Investigation of dynamically modified optical-fiber sensors for pH sensing at the extremes of the pH scale

by Fry, Darrell Ray; Bobbitt II, Donald R.

There exist. a large number of immobilization strategies useful for preparing optical fiber (OF) sensors; one unique approach has been termed dynamic modification. Dynamic modification borrows techniques from reverse-phase high performance chromatography (RP-HPLC) to render the optical fiber surface sufficiently hydrophobic to reversibly immobilize hydrophobic probe molecules. Although RP-HPLC stationary phases are known to hydrolyze under conditions of high or low pH, the hydrophobic surface on the optical fiber shows immunity to hydrolysis under similar conditions, including increased temperature (65 degreesC), and in organic-containing solvents at high and low pH values (33% acetonitrile at pH 12 and 2). Since the surface is stable at the extremes of the pH scale, pH sensing in these regions; is possible using this strategy. Two hydrophobically derivatized, pH-sensitive fluorescein dyes were immobilized on the surface of a C-18 optical fiber; however, upon immobilization, the dyes were found to convert into a non-pH-sensitive, non-fluorescent lactone form, pH sensing was achieved over the pH range 7.5-10 by controlling the hydrophobicity of the optical fiber surface. The limitations and advantages of this approach are evaluated and discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Microchemical Journal
Start Page
1095-9149; 0026-265X