyme immunoassay was demonstrated for detecting ovalbumin (OVA). The immunoassay sandwich was made by attaching a biotinylated antibody to the streptavidin coated beads as a mobile solid phase, capturing antigen, and then exposing the antigen to an antibody conjugated with β-galactosidase. β-Galactosidase converts p-aminophenyl galactopyranoside (PAPG) and fluorescein di-β-D-galactopyranoside (FDG) to p-aminophenol (PAP) and fluorescein, respectively. The current response of PAP generated by the enzymatic reaction of β-galactosidase was detected with hydrodynamic voltammetry in a droplet using a rotating disk electrode (RDE) system. The performance of this electrochemical assay was compared with fluorometric detection of fluorescein produced by the same assay system. The limits of detection for OVA determined by hydrodynamic amperometry and fluorometry were 2.1 nM (43 fmol) and 2.9 nM (58 fmol), respectively. Furthermore, the effects of the conditions commonly found in drinking water supply systems on the OVA assay were also evaluated.
Co-reporter:Robert A. Wilson, Carl J. Seliskar, Glenn Talaska, and William R. Heineman
Analytical Chemistry 2011 Volume 83(Issue 10) pp:3725
Publication Date(Web):April 19, 2011
DOI:10.1021/ac200161s
Spectroelectrochemical sensing in an optically transparent thin layer electrode (OTTLE) cell was used for detecting the polycyclic aromatic hydrocarbon (PAH) biomarkers 1-hydroxypyrene (1-pyOH) and 1-hydroxypyrene-glucuronide (1-pyOglu) in phosphate buffer and artificial urine. This approach uses selective electrochemical modulation of a fluorescence signal by sequentially oxidizing the analytes in an OTTLE cell to distinguish between their overlapping fluorescence spectra. This technique allows for complete oxidation and signal modulation in approximately 15 min for each analyte; a mixture of 1-pyOH and its glucuronic acid conjugate can be analyzed in 30 min. Calibration curves consisting of the fluorescence change vs analyte concentration for 1-pyOH and 1-pyOglu yielded linear ranges from 10 nM to 1 μM and from 1 nM to 1 μM, respectively. With the use of these results, the calculated limits of detection were determined to be 1 × 10−8 M for 1-pyOH and 9 × 10−11 M for 1-pyOglu.
Co-reporter:Sayandev Chatterjee, Andrew S. Del Negro, Matthew K. Edwards, and Samuel A. Bryan , Necati Kaval, Nebojsa Pantelic, Laura K. Morris, William R. Heineman, and Carl J. Seliskar
Analytical Chemistry 2011 Volume 83(Issue 5) pp:1766
Publication Date(Web):February 4, 2011
DOI:10.1021/ac1030368
A spectroelectrochemical sensor consisting of an indium tin oxide (ITO) optically transparent electrode (OTE) coated with a thin film of partially sulfonated polystyrene-blockpoly(ethylene-ran-butylene)-block-polystyrene (SSEBS) was developed for [Tc(dmpe)3]+ (dmpe = 1,2-bis(dimethylphosphino)ethane). [Tc(dmpe)3]+ was preconcentrated by ion-exchange into the SSEBS film after a 20 min exposure to aqueous [Tc(dmpe)3]+ solution, resulting in a 14-fold increase in cathodic peak current compared to a bare OTE. Colorless [Tc(dmpe)3]+ was reversibly oxidized to colored [Tc(dmpe)3]2+ by cyclic voltammetry. Detection of [Tc(dmpe)3]2+ was accomplished through emission spectroscopy by electrochemically oxidizing the complex from nonemissive [Tc(dmpe)3]+ to emissive [Tc(dmpe)3]2+. The working principle of the sensor consisted of electrochemically cycling between nonemissive [Tc(dmpe)3]+ and emissive [Tc(dmpe)3]2+ and monitoring the modulated emission (λexc = 532 nm; λem = 660 nm). The sensor gave a linear response over the concentration range of 0.16−340.0 μM of [Tc(dmpe)3]2+/+ in aqueous phase with a detection limit of 24 nM.
