In situ Plasmon-Enhanced CARS and TPEF for Gram staining identification of non-fluorescent bacteria

Early-stage oral cancer diagnosis by artificial intelligence-based SERS using Ag NWs@ZIF core-shell nanochains

Surface-enhanced Raman spectroscopy (SERS) has great potential in the early diagnosis of diseases by detecting the changes of volatile biomarkers in exhaled breath, because of its high sensitivity, rich chemical molecular fingerprint information, and immunity to humidity. Here, an accurate diagnosis of oral cancer (OC) is demonstrated using artificial intelligence (AI)-based SERS of exhaled breath in plasmonic-metal organic framework (MOF) nanoparticles. These plasmonic-MOF nanoparticles were prepared using a zeolitic imidazolate framework coated on Ag nanowires (Ag NWs@ZIF), which offers Raman enhancement from the plasmonic nanowires and gas enrichment from the ZIF shells. Then, the core-shell nanochains of Ag NWs@ZIF prepared with 0.5 mL Ag NWs were selected to capture gaseous methanethiol, which is a tumor biomarker, from the exhalation of OC patients. The substrate was used to collect a total of 400 SERS spectra of exhaled breath of simulated healthy people and simulated OC patients. The artificial neural network (ANN) model in the AI algorithm was trained with these SERS spectra and could classify them with an accuracy of 99%. Notably, the model predicted OC with an area under the curve (AUC) of 0.996 for the simulated OC breath samples. This work suggests the great potential of the combination of breath analysis and AI as a method for the early-stage diagnosis of oral cancer.

Recent advances of Au@Ag core-shell SERS-based biosensors

The methodological advancements in surface-enhanced Raman scattering (SERS) technique with nanoscale materials based on noble metals, Au, Ag, and their bimetallic alloy Au-Ag, has enabled the highly efficient sensing of chemical and biological molecules at very low concentration values. By employing the innovative various type of Au, Ag nanoparticles and especially, high efficiency Au@Ag alloy nanomaterials as substrate in SERS based biosensors have revolutionized the detection of biological components including; proteins, antigens antibodies complex, circulating tumor cells, DNA, and RNA (miRNA), etc. This review is about SERS-based Au/Ag bimetallic biosensors and their Raman enhanced activity by focusing on different factors related to them. The emphasis of this research is to describe the recent developments in this field and conceptual advancements behind them. Furthermore, in this article we apex the understanding of impact by variation in basic features like effects of size, shape varying lengths, thickness of core-shell and their influence of large-scale magnitude and morphology. Moreover, the detailed information about recent biological applications based on these core-shell noble metals, importantly detection of receptor binding domain (RBD) protein of COVID-19 is provided.

Optical Physical Mechanisms of Helicene Carbon Nanohoop with Möbius Topology

Optical and spectral properties of carbon nanohoop with Möbius topology is of great interest in nano-science and nano-technology. And it can be imagined that it has a lot of unexpected potential application prospects. However, theoretical calculations based on some figure-of-eight helicene carbon nanohoop with Möbius topology are still insufficient. Therefore, in this paper, we theoretically study the optical and spectral properties of figure-of-eight helicene carbon nanohoop with Möbius topology. Optical and spectral properties are analyzed with visualization method of transition density matrix and charge density difference, which reveal the unique characterization of carbon nanohoop with Möbius topology. Our results can not only deepen the understanding of the optical physical mechanisms of the nanorings with mobius carbons, but also provide deeper insight on optical properties and potential design on optical nanodevices.

Physical mechanism on linear spectrum and nonlinear spectrum in double helical carbon nanomolecule-infinitene

In this work, based on density functional theory (DFT) and wave function analysis, the properties of absorption spectrum, electronic circular dichroism (ECD) spectrum and Raman spectrum of infinitene (monomer and dimer) with double helical structure are theoretically studied. The electronic excitation properties of infinitene were investigated based on the visualization method charge density difference (CDD) and transition density matrix (TDM). It is found that there is obvious intermolecular charge transfer behavior in the dimer. The electromagnetic interaction mechanism of the chirality of infinitene is explained by decomposing transition electric\magnetic dipole moments (TEDMs\TMDMs). The response of Raman spectra to excitation light of different wavelengths was calculated. Then, the electron delocalization degree and magnetic response intensity of infinitene were studied based on the magnetically induced current under external magnetic field. The interaction of infinitene with the external environment was studied by electrostatic and van der Waals potentials, and it was shown that non-polar or low-polar molecules are more inclined to be adsorbed at the groove position of infinitene. Finally, the mechanism of intermolecular interactions in dimer was investigated based on independent gradient model based on Hirshfeld partition (IMGH), Atoms-In-Molecules (AIM), and energy decomposition analysis based on forcefield (EDA-FF). And revealed that the stacking in the dimer is dominated by dispersive interactions.

