Enhancing the lateral-flow immunoassay for detection of proteins using an aqueous two-phase micellar system

The lateral-flow (immuno)assay (LFA) has been widely investigated for the detection of molecular, macromolecular, and particle targets at the point-of-need due to its ease of use, rapid processing, and minimal power and laboratory equipment requirements. However, for some analytes, such as certain proteins, the detection limit of LFA is inferior to lab-based assays, such as the enzyme-linked immunosorbent assay, and needs to be improved. One solution for improving the detection limit of LFA is to concentrate the target protein in a solution prior to the detection step. In this study, a novel approach was used in the context of an aqueous two-phase micellar system comprised of the nonionic surfactant Triton X-114 to concentrate a model protein, namely transferrin, prior to LFA. Proteins have been shown to partition, or distribute, fairly evenly between the two phases of an aqueous two-phase system, which in turn results in their limited concentration in one of the two phases. Therefore, larger colloidal gold particles decorated with antibodies for transferrin were used in the concentration step to bind to transferrin and aid its partitioning into the top, micelle-poor phase. By manipulating the volume ratio of the two coexisting micellar phases and combining the concentration step with LFA, the transferrin detection limit of LFA was improved by tenfold from 0.5 to 0.05?μg/mL in a predictive manner. In addition to enhancing the sensitivity of LFA, this universal concentration method could also be used to improve other detection assays.     

Effect of non-aqueous solvents on stoichiometry and selectivity of complexes formed between 4′-nitrobenzo-15-crown-5 with Fe3+, Y3+, Cd2+, Sn4+, Ce3+ and Au3+ metal cations

The complexation processes between Fe³⁺, Y³⁺, Cd²⁺, Sn⁴⁺, Ce³⁺ and Au³⁺ metal cations with macrocyclic ligand, 4′-nitrobenzo-15-crown-5 (4′NB15C5), were studied in acetonitrile (AN), methanol (MeOH) and nitromethane (NM) solvents at different temperatures using conductometric method. The conductance data show that the stoichiometry of the complexes formed between this macrocyclic ligand and Cd²⁺, Au³⁺ cations is 1: 1 (ML), but in the case of Fe³⁺, Y³⁺ and Ce³⁺ metal cations, 2: 1 (M₂: L) and 2: 2 [M₂: L₂] complexes are formed in nitromethane solutions. The results show, that the selectivity of 4’NB15C5 for the studied metal cations in methanol solutions at 15°C is: Sn⁴⁺ > Cd²⁺ > Y³⁺ > Fe³⁺ ∼ Ce³⁺ > Au³⁺, but in the case of acetonitrile, the stability order was found to be: Y³⁺ > Au³⁺ > Fe³⁺ > Cd²⁺. The values of stability constants of the 1: 1 [M: L] complexes were determined from conductometric data using a GENPLOT computer program. The values of thermodynamic parameter (ΔH _c ^o and ΔH _c ^o) for formation of the complexes were obtained from temperature dependence of the stability constants, using the van’t Hoff plots. The results show that the values of standard enthalpy (ΔH _c ^o) and standard entropy (ΔH _c ^o) change with the nature of the non aqueous solvents.