| We studied the ultrasensitive detector system with evanescent wave coupled whispering gallery mode (WGM). We tested this on Rhodamine 6G, E. coli, and glycine. Rhodamine 6G is a well-known simple dye that was studied in its aqueous form with normal Raman scattering, nonaggregated surface enhanced Raman scattering (SERS), and WGM/SERS. The gain effect values of the ultrasensitive detector system were calculated and compared to normal Raman scattering. The magnitude of the gain for the Rhodamine 6G WGM/SERS was about 12 orders with the tunable diode laser compared to the normal scattering while the WGM/SERS with the HeNe laser was only 10 orders. The WGM/SERS of E. coli enhancement was 5 orders compared to the SERS this time because the normal signal was too weak. The glycine's WGM/SERS was 7 orders times the glycine's normal Raman scattering. The reason why the WGM/SERS of the glycine and E. coli had a lower enhancement than Rhodamine 6G the analyte size for the biological molecules was larger Rhodamine 6G. Both the E. coli and glycine experiments were tested using a HeNe laser instead of the tunable diode laser. So to compensate for the lower WGM/SERS gain, we can use a diode laser instead as experiments with the Rhodamine 6G shows that the WGM/SERS was greater and the distance could be longer for the tunable diode laser than for the HeNe laser. The experiments though were a success; even though we used low power and a low sensitive CCD camera, we still got great signal. |
