Enhance Raman scattering for probe methylene blue molecules adsorbed on ZnO microstructures due to charge transfer processes

Ag nanoparticles on ZnO nanoplates as a hybrid SERS-active substrate for trace detection of methylene blue

“…The shortening of the interface gap junctions between metal and semiconductor enhanced the local electromagnetic field 69 and the EF of ZnO/Ag3 is highest at the band of 1436 cm −1 with a value of 6.2 × 10 6 , which is superior to that of 2.9 × 10 4 obtained in our previous ZnO nanoplates-based SERS-active substrate at a same concentration of MB (10 −4 M). 30 The strongest Raman band at 1436 cm −1 was related to the N -phenyl stretching vibration in MB molecules. However, for higher Ag amounts (ZnO/Ag4 and ZnO/Ag5), the EF values were reduced due to the screening of Ag to the charge transfer between ZnO and MB molecules.…”

“… 63 Two bands at 1395 cm −1 and 888 cm −1 belong to C–H bending vibrations. 30 In addition, the relative intensities of the absorption peaks from the ZnO/Ag3 + MB sample are lower than those of MB molecules, which implies a strong interaction between MB molecules and the ZnO/Ag substrate.…”

“… 7 The strongest intense band at 1625 cm −1 is attributed to the C–C ring stretching mode of MB molecules. 30 The characteristic Raman band of MB molecules at 445 cm −1 is ascribed to the C–N–C skeletal deformation mode. As illustrated in Fig.…”

“…The limit of detection (LOD) of MB using ZnO/Ag3 nanosystem can be achieved as 10 −9 M, much better than that of a pristine ZnO-based SERS substrate (10 −4 M). 30 Moreover, the detection limit of molecular probes increases due to the polarization of the excitation laser at the rough ZnO/Ag surface. 70 This result agrees with some other reports.…”

“… 37,38 ZnO nanostructures from pure to hybrid structures have been developed as SERS substrates due to their non-toxicity and biocompatibility. 10,15,16 In order to meet the demands of their applications, a wide range of morphologies of ZnO semiconductor nanostructures, including nanowire, 39,40 nanodome, 10 nanoplate, 41 nanorod, 42,43 nanoparticle, 25,44 dumbbell, 45 nanotube, 46,47 and hexagon, 30 have been developed. Semiconductor-based SERS substrates are generally less efficient than noble metal substrates.…”