Abstract
We describe the development and performance of a new type of optical sensor suitable for registering the binding/dissociation of nanoscopic particles near a gold sensing surface. The method shares similarities with surface plasmon resonance microscopy but uses a completely different optical signature for reading out binding events. This new optical read-out mechanism, which we call confined optical field enhanced fluorescence emission (Cofefe), uses pulsed surface plasmon polariton fields at the gold/liquid interface that give rise to confined optical fields upon binding of the target particle to the gold surface. The confined near-fields are sufficient to induce two-photon absorption in the gold sensor surface near the binding site. Subsequent radiative recombination of the electron-hole pairs in the gold produces fluorescence emission, which can be captured by a camera in the far-field. Bound nanoparticles show up as bright confined spots against a dark background on the camera. We show that the Cofefe sensor is capable of detecting gold and silicon nanoparticles, as well as polymer nanospheres and sub-μm lipid droplets in a label-free manner with average illumination powers of less than 10 μW/μm2.
Highlights
Surface plasmon resonance (SPR) sensing is a technology used for measuring binding and dissociation kinetics of biomolecules at a gold sensor surface. [1,2,3,4,5,6,7] Such biomolecular interactions include interactions among proteins, peptides, nucleotides, sugars and other molecules
We present an optical signature at the gold sensor surface that overcomes the aforementioned issues
A representative result is depicted in Fig. 2, which shows the detected image on the camera after 20 nm gold particles physisorbed to the sensor surface from solution
Summary
Surface plasmon resonance (SPR) sensing is a technology used for measuring binding and dissociation kinetics of biomolecules at a gold sensor surface. [1,2,3,4,5,6,7] Such biomolecular interactions include interactions among proteins, peptides, nucleotides, sugars and other molecules. Surface plasmon resonance (SPR) sensing is a technology used for measuring binding and dissociation kinetics of biomolecules at a gold sensor surface. Kinetic SPR data is typically the result of ensemble averaging over many events, integrated over both space and time. Rapid on/off events at particular sites on the sensor surface are not registered, as they are averaged out by the slower dynamics of the ensemble. Other unexpected binding patterns at particular sites go unnoticed. Such outlier behavior can be important, as these events may signify functional aspects of the molecular interaction, related to particular conformations, density related binding kinetics or other effects of direct relevance. The ability to see all binding/dissociation events in parallel would significantly enhance the analytical capabilities of the SPR sensor
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