Metal ion-sensitive holographic sensors.
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 (approximately 10 m 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 (< or = 200 nm) within 30 s at ion concentrations of < or = 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 (approximately 0.13-0.15 M) and shows promise for developing simple, low-cost K+ sensors for medical applications.
Mayes
Andrew G
AG
Institute of Biotechnology, University of Cambridge, UK.
Blyth
Jeff
J
Millington
Roger B
RB
Lowe
Christopher R
CR
D004988:Ethers, Cyclic / Q000737:chemistry; D006696:Holography / Q000379:methods* / Q000592:standards; D020100:Hydrogels / Q000737:chemistry / Q000592:standards; D008672:Metals, Alkali / Q000032:analysis*; D008689:Methacrylates / Q000737:chemistry; D011188:Potassium / Q000032:analysis; D012680:Sensitivity and Specificity; D012964:Sodium / Q000032:analysis
D004988:Ethers, Cyclic; D020100:Hydrogels; D008672:Metals, Alkali; D008689:Methacrylates; D012964:Sodium; D011188:Potassium