Abstract
Electrografting of aryldiazonium species is useful for linkage between electrochemical transducer surface and biosensor recognition elements. However, the process proceeds uncontrollably to form branched/multilayer growth. This paper reports harnessing steric hindrance for controlled growth of aryldiazonium coupling agent during electrografting to screen-printed carbon electrode surface, which was subsequently used for linkage of CRP recognition elements to form a biosensor with greater sensitivity (32.0 ± 0.5 μA/(ng/mL) than that formed by way of uncontrolled growth (26.6. ± 5.3 μA/(ng/mL) across a highly sensitive operating range of 0.01–10 ng/mL. To the best of our knowledge, this is the first report of this approach demonstrated as a route for biosensor fabrication. This finding suggests the approach can be exploited in immunosensor assays.
| Original language | English |
|---|---|
| Article number | 100060 |
| Journal | Sensors International |
| Volume | 2 |
| DOIs | |
| Publication status | Published - 2021 |
| MoE publication type | A1 Journal article-refereed |
Keywords
- Aryldiazonium grafting
- Aryldiazonium salt
- C-reactive protein
- Electrochemical biosensor
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In: Sensors International, Vol. 2, 100060, 2021.
Research output: Contribution to journal › Article › Scientific › peer-review
TY - JOUR
T1 - Controlled diazonium electrodeposition towards a biosensor for C-reactive protein
AU - Gillan, Liam
AU - Teerinen, Tuija
AU - Johansson, Leena-Sisko
AU - Smolander, Maria
N1 - Funding Information: This research was supported by VTT Technical Research Centre of Finland Ltd. In XPS analysis this work made use of Aalto University Bioeconomy Facilities. Asko Sneck (VTT) and Ramesh Raju (Aalto University) are gratefully acknowledged for performing AFM measurements. Funding Information: Inability to use AFM for insight into thickness of electrodeposited films led to use of electrochemical methods for investigating differences between the ABA and AMBA modified electrodes. EIS analysis was performed using [Fe(CN)6]4–/3– redox probe, where greater film thickness of grafted organic molecules, coupled with increased negative charge from carboxyl functionality is expected to hinder anionic redox probe access to the carbon transducer surface such that film thickness would appear proportional to electrochemical signal, with thicker films yielding greater electrical impedance. EIS analysis of bare (unmodified) carbon electrode surface was compared to that of ABA and AMBA modified surface, with results presented in Fig. 1a and b, respectively. Functionalisation with either ABA or AMBA results in increased resistance of the system, as was expected. However, there does not appear to be a notable difference between the two. Further electrochemical characterisation was performed by voltammetry, where greater film thickness (such as multilayer growth or branching) with corresponding increase in negatively charged carboxyl functionality, is expected to be observed as reduced intensity of [Fe(CN)6]4–/3– redox activity by mechanism of restricting anionic redox probe to the transducer surface. Fig. 1c and d, depict CV and SWV plots, respectively, where both electrografted ABA and AMBA films suppress the redox activity of the probe. Lower redox signal was observed for AMBA than for ABA, which supports the hypothesis that a greater amount of ABA than AMBA was electrografted to the carbon electrode surface. The oxidation peak of ABA and AMBA modified electrodes in Fig. 1d is shifted by +0.4 V compared to the bare unmodified carbon electrode. This is suspected to be caused by carboxylic acid functionality in an unbuffered system of 5 mM [Fe(CN)6]4–/3–.Both ABA and AMBA films are expected to provide terminal carboxyl functionality in para position relative to the bond linking the deposited molecule to the transducer surface. Analysis of carboxylic acid component could provide information on whether grafting is controlled (lesser carboxyl component from monolayer coverage), or uncontrolled (larger carboxyl component due to extensive growth). Fig. S3 depicts FTIR spectra, where ABA provides larger O–H stretching signal (at around 2750 cm−1) than AMBA modified electrodes. This suggests higher carboxylic acid content in the ABA modified electrode, indicative of multilayer or branched growth. Carboxylic acid functional groups are strongly hydrophilic, in contrast to hydrophobic screen-printed carbon electrode surface. Therefore, contact angle measurements were performed with water, to identify any difference in wetting of electrode surface following ABA or AMBA modification. As depicted in Fig. 2, AMBA modification enhances wetting of electrode surface by water from a contact angle of 133° for bare carbon, to 80° for AMBA modified surface. This effect of increased wetting is even greater for ABA modified surface, with a contact angle of 59° presenting evidence for a larger carboxyl functionality density than that of ABA modified electrode surface, plausibly resulting from multilayer or branched growth of ABA. XPS C 1s spectra signal at around 