Quantum dots (QDs) are promising fluorescent tags for microarrays. Because most microarrays are analyzed under dry conditions, it is necessary to examine the photo properties of QDs in air. We demonstrate that the photophysical characteristics of individual quantum dots are different at the liquid/solid interface compared with QDs at the air/solid interface by observing them through a wide-field fluorescence microscope. QDs in air show higher photo-stability, higher fluorescence signal, slower spectral blue shift rate, less blinking and shorter bulk fluorescence lifetime than those in solution. These beneficial properties indicate QDs are good alternative fluorescent probes for microarrays.

Photobleaching and spectral diffusion (blue shift) of quantum dots at the solid/liquid interface are suppressed by adding mercaptoethylamine.

Scattering images of single quantum dots (QDs) are obtained with a standard dark-field microscope at a video rate. The counts of QDs under dark-field remained constant while the scattering intensity decreased, providing direct proof of quantum dot photophysical bleaching as opposed to desorption or photodecomposition.

A spectral imaging method of single protein molecules labeled with a single fluorophore is presented. The method is based on a transmission grating and a routine fluorescence microscope. The bovine serum alubmin (BSA) and antiBSA molecules labeled with Alexa Fluor 488 and Alexa Fluor 594, respectively, are used as the model proteins. The fluorescence of single molecules is dispersed into zeroth-order spectrum and first-order spectrum by the transmission grating. Results show that the fluorescence emission spectrum of single molecule converted from the first-order spectral imaging is in good agreement with the bulk fluorescence spectrum. The spectral resolution of 2.4 nm/pixel is obtained, which is sufficient for identifying the molecular species in a multicomponent system.

Thermal motions of semiconductor quantum dots (QDs) are suppressed on a dehydrated agarose-modified surface. The diffusion coefficients (D) of particles can be controlled by modifying the surface with an appropriate agarose concentration. The value of D is more than 100 times lower than the theoretical value when the dried agarose surface is made with an 8% agarose solution. This makes it possible to real-time record the diffusion process of single particles and single molecules in low-viscosity solution. A transmission grating installed in front of the charge-coupled device separates the QD fluorescence into the zeroth-order and first-order spectrum. Therefore, the spectrum of dynamic QDs is tracked on the modified surface. Tracking the dynamic QD spectral image is a promising method to explore the process of the molecular interactions in the physiological buffer.

Photobleaching and spectral diffusion (blue shift) of quantum dots at the solid/liquid interface are suppressed by adding mercaptoethylamine.