Co-reporter:Tatyana S. Pinyayev, Carl J. Seliskar, and William R. Heineman
Analytical Chemistry 2010 Volume 82(Issue 23) pp:9743
Publication Date(Web):November 5, 2010
DOI:10.1021/ac101883a
A spectroelectrochemical sensor was demonstrated for an organic compound whose oxidation proceeds through an electron transfer−chemical reaction−electron transfer (ECE) mechanism to generate new chemical species that are used for detection by fluorescence. The polycyclic aromatic hydrocarbon 1-hydroxypyrene (1-PyOH) served as a representative model analyte. The spectroelectrochemical properties of 1-PyOH in solution were explored with an optically transparent thin layer electrode. Electrochemical oxidation of 1-PyOH under acidic conditions proceeds via the ECE mechanism to a diquinonepyrene, which shows reversible electrochemistry and fluoresces at 425 nm in its reduced form, dihydroxypyrene. The sensor consisted of a tin-doped indium optically transparent electrode coated with a Nafion thin-film (20 nm) that rapidly preconcentrated the analyte at the sensor surface. Fluorescence in the film was excited by the evanescent wave from attenuated total reflection spectroscopy. Electrochemical modulation of dihydroxypyrene fluorescence at 425 nm in the 500 to −200 mV (vs Ag/AgCl) potential range was used for indirect detection of 1-PyOH. The spectroelectrochemical sensor calibration curve had a range of 5 × 10−9 to 1 × 10−6 M with a calculated detection limit of 1 × 10−9 M.
Co-reporter:Rebecca E. Barlag;H. Brian Halsall
Analytical and Bioanalytical Chemistry 2010 Volume 396( Issue 2) pp:675-680
Publication Date(Web):2010 January
DOI:10.1007/s00216-009-3253-3
The effect of a perfluorocarbon emulsion oxygen therapeutic (PEOT) on detecting theophylline was explored using a commercial EMIT® (enzyme multiplied immunoassay technique) immunoassay. The EMIT technique is based on a colorimetric reaction, the product of which can be measured spectrophotometrically. The intent was to determine whether the presence of PEOT interferes with this detection. We found that the immunoassay yields excellent quantitative data in the therapeutic range (10–20 ppm theophylline) in 2–10% PEOT, but as the amount of PEOT in the sample increases, the accuracy of the detection method decreases.
Co-reporter:Nebojša Pantelić, Sara E. Andria, William R. Heineman and Carl J. Seliskar
Analytical Chemistry 2009 Volume 81(Issue 16) pp:6756
Publication Date(Web):July 23, 2009
DOI:10.1021/ac900765t
The spectroelectrochemical sensor uses thin, solid polyelectrolyte films as an essential element in its operation. In this work we explored the potential of partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SSEBS) thin polymer films for chemical sensing. Spectroscopic ellipsometry was used to measure optical and surface properties of the air-dried and hydrated material. SSEBS incorporates a relatively small amount of water (overall change of 25%) mainly determined by the complex dynamics of the film. The decrease in the refractive index after complete hydration of the film can be predicted based on the magnitude of swelling using effective medium approximation models. Adhesion of the material on various surfaces (glass, indium tin oxide, gold) was evaluated with the tape peel-off method. The ability of the SSEBS material to preconcentrate cations was evaluated by cyclic voltammetry, absorbance, and luminescence measurements using model analytes (Ru(bpy)32+, phenosafranine, and rhodamine 6G). The detection limits of the sensor for Ru(bpy)32+ under unoptimized conditions can be significantly improved if luminescence is used as the detection modality (DL = 5 × 10−10 M) instead of absorbance (DL = 5 × 10−7 M). Overall, the results demonstrate the effectiveness of the SSEBS material for spectroelectrochemical sensing.