289 eV can be interpreted as being proportional to carboxyl functionality [41]. XPS C1 s spectra (black curve) was deconvoluted using a graphitic reference to reveal four constituent chemical environments of carbon (green, blue, red, and purple curves). The peak around 289 eV evident in the green component is attributed to carboxyl groups. The magnitude of this signal is largest from carbon electrode modified by ABA, followed by AMBA and bare carbon electrode, respectively. This XPS data supports the contact angle, FTIR, and electrochemical analysis observations of larger carboxyl component present in ABA modified electrodes than that of AMBA modified, or unmodified electrodes, respectively. In addition, this observed trend of carboxyl functionality is also revealed by XPS O 1s spectra (Fig. S4). Because carboxyl functionality of the grafted molecules dominates the oxygen chemical environment in this case, oxygen signal is considered proportional to carboxyl density. O 1s signal at 532.5 eV reveals that the largest oxygen content is present in ABA modified sensors, followed by AMBA modified sensors, with the smallest oxygen signal being generated by the unmodified electrode surface.Stepwise assembly of CRP sensor fabrication was monitored by EIS and CV, using [Fe(CN)6]4–/3– redox probe, with results presented in Figs. S7 and 3, respectively. Bare unmodified carbon electrode surface enables free access to redox probe, with low impedance in EIS and large redox behavior in CV. Upon modification with ABA or ABMA, impedance increases and redox activity decreases due to formation of an electrostatic barrier from negatively charged carboxyl groups. EDC/NHS activation of carboxyl terminated ABA or AMBA film alleviates the electrostatic barrier by removing the negatively carboxyl groups, reducing impedance in EIS, and allowing increased [Fe(CN)6]4–/3– redox activity in CV. Immobilization of antibody is observed as a slight increase in electron transfer resistance in EIS, and decreased redox signal in CV. This could be caused by the antibody acting as a kinetic barrier to electron transfer, size exclusion, or hydrophobic/hydrophilic interactions generating hindrance to the redox probe. The final step of carboxyl deactivation with ethanolamine results in further increase in electron transfer resistance in EIS, and further decrease in redox activity in CV from the dense surface coverage hindering redox probe access to transducer [46]. Importantly, Fig. 3 reveals that there is larger absolute CV redox signal for AMBA than ABA, and Fig. S7 shows EIS electron transfer resistance is larger for ABA than AMBA, therefore ABA presents a greater barrier to [Fe(CN)6]4–/3– redox probe, supporting the notion of uncontrolled growth.This research was supported by VTT Technical Research Centre of Finland Ltd. In XPS analysis this work made use of Aalto University Bioeconomy Facilities. Asko Sneck (VTT) and Ramesh Raju (Aalto University) are gratefully acknowledged for performing AFM measurements. Publisher Copyright: © 2020 The Authors
PY - 2021
Y1 - 2021
N2 - Electrografting of aryldiazonium species is useful for linkage between electrochemical transducer surface and biosensor recognition elements. However, the process proceeds uncontrollably to form branched/multilayer growth. This paper reports harnessing steric hindrance for controlled growth of aryldiazonium coupling agent during electrografting to screen-printed carbon electrode surface, which was subsequently used for linkage of CRP recognition elements to form a biosensor with greater sensitivity (32.0 ± 0.5 μA/(ng/mL) than that formed by way of uncontrolled growth (26.6. ± 5.3 μA/(ng/mL) across a highly sensitive operating range of 0.01–10 ng/mL. To the best of our knowledge, this is the first report of this approach demonstrated as a route for biosensor fabrication. This finding suggests the approach can be exploited in immunosensor assays.
AB - Electrografting of aryldiazonium species is useful for linkage between electrochemical transducer surface and biosensor recognition elements. However, the process proceeds uncontrollably to form branched/multilayer growth. This paper reports harnessing steric hindrance for controlled growth of aryldiazonium coupling agent during electrografting to screen-printed carbon electrode surface, which was subsequently used for linkage of CRP recognition elements to form a biosensor with greater sensitivity (32.0 ± 0.5 μA/(ng/mL) than that formed by way of uncontrolled growth (26.6. ± 5.3 μA/(ng/mL) across a highly sensitive operating range of 0.01–10 ng/mL. To the best of our knowledge, this is the first report of this approach demonstrated as a route for biosensor fabrication. This finding suggests the approach can be exploited in immunosensor assays.
KW - Aryldiazonium grafting
KW - Aryldiazonium salt
KW - C-reactive protein
KW - Electrochemical biosensor
UR - http://www.scopus.com/inward/record.url?scp=85118534269&partnerID=8YFLogxK
U2 - 10.1016/j.sintl.2020.100060
DO - 10.1016/j.sintl.2020.100060
M3 - Article
SN - 2666-3511
VL - 2
JO - Sensors International
JF - Sensors International
M1 - 100060
ER -