The Research On Single-molecule Tracking Of Quantum Dots In Free Solution

Single molecule tracking can record the trajectories of single dynamic molecules or particles and real-time monitor the biomolecular interactions process and the signal transduction process. High luminescence, wide excitation, ultra-narrow and symmetric emission, a size-dependent tunable spectrum of the quantum dot(QDs) make it be a valuable tool in molecular biology and bioengineering. However, the fluorescence intermittency of QDs affects the authenticity of single-molecule tracking. Microfluidic chip can be used for low-cost, high-flux, large-scale studies with the characteristics of the highly parallel, and integrated, automation, miniaturization, and plays more and more important roles in the fields of genetic diagnosis, protein analysis, cell biology, medicine, et al. In this paper, we achieved the single QDs tracking in the free solution and the preliminary exploration of sing-molecule imaging based on the microfluidic chip. The main works were as follows:1. Single-molecule imaging with a routine microscopy studied the emission behaviors of single QDs on the glass and the dried agarose surface. For the quantum dots on the dehydrated agarose-modified glass slides, it has been observed that the fluorescence intensity is enhanced as compared to that on the glass slides. The average values of the fluorescence intensity of QDs on the surface of 4 and 8% agarose enhanced 2 and 3 times than that on the glass, respectively. Single-molecule imaging also revealed that the blinking suppression of quantum dots absorbed onto the dehydrated agarose-modified glass.2. The diffusion coefficients (D) can be controlled according to research needs by modifying the glass slide with different agarose concentrations. We real-time recorded the diffusion process of single QDs in low-viscosity solution. The average D of 12 nm QDs on the modified surfaces made with agarose solution of 5 and 8% concentrations are 11.6 and 118.7 times smaller than the theoretical values of D in bulk solution, respectively. We successfully tracked the spectral images of single dynamic QDs in the aqueous solution between the dried agarose-modified surface and the cover slide by the standard epi-fluorescence microscopy with a transmission grating installed in front of the charge-coupled device. Tracking the dynamic QD spectral image is a promising method to explore the process of the molecular interactions in the physiological buffer. 3. In this work, epoxy-modified hydrophilic polymers had been covalently linked to the PDMS surface to produce the hydrophilic surface. The surface coating process can be completed within 30 min and the stability can be kept for～30 days. The microchannel becomes hydrophilic and resists protein adsorption to a high extent. Single-molecule imaging of quantum dots coated and non-coated with liposome based on the glass microfluidic chip observed the reaction of them andλ-DNA.