The use of plasmonic nanopores for single molecule detection has attracted considerable attention due to their high sensitivity and selectivity. In this study, we present a phase analysis approach for characterizing the trapping of single molecules in an AC-driven plasmonic nanopore. By analyzing the phase response of the plasmonic nanopore at select frequencies, we can differentiate between a test ligand, the antibody targeting this ligand, and the complexes that these ligands form, as well as observe their dynamics while inside the optical trap of the plasmonic nanopore. This pilot work shows the feasibility of a new approach for rapid and accurate identification of single molecules in complex mixtures.
We present the effects of a Chebyshev filter circuit on the transient electrical current responses of a plasmonic nanopore sensor during abrupt voltage reversals. Those reversals are similar to ones used for single molecule capture-recapture with electrical nanopores. Our plasmonic nanopore sensor allows simultaneous recording of optical and electrical data during optical trapping of nanoparticles and their subsequent translocation through the nanopore located at the sensor’s center. The technical challenge this work aims to resolve is that the sensor’s transient response to abrupt voltage reversals is strong (near-saturation current spikes) and is also slow (return to baseline in the ms range). During this refractory period an analyte’s translocation may be obfuscated by the sensor’s transient response. Here we test the use of a Chebyshev filter as a possible means of significantly reducing the sensor’s transient response to voltage reversals so that analyte translocations are not masked by those transient responses. At the same time, we also test that electrical signatures detected during trapping of a test analyte (20 nm SiO2 nanoparticles) are not unintentionally also removed by the same filter. This work is as a first step towards developing a methodology for enabling rapid analyte recapture by our plasmonic nanopore sensor.
Alternating current (AC) modulation of command voltage applied across a Self-induced Back Action Actuated Nanopore Electrophoresis (SANE) sensor, a type of plasmonic nanopore sensor that we have developed previously, enables acquisition of new data types that could potentially enhance the characterization of nanoparticles (NPs) and single molecules. In particular, AC voltage frequency response provides insight into the charge and dielectric constant of analytes that are normally obfuscated using DC command voltages. We first analyzed Axopatch 200B data to map the frequency response of the empty SANE sensor in terms of phase shift and amplitude modulation, with and without plasmonic excitation. We then tested the frequency response of 20 nm diameter silica NPs and 20 nm gold NPs trapped optically, which made these particles hover over an underlying 25 nm nanopore at the center of the SANE sensor. By applying a DC command voltage with a superimposed AC frequency sweep while keeping the NPs optically trapped in the vicinity of the nanopores’s entrance, we have found that silica and gold NPs to have distinctly different electrical responses. This pilot work demonstrates the feasibility of performing AC measurements with a plasmonic nanopore, which encourages us to pursue more detailed characterization studies with NPs and single molecules in future work.
This work presents Multiphysics COMSOL simulations that help dissect the relative contributions of multiple forces of optical and electrical origin acting on a 20 nm diameter silica nanoparticle trapped by a plasmonic nanopore sensor. Specifically, the nanosensor uses the principle of self-induced back action (SIBA) to trap nanoparticle optically at the center of a double nanohole (DNH) structure integrated on top of a solid-state nanopores (ssNP). This novel SIBA actuated nanopore electrophoresis (SANE) sensor allows simultaneous recording of optical and electrical data features that are generated by the interaction of multiple underlying forces: Plasmonic optical trapping, electroosmosis, electrophoresis, viscous drag and heat conduction forces are all felt by a silica nanoparticle trapped by the sensor. This work aims to simulate these underlying forces in order to help understand how they contribute to the optical-electrical measurements generated by sensor. Furthermore, experimental measurements of 20 nm silica nanoparticles trapped the SANE sensor were compared against computational predictions to test the qualitatively trends seen in experimentally measured signal profiles during the nanoparticle’s approach to the optical trap and its translocation through the plasmonic nanopore, located immediately below the optical trap.
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