PH PHOTOTHERMAL SPECTROMETER AND PERFORMING PH PHOTOTHERMAL SPECTROSCOPY

patent description

Although the determination of pH (H+ concentration in solution) is a standard laboratory measurement, new techniques capable of accurately measuring pH are being developed to meets the demands of bio-industrial processing, and tissue engineering industry. These specific applications require small footprint probes that are compatible with biological environment (i.e. do not inhibit or harm cell growth), can operate in complex, high ionic strength solution environment, can be embedded in substrate to allow measurement access to optically dark areas and are either cost-effective enough to be disposable and/or are stable over a very long time period and therefore do not require frequent re-calibrations.

Here we disclose a device that uses multiple wavelengths (colors) of light to probe the pH dependent changes in absorbance of pH-sensitive dye by determining the difference in temperature rise due to differences in light absorbance at different colors. The pH dependent changes in absorption profile directly impact the amount of light absorbed at a particular color. The absorbed light is thermalized resulting in an increase in sample temperature, which is detected using an optical thermometer.

The use optical waveguides to deliver light and detect temperature changes allow us to embed the sensor in biocompatible matrix in regions inaccessible to optical microscopy. Furthermore, the use of soft biocompatible materials allows us to best match mechanical and chemical environment conducive to cellular/tissue growth while minimizing biofouling of the sensor.

The use of pH sensitive chromophores, covalently attached within the structure of the protonpermeable waveguide, allows for both optical and photothermal spectroscopy as accurate measurements of pH.

The use of photo-thermal spectroscopy as mean to measure pH, as opposed to volumetric changes in hydrogel probed via changes in bandgap resonance wavelength (add ref to sandy and OPEX paper), allows us to operate in ionic solutions (0.1 mM), overcoming a major limitation of polymeric waveguide sensors that are limited to low ionic strengths due to inferring effects of osmotic pressure induced swelling of hydrogels.

Lastly, the pH sensor described here does not undergo a significant hysteresis upon dehydration and thus eliminates a major source of device failure common to electrical pH device in widespread use.