Temperature Spatially Offset Raman Spectroscopy (T-SORS): Subsurface Chemically Specific Measurement of Temperature in Turbid Media Using Anti-Stokes Spatially Offset Raman Spectroscopy.

Benjamin Gardner,Pavel Matousek,Nicholas Stone

doi:10.1021/acs.analchem.5b03360

Abstract

Here we propose and demonstrate a new analytical method for the noninvasive measurement of subsurface temperatures within diffusely scattering (turbid) media in combination with high chemical selectivity. The method is based upon the first combination of Stokes/anti-Stokes light scattering measurements and the recently developed spatially offset Raman spectroscopy (SORS). This approach has been conceptually demonstrated by measuring material-specific temperatures within a turbid sublayer of poly(tetrafluoroethylene) (PTFE) through a highly diffusely scattering overlayer of poly(oxymethylene) POM (3 mm thick). Root-mean-square errors (RMSEs) of 0.16-0.71 °C were achieved when measuring temperatures over ranges between 24 and 45 °C. This unique capability complements the array of existing, predominantly surface-based, temperature measurement techniques. It paves the way for a wide range of topical applications including subsurface, chemically specific, noninvasive temperature measurements within translucent media including the human body, subsurface monitoring of chemical or catalytic processes in manufacture quality and process control, and research.

Highlights

The measurement of subsurface temperature in turbid media is a highly topical area in analytical sciences with potential applications ranging from monitoring subsurface temperature in the human body to monitoring chemical and materials processes during production and storage
For accurate temperature measurements using thermography, the emissivity of the object needs to be known and correctly calibrated for. This value can theoretically range from 1 if the object acts as a perfect blackbody to 0.1. The precision of these different techniques can vary, with the resolvable temperature for thermocouples at 0.0025 °C, whereas the precision of infrared thermography has an average of ∼0.02−0.1 °C.1,2
A new prospect for deep subsurface probing of chemical composition in turbid materials using Raman spectroscopy recently emerged from the advent of spatially offset Raman spectroscopy (SORS).[7,8]

Summary

Introduction

The measurement of subsurface temperature in turbid media is a highly topical area in analytical sciences with potential applications ranging from monitoring subsurface temperature in the human body to monitoring chemical and materials processes during production and storage. Current mainstream methods, such as contact thermometers and infrared probes, are confined to measuring only the surface temperature in non-IR transparent or diffusely scattering media. Lattice) relaxation time and T2 (spin−spin) relaxation time of water molecules Both of these approaches are complex to accurately calibrate and are limited to specific tissue types.[4] In addition, MRI methods are often prohibitively costly for many practical applications. SORS has opened the way for a host of new applications including the scanning of liquids in sealed

Methods

Results

Conclusion