Noninvasive Photonic-Crystal Material for Sensing Glucose in Tears

Abstract

Most noninvasive (NI) methods for the determination of glucose either detect a small specific glucose signal or measure the effect of glucose on a tissue optical property (1)(2). A recent review identified the three main issues in NI glucose measurements as specificity, compartmentalization of glucose values, and calibration (1). This editorial discusses a photonic crystal method (3), with respect to these issues. Asher’s group have developed a novel photonic sensing material that responds to glucose concentrations via diffraction of visible light. Polymerized crystalline colloidal arrays (PCCAs) are periodic crystalline lattices of polystyrene microspheres polymerized within thin hydrogel films (3)(4)(5)(6)(7). The arrays are brightly colored and act as diffraction gratings for white light according to the Bragg diffraction equation (4)(5): \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[{\Delta}{\lambda} {=} \frac{n {\times} d}{\mathrm{sin}{\Theta}}\] \end{document} In Eq. 1, n is the refractive index of the system (medium, hydrogel, and colloids), d is the spacing between the diffracting planes, λ is the diffracted wavelength, and Θ is the glancing angle between the incident light and the diffracting planes. A change in electric charge in the PCCAs resulting from binding of molecular or ionic species causes changes the spacing, d , and there is a subsequent wavelength shift, Δλ, of the light reflected off the array. Asher’s group have constructed a photonic glucose sensor in the form of thin acrylamide PCCA hydrogel films that contain glucose molecular recognition elements (3)(6)(7). Phenylboronic acid derivatives …