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Fluorescent carbon dots (NSCDs) with a size of ∼5 nm (λex = 320 nm and λem = 386 nm) have been synthesized under reflux from an alkaline mixture of dopamine and cysteine. The synthesized NSCDs are hybridized with in situ generated silver nanoparticles (AgNPs) obtained by mixing AgNO3 at room temperature. NSCDs enrich the plasmonic bands of AgNPs due to the localized surface plasmon resonance (LSPR) effect. Further enrichment of plasmon band, depending on the acetone concentration, enables acetone sensing down to 8 × 10−5 M admixed in 1 M water. Thus, acetone induced hybrid particles with a sharp plasmon band (λex = 410 nm) become a sulfide sensing platform. Furthermore, vacuum dried stable particles (with or without acetone) have been proven to be an excellent catalyst for selective reduction of cationic dyes and they exhibit intriguing antimicrobial activity. These two types of dry particle act differently, which enables us to distinguish their altered surface functionalization in terms of catalysis and bacterial growth. [ABSTRACT FROM AUTHOR]

Highly fluorescent Au(i)@Ag particles (emission maximum at 635 nm) have been obtained from a mixture of AgNO3, HAuCl4 and glutathione. Au(i)@Ag particles containing Ag2 and Ag3 clusters are produced when the reaction mixture is subjected to a modified hydrothermolysis (MHT) reaction. The silver clusters make the solution intensely fluorescent and the Au(i) moiety provides long term stability to the silver clusters by withdrawing electron density from the silver clusters. The vacuum-dried aqueous fluorescent solution leaves a yellow solid that exhibits higher emissive properties when re-dispersed in non-aqueous solvents. Fluorescent Au(i)@Ag particles have been found to be cytocompatible and efficient candidates for live cell imaging. Addition of S2− ions selectively and successively quenches the fluorescence of Au(i)@Ag particles without any significant interference from common anions. Thus, sensitive detection of S2− is possible with the fluorescent Au(i)@Ag particles in water and water-miscible non-aqueous solvents. Furthermore, Pb(ii) induced fluorescence enhancement of the solution containing Au(i)@Ag particles has been used to enable S2− detection free from interference by S2O32− and I−. The possibility of naked eye detection of S2− is also an additional advantage of this method as an orange color solution is developed exclusively with the S2− ion. Fluorometric determination of S2− has been rationalized for real environmental samples. [ABSTRACT FROM AUTHOR]

Metal enhanced fluorescence (MEF) from organic molecules has been the focus of plasmonic/photonic research. In this regard, silver and gold particle stimulated fluorescence has received much attention. However, the involvement of small organic molecules in solution has not been accounted for in MEF. We have reported here that the aqueous alkaline solution of salicylaldehyde exhibits highly enhanced fluorescence at room temperature (λem∼ 420 nm, Stokes shift 120 nm, stability ＞ a year) in the presence of Ag(i) or Au(iii) after simple ageing for two days. The increased scattering cross-section of the in situ produced aggregated metal particles and the lightening rod effect of the metal aggregates that concentrate the electric field around the fluorophore (i.e., alkaline solutions of salicylaldehyde) are ascribed to such extraordinary fluorescence enhancement caused by Ag and Au particles. Finally, selective fluorescence enhancement due to silver particles alone has been made possible in the presence of ammonia or primary amines due to imine bond formation that eliminates Au enhanced fluorescence quantitatively. This finding allows us to design a highly selective Ag(i) sensor in the solution phase with a cheap and commercially available compound with LOD far below EPA-permissible levels. The imine induced selective silver enhanced fluorescence phenomenon becomes a general matter in our studies even with different Schiff bases. [ABSTRACT FROM AUTHOR]

Highly stable Au(I)core-Ag(0)shell particles have been synthesized in aqueous solution via a green chemistry pathway utilising sunlight irradiation. The shell of the particles is composed of fluorescent Ag2 and Ag3 clusters which make the large core-shell particles highly fluorescent. The Au(I) core of the particles offers long-term stability to the silver clusters, which are otherwise unstable in solution at room temperature, by the transfer of electron density from the shell. Successive additions of Hg(II) ions to the fluorescent solution cause efficient and selective quenching of the fluorescence with gradual red shifting of the emission peak. The metallophilic 5d10(Hg2+)-4d10(Agδ+) interaction as well as Hg(II) stimulated aggregation have been ascribed to causing the fluorescence quenching and red shift. The fluorescent Au(I)core-Ag(0)shell particles are a highly selective and sensitive sensing platform for the detection of Hg(II) down to 6 nM in the presence of various metal ions. The detection limit is far below the permissible level as determined by the EPA. Interferences due to Cu(II) and Fe(III) have been eliminated using Na2-EDTA and NH4HF2, respectively. The fluorescent particles are successfully transferred to various solvent systems making Hg(II) determination also possible in non-aqueous media. Finally, the temperature dependent fluorescence change with and without Hg(II) provides information about the metallophilic interaction. [ABSTRACT FROM AUTHOR]

Thermochromic properties of a series of non-ionic copper compounds have been reported. Herein, we demonstrate that Cu(II) ion with straight-chain primary amine (A) and alpha-linolenic (fatty acid, AL) cojointly exhibit thermochromic properties. In the current case, we determined that thermochromism becomes ligand chain length-dependent and at least one of the ligands (A or AL) must be long chain. Thermochromism is attributed to a balanced competition between the fatty acids and amines for the copper(II) centre. The structure-property relationship of the non-ionic copper compounds Cu(AL)2(A)2 has been substantiated by various physical measurements along with detailed theoretical studies based on time-dependent density functional theory. It is presumed from our results that the compound would be a useful material for temperature-sensor applications. [ABSTRACT FROM AUTHOR]

Stable coinage metal nanoparticles (NPs) have been synthesized individually in an aqueous alkaline solution from the corresponding metal salts as precursors using the condensation product (CP) of salicylaldehyde and triethylenetetramine as a reagent. Silver and gold NPs are obtained with and without light illumination but UV irradiation is essential for Cu(0)NP formation. During nanoparticle formation the CP is oxidized to OCP which eventually becomes a fluorophore and also a stabilizer for the in situ produced NPs. It has been observed that silver and gold particle formation kinetics is accelerated by UV exposure. Thus the ease of evolution of coinage metal NP formation relates to their nobility. The as prepared OCP solutions containing coinage metals exhibit a fluorescence contrast behaviour (fluorescence enhancement by Cu and Ag; quenching by AuNP) due to the match and mismatch of wave vectors. The electric field evident from the FDTD simulation abreast of the scattering cross section of the NPs governed from Mie theory as a consequence of surface plasmon coupled emission (SPCE), near field electromagnetic intensity enhancement and lightening rod effect concentrating the electric field around the fluorophore are responsible for the Cu and AgNPs stimulated fluorescence. Again, lossy surface waves are anticipated for efficient quenching by the AuNPs. The most unprecedented observation is 'Turn On' fluorescence which is reported here as a result of the substitution of Au(0) or Cu(0) by Ag(0). Finally, the preferential fluorescence enhancement helps the selective detection of Ag(I) and Cu(II) well below the US Environmental Protection Agency (EPA) permissible level by tuning the experimental conditions. [ABSTRACT FROM AUTHOR]