Abstract: In the present article, the utility of a special potentiometric titration approach for recognition and calculation of biomolecule/small molecule interactions is reported. This approach is fast, sensitive, reproducible and inexpensive in comparison to the other methods for the determination of the association constant values (Ka) and the interaction energies (ΔG). The potentiometric titration measurement is based on the use of a classical polymeric membrane indicator electrode in a solution of the small molecule ligand. The biomolecule is used as a titrant. The potential is measured versus a reference electrode and transformed to a concentration related signal over the entire concentration interval, also at low concentrations, where the mV (y-axis) versus logcanalyte (x-axis) potentiometric calibration curve is not linear. In the procedure, the Ka is calculated for the interaction of cocaine with a cocaine binding aptamer and with an anti-cocaine antibody. To study the selectivity and cross-reactivity, other oligonucleotides and aptamers are tested, as well as other small ligand molecules such as tetrakis (4-chlorophenyl)borate, metergoline, lidocaine, and bromhexine. The calculated Ka compared favorably to the value reported in the literature using SPR. The potentiometric titration approach called Concentration related Response Potentiometry, is used to study molecular interaction for 7 macromolecular target molecules and 4 small molecule ligands.

Abstract: The analytical methods which are often used for the determination of cocaine in complex biological matrices are a prescreening immunoassay and confirmation by chromatography combined with mass spectrometry. We suggest an ultra-high-pressure liquid chromatography combined with a potentiometric detector, as a fast and practical method to detect and quantify cocaine in biological samples. An adsorption/desorption model was used to investigate the usefulness of the potentiometric detector to determine cocaine in complex matrices. Detection limits of 6.3ngmL(-1) were obtained in plasma and urine, which is below the maximum residue limit (MRL) of 25ngmL(-1). A set of seven plasma samples and 10 urine samples were classified identically by both methods as exceeding the MRL or being inferior to it. The results obtained with the UPLC/potentiometric detection method were compared with the results obtained with the UPLC/MS method for samples spiked with varying cocaine concentrations. The intraclass correlation coefficient was 0.997 for serum (n =7) and 0.977 for urine (n =8). As liquid chromatography is an established technique, and as potentiometry is very simple and cost-effective in terms of equipment, we believe that this method is potentially easy, inexpensive, fast and reliable. Copyright (c) 2014 John Wiley & Sons, Ltd.

Abstract: The most successful binding kinetics analysis systems at this moment include surface plasmon resonance (SPR), quartz microcrystal balance (QMB) and surface acoustic wave (SAW). Although these are powerful methods, they generally are complex, expensive and require the use of monolayers. Here, we report on potentiometric sensors as an inexpensive and simple alternative to do binding kinetics analysis between small molecules in solution and biomolecules (covalently) attached in a biopolymer sensor coating layer. As an example, dopamine and an anti-dopamine aptamer were used as the small molecule and the biomolecule respectively. Binding between both follows a Langmuir adsorption type model and creates a surface potential. The system operates in Flow Injection Analysis mode (FIA). Besides being an interesting new binding kinetics tool, the approach allows systematic design of potentiometric biosensors (in the present study a dopamine sensor), and gives new insights into the functioning of ion-selective electrodes (ISEs).

Abstract: Potentiometric sensors were used to study molecular interactions in liquid environments, with sensorgram methodology. This is demonstrated with a lipophilic rubber-, and with a collagen based hydrogel sensor coating. The investigated molecules were promazine and tartaric acid respectively. The sensors were placed in a hydrodynamic wall jet system for the recording of sensorgrams. mV sensor responses were first converted to a signal, expressing the concentration of adsorbed organic ions. Using a linearization method, a pseudo first order kinetic model of adsorption was shown to fit the experimental results perfectly. Kass, kon and koff values were calculated.. The technique can be used over 4 decades of concentration, and it is very sensitive to low MW compounds as well as to multiply charged large biomolecules. This study is the first to demonstrate the application of potentiometric sensors as an alternative and complement to SPR methods.