Amphiphilic Co-Networks as matrices for (bio)chemical sensors
Sensitive chlorine gas detection at the sub-ppm level using amphiphilic co-networks as highly convenient matrices
APCNs are copolymeric two-component networks consisting of hydrophilic and hydrophobic phases. These contrary phases build covalently co-connected networks and form nanophase-separated areas [Fig.1]. Silicon-hydrogel-APCNs are i.a. used for long term contact lenses and drug delivery systems. Another innovative application of these amphiphilic networks includes the use as optochemical sensors.
We present a new optical polymer thin film sensor for high sensitivity and rapid response gas detection. The sensor consists of an amphiphilic co-network (APCN) in which the indicator has been embedded.
Due to the unique properties of APCNs, accurate gas detec-tion at the sub-ppm level is feasible within seconds.
Here, we describe the first systematic determination of chlorine gas in the sub ppm-range within seconds, using o-tolidine as a suitable oxidation indicator.
Figure 2. Synthesis route for PHEA-l-PDMS
Chlorine gas measurements were taken in a modified UV-VIS spectrophotometer, with an adjusted flow of 1000 ml/min at several chlorine gas concentrations and variable humidity. Spectral development at the wavelength of 650 nm was detected and evaluated by correlating the change of absorbance in the starting phase with the chlorine gas concentration. (1)[Fig. 3].
(1)
The linear fit of the slope between two setting points of the detected absorbance leads to a maximum slope within the first seconds. As setting points we chose 0.004 and 0.008, similar to a change of transmission from 99.5% to 98.5%.
Detection times between 6 to 31 seconds for 1.0 to 0.2 ppm chlorine gas at 0% rH were achieved.
Chemical reaction of chlorine gas with o-tolidine is strongly affected by humidity which leads to decreasing sensitivity with increasing humidity [Fig. 4].
Figure 4. Measurement times for different chlorine gas concentrations at different humidity
Detecting at the OEL (occupational exposure limit) of 0.5 ppm chlorine gas (
In accordance with lower sensitivity below 0.2 ppm of chlorine gas concentration and higher humidity, using a similar procedure of evaluation, analysis of the slope within the first 400 sec, yields a similiar result [Table 1].
Table 1. Slope values and measurement time
Compared to other polymeric optochemical sensors, we have increasing sensitivity of about 20%, while decreasing indicator concentration by one order of magnitude [2].
References
[2] M. Ralfs, J. Heinze, Sens. Actuators B 44, 257-261, 1997
[3] M. Hanko, N. Bruns, J. C. Tiller, J. Heinze, J. Anal. Bioanal. Chem. 386, 1273-1283, 2006