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  • 1.
    Makaraviciute, Asta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Xu, Xingxing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Systematic approach to the development of microfabricated biosensors: relationship between the gold surface pretreatment and thiolated molecule binding2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 31, p. 26610-26621Article in journal (Refereed)
    Abstract [en]

    Despite the increasing popularity of microfabricated biosensors due to advances in technologic and surface functionalization strategies, their successful implementation is partially inhibited by the lack of consistency in their analytical characteristics. One of the main causes for the discrepancies is the absence of a systematic and comprehensive approach to surface functionalization. In this article microfabricated gold electrodes aimed at biosensor development have been systematically characterized in terms of surface pretreatment, thiolated molecule binding, and reproducibility by means of X-ray photoelectron scattering (XPS) and cyclic voltammetry (CV). It has been shown that after SU-8 photolithography gold surfaces were markedly contaminated, which decreased the effective surface area and surface coverage of a model molecule mercaptohexanol (MCH). Three surface pretreatment methods compatible with microfabricated devices were compared. The investigated methods were (i) cyclic voltammetry in dilute H2SO4, (ii) gentle basic piranha followed by linear sweep voltammetry in dilute KOH, and (iii) oxygen plasma treatment followed by incubation in ethanol. It was shown that all three methods significantly decreased the contamination and increased MCH surface coverage. Most importantly, it was also revealed that surface pretreatments may induce structural changes to the gold surfaces. Accordingly, these alterations influence the characteristics of MCH functionalization.

  • 2.
    Pan, Ruijun
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Xu, Xingxing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sun, Rui
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Wang, Zhaohui
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Lindh, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Nanocellulose Modified Polyethylene Separators for Lithium Metal Batteries2018In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 14, no 21, article id 1704371Article in journal (Refereed)
    Abstract [en]

    Abstract Poor cycling stability and safety concerns regarding lithium (Li) metal anodes are two major issues preventing the commercialization of high‐energy density Li metal‐based batteries. Herein, a novel tri‐layer separator design that significantly enhances the cycling stability and safety of Li metal‐based batteries is presented. A thin, thermally stable, flexible, and hydrophilic cellulose nanofiber layer, produced using a straightforward paper‐making process, is directly laminated on each side of a plasma‐treated polyethylene (PE) separator. The 2.5 µm thick, mesoporous (≈20 nm average pore size) cellulose nanofiber layer stabilizes the Li metal anodes by generating a uniform Li+ flux toward the electrode through its homogenous nanochannels, leading to improved cycling stability. As the tri‐layer separator maintains its dimensional stability even at 200 °C when the internal PE layer is melted and blocks the ion transport through the separator, the separator also provides an effective thermal shutdown function. The present nanocellulose‐based tri‐layer separator design thus significantly facilitates the realization of high‐energy density Li metal‐based batteries.

