Sensitive detection of 2,4,6-trinitrotoluene by tridimensional monitoring of molecularly imprinted polymer with optical fiber and five-branched gold nanostars

A new approach for optical chemical sensor based on molecularly imprinted polymer (MIP) and localized surface plasmon resonance (LSPR) in plastic optical fibers (POFs), for the selective detection and analysis of 2,4,6-trinitrotoluene (TNT) in aqueous solution, has been developed. LSPR is excited in five-branched gold nanostars (GNS), suspended in an MIP specific for TNT (GNS-MIP), which assures the selectivity. This sensing layer has been deposited directly on two different POF platforms, i.e. tapered and not-tapered POF. Both sensors show better performance than a similar one previously proposed, in which the surface plasmon resonance (SPR) was excited in a thin gold layer at the surface of the POF in contact with the MIP layer (specific for TNT). In particular, in the sensor with a GNS-MIP sensing layer on the not-tapered POF the sensitivity was 8.5 × 104 nm/M, three times higher than in the gold layer sensor. In the sensor with GNS-MIP sensing layer on tapered POF the sensitivity increases further up to 8.3 × 105 nm/M, thirty times higher than in the gold layer sensor, because the penetration depth of the evanescent field increases and the number of the interaction sites of TNT, in the MIP involved in the generation of the signal, increases accordingly.