Shaoli Zhu

Optical properties and immunoassay applications of noble metal nanoparticles

Noble metal, especially gold (Au) and silver (Ag) nanoparticles exhibit unique and tunable optical properties on account of their surface plasmon resonance (SPR). In this paper, we mainly discussed the theory background of the enhanced optical properties of noble metal nanoparticles. Mie theory, transfer matrix method, discrete dipole approximation (DDA) method, and finite-difference time domain (FDTD) method applied brute-force computational methods for different nanoparticles optical properties. Some important nanostructure fabrication technologies such as nanosphere lithography (NSL) and focused ion beam (FIB) are also introduced in this paper. Moreover, these fabricated nanostructures are used in the plasmonic sensing fields. The binding signal between the antibody and antigen, amyloid-derived diffusible ligands (ADDLs)-potential Alzheimers disease (AD) biomarkers, and staphylococcal enterotixn B (SEB) in nano-Moore per liter (nM) concentration level are detected by our designed nanobiosensor. They have many potential applications in the biosensor, environment protection, food security, and medicine safety for health, and so forth, fields.

Hybrid metallic nanoparticles for excitation of surface plasmon resonance

A Ag nanostructure was put forward in this paper. There are two types of Ag nanoparticles, spherical and pyramidal particles. Both of them have the same period, but different height and shapes. The hybrid nanoparticles can produce the localized surface plasmon resonance (LSPR), which couples each other and leads to an extra peak transmission. Our UV-visible-IR spectrophotometer measurement results show that some extra small and sharp peaks appear besides the normal LSPR wave peaks in the transmittance spectrum. The hybrid Ag nanoparticles being used as nanosensors will be more sensitive and selective than the conventional LSPR-based nanosensors.

Split of surface plasmon resonance of gold nanoparticles on silicon substrate: a study of dielectric functions

The split of surface plasmon resonance of self-assembled gold nanoparticles on Si substrate is observed from the dielectric functions of the nanoparticles. The split plasmon resonances are modeled with two Lorentz oscillators: one oscillator at ~1 eV models the polarization parallel to the substrate while the other at ~2 eV represents the polarization perpendicular to the substrate. Both parallel and perpendicular resonances are red-shifted when the nanoparticle size increases. The red shifts in both resonances are explained by the image charge effect of the Si substrate.

Hybridization of localized surface plasmon resonance-based Au-Ag nanoparticles

The hybrid Au–Ag triangular nanoparticles were proposed for the purpose of biosensing. To construct the nanoparticles, an Au thin film was deposited on top of the Ag nanoparticles supported with glass substrate. The hybrid nanoparticles can prevent oxidation of the pure Ag nanoparticles due to the Au protective layer caped on the Ag nanoparticles. The hybrid nanoparticles were designed using finite-difference and time-domain algorithm. Extinction spectra of the hybrid nanoparticles excited by visible light beam with plane wave were calculated, and the corresponding electric fields at peak position of the extinction spectra were expressed also. It is clear that the hybrid nanoparticles can excite the localized surface plasmon resonance wave which can be used to detect biomolecules. As an application example, we presented relevant detection results by means of using protein A to covalently link surface of the hybrid nanoparticles. Refractive index sensitivity of the hybrid nanoparticles was derived through both computational numerical calculation and experimental detection. Both the calculated and the experimental extinction spectra show that the hybrid Au–Ag nanoparticles are useful for detecting the biomolecules.

Novel bio-nanochip based on localized surface plasmon resonance spectroscopy of rhombic nanoparticles.

A new silver (Ag) nanostructure with a rectangular distribution array composed of rhombic nanoparticles is described here. The structure has an apparent advantage of strong hot spots that have a much higher signal intensity than that of the previously reported traditional triangular structures. It generates a great enhancement of a localized surface plasmon resonance (LSPR) effect. Moreover, an antigen with longer arm length is applied to strengthen the binding signals of both the antigen and antibody. We performed experiments for the LSPR-induced extinction spectra in each step of the surface modification of the Ag nanoparticles in atmosphere environment. A spectrophotometer was used to measure the extinction spectrum of our proposed nanochip. The results obtained indicate a better sensitivity for our current nanochip than that of the other reported LSPR-based nanochips. Theoretical computational numerical simulation is also carried out with a discrete dipole approximation algorithm. Our computational results are in agreement with the corresponding experimental spectrum. This type of nanochip may have potential utility in many applications, including medical science, biological fields and biochemical analysis.