  • 3.
    Tseng, Chiao-Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wen, Chenyu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Huang, Ding-Chi
    Institute of Chemistry, Academia Sinica, Taiwan.
    Lai, Chin-Hung
    Department of Medical Applied Chemistry, Chung Shan Medical University, Taiwan.
    Chen, Si
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Hu, Qitao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Chen, Xi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Xu, Xingxing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Tao, Yu-Tai
    Institute of Chemistry, Academia Sinica, Taiwan.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Synergy of Ionic and Dipolar Effects by Molecular Designfor pH Sensing beyond the Nernstian Limit2019In: Advanced Science, ISSN 2198-3844Article in journal (Refereed)
  • 4.
    Xu, Xingxing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Interface Studies for Gold-based Electrochemical DNA Sensors2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Gold based label-free electrochemical DNA sensors have been widely studied for biomarker diagnostics. The sensitivity and reproducibility of these sensors are determined by the sensing interface: the DNA modified gold surfaces. This thesis systematically studies the preparation processes of the DNA sensor interfaces as well as their effects on the sensor performance. First, three pretreatment methods to clean the gold electrode surface and their influence on the subsequent binding of thiolated molecules were carefully investigated. As we found that the surface pretreatment method involving cyclic voltammetry (CV) in H2SO4 may induce structural changes to the gold surface, thus greatly impacting the thiolated molecule binding, the factors influencing this pretreatment method were studied. Practical guidelines were summarized for preparing a clean and reproducible gold surface prior to functionalization. Afterwards, the effects of the surface coverage density of probe DNA and the salt concentration on the probe-target DNA hybridization on a gold sensing surface were systematically investigated using surface plasmon resonance (SPR) analysis. Based on the SPR results, the maximum potentiometric signal that could be generated by the DNA hybridization on the surface, and the detection limits, were estimated for different experimental conditions. These estimations were further compared with experimental results obtained using silicon nanowire field effect transistors (SiNW FET) with DNA modified gold on the gate oxide. Practical limitations for the potentiometric DNA sensor were analysed and discussed. Finally, the stability and reproducibility issues on the electrochemical impedance spectroscopy (EIS) analyses of DNA hybridization were also studied on the aptamer/mercaptohexanol (MCH)-modified gold surface. The root cause for the drift problems in this type of sensor and the temperature effects on the aptamer/MCH modified surface were identified. This thesis could serve as a practical reference for the preparation and understanding of the sensing interface of gold-based electrochemical DNA sensors.

    List of papers
    1. Systematic approach to the development of microfabricated biosensors: relationship between the gold surface pretreatment and thiolated molecule binding
    Open this publication in new window or tab >>Systematic approach to the development of microfabricated biosensors: relationship between the gold surface pretreatment and thiolated molecule binding
    2017 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 31, p. 26610-26621Article in journal (Refereed) Published
    Abstract [en]

    Despite the increasing popularity of microfabricated biosensors due to advances in technologic and surface functionalization strategies, their successful implementation is partially inhibited by the lack of consistency in their analytical characteristics. One of the main causes for the discrepancies is the absence of a systematic and comprehensive approach to surface functionalization. In this article microfabricated gold electrodes aimed at biosensor development have been systematically characterized in terms of surface pretreatment, thiolated molecule binding, and reproducibility by means of X-ray photoelectron scattering (XPS) and cyclic voltammetry (CV). It has been shown that after SU-8 photolithography gold surfaces were markedly contaminated, which decreased the effective surface area and surface coverage of a model molecule mercaptohexanol (MCH). Three surface pretreatment methods compatible with microfabricated devices were compared. The investigated methods were (i) cyclic voltammetry in dilute H2SO4, (ii) gentle basic piranha followed by linear sweep voltammetry in dilute KOH, and (iii) oxygen plasma treatment followed by incubation in ethanol. It was shown that all three methods significantly decreased the contamination and increased MCH surface coverage. Most importantly, it was also revealed that surface pretreatments may induce structural changes to the gold surfaces. Accordingly, these alterations influence the characteristics of MCH functionalization.

    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:uu:diva-326715 (URN)10.1021/acsami.7b08581 (DOI)000407540400106 ()28726367 (PubMedID)
    Funder
    Swedish Foundation for Strategic Research , SSF ICA 12-0047, FFL15-0174Swedish Research Council, VR 2014-5588Carl Tryggers foundation
    Available from: 2017-07-26 Created: 2017-07-26 Last updated: 2019-11-26Bibliographically approved
    2. Revisiting the factors influencing gold electrodes prepared using cyclic voltammetry
    Open this publication in new window or tab >>Revisiting the factors influencing gold electrodes prepared using cyclic voltammetry
    Show others...
    2019 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 283, p. 146-153Article in journal (Refereed) Published
    Abstract [en]

