Functionalization of silver nanoparticles with 1-naphthol-4-sulfonate for evaluation of ethylenediamine and diethylenetriamine

Direct determination of polyamines (PAs) is an acute problem as PAs are not having any chromophoric or fluorophoric groups. Thus, a sensor is highly demanding to be developed for determining without derivatizing PAs from their aqueous solutions. In this context, functionalized metal nanoparticles (MNPs) having surface Plasmon resonance (SPR) band in the UV-Vis region could be the ultimate choice. Citrate stabilized spherical silver nanoparticle (cit-SNPs, d = 6.3 nm, sigma = 1.23) were thus synthesized and functionalized with a photoacid, 1-naphthol-4-sulfonic (1Np4S) acid. The 1Np4S exhibits absorption maxima at 330 nm in water and pH > 7, which is the characteristic band of its anionic form. It shows two well defined excitation peaks (lambda(ex)) at 280 nm and 370 nm and an emission peak (lambda(em)) at 434 nm. Thus, 1Np4S is a fluorescent active species. In 1Np4S functionalized cit-SNPs, the fluorescent activity is ceased by the particles, because 1Np4S species get adsorbed onto the surface of cit-SNPs. The adsorption constant (K-ad) was determined using quenching phenomenon occurring at excitation and emission wavelengths of 1Np4S which is very high ranging, 6.23x10(8)-16.47x10(8) M-1, indicating very strong interaction of the photoacid, 1Np4S with the cit-SNPs. The 1Np4S functionalized cit-SNPs were then used as nanoprobe for evaluating polyamines: ethylenediamine (EDA) and diethylenetriamine (DETA), as mimic of biogenic amines (BGAs). The calibration curves of EDA and DETA are straight lines with concentration ranges, (5.9-52.1 mM) and (3.9-50.6 mM), respectively. The result indicates that the sensitivity of evaluating DETA is higher than that of EDA.