A Nanoscale Optical Biosensor:  Sensitivity and Selectivity of an Approach Based on the Localized Surface Plasmon Resonance Spectroscopy of Triangular Silver Nanoparticles

Abstract

Triangular silver nanoparticles ( approximately 100 nm wide and 50 nm high) have remarkable optical properties. In particular, the peak extinction wavelength, lambda(max) of their localized surface plasmon resonance (LSPR) spectrum is unexpectedly sensitive to nanoparticle size, shape, and local ( approximately 10-30 nm) external dielectric environment. This sensitivity of the LSPR lambda(max) to the nanoenvironment has allowed us to develop a new class of nanoscale affinity biosensors. The essential characteristics and operational principles of these LSPR nanobiosensors will be illustrated using the well-studied biotin-streptavidin system. Exposure of biotin-functionalized Ag nanotriangles to 100 nM streptavidin (SA) caused a 27.0 nm red-shift in the LSPR lambda(max). The LSPR lambda(max) shift, DeltaR/DeltaR(max), versus [SA] response curve was measured over the concentration range 10(-)(15) M < [SA] < 10(-)(6) M. Comparison of the data with the theoretical normalized response expected for 1:1 binding of a ligand to a multivalent receptor with different sites but invariant affinities yielded approximate values for the saturation response, DeltaR(max) = 26.5 nm, and the surface-confined thermodynamic binding constant K(a,surf) = 10(11) M(-)(1). At present, the limit of detection (LOD) for the LSPR nanobiosensor is found to be in the low-picomolar to high-femtomolar region. A strategy to amplify the response of the LSPR nanobiosensor using biotinylated Au colloids and thereby further improve the LOD is demonstrated. Several control experiments were performed to define the LSPR nanobiosensor's response to nonspecific binding as well as to demonstrate its response to the specific binding of another protein. These include the following: (1) electrostatic binding of SA to a nonbiotinylated surface, (2) nonspecific interactions of prebiotinylated SA to a biotinylated surface, (3) nonspecific interactions of bovine serum albumin to a biotinylated surface, and (4) specific binding of anti-biotin to a biotinylated surface. The LSPR nanobiosensor provides a pathway to ultrasensitive biodetection experiments with extremely simple, small, light, robust, low-cost instrumentation that will greatly facilitate field-portable environmental or point-of-service medical diagnostic applications.

Large‐Area Low‐Cost Plasmonic Nanostructures in the NIR for Fano Resonant Sensing

“…Among the many unique features of plasmonic structures, this fi eld enhancement phenomenon has inspired researchers to construct refractive index sensors that utilize localized surface plasmon resonances (LSPRs). [1][2][3] Complex metallic nanostructures are able to support bright as well as dark optical modes. [ 4 ] When designed with the appropriate geometry and symmetry, metallic nanostructures have the potential to exhibit narrow Fano resonances due to destructive interference of the different modes.…”

Surface Patterning with Colloidal Monolayers

“…In the simplest case, a drop of the colloidal dispersion is placed on a substrate (typically glass or silicon wafer) and after evaporation, areas covered with a close-packed monolayer are obtained. [45][46][47] Pioneered by the Nagayama group in the 1990s, this method has been extensively employed to study the fundamental mechanism of the crystallization process. A two stage mechanism was proposed.…”

“…[277][278] Only recently, this problem has started to attract attention and first solutions have been proposed. [45,279] Nanoparticles have been anchored to small holes in the substrates and the decrease in signal intensity over one hour improved from 50% loss in untreated samples to 13% loss for surface anchored particles. [279] Next to stability, the reusability of the architecture is important for possible applications, however rarely discussed in literature.…”

Selective synthesis of hexagonal Ag nanoplates in a solution-phase chemical reduction process

“…The flask was kept in an ice-water bath to maintain a low temperature between 4 and 10 °C . To this flask was added 2.0 mL of a freshly prepared mixture of 1.4 mL water, 0.2 mL N 2 H 4 ·H 2 O aqueous solution (0.2 mol/L), 0.2 mL NH 4 Cl aqueous solution (0.5 mmol/L) and 0.2 mL HNO 3 aqueous solution (0.1 mol/L). This mixture is known as the reduction solution.…”

“…Among the multipolar resonant modes, the in-plane dipole resonance peak is found to be very intense and sensitive to the particle size and aspect ratio, as well as to the surrounding medium, which allows the extinction wavelength to be tuned from the visible to the near-IR region [2,3]. The sensitivity of the in-plane resonance peak to changes in the surrounding medium has been utilized in biological and chemical sensing of, e.g., proteins [4], polypeptides [5], anti-biotin [6] or carbohydrates [7]. The surface plasmons of an Ag nanoplate can also enhance the evanescent waves of a separated object.…”