Optical Properties of Gold Nanoparticles on Heavily-Doped Si Substrate Synthesized with an Electrochemical Process

Gold nanoparticles on a heavily-doped Si substrate were synthesized through direct electroreduction of bulk AuCl 4 ― ions. The optical properties of the nanoparticles were determined from ellipsometric analysis. The Lorentz-Drude model was used to represent the effective dielectric function of the gold nanoparticles. A prominent peak at ∼ 1.7 eV is identified in the imaginary part e 2 , which is attributed to the surface plasmon resonance. There are also two minor peaks located at ∼ 3.1 and ∼ 4.2 eV, respectively, which are related to the interband transitions. The interband transitions are greatly suppressed, which could be due to the modified lattice structures of the nanoparticles.

Topical review: design, fabrication, and applications of hybrid nanostructured array

Nanohybrid materials have been widely used in the material chemistry research areas. In this paper, we mainly discussed the hybrid nanostructures used for nanobiosensor applications. It is one of the most promising and rapidly emerging research areas in nanotechnology field. Design, fabrication, and applications of hybrid nanostructures are reviewed, respectively. Finite difference time domain (FDTD) methods are applied to design different materials of hybrid nanostructures. Nanosphere lithography (NSL) is used to fabricate our designed hybrid nanostructures. Moreover, protein A and staphylococcal enterotoixn B (SEB), an enterotoxin, are detected by our designed hybrid nanostructures. From all the experiment results, we can see that our designed hybrid nanostructures are one of important nanohybrid materials. They have many potential applications in the nanobiosensor in the future.

Effect of femtosecond laser irradiation on structure of UV grade fused silica

A p-polarized femtosecond laser beam was used to irradiate a UV grade fused silica to create microchannels, which are useful for producing optical gratings or micro fluidics devices. The laser irradiated surface was characterized using optical microscope, stylus profiler, SEM, XRD and TEM. A special technique was used to protect the laser irradiated surfaces in preparing cross-sectional TEM samples. The XRD spectra and TEM observation reveal that structure of the fused silica remain amorphous after the femtosecond laser irradiation.

RHOMBIC SILVER NANOPARTICLES ARRAY-BASED PLASMONIC FILTER

A plasmonic filter applied invisible regime is proposed. A method using discrete dipole approximation (DDA) to aid design parameters of rhombic Ag nanoparticle array is adopted for the filter design and optimization on the basis of computational numerical calculation. Influence of the particle parameters such as thickness, period and effective index of medium around the particles on the extinction spectrum is studied using the DDA-based computational analysis. The calculation results show that the thickness ranging from 35 to 45 nm and the period ranging from 350 to 560 nm are the better geometrical parameters of the rhombic Ag nanoparticle array. Considering the nano-fabrication condition, 40 nm thickness and 440 nm period were selected and fabricated using nanosphere lithography (NSL) technique. The experimental results demonstrated that the measured spectrum is basically in agreement with the theoretical spectrum derived by the DDA calculation.

Key technologies for LSPR-sensing microfluidic biochip

New structures of micro-pump, biosensor in LOC (Lab-on-a-Chip) are studied. A round-path-chamber pumping principle is proposed to depress output fluctuation and increase output pressure of micro valve-less mechanical pump. Its prototype produces higher output pressure than the one with traditional column chamber. Two types of metal nanostructure array for LSPR (Localized Surface Plasmonic Resonance) biosensor were fabricated and tested, showing high sensitivity. Micro-channel is also discussed for realizing laminar flow above the metal nano-particles, to enable analytic samples to contact the metal nano-particles fully and stably.