Precise size-control and functionalization of gold nanoparticles synthesized by plasma-liquid interactions: using carboxylic, amino, and thiol ligands

Using gold nanoparticles (GNPs) in high-standard applications requires GNPs to be fabricated with high-quality size and surface properties. Plasma-liquid interactions (PLIs) have the unique ability to synthesize GNPs without using any reducing agents, and the GNP surface is free of stabilizing agents. It is an extreme advantage that ensures success for the subsequent functionalization processes for GNPs. However, fabricating GNPs via PLIs at the desired size has still been a challenge. Here, we present a simple approach to achieving the precise size-control of GNPs synthesized by PLIs. By adding suitable ligands to the precursor solution, the ligands wrap GNPs which interrupts and slows down the rapid growth of GNPs under PLIs. This way, the size of the GNPs can be precisely controlled by adjusting the ligand concentration. Our results showed that the size of the GNPs in the range of 10-60 nm can be fitted to reciprocal functions of the ligand concentration. The potency of the size-control depends on the type of ligands in the order of thiol > amine > carboxylate. The size-control has been well investigated with four common ligands: l-cysteine, glucosamine, salicylic acid, and terephthalic acid. XPS, FTIR, and zeta potential techniques confirmed the presence of these ligands on GNPs. The results indicated that functionalized ligands could be utilized to control the size and functionalize the GNP surface. Hence our approach could simultaneously achieve two goals: precise size-control and functionalization of GNPs without the ligand-exchange step.

Gold nanoblackbodies mediated plasmonic photothermal cancer therapy for melanoma

Aim: Gold nanoblackbodies (AuNBs)-mediated plasmonic photothermal cancer therapy was investigated through melanoma-bearing mice. Materials & methods: Polydopamine-coated Au nanoclusters were synthesized, termed AuNBs and PEGylated AuNBs (AuNBs-PEG). The photothermal response of AuNBs-PEG was evaluated upon low-intensity broadband near-infrared irradiation (785/62 nm; 0.9 Wcm^-2), and cytotoxicity was assessed on B16-F10 cells. Further, the therapeutic potential of intravenously administered AuNBs-PEG was evaluated on B16-F10 melanoma in C57BL/6 mice. Results: AuNBs-PEG showed an excellent photothermal response (photothermal conversion efficiency of 60.3%), robust photothermal stability and no cytotoxicity. For AuNB-mediated plasmonic photothermal therapy, an average temperature of 63°C was attained within 5 min of irradiation, and tumors were eradicated. Conclusion: AuNBs-PEG are promising photothermal agents for treating melanoma through low-intensity broadband near-infrared irradiation.

Significant Enhancement of Two-Photon Excited Fluorescence in Water-Soluble Triphenylamine-Based All-Organic Compounds

Understanding water-soluble and environmentally friendly two-photon absorption (TPA) molecules benefits the design of superior organic complexes for biomedical, illumination, and display applications. In this work, we designed two triphenylamine-based all-organic compounds and explored the mechanism of enhanced TP fluorescence in water solutions for potential applications. Experimentally, we showed that adding protein into our TPA molecule solution can drastically boost the TP fluorescence. Numerical simulations reveal that the TPA molecules prefer to dock inside the protein complex. We hypothesize that the interaction between our triphenylamine-based all-organic compounds and water molecules lead to non-radiative decay processes, which prevent strong TP fluorescence in the water solution. Therefore, the protection by, for example, protein molecules from such interactions can be a universal strategy for superior functioning of organic TPA molecules. Further experiments and numerical simulations support our hypothesis. The present study may facilitate the design of superior water-soluble and environmentally friendly superior organic complexes.

Surface-enhanced coherent anti-Stokes Raman scattering based on coupled nanohole-slit arrays

Metal nanohole arrays show excellent performance when applied for sensing, optical fibers, and surface-enhanced spectroscopy, but they are not ideal candidates for surface-enhanced coherent anti-Stokes Raman scattering (SECARS) because of their low enhancement factor (EF). Here, the finite element method was used to study the dependence of the period, width, and thickness of nanoslits on the EF of SECARS and optical transmission in Au nanohole-slit arrays. Nanoslits across the nanoholes significantly modulated the SECARS signal, and we observed an ∼10⁶ improvement in the EF of SECARS compared with the nanohole-only structure. Uniform and stable 2D hotspots at the open surface of plasmonic nanohole-slit structures provided a huge SECARS EF as high as 18 orders of magnitude. Directional SECARS emission revealed strong forward and backscattering with high directionality, showing a smaller divergence angle of 14° on the reflective side of the nanohole-slit array. These results provide a fundamental understanding of SECARS in coupled nanohole-slit arrays and are useful for designing a SECARS platform with high sensitivity.

Nonlinear plexcitons: excitons coupled with plasmons in two-photon absorption

The nonlinear optical properties of a D-A (donor-acceptor) conjugated organic molecule with polythiophene (PT) as the donor and indene-C₆₀ bisadduct (IC₆₀BA) as the acceptor are theoretically investigated, which exhibits a large two-photon absorption (TPA) cross-section up to 8000 GM at the wavelength of 780 nm. Combining surface plasmon resonances (SPRs) with nonlinear optics, nonlinear properties can be strongly enhanced. In this paper, an appropriate nonlinear plexciton method by the coupling of Au@Ag nanorods and an Ag film is designed, in which the TPA properties of the PT:IC₆₀BA complex can be increased by 10⁶ times. The angle dependence on polarization and incidence is investigated to obtain the maximum of plasmonic enhancement. Our results emphasize the physical mechanism of nonlinear plexcitons and provide a feasible method to improve the nonlinear properties of organic solar cell materials.

