Development of dual-tool nanosensor for cysteine based on N-(1-naphthyl)ethylenediamine cation functionalized silver nanoparticles.

In an accomplishment of development of silver nanoparticles (AgNPs) based nanosensor for cysteine in its anionic and neutral forms, we have preferred N-(1-naphthyl)ethylenediamine cation (NEDA+) stabilized AgNPs (NEDA-AgNPs), because NEDA+ is a fluorescent active ion and it imparts excellent stability to AgNPs. Surface Plasmon resonance (SPR) of AgNPs and fluorescence property of NEDA+ are thus useful for presenting NEDA-AgNPs as a dual-tool nanosensor for cysteine molecules. The surface adsorbed NEDA+ cations interact selectively with cysteine as a consequence, the particles get aggregated, which was monitored using spectrophotometric method. The fluorescence property of NEDA+ is heavily quenched in NEDA-AgNPs, which could be reversed in presence of cysteine. The spectrofluorimetric method was thus used for quantification of cysteine as well. The detection limits (LOD to LOL) of anionic cysteine are 0.1784-1.598 µM and 0.0842-2.0 µM, respectively in spectrophotometric and spectrofluorimetric methods. From a real sample matrix, the recovery results are excellent, >95%. For neutral cysteine, the sensitivity is a bit low; 0.308-2.8 µM for spectrophotometric and 0.131-2.8 µM for spectrofluorimetric methods. It is found that the anionic cysteine (Kasso = 2.24 × 105 M-1/4.02 × 105 M-1) binds surface adsorbed NEDA+ cations strongly than that of neutral cysteine (Kasso = 3.69 × 104 M-1/1.24 × 105 M-1). Thus, NEDA-AgNPs show its potentials for being a dual-tool nanosensor as well as dual-form nanosensor for quantification of cysteine in a sample which may be the attractive system to an analyst.

Recognition of silver nanoparticles surface-adsorbed citrate anions by macrocyclic polyammonium cations: a spectrophotometric approach to study aggregation kinetics and evaluation of association constant.

In this report, we have studied the recognition of citrate anions adsorbed on the surface of silver nanoparticles (cit-Ag-NPs), by macrocyclic polyammonium cations (MCPACs): Me6 [14]ane-N4 H8 (4+) (Tet-A/Tet-B cations) and [32]ane-N8 H16 (8+) , which are well reputed anion recognizers and are treated as to mimic of biological polyamines. The study was monitored on ultraviolet-visible spectroscopy by performing a titration of the aqueous dispersion of the cit-Ag-NPs by the aqueous solution of MCPACs. The ultraviolet-visible time-scan plots over the reduction of the absorption band of surface plasmon resonance of cit-Ag-NPs at 390 nm are well fitted with fourth-order polynomial equation and are employed to determine the initial aggregation rate constants. It has been stated that the aggregation is the result in electrostatic attraction followed by H-bond formation between the surface-adsorbed citrate anions and added MCPACs. The atomic force microscopy results have evidenced aggregation of cit-Ag-NPs in presence of MCPACs. The evaluated H-bonded association constant (Kasso ) using Benesi-Hildebrand method reveals that [32]ane-N8 H16 (8+) cations form stronger association complex, as expected, with the citrate anions than the Me6 [14]ane-N4 H8 (4+) cations. The study would thus provide the insight of molecular interactions involved in nanoparticle surface-adsorbed anions with biological polyamines. Copyright © 2016 John Wiley & Sons, Ltd.