Plasmonic-polymer hybrid hollow microbeads for surface-enhanced Raman scattering (SERS) ultradetection

DNA-induced assembly of gold nanoprisms and polystyrene beads into 3D plasmonic SERS substrates

The utilization of nanoparticle-polymer bead hybrid nanostructures as a SERS substrate depends on the control of the deposition, density, and distribution of nanoparticles on the bead surface. Here we demonstrate the fabrication of a large area SERS substate via a two- step DNA mediated assembly of gold nanoprisms and polystyrene (PS) beads into a large ensemble of beads that are densely coated with nanoprisms. First, nanoprisms are loaded on PS beads through DNA hybridization. The close packed arrangement of anisotropic nanoprisms in different orientations on a bead surface results in a plasmonic substrate with a variable nanogap size ranging 1-20 nm. Nanoprisms-coated beads are then assembled into a large stack or aggregate of beads using a DNA-induced crystallization approach. Each aggregate consists of 20-50 nanoprisms-coated beads, leading to the formation a large area of three-dimensional SERS substrate with a high-density of hot spots for SERS enhancement. An excellent enhancement factor (EF) of [Formula: see text] and a very high detection sensitivity (up to 10^-10 M) are observed for the analysis of a probe molecule (Methylene blue) using the SERS substrate.

Ratiometric optical nanoprobes enable accurate molecular detection and imaging

Exploring and understanding biological and pathological changes are of great significance for early diagnosis and therapy of diseases. Optical sensing and imaging approaches have experienced major progress in this field. Particularly, an emergence of various functional optical nanoprobes has provided enhanced sensitivity, specificity, targeting ability, as well as multiplexing and multimodal capabilities due to improvements in their intrinsic physicochemical and optical properties. However, one of the biggest challenges of conventional optical nanoprobes is their absolute intensity-dependent signal readout, which causes inaccurate sensing and imaging results due to the presence of various analyte-independent factors that can cause fluctuations in their absolute signal intensity. Ratiometric measurements provide built-in self-calibration for signal correction, enabling more sensitive and reliable detection. Optimizing nanoprobe designs with ratiometric strategies can surmount many of the limitations encountered by traditional optical nanoprobes. This review first elaborates upon existing optical nanoprobes that exploit ratiometric measurements for improved sensing and imaging, including fluorescence, surface enhanced Raman scattering (SERS), and photoacoustic nanoprobes. Next, a thorough discussion is provided on design strategies for these nanoprobes, and their potential biomedical applications for targeting specific biomolecule populations (e.g. cancer biomarkers and small molecules with physiological relevance), for imaging the tumor microenvironment (e.g. pH, reactive oxygen species, hypoxia, enzyme and metal ions), as well as for intraoperative image guidance of tumor-resection procedures.