Enhanced photoluminescence and shortened lifetime of DCJTB by photoinduced metal deposition on a ferroelectric lithography substrate

The photodeposition of metallic nanostructures onto ferroelectric surfaces could enable new applications based on the assembly of molecules and patterning local surface reactivity by enhancing surface field intensity. DCJTB (4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran) is an excellent fluorescent dye and dopant material with a high quantum efficiency used for OLED displays on the market. However, how to raise the photoluminescence (PL) and reduce the lifetime of DCJTB in a substrate remain extraordinary challenges for its application. Here, we demonstrate a tunable ferroelectric lithography plasmon-enhanced substrate to generate photo-reduced silver nanoparticles (AgNPs) and achieve enhanced PL with a shortened lifetime depending on the substrate's annealing time. The enhanced PL with shortened lifetimes can attribute to the localized electromagnetic (EM) wave produced by the nanotextured AgNPs layers' surface and gap plasmon resonances. The simulation is based on the three-dimensional finite element method to explain the mechanism of experimental results. Since the absorption increases, the remarkable enhanced PL of DCJTB can attain in the fabricated periodically proton exchanged (PPE) lithium niobate (LiNbO₃) substrate. Furthermore, the proposed fabrication method demonstrates to help tune the surface EM wave distribution in the substrate, which can simultaneously achieve the significantly shortened lifetime and high PL intensity of DCJTB in the substrate. Compared with the un-annealed substrate, the PL intensity of DCJTB in the assembly metallic nanostructures is enhanced 13.70 times, and the PL's lifetime is reduced by 12.50%, respectively. Thus, the fabricated substrate can be a promising candidate, verifying chemically patterned ferroelectrics' satisfaction as a PL-active substrate.

Nonlinear Optical Microscopy and Plasmon Enhancement

Improving nonlinear optics efficiency is currently one of the hotspots in modern optical research. Moreover, with the maturity of nonlinear optical microscope systems, more and more biology, materials, medicine, and other related disciplines have higher imaging resolution and detection accuracy requirements for nonlinear optical microscope systems. Surface plasmons of metal nanoparticle structures could confine strong localized electromagnetic fields in their vicinity to generate a new electromagnetic mode, which has been widely used in surface-enhanced Raman scattering, surface-enhanced fluorescence, and photocatalysis. In this review, we summarize the mechanism of nonlinear optical effects and surface plasmons and also review some recent work on plasmon-enhanced nonlinear optical effects. In addition, we present some latest applications of nonlinear optical microscopy system research.

Molecular and plasmonic resonances on tip-enhanced Raman spectroscopy

Plasmon has been widely investigated and applied, because it can greatly enhance molecular Raman spectral intensity. In this study, the resonance Raman effect of the tetra-tert-butylnaphthalocyanine (TTBN) is analyzed, including the Raman wave number shift and enhancement factor, resulting from light of different incident wavelengths. Furthermore, the optical properties of TTBN are obtained, such as charge transfer, the electronic circular dichroism (ECD) spectrum, etc. Lastly, we study the tip-enhanced Raman spectroscopy (TERS) by adjusting the parameters of the metal tip to achieve the highest electromagnetic enhancement at different incident wavelengths. Combining the resonance excitation effect and the tip enhanced Raman effect, the enhancement factor of TERS can reach up to 10⁸-10⁹. This study provides significant help for a profound understanding of the TERS mechanism.

Femtosecond coherent anti-Stokes Raman spectroscopy study of vibrational dynamics of liquid chloroform

Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) was used to study the dynamics of the vibrational modes of liquid chloroform. The vibrational modes were selectively excited and their coherent vibrational dynamics were obtained. Some subtle features that are difficult to distinguish in the ordinary spontaneous Raman spectrum, such as overtones and combinations of some fundamental vibrational modes, were recognized from the CARS transients. Combined with theoretical calculations, the contributions of chlorine isotopes were also confirmed from the CARS transients of the vibrational modes involving the motion of chlorine atoms.

The vibrational dynamics of liquid chloroform was systematically investigated using femtosecond CARS. Subtle features (such as overtones and combinations) and contributions of chlorine isotopes were confirmed from the CARS transients.

Ionic liquid-based liposome for selective SERS detection

An ionic liquid (IL)-based liposome was utilized as a substrate to construct a SERS platform. The isotropy of the IL outer surface together with its ion-exchange property led to the array-like growth of Au nanoparticles (NPs), generating hot-spots and resulting in anionic probes being present on the hot-spot regions. The simultaneous strategy of enrichment and localization endowed the platform with ability to detect trace amounts of anionic probes.