Co-reporter:F. Ceyda Dudak;İsmail H. Boyacı
Analytical and Bioanalytical Chemistry 2009 Volume 393( Issue 3) pp:
Publication Date(Web):2009 February
DOI:10.1007/s00216-008-2531-9
A rapid and convenient assay system was developed to detect viable Escherichia coli in water. The target bacteria were recovered from solution by immunomagnetic separation and incubated in tryptic soy broth with isopropyl-β-d-thiogalactopyranoside, which induces formation of β-galactosidase in viable bacteria. Lysozyme was used to lyse E. coli cells and release the β-galactosidase. β-Galactosidase converted 4-methylumbelliferyl-β-d-galactoside to 4-methylumbelliferone (4-MU), which was measured by fluorescence spectrophotometry using excitation and emission wavelengths of 355 and 460 nm, respectively. Calibration graphs of 4-MU fluorescence intensity versus E. coli concentration showed a detection range between 8 × 104 and 1.6 × 107 cfu mL−1, with a total analysis time of less than 3 h. The advantage of this method is that it detects viable cells because it is based on the activity of the enzyme intrinsic to live E. coli.
Co-reporter:Hideki Kuramitz, Aigars Piruska, H. Brian Halsall, Carl J. Seliskar and William R. Heineman
Analytical Chemistry 2008 Volume 80(Issue 24) pp:9642
Publication Date(Web):November 16, 2008
DOI:10.1021/ac801289t
A new binding assay for a protein and its ligand based on a spectroelectrochemical method was demonstrated using avidin−biotin and 17β-estradiol−antiestradiol antibody. The sensor consists of a selective film coated on an optically transparent electrode (OTE) consisting of indium tin oxide (ITO). Attenuated total reflection (ATR) was used for optical detection. The binding event of the ligand to the protein was detected using the ligand labeled with the electroactive dye Nile blue (NB). The spectroelectrochemical behaviors of NB and the labeled ligand were investigated using various ion-exchange films, such as perfluorosulfonated ionomer (Nafion), Nafion-silica, poly(acrylic acid) (PAA)-silica, poly(styrenesulfonic acid) (PSSA)-silica, and heparin-silica films, which were spin-coated on the ITO electrode. The optical signal was monitored to follow the accumulation of labeled ligand in the film and its electrochemical modulation. The signal from the labeled ligand possesses three modes of selectivity based on charge-selective partitioning, the chosen electrolysis potential, and the particular wavelength for measuring absorbance. The interaction between the labeled ligand and its protein was observed by the decrease in the changes of optical response of the labeled ligand, indicating the specific binding of labeled ligand to the protein.
Co-reporter:Maojun Gong, Kenneth R. Wehmeyer, Patrick A. Limbach, William R. Heineman
Journal of Chromatography A 2007 Volume 1167(Issue 2) pp:217-224
Publication Date(Web):12 October 2007
DOI:10.1016/j.chroma.2007.08.042
Flow manipulation in sweeping microchip capillary electrophoresis (CE) is complicated by the free liquid communication between channels at the intersection, especially when the electroosmotic flows are mismatched in the main channel. Sweeping in traditional CE with cationic micelles is an effective way to concentrate anionic analytes. However, it is a challenge to transfer this method onto microchip CE because the dynamic coating process on capillary walls by cationic surfactants is interrupted when the sample solution free of surfactants is introduced into the microchip channels. This situation presents a difficulty in the sample loading, injection and dispensing processes. By adding surfactant at a concentration around the critical micelle concentration and by properly designing the voltage configuration, the flows in a microchip were effectively manipulated and this sweeping method was successfully moved to microchip CE using tetradecyltrimethylammonium bromide (TTAB). The sweeping effect of cationic surfactant in the sample solution was discussed theoretically and studied experimentally in traditional CE. The flows in a microchip were monitored with fluorescence imaging, and the injection and sweeping processes were studied by locating the detection point along the separation channel. A detection enhancement of up to 500-fold was achieved for 5-carboxyfluorescein.
