Single Molecule Quantum-Confined Stark Effect Measurements of Semiconductor Nanoparticles at Room Temperature

Abstract

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.

Optical Strategies for Sensing Neuronal Voltage Using Quantum Dots and Other Semiconductor Nanocrystals

“…Using this framework, we examined how a nanocrystal's voltage sensitivity depends on its material and structural properties, across a range of pertinent materials and sizes. These calculations agree with previous modeling studies and experimental measurements at both cryogenic [24][25][26] and room 27 temperatures.…”

“…30 Because the tails of the individual carrier wave functions are more voltage-sensitive than the rest, a probe with electron-hole overlap confined to the tails of either wave function will show enhanced voltage sensitivity ( Figure 3B). 25,27 The asymmetry of the structure has an effect similar to electrically prebiasing the quantum dot, creating a fixed electric dipole moment that is more sensitive to small field shifts. This changes the dependence of the fluorescence shift on the applied field strength to a linear dependence, as opposed to the quadratic dependence for conventional qdots.…”

“…Qdots are known to possess voltagesensitive optical properties, including a red-shifting of the qdot's fluorescence emission peak, spectral broadening, and a decrease in the intensity of fluorescence emission ( Figure 1C,D). [24][25][26][27] Qdots also are highly resistant to photobleaching and exhibit large quantum yields and absorption cross sections for one-(σ 1 ) and two-photon (σ 2 ) excitation. For example, CdSe qdots with radius R ~ 3 nm exhibit cross sections of σ 1 > 1 nm 2 and σ 2 > 3 × 10 4 GM, as compared to σ 1 ~ 10 −2 nm 2 and σ 2 ~ 3 × 10 2 GM for green fluorescent protein.…”

Electric Field Modulation of Semiconductor Quantum Dot Photoluminescence: Insights Into the Design of Robust Voltage-Sensitive Cellular Imaging Probes

“…48 Insufficient time resolution and instrument response time in the trPL experiment preclude experimental confirmation of these hypotheses; however, these conclusions are in agreement with interpretations elsewhere in the literature. 12,29,34,47 Efforts to compare the e-field dependence of QD emission with that of a widely used VSD, di-4-ANEPPS, proved difficult. The known photobleaching of organic dyes prompted us first to test the photostability of both the dye and the Quasi-Type II QDs (see Supporting Information, Section S2).…”

Voltage-sensitive rhodol with enhanced two-photon brightness

“…The challenge of achieving optical voltage sensing is a longstanding goal within the scientific community (4,5), and recent approaches have included fluorinated styryl dyes (6), annulated hemicyanines (7,8) and cyanines (9), lipophilic anions (10,11), hybrid small-molecule/fluorescent protein probes (12,13), porphyrins (14), and nanoparticles (15,16). However, combinations of poor sensitivity, slow kinetics, ineffective membrane localization, rapid photobleaching, and/or limited two-photon crosssection, which is important for imaging in thick tissue, have hampered rapid progress toward a general solution for optical voltage imaging.…”