    Gold is widely used as the electrode material in different chemi- and biosensing applications while cyclic voltammetry (CV) in sulfuric acid solutions is a commonly employed method for gold surface preparation and characterization. However, as shown herein, chloride leakage from the Ag/AgCl/sat. KCl reference electrode and platinum dissolution from the platinum counter electrode can severely compromise the reproducibility and hence the reliability of the prepared gold electrodes. The aim of this work is to obtain a comprehensive understanding of the separate and interdependent effects of the aforementioned factors on the voltammetric behavior of microfabricated polycrystalline gold electrodes. It is shown that the leakage of chloride gives rise to etching of both the gold working and the platinum counter electrodes and that the chloride concentration has a strong influence on the ratio between the obtained gold and platinum concentrations in the electrolyte. The dissolved gold and platinum are then re-deposited on the gold electrode on the cathodic voltammetric scan, changing the structure and properties of the electrode. It is also demonstrated that the changes in the properties of the gold electrode are determined by the ratio between the co-deposited platinum and gold rather than the absolute amount of platinum deposited on the gold electrode. In addition, the chloride and sulfate adsorption behavior on the gold electrode is carefully investigated. It is proposed that redox peaks due to the formation ofthe corresponding Au(I) complexes can be seen in the double layer region of the voltammogram. The results show that the chloride leakage from the reference electrode needs to be carefully controlled and that platinum counter electrodes should be avoided when developing gold sensing electrodes. The present comprehensive understanding of the electrochemical performance of gold electrodes prepared using CV should be of significant importance in conjunction with both fundamental investigations and practical applications.

    Keywords
    gold electrode, cyclic voltammetry, platinum, electrde etching, chloride leakage, Au(I) complexes
    National Category
    Analytical Chemistry Engineering and Technology
    Research subject
    Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-372135 (URN)10.1016/j.snb.2018.12.008 (DOI)000455854000018 ()
    Funder
    Swedish Foundation for Strategic Research , ICA 12-0047Swedish Foundation for Strategic Research , FFL15-0174Swedish Research Council, 2014-5588Wallenberg Foundations, Academy Fellow
    Available from: 2019-01-06 Created: 2019-01-06 Last updated: 2020-01-08Bibliographically approved
    3. Estimating Detection Limits of Potentiometric DNA sensors Using Surface Plasmon Resonance Analyses
    Open this publication in new window or tab >>Estimating Detection Limits of Potentiometric DNA sensors Using Surface Plasmon Resonance Analyses
    Show others...
    2020 (English)In: ACS Sensors, E-ISSN 2379-3694, Vol. 5, no 1, p. 217-224Article in journal (Refereed) Published
    Abstract [en]

    As the signals of potentiometric-based DNA ion-selective field effect transistor (ISFET) sensors differ largely from report to report, a systematic revisit to this method is needed. Herein, the hybridization of the target and the probe DNA on the sensor surface and its dependence on the surface probe DNA coverage and the ionic strength were systematically investigated by surface plasmon resonance (SPR). The maximum potentiometric DNA hybridization signal that could be registered by an ISFET sensor was estimated based on the SPR measurements, without considering buffering effects from any side interaction on the sensing electrode. We found that under physiological solutions (200 to 300 mM ionic strength), the ISFET sensor could not register the DNA hybridization events on the sensor surface due to Debye screening. Lowering the salt concentration to enlarge the Debye length would at the same time reduce the surface hybridization efficiency, thus suppressing the signal. This adverse effect of low salt concentration on the hybridization efficiency was also found to be more significant on the surface with higher probe coverage due to steric hindrance. With the method of diluting buffer, the maximum potentiometric signal generated by the DNA hybridization was estimated to be only around 120 mV with the lowest detection limit of 30 nM, occurring on a surface with optimized probe coverage and in the tris buffer with 10 mM NaCl. An alternative method would be to achieve high-efficiency hybridization in the buffer with high salt concentration (1 M NaCl) and then to perform potentiometric measurements in the buffer with low salt concentration (1 mM NaCl). Based on the characterization of the stability of the hybridized DNA duplexes on the sensor surface in low salt concentration buffer solutions, the estimated maximum potentiometric signal could be significantly higher using the alternative method. The lowest detection limit for this alternative method was estimated to be around 0.6 nM. This work can serve as an important quantitative reference for potentiometric DNA sensors.

