Plasmonic nanoparticles are excellent nonbleaching probes for bio-imaging. Due to their anisotropic properties, polarization analysis of individual nanoparticles allows for revealing orientational information, plasmon mode assignment, and the local microenvironment. Previous implementations utilize mechanical rotation of conventional polarizers to align the polarization angles with specific axes of nanoparticles. However, the manufacturing defects of the polarizer (e.g., non-parallelism) limit the measurement stability (e.g., beam wobbling) in polarimetric imaging, while the mechanical rotation limits the measurement speed, and thus hinders accurate, real-time acquisition of individual nanoparticles. Here, we demonstrate a high-speed nano-polarimetric system for stable plasmonic bio-imaging by integrating our voltage-tunable polarizer (VTP) into a microscope. The angular rotation of the polarization (0~π) can be realized by applying voltage on the VTP. We show that our voltage-tunable system offers high extinction ratio (~up to 250), and uniform transmission (~55%) over a large input power range (less than 5% deviation for input power from 50 µW to ~20 mW). Meanwhile, the transmission polarization can be rapidly tuned with a response time up to 50 ms. Compared to conventional polarizers, our system is able to provide reproducible and high-speed polarimetric images of individual nanoparticles with sub-pixel spatial precision. Such a polarimetric nanoimaging system could be a useful tool for real-time single nanoparticle bio-imaging with both high stability and time resolution.
Precise polarimetric imaging of polarization-sensitive nanoparticles is essential for resolving their accurate spatial positions beyond the diffraction limit. However, conventional technologies currently suffer from beam deviation errors which cannot be corrected beyond the diffraction limit. To overcome this issue, we experimentally demonstrate a spatially stable nano-imaging system for polarization-sensitive nanoparticles. In this study, we show that by integrating a voltage-tunable imaging variable polarizer with optical microscopy, we are able to suppress beam deviation errors. We expect that this nano-imaging system should allow for acquisition of accurate positional and polarization information from individual nanoparticles in applications where real-time, high precision spatial information is required.
We propose and theoretically demonstrate a mechano-optical nano-antenna over a broad temperature range. We show that there is a tunable, temperature-dependent plasmonic resonance associated with the nano-antenna geometry. We also theoretically demonstrate a matching condition for mechanical properties that is essential for maximizing thermal expansion differences across a broad temperature range. We expect that mechano-optical ano-antennas should allow for spatiotemporal temperature mapping in applications where precise measurement of local temperature is needed in real time.
11. Lee, S.E., Chen, Q., Bhat, R., Petkiewicz, S., Smith, J.M., Ferry, V.E., Correia, A.L., Alivisatos, A.P., Bissell, M.J. “Reversible aptamer-gold plasmon rulers for secreted single molecules,” Nano Letters 2015, 15 (7), pp 4564–4570.Link to article
Plasmon rulers, consisting of pairs of gold nanoparticles, allow single-molecule analysis without photobleaching or blinking; however, current plasmon rulers are irreversible, restricting detection to only single events. Here, we present a reversible plasmon ruler, comprised of coupled gold nanoparticles linked by a single aptamer, capable of binding individual secreted molecules with high specificity. We show that the binding of target secreted molecules to the reversible plasmon ruler is characterized by single-molecule sensitivity, high specificity, and reversibility. Such reversible plasmon rulers should enable dynamic and adaptive live-cell measurement of secreted single molecules in their local microenvironment.
Spatiotemporal activity patterns of proteases such as matrix metalloproteinases and cysteine proteases in organs have the potential to provide insight into how organized structural patterns arise during tissue morphogenesis and may suggest therapeutic strategies to repair diseased tissues. Toward imaging spatiotemporal activity patterns, recently increased emphasis has been placed on imaging activity patterns in three-dimensional culture models that resemble tissues in vivo. Here, we briefly review key methods, based on fluorogenic modifications either to the extracellular matrix or to the protease-of-interest, that have allowed for qualitative imaging of activity patterns in three-dimensional culture models. We highlight emerging plasmonic methods that address significant improvements in spatial and temporal resolution and have the potential to enable quantitative measurement of spatiotemporal activity patterns with single-molecule sensitivity.
