Microsurface plasmon resonance biosensing based on gold-nanoparticle film

Accurate and fast modeling of scattering from random arrays of nanoparticles using the discrete dipole approximation and angular spectrum method

Lens-free microscopes can utilize holographic reconstruction techniques to recover the image of an object from the digitally recorded superposition of an unperturbed plane wave and a wave scattered by the object. Image reconstruction most commonly relies on the scalar angular spectrum method (ASM). While fast, the scalar ASM can be inaccurate for nanoscale objects, either because of the scalar approximation, or more generally, because it only models field propagation and not light-matter interaction, including inter-particle coupling. Here we evaluate the accuracy of the scalar ASM when combined with three different light-matter interaction models for computing the far-field light scattered by random arrays of gold and polystyrene nanoparticles. Among the three models-a dipole-matched transmission model, an optical path length model, and a binary amplitude model-we find that which model is most accurate depends on the nanoparticle material and packing density. For polystyrene particles at any packing density, there is always at least one model with error below 20%, while for gold nanoparticles with 40% or 50% surface coverage, there are no models that can provide errors better than 30%. The ASM error is determined in comparison to a discrete dipole approximation model, which is more computationally efficient than other full-wave modeling techniques. The knowledge of when and how the ASM fails can serve as a first step toward improved resolution in lens-free reconstruction and can also be applied to other random nanoparticle array applications such as lens-based super-resolution imaging, sub-diffraction beam focusing, and biomolecular sensing.

Plasmon field enhancement in silver core-protruded silicon shell nanocylinder illuminated with light at 633 nm

We show, to the best of our knowledge, the first simulation result of the strong plasmonic field coupling and enhancement at the Ag/Si interface of a silver core/protruded silicon shell nanocylinder by using the finite-element method. The strong plasmon field, with a slow effective phase velocity accumulated at the Ag/Si interface, which results from the large effective index of the surface plasmon due to the nearly identical real parts with opposite signs of the permittivities of silver and silicon at 633 nm, is analyzed. When the silicon shell has shallow protrusions of proper periodicity to meet the phase matching condition between the incident light and the surface plasmon wave at the Ag/Si interface, a higher scattered electric field and a higher sensitivity to the refractive index change of the surrounding medium can be achieved. Furthermore, a feasible implementation of the core-shell nanocylinder design concept is studied and discussed.

Detection of gold nanoparticles using an immunoglobulin-coated piezoelectric sensor

Since the existence of nanoparticles in our environment has already attracted considerable attention due to their possible toxic impact on biological systems, the field detection of nanoparticles is becoming a technology that will be much in need. We have constructed a piezoelectric sensor with an antibody-coated electrode. The antiserum can bind gold nanoparticles with a high degree of selectivity and sensitivity. The biosensor thus constructed can detect 4, 5, or 6 nm gold nanoparticles (GNPs) depending on the coated antiserum. The sensitivity for the detection of 5 nm GNPs was 10.3 ± 0.9 ng Hz(-1), with the low limit of detection at 5.5 ng. A quartz crystal microbalance (QCM) sensor was capable of detecting GNPs and other types of nanoparticle, such as ZnO, or Fe(3)O(4). The current study provides, for the first time, a platform for detecting nanoparticles in a convenient, economical manner.

Label-free and dynamic detection of biomolecular interactions for high-throughput microarray applications

Direct monitoring of primary molecular-binding interactions without the need for secondary reactants would markedly simplify and expand applications of high-throughput label-free detection methods. A simple interferometric technique is presented that monitors the optical phase difference resulting from accumulated biomolecular mass. As an example, 50 spots for each of four proteins consisting of BSA, human serum albumin, rabbit IgG, and protein G were dynamically monitored as they captured corresponding antibodies. Dynamic measurements were made at 26 pg/mm(2) SD per spot and with a detectable concentration of 19 ng/ml. The presented method is particularly relevant for protein microarray analysis because it is label-free, simple, sensitive, and easily scales to high-throughput.

Label-Free Detection of Peptide Nucleic Acid−DNA Hybridization Using Localized Surface Plasmon Resonance Based Optical Biosensor

The development of label-free optical biosensors for DNA and other biomolecules has the potential to impact life sciences as well as screening in medical and environmental applications. In this report, we developed a localized surface plasmon resonance (LSPR) based label-free optical biosensor based on a gold-capped nanoparticle layer substrate immobilized with peptide nucleic acids (PNAs). PNA probe was designed to recognize the target DNA related to tumor necrosis factor. The nanoparticle layer was formed on a gold-deposited glass substrate by the surface modified silica nanoparticles using silane-coupling reagent. The optical properties of gold-capped nanoparticle layer substrate were characterized through monitoring the changes in the absorbance strength, as the thickness of the biomolecular layer increased with hybridization. The detection of PNA-DNA hybridization with target oligonucleotides and PCR-amplified real samples were performed with a limit of detection value of 0.677 pM target DNA. Selective discrimination against a single-base mismatch was also achieved. Our LSPR-based biosensor with the gold-capped nanoparticle layer substrate is applicable to the design of biosensors for monitoring of the interaction of other biomolecules, such as proteins, whole cells, or receptors with a massively parallel detection capability in a highly miniaturized package.