Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable 'fingerprint' for ...such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex. However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3-15 nanometres, which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.
We demonstrate single-photon superradiance from artificially constructed nonbonded zinc-phthalocyanine molecular chains of up to 12 molecules. We excite the system via electron tunneling in a ...plasmonic nanocavity and quantitatively investigate the interaction of the localized plasmon with single-exciton superradiant states resulting from dipole-dipole coupling. Dumbbell-like patterns obtained by subnanometer resolved spectroscopic imaging disclose the coherent nature of the coupling associated with superradiant states while second-order photon correlation measurements demonstrate single-photon emission. The combination of spatially resolved spectral measurements with theoretical considerations reveals that nanocavity plasmons dramatically modify the linewidth and intensity of emission from the molecular chains, but they do not dictate the intrinsic coherence of the superradiant states. Our studies shed light on the optical properties of molecular collective states and their interaction with nanoscopically localized plasmons.
Chemical enhancement is an important mechanism in surface-enhanced Raman spectroscopy. It is found that mildly reduced graphene oxide (MR-GO) nanosheets can significantly increase the chemical ...enhancement of the main peaks by up to 1 order of magnitude for adsorbed Rhodamine B (RhB) molecules, in comparison with the mechanically exfoliated graphene. The observed enhancement factors can be as large as ∼103 and show clear dependence on the reduction time of graphene oxide, indicating that the chemical enhancement can be steadily controlled by specific chemical groups. With the help of X-ray photoelectron spectra, these chemical species are identified and the origin of the observed large chemical enhancement can thus be revealed. It is shown that the highly electronegative oxygen species, which can introduce a strong local electric field on the adsorbed molecules, are responsible for the large enhancement. In contrast, the local defects generated by the chemical reduction show no positive correlation with the enhancement. Most importantly, the dramatically enhanced Raman spectra of RhB molecules on MR-GO nanosheets reproduce all important spectral fingerprints of the molecule with a negligible frequency shift. Such a unique noninvasive feature, along with the other intrinsic advantages, such as low cost, light weight, easy availability, and flexibility, makes the MR-GO nanosheets very attractive to a variety of practical applications.
ABSTRACT Big Bang nucleosynthesis (BBN) theory predicts the abundances of the light elements D, 3He, 4He, and 7Li produced in the early universe. The primordial abundances of D and 4He inferred from ...observational data are in good agreement with predictions, however, BBN theory overestimates the primordial 7Li abundance by about a factor of three. This is the so-called "cosmological lithium problem." Solutions to this problem using conventional astrophysics and nuclear physics have not been successful over the past few decades, probably indicating the presence of new physics during the era of BBN. We have investigated the impact on BBN predictions of adopting a generalized distribution to describe the velocities of nucleons in the framework of Tsallis non-extensive statistics. This generalized velocity distribution is characterized by a parameter q, and reduces to the usually assumed Maxwell-Boltzmann distribution for q = 1. We find excellent agreement between predicted and observed primordial abundances of D, 4He, and 7Li for 1.069 ≤ q ≤ 1.082, suggesting a possible new solution to the cosmological lithium problem.
Graphene is an important material with potential application in spintronics. Edge-modified zigzag graphene nanoribbons (ZGNR) are investigated with density functional theory. The modifications are ...realized by saturating the dangling edge bonds by different terminal groups, such as H, NH2, NO2, and CH3. Such modification has a significant impact on the ZGNR electronic structure. Half-metallicity is observed when ZGNR is terminated by NO2 groups at one edge and by CH3 groups on the other side. Free energy analysis suggests that edge-modification is a practical way in experiment to realize half-metallicity.
