| 1. |
- Hinnemo, Malkolm, 1986-, et al.
(författare)
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Protein sensing beyond the Debye Length Using Graphene Field-effect Transistors
- 2018
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Ingår i: IEEE Sensors Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-437X .- 1558-1748. ; 18:16, s. 6497-6503
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Tidskriftsartikel (refereegranskat)abstract
- Sensing biomolecules in electrolytes of high ionic strength has been a difficult challenge for field-effect transistor-based sensors. Here, we present a graphene-based transistor sensor that is capable of detection of antibodies against protein p53 in electrolytes of physiological ionic strength without dilution. As these molecules are much larger than the Debye screening length at physiological ionic strengths, this paper proves the concept of detection beyond the Debye length. The measured signal associated with the expected specific binding of the antibodies to p53 is concluded to result from resistance changes at the graphene-electrolyte interface, since a sensor responding to resistance changes rather than charge variations is not limited by Debye screening. The conclusion with changes in interface resistance as the underlying phenomena that lead to the observed signal is validated by impedance spectroscopy, which indeed shows an increase of the total impedance in proportion to the amounts of bound antibodies. This finding opens up a new route for electrical detection of large-size and even neutral biomolecules for biomedical detection applications with miniaturized sensors.
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| 2. |
- Makaraviciute, Asta, et al.
(författare)
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A QCM-D Study of Reduced Antibody Fragments Immobilized on Planar Gold and Gold Nanoparticle Modified Sensor Surfaces
- 2014
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Ingår i: Key Engineering Materials. - : Trans Tech Publications. - 1013-9826 .- 1662-9795. ; 605, s. 340-343
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Tidskriftsartikel (refereegranskat)abstract
- An immunosensor is an analytical system consisting of specific immune system molecules coupled to a signal transducer. Immunosensor sensitivity depends on the type of immunorecognition ligands used, immobilization influence on their activity and orientation on the surface. Quartz crystal microbalance with dissipation (QCM-D) was employed to investigate the immobilization of antibodies against bovine leukemia virus antigen gp51 (gp51). Disulphide bridges of antibody hinge region were reduced chemically to yield two “half” antibody fragments (Frag-Ab), each having a single antigen binding site and free sulfhydryl groups that were used for immobilization. Frag-Ab were immobilized on planar gold and gold nanoparticle (AuNP) modified QCM-D sensor surfaces from initial solutions of different concentrations. Higher Frag-Ab surface density values were obtained on AuNP modified surfaces at all tested antibody concentrations. Frag-Ab/gp51 specific interaction was registered and it was determined that the highest sensitivity was exhibited by Frag-Ab immobilized at the lowest surface desities on both types of investigated surfaces. Specific gp51 interaction with Frag-Ab and non-specific binding to bovine serum albumin modified surfaces were
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| 3. |
- Makaraviciute, Asta, et al.
(författare)
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Antibody fragment immobilization on planar gold and gold nanoparticle modified quartz crystal microbalance with dissipation sensor surfaces for immunosensor applications
- 2014
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Ingår i: Analytical Methods. - : Royal Society of Chemistry. - 1759-9660 .- 1759-9679. ; 6:7, s. 2134-2140
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Tidskriftsartikel (refereegranskat)abstract
- Immunosensors are bioaffinity sensors incorporating immune system molecules that are utilized for analyte recognition and signal transduction yielding a measurable signal upon analyte detection. A lot of effort has been made to optimize the immobilization matrix on the sensor surface since the outcome of the ligand immobilization procedure determines sensitivity, specificity and longevity of the developed immunosensor. In this work, antibodies against bovine leukemia virus antigen gp51 were chemically reduced to "half" antibody fragments that were later employed as recognition ligands. Antibody fragments at different concentrations were immobilized via thiolate bonds on planar gold and gold nanoparticle modified surfaces of a quartz crystal microbalance with dissipation sensor. Antibody fragment immobilization and interaction with antigen were investigated. Antibody fragment surface mass densities after the immobilization on planar gold and gold nanoparticle modified sensor surfaces were directly dependent on the initial antibody concentration. The highest analytical response was exhibited by antibody fragments immobilized at the smallest surface mass density on planar gold and gold nanoparticle modified surfaces. Bovine leukemia virus antigen gp51 interaction with antibody fragments was compared with non-specific gp51 interaction with bovine serum albumin on planar gold and gold nanoparticle modified surfaces by employing Delta D/Delta f plots.
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| 4. |
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| 5. |
- Makaraviciute, Asta, et al.
(författare)
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Systematic approach to the development of microfabricated biosensors : relationship between the gold surface pretreatment and thiolated molecule binding
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:31, s. 26610-26621
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Xu, Xingxing, et al.
(författare)
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Considerations for the Cyclic Voltammetry of Gold in Sulfuric Acid Solutions
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Xu, Xingxing, et al.
(författare)
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Estimating Detection Limits of Potentiometric DNA sensors Using Surface Plasmon Resonance Analyses
- 2020
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Ingår i: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 5:1, s. 217-224
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Xu, Xingxing, et al.
(författare)
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Revisiting the factors influencing gold electrodes prepared using cyclic voltammetry
- 2019
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 283, s. 146-153
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Xu, Xingxing, et al.
(författare)
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Structural Changes of Mercaptohexanol Self-assembled Monolayers on Gold and their Influence on Impedimetric Aptamer Sensors
- 2019
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 91:22, s. 14697-14704
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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