Us Patent Plasmonic Nanopore Protein Trapping

US Patent Plasmonic Nanopore Protein Trapping: A Breakthrough in Single‑Molecule Biosensing

The convergence of plasmonics and nanopore technology has ushered in a new era for detecting and manipulating individual biomolecules. A notable US patent (US 10,842,317 B2) titled “Plasmonic Nanopore Device for Trapping and Detecting Proteins” outlines a method that leverages localized surface plasmon resonance (LSPR) to stably capture proteins within a nanoscale pore, enabling real‑time, label‑free analysis. This article explores the scientific foundation of the invention, the core innovations claimed in the patent, its practical advantages, and the broader impact on fields ranging from proteomics to point‑of‑care diagnostics Worth knowing..

Some disagree here. Fair enough Worth keeping that in mind..

1. Background: Why Plasmonic Nanopores Matter

1.1 Nanopore Sensing Basics

Biological or solid‑state nanopores function as tiny channels (typically 1–10 nm in diameter) through which molecules translocate under an applied electric field. As a protein passes through, it momentarily blocks ionic current, producing a signature current blockade that reveals size, charge, and conformational information. Traditional nanopore approaches, however, suffer from short dwell times (microseconds to milliseconds) and limited control over molecule positioning Not complicated — just consistent..

1.2 Plasmonic Enhancement

Plasmonic nanostructures—most commonly gold or silver nanoparticles—support collective oscillations of conduction electrons known as localized surface plasmon resonance. When illuminated with light at the plasmon frequency, intense electromagnetic fields are generated near the metal surface, enhancing optical phenomena such as Raman scattering, fluorescence, and photothermal effects. By integrating plasmonic hotspots with a nanopore, researchers can simultaneously probe a trapped molecule optically while monitoring its ionic signature electrically.

1.3 The Patent’s Core Idea

The US patent describes a device where a plasmonic nanostructure is fabricated inside or immediately adjacent to a solid‑state nanopore. When a target protein diffuses into the pore, the plasmonic field creates an optical potential well that draws the protein toward the region of highest field intensity. Simultaneously, an electrophoretic force drives the protein through the pore. The balanced interplay results in stable trapping for seconds to minutes—orders of magnitude longer than in conventional nanopores—allowing multimodal readout (electrical current, surface‑enhanced Raman spectroscopy, and photothermal imaging) Nothing fancy..

2. Detailed Description of the Patented Invention

2.1 Device Architecture

• Substrate: A silicon nitride membrane (≈50 nm thick) provides mechanical stability and low background conductivity.
• Nanopore: A single cylindrical pore, fabricated via focused ion beam (FIB) drilling, with a diameter of 8 nm and length matching the membrane thickness.
• Plasmonic Element: A bow‑tie shaped gold nanoantenna (arm length ≈30 nm, gap ≈2 nm) is positioned such that its gap aligns with the nanopore aperture. The nanoantenna is defined by electron‑beam lithography and lifted‑off gold deposition.
• Illumination Path: A continuous‑wave laser (λ = 785 nm) couples to the nanoantenna via a high‑NA objective, exciting LSPR and generating a hotspot within the gap.
• Electrodes: Platinum layers on either side of the membrane enable application of a bias voltage (±200 mV) for ionic current measurement.

2.2 Trapping Mechanism

1. Optical Potential Gradient: The LSPR creates a steep intensity gradient; the protein’s polarizability leads to a dipole force Fₒₚₜ ≈ ½ α∇|E|², pulling it toward the high‑field region.
2. Electrophoretic Force: An applied voltage drives the protein (net charge q) through the pore: Fₑₗ = qE.
3. Viscous Drag: Opposes motion, F_drag = 6πηrv, where η is solvent viscosity and r the protein’s effective radius.
4. Equilibrium Condition: When Fₒₚₜ + Fₑₗ ≈ F_drag, the protein settles at a stable locus within the nanopore gap, resulting in prolonged residence times.

The patent emphasizes that the trap depth can be tuned by adjusting laser power, bias voltage, or the nanoantenna geometry, providing versatility for proteins of different size and charge.

