Novel Optofluidic Refractometer Based on Wedge Interferometry for Handheld Testing Devices

Abstract

Abstract Interferometric methods are known for their high sensitivity, but on the expense of their large size. By using wedge interferometry, the size can be drastically reduced while maintaining adequate detection capabilities. In this article, a miniaturized refractometer based on this interferometer type is demonstrated to be able to achieve Sensitivity of 3.65×10-5 RIE/pixel and Detection Limit of 8.7×10-5 RIE for bulk refractometry of glucose aqueous solution. The device consists of two semitransparent mirrors made of glass slide coated by sputtered Aluminum thin film, enclosing a tapered frame that maintains one mirror slightly tilted with respect to the other, and simultaneously encloses the liquid under test. This structure causes interference pattern that depends on the refractive index of the test liquid when illuminated by a collimated laser beam. Analytical modeling is developed for the structure, from which a very promising estimation of the sensitivity is evaluated that exceeds the state-of-the-art for volume refractometry, and can be achieved upon using suitable microfabrication techniques. Numerical simulations are also presented for principle validation. The proposed novel device opens a new avenue for optofluidic detection and is very suitable for point-of-care-testing and handheld devices due to its compact size, simple and cheap fabrication.