In most optical measurements light passes through the sample only once, whereas optical microcavities can be used to increase the sensitivity of optical measurements by reflecting light through the sample more than 10,000 times, amplifying the signal, and allowing the measurement of very small sample volumes with high sensitivity.

This technique can be used to amplify signals from almost any type of optical technique used in chemical sensing, including absorption, fluorescence, Raman scattering, and refractive index sensing, allowing the development of compact, fast, and accurate chemical and nanoparticle sensors for use in medicine, environmental monitoring, research, bio-diagnostics and security & defence.

Oxford HighQ’s microcavities consist of two opposing mirrors, one of which is planar and one of which is concave with a radius of curvature of a few micrometres, spaced so that a fluid to be analysed can be flowed between the two (Figure 2: Illustration of an optical microcavity). The mirrors are highly reflective such that photons of light in the cavity reflect back and forth around 10,000 times or more before escaping. These multiple reflections increase the degree of interaction with the sample, thereby amplifying any optical signal when compared with conventional single-pass optical sensing techniques.

Microcavities offer benefits for most optical measurement methods, providing a general tool for enhanced sensing.

Direct benefits of the small sample volumes required by Oxford HighQ sensors are to be found in applications such as pharmaceuticals, environmental monitoring, security and defence, and medical diagnostics where samples are costly, hazardous, or difficult to obtain. Current sensing tools in these areas are generally either bulky and expensive or lack the required sensitivity.

In particle sensing, the small, interrogated volume allows for measurement of individual particles in the fluid environment with a level of quantitative detail hitherto unavailable. In applications where the availability of sample fluid is not an obstacle, indirect benefits of small sample volumes are achieved where complex sample preparation steps are required prior to detection.

Techniques such as colorimetry, immunoassays, and polymerase chain reactions are widely used to target specific chemical and biological species. The chemical reactions involved require reagents and often some mixing and heating, all of which benefit from reduced sample volumes. An example is the colorimetric sensing of nutrients in water, where the utility of existing systems is limited by the need for the replacement and disposal of azo-dye reagents and, in the case of phosphates, the need for heating during a digestion step.


Optical Microcavities

Figure 1: Optical Microcavities

Illustration of Optical Microcavity

Figure 2: Illustration of an Optical Microcavity

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