Au nanoparticles functionalized 3D-MoS2 nanoflower: An efficient SERS matrix for biomolecule sensing.

Fabrication of Molybdenum disulfide (MoS2) nanostructures and surface functionalization with noble metal nano particles is an emerging field of research as it has potential applications in electronic devices and chemical sensing. Here we report application of gold nanoparticles (AuNPs) decorated MoS2 nanoflowers (Au-MoS2 NFs) as an efficient bio-sensor. MoS2 NFs, synthesized using green synthesis process, are further functionalized with AuNPs to tune their physical properties and make them more appropriate for biological applications. The abundant 'hot-spots' created by AuNPs through localization of electromagnetic field endows the Au-MoS2 hybrid structure as an excellent substrate for biochemical sensing through surface enhanced Raman scattering (SERS). The sensing efficiency of the SERS substrate is examined using Rh6G as probe molecule with concentration as low as 10-12 M. Main emphasis is given in detecting free bilirubin, an important component of human blood, using SERS technique. Au-MoS2 NF SERS substrate exhibits high sensitivity, stability and excellent reproducibility in sensing bilirubin from high level (10-3 M) to picomolar level. The concentration (C) dependent SERS intensity (I) is found to follow the general relationship I = Cα, with α ranging from 0.09 to 0.12. The substrate shows excellent selectivity and reliability while sensing of free bilirubin performed in human serum in the presence of crucial interferences such as dextrose, cholesterol and phosphate. In the present study, this Au-MoS2 hybrid offers a new potential biosensing technology for free bilirubin detection and is anticipated to be applied for clinic diagnosis.

Hassle free synthesis of nanodimensional Ni, Cu and Zn sulfides for spectral sensing of Hg, Cd and Pb: A comparative study.

A simple room temperature synthesis method of Ni, Cu and Zn sulfide nanoparticles (NPs) in aqueous medium is reported here. The NPs stabilized in aqueous medium by the citrate ions were characterized by UV-vis, ζ potentials, TEM and Raman spectroscopic techniques. The solid NPs could be isolated from the aqueous medium when allowed to stand for a prolonged time (~20h). The solids were also characterized by IR and powder X-ray analysis. The nanoparticles were further used for the development of facile optical sensing and detection of heavy metal ions at trace scale. Alterations in the absorption spectra of the generated NPs were indicative of their interactions with heavy metal ions. Raman spectral measurements further validate the detection technique. It is found that out of the three synthesized nanoparticles, nickel sulfide NP is a specific sensor for mercury ions whereas zinc sulfide and copper sulfide NPs act as sensors for Hg2+, Cd2+ and Pb2+.

Sensitization of an endogenous photosensitizer: electronic spectroscopy of riboflavin in the proximity of semiconductor, insulator, and metal nanoparticles.

Riboflavin (Rf) is a class of important vitamins (Vitamin B2) and a well-known antioxidant. Here we have synthesized nanohybrids of Rf with a number of inorganic nanoparticles (NPs); namely zinc oxide (ZnO), titanium oxide (TiO2), aluminum oxide (Al2O3) and gold NPs of similar sizes. While high resolution transmission electron microscopy (HRTEM) confirms integrity and sizes of the NPs, intactness of the molecular structure of the drug Rf is revealed from absorption and steady-state emission spectra of the drug in the nanohybrid. Raman spectroscopy on the nanohybrids shows the nature of molecular complexation of the drug with the inorganic NPs. For the semiconductor and insulator NPs, the complexation is found to be noncovalent, however, a covalent attachment of the drug with the dangling bonds of metal atoms at the surface is observed. In order to investigate antioxidant activity of the nanohybrids, we have performed 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay of the nanohybrids in dark as well as under blue light irradiation. Whereas change of the antioxidant activity of the nanohybrids with respect to free riboflavin in the absence of light is observed to be insignificant, a drastic change in the activity in the case of TiO2 and ZnO in the presence of light is evident. No change in the case of Al2O3 and a significant decrease in the antioxidant activity for gold nanohybrids are also remarkable. Picosecond-resolved fluorescence studies on the nanohybrids reveal a molecular picture of the differential antioxidant activities. An ultrafast photoinduced electron transfer from Rf to ZnO and TiO2 are clearly evident from the corresponding fluorescence transients. We have compared the picosecond-resolved transients with that of Rf in the presence of a well-known electron acceptor benzoquinone (BQ) and found similar time scales. No temporal change in the fluorescence transient of riboflavin in Al2O3 nanohybrids compared to that of free Rf is observed indicating uneventful excited state relaxation of the nanohybrids. Nanosurface energy transfer (NSET) over Förster resonance energy transfer (FRET) is found to be the prevailing de-excitation mechanism in the case of gold nanohybrids, because of the strong spectral overlap between Rf emission and surface plasmon absorption of the gold NPs. Different excited state mechanisms as revealed from our studies are expected to be useful for the design of NP-sensitized drugs, which are reported sparsely in the literature.