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Dynamic Electrochemical Control of Cell Capture-and -Release Based on Redox-Controlled Host-Guest Interactions Tao Gao, Liudi Li, Bei Wang, Jun Zhi, Yang Xiang, and Genxi Li Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b02156 • Publication Date (Web): 16 Sep 2016 Downloaded from http://pubs.acs.org on September 17, 2016
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Analytical Chemistry
Dynamic Electrochemical Control of Cell Capture−and−Release Based on Redox−Controlled Host−Guest Interactions Tao Gao†, Liudi Li†, Bei Wang†, Jun Zhi†, Yang Xiang†, Genxi Li†, ‡,* †. State Key Laboratory of Pharmaceutical Biotechnology and Collaborative Innovation Center of Chemistry for Life Sciences, Department of Biochemistry, Nanjing University, Nanjing 210093, China. ‡.Center for Molecular Recognition and Biosensing, School of Life Sciences, Shanghai University, Shanghai 200444, P. R. China. ABSTRACT: Artificial control of cell adhesion on smart surface is an on−demand technique in areas ranging from tissue engineering, stem cell differentiation to the design of cell−based diagnostic system. In this paper, we report an electrochemical system for dynamic control of cell catch−and−release, which is based on the redox−controlled host−gest interaction. Experimental results reveal that the interaction between guest molecule (ferrocene, Fc) and host molecule (βcyclodextrin, β-CD) is highly sensitive to electrochemical stimulus. By applying a reduction voltage, the uncharged Fc can bind to β-CD that is immobilized at the electrode surface. Otherwise, it is disassociated from the surface as a result of electrochemical oxidation, thus releasing the captured cells. The catch−and−release process on this voltage−responsive surface is noninvasive with the cell viability over 86%. Moreover, because Fc can act as an electrochemical probe for signal readout, the integration of this property has further extended the ability of this system to cell detection. Electrochemical signal has been greatly enhanced for cell detection by introducing branched polymer scaffold that are carrying large quantities of Fc moieties. Therefore, a minimum of 10 cells can be analyzed. It is anticipated that such redox−controlled system can be an important tool in biological and biomedical research, especially for electrochemical stimulated tissue engineering and cell−based clinical diagnosis.
Introduction
addressable electrodes. Through changing the electrochemical techniques and parameters such as potential, scan rate, time etc., cell catch−and−release should be easy to operate with fast response and high efficiency. Furthermore, electrochemical device can be the optimal choice for miniaturization and integration of a cell catch−and−release system. Therefore, the development of an electrochemical platform that can catch and release a specific cell would dramatically advance the technique for cell research.
The ability to selectively control cell attachment and detachment on solid supports is important to research areas ranging from fundamental cell biology,1 tissue engineering2,3 to cell based diagnostics.4,5 For example, the capture and enrichment of circulation tumor cells (CTCs) are of great importance for clinical cancer diagnosis, because CTCs is “liquid biopsy” that can provide precise information for detection, characterization, and monitoring of cancers in early stage.6,7 Recently, approaches to operate cell catch−and−release switches have been developed through fabricating smart surfaces, introducing various stimulus such as enzyme,8 temperature,9,10 light11,12 or chemicals.13 Physicochemical properties of these surfaces (such as wettability, stiffness, structure integrity, mechanical stretching, and photosensitivity) are thus adjusted for controlling cell adhesion. However, harsh and unfavorable conditions involved in these approaches may threaten cell viability, which hinders cell retrieval and further culture for single-cell analysis.14-16 It is therefore desirable to design friendly method to regulate the adhesion behavior of targeted cells.
Electrochemical stimuli−responsive materials or switch surfaces play the central role in design such a device. Electrical potential has been applied to single−layered molecules to undergo conformational transition17 and further controlling of cell adhesion.18,19 Nevertheless, although cells are efficiently captured and released at the surface, selectivity of such system is limited. So, the nano-structured surfaces that couple antibody recognition and electrochemical cleavage have been proposed to improve the selectivity and sensitivity.20 However, up to now, the electrochemically responsive surfaces can only give simple response, which cannot satisfy the advancing requirements for cell diagnosis that also needs signal readout. Therefore, the development of an integrated platform that enables cell capture, detection, and releasing is desirable.
Among all of the stimuli methodologies, the electrochemical stimuli−based method is particularly promising because electronic potential stimuli is noninvasive, and can be easily tuned by applying voltage to individually
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Analytical Chemistry
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In this work, based on the host−guest interaction between β-cyclodextrin (β-CD) and ferrocene (Fc), we have proposed an electrochemical system for controllable catching and releasing of cancer cells. The system utilizes two inherent nature of the guest molecule (Fc): voltage−excited changes of redox states and corresponding electron transfer ability. On the one hand, electrochemically responsive Fc can reversibly switch the host−guest interaction,21 enabling cell catch−and−release. On the other, the resulted electron transfer may provide amperometric response for cell detection. So the integration of the two properties of Fc enables controlled host−guest interaction and electrochemical signal readout once for all. Thus the whole system is constructed as “recognition ligand–polymer linker–Fc” and β-CD modified electrode surface, which is shown in Scheme 1. Specifically, Fc moieties are conjugated to the polyethyleneimine (PEI) polymer scaffold. The scaffold is also co-linked with folic acid (FA), which target overexpressed folic acid receptors (FR) on cancer cells.22,23 Thus a bifunctional polymer (FA−PEI−Fc) is synthesized. Besides, β-CD moieties are immobilized on the surface of an indium tin oxide (ITO) electrode for cell capture. Normally, uncharged Fc moieties can bind to the cavity of β-CD to form β-CD/Fc inclusion complex, thus dragging cells to the electrode surface. On the contrary, when applying an electrochemical oxidative potential, the charged Fc+ species are excluded from the cavity.21,24,25 Cells are then released from the surface under oxidative potential, giving electrochemical oxidative current at the same time. As a result, the designed electrochemical system can undergo redox−modulated cell catch−and−release, and can also be used to detect the targeted cells.
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Material and regents. Branched polyethyleneimine (PEI, Mn ~ 10,000), folic acid (FA), ferrocene carboxaldehyde (Fc-CHO, 98%), 3-aminopropyl-triethoxysilane (APTES), 6-carboxyl-β-CD and NHS-methyl-poly(ethylene glycol) (NHS-PEG-OH, Mn ~ 5,000), EDC, HNS, dimethyl sulfoxide (DMSO) were purchased from Sigma-Aldrich. Membrane fluorescent dye DiI, DiO and the Typan Blue Staining Cell Viability Assay Kit were from Beyotime Biotech. Co. Ltd. (Shanghai, China). Other chemicals are all of analytical grade without further purification. ITO electrode (ITO-P001, sheet resistance (1800 ± 250 Å)
