Plasmons in strongly coupled metallic nanostructures.

Sensitive optical biosensors for unlabeled targets: a review.

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

An approach to achieve simultaneous measurement of refractive index and temperature is proposed by using a Mach–Zehnder interferometer realized on tapered single-mode optical fiber. The attenuation peak wavelength of the interference with specific order in the transmission spectrum shifts with changes in the environmental refractive index and temperature. By utilizing S-band and C/L-band light sources, simultaneous discrimination of refractive index and temperature with the tapered fiber Mach–Zehnder interferometer is demonstrated with the corresponding sensitivities of −23.188 nm/RIU (refractive index unit) and 0.071 nm/ °C, and −26.087 nm/RIU (blueshift) and 0.077 nm/°C (redshift) for the interference orders of 169 and 144, respectively.

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Tapered fiber Mach–Zehnder interferometer for simultaneous measurement of refractive index and temperature

A Review on Surface-Enhanced Raman Scattering.

A highly sensitive liquid-level sensor based on etched fiber Bragg grating (FBG) is proposed and demonstrated. The transmission dips of FBG spectra are affected by the fraction of the length of the etched FBG that is surrounded by the liquid. The experiments show that for a liquid-level variation of 24 mm, the transmission dip difference changes about 32 dB. Also in the linear region, a high sensitivity of 2.56 dB/mm is achieved.

Highly Sensitive Liquid-Level Sensor Based on Etched Fiber Bragg Grating

Gap-plasmon-enhanced gold nanoparticle photoluminescence is studied experimentally at the single-particle level. The photoluminescence spectra of gold nanoparticles on an Al2O3-coated gold film under both 532 and 633 nm excitation show a clear peak near the measured gap-plasmon resonance wavelength. Comparing the collected emission spectrum with that from a gold reference film under 633 nm excitation, a peak photoluminescence enhancement factor of 28 000 is observed. The spectral shape and absolute magnitude of the enhancement factors for both excitation wavelengths are reproduced using numerical calculations without the use of any free parameters. The photoluminescence enhancement is explained in terms of a gap-mode-enhanced e–h pair generation rate and a wavelength-dependent enhancement of the emission efficiency.

/pdf/gap-plasmon-enhanced-gold-nanoparticle-photoluminescence-448sa03hll.pdf

Gap-Plasmon Enhanced Gold Nanoparticle Photoluminescence

Isolating and in situ profiling the heterogeneous molecular phenotype of circulating tumor cells are of great significance for clinical cancer diagnosis and personalized therapy. Herein, an on-chip strategy is proposed that combines size-based microfluidic cell isolation with multiple spectrally orthogonal surface-enhanced Raman spectroscopy (SERS) analysis for in situ profiling of cell membrane proteins and identification of cancer subpopulations. With the developed microfluidic chip, tumor cells are sieved from blood on the basis of size discrepancy. To enable multiplex phenotypic analysis, three kinds of spectrally orthogonal SERS aptamer nanovectors are designed, providing individual cells with composite spectral signatures in accordance with surface protein expression. Next, to statistically demultiplex the complex SERS signature and profile the cellular proteomic phenotype, a revised classic least square algorithm is employed to obtain the 3D phenotypic information at single-cell resolution. Combined with categorization algorithm partial least square discriminate analysis, cells from different human breast cancer subtypes can be reliably classified with high sensitivity and selectivity. The results demonstrate that this platform can identify cancer subtypes with the spectral information correlated to the clinically relevant surface receptors, which holds great potential for clinical cancer diagnosis and precision medicine.

Combining Multiplex SERS Nanovectors and Multivariate Analysis for In Situ Profiling of Circulating Tumor Cell Phenotype Using a Microfluidic Chip.

A compact and nanometric surface plasmon polariton (SPP) band-pass filter based on a rectangular ring resonator composed of metal–insulator–metal waveguides is proposed. Using the finite difference time domain method, the effects of the structure parameters on the transmission characteristics of this SPP band-pass filter are analysed in detail. The results show that the proposed SPP filter has narrow transmission peaks and the corresponding resonance wavelengths can be linearly tuned by altering the resonator's cavity length. Moreover, the transmission ratios of the pass bands can be tuned by changing the coupling gaps between the input/output MIM waveguides and the resonator. Also the metal loss and dispersion effects on the filter responses are included. The simple band-pass SPP filter is very promising for high-density SPP waveguide integrations.

https://iopscience.iop.org/article/10.1088/0022-3727/43/38/385102/pdf

Theoretical analysis of a nanoscale plasmonic filter based on a rectangular metal-insulator-metal waveguide

In this Letter, the cladding mode resonances of a chemical etch-eroded fiber Bragg grating are proposed for highly sensitive ambient refractive index sensing. The varying characteristics of several different order cladding mode resonances with ambient refractive index are explored experimentally. The maximum sensing sensitivity of 172nm∕riu for the third-order cladding mode resonance is achieved in the experiments. Under the same cladding diameter, the cladding mode resonances have narrower bandwidth and response much more sensitive to the ambient refractive index changing than conventional Bragg core mode resonance, which would enable them to achieve a higher resolution.

Binfeng Yun

Papers

Highly Sensitive Liquid-Level Sensor Based on Etched Fiber Bragg Grating

Gap-Plasmon Enhanced Gold Nanoparticle Photoluminescence

Combining Multiplex SERS Nanovectors and Multivariate Analysis for In Situ Profiling of Circulating Tumor Cell Phenotype Using a Microfluidic Chip.

Theoretical analysis of a nanoscale plasmonic filter based on a rectangular metal-insulator-metal waveguide

Cladding mode resonances of etch-eroded fiber Bragg grating for ambient refractive index sensing