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A new technique to generate and distribute a wide-band continuously tunable millimeter-wave signal using an optical external modulator and a wavelength-fixed optical notch filter is proposed. The optical intensity modulator is biased to suppress the odd-order optical sidebands. The wavelength-fixed optical notch filter is then used to filter out the optical carrier. Two second-order optical sidebands are obtained at the output of the notch filter. A millimeter-wave signal that has four times the frequency of the microwave drive signal is generated by beating the two second- order optical sidebands at a photodetector. Since no tunable optical filter is used, the system is easy to implement. A system using an LiNbO3 intensity modulator and a fiber Bragg grating filter is built. A stable and high spectral purity millimeter-wave signal tunable from 32 to 50 GHz is obtained by tuning the microwave drive signal from 8 to 12.5 GHz. The integrity of the generated millimeter-wave signal is maintained after transmission over a 25-km standard single-mode fiber. Theoretical analysis on the harmonic suppression with different modulation depths and filter attenuations is also discussed. [ABSTRACT FROM AUTHOR]

A highly sensitive and facile ‘turn-off’ surface-enhanced Raman scattering (SERS) sensor based on the etching effect on silver nanoparticles (Ag NPs) was designed for the determination of glucose. Ag NPs marked with Raman tags of 4-mercaptopyridine (4-mpy) were assembled on the glass slide by layer-by-layer self-assembly to form a SERS chip. When this SERS chip was exposed to different concentrations of glucose and glucose oxidase-mixed solutions, the produced H2O2 started to etch the Ag NPs, leading to the SERS signal of 4-mpy decreasing. Therefore, we can trace the SERS intensity of 4-mpy to determine the glucose concentration, and the lowest detectable concentration can reach 10 μM. This glucose sensor has the promising potential of detection for clinical blood in the future. [ABSTRACT FROM AUTHOR]

Ag nanoparticles and nanostructured surfaces have been widely used as surface-enhanced Raman scattering (SERS) substrates, which can enhance the Raman signals when molecules are adsorbed on the surface of Ag by the effect of Ag-thiol bonds. In this paper, we propose an efficient method to remove the molecules adsorbed on Ag with sodium borohydride solution, providing a protocol to realize a reproducible and practicable Ag SERS substrate. A theoretical density function theory approach has been used to explain the mechanism of desorption. [ABSTRACT FROM AUTHOR]