量子点荧光光谱学与生命科学

近年来,量子点(半导体纳米微晶体)的研究引起国内外研究者的广泛兴趣,其研究内容涉及物理学、化学、材料等多学科,已成为一门新兴的交叉学科。虽然量子点在生物学中的应用才刚刚起步,但是已经取得了有意义的进展,成为人们极为关注的一个热点。现就量子点的光学特性、制备方法,以及在生物学中的研究进展和应用前景作一简要综述。     

ZnS量子点的生物合成及对阿萨尔基亚芽胞杆菌的标记

通过微生物合成金属量子点是目前研究的热点。本研究通过白色念珠菌合成ZnS量子点,对合成的量子点用高分辨透射电镜(HR-TEM)和X射线衍射(XRD)进行表征,用生物合成的ZnS量子点标记生防菌阿萨尔基亚芽胞杆菌,为建立生防菌阿萨尔基亚芽胞杆菌的荧光探针标记提供科学依据。实验结果表明,ZnSO4浓度为20 mmol/L时白色念珠细胞内合成ZnS量子点,通过反复冻融破细胞壁提出胞内ZnS量子点,紫外-可见光谱(UV)检测ZnS量子点在348 nm处显示有吸收带,HR-TEM测其粒径约7. 06 nm,荧光分光光谱分析量子点激发波在280 nm和363 nm,XRD显示ZnS量子点特征峰。ZnS量子点中加入1-乙基-3-(3-二甲基氨丙基)-碳化二亚胺(EDC)和N-羟基琥珀酰亚胺(NHS)偶联剂的芽胞杆菌样本的标记效率明显高于不加偶联剂的样本。白色念珠菌合成的ZnS量子点可以用于微生物标记。     

Fluorescence resonance energy transfer in single enzyme molecules with a quantum dot as donor

H(+)-ATPsynthases couple a transmembrane proton transport with ATP synthesis and ATP hydrolysis. Previously, the relative subunit movement during this process has been measured by fluorescence resonance energy transfer (FRET) between two organic fluorophores covalently bound to different subunits. To improve the photophysical stability, a luminescent CdSe/ZnS nanocrystal (quantum dot) was bound to the enzyme and an organic fluorophore, Alexa568, was used as fluorescence acceptor. Single-molecule spectroscopy with the membrane integrated labeled H(+)-ATPsynthase was carried out. Single-pair FRET indicates three different conformations of the enzyme. During ATP hydrolysis relative intramolecular subunit movements are observed in real time.     

Mortalin imaging in normal and cancer cells with quantum dot immuno-conjugates

Quantum dots are the nanoparticles that are recently emerging as an alternative to organic fluorescence probes in cell biology and biomedicine, and have several predictive advantages. These include their ⑴broad absorption spectra allowing visualization with single light source, ⑵exceptional photo-stability allowing long term studies and ⑶narrow and symmetrical emission spectrum that is controlled by their size and material composition. These unique properties allow simultaneous excitation of different size of quantum dots with a single excitation light source, their simultaneous resolution and visualization as different colors. At present there are only a few studies that have tested quantum dots in cellular imaging. We describe here the use of quantum dots in mortalin imaging of normal and cancer cells. Mortalin staining pattern with quantum dots in both normal and cancer cells mimicked those obtained with organic florescence probes and were considerably stable.     

The frequency spectrum of a mutation,and its age,in a general diffusion model

General formulae are derived for the probability density and expected age of a mutation of frequency x in a population, and similarly for a mutation with b copies in a sample of n genes. A general formula is derived for the frequency spectrum of a mutation in a sample. Variable population size models are included. Results are derived in two frameworks: diffusion process models for the frequency of the mutation; and birth and death process models. The coalescent structure within the mutant gene group and the non-mutant group is considered.     

Luminescence of lemon‐derived carbon quantum dot and its potential application in luminescent probe for detection of Mo6+ ions

This article reports on the first attempt of a systematic study on the synthesis of carbon dots (C‐dots) for the potential applications in labeling and detection of molybdenum ion (Mo⁶⁺). Carbon dots (C‐dots) were synthesized directly via a simple hydrothermal method using lemon juices as carbon precursor with different temperatures to control the luminescence of C‐dots. The obtained C‐dots had strong green light emission and the ability to use its luminescence properties as probes for Mo⁶⁺ detection application, which is based on Mo⁶⁺ induced luminescence quenching of C‐dots. This analysis system exhibits strong sensitivity and good selectivity for Mo⁶⁺ ion, and a detection limit as low as 20 ppm is achieved. These results suggest that the present C‐dots have potential application in optoelectronic, labeling and luminescent probing of Mo⁶⁺ ions.     

