Redox Switchable Polydopamine-Modified AFM-SECM Probes: A Probe for Electrochemical Force Spectroscopy

Abstract

Polydopamine (PDA) has high potential in biorelevant applications as a versatile thin film material, e.g., as adhesive coating for cell immobilization or for sensing applications due to the plethora of functional groups. In this study we present the modification of conductive colloidal atomic force−scanning electrochemical microscopy (AFM-SECM) probes with electrochemically deposited PDA resulting in functional probes for quantitative electrochemical adhesion studies. Surface functionality of PDA can be altered by oxidation or reduction of functional groups applying an appropriate potential to the PDA-modified AFM-SECM probe, thereby enabling adhesion measurements under potential control. This facilitates probing specific interactions of surface groups present in PDA with various surfaces of different wettabilities. The versatility of such switchable AFM-SECM probes is demonstrated for electrochemical force spectroscopic studies at model samples such as plasma-treated gold substrates, hydrophobic or hydrophilic self-assembled monolayers, and for adhesion measurements of bacteria in dependence of altered surface charges of the colloidal probe. The maximum obtained adhesion force of a positively polarized PDA-modified AFM-SECM probe was 6.2 ± 2.2 nN, and it was about 50% less (i.e., 2.6 ± 1.1 nN) for a negatively polarized probe at a hydrophilic OHterminated gold surface. In situ control of the active surface groups enabled investigations on the influence of surface charges on adhesion. Furthermore, plateaus of constant force were observed, which are a characteristic of polymer structures. Finally, electrochemical force measurements with switchable probes were used for the first time during adhesion studies of bacterial cells (i.e., Pseudomonas f luorescens). Positively biased PDA-coated colloidal probes revealed adhesion forces of 6.0 ± 1.1 nN, whereas significantly reduced adhesion forces 1.1 ± 0.7 nN were observed for negatively biased PDA-modified colloidal probes.

Physicochemical and Electrochemical Characterization of Electropolymerized Polydopamine Films: Influence of the Deposition Process

“…Predominantely, cyclic voltammetry (CV) in oxygen-free basic dopamine solution is employed to deposit PDA [ 13 ]. Other electrochemical methods, such as galvanostatic deposition [ 14 ] and pulsed deposition [ 15 , 16 , 17 ], have been described in the literature. Although electrochemical PDA deposition is limited to (semi)conductive substrates, the electrochemical route allows fast deposition times in the range of seconds, in contrast to dip coating, which usually takes several hours to form PDA.…”

Strategic Advances in Spatiotemporal Control of Bioinspired Phenolic Chemistries in Materials Science

“…In addition, the catechol/quinone redox could be manipulated by applying a sufficiently positive or negative potential. [140][141] Harnessing the electrochemically dynamic switching, Daboss et al recently prepared a PDA-modified colloidal atomic force-scanning electrochemical microscopy probe, which could provide instrumental insights into the adhesion properties of bacteria, cells, and tissues. [141] In addition, the electrochemical catechol/quinone switching can be a facile way to in situ tailor the adhesiveness of catechol-based materials.…”

“…[140][141] Harnessing the electrochemically dynamic switching, Daboss et al recently prepared a PDA-modified colloidal atomic force-scanning electrochemical microscopy probe, which could provide instrumental insights into the adhesion properties of bacteria, cells, and tissues. [141] In addition, the electrochemical catechol/quinone switching can be a facile way to in situ tailor the adhesiveness of catechol-based materials. Recently, Akram Bhuiyan et al evaluated the effect of electrical field on the adhesive property of catechol using a Johnson-Kendall-Roberts (JKR) contact mechanics test setup ( Figure 5C, g).…”

“…recently prepared a PDA‐modified colloidal atomic force‐scanning electrochemical microscopy probe, which could provide instrumental insights into the adhesion properties of bacteria, cells, and tissues. [ 141 ] In addition, the electrochemical catechol/quinone switching can be a facile way to in situ tailor the adhesiveness of catechol‐based materials. Recently, Akram Bhuiyan et al.…”

Scanning electrochemical microscopy and its potential for studying biofilms and antimicrobial coatings

“…mapping the flux of biomedically relevant electroactive molecules [ 128 ], detection of single-protein molecules at isolated viruses [ 127 , 135 ] and mapping adhesion properties of mouse fibroblasts using conductive polymer–modified colloidal AFM-SECM probes [ 136 ]. Recently, Daboss et al [ 137 ] investigated the adhesion of Pseudomonas fluorescens at the single bacterial cell level using polydopamine (PDA)-modified colloidal AFM-SECM probes. The functional groups of PDA can be selectively switched via the applied potential of the AFM-SECM probe, changing the adhesion forces due to the change in surface charges (as shown Fig.…”