Co-reporter:Irena Nikcevic, Se Hwan Lee, Aigars Piruska, Chong H. Ahn, Thomas H. Ridgway, Patrick A. Limbach, K.R. Wehmeyer, William R. Heineman, Carl J. Seliskar
Journal of Chromatography A 2007 Volume 1154(1–2) pp:444-453
Publication Date(Web):22 June 2007
DOI:10.1016/j.chroma.2007.03.125
Injection molded poly(methylmethacrylate) (IM-PMMA), chips were evaluated as potential candidates for capillary electrophoresis disposable chip applications. Mass production and usage of plastic microchips depends on chip-to-chip reproducibility and on analysis accuracy. Several important properties of IM-PMMA chips were considered: fabrication quality evaluated by environmental scanning electron microscope imaging, surface quality measurements, selected thermal/electrical properties as indicated by measurement of the current versus applied voltage (I–V) characteristic and the influence of channel surface treatments. Electroosmotic flow was also evaluated for untreated and O2 reactive ion etching (RIE) treated surface microchips. The performance characteristics of single lane plastic microchip capillary electrophoresis (MCE) separations were evaluated using a mixture of two dyes—fluorescein (FL) and fluorescein isothiocyanate (FITC). To overcome non-wettability of the native IM-PMMA surface, a modifier, polyethylene oxide was added to the buffer as a dynamic coating. Chip performance reproducibility was studied for chips with and without surface modification via the process of RIE with O2 and by varying the hole position for the reservoir in the cover plate or on the pattern side of the chip. Additionally, the importance of reconditioning steps to achieve optimal performance reproducibility was also examined. It was found that more reproducible quantitative results were obtained when normalized values of migration time, peak area and peak height of FL and FITC were used instead of actual measured parameters.
Co-reporter:Maojun Gong, Kenneth R. Wehmeyer, Patrick A. Limbach, William R. Heineman
Journal of Chromatography A 2006 Volume 1125(Issue 2) pp:263-269
Publication Date(Web):1 September 2006
DOI:10.1016/j.chroma.2006.05.058
On-line sample preconcentration of oligonucleotides with a new sweeping carrier was developed by using dodecyltrimethylammonium bromide (DTAB) below the critical micelle concentration (CMC). The sweeping results with DTAB below and above the CMC were compared. The use of DTAB below the CMC benefits the preconcentration of the oligonucleotides, while the use of DTAB above the CMC is good for hydrophobic small molecules. The factors affecting the sweeping results were optimized and this method was evaluated by constructing calibration curves for thrombin aptamers. The sweeping scheme produced a 112-fold sensitivity enhancement for the oligonucleotides relative to that run in a running buffer without DTAB. The sweeping method developed here can be a good reinforcement of the preconcentration scheme by sweeping when less-hydrophobic analytes or large negatively-charged molecules need to be preconcentrated.
Co-reporter:Christa A. Currie, William R. Heineman, H. Brian Halsall, Carl J. Seliskar, Patrick A. Limbach, Francisco Arias, Kenneth R. Wehmeyer
Journal of Chromatography B 2005 Volume 824(1–2) pp:201-205
Publication Date(Web):25 September 2005
DOI:10.1016/j.jchromb.2005.07.035
Microchip capillary electrophoresis (CE), coupled with indirect fluorescence detection was investigated for estimating the pKa values of non-fluorescent compounds. The CE method is based on the differences in electrophoretic mobility of the analyte as a function of the pH of the running buffer. Nine compounds were tested, including several of pharmaceutical importance, with pKa values from 10.3 to 4.6. All buffers contained 5-TAMRA as the fluorescent probe for indirect detection. Calculated pKa values agreed well with literature values obtained by traditional methods, differing not more than 0.2 from the literature value. The current work on single lane chips demonstrates the principle of microchip CE with indirect detection as a viable method for estimating pKa values. However, increased throughput will be required using a multilane chip to enable the approach to be used practically.