    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-397806 (URN)10.1021/acssensors.9b02086 (DOI)000510079300029 ()31833355 (PubMedID)
    Funder
    Swedish Foundation for Strategic Research , ICA 12-0047Swedish Foundation for Strategic Research , FFL15-0174Swedish Research Council, VR 2014-5588Wallenberg Foundations
    Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2020-03-20Bibliographically approved
    4. Structural Changes of Mercaptohexanol Self-assembled Monolayers on Gold and their Influence on Impedimetric Aptamer Sensors
    Open this publication in new window or tab >>Structural Changes of Mercaptohexanol Self-assembled Monolayers on Gold and their Influence on Impedimetric Aptamer Sensors
    Show others...
    2019 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 91, no 22, p. 14697-14704Article in journal (Refereed) Published
    Abstract [en]

    Despite a large number of publications describing biosensors based on electrochemical impedance spectroscopy (EIS), little attention has been paid to the stability and reproducibility issues of the sensor interfaces. In this work, the stability and reproducibility of faradaic EIS analyses on the aptamer/mercaptohexanol (MCH) self-assembled monolayer (SAM) functionalized gold surfaces in ferri- and ferrocyanide solution were systematically evaluated prior to and after the aptamer-probe DNA hybridization. It is shown that the EIS data exhibited significant drift, and this significantly affected the reproducibility of the EIS signal of the hybridization. As a result, no significant difference between the charge transfer resistance (RCT) changes induced by the aptamer-target DNA hybridization and that caused by the drift could be identified. A conditioning of the electrode in the measurement solution for more than 12 hours was required to reach a stable RCT baseline prior to the aptamer-probe DNA hybridization. The monitored drift in RCT and CDL during the conditioning suggests that the MCH SAM on the gold surface reorganized to a thinner but more closely packed layer. We also observed that the hot binding buffer used in the following aptamer-probe DNA hybridization process could induce additional MCH and aptamer reorganization thus further drift in RCT. As a result, the RCT change caused by the aptamer-probe DNA hybridization was less than that caused by the hot binding buffer (blank control experiment). Therefore, it is suggested that the use of high temperature in the EIS measurement should be carefully evaluated or avoided. This work provides practical guidelines for the EIS measurements. Moreover, since SAM functionalized gold electrodes are widely used in biosensors, e.g., DNA sensors, an improved understanding of the origin of the observed drift is very important for the development of well-functioning and reproducible biosensors.

    National Category
    Analytical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-397690 (URN)10.1021/acs.analchem.9b03946 (DOI)000498280100072 ()31650834 (PubMedID)
    Funder
    Swedish Foundation for Strategic Research , ICA 12-0047Swedish Foundation for Strategic Research , FFL15-0174Swedish Research Council, VR 2014-5588Knut and Alice Wallenberg Foundation, Wallenberg Academy Fellow Program
    Available from: 2019-11-22 Created: 2019-11-22 Last updated: 2020-01-13Bibliographically approved
  • 5.
    Xu, Xingxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Makaraviciute, Asta
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Abdurakhmanov, Eldar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Werneling, Fredrik
    Center for Molecular Medicine, Division of Rheumatology, Department of Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.
    Li, Shiyu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Danielson, U. Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Estimating Detection Limits of Potentiometric DNA sensors Using Surface Plasmon Resonance Analyses2020In: ACS Sensors, E-ISSN 2379-3694, Vol. 5, no 1, p. 217-224Article in journal (Refereed)
    Abstract [en]

