Enhanced green fluorescent protein (EGFP)—one of the most widely applied genetically encoded fluorescent probes—carries the threonine-tyrosine-glycine (TYG) chromophore. EGFP efficiently undergoes green-to-red oxidative photoconversion (“redding”) with electron acceptors. Enhanced yellow fluorescent protein (EYFP), a close EGFP homologue (five amino acid substitutions), has a glycine-tyrosine-glycine (GYG) chromophore and is much less susceptible to redding, requiring halide ions in addition to the oxidants. In this contribution we aim to clarify the role of the first chromophore-forming amino acid in photoinduced behavior of these fluorescent proteins. To that end, we compared photobleaching and redding kinetics of EGFP, EYFP, and their mutants with reciprocally substituted chromophore residues, EGFP-T65G and EYFP-G65T. Measurements showed that T65G mutation significantly increases EGFP photostability and inhibits its excited-state oxidation efficiency. Remarkably, while EYFP-G65T demonstrated highly increased spectral sensitivity to chloride, it is also able to undergo redding chloride-independently. Atomistic calculations reveal that the GYG chromophore has an increased flexibility, which facilitates radiationless relaxation leading to the reduced fluorescence quantum yield in the T65G mutant. The GYG chromophore also has larger oscillator strength as compared to TYG, which leads to a shorter radiative lifetime (i.e., a faster rate of fluorescence). The faster fluorescence rate partially compensates for the loss of quantum efficiency due to radiationless relaxation. The shorter excited-state lifetime of the GYG chromophore is responsible for its increased photostability and resistance to redding. In EYFP and EYFP-G65T, the chromophore is stabilized by π-stacking with Tyr203, which suppresses its twisting motions relative to EGFP.
Understanding the
effect of heteroatom doping is crucial for the
design of carbon nanodots (CNDs) with enhanced luminescent properties
for fluorescence imaging and light-emitting devices. Here, we study
the effect and mechanisms of luminescence enhancement through nitrogen
doping in nanodots synthesized by the bottom-up route in an intense
femtosecond laser field using the comparative analysis of CNDs obtained
from benzene and pyridine. We demonstrate that laser irradiation of
aromatic compounds produces hybrid nanoparticles consisting of a nanocrystalline
core with a shell of surface-bonded aromatic rings. These nanoparticles
exhibit excitation-dependent visible photoluminescence typical for
CNDs. Incorporation of nitrogen into pyridine-derived CNDs enhances
their luminescence characteristics through the formation of small
pyridine-based fluorophores peripherally bonded to the nanoparticles.
We identify oxidation of surface pyridine rings as a mechanism of
formation of several distinct blue- and green-emitting fluorophores
in nanodots, containing pyridine moieties. These findings shed additional
light on the nature and formation mechanism of effective fluorophores
in nitrogen-doped carbon nanodots produced by the bottom-up route.
We report on a new method of preparation of AgN-TiO2 nanoparticulate coatings with stable and highly
reproducible
morphology. The silver nanoparticles are grown on monolayer titanium-oxo-alkoxy
nanoparticulate coatings by silver ions reduction at UV-A light illumination.
Their size and surface number density increase with the irradiation
time. The AFM and high-resolution SEM and TEM measurements of height
(h) and lateral size (D) of the
silver nanoparticles show that their shape approaches spherical segment
with h/D = 1/4 at long irradiation
times. The size correspondent to the maximum of the particles size
distribution curve tends to D = 12 nm with half width
at full-maximum ΔD = 4 nm. The evaluation of
the deposited silver mass results in the quantum yield of the deposition
process close to 100% at the process beginning and the atomic surface
density of N
Ag = 1.25 × 107 at/μm2 at the process saturation. The absorption
spectra of the surface plasmon shift from 425 to 525 nm. The spectra
are successfully modeled assuming small dispersion of the oblate particle
shape asymmetry Δ(h/D) ≈
0.25 and surface number density below 2500 part/μm2. Mutual interaction between the silver particles is shown to weakly
affect the spectra. Two-photon photoluminescence images of the composite
nanocoatings show the characteristic hot-spot pattern
of surface plasmons.
We report the effect of laser cavitation in water initiated by femtosecond pulses confined into subwavelength volume of photonic nanojet of spherical microparticles. The effect of nanoscale optical breakdown was employed for controllable and nondestructive micromanipulation of silica microspheres. We combine this technique with optical trapping for cyclic particle movements and estimate a peak velocity and an acceleration acquired by microspheres propelled by nanojet cavitation. Our study provides a strategy for nondestructive optical micromanipulation, cavitation-assisted drug delivery, and laser energy transduction in microdevices.
In this work, the photostimulated processes of O2 and NO2 molecules with the surface of ZnO under UV radiation were studied by in situ mass spectrometry in the temperature range of 30–100 ∘C. Nanocrystalline needle-like ZnO was synthesized by decomposition of basic zinc carbonate at 300 ∘C, and the surface concentration of oxygen vacancies in it were controlled by reductive post-annealing in an inert gas at 170 ∘C. The synthesized materials were characterized by XRD, SEM, low-temperature nitrogen adsorption (BET), XPS, Raman spectroscopy, and PL spectroscopy. Irradiation of samples with UV light causes the photoabsorption of both O2 and NO2. The photoadsorption properties of ZnO are compared with its defective structure and gas-sensitive properties to NO2. A model of the sensor response of ZnO to NO2 under UV photoactivation is proposed.
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