The first observations of surface-enhanced resonance Raman scattering (SERRS) from tris(bipyridine)ruthenium(II), Ru(bpy),2+, at monolayer (or less) coverage on n-GaAs(100) semiconductor (SC) electrodes modified by the electrodeposition of ca. 100 monolayers of Ag metal are reported. In addition to the SERRS studies, the photoelectrochemical and surface microstructural properties of Ag/GaAs/Ru(bpy)32+ electrodes were studied by cyclic voltammetry (CV) and scanning electron microscopy (SEM).

We have prepared and characterized several lanthanide ion complexes of multidentate ligands or chelates in an effort to develop new upconverting luminescent labels that can be immune to autofluorescence and photobleaching. This study has involved the characterization of various chelates of Nd, Er, and Tm with respect to relative luminescent efficiency and excited-state lifetimes and explored various two-photon stepwise excitation mechanisms. Using peak laser powers near 100 kW, the upconversion emissions of Nd in Nd(EDTA) 2 5− at 386 nm, Er in Er(DPA) 3 3− at 550 nm, and Tm in Tm(DPA) 3 3− at 480 nm, at levels of ~10 −12 moles can be detected.Upconversion refers to conversion of excitation light to shorter wavelengths or higher energy. Efficient upconversion has been obtained in crystalline materials containing trivalent lanthanide ions in the form of phosphor particles, 1-4 displays, 5 or fibers for upconversion lasers. 6,7 Upconversion in Er has been obtained also in low-phonon-energy liquids. 8 To date, upconversion has not been achieved in aqueous solutions. 9 We demonstrate upconversion in aqueous phase lanthanide chelates using stepwise infrared excitation. This work is a step in the direction of realizing molecular scale upconverting reporters for biomedical diagnostics.Lanthanides have been applied to biomedical assays in two forms previously: as chelated ligands in a downconverting method or as upconverting phosphor particles. Downconverting lanthanide chelates have been studied for immunoassay 10 or labeling cells. 11 Autofluorescent backgrounds for these materials can be reduced by time-gated detection. 10 Upconverting phosphors have also been applied as reporters for biomedical assays. 12,13 Advantages of these materials include freedom from autofluorescent backgrounds, no photobleaching, narrow emission profiles (which is beneficial for multiplexing), and excitation with diode lasers. Upconversion in lanthanide chelates combines attributes of these two research directions: the small size of the downconverting chelates with the low backgrounds and infrared excitation of the upconverting phosphors.The chemistry of the upconverting chelate is similar to downconverting chelates: a lanthanide ion is complexed with a multidentate ligand or chelating agent that can be covalently bound to a biological probe molecule such as an antibody or DNA oligomer. In the work reported here the light is absorbed and emitted by lanthanide ions, which cannot photobleach. We prefer excitation schemes using near-infrared excitation and visible emission. There are several reasons for using such transitions. With near-infrared excitation, compact and inexpensive laser diodes may be used as excitation sources and the phototoxicity for living cells is low. Visible emission can be detected with high efficiency by using silicon detectors or photocathode materials.In this Letter we report direct pumping of a lanthanide ion by use of both one-and twowavelength upconverting pathways for Nd, Er, and Th ions complexed with the...

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Thermal blooming has been used to measure weak absorption. The thermal lens was generated with a chopper ion laser (488 nm) and monitored with a helium-neon laser, using lock-in detection. The generation of dopachrome by enzyme-catalyzed air oxidation of dopamine was monitored as the rise of the dopachrome absorption signal. Dopamine concentrations were found to be proportional to initial slopes. Modifications to the existing apparatus to improve detection limits are suggested.

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