Micro-miniature Autonomous Optical Sensor Array for Monitoring Ions and Metabolites 1: Design, Fabrication, and Data Analysis

Abstract

A micro-miniature array of sensing capsules for optical monitoring of pH, potassium and glucose is described. Optode technology translates the respective ionic levels into variable colors of ionophore/dye/polymeric liquid micro-beads stuffed into individual capsules. Glucose is monitored indirectly, by coupling through glucose oxidase (GOX) immobilized in cellulose acetate phthalate (CAP) based microscopic beads that are stuffed into another microcapsule together with pH sensitive optical microscopic beads. The electrolyte and glucose sensing capsules are embedded in a transparent cellulose acetate bar 300 -500 µm wide and 2 -2.5 mm long called the sliver sensor that includes also a white capsule made of micro-beads without dye for optical reference. By adding further capsules custom combinations of analytes can be monitored in biomedical and non-biological contexts. In this work, as an example, design, fabrication and testing of a sliver sensor that could be developed for in vivo use are described.

Micro-miniature Autonomous Optical Sensor Array for Monitoring Ions and Metabolites 2: Color Responses to pH, K+ and Glucose

“…3A in Part 1). 1 The generated protons accumulate in the capsule due to the moderately hydrophobic PU membrane that amplifies the optical response.…”

“…While varying the glucose level, the K-M function of the reference Na + /pH sensing spot remained essentially constant. Figure 3 in Part 1 1 shows an image of the sensor in contact with 300 mg/dL of glucose in PBS as well as the respective RGB color intensities; the corresponding red K-M function variables are plotted in Fig. 2B versus glucose concentration.…”

“…1 Besides ions, metabolites such as glucose can also be monitored by immobilizing the respective enzyme together with suitable optode beads in the same compartment. Diffuse reflectance of each capsule can be linked to dye concentration via Kubelka-Munk analysis 2 which is facilitated by incorporating a white capsule in the sliver for optical reference.…”

Single-ion activity: Optical sensing vs. electrochemical sensing

“…These are ion-selective bulk optodes [1,4,5]. These sensors bear several advantages over ISEs: distant signal acquisition allowing for non-contact reading [6], remarkably low detection limits (down to 10 −12 M) without special precautions or treatment needed to achieve the same with ISEs [7][8][9][10][11], and robustness against biofouling. The chemistry of the ionophore-based optodes is very similar to that of ISEs with membranes containing ionophores [1,12].…”

Use of digital reflection devices for measurement using hue-based optical sensors

“…We are concerned with the use of color -qualities that are present or represented in visual experiences coming from the human perception of the electromagnetic spectrum -as analytical parameter, which is typically used in qualitative analysis resulting from separation or identification reactions. The specification of a color by a color space, a mathematical model representing color as tuples of color components, permits their use for quantitative purposes using data from various imaging devices including hand-held [2] and desktop scanners [3][4][5], CCD arrays [6], video cameras [7,8], digital photographic cameras [9], mobile phone cameras [5,[10][11][12] and digital color analyzers [13][14][15].…”