Development of sensitive holographic devices for physiological metal ion detection

The development of selective alkali metal ions sensors in particular is a subject of significant interest. In this respect, the level of blood electrolytes, particularly H⁺, Na⁺, K⁺ and Cl^-, is widely used to monitor aberrant physiologies associated with pulmonary emphysema, acute and chronic renal failure, heart failure, diabetes. The sensors reported in this paper are created by holographic recording of surface relief structures in a self-processing photopolymer material. The structures are functionalized by ionophores dibenzo-18-crown-6 (DC) and tetraethyl 4-tert-butylcalix[4]arene (TBC) in plasticised polyvinyl chloride (PVC) matrix. Interrogation of these structures by light allows indirect measurements of chemical analytes' concentration in real time. We present results on the optimisation and testing of the holographic sensor. A self-processing acrylamide-based photopolymer was used to fabricate the required photonic structures. The performance of the sensors for detection of K⁺ and Na⁺ was investigated. It was observed that the functionalisation with DC provides a selective response of the devices to K⁺ over Na⁺ and TBC coated surface structures are selectively sensitive to Na⁺. The sensor responds to Na+ within the physiological ranges. Normal levels of Na⁺ and K⁺ in human serum lie within the ranges 135-148mM and 3.5-5.3 mM respectively.