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Interface Studies for Gold-based Electrochemical DNA Sensors
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
2019 (English)Doctoral 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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 83
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1882
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-397807ISBN: 978-91-513-0824-1 (print)OAI: oai:DiVA.org:uu-397807DiVA, id: diva2:1372955
Public defence
2020-01-20, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-12-18 Created: 2019-11-25 Last updated: 2020-01-14
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
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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
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2019 (English)In: ACS Sensors, E-ISSN 2379-3694Article in journal (Refereed) Accepted
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
Identifiers
urn:nbn:se:uu:diva-397806 (URN)10.1021/acssensors.9b02086 (DOI)
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: 2020-01-20Bibliographically 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
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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

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