    As the signals of potentiometric-based DNA ion-selective field effect transistor (ISFET) sensors differ largely from report to report, a systematic revisit to this method is needed. Herein, the hybridization of the target and the probe DNA on the sensor surface and its dependence on the surface probe DNA coverage and the ionic strength were systematically investigated by surface plasmon resonance (SPR). The maximum potentiometric DNA hybridization signal that could be registered by an ISFET sensor was estimated based on the SPR measurements, without considering buffering effects from any side interaction on the sensing electrode. We found that under physiological solutions (200 to 300 mM ionic strength), the ISFET sensor could not register the DNA hybridization events on the sensor surface due to Debye screening. Lowering the salt concentration to enlarge the Debye length would at the same time reduce the surface hybridization efficiency, thus suppressing the signal. This adverse effect of low salt concentration on the hybridization efficiency was also found to be more significant on the surface with higher probe coverage due to steric hindrance. With the method of diluting buffer, the maximum potentiometric signal generated by the DNA hybridization was estimated to be only around 120 mV with the lowest detection limit of 30 nM, occurring on a surface with optimized probe coverage and in the tris buffer with 10 mM NaCl. An alternative method would be to achieve high-efficiency hybridization in the buffer with high salt concentration (1 M NaCl) and then to perform potentiometric measurements in the buffer with low salt concentration (1 mM NaCl). Based on the characterization of the stability of the hybridized DNA duplexes on the sensor surface in low salt concentration buffer solutions, the estimated maximum potentiometric signal could be significantly higher using the alternative method. The lowest detection limit for this alternative method was estimated to be around 0.6 nM. This work can serve as an important quantitative reference for potentiometric DNA sensors.

  • 6.
    Xu, Xingxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Makaraviciute, Asta
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Kumar, Shalen
    Wen, Chenyu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Sjödin, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Abdurakhmanov, Eldar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Danielson, U. Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Structural Changes of Mercaptohexanol Self-assembled Monolayers on Gold and their Influence on Impedimetric Aptamer Sensors2019In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 91, no 22, p. 14697-14704Article in journal (Refereed)
    Abstract [en]

    Despite a large number of publications describing biosensors based on electrochemical impedance spectroscopy (EIS), little attention has been paid to the stability and reproducibility issues of the sensor interfaces. In this work, the stability and reproducibility of faradaic EIS analyses on the aptamer/mercaptohexanol (MCH) self-assembled monolayer (SAM) functionalized gold surfaces in ferri- and ferrocyanide solution were systematically evaluated prior to and after the aptamer-probe DNA hybridization. It is shown that the EIS data exhibited significant drift, and this significantly affected the reproducibility of the EIS signal of the hybridization. As a result, no significant difference between the charge transfer resistance (RCT) changes induced by the aptamer-target DNA hybridization and that caused by the drift could be identified. A conditioning of the electrode in the measurement solution for more than 12 hours was required to reach a stable RCT baseline prior to the aptamer-probe DNA hybridization. The monitored drift in RCT and CDL during the conditioning suggests that the MCH SAM on the gold surface reorganized to a thinner but more closely packed layer. We also observed that the hot binding buffer used in the following aptamer-probe DNA hybridization process could induce additional MCH and aptamer reorganization thus further drift in RCT. As a result, the RCT change caused by the aptamer-probe DNA hybridization was less than that caused by the hot binding buffer (blank control experiment). Therefore, it is suggested that the use of high temperature in the EIS measurement should be carefully evaluated or avoided. This work provides practical guidelines for the EIS measurements. Moreover, since SAM functionalized gold electrodes are widely used in biosensors, e.g., DNA sensors, an improved understanding of the origin of the observed drift is very important for the development of well-functioning and reproducible biosensors.

