Development of a Reversible Indicator Displacement Assay Based on the 1-(2-Pyridylazo)-2-naphthol for Colorimetric Determination of Cysteine in Biological Samples and Its Application to Constructing the Paper Test Strips and a Molecular-Scale Set/Reset Memorized Device.

A new colorimetric chemosensor for naked-eye detection and determination of cysteine (Cys) based on indicator displacement assay (IDA) was designed using 1-(2-pyridylazo)-2-naphthol (PAN). The indicator exchange occurred between PAN and Cys by the addition of Cys to the Cu(PAN)2 complex, which is accomplished by an immediate visible color change from magenta to yellow, in the solution phase and paper-based test strips. The proposed method exhibits 0.35 µmol L-1 detection limit and good linearity in the range of 2.25-42.91 µmol L-1. Paper test strips presented a detection limit of 38.0 µmol L-1, fabricating an easy to use test kit for compatible "in-the-field" detection of Cys. The computer image analysis of the paper test strips, obtained from the CMYK color analysis system, showed a linear increase in Y (yellow) intensity with enhancement in the Cys concentration of 50.0-550.0 µmol L-1. Additionally, the absorption and color change obtained in this chemosensor operate as an "INHIBIT" logic gate considering Cu2+ and Cys as inputs. Eventually, based on such a fast, reversible, and reproducible signal, a molecular-scale sequential memory unit was designed displaying "Writing-Reading-Erasing-Reading" and "Multi-Write" behavior. The developed chemosensor presented a satisfactory repeatability, intermediate precision, and successful application for the selective determination of Cys in human biological fluids. Graphical abstract .

Indigo Carmine-Cu complex probe exhibiting dual colorimetric/fluorimetric sensing for selective determination of mono hydrogen phosphate ion and its logic behavior.

A new selective probe based on copper complex of Indigo Carmine (IC-Cu2) for colorimetric, naked-eye, and fluorimetric recognition of mono hydrogen phosphate (MHP) ion in H2O/DMSO (4:1v/v, 1.0mmolL-1 HEPES buffer solution pH7.5) was developed. Detection limit of HPO42- determination, achieved by fluorimetric and 3lorimetric method, are 0.071 and 1.46µmolL-1, respectively. Potential, therefore is clearly available in IC-Cu2 complex to detect HPO42- in micromolar range via dual visible color change and fluorescence response. Present method shows high selectivity toward HPO42- over other phosphate species and other anions and was successfully utilized for analysis of P2O5 content of a fertilizer sample. The results obtained by proposed chemosensor presented good agreement with those obtained the colorimetric reference method. INHIBIT and IMPLICATION logic gates operating at molecular level have been achieved using Cu2+and HPO42- as chemical inputs and UV-Vis absorbance signal as output.