Tunable Plasmonic Nanocomposite Coatings Enable NIR-Compatible Distributed Fiber Optic pH Sensing

This technology is an optical fiber-based sensor featuring a silica nanocomposite coating embedded with gold nanoparticles and/or gold nanotubes that surrounds a sensing region of the fiber. By exploiting the tunable optical (plasmonic) behavior of the embedded gold nanostructures, the coating produces a strong, wavelength-tailorable response that is compatible with standard telecom-band interrogation equipment, opening a path to real-time, distributed pH monitoring over long fiber lengths.

Description

Unmet Need: Existing fiber optic pH sensing coatings—are largely confined to visible-wavelength responses, prone to dye leaching or coating delamination, and poorly suited to long-length, distributed deployment, leaving no durable, NIR-compatible coating solution for real-time distributed pH monitoring with standard interrogation systems. The sensor consists of an optical fiber surrounded, over at least a portion of its length, by a nanocomposite layer built from a silicon dioxide (SiO₂) matrix in which gold nanoparticles, gold nanotubes, or a combination of the two are dispersed. In one configuration, the coated section is a no-core fiber segment spliced between two multimode fiber segments, allowing the sensing region to be precisely localized within a standard fiber path. The embedded gold nanostructures can be spherical in shape, and their size and shape distribution can be engineered to be either uniform or non-uniform within the matrix — a design lever that shifts and shapes the optical (plasmon) response of the coating. The surrounding SiO₂ matrix itself is a sol-gel derived material formulated to be crack-free and hydrophobic, supporting a durable, moisture-resistant coating suited to long-term exposure in liquid environments. Because the optical response of embedded gold nanostructures is highly sensitive to their size, shape, and spacing, the coating's spectral behavior can be engineered toward specific wavelength bands used by common fiber-optic interrogation equipment, rather than being fixed to the visible-light range typical of conventional pH-indicator coatings. This tunability, combined with the durability of the sol-gel silica host, forms the structural basis of the sensor's distributed pH-sensing capability.

Applications

- Subsea and coastal ocean pH / acidification monitoring
- Oil and gas wellbore integrity monitoring
- Pipeline and subsurface corrosion monitoring
- Marine infrastructure and mobile marine platform sensing
- Industrial process and environmental water-quality monitoring

Advantages

- Optical response is tunable via nanostructure size, shape, and spacing, allowing the coating to be engineered toward wavelength bands compatible with standard fiber-optic interrogation hardware
- Flexible material design (gold nanoparticles, gold nanotubes, or a combination) provides multiple routes to tailor sensitivity and spectral response
- Crack-free, hydrophobic sol-gel silica matrix supports a durable, moisture-resistant coating for sustained use in liquid or humid environments
- Controllable nanostructure distribution offers an additional design parameter for tuning sensor response
- Defined fiber architecture allows the sensing region to be precisely localized using standard fiber segments

Invention Readiness

The technology has been demonstrated at the laboratory scale, with nanocomposite-coated fiber sensors fabricated and evaluated under controlled conditions using both transmission-based and backscatter-based (OTDR) optical interrogation. Testing has included coated fiber segments of at least a few centimeters as well as a longer (≥1 meter) coated length produced using a reel-to-reel coating process, with performance data collected across a defined pH range. No field deployment or long-duration environmental stability data has yet been reported. Further studies would be needed to validate performance over extended fiber lengths, in field or extreme-environment conditions, and over longer-term exposure cycles before the technology would be ready for deployment-scale use.

IP Status

Patent Pending