  • 7.
    Xu, Xingxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Makaraviciute, Asta
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Pettersson, Jean
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyholm, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Revisiting the factors influencing gold electrodes prepared using cyclic voltammetry2019In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 283, p. 146-153Article in journal (Refereed)
    Abstract [en]

    Gold is widely used as the electrode material in different chemi- and biosensing applications while cyclic voltammetry (CV) in sulfuric acid solutions is a commonly employed method for gold surface preparation and characterization. However, as shown herein, chloride leakage from the Ag/AgCl/sat. KCl reference electrode and platinum dissolution from the platinum counter electrode can severely compromise the reproducibility and hence the reliability of the prepared gold electrodes. The aim of this work is to obtain a comprehensive understanding of the separate and interdependent effects of the aforementioned factors on the voltammetric behavior of microfabricated polycrystalline gold electrodes. It is shown that the leakage of chloride gives rise to etching of both the gold working and the platinum counter electrodes and that the chloride concentration has a strong influence on the ratio between the obtained gold and platinum concentrations in the electrolyte. The dissolved gold and platinum are then re-deposited on the gold electrode on the cathodic voltammetric scan, changing the structure and properties of the electrode. It is also demonstrated that the changes in the properties of the gold electrode are determined by the ratio between the co-deposited platinum and gold rather than the absolute amount of platinum deposited on the gold electrode. In addition, the chloride and sulfate adsorption behavior on the gold electrode is carefully investigated. It is proposed that redox peaks due to the formation ofthe corresponding Au(I) complexes can be seen in the double layer region of the voltammogram. The results show that the chloride leakage from the reference electrode needs to be carefully controlled and that platinum counter electrodes should be avoided when developing gold sensing electrodes. The present comprehensive understanding of the electrochemical performance of gold electrodes prepared using CV should be of significant importance in conjunction with both fundamental investigations and practical applications.

  • 8.
    Xu, Xingxing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. Uppsala University.
    Makaraviciute, Asta
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Pettersson, Jean
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Considerations for the Cyclic Voltammetry of Gold in Sulfuric Acid Solutions2018Conference paper (Other academic)
    Abstract [en]

    A comprehensive understanding of the cyclic voltammetry (CV) for gold surfaces is essential for advanced applications. In the present study, a series of experiments were designed to investigate CV for gold under different experimental conditions when using a conventional configuration of a Ag/AgCl/sat. KCl reference electrode and a platinum wire counter electrode. The interferences introduced by the configuration were reflected in the three fingerprint regions of the voltammograms. It was found that the shape of the voltammograms was less reproducible at a lower sample volume when the cycle number was increased. This observation could be explained by different concentrations of Cl- leaking from the reference electrode and platinum dissolved from the counter electrode. The reproducibility of the gold oxidation and reduction (Ox/Re) region in the voltammograms was improved when gold dissolution and re-deposition caused by Cl- leakage was eliminated by using a bridge. In the hydrogen evolution and oxidation reactions (HER/HOR) region the catalytic performance of the gold electrode could be minimized by replacing the platinum counter electrode with a graphite rod. Alternatively, it could be enhanced by increasing the surface ratio of the co-deposited platinum to gold. In the electric double layer (EDL) region, peaks dependent on the concentrations of Cl- and SO42- were observed. To account for the occurrence of these peaks, a new mechanism based on the formation of neutral gold (I) complexes at very low Au+ concentrations, was proposed. 

  • 9.
    Zhang, Da
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Must, Indrek
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Netzer, Nathan L.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Xu, Xingxing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Solomon, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Direct assessment of solid–liquid interface noise in ion sensing using a differentialmethod2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 15, article id 151603Article in journal (Refereed)
    Abstract [en]

    This letter presents a microelectrode cell dedicated to direct assessment of the solid-liquid interface noise without recourse to a reference electrode. In the present design, two identical TiN electrodes of various sizes are used for differential measurements in KCl-based electrolytes. Measured noise of the TiN vertical bar electrolyte system is found to be of thermal nature. Scaling inversely with electrode area, the noise is concluded to mainly arise from the solid-liquid interface. This noise is comparable to or larger than that of the state-of-the-art MOSFETs. Therefore, its influence cannot be overlooked for the design of future ion sensors.

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