Optical Properties of Silver Nanoparticles for Surface Plasmon Resonance (SPR)-Based Biosensor Applications

It has been successfully carried out the synthesis of silver nanoparticles by chemical reduction method. Silver nitrate (AgNO3) is used as the metal precursor and trisodium citrate as the reducing agent as well as the use of polyvinyl alcohol (PVA) as a stabilizer. The formation of silver nanoparticles was observed visually with discoloration (yellow). To excite surface plasmons, attenuated total reflection (ATR) method is used with Krestchmann configuration of the prism coupling. The maximum absorption band in the UV-Vis spectrometer shows a red shift of 429.43 nm wavelength for a colloidal solution of silver nanoparticles without PVA and 429.01 nm with PVA. The addition of PVA sharpened absorption spectrum curve and produce a broad absorption band which is indicative of a smaller particle size. TEM images showed that the morphology (crystallites) silver nanoparticles have nearly spherical geometry with dispersive particle distribution. Dispersibility of nanoparticles such as this could potentially be used as an active ingredient of SPR biosensor. The observation of the SPR phenomenon shows the SPR angle shift of 0.1° when a thin layer of silver as an active ingredient a biosensor coated with silver nanoparticles and 0.2° when silver nanoparticles with PVA. SPR angle shift and increase the reflectance values caused by changes in surface Plasmon, which can be a reference that the SPR phenomenon with the sensing surface modification using an additional layer of silver nanoparticles can increase sensitivity.

Green synthesis of magnetically separable and reusable Fe_(3)O_(4)/Cdots nanocomposites photocatalyst utilizing Moringa oleifera extract and watermelon peel for rapid dye degradation

This study focused on green-synthesized magnetite/carbon dots nanocomposites(GS-Fe_(3)O_(4)/Cdots)utilizing Moringa oleifera leaf extract and watermelon peel waste for rapid degradation of methylene blue(MB)dye.Co-precipitation and hydrothermal method were used to synthesize GS-Fe_(3)O_(4) and Cdots,respectively.In addition,the sonication method was used to link Cdots on Fe_(3)O_(4) surface.X-ray diffraction spectrum of GS-Fe_(3)O_(4)/Cdots inform the cubic inverse spinel and has crystallite size in the range of 10.1-7.2 nm.The crystallite size also decreased with the increase of Cdots concentration.The transmission electron microscope showed the most uniform size of nanocomposites at around 13.4 nm.The functional group of Fe-O was detected on the nanocomposites,proof that Fe_(3)O_(4) still exists after fabrication.The presence of C=C,C-O,and C-O-C also indicates the existence of Cdots on the surface of Fe_(3)O_(4).The addition of Cdots affected the saturation magnetization and coercivity value in the range of 29.2-38.3 emu/g and 59-65 Oe,respectively,which showed a good magnetic properties.As an organic dye,MB was used for a photocatalytic process under UV irradiation.The degradation efficiency was raised to 98% for 30 min photocatalytic process.The magnetically separable capability makes nanocomposites could be recycled and reused three times with high degradation.Furthermore,GS-Fe_(3)O_(4)/Cdots potential as a low-cost and environmentally friendly reusable photocatalyst for rapid wastewater degradation.