Improving the optoelectronic properties of monolayer MoS2field effect transistor through dielectric engineering

The reduced dielectric screening in atomically thin two-dimensional materials makes them very sensitive to the surrounding environment, which can be modulated to tune their optoelectronic properties. In this study, we significantly improved the optoelectronic properties of monolayer MoS2by varying the surrounding environment using different liquid dielectrics, each with a specific dielectric constant ranging from 1.89 to 18. Liquid mediums offer the possibility of environment tunability on the same device. For a back-gated field effect transistor, the field effect mobility exhibited more than two-order enhancement when exposed to a high dielectric constant medium. Further investigation into the effect of the dielectric environment on the optoelectronic properties demonstrated a variation in photoresponse relaxation time with the dielectric medium. The rise and decay times were observed to increase and decrease, respectively, with an increase in the dielectric constant of the medium. These results can be attributed to the dielectric screening provided by the surrounding medium, which strongly modifies the charged impurity scattering, the band gap, and defect levels of monolayer MoS2. These findings have important implications for the design of biological and chemical sensors, particularly those operating in a liquid environment. By leveraging the tunability of the dielectric medium, we can optimize the performance of such sensors and enhance their detection capabilities.

Opto-thermoelectric trapping of fluorescent nanodiamonds on plasmonic nanostructures

Deterministic optical manipulation of fluorescent nanodiamonds (FNDs) in fluids has emerged as an experimental challenge in multimodal biological imaging. Designing and developing nano-optical trapping strategies to serve this purpose is an important task. In this Letter, we show how chemically prepared gold nanoparticles and silver nanowires can facilitate an opto-thermoelectric force to trap individual entities of FNDs using a long working distance lens, low power-density illumination (532-nm laser, 12 µW/µm²). Our trapping configuration combines the thermoplasmonic fields generated by individual plasmonic nanoparticles and the opto-thermoelectric effect facilitated by the surfactant to realize a nano-optical trap down to a single FND that is 120 nm in diameter. We use the same trapping excitation source to capture the spectral signatures of single FNDs and track their position. By tracking the FND, we observe the differences in the dynamics of the FND around different plasmonic structures. We envisage that our drop-casting platform can be extrapolated to perform targeted, low-power trapping, manipulation, and multimodal imaging of FNDs inside biological systems such as cells.

Single Molecule Surface Enhanced Raman Scattering in a Single Gold Nanoparticle-Driven Thermoplasmonic Tweezer

Surface enhanced Raman scattering (SERS) is optically sensitive and chemically specific to detect single-molecule spectroscopic signatures. Facilitating this capability in optically trapped nanoparticles at low laser power remains a significant challenge. In this letter, we show single molecule SERS signatures in reversible assemblies of trapped plasmonic nanoparticles using a single laser excitation (633 nm). Importantly, this trap is facilitated by the thermoplasmonic field of a single gold nanoparticle dropcasted on a glass surface. We employ the bianalyte SERS technique to ascertain the single molecule statistical signatures and identify the critical parameters of the thermoplasmonic tweezer that provide this sensitivity. Furthermore, we show the utility of this low power (≈ 0.1 mW/μm²) tweezer platform to trap a single gold nanoparticle and transport assembly of nanoparticles. Given that our configuration is based on a dropcasted gold nanoparticle, we envisage its utility to create reconfigurable plasmonic metafluids in physiological and catalytic environments and to be potentially adapted as an in vivo plasmonic tweezer.

Optothermal pulling, trapping, and assembly of colloids using nanowire plasmons

Optical excitation of colloids can be harnessed to realize soft matter systems that are out of equilibrium. In this paper, we present our experimental studies on the dynamics of silica colloids in the vicinity of a silver nanowire propagating surface plasmon polaritons (SPPs). Due to the optothermal interaction, the colloids are directionally pulled towards the excitation point of the nanowire. Having reached this point, they are spatio-temporally trapped around the excitation location. By increasing the concentration of colloids in the system, we observe multi-particle assembly around the nanowire. This process is thermophoretically driven and assisted by the SPPs. Furthermore, we find such an assembly to be sensitive to the excitation polarization at the input of the nanowire. Numerically-simulated temperature distribution around an illuminated nanowire corroborates sensitivity to the excitation polarization. Our study will find relevance in exploration of SPP-assisted optothermal pulling, trapping and assembly of colloids, and can serve as a test-bed of plasmon-driven active matter.

