Demonstration of a Low-Cost, Single-Molecule Capable, Multimode Optical Microscope

We demonstrate a low-cost optical microscope capable of single-molecule detection that operates in confocal, total internal reflection, epifluorescence, and brightfield transmitted light modes. The microscope detects the blinking of single CdSe/ZnS core/shell quantum dots as well as the fluorescence of single CdSe nanowires. In addition, the Brownian motion of 40-nm and 500-nm diameter dye-doped polystyrene beads suspended in water has been observed, demonstrating a wide range of applications for the microscope. Modifications to the system include the addition of a fiber-based spectrometer allowing the acquisition of fluorescence spectra from selected areas of a sample. The assembly and alignment of such a microscope not only shows different forms of modern single-molecule microscopy to both undergraduates and high school students alike but also provides a useful platform for studying microscopic processes at the single-fluorophore limit.