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Study of polycation-capped Mn:ZnSe quantum dots as a novel fluorescent probe for living cells
Xiaobo Pan
Supervisor: Pei-nan Wang, Lan Mi
Semiconductor quantum dots (QDs) have been considered as promising fluorescence probes due to their excellent optical properties, such as high quantum yields, wide absorption range, and high extinction coefficient. Ever since Alivisatos’ and Nie’s groups reported their results in the application of QDs as biological fluorescent probes in 1998 [1,2], great attention has been focused on the preparation and the applications of QDs [3-5]. However, most QDs contain toxic heavy metals (i.e. Cd, Pb, Hg), which limited their application in biological systems.
Transition metal manganese ion (Mn2+) doped zinc selenide quantum dots (Mn:ZnSe D-Dots) have been considered as a new material for fluorescent probes in biological labeling. However, this application is limited by the low membrane permeability of quantum D-Dots. For example, the living cell imaging using Mn:ZnS D-Dots was achieved by Geszke et al. [6], with a long incubation time of 72 h and a high concentration of 50 µM as reported.
In this work, Mn:ZnSe D-Dots were capped with the polycation Sofast to label living cells. For the first time, the efficiency of cellular uptake in living cells is significantly enhanced. Various molar ratios of Sofast to D-Dots were explored and compared to obtain the optimal reaction conditions between Sofast and D-Dots. A comparison on the fluorescence labeling ability of living cells were made between Sofast/D-Dots and pure D-Dots. Results from laser scanning confocal microscope show that Sofast/D-Dots complexes enter the cells more efficiently than pure D-Dots, even with a lower concentration and shorter incubation time. The cytotoxicities of D-Dots and Sofast/D-Dots were also studied. It was found that Sofast/D-Dots have a much lower cytotoxicity than cadmium-containing quantum dots (i.e. CdTe and CdTe/ZnS). Our results suggest that the non-heavy-metal-containing Sofast/D-Dots complexes have a great potential in the application of biological labeling, especially of long-time bioimaging in living cells.
参考文献:
[1] Bruchez M, Moronne M, Gin P, Weiss S, Alivisatos AP (1998) Semiconductor nanocrystals as fluorescent biological labels. Science 281:2013-2016
[2]Chan WCW, Nie S (1998) Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection Science 281:2016-2018
[3]Medintz IL, Uyeda HT, Goldman ER, Mattoussi H (2005) Quantum dot bioconjugates for imaging, labelling and sensing. Nat Mater 4:435-446
[4]Chang B, Yang X, Wang F, Wang Y, Yang R, Zhang N, Wang B (2013) Water soluble fluorescence quantum dot probe labeling liver cancer cells. J Mater Sci: Mater Med:1-4
[5]Delehanty J, Mattoussi H, Medintz I (2009) Delivering quantum dots into cells: strategies, progress and remaining issues. Anal Bioanal Chem 393:1091-1105
[6] Geszke M, Murias M, Balan L, Medjahdi G, Korczynski J, Moritz M, Lulek J, Schneider R (2011) Folic acid-conjugated core/shell ZnS:Mn/ZnS quantum dots as targeted probes for two photon fluorescence imaging of cancer cells. Acta Biomater 7:1327-1338
Fiber laser in-band pumped Er:YAG ceramic lasers
Ting Zhao
Supervisor: Deyuan Shen
Transparent ceramics doped with rare earth elements have drawn great attention in recent years as new laser gain media due to a number of important advantages over single crystals. With the progress in fabrication technology, Nd3+- and Yb3+-doped high quality YAG ceramics are now routinely available with essentially the same lasing efficiency as that of the single crystals. Laser sources operating in the eye-safe wavelength regime around ~1.5-1.6 µm have numerous applications, including range finding, remote sensing, medicine treatment, etc. and provide a good starting point for 3-5µm mid-infrared generation via nonlinear frequency conversion .
