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

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 (K_asso = 2.24 × 10⁵ M^-1/4.02 × 10⁵ M^-1) binds surface adsorbed NEDA⁺ cations strongly than that of neutral cysteine (K_asso = 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.

Association models for binding of molecules to nanostructures

The interaction between nanoparticles and molecules determines the activity of nanostructures.