RUI: Studying the photodynamics of FRET paired fluorescent molecules near gold nanogratings

目前，金属表面上的图案可以用纳米(十亿分之一米)大小的特征来制造。这些图案可以与特定颜色的光产生强烈的相互作用。荧光分子被设计成发出特定颜色的光，并在生物应用中用于标记特定的分子和蛋白质。可以制作纳米金属表面，使其光学特性与特定的荧光分子相匹配，并增强来自该分子的光信号。荧光分子也可以将光从一个分子转移到另一个分子，这种转移对分子之间的距离非常敏感。生物学家利用这一特性在亚纳米尺度上测量距离。该团队将利用数百纳米宽的金丝阵列的独特光学特性来加强这种能量传递。这项工作的结果将有助于研究光合作用中的这种能量转移，并有助于改善有机太阳能电池的光收集等应用。该团队将完全由三一大学的不同本科生组成。学生们将在实验的每个方面发挥主导作用，将在国家科学会议上展示他们的发现，并将成为这项工作产生的任何出版物的共同作者。该项目的设备和实验技术将被整合到高级实验室课程中，扩大对三一大学更多学生的影响。该项目描述了金纳米级附近Forster共振能量转移(FRET)配对的供体和受体荧光分子的光物理特性。结构金属表面的光学性质可以被设计成影响附近量子发射体的荧光。将其应用于FRET具有许多潜在的优点，包括能够提高FRET对的能量传递速率和增加FRET对的Forster半径。金属荧光增强是由两种效应引起的，一种是荧光团的激发速率增加，另一种是改变局域光学态密度(LDOS)导致荧光团的激发态寿命缩短。格栅的几何形状独一无二地允许这两种机制被分开测量，为系统的光物理提供了更好的洞察力。光栅上的表面等离子激元模式遵循色散关系，允许使用单一衬底的较宽波长范围的相对较窄的表面等离子激元共振覆盖荧光团的吸收光谱和发射光谱。时间相关的单光子计数将被用来直接测量FRET的能量转移率和效率随表面等离子激元波长的变化。DNA将被用来将供体和受体分子连接到纳米级，允许供体和受体分子之间以及纳米级表面之间的精确间距。这些实验的结果将使人们能够优化FRET速率和效率的增强，以及直接测量Forster半径的任何增加。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Currently patterns on metal surfaces can be fabricated with features in the nanometer (one billionth of a meter) size range. These patterns can interact strongly with particular colors of light. Fluorescent molecules are designed to give off certain colors of light, and are used to mark specific molecules and proteins in biological applications. A nanopatterned metal surface can be made such that its optical properties match a particular fluorescent molecule and enhance the light signal from the molecule. Fluorescent molecules can also transfer light from one molecule to another, and this transfer is extremely sensitive to the distance between molecules. Biologists have used this property to measure distances at the sub-nanometer scale. The team will use the unique optical properties of arrays of gold wires hundreds of nanometers wide to enhance this transfer of energy. The result of this work will aid in the study of this energy transfer in photosynthesis and in applications such as improving light harvesting in organic solar cells. The team will be completely comprised of a diverse set of undergraduate students at Trinity University. The students will take a leading role in every aspect of the experiments, will present their finding at national scientific meetings, and will be co-authors on any publication resulting from this work. Equipment and experimental techniques from this project will be integrated into upper division lab courses, broadening the impact to additional students at Trinity University. This project characterizes the photophysics of Forster resonance energy transfer (FRET) paired donor and acceptor fluorescent molecules near a gold nanograting. The optical properties of structured metal surfaces can be engineered to influence the fluorescence of nearby quantum emitters. Applying this to FRET has many potential advantages, including the ability to enhance the energy transfer rate and increasing the Forster radius of FRET pairs. Metal enhanced fluorescence results from two effects, an enhanced excitation rate of the fluorophores and a decrease in their excited state lifetime of the fluorophore arising from altering the local density of optical states (LDOS). The geometry of gratings uniquely allows these two mechanisms to be measured separately, providing greater insight to the photophysics of the system. Surface plasmon modes on gratings follow a dispersion relationship, allowing for a wide wavelength range of relatively narrow surface plasmon resonances covering both fluorophores’ absorption and emission spectra using a single substrate. Time-correlated single photon counting will be used to directly measure both the FRET energy transfer rate and efficiency as a function of surface plasmon wavelength. DNA will be utilized to attach the donor and acceptor molecules to the nanogratings, allowing for precise spacing between donor and acceptor molecules with respect to each other as well as the nanograting surface. The results of these experiments will allow one to optimize the enhancement in FRET rate and efficiency, as well as directly measure any increase in the Forster radius.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.