温带森林阔叶植物幼苗叶经济谱及其与防御性状的关系

植物叶片功能性状之间的权衡关系一直是生态学研究的热点问题。其中叶经济谱相关性状的研究较多, 但叶片防御性状方面的研究, 尤其是幼苗阶段的研究较少。该研究以黑龙江凉水国家级自然保护区典型阔叶红松(Pinus koraiensis)林和谷地云冷杉林内共有的8种阔叶乔木和11种阔叶灌木物种的幼苗叶片为研究对象, 通过测定5个叶经济谱性状和4个叶片防御性状, 分析了叶性状在不同生活型、林型间的差异以及性状之间的协调关系。结果表明: 所有叶片性状在乔木和灌木幼苗之间不存在显著差异, 谷地云冷杉林中的幼苗的叶总酚含量和单宁含量显著高于阔叶红松林中的幼苗, 其原因为谷地云冷杉林林下光照强度弱于阔叶红松林, 且空气和土壤湿度较高, 该环境更有利于自然天敌的聚集, 可能有更强的天敌破坏效应, 而这种更强的生物相互作用反过来驱动幼苗提高其防御能力; 幼苗叶绿素含量与比叶面积呈极显著正相关关系, 与叶氮含量、叶磷含量呈显著正相关关系; 幼苗叶氮含量与叶磷含量呈显著正相关关系; 幼苗叶防御性状之间呈显著正相关关系; 幼苗叶绿素含量与叶总酚含量、单宁含量和类黄酮含量呈显著负相关关系, 叶氮含量与叶总酚含量、单宁含量呈显著负相关关系, 与类黄酮含量呈极显著负相关关系; 说明幼苗叶经济谱性状与防御性状之间存在权衡关系, 即对叶片碳代谢性状的更多投资意味着对叶防御性状更少的投资; 乔、灌木幼苗具有相似的资源利用策略。     

Dynamics of single cell property distributions in Chinese hamster ovary cell cultures monitored and controlled with automated flow cytometry

Two important variables that are often not measured online in Chinese hamster ovary (CHO) cell cultures are cell number concentration and culture viability. We have developed an automated flow cytometry system that measured the cell number concentration, single cell viability based on propidium iodide (PI) exclusion, and single cell light scattering from bioreactor samples every 30 min. The bioreactor was monitored during batch growth, and then the cell number concentration was controlled at a set point during cytostat operation. NH₄Cl was added during steady state operation in cytostat mode to monitor the transient cell population response to adverse growth conditions. The automated measurements correlated well to cell concentration and viability determined manually using a hemacytometer. The described system provides a method to study mammalian cell culture physiology and dynamics in great detail. It presents a new method for the monitoring and control of animal cell culture.     

NMR characterization of the Escherichia coli nitrogen regulatory protein IIANtr in solution and interaction with its partner protein, NPr

The solution form of IIA(Ntr) from Escherichia coli and its interaction with its partner protein, NPr, were characterized by nuclear magnetic resonance (NMR) spectroscopy. The diffusion coefficient of the protein (1.13 x 10(-6) cm/sec) falls between that of HPr (approximately 9 kDa) and the N-terminal domain of E. coli enzyme I (approximately 30 kDa), indicating that the functional form of IIA(Ntr) is a monomer (approximately 18 kDa) in solution. Thus, the dimeric structure of the protein found in the crystal is an artifact of crystal packing. The residual dipolar coupling data of IIA(Ntr) (covering residues 11-155) measured in the absence and presence of a 4% polyethyleneglycol-hexanol liquid crystal alignment medium fit well to the coordinates of both molecule A and molecule B of the dimeric crystal structure, indicating that the 3D structures in solution and in the crystal are indeed similar for that protein region. However, only molecule A possesses an N-terminal helix identical to that derived from chemical shifts of IIA(Ntr) in solution. Further, the (15)N heteronuclear nuclear Overhauser effect (NOE) data also support molecule A as the representative structure in solution, with the terminal residues 1-8 and 158-163 more mobile. Chemical shift mapping identified the surface on IIA(Ntr) for NPr binding. Residues Gly61, Asp115, Ser125, Thr156, and nearby regions of IIA(Ntr) are more perturbed and participate in interaction with NPr. The active-site His73 of IIA(Ntr) for phosphoryl transfer was found in the Ndelta1-H tautomeric state. This work lays the foundation for future structure and function studies of the signal transducing proteins from this nitrogen pathway.