Metal Ion-Sensitive Holographic Sensors

• Published in: Analytical chemistry (Washington) 2002-08, Vol.74 (15), p.3649-3657
• Main Authors: Mayes, Andrew G, Blyth, Jeff, Millington, Roger B, Lowe, Christopher R
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Chemistry; Ethers, Cyclic - chemistry; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General, instrumentation; Holography - methods; Holography - standards; Hydrogels - chemistry; Hydrogels - standards; Inorganic compounds; Ions; Metals; Metals, Alkali - analysis; Methacrylates - chemistry; Other biological molecules; Potassium - analysis; Sensitivity and Specificity; Sensors; Sodium - analysis
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac020131d

Holographic sensors for Na+ and K+ have been fabricated from crown ethers incorporated into polymeric hydrogels. The methacrylate esters of a homologous series of hydroxyether crown ethers were synthesized and copolymerized with hydroxyethyl methacrylate and the cross-linker ethylene dimethacrylate (3 mol %) to form stable hydrogel films (∼10 μm thick) containing covalently bound (0−97 mol %) 12-crown-4, 15-crown-5, and 18-crown-6 pendant functionalities. The films were transformed into silver-based volume holograms using a diffusion method coupled with a holographic recording using a frequency-doubled Nd:YAG laser. The resulting holographic reflection spectrum was used to characterize the shrinkage and swelling behavior of the holograms as a function of polymer composition and the nature and concentration of alkali, alkaline earth, and NH4 + ions in the test media. Optimized film compositions containing 50 mol % crown ether showed substantial responses (≤200 nm) within 30 s at ion concentrations of ≤30 mM, which could be rationalized on the basis of the known complexation behavior of the crown ethers. An 18-crown-6 holographic film was shown to be able to quantitate K+ concentrations over the physiologically relevant range. It was virtually unaffected by variations in the Na+ background concentration within the normal physiological variation (∼0.13−0.15 M) and shows promise for developing simple, low-cost K+ sensors for medical applications.