Response characterization of a fiber optic sensor array with dye-coated planar waveguide for detection of volatile organic compounds.

Jae-Sung Lee,Na-Rae Yoon,Seung-Ha Lee,Dae-Hyuk Kwon,Sai-Anand Gopalan,Byoung-Ho Kang,Hyun-Min Jeong,Sang-Won Lee,Shin-Won Kang

doi:10.3390/s140711659

Abstract

We have developed a multi-array side-polished optical-fiber gas sensor for the detection of volatile organic compound (VOC) gases. The side-polished optical-fiber coupled with a polymer planar waveguide (PWG) provides high sensitivity to alterations in refractive index. The PWG was fabricated by coating a solvatochromic dye with poly(vinylpyrrolidone). To confirm the effectiveness of the sensor, five different sensing membranes were fabricated by coating the side-polished optical-fiber using the solvatochromic dyes Reinhardt's dye, Nile red, 4-aminophthalimide, 4-amino-N-methylphthalimide, and 4-(dimethylamino)cinnamaldehyde, which have different polarities that cause changes in the effective refractive index of the sensing membrane owing to evanescent field coupling. The fabricated gas detection system was tested with five types of VOC gases, namely acetic acid, benzene, dimethylamine, ethanol, and toluene at concentrations of 1, 2,…,10 ppb. Second-regression and principal component analyses showed that the response properties of the proposed VOC gas sensor were linearly shifted bathochromically, and each gas showed different response characteristics.

Highlights

Volatile organic compound (VOC) gases are often present in workplaces, especially in chemical industries
The volatile organic compound (VOC) gases were emitted from the gas cabinet, so the precise concentration of the gases could be controlled using computerized mass flow controllers (MFCs) and mass flow meter (MFM)
In the absence of VOC gas in the gas chamber, the system was adjusted so that almost equal amounts of light passed through the sensing optical-fiber, and there was no change in the refractive index

Summary

Introduction

Volatile organic compound (VOC) gases are often present in workplaces, especially in chemical industries. Semiconductor gas sensors based on micro-electromechanical systems (MEMS) and complementary metal oxide semiconductor transistors (CMOSs) can detect precise gas concentrations and allow real-time monitoring, but they need additional heating systems to detach the bound gas molecules, and the sensing membrane must be periodically changed [8,9]. We propose a simple multi-array VOC gas detection system based on changing the effective refractive index. The different polarities of the VOC gases cause changes in the effective refractive index of the sensing membrane owing to evanescent field coupling. Upon contact between the VOC gases and the sensing membrane, the refractive index changes on the basis of the charge-transfer (CT) characteristics of the solvatochromic dye in the device’s polymer planar waveguide (PWG). Principal component analysis (PCA) was used to explore the data distribution and classify the VOCs [18,19]

Solvatochromism and Solvatochromic Dyes

Fabrication of Sensing Membrane

VOC Gas Detection System

Results and Discussion

Conclusions