In this work Ag-Cu, Ag-Au and Au-Cu bimetallic alloy nanoparticles of different compositions were synthesized by different methods i.e., polyol, aqueous polymer solution, co-reduction, reverse micellar, co-precipitation and chemical reduction methods. The synthesized alloy nanoparticles were characterized by UVVisible spectroscopy, fluorescence spectroscopy, XRD, SEM, TEM, HR-TEM and EDS. The XRD pattern showed high crystallinity and phase formation of the nanoparticles. TEM evidenced the formation of Ag-Cu, Ag-Au and Au-Cu nanoparticles with diameters ranging from 10-15, 20-30 and 15-25 nm respectively. Ag-Cu bimetallic alloy nanoparticles were coated over a well-polished glassy carbon electrode and the designed sensor was applied for the detection of a highly carcinogenic carbonyl compound, 2-butanone. Electrochemical studies revealed that polyethylene imine (PEI) used as a capping agent also enhances the sensing of the modified electrode for the recognition of 2-butanone. The sensor developed from AgCu (1:1) alloy nanoparticles showed the best sensing properties for the detection of 2- butanone as evidenced by electrochemical impedance spectroscopy and a 0.1 μM detection limit. Glassy carbon electrode (GCE) was modified with potentiodynamic polymerization of pyrrole into polypyrrole which was over oxidized in order to increase its sensitivity towards polycyclic aromatic hydrocarbons (PAHs). The electrode was further modified with Au-Ag bimetallic alloy nanoparticles. The fabricated GCE was successfully applied to detect an environmental toxin, pyrene. Ag and Au in ratio of 3:1, showed best response for the detection of pyrene with a detection limit of 0.1 µM. Au-Cu (1:3) alloy nanoparticles synthesized by chemical reduction method were intentially engineered with their desired ratio and chemical composition on the surface of clean GCE that was already fabricated with over oxidized poly pyrrole. This composite electrode (PPyox/Au-Cu/GCE) was successfully applied for the detection of environmental toxin anthracene (with lowest concentration, 0.15 μM). The effect of alloy nanoparticles was tested on seed germination frequency, antioxidant activity and biochemical characterization of medicinally important plants, Silybum marianum and Eruca sativa. Chemical composition of alloy nanoparticles, size and shape matters for nanoparticles to exert effect on plants. Phytotoxicity study of nanoparticles showed that bimetallic alloy nanoparticles are more stress inducing factor in plants acting as external factor that disturb the internal mechanisms of plant seeds. In response to the induced stresses, plants release secondary metabolites (protein content, flavonoids and phenolic contents), antioxidants and some important enzymes like super oxide dismutase (SOD) and peroxidase (POD) by their defensive mechanisms. The secondary metabolites produced in response to stress induced by bimetallic nanoparticles were also evaluated and it was found that nanoparticles of small size and high toxicity produce more secondary metabolites. Such secondary metabolites produced in medicinal plants have a great potential in treating the human ailments.
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