Application of ZnO Nanorods Based Whispering Gallery Mode Resonator in Optical Immunosensors.

In this research a whispering gallery mode (WGM) resonator based on vertically oriented ZnO nanorods, which were formed on silicon surface (silicon/ZnO-NRs), has been applied in the design of optical immunosensor that was dedicated for the determination of grapevine virus A-type (GVA) proteins. Vertically oriented ZnO-NRs were grown on silicon substrates by atmospheric pressure metal organic chemical vapor deposition (APMOCVD) and the silicon/ZnO-NRs structures formed were characterized by structural and optical methods. Optical characterization demonstrates that silicon/ZnO-NRs-based structures can act as 'whispering gallery mode' (WGM) resonator where quasi-whispering gallery modes (quasi-WGMs) are generated. These quasi-WGMs were experimentally observed in the visible and infrared ranges of the photoluminescence spectra. In order to design an immuno-sensing system the anti-GVA antibodies were immobilized on the surface of silicon/ZnO-NRs and in this way silicon/ZnO-NRs/anti-GVA structure was formed. The immobilization of anti-GVA antibodies and then the interaction of silicon/ZnO-NRs/anti-GVA structure with GVA proteins (GVA-antigens) resulted in an opposite shifts of the WGMs peaks in the visible range of the photoluminescence spectra observed as a defect-related photoluminescence emission of ZnO-NRs. Here designed silicon/ZnO-NRs/anti-GVA immuno-sensing structure demonstrates the sensitivity towards GVA-antigens in the concentration range of 1-200 ng/ml. Bioanalytical applicability of the silicon/ZnO-NRs-based structures in the WGMs registration mode is discussed.

Lead (Pb) interfacing with epitaxial graphene.

Here, we report the electrochemical deposition of lead (Pb) as a model metal on epitaxial graphene fabricated on silicon carbide (Gr/SiC). The kinetics of electrodeposition and morphological characteristics of the deposits were evaluated by complementary electrochemical, physical and computational methods. The use of Gr/SiC as an electrode allowed the tracking of lead-associated redox conversions. The analysis of current transients passed during the deposition revealed an instantaneous nucleation mechanism controlled by convergent mass transport on the nuclei locally randomly distributed on epitaxial graphene. This key observation of the deposit topology was confirmed by low values of the experimentally-estimated apparent diffusion coefficient, Raman spectroscopy and scanning electron microscopy (SEM) studies. First principles calculations showed that the nucleation of Pb clusters on the graphene surface leads to weakening of the interaction strength of the metal-graphene complex, and only spatially separated Pb adatoms adsorbed on bridge and/or edge-plane sites can affect the vibrational properties of graphene. We expect that the lead adatoms can merge in large metallic clusters only at defect sites that reinforce the metal-graphene interactions. Our findings provide valuable insights into both heavy metal ion electrochemical analysis and metal electroplating on graphene interfaces that are important for designing effective detectors of toxic heavy metals.

Tuning the Emission Energy of Chemically Doped Graphene Quantum Dots.

Tuning the emission energy of graphene quantum dots (GQDs) and understanding the reason of tunability is essential for the GOD function in optoelectronic devices. Besides material-based challenges, the way to realize chemical doping and band gap tuning also pose a serious challenge. In this study, we tuned the emission energy of GQDs by substitutional doping using chlorine, nitrogen, boron, sodium, and potassium dopants in solution form. Photoluminescence data obtained from (Cl- and N-doped) GQDs and (B-, Na-, and K-doped) GQDs, respectively exhibited red- and blue-shift with respect to the photoluminescence of the undoped GQDs. X-ray photoemission spectroscopy (XPS) revealed that oxygen functional groups were attached to GQDs. We qualitatively correlate red-shift of the photoluminescence with the oxygen functional groups using literature references which demonstrates that more oxygen containing groups leads to the formation of more defect states and is the reason of observed red-shift of luminescence in GQDs. Further on, time resolved photoluminescence measurements of Cl- and N-GQDs demonstrated that Cl substitution in GQDs has effective role in radiative transition whereas in N-GQDs leads to photoluminescence (PL) quenching with non-radiative transition to ground state. Presumably oxidation or reduction processes cause a change of effective size and the bandgap.