Beaming Elastic and SERS Emission from Bent-Plasmonic Nanowire on a Mirror Cavity

We report on the experimental observation of beaming elastic and surface enhanced Raman scattering (SERS) emission from a bent-nanowire on a mirror (B-NWoM) cavity. The system was probed with polarization resolved Fourier plane and energy-momentum imaging to study the spectral and angular signature of the emission wavevectors. The out-coupled elastically scattered light from the kink occupies a narrow angular spread. We used a self-assembled monolayer of molecules with a well-defined molecular orientation to utilize the out-of-plane electric field in the cavity for enhancing Raman emission from the molecules and in achieving beaming SERS emission. Calculated directionality for elastic scattering and SERS emission was found to be 16.2 and 12.5 dB, respectively. The experimental data were corroborated with three-dimensional numerical finite element and finite difference time domain based numerical simulations. The results presented here may find relevance in understanding coupling of emitters with elongated plasmonic cavities and in designing on-chip optical antennas.

Modal and wavelength conversions in plasmonic nanowires

We show that plasmonic nanowire-nanoparticle systems can perform nonlinear wavelength and modal conversions and potentially serve as building blocks for signal multiplexing and novel trafficking modalities. When a surface plasmon excited by a pulsed laser beam propagates in a nanowire, it generates a localized broadband nonlinear continuum at the nanowire surface as well as at active locations defined by sites where nanoparticles are absorbed (enhancement sites). The local response may couple to new sets of propagating modes enabling a complex routing of optical signals through modal and spectral conversions. Different aspects influencing the optical signal conversions are presented, including the parameters defining the local formation of the continuum and the subsequent modal routing in the nanowire.

Observation of photonic spin-momentum locking due to coupling of achiral metamaterials and quantum dots

Chiral interfaces provide a new platform to execute quantum control of light-matter interactions. One phenomenon which has emerged from engineering such nanophotonic interfaces is spin-momentum locking akin to similar reports in electronic topological materials and phases. While there are reports of spin-momentum locking with combination of chiral emitters and/or chiral metamaterials with directional far field excitation it is not readily observable with both achiral emitters and metamaterials. Here, we report the observation of photonic spin-momentum locking in the form of directional and chiral emission from achiral quantum dots (QDs) evanescently coupled to achiral hyperbolic metamaterials (HMM). Efficient coupling between QDs and the metamaterial leads to emergence of these photonic topological modes which can be detected in the far field. We provide theoretical explanation for the emergence of spin-momentum locking through rigorous modeling based on photon Green's function where pseudo spin of light arises from coupling of QDs to evanescent modes of HMM.

Self-Assembled Helical Arrays for the Stabilization of the Triplet State

Room-temperature phosphorescence of metal and heavy atom-free organic molecules has emerged as an area of great potential in recent years. A rational design played a critical role in controlling the molecular ordering to impart efficient intersystem crossing and stabilize the triplet state to achieve room-temperature ultralong phosphorescence. However, in most cases, the strategies to strengthen phosphorescence efficiency have resulted in a reduced lifetime, and the available nearly degenerate singlet-triplet energy levels impart a natural competition between delayed fluorescence and phosphorescence, with the former one having the advantage. Herein, an organic helical assembly supports the exhibition of an ultralong phosphorescence lifetime. In contrary to other molecules, 3,6-phenylmethanone functionalized 9-hexylcarbazole exhibits a remarkable improvement in phosphorescence lifetime (>4.1 s) and quantum yield (11 %) owing to an efficient molecular packing in the crystal state. A right-handed helical molecular array act as a trap and exhibits triplet exciton migration to support the exceptionally longer phosphorescence lifetime.

