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Exploration of the Cellular Galaxy: Search for the Inner Life of the Cell

By Luke P. Lee

Humankind has always been fascinated with space exploration and reaching up to the stars. Scientific discovery and breakthroughs in technology allow us to explore space outside our solar system. Now we are learning how to explore inner life of living cells. By creating innovative ‘satellite nanoscopes’, we can enjoy exploring cellular space of living cells and obtain snapshots of what we metaphorically refer to as the cellular galaxy. Satellite nanoscopes can also be used to produce desired changes in proteins and genes.

What are Satellite Nanoscopes?

Satellite nanoscopes are tiny optical antennae with specific resonant wavelengths. They use a phenomenon known as ‘nanoplasmonics’ which involves ultrahigh frequency waves propagating in the free electrons on the surface of metals. These nanoscopes can be placed within living cells or in the space between cells. Nanoscopes with multiple functions (i.e. precise targeting, imaging, gene delivery, and gene regulations) will generate new fundamental knowledge in basic biological science as well as advancing the new field of translational medicine.

Applications

Despite our understanding of cells as the basic building blocks of life, little is known about the dynamics of their intracellular processes and extracellular communication. The information transferred by signaling molecules transfer depends not only upon their biochemical composition but also upon they are distributed. It is thus important to measure how the signaling molecules are distributed between cells and to obtain ultrafast detection of biomolecule release and of growth factors administrated during different stages of tissue development. Yet, doing this is still a major challenge. To address this challenge, we have been developing nanosatellites for real-time monitoring of dynamic cellular activities in living cells. We will describe two ways in which nanosatellites can be of use:

  • Imaging cellular activities
  • Regulating and sensing gene expression

Real-Time Nanoscale Molecular Imaging of Cellular Activities

Our understanding of biological systems is increasingly dependent on our ability to visualize and measure biomolecules and biological events with high spatial and temporal resolution within living cells. Novel cellular and molecular imaging techniques are essential to the advancement of basic life science and translational medicine. The challenge is to develop techniques to noninvasively capture cellular information and resolve dynamic intracellular processes. In response to this challenge we developed satellite nanoscopes capable of specific molecular-level targeting, imaging and intervention (Fig.1).

Figure 1: (Left) Images of cosmic space galaxy and diverse kind of satellite telescopes vs. (Right) Images of cellular galaxy by satellite nanoscopes with multiple functions and innovative designs for selective targeting, sensing, gene delivery, and gene regulations.
Figure 1: (Left) Images of cosmic space galaxy and diverse kind of satellite telescopes vs. (Right) Images of cellular galaxy by satellite nanoscopes with multiple functions and innovative designs for selective targeting, sensing, gene delivery, and gene regulations.

Click to enlarge

These nanoscopes will enable high-resolution monitoring of the dynamics of proteins, enzymes, and subcellular organelles without causing damage or exogenous artifacts that affect cell function. Current techniques require fluorescent labeling, which has limitations and cannot provide the dynamics of molecular fingerprint changes. The electron microscope (EM) can resolve subcellular structures without labeling, but EM irreversibly damages living cells. Moreover, EM and fluorescence imaging cannot provide spectroscopic data (i.e. chemical fingerprints). Our recent accomplishments offer striking advantages over traditional imaging techniques: stability, biocompatibility, selectivity, and potential for spectroscopic imaging of electronic states of biomolecules in living cells.

By utilizing satellite nanoscopes, we can obtain snapshots of what we metaphorically refer to as the cellular galaxy. Using optical antennas with specific resonant wavelengths within living cells as well as in the space between cells, we can measure localized biochemical features (i.e. structural and kinetic features) by spectroscopic imaging. The nanoplasmonic optical antenna function as “nanosatellites”, exploratory devices in the living cellular environment for selective targeting, sensing, and gene regulations. Remote optical controls of localized gene delivery and the generation of transcriptional pulses via satellite nanoscopes allows spatio-temporal control of gene regulations on demand and precision molecular level optogenetics for systems biologists and clinicians, while the local dynamic response of chemicals of interest can be investigated with the spectroscopic sensing functionality.

Satellite Nanoscopes as Remote Optical Switches for Gene, Protein Regulations and Sensing

After performing optical gene regulation or transcriptional pulse generation in living cells by satellite nanoscopes (Fig 2), we can utilize them to capture the images of electron transfer dynamics of some key enzymes. Precise remote control of gene regulation and protein expression in living cells is a powerful tool for studying cellular signaling pathways and systems biology. To advance the studies of intracellular & extracellular signaling pathways, we have assembled nanoscale transmitter and receiver systems for remote manipulation of biological systems. Because of their large surface-to-volume ratio, nanoplasmonic gene or protein switches are ideal carriers of oligonucleotides (short nucleic acid sequences). Proteins can also be attached to these optical switches, and we can liberate them at a specific time in order to control the effects of intracellular and extracellular signaling molecules. While attached to their carriers, oligonucleotides are inactive. In the presence of near-infrared incident light that is matched to the resonance wavelength of carrier, the formerly bound substance is released, to freely interact with the local environment. Using such gene switches, intracellular genes can be silenced on-demand. Similar methods will be used for the precision delivery of peptides and protein drugs in the extracellular space. Satellite nanoscopes can deliver both extracellular and intracellular signaling molecules for the systematic studies of living cells.

Figure 2: Optical gene regulations by external near-infrared remote controls: (a) nucleic acid sequences can be attached to nanoplasmonic optical antennas, then locally released by selective light sources. (b) On-demand gene regulations in living cells. Similar methods will be applied for the delivery of peptides and protein drugs in extracellular matrix.
Figure 2: Optical gene regulations by external near-infrared remote controls: (a) nucleic acid sequences can be attached to nanoplasmonic optical antennas, then locally released by selective light sources. (b) On-demand gene regulations in living cells. Similar methods will be applied for the delivery of peptides and protein drugs in extracellular matrix.

Click to enlarge

In summary, the possibility to use the satellite nanoscopes as carriers for oligonucleotides, which can be released in response to an optical pulse at a specific wavelength, is exciting and promising. This approach holds enormous power to regulate gene expression in a way that has not been previously possible, such as in the form of “transcriptional pulses” that can switch cellular signaling pathways on or off. The ability to target, sense, modify and control cellular function will have vast implications beyond our imagination.

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April 2012 Contributors

Bin HeBin He is a Distinguished McKnight University Professor, a Professor of Biomedical Engineering, Electrical Engineering, and Neuroscience, and Director of Biomedical Functional Imaging and Neuroengineering Laboratory at the University of Minnesota. Read more

Mathukumalli VidyasagarMathukumalli Vidyasagar received B.S., M.S. and Ph.D. degrees in electrical engineering from the University of Wisconsin in Madison, in 1965, 1967 and 1969 respectively. Between 1969 and 1989, he was a professor of Electrical Engineering at various universities in the USA and Canada. Read more

Nitish V. ThakorNitish V. Thakor is a Professor of Biomedical Engineering at Johns Hopkins University, Baltimore, USA, as well as the Director of the newly formed institute for neurotechnology, SiNAPSE, at the National University of Singapore. Read more

Luke P. LeeLuke P. Lee is a 2010 Ho-Am Laureate. He is an Arnold and Barbara Silverman Distinguished Professor of Bioengineering at UC Berkeley, the Director of the Biomedical Institute of Global Healthcare Research & Technology (BIGHEART) and a co-director of the Berkeley Sensor & Actuator Center. Read more