Ambitions to reach atomic resolution with light have been a major force in shaping nano-optics, whereby a central challenge is achieving highly localized optical fields. A promising approach employs ...plasmonic nanoantennas, but fluorescence quenching in the vicinity of metallic structures often imposes a strict limit on the attainable spatial resolution, and previous studies have reached only 8 nm resolution in fluorescence mapping. Here, we demonstrate spatially and spectrally resolved photoluminescence imaging of a single phthalocyanine molecule coupled to nanocavity plasmons in a tunnelling junction with a spatial resolution down to ∼8 Å and locally map the molecular exciton energy and linewidth at sub-molecular resolution. This remarkable resolution is achieved through an exquisite nanocavity control, including tip-apex engineering with an atomistic protrusion, quenching management through emitter–metal decoupling and sub-nanometre positioning precision. Our findings provide new routes to optical imaging, spectroscopy and engineering of light–matter interactions at sub-nanometre scales.Through the use of a plasmon-active atomically sharp tip and an ultrathin insulating film, and precise junction control in a highly confined nanocavity plasmon field at the scanning tunnelling microscope junction, sub-nanometre-resolved single-molecule near-field photoluminescence imaging with a spatial resolution down to ∼8 Å is achieved.
We report that the Kondo effect exerted by a magnetic ion depends on its chemical environment. A cobalt phthalocyanine molecule adsorbed on an Au(111) surface exhibited no Kondo effect. Cutting away ...eight hydrogen atoms from the molecule with voltage pulses from a scanning tunneling microscope tip allowed the four orbitals of this molecule to chemically bond to the gold substrate. The localized spin was recovered in this artificial molecular structure, and a clear Kondo resonance was observed near the Fermi surface. We attribute the high Kondo temperature (more than 200 kelvin) to the small on-site Coulomb repulsion and the large half-width of the hybridized d-level.
We report a rational design of CaHPO4-α-amylase hybrid nanobiocatalytic system based on allosteric effect and an explanation of the increase in catalytic activity when certain enzymes are immobilized ...in specific nanomaterials. Employing a calcification approach in aqueous solutions, we acquired such new nanobiocatalytic systems with three different morphologies, i.e., nanoflowers, nanoplates, and parallel hexahedrons. Through studying enzymatic performance of these systems and free α-amylase with/without Ca2+, we demonstrated how two factors, allosteric regulation and morphology of the as-synthesized nanostructures, predominantly influence enzymatic activity. Benefiting from both the allosteric modulation and its hierarchical structure, CaHPO4-α-amylase hybrid nanoflowers exhibited dramatically enhanced enzymatic activity. As a bonus, the new system we devised was found to enjoy higher stability and durability than free α-amylase plus Ca2+.
Palliative pemetrexed-based chemotherapy remains a standard of care treatment for the majority of patients with advanced non-squamous non-small-cell lung cancer (NSCLC). Currently, no predictive ...markers for pemetrexed treatment are available.
Resected tumour samples from pemetrexed-naïve NSCLC patients were collected. Gene expression profiling with respect to predicted sensitivity to pemetrexed classified predicted responders (60%) and non-responders (40%) based on differentially expressed genes encoding for pemetrexed target enzymes. Genes showing a strong correlation with these target genes were selected for measurement of corresponding protein expressions by immunohistochemical (IHC) staining. A semi-quantitative IHC scoring method was applied to construct a prediction model for response to pemetrexed. A retrospective cohort of patients with advanced NSCLC treated with first-line pemetrexed-based chemotherapy was used for external validation.
From ninety-one patients resected tumour samples were collected. The majority of patients had early or locally advanced NSCLC (96.3%). Gene expression profiling revealed five markers, which mRNA levels strongly correlated to pemetrexed target genes mRNA levels: TPX2, CPA3, EZH2, MCM2 and TOP2A. Of 63 (69%) patients IHC staining scores of these markers were obtained, which significantly differed between predicted non-responders and responders (P < 0.05). The optimized prediction model included EZH2 (OR = 0.56, 95% CI 0.35-0.90) and TPX2 (OR = 0.55, 95% CI 0.30-1.01). The model had a sensitivity of 86.8%, specificity of 63.6% and showed a good ability to distinct between responders and non-responders (C-index 0.86). In the external study population (N = 23) the majority of patients had metastatic NSCLC (95.7%). Partial response (PR) was established in 26.1%. The sensitivity decreased drastically to 33.3%, with a specificity of 82.4% and a C-index of 0.73.
Using external validation this prediction model with IHC staining of target enzyme correlated markers showed a good discrimination, but lacked sensitivity. The role of IHC markers as response predictors for pemetrexed in clinical practice remains questionable.
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