Large-scale optothermal assembly of colloids mediated by a gold microplate

Light-activated colloidal assembly and swarming can act as model systems to explore non-equilibrium state of matter. In this context, creating new experimental platforms to facilitate and control two-dimensional assembly of colloidal crystals are of contemporary interest. In this paper, we present an experimental study of assembly of colloidal silica microparticles in the vicinity of a single-crystalline gold microplate evanescently excited by a 532 nm laser beam. The gold microplate acts as a source of heat and establishes a thermal gradient in the system. The created optothermal potential assembles colloids to form a two-dimensional poly-crystal, and we quantify the coordination number and hexagonal packing order of the assembly in such a driven system. Our experimental investigation shows that for a given particle size, the variation in assembly can be tuned as a function of excitation-polarization and surface to volume ratio of the gold microplates. Furthermore, we observe that the assembly is dependent on size of the particle and its material composition. Specifically, silica colloids assemble but polystyrene colloids do not, indicating an intricate behaviour of the forces under play. Our work highlights a promising direction in utilizing metallic microstructures that can be harnessed for optothermal colloidal crystal assembly and swarming studies. Our experimental system can be utilized to explore optically driven matter and photophoretic interactions in soft-matter including biological systems such as cells and micro organisms.

V-shaped active plasmonic meta-polymers

We report the design and fabrication of V-shaped plasmonic meta-polymers on a glass substrate or silicon wafer using a surface functionalization approach. The efficacy of the assembly method is examined by analyzing the surface enhanced Raman scattering by an individual V-shaped antenna experimentally and using computational simulations to determine the polarization dependence of local electromagnetic field enhancement.

Directional second-harmonic generation controlled by sub-wavelength facets of an organic mesowire

Directional harmonic generation is an important property characterizing the ability of nonlinear optical antennas to diffuse the signal in a well-defined region of space. Herein, we show how sub-wavelength facets of an organic molecular mesowire crystal can be utilized to systematically vary the directionality of second-harmonic generation (SHG) in the forward-scattering geometry. We demonstrate this capability on crystalline diamonoanthraquinone (DAAQ) mesowires with sub-wavelength facets. We observed that the radial angles of the SHG emission can be tuned over a range of 130 deg. This angular variation arises due to spatially distributed nonlinear dipoles in the focal volume of the excitation as well as the geometrical cross section and facet orientation of the mesowire. Numerical simulations of the near-field excitation profile corroborate the role of the mesowire geometry in localizing the electric field. In addition to directional SHG from the mesowire, we experimentally observe optical waveguiding of the nonlinear two-photon excited fluorescence (TPEF). Interestingly, we observed that for a given pump excitation, the TPEF signal is isotropic and delocalized, whereas the SHG emission is directional and localized at the location of excitation. All the observed effects have direct implications not only in active nonlinear optical antennas but also in nonlinear signal processing.

Spin-Hall effect in the scattering of structured light from plasmonic nanowire

Spin-orbit interactions are subwavelength phenomena that can potentially lead to numerous device-related applications in nanophotonics. Here, we report the spin-Hall effect in the forward scattering of Hermite-Gaussian (HG) and Gaussian beams from a plasmonic nanowire. Asymmetric scattered radiation distribution was observed for circularly polarized beams. Asymmetry in the scattered radiation distribution changes the sign when the polarization handedness inverts. We found a significant enhancement in the spin-Hall effect for a HG beam compared to a Gaussian beam for constant input power. The difference between scattered powers perpendicular to the long axis of the plasmonic nanowire was used to quantify the enhancement. In addition, the nodal line of the HG beam acts as the marker for the spin-Hall shift. Numerical calculations corroborate experimental observations and suggest that the spin flow component of the Poynting vector associated with the circular polarization is responsible for the spin-Hall effect and its enhancement.

