Photo-Cross-Linked Decyl Methacrylate Films for Electrochemical and Optical Polyion Probes

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Abstract
Potentiometric and optical polyion probes based on photo-cross-linked thin films of decyl methacrylate (DMA) are described, and the effects of film composition on the response toward heparin are examined in detail. In accordance with existing theory governing potentiometric polyion response, lowering the amounts of plasticizer and tridodecylmethylammonium chloride ion exchanger within the film enhances its sensitivity toward heparin. Varying the cross-linker content of a DMA-based film, however, provides an additional mechanism to regulate its physical structure and, hence, the observed potentiometric polyion response. Films with low hexanedioldimethacrylate cross-linker content yield optimal potentiometric heparin detection limits (0.04 μM), suggesting a lower diffusion coefficient within such films, apparently due to interactions between adjacent pendant decyl groups. Increasing cross-linker content interrupts these interactions and facilitates diffusion. This knowledge is applied to optimize optical heparin sensing via DMA films covalently attached to glass substrates. When used in a limited volume/fixed exposure time measurement mode, such optically sensitive films can detect clinically relevant levels of heparin (0.5−5.0 units/mL) in undiluted human plasma.