Paper-Based System for Ion Transfer Across the Liquid–Liquid Interface

Electroanalytical applications of ITIES - A review

Over the last decades, the interface between two immiscible electrolyte solutions (ITIES) attracted considerable attention of the scientific community due to their vast applications, such as extraction, catalysis, partition studies and sensing. The aim of this Review is to highlight the potential of electrochemistry at the ITIES for analytical purposes, focusing on ITIES-based sensors for detection and quantification of chemically and biologically relevant (bio)molecules. We start by addressing the evolution of ITIES in terms of number of publications over the years along with an overview of their main applications (Chapter 1). Then, we provide a general historical perspective about pioneer voltammetric studies at water/oil systems (Chapter 2). After that, we discuss the most impacting improvements on ITIES sensing systems from both perspectives, set-up design (interface stabilization and miniaturization, selection of the organic solvent, etc.) and optimization of experimental conditions to improve selectivity and sensitivity (Chapter 3). In Chapter 4, we discuss the analytical applications of ITIES for electrochemical sensing of several types of analytes, including drugs, pesticides, proteins, among others. Finally, we highlight the present achievements of ITIES as analytical tool and provide future challenges and perspectives for this technology (Chapter 5).

Electrified liquid - liquid interface strategy for sensing lactic acid in buttermilk extract

Lactic acid (LA) serves as a freshness marker in certain foods. In the present work, electrified interfaces of different nature (i.e., liquid-liquid and liquid-organogel) have been developed for the quantification of LA. Electrochemical sensing of LA at the liquid-organogel interface revealed that adsorptive stripping voltammetry, with a preconcentration time of 500 s offered better sensitivity. Electroanalytical ability of LA under optimized conditions displayed a detection limit of 0.97 μM and 0.71 μM with sensitivity of 2.84 nA μM-1 and 3.59 nA μM-1 for liquid-liquid and liquid-organogel interfaces respectively. Quantification of LA using the developed methodology has been demonstrated in buttermilk as the real matrix. Analysis demonstrate that electrified liquid-liquid and liquid-organogel interfaces are promising approach for sensing LAin buttermilk extract.

Advances on microfluidic paper-based electroanalytical devices

Since the inception of the first electrochemical devices on paper substrates, many different reports of microfluidic paper-based electroanalytical devices (μPEDs), innovative hydrophobic barriers and electrode fabrication processes have allowed the incorporation of diverse materials, resulting in different applications and a boost in performance. These advancements have led to the creation of paper-based devices with comparable performance to many standard conventional devices, with the added benefits of pumpless fluidic transport, component separation and reagent storage that can be exploited to automate and handle sample preprocessing. Herein, we review μPEDs, summarize the characteristics and functionalities of μPEDs, such as separation, fluid flow control and storage, and outline the conventional and emerging fabrication and modification approaches for μPEDs. We also examine the recent application of μPEDs in biomedicine, the environment, and food and water safety, as well as some limitations and challenges that must be addressed.

Ion Transfer Voltammetry with an Electrochemical Pen

We present a new electrochemical system that combines paper-based sensing and ion-transfer voltammetry, bringing the latter a step closer toward point-of-care applications. Studies at the interface between two immiscible electrolyte solutions (ITIES) are often performed to detect redox-inactive species; unfortunately, due to the inherent instability of the interface, it is rather poorly explored outside specialized laboratories. Here, we address this limitation by combining a pen-like device containing the gelled organic phase with a paper-supported aqueous phase. This combination makes the system more user-friendly, potentially low-cost, and easy to assemble. We show the applicability of the new cell to analyze both simple and ionophore-facilitated transfer of ions and proteins, preconcentration of species, and analysis of mixtures through combination with paper chromatography. The native ion content of the paper also enabled measurements without added electrolytes. Those studies could broaden the scope for the application of the label-free electrochemical detection of nonredox-active species at points-of-need.

Chronopotentiometric aptasensing with signal amplification based on enzyme-catalyzed surface polymerization

A signal amplification strategy based on the horseradish peroxidase catalyzed polymerization of dopamine on a polymeric ion-selective membrane surface is proposed for the sensitive chronopotentiometric detection of an aptamer-target binding event.