Light Activated Electrochemistry on Silicon Electrodes: Application to the Isolation and Characterization of Single Cells

Abstract

Recent studies have shown the clinical significance of detecting viable circulating tumor cells (CTCs) in blood from cancer patients, as CTCs are probably the origin of the metastatic disease. However, the isolation of CTCs from blood is technically challenging because they are extremely rare. Preexisting strategies to isolate CTCs are normally limited to the laborious procedures that may be also invasive or introduce impurity. Herein a new and effective strategy for accurate isolation of single cells is presented. By taking the advantage of light activated electrochemistry (LAE) on semiconducting silicon, light is utilized for spatially resolving the release of single cells isolated on a surface. The strategy developed involved three main steps. Firstly the poorly doped p-type silicon was passivated to resist the corrosion but with a layer thin enough to allow efficient tunnelling. Coupled to this layer was a redox active anthraquinone derivative. LAE was demonstrated on the anthraquinone modified silicon electrode where there was no faradaic electrochemistry in the dark but upon illumination the surface was activated and electron transfer was observed. The results showed the thermodynamics and kinetics can be tuned by light intensity or pH. Secondly, a novel sensor for the determination of the achievable spatial resolution was developed by forming anthraquinone stripes of known thickness on a p-type silicon photocathode. Rastering a light source across this stripe and recording a current-distance curve allowed the spatial resolution to be determined. The effects of light intensity/applied potential on spatial resolution were determined, and the results offer importance for practical application of LAE. Using the optimal experimental parameters, the system achieved a spatial resolution of ~30 μm, demonstrating the potential application for single cell release. Finally, a “cleavable” linker, which is a trimethyl locker will undergo a locatonization under a negative potential and could release the attached molecular of interest, was modified on silicon. Followed antifouling molecular and antibody Ep–CAM were attached. MCF-7 cells (representative CTCs) were captured by Ep–CAM, and single cell release was realized by shining light on specific cell while applying a negative potential. The released cells were isolated by using a micromanipulator, shown to be satisfactorily viable and gene analysis were performed on these released single cells.