Studies Of Several Fluorescence Sensors Based On Silicon Quantum Dots

In recent years, silicon quantum dots（SiQDs） have attracted considerable attention owing to their special properties including good fluorescence properties, high biocompatibility and low toxicity. Up to date, SiQDs have been widely used in bioimaging and photoelectric device. Based on the excellent properties of SiQDs, several sensors have been built for highly sensitive and simple detection of protamine, heparin, Hg²⁺ and pH. The main contents are summarized as follows:1. An ultrasensitive “turn on-off” fluorescence sensor was presented for determination of protamine and heparin. The fluorescence of SiQDs was quenched significantly by adding AuNPs into SiQDs solution. Upon addition of protamine, the AuNPs aggregated and the fluorescence of SiQDs was recovered due to the competitive adsorption of protamine and SiQDs on AuNPs. Addition of heparin disturbed the interaction of protamine and AuNPs due to the strong affinity between heparin and protamine, resulting in an adsorption of SiQDs on the surface of Au NPs. Thus the fluorescence of SiQDs was quenched. The strategy was simply achieved by measuring the changes in the fluorescence of SiQDs. The research results suggested that the developed method has several advantages such as label-free, high sensitivity, low cost, ease of operation. The low detection limit of protamine and heparin are 6.7 ng/mL and 0.67 ng/mL, respectively. The sensing platform was successfully applied to determination of heparin and protamine in serum samples.2. A novel nanohybrid ratiometric fluorescence sensor for determination of mercuric ions(Hg²⁺) has been designed. The hybrid sensor comprises blue-colored SiQDs and orange-colored emission Rhodamine B（RhB）. Such hybridized sensor exhibits dual emission bands centered at 449 and 581 nm under a single excitation wavelength of 350 nm, respectively. The orange fluorescence of RhB is insensitive to the analyte, whereas the blue emissive of SiQDs is selectively quenched by the analyte. Upon exposure to different amounts of Hg²⁺, the ratiometric fluorescence sensor dispays a distinguishable color change from violet to orange, which can be clearly observed by the naked eye. This ratiometric fluorescence sensor exhibited good selectivity to Hg²⁺ over other metal ions. The ratio of I449/I581 linearly decreased with the increasing of Hg²⁺ concentration over the two ranges of 0-0.1 μM and 0.1-7 μM, a detection limit as low as 4.9 nM was achieved. Additionally, the practical use of this system for Hg²⁺ determination in real water samples is also demonstrated successfully.3. A simple and highly efficient fluorescence sensor for pH sensing using water-soluble SiQDs was reported. The SiQDs were synthesized by using a one-pot microwave-assisted method. The pH sensor consists of SiQDs and a pH indicator（Phenol red） that found to be able to quench the fluorescence of SiQDs effectively. The SiQDs generate blue luminescence upon excitation of 350 nm wavelength. The pH probe undergoes a large spectral shift（from 435 to 560 nm）, and a distinct color change（from yellow to pink） with increasing pH. The blue emission peaks of the SiQDs is affected by the absorption of the pH indicator, due to an inner filter effect. This new, cheap, low-toxic, and effective fluorescent pH sensor based on label-free SiQDs coupled with phenol red would be a promising candidate in biological field.