Determination of Critical Micelle Concentration (CMC) of Surfactants Using Environmentally Sensitive Carbonized Polymer Dots

Critical micelle concentration (CMC) is one of the essential parameters for surfactants. To accurately measure this value, we prepared a new type of carbonized polymer dots (CPDs) based on a solvothermal method of N,N-diethyl-p-phenylenediamine. This CPD exhibits significant fluorescence enhancement (600×) in various surfactant-contained solutions relative to its aqueous solution due to the charge transfer (CT) effect. It also shows a fluorescence change performance in different concentrations of surfactants, allowing a fluorescence measurement for CMC. Its responsive mechanism was discussed by the fluorescence lifetime and quantum yield results. Compared to the previously reported CMC probes, our developed CPD-based probe has merits in simple preparation, low cost, high availability, and easy use. This study utilized the CT feature of carbon material and widened the applications of CPDs for practical detection purposes

Multicolor Lipid Droplet-Targeted Carbonized Polymer Dots with Luminescence Regulation for Bioimaging Applications

Color-tunable, lipid droplet-targeted carbonized polymer dots (CPDs) were fabricated by varying reaction precursors through one-pot solvothermal synthesis. They exhibit gradual luminescence ranging from red to blue via the separation of the reaction products by means of column chromatography. We analyzed the structures of these multicolor CPDs and discovered that their emission wavelengths are regulated by both particle size and surface state. The blueshifts of their emission wavelength from 630 to 500 nm can be attributed to the band gap change, primarily manifested by an increase in N content, a decrease in O content, and a difference in grain size. Multiple photophysical parameters reveal that the synthesized CPDs have excellent luminescent properties. Fluorescence colocalization imaging of our full-color CPDs with lipid droplet-type commercial dyes yielded satisfactory results, displaying no cross-color with commercial dyes. Also, they were feasible for full-color lipid-droplet-targeted in vivo bioimaging of zebrafish, highlighting the lipid-rich yolk sac of zebrafish embryos. In conclusion, these nanoprobes exhibit significant promise in investigating lipid droplet metabolism regulation and offer the benefits of good biocompatibility, ease of fabrication, and lipophilicity

Comparison of Shearing Force and Hydrostatic Pressure on Molecular Structures of Triphenylamine by Fluorescence and Raman Spectroscopies

Luminescent mechanochromism (e.g., shearing force and hydrostatic pressure) has been intensively studied in recent years. However, there are few reported studies on the difference of the molecular configuration changes induced by these stresses. In this study, we chose triphenylamine, C₁₈H₆N (TPA), as a model molecule to study different molecular configuration changes under shearing force and hydrostatic pressure. Triphenylamine is an organic optoelectric functional molecule with a propeller-shaped configuration, a large conjugate structure, and a single molecular fluorescence material. Fluorescence and Raman spectra of TPA were recorded in situ under different pressures (0–1.9 GPa) produced by the mechanical grinding or using a diamond anvil cell (DAC). Our results show that the crystal phase of TPA transformed to the amorphous phase by grinding, whereas no obvious phase transition was observed under hydrostatic pressure up to 1.9 GPa, indicating the stability of TPA. Hydrostatic pressure by DAC induces molecular conformation changes, and the pressure-induced emission enhancement phenomenon of TPA is observed. By analyzing the Raman spectra at high pressure, we suggest that the molecular conformation changes under pressure are caused by the twisted dihedral angle between the benzene and the nitrogen atom, which is different from the phase transformation induced by the shearing force of grinding

Ag Nanoparticles Decorated Small-Sized AgTCNQF₄ Nanorod: Synthesis in Aqueous Solution and Its Photoinduced Charge Transfer Reactions

A kind of functional noble metal nanoparticles and metal/organic semiconductor composite nanomaterials, Ag nanoparticles (AgNPs, 6–10 nm in diameter) decorated small-sized Ag-tetracyano-<i>p</i>-tetrafluoroquinodimethane (AgTCNQF₄) nanorods (150–400 nm in length and 60–100 nm in diameter), have been successfully synthesized through a rapid microemulsion reaction between TCNQF₄ molecules and an AgNP colloid under a soft template of poly­(ethylene glycol)-<i>block</i>-poly­(propylene glycol)-<i>block</i>-poly­(ethylene glycol). The morphology, chemical structure, and elemental composition of the prepared AgNPs–AgTCNQF₄ composite nanorods were studied by transmission electron microscopy, selected-area electron diffraction, and X-ray photoelectron spectroscopy. The real-time ultraviolet–visible spectroscopy assisted with two-dimensional correlation spectroscopic analysis was employed to explore the growth of AgNPs–AgTCNQF₄ composite nanorods in microemulsion. These composite nanorods display the photoinduced charge transfer (CT) property from the monoanion (TCNQF₄^–) to dianion (TCNQF₄^2–) selectively under 532 nm light irradiation. The larger content of AgNPs on the surface of AgTCNQF₄ led to the higher conversion of dianion due to the plasmon-assisted photocatalysis. This photoelectric composite material is promising for the applications of light-writing data storage and photocatalysis

Highly Efficient Construction of Silver Nanosphere Dimers on Poly(dimethylsiloxane) Sheets for Surface-Enhanced Raman Scattering

We reported a highly efficient and low-cost way to synthesize silver nanosphere dimers on a poly­(dimethylsiloxane) (PDMS) sheet by using a stepwise upright assembly method for the “hot spots” study of surface-enhanced Raman scattering (SERS). The first silver nanoparticle (NP) layer is almost entirely embedded in PDMS, and the second-layered silver NPs directionally position the tops of the embedded particles. The analysis of the localized electric field distributions of the silver nanosphere dimer presents that the strongest electric field coupling appears at the gap of two nanospheres when the incident angle is about 45° and its intensity achieves 400 times enhancement. The SERS enhancement activity on this novel substrate was determined, and the results showed that SERS intensities on nanodimers were much stronger than those on the silver NP monolayer due to the electromagnetic field coupling of upright NP-NP. By using this novel SERS substrate, the lowest detection concentration for 4-mercaptopyridine is 4.0 × 10^–14 M

