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Holographic recording materials can be utilised in the fabrication of microstructures for use as sensors [1,2]. In order to achieve this the holographic recording material/structure has to be functionalized by incorporation of a chemical component providing sensitivity to a specific analyte/stimuli. We introduce the different approaches to photosensitive material/photonic structure functionalization and present experimental results of fabrication of two examples of sensing devices: for selective detection of sodium and potassium ions and temperature indicator with controlled reversibility.
The first example reported here compares the performance of a surface relief grating (SRG) fabricated by holographic lithography in an acrylamide photopolymer and a volume holographic grating (VHG) recorded in a water resistant novel cellulose based photopolymer. The surface relief gratings were modified by incorporation of either dibenzo-18-crown-6 (DC) or tetraethyl 4-tert-butylcalix[4]arene (TBC) as chelating agents [3]. DC coated layers show a selective response to K+ over Na+, whereas for TBC there is a dominant response for Na+ over K+. The sensors respond to Potassium and Sodium metal ions within the physiological ranges. Normal levels of Na+ in human serum lie in the range 135-148 mmol/L and the normal K+ level is 3.5-5.0 mmol/L. The response of the SRG sensor to Sodium is compared to the response of a VHG recorded in a cellulose based novel material functionalized by incorporation of TBC. The advantages and challenges of each of these two approaches to material/structure functionalization are analysed.
The second example is a volume phase hologram, recorded in a low-toxicity thermally sensitive photopolymer Poly(N-isopropylacrylamide). Both transmission and reflection holograms were studied by exposing them to temperature ranging within 8-60 oC. It was observed that the reversibility of the hologram response to temperatures above the polymer Lower Critical Solution Temperature (32 oC) can be controlled, thus these devices can be used as elevated temperature indicators.
References
[1] A. K. Yetisen, et al, Chem. Rev. 114, 10654–10696 (2014).
[2] D. Cody, et al, Appl. Opt, 57, No. 22, pp. E173-E183 (2018).
[3] Sabad-E Gul, et al, Sensors, 19 No 5, p 1026 (2019).
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