** Selected as cover article**
** Highlighted in ACS Nano, 2012, 6(9), 7548-7552**
The precise perturbation of gene circuits and the direct observation of signaling pathways in living cells are essential for both fundamental biology and translational medicine. Current optogenetic technology offers a new paradigm of optical control for cells; however, this technology relies on permanent genomic modifications with light-responsive genes, thus limiting dynamic reconfiguration of gene circuits. Here, we report precise control of perturbation and reconfiguration of gene circuits in living cells by optically addressable siRNA-Au nanoantennas. The siRNA-Au nanoantennas fulfill dual functions as selectively addressable optical receivers and biomolecular emitters of small interfering RNA (siRNA). Using siRNA-Au nanoantennas as optical inputs to existing circuit connections, photonic gene circuits are constructed in living cells. We show that photonic gene circuits are modular, enabling subcircuits to be combined on-demand. Photonic gene circuits open new avenues for engineering functional gene circuits useful for fundamental bioscience, bioengineering, and medical applications.
This review focuses on the recent developments in nanoplasmonic gene regulations. Types of nanoplasmonic carriers and DNA/RNA cargo are described. Strategies to liberate cargo from their carriers using NIR and enable on-demand silencing of endogenous intracellular genes are reviewed. In addition to inhibitory effects, exogenous foreign genes are also introduced and expressed on-demand using nanoplasmonic optical switches. The magnitude and timing of genetic activities can therefore be systematically controlled on-demand remotely. Equipped with new nanoplasmonic optics to directly probe the intracellular space, quantitative approaches should capture many dynamic activities within living systems that were otherwise previously impossible to control using conventional methods.
Free electrons in a noble metal nanoparticle can be resonantly excited, leading to their collective oscillation termed as a surface plasmon. These surface plasmons enable nanoparticles to absorb light, generate heat, transfer energy, and re-radiate incident photons. Creative designs of nanoplasmonic optical antennae (i.e. plasmon resonant nanoparticles) have become a new foundation of quantitative biology and nanomedicine. This review focuses on the recent developments in dual-functional nanoplasmonic optical antennae for label-free biosensors and nanoplasmonic gene switches. Nanoplasmonic optical antennae, functioning as biosensors to significantly enhance biochemical-specific spectral information via plasmon resonance energy transfer (PRET) and surface-enhanced Raman spectroscopy (SERS), are discussed. Nanoplasmonic optical antennae, functioning as nanoplasmonic gene switches to enable spatiotemporal regulation of genetic activity, are also reviewed. Nanoplasmonic molecular rulers and integrated photoacoustic–photothermal contrast agents are also described.
6. Lee, S.E., Sasaki, D.Y., Perroud, T.D., Yoo, D., Patel, K.D. and Lee, L.P. “Biologically functional cationic phospholipid-gold nanoplasmonic carriers,” Journal of the American Chemical Society (JACS), 2009, 131(39), 14066–14074.Link to article
Biologically functional cationic phospholipid−gold nanoplasmonic carriers have been designed to simultaneously exhibit carrier capabilities, demonstrate improved colloidal stability, and show no cytotoxicity under physiological conditions. Cargo, such as RNA, DNA, proteins, or drugs, can be adsorbed onto or incorporated into the cationic phospholipid bilayer membrane. These carriers are able to retain their unique nanoscale optical properties under physiological conditions, making them particularly useful in a wide range of imaging, therapeutic, and gene delivery applications that utilize selective nanoplasmonic properties.
** Highlighted in Nature Photonics, 2009, 3, 126-127**
Near infrared-absorbing gold nanoplasmonic particles (GNPs) are used as optical switches of gene interference and are remotely controlled using light. We have tuned optical switches to a wavelength where cellular photodamage is minimized. Optical switches are functionalized with double-stranded oligonucleotides. At desired times and at specific intracellular locations, remote optical excitation is used to liberate gene-interfering oligonucleotides. We demonstrate a novel gene-interfering technique offering spatial and temporal control, which is otherwise impossible using conventional gene-interfering techniques.