Doughnut-shaped emission from vertical organic nanowire coupled to thin plasmonic film

Vertical nanowires facilitate an innovative mechanism to channel the optical field in the orthogonal direction and act as a nanoscale light source. Subwavelength, vertically oriented nanowire platforms, both of plasmonic and semiconducting variety, can facilitate interesting far-field emission profiles and potentially carry orbital angular momentum states. Motivated by these prospects, in this Letter, we show how a hybrid plasmonic-organic platform can be harnessed to engineer far-field radiation. The system that we have employed is an organic nanowire made of diaminoanthroquinone grown on a plasmonic gold film. We experimentally and numerically studied angular distribution of surface plasmon polariton mediated emission from a single, vertical organic nanowire by utilizing evanescent excitation and Fourier plane microscopy. Photoluminescence and elastic scattering from a single nanowire was analyzed individually in terms of inplane momentum states of the outcoupled photons. We found that the emission is doughnut-shaped in both photoluminescence and elastic scattering regimes. We anticipate that the discussed results can be relevant in designing efficient, polariton-mediated nanoscale photon sources that can carry orbital angular momentum states.

Differential Wavevector Distribution of Surface-Enhanced Raman Scattering and Fluorescence in a Film-Coupled Plasmonic Nanowire Cavity

We report on the experimental observation of differential wavevector distribution of surface-enhanced Raman scattering (SERS) and fluorescence from dye molecules confined to a gap between plasmonic silver nanowire and a thin, gold mirror. The fluorescence was mainly confined to higher values of in-plane wavevectors, whereas SERS signal was uniformly distributed along all the wavevectors. The optical energy-momentum spectra from the distal end of the nanowire revealed strong polarization dependence of this differentiation. All these observations were corroborated by full-wave three-dimensional numerical simulations, which further revealed an interesting connection between out-coupled wavevectors and parameters such as hybridized modes in the gap-plasmon cavity, and orientation and location of molecular dipoles in the geometry. Our results reveal a new prospect of discriminating electronic and vibrational transitions in resonant dye molecules using a subwavelength gap plasmonic cavity in the continuous-wave excitation limit, and can be further harnessed to engineer molecular radiative relaxation processes in momentum space.

Exciton Emission Intensity Modulation of Monolayer MoS2 via Au Plasmon Coupling

Modulation of photoluminescence of atomically thin transition metal dichalcogenide two-dimensional materials is critical for their integration in optoelectronic and photonic device applications. By coupling with different plasmonic array geometries, we have shown that the photoluminescence intensity can be enhanced and quenched in comparison with pristine monolayer MoS2. The enhanced exciton emission intensity can be further tuned by varying the angle of polarized incident excitation. Through controlled variation of the structural parameters of the plasmonic array in our experiment, we demonstrate modulation of the photoluminescence intensity from nearly fourfold quenching to approximately threefold enhancement. Our data indicates that the plasmonic resonance couples to optical fields at both, excitation and emission bands, and increases the spontaneous emission rate in a double spacing plasmonic array structure as compared with an equal spacing array structure. Furthermore our experimental results are supported by numerical as well as full electromagnetic wave simulations. This study can facilitate the incorporation of plasmon-enhanced transition metal dichalcogenide structures in photodetector, sensor and light emitter applications.

Plasmon-controlled excitonic emission from vertically-tapered organic nanowires

Organic molecular nanophotonics has emerged as an important avenue to harness molecular aggregation and crystallization on various functional platforms to obtain nano-optical devices. To this end, there is growing interest to combine organic molecular nanostructures with plasmonic surfaces and interfaces. Motivated by this, herein we introduce a unique geometry: vertically-tapered organic nanowires grown on a plasmonic thin film. A polarization-sensitive plasmon-polariton on a gold thin-film was harnessed to control the exciton-polariton propagation and subsequent photoluminescence from an organic nanowire made of diaminoanthraquinone (DAAQ) molecules. We show that the exciton-polariton emission from individual DAAQ nanowires can be modulated up to a factor of 6 by varying the excitation polarization state of surface plasmons. Our observations were corroborated with full-wave three-dimensional finite-difference time-domain calculations performed on vertically-tapered nanowire geometry. Our work introduces a new optical platform to study coupling between propagating plasmons and propagating excitons, and may have implications in emerging fields such as hybrid-polariton based light emitting devices and vertical-cavity nano-optomechanics.