2.3 Readout Modalities

• Electrical: Ionic current blockade amplitude and duration give kinetic data (on/off rates).
• Optical: Surface‑enhanced Raman scattering (SERS) spectra collected from the hotspot reveal vibrational fingerprints, enabling identification of post‑translational modifications or ligand binding.
• Photothermal: Changes in local temperature due to non‑radiative plasmon decay can be detected via shifts in the nanopore’s conductance, offering a label‑free alternative when Raman signals are weak.

3. Advantages Over Conventional Approaches

These benefits translate into improved limits of detection (down to single‑molecule levels), the ability to observe transient conformational states, and the capacity to screen ligand‑protein interactions in real time The details matter here. That's the whole idea..

4. Experimental Validation Cited in the Patent

The inventors demonstrated the technology using ** bovine serum albumin (BSA)** and immunoglobulin G (IgG) as model proteins:

1. Fabrication: A 30 nm‑thick SiN membrane with an 8 nm pore was milled; bow‑tie gold antennas were fabricated via e‑beam lithography.
2. Protein Injection: 100 pM protein solution in 100 mM

4. Experimental Validation (continued)

4.1 Sample Preparation and Functionalisation

The protein‑laden electrolyte was introduced through a pressure‑controlled syringe pump set to a gentle 0.2 µL min⁻¹ flow rate. The feed buffer consisted of 100 mM KCl, 10 mM Tris‑HCl (pH 7.5) supplemented with 0.05 % (w/v) pluronic F‑68 to suppress nonspecific adsorption. Prior to protein exposure, the nano‑antenna area was functionalised with a self‑assembled monolayer of 11‑mercaptoundecanoic acid, followed by EDC/NHS coupling of anti‑BSA or anti‑IgG capture antibodies (≈ 5 × 10⁸ molecules cm⁻²). This chemistries ensured oriented immobilisation while preserving the nanopore’s ionic pathway.

4.2 Acquisition Protocol

During each measurement the system was biased at +150 V applied across the SiN membrane. The trapping laser (λ = 785 nm) was set to 1.2 mW at the hotspot, delivering a calibrated optical potential that kept the target protein within the 8 nm aperture for the duration of the recording. The ionic current was sampled at 5 MS/s using a low‑noise amplifier, while simultaneous SERS spectra were collected in the 1500–3500 cm⁻¹ region with a gated EMCCD (exposure = 10 ms). Photothermal signatures were extracted from the high‑frequency component of the conductance trace (10–200 kHz) using a band‑pass filter.

4.3 Representative Data

The dwell‑time histograms exhibit a bi‑exponential decay, reflecting two dominant conformational states of each protein while trapped. SERS spectra captured at the hotspot display the characteristic amide I band for BSA (≈ 1655 cm⁻¹) and a distinct IgG Fc fingerprint near 1620 cm⁻¹. The photothermal response, proportional to the absorbed

power, was found to correlate with the protein’s absorption cross‑section at the laser wavelength, providing an additional label‑free contrast mechanism. The observed correlation between the photothermal signal and the SERS‑derived secondary structure suggests that the technique can simultaneously report on both the mechanical (dwell time, blockade depth) and spectroscopic (vibrational fingerprint, thermal response) properties of a single protein as it traverses the nanopore.

The integration of plasmonic trapping, SERS, and photothermal sensing within a single nanopore platform represents a significant step toward comprehensive single‑molecule characterization. The bi‑exponential dwell‑time distributions, for instance, could be directly linked to the observed SERS peak shifts, offering a real‑time view of folding or unfolding dynamics. By acquiring ionic current, Raman scattering, and photothermal signals concurrently, the system extracts multiple independent observables from each translocation event, enabling richer classification of protein conformational states and interactions than any one modality alone. To build on this, the high temporal resolution (10 ms SERS exposure, 5 MS/s current sampling) captures transient intermediates that would be averaged out in bulk measurements.

All in all, the experimental validation demonstrates that the hybrid nanopore‑antenna device can reliably trap, detect, and spectroscopically analyze individual protein molecules in real time. The simultaneous acquisition of ionic blockade, Raman spectra, and photothermal signals establishes a new paradigm for label‑free, multi‑parametric single‑molecule biophysics. Future work will focus on extending this approach to dynamic protein‑protein interactions, enzyme kinetics, and the detection of post‑translational modifications, with the ultimate goal of building a universal platform for real‑time structural biology at the single‑molecule level.