Co-reporter:Anne T. Maghasi, Kevin T. Schlueter, H.Brian Halsall, William R. Heineman, Horacio L. Rodriguez Rilo
Analytical Biochemistry 2003 Volume 314(Issue 1) pp:38-45
Publication Date(Web):1 March 2003
DOI:10.1016/S0003-2697(02)00626-7
Insulin is stored in pancreatic islets as a zinc–insulin complex, and stimulating the islets results in the release of insulin and zinc. Simulant pancreatic islet beads have been developed using agarose beads (50–250 μm diameter) derivatized with iminodiacetic acid that have been loaded with zinc. A qualitative comparison of the simulant beads with pancreatic islets has been made by staining with dithizone and a zinc-binding fluorescent dye, TSQ. The binding capacity of simulant beads was determined to be 34 μmol Zn2+/g of dried beads using anodic stripping voltammetry. Hydrochloric acid was used to release zinc from beads to mimic the secretion of insulin from pancreatic islets and a release profile was established. The simulant beads can be used to optimize the islet isolation process and reduce the use of real islets in method development.
Co-reporter:
Science 1920 Vol 51(1309) pp:108-109
Publication Date(Web):30 Jan 1920
DOI:10.1126/science.51.1309.108
Co-reporter:Lancaster D. Burling
Science 1918 Vol 47(1226) pp:639-640
Publication Date(Web):28 Jun 1918
DOI:10.1126/science.47.1226.639
Co-reporter:John J. Vennemeyer, Tracy Hopkins, Julia Kuhlmann, William R. Heineman, Sarah K. Pixley
Neuroscience Research (July 2014) Volume 84() pp:72-78
Publication Date(Web):1 July 2014
DOI:10.1016/j.neures.2014.05.001
•We studied the effects of elevating magnesium ions on cultured neuronal stem cells.•Adding magnesium resulted in increased cell survival and increased neurite length.•Plating the cells on laminin negated the effects of magnesium.•Neither additional magnesium nor laminin altered neuronal differentiation.•Magnesium ions did not interfere with the crystal violet cell viability assay.Because a potential treatment for brain injuries could be elevating magnesium ions (Mg2+) intracerebrally, we characterized the effects of elevating external Mg2+ in cultures of neonatal murine brain-derived neural stem/progenitor cells (NSCs). Using a crystal violet assay, which avoids interference of Mg2+ in the assay, it was determined that substrate influenced Mg2+ effects on cell numbers. On uncoated plastic, elevating Mg2+ levels to between 2.5 and 10 mM above basal increased NSC numbers, and at higher concentrations numbers decreased to control or lower levels. Similar biphasic curves were observed with different plating densities, treatment durations and length of time in culture. When cells were plated on laminin-coated plastic, NSC numbers were higher even in basal medium and no further effects were observed with Mg2+. NSC differentiation into neurons was not altered by either substrate or Mg2+ supplementation. Some parameters of neurite outgrowth were increased by elevated Mg2+ when NSCs differentiated into neurons on uncoated plastic. Differentiation on laminin resulted in increased neurites even in basal medium and no further effects were seen when Mg2+ was elevated. This system can now be used to study the multiple mechanisms by which Mg2+ influences neuronal biology.Download high-res image (224KB)Download full-size image
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Analytical Methods (2009-Present) 2012 - vol. 4(Issue 6) pp:
Publication Date(Web):
DOI:10.1039/C2AY05738G
A paramagnetic microbead-based enzyme immunoassay was demonstrated for detecting ovalbumin (OVA). The immunoassay sandwich was made by attaching a biotinylated antibody to the streptavidin coated beads as a mobile solid phase, capturing antigen, and then exposing the antigen to an antibody conjugated with β-galactosidase. β-Galactosidase converts p-aminophenyl galactopyranoside (PAPG) and fluorescein di-β-D-galactopyranoside (FDG) to p-aminophenol (PAP) and fluorescein, respectively. The current response of PAP generated by the enzymatic reaction of β-galactosidase was detected with hydrodynamic voltammetry in a droplet using a rotating disk electrode (RDE) system. The performance of this electrochemical assay was compared with fluorometric detection of fluorescein produced by the same assay system. The limits of detection for OVA determined by hydrodynamic amperometry and fluorometry were 2.1 nM (43 fmol) and 2.9 nM (58 fmol), respectively. Furthermore, the effects of the conditions commonly found in drinking water supply systems on the OVA assay were also evaluated.
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