Large-scale dynamic assembly of metal nanostructures in plasmofluidic field

We discuss two aspects of the plasmofluidic assembly of plasmonic nanostructures at the metal–fluid interface. First, we experimentally show how three and four spot evanescent-wave excitation can lead to unconventional assembly of plasmonic nanoparticles at the metal–fluid interface. We observed that the pattern of assembly was mainly governed by the plasmon interference pattern at the metal–fluid interface, and further led to interesting dynamic effects within the assembly. The interference patterns were corroborated by 3D finite-difference time-domain simulations. Secondly, we show how anisotropic geometry, such as Ag nanowires, can be assembled and aligned in unstructured and structured plasmofluidic fields. We found that by structuring the metal-film, Ag nanowires can be aligned at the metal–fluid interface with a single evanescent-wave excitation, thus highlighting the prospect of assembling plasmonic circuits in a fluid. An interesting aspect of our method is that we obtain the assembly at locations away from the excitation points, thus leading to remote assembly of nanostructures. The results discussed herein may have implications in realizing a platform for reconfigurable plasmonic metamaterials, and a test-bed to understand the effect of plasmon interference on assembly of nanostructures in fluids.

Directional out-coupling of light from a plasmonic nanowire-nanoparticle junction

We experimentally show how a single Ag nanoparticle (NP) coupled to an Ag nanowire (NW) can convert propagating surface plasmon polaritons to directional photons. By employing dual-excitation Fourier microscopy with spatially filtered collection-optics, we show single- and dual-directional out-coupling of light from NW-NP junction for plasmons excited through glass-substrate and air-superstrate. Furthermore, we show NW-NP junction can influence the directionality of molecular-fluorescence emission, thus functioning as an optical antenna. The results discussed herein may have implications in realizing directional single-photon sources and quantum plasmon circuitry.

Allosteric transition induced by Mg²⁺ ion in a transactivator monitored by SERS

We demonstrate the utility of the surface-enhanced Raman spectroscopy (SERS) to monitor conformational transitions in protein upon ligand binding. The changes in protein's secondary and tertiary structures were monitored using amide and aliphatic/aromatic side chain vibrations. Changes in these bands are suggestive of the stabilization of the secondary and tertiary structure of transcription activator protein C in the presence of Mg(2+) ion, whereas the spectral fingerprint remained unaltered in the case of a mutant protein, defective in Mg(2+) binding. The importance of the acidic residues in Mg(2+) binding, which triggers an overall allosteric transition in the protein, is visualized in the molecular model. The present study thus opens up avenues toward the application of SERS as a potential tool for gaining structural insights into the changes occurring during conformational transitions in proteins.

Single-Molecule Surface-Enhanced Raman Scattering Sensitivity of Ag-Core Au-Shell Nanoparticles: Revealed by Bi-Analyte Method

Single-molecule surface-enhanced Raman scattering (SM-SERS) is an important application of localized surface plasmons in metallic nanostructures. Conventionally, Ag nanoparticles are used in solution-based SM-SERS experiments, but their usage is limited due to toxicity and oxidation issues. Au nanoparticle solutions are relatively biocompatible and SERS-active, but they do not facilitate large-scale SERS enhancement factors, which is an important prerequisite for SM-SERS. Under such constraints, silver-core gold-shell nanoparticles can be an excellent alternative for SM-SERS. Motivated by this, herein we report on the experimental evidence of SM-SERS sensitivity of Ag-core Au-shell nanoparticles by employing bianalyte method. Additionally, by detecting resonant molecules at femtomolar concentrations, we show that Ag-core Au-shell nanoparticle can be harnessed for ultrasensitive detection of molecules. The provided evidence will further motivate usage of such gold-shell-based bimetallic nanostructures for SM-SERS in biological environments.

