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Schiff base compounds were reported to make a complex with Cu2+ and Ag+ and subsequent reduction produced Cu0 and Ag0 nanoparticles separately via UV irradiation. Here, we synthesized a Schiff base, which initially formed a complexation with Cu2+ and made Cu0 nanoparticles after 8 h aging. In that reaction mixture, addition of Ag+ resulted in Ag0 nanoparticles. Emissive semi-carbazone (a Schiff base synthesized from semicarbazide and salicylaldehyde) was employed for the first time to selectively and sensitively detect Cu2+ (linear range of detection 10–4 to 5 × 10–8 M and limit of detection 13 μM) with the formation of copper oxide nanoparticles via complexation–reduction method. The introduction of Ag+ in it produced Ag0 and Cu0 (CuO via aerial oxidation) nanoparticles with a gigantic increase of fluorescence to obtain selective and sensitive Ag+ detection (linear detection range 10–3–10–7 M, and limit of detection 7. 7 μM). Thus, Cu2+ and Ag+ were detected based on turn-off/on fluorescence in one pot. As the evolution of copper and silver nanoparticles was the fundamental reason for sensing, response time is similar to the stable fluorescence behavior of oxidized SC (capping agent) with in situ generated copper and silver nanoparticles. CuO-induced fluorescence quenching was due to the formation of the trapped plasmon, while Ag+-induced fluorescence enhancement was owing to the lightning rod effect. The synergism of Cu and Ag was also investigated in this paper as a driving force of the lightning rod effect for the first time. Both the metals (Cu and Ag) were estimated in natural water, justifying the utility of the sensing platform for practical applications. Besides, the evolution of brilliant red color with semi-carbazone for Ag+ was employed for the colorimetric sensing of Ag+. [ABSTRACT FROM AUTHOR]

Weakly fluorescent AuAg nanoclusters were obtained from glutathione, chloroauric acid, and silver nitrate aqueous solution under a modified hydrothermal method. Such glutathione-capped synergistically evolved clusters were obtained for the first time by employing our experimental conditions. Such weak fluorescence was made significantly brighter by employing Na + and a Na + sensor was obtained with a linear detection range of 10 -5 -5 × 10 -9 M, while the limit of detection was 1.02 × 10 -6 M. Na + made the GSH matrix positively charged to stabilize AuAg clusters resulting in strong emissive properties. Furthermore, the effect of solvents, sunlight exposure, and temperature was gauged. Estimation of Na + concentration was undertaken for natural water samples to demonstrate the practical utility of the designed nanosensor., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The strong fluorescence of green tea was quenched with Fe 3+ because of ligand-to-metal charge transfer and subsequent formation of magnetite (Fe 3 O 4 ) nanoparticles (heavy metal effect). Ag + restored the lost fluorescence by confining iron particles (capped with Cl - ) with the formation of AgCl. Thus, toxic Ag was sensed in the aqueous system with a linear detection range of 10 -4 M to 10 -7 M and a detection limit of 4.1 × 10 -9 M. The sensing protocol was applied for natural samples to detect Ag + . Gallic acid was found to be the pivotal component in the tea extract used to design a sensing platform. The company of the green tea were also varied and obtained comparable results., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A highly fluorescent quinone-capped silver hydrosol (AgOSA) was obtained using salicylaldehyde and an ionic silver solution. Such metal-enhanced fluorescence was efficiently quenched with Congo red dye (CR), producing CRAgOSA, due to the strong silver-sulfur interaction, replacing the capping of quinone (oxidized salicylaldehyde). The introduction of cobalt ions restored the fluorescence by engaging CR (CoCRAgOSA). Cobalt-induced fluorescence enhancement was 8.3 times higher than that of AgOSA due to the freeing of CR and the release of self-quenching of excess quinone molecules in CoCRAgOSA. The mammoth and selective fluorescence enhancement with ionic cobalt assisted in designing a turn-on ionic cobalt sensor with a limit of detection (LOD) of 9.4 × 10 -11 M and a linear detection range (5 × 10 -5 to 10 -9 M). Moreover, toxic CR dye was eliminated by quinone-capped silver nanoparticles and Co 2+ due to chemisorption. Not only the fluorimetric sensing of ionic cobalt but also the colorimetric sensing of Hg 2+ was designed due to the simultaneous aggregation of AgNPs and complexation with CR induced by Hg 2+ (LOD 1.36 × 10 -5 M and linear detection range from 1.00 × 10 -4 to 5 × 10 -7 M). We applied our sensing method to estimate ionic cobalt and mercury in natural samples. The experiment was a unique case of circular economy, where a toxic dye was used for making a nanosensor., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

Silver metal, being a 3d transition metal in group 11 in the periodic table, is widely used in material science for its distinguished plasmonic properties. Nanoparticles (NPs) and nanoclusters (NCs) are widely used in sensing applications having a surface plasmon band and emissive properties, respectively. Mercury is one of the detrimental toxins and threats to various ecosystems. The distinction between nanoparticles and nanoclusters, the utility and toxicity of heavy metal mercury, fluorometric and colorimetric approaches to the recognition of mercury ions with NPs and NCs, the mechanism of detection, spot detection, and natural water sample analyses were illustrated in detail in this review article. Moreover, the sensing platform and analyte (Hg 2+ ) fate were described for substantiating the mechanism. It was observed that NCs are mostly utilized for fluorometric approaches, while NPs are mostly employed for colorimetric approaches. Fluorometric detection is mainly quenching-based. However, sensing with enhancement was found in a few reports. Adulteration of other metals with silver particles often modifies the sensing platform., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A condensation polymer (urea-formaldehyde resin) passivated ZnO nanoparticles were used as an efficient photocatalyst for methyl blue degradation in the presence of H 2 O 2 involving a Fenton-like reaction. The formation of OH˙ radicals were attributed to the pivotal factor for the degradation process. The method was easy and recyclable. The dose of photocatalyst, initial dye concentration, pH variation, variations of the composition of the photocatalyst, and the effect of scavengers were gauged. The degraded product was highly fluorescent and fluorometric detection of H 2 O 2 was achieved along with a colorimetric recognition pathway. No other dye could be degraded under similar experimental conditions, implying the novel utility of methyl blue for environmental remediation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)