All-optical tunable plasmonic nano-aggregations for surface-enhanced Raman scattering

Efficient optical plasmonic tweezer-controlled single-molecule SERS characterization of pH-dependent amylin species in aqueous milieus

It is challenging to characterize single or a few biomolecules in physiological milieus without excluding the influences of surrounding environment. Here we utilize optical plasmonic trapping to construct a dynamic nanocavity, which reduces the diffraction-limited detection volume and provides reproducible electromagnetic field enhancements to achieve high-throughput single-molecule surface-enhanced Raman spectroscopy (SERS) characterizations in aqueous environments. Specifically, we study human Islet Amyloid Polypeptide (amylin, hIAPP) under different physiological pH conditions by combining spectroscopic experiments and molecular dynamics (MD) simulations. Based on a statistically significant amount of time-dependent SERS spectra, two types of low-populated transient species of hIAPP containing either turn or β-sheet structure among its predominant helix-coil monomers are characterized during the early-stage incubation at neutral condition, which play a crucial role in driving irreversible amyloid fibril developments even after a subsequent adjustment of pH to continue the prolonged incubation at acidic condition. Our results might provide profound mechanistic insight into the pH-regulated amyloidogenesis and introduce an alternative approach for investigating complex biological processes at the single-molecule level.

Label-free plasmonic assisted optical trapping of single DNA molecules

DNA molecules are hard to catch using traditional optical trapping due to the nanometer width of their chains. Here we experimentally demonstrate a label-free optical trapping of a single micrometer λ-DNA in solution by the aid of plasmonic gold nanoparticles (GNPs), where a double-laser trap induces strong optical interparticle forces for the tweezer. We examine such sub-resolved interparticle forces by tracking the GNP dynamics in solution. Moreover, surface-enhanced Raman scattering signals of trapped λ-DNA have also been measured simultaneously in the same setup. In comparison with prior works, ours benefit from the excitation in a dynamic configuration without fabrication. This technique opens a new avenue for all-optical manipulation of biomolecules, as well as ultra-sensitive bio-medical sensing applications.

Comparative study of serum sample preparation methods in aggregation-based plasmonic sensing

The use of nanoparticle-based colorimetric methods has received considerable attention for clinical analysis in biofluids. Sample preparation methods are surveyed here to minimize the impact of the sample matrix on the performance of a nanoparticle aggregation assay.

The laser-triggered dynamical plasmonic optical trapping of targets and advanced Raman detection sensitivity

Targets can be captured at hot spots during the laser-induced agglomeration of AgNPs via dynamical plasmonic optical trapping.