Method of evaluating pH using an inorganic-oxide nanoparticle based optical pH sensor
Inventors
Kauffman, Douglas • Matranga, Christopher • Ohodnicki, JR., Paul R. • Su, Xin • Wang, Congjun
Assignees
Publication Number
US-10274431-B1
Publication Date
2019-04-30
Expiration Date
2036-04-14
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Abstract
A method for evaluating the pH of an aqueous solution by utilizing the optical properties of a pH sensing material includes optically active nanoparticles fixed to a substrate. The optically active nanoparticles have a localized refractive index modulation over a pH range from 2.0 to 12.0 of at least 1% and, where the plurality of optically active nanoparticles have an average nanoparticle diameter of less than about 500 nanometers. The method includes contacting the pH sensing material with the aqueous solution, illuminating the pH sensing material, and monitoring an optical signal generated through comparison of incident light and exiting light to determine the optical transmission, absorption, reflection, and/or scattering of the pH sensitive material. The optical signal of the pH sensitive material varies in response to the pH of the aqueous solution, providing a means by which the pH and any changes in the pH may be analyzed.
Core Innovation
The invention discloses a method for evaluating the pH of an aqueous solution by utilizing the optical properties of a pH sensing material comprising a plurality of inorganic oxide-based optically active nanoparticles fixed to a substrate. These optically active nanoparticles exhibit a localized refractive index modulation over a pH range from 2.0 to 12.0 of at least 1%, with an average diameter of less than about 500 nanometers. The method involves contacting the pH sensing material with the aqueous solution, illuminating the material, and monitoring an optical signal generated by comparing incident and exiting light to determine optical transmission, absorption, reflection, and/or scattering, which varies responsively with the pH.
The problem addressed by this invention arises from the need for accurate pH measurement in harsh environments such as downhole and underwater conditions encountered in fossil energy applications. These environments are challenging due to high temperatures (up to 300°C), pressures (up to 30,000 psi), chemically corrosive species, and high salinity, which limit the stability and deployment of conventional electrical or electronic pH sensors. Existing optical fiber sensors for chemical sensing have not been commercially deployed mainly due to a lack of sensing materials with reversible, stable, and rapid pH responses under such conditions. Moreover, existing pH sensing technologies rely on organic dyes or matrices which are temperature-sensitive or prone to leaching, limiting their use in harsh environments.
This invention overcomes these limitations by exploiting inorganic oxide-based nanoparticles that are chemically and thermally stable and do not rely on organic dyes or protonation/deprotonation reactions, thus enabling robust, reversible, and stable pH sensing. The optical response is strongly associated with the inorganic oxide nanoparticles, which may be further tailored in size, shape, and composition, including metal-oxide/core-shell structures, to optimize pH dependence of their optical properties. The method allows for real-time, spatially resolved pH monitoring through optical interrogation without reliance on electrical components at the sensing site, making it suitable for harsh and chemically aggressive environments.
Claims Coverage
The patent includes two independent claims encompassing methods of evaluating pH using distinct compositions of optically active nanoparticles. Each claim specifies unique features related to nanoparticle composition, configuration, and optical interrogation.
Use of inorganic metal oxide nanoparticles fixed to a substrate for pH sensing
The method comprises a pH sensing material including a plurality of optically active inorganic metal oxide nanoparticles fixed to a substrate, having a localized refractive index modulation over pH 2.0 to 12.0 of at least 1%, average diameter less than about 500 nanometers, with monitoring of optical signals generated by comparing incident and exiting light to evaluate pH.
Use of metal-inorganic oxide/core-shell nanoparticles for pH sensing
The method uses a pH sensing material comprising metal-inorganic oxide/core-shell nanoparticles with a metal core and inorganic oxide shell, where one or more nanoparticles exhibit localized refractive index modulation over pH 2.0 to 12.0 of at least 1%, average diameter less than about 500 nanometers, and pH evaluation is conducted by monitoring optical signals derived from incident and exiting light.
The claims cover methods employing inorganic oxide-based nanoparticles, either as metal oxides fixed to substrates or as metal-core/inorganic oxide-shell core-shell nanoparticles, to generate pH-dependent optical signals via spectroscopic comparison of incident and exiting light, enabling pH evaluation over a broad pH range with nanoparticles sized below 500 nanometers.
Stated Advantages
Provides a robust and reversible pH measurement method suitable for harsh environments with high temperature and pressure, overcoming limitations of unstable organic dye-based sensors.
Eliminates the need for electrical components and connections at the sensing location, enhancing sensor stability and safety in corrosive and flammable environments.
Allows for real-time, spatially resolved pH mapping using optical interrogation techniques.
Improves temperature and chemical stability due to use of inorganic oxide nanoparticles and core-shell nanoparticle architectures, extending operational lifetime and reliability.
Enables tailoring of nanoparticle size, shape, and composition to optimize optical response and multi-parameter sensing capabilities.
Documented Applications
Measurement of pH in harsh downhole environments during oil and gas drilling and hydraulic fracturing processes.
Environmental monitoring in geological reservoirs for CO2 sequestration and related formations.
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