Wireless electrochemical light emission in ultrathin 2D nanoconfinements

Abstract

Spatial confinement of chemical reactions or physical effects may lead to original phenomena and new properties. Here, the generation of electrochemiluminescence (ECL) in confined free-standing 2D spaces, exemplified by surfactant-based air bubbles is reported. For this, the ultrathin walls of the bubbles (typically in the range of 100-700 nm) are chosen as a host where graphene sheets, acting as bipolar ECL-emitting electrodes, are trapped and dispersed. The proposed system demonstrates that the required potential for the generation of ECL is up to three orders of magnitude smaller compared to conventional systems, due to the nanoconfinement of the potential drop. This proof-of-concept study demonstrates the key advantages of a 2D environment, allowing a wireless activation of ECL at rather low potentials, compatible with (bio)analytical systems.

Scheme 1. Schematic overview of ECL occurring within the thin layer of a soap bubble using graphene sheets as bipolar electrodes, in the presence of Ru(bpy)₃²⁺ and 2-(dibutylamino) ethanol (DBAE) as a luminophore and co-reactant, respectively; the bubble images are schematic.

Fig. 1. Bubble formation and stabilization. (a) Images of bubbles of different sizes. (b) Schematic illustrations of the bipolar setup and the tuning of the temperature using liquid nitrogen (LN₂). (c) Temperature of the container of the bipolar setup as a function of time; inset: images of frozen bubbles at −15 °C, and −10 °C, in which the bubbles are stable for ECL measurements. All experiments are measured using bubbles with an initial temperature of −15 °C.

Fig. 2. ECL intensity of bubbles placed in a 6 mm setup. (a) The impact of the magnitude of the average electric field on ECL intensity in the presence of 0.1, 1 and 4 mg ml⁻¹ graphene microplatelets. (b) The intensity of ECL in the presence of a wide concentration range of graphene microplatelets (0.001–12 mg ml⁻¹) at a constant electric field of 33 V cm⁻¹.

Fig. 3. The correlation between ECL and the aggregation of graphene sheets; (a) schematic illustration of a bipolar electrochemical setup (left) and an image of an initially frozen bubble at −15 °C placed between feeder electrodes that are covered with a membrane to avoid their direct contact with the bubble (right, 6 mm bubble) (see also Fig. S5†). (b) Images of the light-emitting bubbles (taken from the upper side angle, as shown in Fig. 1b) with 0.1, 1, and 4 mg ml⁻¹ graphene content; 6 mm bubbles. (c) Dispersibility of graphene sheets in the original solution, which was used to prepare the bubbles, during 4 minutes after bath sonication.

Fig. 4. ECL of a bubble during its lifetime. ECL images of a bubble (taken from the upper side angle, as shown in Fig. 1b), kept in a −15 °C environment, for 30 seconds with 5 seconds exposure time during the imaging (a) and the corresponding ECL intensities (b). 6 mm bubbles.