Effects of the cone angle on the SERS detection sensitivity of tapered fiber probes.

In this paper, we investigate the effects of taper angle on the SERS detection sensitivity using tapered fiber probes with single-layer uniform gold spherical nanoparticles (GSNs). We show that the photothermal damage caused by excessive excitation laser power is the main factor that restricts the improvement of detection sensitivity of tapered fiber probes. Only when the cone angle is appropriate can a balance be achieved between increasing the excitation laser power and suppression of the transmission and scattering losses of the nanoparticles on the tapered fiber surface, thereby obtaining the best SERS detection sensitivity. Furthermore, the optimal cone angle depends on the complex refractive index of the equivalent composite dielectric (ECD) layer containing GSNs. For three SERS fiber probes with different ECD layers, the optimal cone angles measured are between 11-13°.