Electrochemical Desorption Of Self-assembled Monolayers Research Articles

Electrochemical Manipulation of Living Cells Supported By Polymeric Nanosheets

Introduction Regenerative medicine based on cell sheets has been widely investigated. Developing an effective and minimally invasive cell transplantation process is an important enabling step for such medical treatments. However, cell sheets are fragile and handling them is difficult. Recently, we have investigated the use of biodegradable polymeric nanosheets for introducing cells into the body and found that the flexible nanosheets on which cells are cultured can be aspirated and injected by a syringe needle without significant loss of cell viability. To harvest cell/nanosheet constructs from a substrate, a water soluble sacrificial layer such as polyvinyl alcohol (PVA) was used, however, a drawback in this method is that the timing to detach the cell/nanosheet constructs from the substrate cannot be controlled. In this paper, we use an electrochemical method for harvesting the cell/nanosheet constructs in vitro. Cells are cultured on nanosheets attached on a self-assembled monolayer (SAM) of alkanethiol. The SAM is reductively desorbed from the gold substrate by the application of a negative electrical potential, which detaches the cell/nanosheet constructs from the gold surface in a rapid manner. The harvested cell/nanosheet constructs were transplanted into the subretinal space of rat eyes through syringe needles. Material and Method A gold layer was patterned by sputter-depositing gold with a patterned silicon mask. The gold surface was modified with 10-carboxy-1-decanethiol, 7-carboxy-1-heptanethiol or L-cysteine by immersing the substrates in any of the three thiol solutions for 30 min at room temperature. The desorption of the SAMs was performed and analyzed electrochemically. Nanosheets were first prepared on PVA-coated substrates by a combination of a spincoating and microcontact printing technique using poly(dimethyl siloxane) (PDMS) stamps. A solution of poly(lactic-co-glycolic acid) (PLGA) was spincoated onto the PDMS stamp and the resulting PLGA layer was transferred onto a PVA-coated substrate. Freestanding nanosheets were obtained by dissolving the PVA sacrificial layer with water and attached on the SAM-modified gold surface. To desorb the nanosheets with SAMs, a voltage of 1.5 V, supplied by an AA-size dry battery, was applied between the gold electrode (cathode) and the Pt wire (anode) in phosphate buffered saline. Retinal pigment epithelium (RPE) cells were cultured on PLGA nanosheets attached on the SAMs for 2 days to form cell/nanosheet constructs. Electrochemical desorption of SAMs with cell/nanosheet constructs was conducted in culture medium. Sprague-Dawley rats (SLC) weighing 250-300 g were used in this study. After the rats were anesthetized with ketamine hydrochloride and xylazine hydrochloride, RPE cell/nanosheet constructs were injected into the subretinal space using a hand-made glass capillary needle. Result and Discussion Cyclic voltammograms observed in the reductive desorption of SAMs showed a clear dependence of peak potential on the length of the alkyl chain. With longer chains, the peak potential shifted to the negative direction, which has been explained by van der Waals interactions between the alkyl chains. Since the SAM of L-cysteine was reductively desorbed at a lower potential (around -0.7 V vs. Ag/AgCl) than the SAM of the two other thiol molecules and L-cysteine is biocompatible, the SAM of L-cysteine was used for harvesting nanosheets and cell/nanosheet constructs. PLGA nanosheets attached on the SAM of L-cysteine were successively detached from the substrate by gently pipetting within 1 min after applying the reductive potential to the gold electrode. On the other hand, nanosheets on the SAM without applying the voltage did not detach from the substrate. In a similar manner, RPE cell/nanosheet constructs could be detached from the substrate and the live/dead staining showed the cells on the nanosheets are viable.  Finally, we used our system to deliver RPE cell/nanosheet constructs to the subretinal space of a rat eye in vivo. Nanosheets were injected with 2 μL of saline to the subretinal space through the sclera using a glass capillary needle. Optical coherence tomography (OCT) images of the retina taken one week after the injection of the nanosheets showed a shadow of the sheet like structure in the subrentinal space while there was not such shadow in the OCT image of a control. Also, a shadow of the circular nanosheet was observed at the posterior segment of the isolated eye. These results indicate that the nanosheets were successfully injected and spread into the subretinal space of rat eyes. Conclusion  We reported a method for noninvasively harvesting cell/nanosheet constructs from a culture surface by using the electrochemical desorption of SAM. The harvested RPE/nanosheet constructs could be delivered to the subretinal space using a capillary needle. The harvesting and delivering system of cell/nanosheets constructs could be a useful tool for cell transplantation.

