Results
Figure 2a shows the SERS based response of the inkjet printed substrate towards HgS. The Raman
spectra obtained from the test analytes on the bare Si wafer are overlain with the spectra obtained from
the test analytes on the Ag nanoparticle coated Si wafer. Similarly, the spectra for CdS and ZnO are
shown in Fig. 2b and Fig. 2c, respectively. Characteristic Raman peaks for HgS, CdS and ZnO were
observed at 249.13 cm-1, 299.41 cm-1and 415.25 cm-1, respectively and for that of Ag nanoparticles were
observed at 918.49 cm-1and 1391.18 cm-1. The SERS based response of the printed sensor revealed an
enhanced Raman effect by an amplification factor of 5, 3 and 4 for HgS, CdS and ZnO, respectively
immobilized on Ag nanoparticle printed substrate when compared to that of HgS, CdS and ZnO
immobilized on bare Si wafer.
Raman Spectroscopy is based on the elastic and inelastic scattering of the photons in the target
molecules. Depending upon the nature of the target molecules, each photon undergoes different levels of
scattering, thus facilitating the differentiation between each species. The amplification of the Raman
effect can be attributed to a change in frequency due to the enhancement of the electromagnetic field at
hotspots, which is the area between two neighbouring nano-particles [15]. This enhancement of the
electromagnetic field is facilitated because of the embedding of target molecules between adjacent
nanoparticles.
(a) (b)
(c)
Fig. 2. (a) Comparison of the Raman spectrum of HgS on Ag nanoparticle printed substrate vs. HgS on bare Si wafer; (b)
Comparison of the Raman spectrum of CdS on the Ag nanoparticle printed substrate vs. CdS on bare Si wafer; (c) Comparison of
the Raman spectrum of ZnO on Ag nanoparticle printed substrate vs. ZnO on bare Si wafer. The spectra were obtained using 785
nm excitation with an integration time of 1 second at 300 mW