PSA Detection with Femtomolar Sensitivity and a Broad Dynamic Range Using SERS Nanoprobes and an Area-Scanning Method

Recently, surface-enhanced Raman scattering (SERS)-based immunoassays (SIA) have drawn much attention as diagnostic tools with large multiplex capacity and high sensitivity. However, several challengessuch as a low reproducibility, a time-consuming read-out process, and limited dynamic rangeremain. In this study, we report a reliable and sensitive SIA platform for prostate specific antigen (PSA) detection. Reliability and sensitivity were achieved by two approaches: (1) well-established SERS probes, so-called SERS dots that have high sensitivity (single particle detection) and little particle-to-particle variation in SERS intensity; and (2) a whole area-scanning readout method for rapid and reliable chip analysis rather than point scanning. As a feasibility test, PSA could be detected with high sensitivity (ca. 0.11 pg/mL, 3.4 fM LOD), with a wide dynamic range (0.001–1000 ng/mL). Thus, the developed platform will facilitate development of reliable immunoassays with high sensitivity and a wide dynamic range

Ag Shell–Au Satellite Hetero-Nanostructure for Ultra-Sensitive, Reproducible, and Homogeneous NIR SERS Activity

It is critical to create isotropic hot spots in developing a reproducible, homogeneous, and ultrasensitive SERS probe. Here, an Ag shell–Au satellite (Ag–Au SS) nanostructure composed of an Ag shell and surrounding Au nanoparticles was developed as a near-IR active SERS probe. The heterometallic shell-satellite structure based SERS probe produced intense and uniform SERS signals (SERS enhancement factor ∼1.4 × 10⁶ with 11% relative standard deviation) with high detectability (100% under current measurement condition) by 785 nm photoexcitation. This signal enhancement was independent of the laser polarizations, which reflects the isotropic feature of the SERS activity of Ag–Au SS from the three-dimensional (3D) distribution of SERS hot spots between the shell and the surrounding satellite particles. The Ag–Au SS nanostructure shows a great potential as a reproducible and quantifiable NIR SERS probe for in vivo targets

Plasmon-Enhanced Sub-Bandgap Photocatalysis via Triplet–Triplet Annihilation Upconversion for Volatile Organic Compound Degradation

This study demonstrates the first reported photocatalytic decomposition of an indoor air pollutant, acetaldehyde, using low-energy, sub-bandgap photons harnessed through sensitized triplet–triplet annihilation (TTA) upconversion (UC). To utilize low-intensity noncoherent indoor light and maximize photocatalytic activity, we designed a plasmon-enhanced sub-bandgap photocatalyst device consisting of two main components: (1) TTA-UC rubbery polymer films containing broad-band plasmonic particles (Ag-SiO₂) to upconvert sub-bandgap photons, and (2) nanodiamond (ND)-loaded WO₃ as a visible-light photocatalyst composite. Effective decomposition of acetaldehyde was achieved using ND/WO₃ (<i>E</i>_g = 2.8 eV) coupled with TTA-UC polymer films that emit blue photons (λ_Em = 425 nm, 2.92 eV) upconverted from green photons (λ_Ex = 532 nm, 2.33 eV), which are wasted in most environmental photocatalysis. The overall photocatalytic efficiency was amplified by the broad-band surface plasmon resonance of AgNP-SiO₂ particles incorporated into the TTA-UC films

Double-Layer Magnetic Nanoparticle-Embedded Silica Particles for Efficient Bio-Separation

<div><p>Superparamagnetic Fe₃O₄ nanoparticles (NPs) based nanomaterials have been exploited in various biotechnology fields including biomolecule separation. However, slow accumulation of Fe₃O₄ NPs by magnets may limit broad applications of Fe₃O₄ NP-based nanomaterials. In this study, we report fabrication of Fe₃O₄ NPs double-layered silica nanoparticles (DL MNPs) with a silica core and highly packed Fe₃O₄ NPs layers. The DL MNPs had a superparamagnetic property and efficient accumulation kinetics under an external magnetic field. Moreover, the magnetic field-exposed DL MNPs show quantitative accumulation, whereas Fe₃O₄ NPs single-layered silica nanoparticles (SL MNPs) and silica-coated Fe₃O₄ NPs produced a saturated plateau under full recovery of the NPs. DL MNPs are promising nanomaterials with great potential to separate and analyze biomolecules.</p></div

Thin silica shell coated Ag assembled nanostructures for expanding generality of SERS analytes

<div><p>Surface-enhanced Raman scattering (SERS) provides a unique non-destructive spectroscopic fingerprint for chemical detection. However, intrinsic differences in affinity of analyte molecules to metal surface hinder SERS as a universal quantitative detection tool for various analyte molecules simultaneously. This must be overcome while keeping close proximity of analyte molecules to the metal surface. Moreover, assembled metal nanoparticles (NPs) structures might be beneficial for sensitive and reliable detection of chemicals than single NP structures. For this purpose, here we introduce thin silica-coated and assembled Ag NPs (SiO₂@Ag@SiO₂ NPs) for simultaneous and quantitative detection of chemicals that have different intrinsic affinities to silver metal. These SiO₂@Ag@SiO₂ NPs could detect each SERS peak of aniline or 4-aminothiophenol (4-ATP) from the mixture with limits of detection (LOD) of 93 ppm and 54 ppb, respectively. E-field distribution based on interparticle distance was simulated using discrete dipole approximation (DDA) calculation to gain insight into enhanced scattering of these thin silica coated Ag NP assemblies. These NPs were successfully applied to detect aniline in river water and tap water. Results suggest that SiO₂@Ag@SiO₂ NP-based SERS detection systems can be used as a simple and universal detection tool for environment pollutants and food safety.</p></div

FITC-streptavidin separation using biotin-conjugated DL MNPs and bare DL MNPs.

<p>Fluorescence and optical microscopic images of (a, b) biotin-conjugated DL MNPs and (c, d) bare DL MNPs after incubation with FITC-streptavidin and magnet-induced separation. Arrows indicate the detected NPs.</p

Magnetic properties of the prepared magnetic NPs.

<p>a) Accumulation profiles for the DL MNPs (red), SL MNPs (blue), and the silica-coated Fe₃O₄ NPs (black). b) Hysteresis loop of the DL MNPs.</p

Transmission electron microscopic (TEM) images of the prepared magneticNPs.

<p>Images of (a) Fe₃O₄ NPs-immobilized SiO₂ NPs, (b) SL MNPs, (c) Fe₃O₄ NPs-immobilized SL MNPs, and (d) DL MNPs.</p

Limit of detection analysis with two different molecule.

<p>Limit of detection of (a) aniline, (b) 4-ATP at various concentrations based on their corresponding surface-enhanced Raman scattering (SERS) signals using SiO₂@Ag@SiO₂ NPs. All Raman spectra were measured at laser power of 10 mW with acquisition time of 10 s. Intensities were normalized to Raman intensity of ethanol peak at 882 cm⁻¹.</p

Synthetic scheme for the Fe₃O₄ nanoparticles single-layered nanoparticles (SL MNPs) and double-layered nanoparticles (DL MNPs).

<p>Fe₃O₄ NPs are immobilized to catechol-modified silica NPs; then, SL MNPs are prepared by silica-shell encapsulation. DL MNPs are prepared by repeating the aforementioned method to catechol-modified SL MNPs.</p