Electrically modulated attachment and detachment of animal cells cultured on an ITO patterning electrode surface

Background Micropatterning techniques of animal cells have been reported by numerous groups and fall into 6 major classifications (1). There are 1) photolithography, 2) soft lithography, 3) ink jet printing, 4) electron beam writing, 5) electrochemical desorption of self-assembled monolayers, and 6) dielectrophoresis. These six cell micropatterning techniques cannot modulate both the attachment and detachment of animal cells iteratively at the same positions, however. The present work has demonstrated that a weak electrical potential can modulate the attachment and detachment of specifically positioned adhesive animal cells using a patterned indium tin oxide (ITO)/ glass electrode culture system [1], (Figure 1).

Electrochemical Desorption of Self-assembled Monolayers and Its Application for Regenerative Medicine

Electrochemical Desorption of Self-assembled Monolayers and Its Application for Regenerative Medicine

Electrochemical desorption of self-assembled monolayers and its applications in surface chemistry and cell biology

Electrochemical desorption (ECD) of self-assembled monolayers (SAMs) is an important process that can dynamically modify surface properties. ECD of SAMs has found applications in biochemical assays and the precise control of cell adhesion. As cell adhesion is controlled by the chemistry of underlying substrate, ECD provides a means to achieve spatiotemporal control of cell behaviors by electrically addressing the substrate. In this minireview, we first introduce the principles of ECD, followed by its applications in dynamically modifying chemistry and biochemistry at the intersurface. Finally, we highlight its applications in cell biology.

Bottom‐Up Fabricated Asymmetric Electrodes for Organic Electronics

A new method for obtaining asymmetric (nano)electrodes through the adsorption and electrochemical desorption of self-assembled monolayers on gold is described. The selective WF modification is demonstrated by Kelvin Probe Force Microscopy and electrical characterization of organic FETs. The proposed method is simple, fast and could allow parallel, large-scale fabrication of asymmetric electrodes for micro- and large-area electronics.

Electrochemical desorption of self-assembled monolayers for engineering cellular tissues

Adherent cells, cell sheets, and spheroids were harvested noninvasively from a culture surface by means of electrochemical desorption of a self-assembled monolayer (SAM) of alkanethiol. The SAM surface was made adhesive by the covalent bonding of Arg-Gly-Asp (RGD)-peptides to the alkanethiol molecules. The application of a negative electrical potential caused the reductive desorption of the SAM, resulting in the detachment of the cells. Using this approach greater than 90% of adherent cells detached within 5 min. Furthermore, this approach was used to obtain two-dimensional (2D) cell sheets. The detached cell sheets consisted of viable cells, which could be easily attached to other cell sheets in succession to form a multilayered cell sheet. Moreover, spheroids of hepatocytes of a uniform diameter were formed in an array of cylindrical cavities at a density of 280 spheroids/cm 2 and were harvested by applying a negative electrical potential. This cell manipulation technology could potentially be a useful tool for the fabrication and assembly of building blocks such as cell sheets and spheroids for regenerative medicine and tissue engineering applications.

A new cleaning methodology for efficient Au-SAM removal

Abstract The desorption of a self-assembled monolayer (SAM) of 11-amino-1-undecanethiol (AUT) formed on an Au polycrystalline electrode was investigated with the purpose of establishing the most efficient method for SAM removal prior to electrode re-use. The cleanliness of the surface was evaluated by assessing the characteristics (and their reproducibility) of a newly prepared SAM (on a freshly cleaned electrode) in the presence of Ru(NH3)63+/2+ probe species. The simple flame annealing of the modified electrodes showed poor reproducibility. Later, cleaning treatments based on previous reports about the electrochemical desorption of SAMs, were investigated in NaOH, HClO4, and KCl solutions. The anodic removal in alkaline and chloride solutions was not efficient enough due to the effect of the Au surface oxidation and dissolution. The commonly used reductive desorption in alkaline solution did also not offer a high efficiency (in contrast with the behavior described in those reports) probably due to the low stability of the thiolate molecules at high-pH values. In addition, such procedures did not provide a way to visualize the evolution of the process. The oxidative desorption in perchloric acid showed a higher efficiency at each single desorption cycle, and allowed to monitor the extension of the removal by comparing the cyclic voltammograms obtained in that medium with the expected fingerprint for the bare Au. However the voltammetric characterization of new AUT films, prepared on such electrochemically treated surfaces by re-incubation in the AUT solution, showed that the conditions of substrate cleanliness and smoothness necessaries to reproduce a close-packed and compact AUT monolayer were not reached. A new cleaning strategy based on the coupled use of oxidative removal in HClO4 0.1 M and flame annealing showed to be efficient and reproducible, providing the proper substrate precursors for the formation of highly ordered AUT films. The results also showed that the methodology works well in the removal of other SAMs like the one formed by the neutral 1-dodecanethiol (1-DT).

