quasi-3D Plasmonic Nanostructure Research Articles

Label-free detection of live cancer cells and DNA hybridization using 3D multilayered plasmonic biosensor

Three-dimensional (3D) multilayered plasmonic nanostructures consisting of Au nanosquares on top of SU-8 nanopillars, Au asymmetrical nanostructures in the middle, and Au asymmetrical nanoholes at the bottom were fabricated through reversal nanoimprint technology. Compared with two-dimensional and quasi-3D plasmonic nanostructures, the 3D multilayered plasmonic nanostructures showed higher electromagnetic field intensity, longer plasmon decay length and larger plasmon sensing area, which are desirable for highly sensitive localized surface plasmonic resonance biosensors. The sensitivity and resonance peak wavelength of the 3D multilayered plasmonic nanostructures could be adjusted by varying the offset between the top and bottom SU-8 nanopillars from 31% to 56%, and the highest sensitivity of 382 and 442 nm/refractive index unit were observed for resonance peaks at 581 and 805 nm, respectively. Live lung cancer A549 cells with a low concentration of 5 × 103 cells ml−1 and a low sample volume of 2 μl could be detected by the 3D multilayered plasmonic nanostructures integrated in a microfluidic system. The 3D plasmonic biosensors also had the advantages of detecting DNA hybridization by capturing the complementary target DNA in the low concentration range of 10−14–10−7 M, and providing a large peak shift of 82 nm for capturing 10−7 M complementary target DNA without additional signal amplification.

High sensitivity plasmonic biosensor based on nanoimprinted quasi 3D nanosquares for cell detection

Quasi three-dimensional (3D) plasmonic nanostructures consisting of Au nanosquares on top of SU-8 nanopillars and Au nanoholes on the bottom were developed and fabricated using nanoimprint lithography with simultaneous thermal and UV exposure. These 3D plasmonic nanostructures were used to detect cell concentration of lung cancer A549 cells, retinal pigment epithelial (RPE) cells, and breast cancer MCF-7 cells. Nanoimprint technology has the advantage of producing high uniformity plasmonic nanostructures for such biosensors. Multiple resonance modes were observed in these quasi 3D plasmonic nanostructures. The hybrid coupling of localized surface plasmon resonances and Fabry–Perot cavity modes in the quasi 3D nanostructures resulted in high sensitivity of 496 nm/refractive index unit. The plasmonic resonance peak wavelength and sensitivity could be tuned by varying the Au thickness. Resonance peak shifts for different cells at the same concentration were distinct due to their different cell area and confluency. The cell concentration detection limit covered a large range of 5 × 102 to 1 × 107 cells ml−1 with these new plasmonic nanostructures. They also provide a large resonance peak shift of 51 nm for as little as 0.08 cells mm−2 of RPE cells for high sensitivity cell detection.

Investigation of a quasi-3D plasmonic nanostructure for TE and TM polarizations

Quasi-3D plasmonic nanostructures consisting of a metallic film perforated as an array of nanoholes, separated by a gap from a nanodisk array, are theoretically investigated under plane wave illumination with transverse electric and transverse magnetic polarizations. The results are compared with the results of a simple nanodisk array. A full discussion involving the couplings between plasmon resonance in nanodisks, surface plasmon polaritons on the interfaces of metallic film, and different diffractive grating orders that contribute in the couplings will be presented. The large difference between the plasmon behavior of the nanodisk array alone and nanodisk array in the presence of nanohole array will be fully investigated.

Tuning multiple Fano and plasmon resonances in rectangle grid quasi-3D plasmonic-photonic nanostructures

Plasmonic and photonic nanostructures can manipulate light-matter interaction, leading to a wide range of tunable properties. Here, we show that multiple Fano and plasmon resonances can be generated in quasi-3D plasmonic nanostructure arrays on rectangle grid photonic nanostructure substrates. The Fano resonances are the quasiguided modes coupled with the plasmon resonance while the distinct plasmon resonances are the localized surface plasmon resonances of the top gold thin film with sub-wavelength nanohole array and the bottom gold nanodisk array. The Fano and plasmon resonances can be tuned separately and selectively by changing the dimension of photonic and plasmonic nanostructures.

