VolthinSens

Self-Assembled monolayers on glassy carbon electrodes providing effective charge transfer to promote ion-transfer processes across ultra-thin ion-selective membranes

New redox mediator based on ferrocene moieties immobilized on glassy carbon electrodes via self-assembled monolayers. A thin-layer membrane on top facilities ion transfers at the membrane-sample interface that can be tuned according to the membrane composition. The uniqueness of interconnected electron transfer and charge transfer processes for sensing purposes is herein demonstrated.

Understanding the working mechanism behind the sensors developed in the VolThinSens project

As a model example, ITO-POT-membrane electrodes have been investigated by means of spectroelectrochemistry. Conveniently, the absorbance change in the POT film (redox mediator) can be followed at 450 nm in parallel to the voltammetry experiment, so that, the POT oxidation assisting the ion transfer(s) at the membrane-sample interface can be dynamically monitored. Ths work demonstrates the unequivocal interconnection between the electron and ion transfer process (one does not happen without the other). Also, a mathematical model to predict the POT oxidation is developed.

Stripping ion-transfer voltammetry to decrease the limit of detection of ultra-thin membranes. When an accumulation-stripping method is applied to voltammetric thin-layer membranes working under a diffusional regime, limits of detection in the nanomolar level

The limit of detection can be further improved to subnanomolar levels whether the exchange capacity of the ion-selective membrane is reduced via the lowering of the cation-exchange amount in the membrane.

As a proof-of-concept, the idea has been successfully applied to the detection of silver ion in several water samples, including such as complex matrix as seawater. The extablished analytical concept could be extended to other trace metal ions (such as copper and lead).

Revising the field of environmental analysis to demonstrate the potential of the VolThinSens project in EU water issues

Investigating the case of the ammonium ion

One of the targets of the VolThinSens project is the ammonium ion. Its detection is challenging because of the limited selectivity that the available ionophores present. Moreover, ammonium detection is challenging because of the different nature of the matrix of the samples in where this cation is present, for example biological fluids and water. The direction should be pursuing new ionophores but also the inclusion of external barriers to the main interferences (i.e., potassium ion).

Anion-exchange membranes are demonstrated to repeal potassium and other cations present in urine so that ammonium cation can be sense to trace the creatinine content

Creatinine is an important biomarker of kidney disease. It is the second biomolecule more analyzed in clinical labs, just after glucose

VolThinSens have investigated several concepts to analyze creatinine in different biological fluids by a smart tuning of the linear range of response according to the expected biolevels. Self-assembled monolayers has an important role in these new analytical concepts.