The optimal size of spherical silver nanoparticles (AgNPs) for off-resonance surface-enhanced Raman scattering (SERS) was found to be ∼50 nm based on the equivalent Ag content in AgNP colloids. It is understood that the SERS intensity of adsorbates on the surface of metal nanoparticles is dependent on the size and shape of the particles of interest. Herein, we report a seeded growth mechanism for the formation of silver nanoparticles that allows superior control over the size of the resultant nanoparticles with relatively low polydispersity. The high degree of size control allows for a better understanding of the study of the effect of particle size on SERS intensity. The Raman study performed here employed a long-wavelength excitation (785 nm) so as to avoid photochemical degradation of adsorbed species and photochemical transformation under intense excitation. Under these experimental conditions, it was found that the optimal size of AgNPs for providing a maximum SERS intensity of adsorbed R6G is ∼50−60 nm, a result that is expected to extend to other adsorbates as well.

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The present work demonstrates the microwave-assisted synthesis of two different structural morphologies containing nickel oxide nanoparticles (NiO NPs) embedded in nitrogen (N) and sulfur (S) co-doped reduced graphene oxide (NS-rGO) nanosheets. The synthesized NiO anchored on NS-rGO nanosheets (NS-rGO-NiO composites) and NiO covered by NS-rGO nanosheets (NS-rGO:NiO composites) were used as an application in electromagnetic interference (EMI) shielding effectiveness (SE). The EMI SE studies reveal that NS-rGO:NiO composites show improved performance as compared to NS-rGO-NiO composites. In NS-rGO:NiO composites, the covered surface of NiO NPs by conducting NS-rGO nanosheets helps to improve the EMI SE application. The synthesized composite materials were extensively characterized using various techniques including scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. Binding energy of N/S element in rGO nanosheets were analyzed by XPS and it is confirmed that the N atoms were present in three states in carbon skeleton of NS-rGO nanosheets as pyridinic, pyrrolic, and graphitic states; however, S atoms were present in single state as C–S–C configuration. The as synthesized NS-rGO:NiO composites reveal good performance for EMI applications and demonstrate the SE value of more than ∼21 dB at thickness of 1.1 mm film of NS-rGO:NiO composites in microwave X-band range (8.2–12.4 GHz).

The feasibility of using hollow core photonic crystal fiber (HC-PCF) in conjunction with Raman spectroscopy has been explored for real time monitoring of heparin concentration in serum. Heparin is an important blood anti-coagulant whose precise monitoring and controlling in patients undergoing cardiac surgery and dialysis is of utmost importance. Our method of heparin monitoring offers a novel alternative to existing clinical procedures in terms of accuracy, response time and sample volume. The optical design configuration simply involves a 785-nm laser diode whose light is coupled into HC-PCF filled with heparin-serum mixtures. By non-selectively filling HC-PCF, a strong modal field overlap is obtained. Consequently, an enhanced Raman signal (>90 times) is obtained from various heparin-serum mixtures filled HC-PCFs compared to its bulk counterpart (cuvette). The present scheme has the potential to serve as a 'generic biosensing tool' for diagnosing a wide range of biological samples.

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