Effect of the photoresist aging in D-shaped POF SPR Sensors for biochemical applications

This work presents how the altering in the photoresist (Microposit S1813) changes the performances of D-shaped plastic optical fiber (POF) plasmonic sensors. In particular, this photoresist has been used to obtain a buffer layer, deposited on the exposed core in the D-shaped POF region before sputtering the gold film, to improve the performances of the sensor. We have studied how the optical property of the photoresist layer changes when the photoresist is used after the expiry date. In particular, we have compared the performances of two surface plasmon resonance (SPR) sensors realized exploiting two Microposit S1813 photoresists, one before and the other after the expiry date. When the refractive index of the medium of interest (aqueous medium) is minor than 1.36, the sensitivity improves with the use of S1813 after the expiry date, vice versa when the refractive index is major than 1.36