Photothermal Spectro-Microscopy as Benchmark for Optoplasmonic Bio-Detection Assays

Abstract

Optoplasmonic bio-detection assays commonly probe the response of plasmonic nanostructures to changes in their dielectric environment. The accurate detection of nanoscale entities such as virus particles, micelles and proteins requires optimization of multiple experimental parameters. Performing such optimization directly via analyte recognition is often not desirable or feasible, especially if the nanostructures exhibit limited numbers of analyte binding sites and if binding is irreversible. Here we introduce photothermal spectro-microscopy as a benchmarking tool for the characterization and optimization of optoplasmonic detection assays.

Burst-by-Burst Measurement of Rotational Diffusion at Nanosecond Resolution Reveals Hot-Brownian Motion and Single-Chain Binding

“…Rotational Diffusion and Scattering. We performed our experiments using the custom-made confocal microscope (see a simplified sketch in Figure 1a) we had previously utilized for photothermal benchmarking of plasmonic biodetection assays 31 and the fast plasmonic detection of single diffusing proteins on nanosecond timescales. 32 In order to obtain a darkfield-like configuration, we focus the laser into a plane several micrometers away from any interface.…”

Exploring Rotational Diffusion with Plasmonic Coupling

“…The measurement setup has been discussed earlier , and is built around the oil-immersion objective of a confocal microscope (see scheme in Section S2). To measure the fast and weak signals from small diffusing rods, we measure intensity variations in the dark-field scattering by the sensor GNR upon diffusion of rods in its near field.…”

“…As shown in Figure a, the sensor GNR (112 × 40 nm 2 , see the Methods section for details) is immobilized on a glass coverslip in a flow cell. We probe the sensor GNR with linearly polarized light along its long axis and record the scattering time trace with an analyzer in the same orientation. , Suspensions of diffusing rods with 5.0 ± 0.5 nm diameter and three different lengths (15.5, 19.2, and 24.6 nm, see Section S3) were injected into the flow cell consecutively, keeping the same sensor GNR. We chose the incident laser power (38 μW) low enough to avoid any reshaping of the sensor GNR during our measurements, which could extend up to hours (see Section S4).…”

Thousand-Fold Enhancement of Photothermal Signals in Near-Critical CO2

“…Although most single-molecule studies are so far based on fluorescence, in the last few decades several fluorescence-free approaches , have been developed. Among them, photothermal (PT) microscopy − has shown strong promise. The sensitivity of PT microscopy enables the detection of the absorption of a single 1 nm gold nanoparticle (AuNP) and of single non-fluorescent molecules at room temperature.…”