Through-Space Electrochemiluminescence Reveals Bubble Forces at Remote Phase Boundaries

Abstract

Several groups have reported on the curious chemistry and reaction acceleration in confined volumes. These complex multiphase systems most closely resemble natural processes, and new measurement tools are necessary to probe chemistry in such environments. Generally, electrochemiluminescence (ECL) reports on processes immediately near (within a few micrometers) the electrode surface. Here, we introduce through-space ECL, reporting on dynamics of processes far away (100s of μm) from the electrode surface. We achieved this by collecting reflected ECL light. During the heterogeneous oxidation of C 2 O 4 2− in an aqueous phase adjacent to a 1,2-dichlorethane droplet, CO 2 accumulates in the 1,2-dichloroethane droplet. Upon buildup, we demonstrate that a CO 2 bubble forms in the nonaqueous phase and is surprisingly trapped at the water|1,2-dichloroethane interface and continues to grow. The co-oxidation of tris(bipyridine)ruthenium(II) in the aqueous phase lights up the electrode surface and reflects off the edges of the bubble, revealing the bubble growth over time even when the bubble is fractions of a millimeter from the surface. We extend our results to quantifying bubble forces at the water−oil interface at remote distances from the electrode surface.

Electrochemical Characterization of Neurotransmitters in a Single Submicron Droplet

“…Nanoscale electrode [15] Single-entity electrochemistry, a technique designed to measure the characteristics of individual particles that has rarely been studied in macro-sized electrode systems because the loading of a single particle is almost impossible, has undergone significant advancements through the use of detection methods employing the collisional contact of a single particle on UMEs [16,17]. Over the last decade, various single entities, including metal nanoparticles [18][19][20][21][22][23][24][25], biomaterials [26,27], nanobubbles [28,29], vesicles [30,31], and droplets [32][33][34][35][36][37][38][39][40], have been analyzed electrochemically at the single-entity level. The entity size can be determined by measuring the amperometric current response obtained from a single collision event [18,39].…”

Electrochemiluminescence Microscopy

“…Another interesting ECL imaging technique named "through-space ECL" was reported by Dick and coworkers where they exploit the light reflection off the gas/ liquid interface. [26] It can be used to study entities located far away from the electrode surface. This is an important advantage since ECL is intrinsically a surface-confined process.…”

“…[14,15] Thus, effective ECL imaging methods rely on a profound understanding of the underlying electrochemical, photochemical and chemical reactivities, and its implementation to resolve single (biological) objects, and, in specific cases, even single molecules. [16][17][18][19][20][21][22][23][24][25][26][27] Additionally, mapping the distribution of ECL offers a considerable amount of information beyond merely measuring its overall intensity, proving invaluable for understanding dynamic processes or unravelling complex mechanistic situations in various fields.…”

Single Entity Electrocatalysis

“…Stochastic electrochemical methods are commonly employed for single entity measurements, including single doped partially oxidized polyaniline for nitrite reduction, Nafion-based particles for permanganate reduction, and pyrroloquinoline quinone (PQQ) modified multiwalled carbon nanotube for hydrazine oxidation and poly(vinylferrocene)-modified graphene nanoplatelets for cysteine oxidation . One area of great interest moving forward is the development of new measurement modalities to study curious chemistry in electrochemically unreachable environments. ,− One potentially exciting new avenue of inquiry for such studies is single entity electrocatalysis in a dissolving microdroplet. , …”