In-situ fluorescence spectroscopy of self-assembled monolayers of HS-(CH 2) n-fluorescein and HS-(CH 2) 6-poly(dT) 18-fluorescein at gold electrodes under cyclic voltammetric conditions

We present the dynamics of electrochemical desorption of self-assembled monolayers of HS-(CH 2) n -fluorescein ( n = 3 and 12; C 3FAM and C 12FAM) and HS-(CH 2) 6-poly(dT) 18-fluorescein (ssDNAFAM) as monitored in-situ by fluorescence spectroscopy. Surface coverage and fluorescence intensity were also correlated, as sense during electrochemical desorption of the SAM. Changes in potential scan rate did not impact the fluorescence emission. Co-adsorption of mercaptohexanol (MCH) could be detected electrochemically and by in-situ fluorescence spectroscopy. Based on these results, energy transfer from an excited dye to the metal can be used to study interfacial dynamics. The transition of a single stranded DNA self-assembled monolayer from a condensed to an elongated state was monitored by in-situ fluorescence. Its electrochemical desorption from the electrode surface was measured as the electrochemical potential was applied above −1.0 V vs. Ag/AgCl. The DNA transition from condensed to elongated state can be exploited to study DNA hybridization process and other possible recognition events at the interface.

A Method for Patterning Multiple Types of Cells by Using Electrochemical Desorption of Self‐Assembled Monolayers within Microfluidic Channels

Fenced in: Selective electrochemical desorption of self-assembled monolayers of HS(CH2)11(OCH2CH2)6OH was carried out on parts of a gold substrate restricted to microfluidic channels. This chemical transformation activates parts of the surface for adhesion of multiple types of cells with well-controlled geometry.

Electrochemical Desorption of Self-Assembled Monolayers Noninvasively Releases Patterned Cells from Geometrical Confinements

This report describes a method to pattern mammalian cells using self-assembled monolayers (SAMs), and then to use electrochemical desorption of these monolayers to release cells from their patterns. This method uses an oligo(ethyleneglycol)-terminated SAM to prevent,-and a methyl-terminated SAM to allow-adsorption of proteins and attachment of bovine capillary endothelial cells. Electrochemical removal of the oligo(ethyleneglycol)-terminated SAM allowed proteins to adsorb onto areas that had been previously inert and enabled cells to migrate into these areas. This straightforward technique is useful in bioassays for drug screening and for fundamental studies in cell biology.

Patterns of functional proteins formed by local electrochemical desorption of self-assembled monolayers

Patterned self-assembled monolayers (SAMs) were formed using the scanning electrochemical microscope (SECM). The procedures is based on the local electrochemical desorption of an alkanethiolate monolayer by applying a 5 kHz square-wave voltage of 2 V (peak-to-peak) to a two-electrode configuration consisting of an ultramicroelectrode (UME) of 10 μm diameter placed about 5 μm above a macroscopic SAM-covered gold electrode. Desorption occurs on well-defined regions with a diameter of (12.8±2.8) μm. These regions of bare gold are able to chemisorb a ω-functionalized thiol or disulfide such as cystamine to form patterns of amino-terminated surfaces. Functional proteins can be coupled to the amino groups present at the modified regions of the monolayer. This approach was demonstrated by imaging the activity of horseradish peroxidase bound to the patterned SAMs in the generation–collection mode of the SECM. A considerable improvement of the procedure could be achieved by performing the desorption in a solution containing a millimolar concentration of the ω-functionalized thiol/disulfide ensuring effective refilling of the monolayer by the desired molecules and hence high concentration of the immobilized proteins. The method is discussed with respect to prospective application in the field of chip-based bioanalytical assays.

Electrochemical Patterning of Self-Assembled Monolayers onto Microscopic Arrays of Gold Electrodes Fabricated by Laser Ablation

This report demonstrates proof-of-concept application of two established electrochemical techniques affecting self-assembled monolayersthe thermodynamic control of monolayer assembly at gold and the electrochemical desorption of self-assembled monolayers from goldto pattern monolayers onto gold microelectrodes. When combined with a simple laser-based microfabrication technique, using commercially available microscope adaptations, to form arrays of individually-addressable gold microelectrodes from continuous thin gold films on glass, two new patterning methodologies result that enable fabrication of monolayer-based affinity arrays for potential use in chemical and biosensors. The described microfabrication technique is central to the success of these patterning methodologies because it allows SAM patterning of metal arrays immediately after their fabrication, so as to avoid problems associated with forming SAMs on commercially-supplied arrays. In this paper, each patterning methodology is used to fabricat...