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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2014)

Understanding electrical activity of neural network is of great interest. Although electrodes and optical voltage sensors have been evolved over the past few decades, there is no such probe satisfying not only large enough sensitivity but also fast enough time response in large scale yet. Therefore, the reverse engineering on brain circuitry such that `every action potential in every neuron in large field of view' is still far-off.

In this thesis, I introduce the inorganic voltage sensor for neural electricity imaging, based on semiconductor nanoparticles (NPs) via quantum-confined Stark effect (QCSE). Firstly, I validate NPs' QCSE at room temperature (RT) at single molecule level. Based on the experimental results and theoretical investigation, I optimize the NP structure displaying the largest QCSE. Besides, undiscovered physical phenomena including wavelength blue-shift, linear energy-field dependency, and field dependent Auger recombination were revealed from the QCSE experiment for the first time. Secondly, I predict the performance of membrane

inserted NPs by self-consistent Schr�dinger-Poisson calculation, and propose voltage imaging strategies.

As a delivery method, peptide-based surface coating is developed which successfully guides NPs to the membrane. Lastly, delivered NPs are tested under voltage oscillating HEK

cells and they generate voltage dependent emission fluorescence. This voltage information is finally captured and imaged by charge coupled device and analyzed. This result demonstrates the inorganic voltage sensor's high throughput simultaneous multisite voltage imaging.

    Cover page: Imaging membrane potential with semiconductor nanoparticle
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2017)
    Voltage-sensing dyes and voltage-sensing fluorescence proteins have been continually improved and as a result have provided a wealth of insights into neuronal circuits. Further improvements in voltage-sensing dyes and voltage-sensing fluorescence proteins are needed, however, for routine detection of single action potentials across a large number of individual neurons in a large field-of-view of a live mammalian brain. On the other hand, recent experiments and calculations suggest that semiconducting nanoparticles could act as efficient voltage sensors, suitable for the above-mentioned task. This study presents quantum mechanical calculations, including Auger recombination rates, of the quantum-confined Stark effect in membrane-embedded semiconducting nanoparticles, examines their possible utility as membrane voltage sensors, and provide design rules for their structure and composition.
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2012)
      We measured the quantum-confined Stark effect (QCSE) of several types of fluorescent colloidal semiconductor quantum dots and nanorods at the single molecule level at room temperature. These measurements demonstrate the possible utility of these nanoparticles for local electric field (voltage) sensing on the nanoscale. Here we show that charge separation across one (or more) heterostructure interface(s) with type-II band alignment (and the associated induced dipole) is crucial for an enhanced QCSE. To further gain insight into the experimental results, we numerically solved the Schrödinger and Poisson equations under self-consistent field approximation, including dielectric inhomogeneities. Both calculations and experiments suggest that the degree of initial charge separation (and the associated exciton binding energy) determines the magnitude of the QCSE in these structures.
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2018)
        We developed membrane voltage nanosensors that are based on inorganic semiconductor nanoparticles. We provide here a feasibility study for their utilization. We use a rationally designed peptide to functionalize the nanosensors, imparting them with the ability to self-insert into a lipid membrane with a desired orientation. Once inserted, these nanosensors could sense membrane potential via the quantum confined Stark effect, with a single-particle sensitivity. With further improvements, these nanosensors could potentially be used for simultaneous recording of action potentials from multiple neurons in a large field of view over a long duration and for recording electrical signals on the nanoscale, such as across one synapse.
          Cover page: Membrane insertion of—and membrane potential sensing by—semiconductor voltage nanosensors: Feasibility demonstration
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2016)
          We develop membrane voltage nanosensors that are based on inorganic semiconductor nanoparticles. These voltage nanosensors are designed to self-insert into the cell membrane and optically record the membrane potential via the quantum confined Stark effect, with single-particle sensitivity. We present here the approach, design rules, and feasibility proves for this concept. With further improvements, semiconductor nanoparticles could potentially be used to study signals from many neurons in a large field-of-view over a long duration. Moreover, they could potentially report and resolve voltage signals on the nanoscale.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2023)
            One of the key phenomena that determine the fluorescence of nanocrystals is the nonradiative Auger-Meitner recombination of excitons. This nonradiative rate affects the nanocrystals' fluorescence intensity, excited state lifetime, and quantum yield. Whereas most of the above properties can be directly measured, the quantum yield is the most difficult to assess. Here we place semiconductor nanocrystals inside a tunable plasmonic nanocavity with subwavelength spacing and modulate their radiative de-excitation rate by changing the cavity size. This allows us to determine absolute values of their fluorescence quantum yield under specific excitation conditions. Moreover, as expected considering the enhanced Auger-Meitner rate for higher multiple excited states, increasing the excitation rate reduces the quantum yield of the nanocrystals.
              Cover page: Excitation Intensity-Dependent Quantum Yield of Semiconductor Nanocrystals
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