Palladium bridged gold nanocylinder dimer: plasmonic properties and hydrogen sensitivity

Plasmonic nanodimers facilitate electromagnetic hotspots at their gap junction. By loading these gap junctions with nanomaterials, the plasmonic properties of nanodimer can be varied. In this study, we bridged the gap junction of gold (Au) nanocylinder dimer with palladium (Pd), and numerically evaluated the plasmonic properties of the designed nanostructure. We simulated the far-field extinction spectra of Pd bridged Au nanocylinder dimer, and identified the dipole and quadrupole plasmon modes at 839 and 578 nm, respectively. By varying the geometrical parameters of the Pd bridge, we revealed the ability to tune the dipolar plasmon resonance of the bridged dimer. Further, we exploited the hydrogen sensitivity of Pd bridge to harness the bridged-Au dimer as nanoplasmonic hydrogen sensor. Such nano-optical detection platforms have minimal spatial footprint and can be further harnessed for chip-based plasmonic sensing.

Near-field optical properties of silver nanocylinders arranged in a Pascal triangle

The Pascal triangle is a geometric representation of binomial coefficients in triangular form. We utilize this formalism to deterministically arrange silver nanocylinders of different sizes (30, 60, and 90 nm) on a triangle and numerically study their near-field optical properties. We show that near-field intensities at specific points on this triangle depend on the wavelength and angle of incidence. From the wavelength-dependent studies at various junctions of nanocylinders, we obtain maximum near-field intensity at 350 and 380 nm. By varying the angle of incidence of the TM-polarized plane wave, we find systematic variation in the near-field intensity at different junctions of the geometry. Our study will lead to insights in designing controllable electromagnetic hot spots for chip-based plasmonic devices.

Surface-enhanced Raman spectroscopic studies of coactivator-associated arginine methyltransferase 1

We report, for the first time, the surface-enhanced Raman spectra of an important enzyme, coactivator-associated arginine methyltransferase 1 (CARM1), involved in various biological activities such as tumor suppressor function and stem cell differentiation. We have employed surface-enhanced Raman scattering (SERS) to obtain insight into the structural details of CARM1 by adsorbing it to silver (Ag) nanoparticles. The enzyme retains its activity even after its adsorption onto Ag nanoparticles. We observe strong SERS modes arising from amide vibrations and aromatic ring amino acids. The SERS spectra revealed amide I bands at 1637 cm(-1) and 1666 cm(-1), which arise as a result of the alpha helix of the protein and the polypeptide backbone vibration of a random coil, respectively. In order to confirm the amide vibrations, we have performed SERS on deuterated CARM1, which exhibits a clear red shift in amide band positions. The SERS spectra may provide useful information, which could be harnessed to study the functional interactions of CARM1 with small molecule modulators.

Visible fluorescence induced by the metal semiconductor transition in composites of carbon nanotubes with noble metal nanoparticles

We show that single-walled carbon nanotube (SWNT) bundles emit visible fluorescence in the presence of noble metal nanoparticles and nanorods in the solid state. Conductivity measurements with metallic nanotubes, isolated from pristine SWNTs, show that they become semiconducting in the presence of the metal nanoparticles. Nanoparticle binding increases the defects in the nanotube structures which is evident in the Raman spectra. The metal-semiconductor transition removes the nonradiative decay channels of the excited states enabling visible fluorescence. Nanotube structures are imaged using this emission with resolution below the classical limits.

