Intracellular Wireless Analysis of Single Cells by Bipolar Electrochemiluminescence Confined in a Nanopipette

Abstract

The inside walls of a nanopipette tip are decorated by a Pt deposit that is used as an open bipolar electrochemiluminescence (ECL) device to achieve intracellular wireless electroanalysis. The synergetic actions of nanopipette and of bipolar ECL lead to the spatial confinement of the voltage drop at the level of the Pt deposit, which generates ECL emission from luminol. The porous structure of Pt deposit permits the electrochemical transport of intracellular molecules into the nanopipette that is coupled with enzymatic reactions. Thus, the intracellular concentrations of hydrogen peroxide or glucose are measured in vivo as well as the intracellular sphingomyelinase activity. In comparison with the classic bipolar ECL, the remarkably low potential applied in our approach is restricted inside the nanopipette and it minimizes the potential bias of the voltage on the cellular activity. Accordingly, this wireless ECL approach provides a new direction for analysis of single living cells.

Recent Advancements in Bipolar Electrochemical Methods of Analysis

“…Additionally, the luminescent reaction between luminol and hydrogen peroxide is often used as a reporting reaction, especially where hydrogen peroxide is the analyte or is a product of the sensing reaction. 10,[46][47][48] Other luminescent compounds with increased conjugation have been investigated, such as the novel synthesis of a cyclometalated iridium(III) complex, which had an approximately 5-fold higher ECL efficiency with TPA co-oxidation than the Ru(bpy)3 2+ /TPA pair. 8 Additionally, quantum dots (QDs) have been utilized at closed BPEs as ECL reagents and have been shown to have high quantum yields and luminescence in non-aqueous environments.…”

“…This challenge is addressed by confining the BPE in a small volume, thereby focusing the voltage drop to the vicinity of the BPE. 48,121,124 The confinement strategies employed for the recent advancements in nanoscale bipolar electrochemistry reviewed here incorporate nanochannels and nanopipettes.…”

“…127 An exciting recent example of live cell analysis was completed by Chen, Sojic, and coworkers who utilized a luminol reporting reaction to detect small molecules and enzymes contained in a live cell. 48 A porous Pt BPE was deposited in the tip of the nanopipette, and upon insertion of the tip into the cell, intracellular molecules could travel through the porous structure to interact with enzymes in the pipette that resulted in hydrogen peroxide formation, thereby generating an ECL response. Using this approach, hydrogen peroxide and glucose, as well as sphingomyelinase activity, were detected before and after the cell was stimulated, and a notable change in luminescence was observed, as seen in…”

Confined Electrochemiluminescence at Microtube Electrode Ensembles for Local Sensing of Single Cells†

“…[ 28‐29 ] Further in combination with microelectrode or nanoelectrode, local chemical sensing of cells at subcellular level can be achieved with high spatial resolution, but efforts are still made to improve the throughput. [ 30‐31 ] Another strategy uses nanoparticles deposited on the planar electrode ( e.g ., ITO electrode) to promote local ECL generation, and therefore achieves subcellular analysis. [ 32‐33 ] Although the analysis was performed at the nanoparticle in this case, the whole cell was under electrical stimulation.…”

Chemical Analysis of Single Cells and Organelles

“…Wang et al achieved intracellular wireless electroanalysis by using a Pt-deposited nanopipette tip as an open bipolar ECL device. 43 Pt deposited inside the nanopipette transported intracellular molecules into the nanopipette that was coupled to enzymatic reactions. This approach restricted the extremely low potential inside the nanopipette, and it minimized the bias potential on the cellular activity.…”