4. James, C.D., Reuel, N., Lee, E.S., Davalos, R.V., Mani, S.S., Carroll-Portillo, A., Rebeil, R., Martino, A. and Apblett, C.A. “Impedimetric and optical interrogation of single cells in a microfluidic device for real-time viability and chemical response assessment,” Biosensors & Bioelectronics, 2008, 23, 845-851.Link to article
We report here a non-invasive, reversible method for interrogating single cells in a microfluidic flow-through system. Impedance spectroscopy of cells held at a micron-sized pore under negative pressure is demonstrated and used to determine the presence and viability of the captured cell. The cell capture pore is optimized for electrical response and mechanical interfacing to a cell using a deposited layer of parylene. Changes in the mechanical interface between the cell and the chip due to chemical exposure or environmental changes can also be assessed. Here, we monitored the change in adhesion/spreading of RAW264.7 macrophages in response to the immune stimulant lipopolysaccharide (LPS). This method enables selective, reversible, and quantitative long-term impedance measurements on single cells. The fully sealed electrofluidic assembly is compatible with long-term cell culturing, and could be modified to incorporate single cell lysis and subsequent intracellular separation and analysis.
Living cells synthesize and utilize femtomole and picoliter amounts of material, and an important goal of analytical chemistry is to develop artificial interfaces to efficiently study substances on this scale. This could be achieved with a picoliter container that could be controllably loaded, transported, and unloaded, most desirably in a microfluidic environment. Phospholipid vesicles – surfactant multilayers that can form 10 μm spheres – have been studied for this purpose, but they suffer from fragility and high deformability, which have made them difficult to handle and have limited their application. We present an approach in which a gel is formed in vesicles shortly after they are created. Microfluidic mechanical testing of these vesicles shows that, in the absence of gel, vesicles are difficult to maintain in a trapped state, but the reinforced vesicles exhibit a wide window of pressures under which they can be trapped and manipulated. This improvement is likely to be an essential feature of practical applications of vesicles as microfluidic cargo containers.
2. Lee, E.S., Robinson, D.B., Rognlien, J.L., Harnett, C.K., Simmons, B.A., Dentinger, P.M., Ellis, C.R.B. and Davalos, R.V. “Microfluidic electroporation of robust 10-micron vesicles for manipulation of picoliter volumes,” Bioelectrochemistry, 2006, 69, 117-125.Link to article
We present a new way to transport and handle picoliter volumes of analytes in a microfluidic context through electrically monitored electroporation of 10–25 μm vesicles. In this method, giant vesicles are used to isolate analytes in a microfluidic environment. Once encapsulated inside a vesicle, contents will not diffuse and become diluted when exposed to pressure-driven flow. Two vesicle compositions have been developed that are robust enough to withstand electrical and mechanical manipulation in a microfluidic context. These vesicles can be guided and trapped, with controllable transfer of material into or out of their confined environment. Through electroporation, vesicles can serve as containers that can be opened when mixing and diffusion are desired, and closed during transport and analysis. Both vesicle compositions contain lecithin, an ethoxylated phospholipid, and a polyelectrolyte. Their performance is compared using a prototype microfluidic device and a simple circuit model. It was observed that the energy density threshold required to induce breakdown was statistically equivalent between compositions, 10.2 ± 5.0 mJ/m2 for the first composition and 10.5 ± 1.8 mJ/m2 for the second. This work demonstrates the feasibility of using giant, robust vesicles with microfluidic electroporation technology to manipulate picoliter volumes on-chip.
1. Lee, E.S., Howard, D., Liang, E., Collins, S.D. and Smith, R.L. “Removable tubing interconnects for glass-based micro-fluidic systems made using ECDM,” Journal of Micromechanics and Microengineering, 2004, 14, 535-541.Link to article
Reversible tubing connections for glass micro-fluidic systems are realized using electro-chemical discharge machining of three-dimensional glass vias. The connections reversibly connect standard sized plastic tubing to holes in borosilicate microscope slides. Tubing connections are demonstrated on a sealed, micro-fluidic channel which is fabricated between two glass slides using SU-8. The connections are experimentally tested to withstand up to 30 psi (~206 kPa) of air pressure without leaking.