Autoacetylation induced specific structural changes in histone acetyltransferase domain of p300: probed by surface enhanced Raman spectroscopy

Reversible acetylation of histone and non-histone proteins plays an important role in the regulation of gene expression and cellular homeostasis. A balance between acetylation and deacetylation of these proteins are maintained by histone acetyltransferases (HATs) and histone deacetylases (HDACs). Among different HATs, p300/CBP is the most widely studied chromatin modifying enzymes. p300 is involved in several physiological processes like cell growth, regulation of gene expression, development, and tumor suppressor, and therefore its dysfunction causes different diseases. The autoacetylation of p300 is one of the key regulators of its catalytic activity. Mechanistically, autoacetylation induced structural changes in the p300 HAT domain acts as a master switch. In this report, we have shown that the natural HAT inhibitor garcinol could potently inhibit the autoacetylation activity. Furthermore, for the first time, we demonstrate that indeed autoacetylation induces structural changes in p300 HAT domain, as probed by surface-enhanced Raman scattering. Presumably, SERS will be a very useful tool to find out the structural changes in the other self-modifying enzymes like kinases and methyltransferases.

Specific inhibition of p300-HAT alters global gene expression and represses HIV replication

Reversible acetylation of histone and nonhistone proteins plays pivotal role in cellular homeostasis. Dysfunction of histone acetyltransferases (HATs) leads to several diseases including cancer, neurodegenaration, asthma, diabetes, AIDS, and cardiac hypertrophy. We describe the synthesis and characterization of a set of p300-HAT-specific small-molecule inhibitors from a natural nonspecific HAT inhibitor, garcinol, which is highly toxic to cells. We show that the specific inhibitor selectively represses the p300-mediated acetylation of p53 in vivo. Furthermore, inhibition of p300-HAT down regulates several genes but significantly a few important genes are also upregulated. Remarkably, these inhibitors were found to be nontoxic to T cells, inhibit histone acetylation of HIV infected cells, and consequently inhibit the multiplication of HIV.

Activation of p300 Histone Acetyltransferase by Small Molecules Altering Enzyme Structure: Probed by Surface-Enhanced Raman Spectroscopy

Reversible acetylation of nucleosomal histones and nonhistone proteins play pivotal roles in the regulation of all the DNA templated phenomenon. Dysfunction of the enzymes involved in the acetylation/deacetylation leads to several diseases. Therefore, these enzymes are the targets for new generation therapeutics. Here, we report the synthesis of trifluoromethyl phenyl benzamides and their effect on histone acetyltransferase (HAT) activity of p300. One of these benzamides, CTPB (N-(4-chloro-3-trifluoromethyl-phenyl)-2-ethoxy-6-pentadecyl-benzamide), was discovered as a potent activator of the p300 HAT activity. We have found that pentadecyl hydrocarbon chain of CTPB is required to activate the HAT only under certain context. Furthermore, our results show that the relative position of -CF3 and -Cl in CTB (N-(4-chloro-3-trifluoromethyl-phenyl)-2-ethoxy-benzamide) is also very critical for the activation. Surface-enhanced Raman spectroscopy (SERS) of p300 and the HAT activator complexes evidently suggest that the activation of HAT activity is achieved by the alteration of p300 structure. Therefore, apart from elucidating the chemical basis for small molecule mediated activation of p300, this report also describes, for the first time, Raman spectroscopic analysis of the complexes of histone-modifying enzymes and their modulators, which may be highly useful for therapeutic applications.

Surface-Enhanced Raman Scattering Studies of Human Transcriptional Coactivator p300

We report for the first time the surface-enhanced Raman scattering (SERS) studies on p300, a large multidomain transcriptional coactivator protein. Vibration spectral analysis has been performed in an attempt to understand the structure of the p300 in the absence of its crystal structure. Strong Raman bands associated with amides I-III have been observed in the protein spectra. This has been confirmed by performing SERS on deuterated p300. We also observe Raman bands associated with the alpha-helix, tryptophan, phenylalanine, tyrosine, and histidine. These bands will provide an ideal tool to study the drug-protein interactions in therapeutics using SERS. We have successfully demonstrated the chloride ion effect on the SERS of p300. The Raman intensity increases in the SERS spectra upon addition of chloride ion along with appearance of new modes. We have developed a new method, namely, the "sandwich technique", which could be used to perform SERS experiments on proteins in dry conditions.