X-shaped quasi-3D plasmonic nanostructure arrays for enhancing electric field and Raman scattering

We propose and demonstrate strongly enhancing electric field and Raman scattering with a large tolerance to the light incident angle and polarization by using x-shaped quasi-3D plasmonic nanostructure arrays (X-Q3D-PNAs). The finite-difference time-domain simulations were used to study the reflectance spectra and electric field profiles of X-Q3D-PNAs. Results show that both surface plasmon polaritons and localized surface plasmon polaritons (LSPPs) can be generated at the metal/dielectric interfaces of the top gold thin film with square grating x-shaped nanoholes. The resonance of the LSPPs generated at the gold islands formed between x-shaped nanoholes at the top gold thin film greatly enhance the electric fields at the tips of the cross-sectors of the x-shaped nanoholes. Both plasmon resonances and electric field enhancements are affected by the structural dimensions. The strong electric field enhancement and the large tolerance to the laser polarization were demonstrated by surface-enhanced Raman scattering experiments. This unique plasmonic property of X-Q3D-PNAs could be attractive for photovoltaics and biosensing applications.

Understanding the effects of dielectric medium, substrate, and depth on electric fields and SERS of quasi-3D plasmonic nanostructures

The local electric field distribution and the effect of surface-enhanced Raman spectroscopy (SERS) were investigated on the quasi-3D (Q3D) plasmonic nanostructures formed by gold nanohole and nanodisc array layers physically separated by a dielectric medium. The local electric fields at the top gold nanoholes and bottom gold nanodiscs as a function of the dielectric medium, substrate, and depth of Q3D plasmonic nanostructures upon the irradiation of a 785 nm laser were calculated using the three-dimensional finite-difference time-domain (3D-FDTD) method. The intensity of the maximum local electric fields was shown to oscillate with the depth and the stronger local electric fields occurring at the top or bottom gold layer strongly depend on the dielectric medium, substrate, and depth of the nanostructure. This phenomenon was determined to be related to the Fabry-Pérot interference effect and the interaction of localized surface plasmons (LSPs). The enhancement factors (EFs) of SERS obtained from the 3D-FDTD simulations were compared to those calculated from the SERS experiments conducted on the Q3D plasmonic nanostructures fabricated on silicon and ITO coated glass substrates with different depths. The same trend was obtained from both methods. The capabilities of tuning not only the intensity but also the location of the maximum local electric fields by varying the depth, dielectric medium, and substrate make Q3D plasmonic nanostructures well suited for highly sensitive and reproducible SERS detection and analysis.

Light Transmission and Surface-Enhanced Raman Scattering of Quasi-3D Plasmonic Nanostructure Arrays with Deep and Shallow Fabry-Pérot Nanocavities

Light transmission and surface-enhanced Raman scattering (SERS) of quasi-3D plasmonic nanostructure arrays with deep (820 nm) and shallow (80 nm) Fabry-Perot (FP) nanocavities were investigated exp...

Surface-enhanced Raman scattering on gold quasi-3D nanostructure and 2D nanoholearrays

A new method was developed to fabricate unique gold quasi-3D plasmonic nanostructures onpoly(dimethylsiloxane) PDMS and 2D nanohole arrays on silicon as surface-enhanced Ramanscattering (SERS) substrates using electron beam lithography (EBL) with negative tone resistMa–N 2403 and soft lithography. The size and shape of nanopillars fabricated by EBL werewell controlled via different beam conditions. An enhancement factor (EF) as high as6.4 × 105 was obtained for 4-mercaptopyridine molecules adsorbed on the gold quasi-3Dnanostructure array on PDMS with 400 nm diameter, 100 nm spacing and 300 nm depth,while no enhancement was observed for the gold 2D nanohole array on siliconwith the same diameter and spacing. The experimental results were confirmed byfinite-difference time-domain (FDTD) calculations. Furthermore, the calculatedtotal electric fields showed that the strong SERS exhibited by the gold quasi-3Dnanostructure arrays on PDMS is due to the strong localized electric fields atthe gold–air interface of the bottom gold nanodisc. The strong and reproducibleSERS spectroscopy for molecules adsorbed on precisely controlled gold quasi-3Dnanostructure arrays on PDMS makes it possible for the integration of SERS-activenanopatterns into microfluidic devices as chemical and biological sensors with molecularspecificity.