Agarose film coated glass slides for preparation of pH optical sensors

A method for preparation of optical sensors was developed by agarose film coating on aminosilanated glass slides. An optical pH sensor was accordingly prepared by epoxy activation of the agarose film, followed by chemical immobilization of Neutral Red dye. In an optimized coupling pH of 12 and a dye concentration of 10−2 mol L−1 a pH sensor for a pH range of 2–8.5 was obtained. A theoretical equation was derived using the extended Henderson–Hasselbalch equation that reproduced the measured data well.The sensor was mounted in a flow cell and successfully applied for on-line pH measurements. The sensor responded rapidly to the pH changes with a response time of less than 2 min and reproducibility better than 0.40% (R.S.D.).In comparison to a stand-alone agarose membrane, the agarose coated glass slide showed better physical properties and easier handling and application but slightly slower response times. No evidence of leaching of the dye or any signal drift was observed.