Scanning near-field optical microscope working with a CdSe∕ZnS quantum dot based optical detector

We have developed a scanning near-field optical microscope that uses a subwavelength-sized silica sphere covered with CdSe∕ZnS quantum dots as a fluorescent optical detector. Due to the good photostability of these semiconducting particles, we are routinely able to perform several successive scans without a noticeable decrease of fluorescence signals. As an example, we will show some images of the light immediately transmitted through 300nm wide slits made in a thin gold film. We will also discuss the advantages of such fluorescent probes compared to other near-field optical techniques.