Mapping Solvent Entrapment in Multiphase Systems by Electrogenerated Chemiluminescence

Abstract

The interfacial properties of multiphase systems are often difficult to quantify. We describe the observation and quantification of immiscible solvent entrapment on a carbonaceous electrode surface using microscopy-coupled electrogenerated chemiluminescence (ECL). As aqueous microdroplets suspended in 1,2-dichloroethane collide with a glassy carbon electrode surface, small volumes of the solvent become entrapped between the electrode and aqueous phase, resulting in an overestimation of the true microdroplet/electrode contact area. To quantify the contribution of solvent entrapment decreasing the microdroplet contact area, we drive an ECL reaction within the microdroplet phase using tris­(bipyridine)­ruthenium­(II) chloride ([Ru­(bpy)3]­Cl2) as the ECL luminophore and sodium oxalate (Na2C2O4) as the co-reactant. Importantly, the hydrophilicity of sodium oxalate ensures that the reaction proceeds in the aqueous phase, permitting a clear contrast between the aqueous and 1,2-dichloroethane present at the electrode interface. With the contrast provided by ECL imaging, we quantify the microdroplet radius, apparent microdroplet contact area (aqueous + entrapped 1,2-dichloroethane), entrapped solvent contact area, and the number of entrapped solvent pockets per droplet. These data permit the extraction of the true microdroplet/electrode contact area for a given droplet, as well as a statistical assessment regarding the probability of solvent entrapment based on microdroplet size.

Dynamic Electrochemiluminescence Imaging of Single Giant Liposome Opening at Polarized Electrodes

“…Recently, Glasscott et al reported a droplet-confined ECL as a quantitative tool to map solvent entrapment in multiphase systems and to visualize the phase boundaries of such systems. 46,47 Using liposome-encapsulated luminophores, ECL appears particularly adequate to provide unambiguous signature of extravesicular release events, with a better signal/noise ratio than namely electrofluorochromic probes. Since ECL is an electrochemically triggered process ultimately leading to photon emission, 48,49 this technique brings important advantages over other optical methods.…”

“…However, 100 nm size liposomes used in this work were too small for microscopy imaging, and a surfactant was required to permeate liposomes and release the ECL label. Recently, Glasscott et al reported droplet-confined ECL imaging as a quantitative tool to map solvent entrapment in multiphase systems and to visualize the phase boundaries of such systems. , …”

Electrochemiluminescence with semiconductor (nano)materials

“…Since metal-based QDs are toxic, it is important to use low-toxicity, eco-friendly alternatives to develop QD-ECL emitters. Undoubtedly, the versatility offered by the combination of ECL with SC (nano)materials opens a wide range of opportunities to develop new ultrasensitive (bio)sensing and imaging applications, especially in point-of-care testing, conned and multiphase systems, 178,228,229 biological assays, and microscopy of cellular and subcellular structures.…”

A Guide Inside Electrochemiluminescent Microscopy Mechanisms for Analytical Performance Improvement

“…In an another work, the same team described a method to quantify the entrapment of immiscible solvent in aqueous microdroplets through ECL microscopy. In this case, they used hydrophilic ECL reagents, [Ru­(bpy) 3 ] 2+ and oxalate, to confine the ECL reaction in the aqueous phase, leaving the trapped organic solvent obscured . In this way, they were able to assess the actual contact area between the microdroplet and the electrode without using any geometry dependent modeling.…”