Electrochemical Detection of Single Microbeads Manipulated by Optical Tweezers in the Vicinity of Ultramicroelectrodes

8 pagesInternational audienceLatex micrometric beads are manipulated by optical tweezers in the vicinity of an ultramicroelectrode (UME). They are optically trapped in solution and approached the electrode surface. After the electrochemical measurement, they are optically removed from the surface. The residence time of the particle on the electrode is thus controlled by the optical tweezers. The detection is based on diffusional hindrance by the insulating objects which alters the fluxes of the redox Ru(NH3)6 3+ species toward the UME and thus its mass-transfer limited current. We have optically deposited successively 1, 2, and 3 beads of 3-μm radius on the UME surface, and we have recorded the variations of the current depending on their landing locations that were optically controlled. Finally we decreased the current by partially blocking the electroactive surface with a six-bead assembly. The variation of the steady-state current and the approach curves allow for the indirect electrochemical localization of the bead in the vicinity of the UME, not only when the bead is in contact but also when it is levitated at distances lower than the UME radius. ...

How Venture Capital Creates Externalities in the Bioeconomy: a Geographical Perspective

A stream of literature has demonstrated that venture capital generates externalities that enhance the knowledge base of a given region and accordingly assist high technology firms to improve their innovative performance. What has gone largely unexamined in this literature is the geographic extent of such externality impact. In this research we address the issue at hand. We do so by analyzing the association between the patenting rate of all life sciences firms that have won Small Business Innovation Research grants from 1983 to 2006 and the venture capital investments that have occurred at increasingly distant spatial units from those firms. Controlling for firm-specific and environmental factors as well as for endogeneity concerns, we document that life sciences firms tend to produce more patents whenever they are situated in very close proximity to where venture capital investments occur. Further, we find that improvements of the patenting rate of focal firms largely emanate from investments that reflect the expertise of venture capitalists on advancing existing prototypes closer to commercialization. We conclude the paper with a discussion on research and policy implications of our findings