In this work, we achieved high-power and efficient operation of a Er:YAG ceramic laser resonantly pumped (4I15/2�4I13/2) by a cladding-pumped Er,Yb fiber laser at ~ 1532 nm. The fiber pump source was wavelength-locked to the absorption peak of Er:YAG using a volume Bragg grating. Lasing characteristics of 0.5 at.% and 1.0 at.% Er3+-doped YAG ceramic samples were evaluated with output couplers of different transmissions. With an output coupler of 10% transmission, the ceramic laser yielded 16.7 W of continuous-wave output at 1645 nm for 28.8 W of incident pump power, corresponding to a slope efficiency of 61.0% with respect to the incident pump power. The lasing wavelength switched to 1617 nm when a T=20% output coupler was used, and ~16.2 W of output power was generated at this wavelength for 33.0 W of incident pump power, corresponding to a slope efficiency of 51.8%.
Passively Q-switched operation of the Er:YAG ceramic laser at 1.6µm was demonstrated using a few-layer of graphene thin films as the saturable absorber. Stable pulses of 30-74.6 kHz repetition rate and 1.5-6.4 µs pulse widths were generated. The maximum average output power the Q-switched Er:YAG ceramic was over 500 mW and the single pulse energy was 7.1 �J at 74.6 kHz repetition rate. Both repetition-rate and pulse-width of the graphene Q-switched laser change monotonously with the pump power. To the best of our knowledge, this is the first report of graphene passively Q-switched Er:YAG ceramic laser at 1.6 µm.
参考文献：
[1] D. Y. Shen, J. K. Sahu, and W. A. Clarkson, Highly efficient in-band pumped Er:YAG laser with 60 W of output at 1645 nm, Optics Letters, 2006, 31 (6): 754-756.
[2] H. Zhang, D. Y. Tang, L. M. Zhao, Q. L. Bao, and K. P. Loh, Large energy mode locking of an erbium-doped fiber laser with atomic layer graphene, Opt. Express, 2009, 17(20): 017630-017635
[3] Q. L. Bao, H. Zhang, Y. Wang, Z. H. Ni, Y. L. Yan, Z. X. Shen, K. P. Loh, and D. Y. Tang, Atomic-Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers, Adv. Funct. Mater. 2009, 19 (19): 3077-3083.
The injection-molding simulation of plastic optical structure array
Yongqiang Shen
Supervisor: Ming Xu
In recent years，the lens array is widely used in a variety of optical devices. Current main manufacturing methods of optical array are generally hot embossing, laser direct writing, injection molding. Injection molding is usually used to produce plastic optical components complex structure.
However, in the injection-molding process, the shrinkage cannot be avoided. Any small optical surface shrinkage will extremely impact on image quality. So shrinkage analysis is necessary.
Manufacturing parameters includes four important variables, mold temperature, melt temperature, packing pressure, cooling time. In order to study the relationship between manufacturing parameters and the finished shrinkage rate (Finished shrinkage rate is defined as when the object is placed at room temperature after forming the cooling time, shrinkage reaches its steady state the size and the mold size of the difference.), a simulated lens array model is produced. By using the finite element method, the converged finished shrinkage rates can be solved. By the change of the four parameters, finished shrinkage rates can be observed. Therefore, shrinkage maximum impact and molding window are identified.
参考文献：
[1] 陈照彰, 徐睿明, 透镜阵列射出成形之体积收缩模拟分析研究, 2010国际 CAE模具成型技术研讨会, D01-A101
[2] Jansen, K.M.B. , D.J Van Dijk and M.H. Husselman, Effect of Processing Conditions on Shrinkage in Injection molding, Polymer Engineering and Science, 38(5), 838-846, 1988.
[3] 张鲜文, 光学元件射出成形体积收缩与光学均匀性之研究, 国立台湾科技大学机械工程研究所, 2007
[4] Chen, C.-C.A., S.-W. Chang, Shrinkage Analysis on Convex Shell by Injection Molding, Journal of Polymer Processing, 2008.