Long-Range Surface Plasmon Field-Enhanced Raman Scattering Spectroscopy Based on Evanescent Field Excitation

The purpose of this paper is to enhance Raman signals in the evanescent field by using the excitation of long-range surface plasmons (LRSPs). A four-phase Kretschmann LRSP resonance (LRSPR) setup composed of a K9 prism/MgF₂ film/silver film/water configuration was constructed. Incident angle-dependent surface-enhanced Raman scattering (SERS) spectra were measured in the evanescent field on this four-phase configuration. The SERS signal obtained under the evanescent field excitation at the LRSPR angle was 15 times higher than that collected based on the conventional SPR configuration. The experimental result also proved that the LRSPs in this evanescent field-enhanced SERS spectroscopy possessed at least 500 nm in the electric field penetration depth, which is longer than the electric field penetration depth of conventional surface plasmons

Plasmon-Driven Dynamic Response of a Hierarchically Structural Silver-Decorated Nanorod Array for Sub-10 nm Nanogaps

Plasmonic nanogaps serve as a useful configuration for light concentration and local field amplification owing to the extreme localization of surface plasmons. Here, a smart plasmonic nanogap device is fabricated by the dynamic response of an Ag decorated hierarchically structural vertical polymer nanorod array under the light irradiation. Seven nanorods in one unit bend because of plasmonic heating effect and they are centrally collected due to the attraction of the plasmon-induced polaritons, leading to the significantly enhanced local electromagnetic field at the sub-10 nm gaps among the constricted nanorod tops. Compared with tuning capillarity in microscale by wetting and drying, using light as external stimuli is much easier and more tunable in nanoscale. This plasmonic nanogap device is used for a surface-enhanced Raman scattering (SERS) substrate. Its hydrophobic surface with a contact angle of 142 degree can make the probed aqueous solution only access to the Ag tips of nanorods. Thus, the analytes can be driven to the “hot spot” regions where located at the tops of nanorods during the solvent evaporation process, which is beneficial to SERS detection. Discovery of this smart plasmon-driven process broadens the scope for further functionality of both the dynamic nanostructure design and the smart plasmonic devices in the communities of chemistry, biomedicine, and microfluidic engineering

Aptamer-Based Surface-Enhanced Raman Scattering-Microfluidic Sensor for Sensitive and Selective Polychlorinated Biphenyls Detection

A surface-enhanced Raman scattering (SERS) measurement of 3,3′,4,4′-tetrachlorobiphenyl (PCB77) with aptamer capturing in a microfluidic device was demonstrated. To construct the microfluidic chip, an ordered Ag nanocrown array was fabricated over a patterned polydimethylsiloxane (PDMS) that was achieved by replicating an anodic aluminum oxide (AAO) template. The patterned PDMS sheet was covered with another PDMS sheet having two input channel grooves to form a close chip. The Ag nanocrown array was used for the SERS enhancement area and the detection zone. PCB 77 aptamers were injected into one channel and the other allows for analytes (PCBs). The mercapto aptamers captured the targets in the mixed zone and were immobilized to the SERS detection zone via S–Ag bonds so as to further improve both the SERS sensitivity and selectivity of PCB77. Such an aptamer-based microfluidic chip realized a rapid SERS detection. The lowest detectable concentration of 1.0 × 10^–8 M was achieved for PCB77. This work demonstrates that the aptamer-modified SERS microfluidic sensor can be utilized for selective detections of organic pollutants in the environment

Active-Tuned Plasmonic Angle Modulator of Light Beams for Potential Application of 3D Display

We propose a plasmonic angle modulator device based on the extraordinary optical transmission (EOT) phenomenon combined with the liquid crystal (LC)-tuned surface plasmons (SPs). The configuration of this angle modulator mainly involves an Ag nanograting film for the SP coupling and a LC layer for continuously tuning SPs via voltage signals. Accordingly, the directions of the transmission light through the Ag nanograting film can be tuned continuously, realizing a light beam scanning in a 5° range at an operation rate of 60 Hz. We expect this active-tuned plasmonic angle modulator would have potential applications in three-dimensional (3D) display techniques that strictly require the elaborate and rapid angle modulation of light beams. In addition, this active-tuned plasmonic angle modulator can also be applied in other fields, such as photocommunication, optical detection, beam steering, and so on

A Long-Range Surface Plasmon Resonance/Probe/Silver Nanoparticle (LRSPR-P-NP) Nanoantenna Configuration for Surface-Enhanced Raman Scattering

The purpose of this paper is to enhance Raman signals with a plasmonic nanoantenna based on a long-range surface plasmon resonance/probe/silver nanoparticle (LRSPR-P-NP) sandwich configuration. The finite-difference time-domain simulation shows that the electromagnetic field at the gap between the silver film and a silver nanoparticle increases by a factor of about 2.1 × 10⁴. The resonance condition of this plasmonic nanoantenna was optimized by incident angle-dependent surface-enhanced Raman scattering (SERS) spectroscopy under an evanescent field excitation mode. The SERS signal obtained under the LRSPR-P-NP configuration at the LRSPR angle was 40 times higher than that collected on the planar film plasmonic nanoantenna. The enhancement factor of the LRSPR-P-NP configuration was 9.2 × 10⁸. This plasmonic nanoantenna was also applied for pH sensing