Instrumentation & Measurement Magazine 24-5 - 52

points by the interaction with the functional monomers,
and then the complex is fixed by the cross-linking agent in
a highly organized structure. At the end of the process, the
template is removed, leaving the molecular recognition sites
free [22].
Initially, MIPs were mainly used as sorbents media for stationary
phases in chromatography, in solid phase extraction
(SPE), carriers in drug delivery and diagnosis, in reactors for
catalysis, and for remediation purposes [23]. Although these
first applications were very focused, later they have increasingly
been exploited also as recognition elements in sensors
development, establishing their role as potential substitutes
for biological recognition elements [24].
Indeed, compared to their biological counterparts, MIPs
demonstrated many advantages: higher stability in thermal,
chemical and mechanical conditions; high performance
in aqueous/organic mixtures and pure solvents; low-cost in
manufacturing processes without animal experimentation
phases; template recovery; and the possibility to use template
analogues instead of harmful analytes [25].
Although the first applications of MIPs as MRE in sensors
were of interest mainly for electrochemical transducers, their
use gradually extended to optical sensors, thanks to their immunity
to electromagnetic field interferences. Up to now,
several MIP-based SPR sensors have been realized in the most
varied application fields.
In 2013, Cennamo et al. realized an optical chemical sensor
based on SPR and MIP for the detection of Trinitrotoluene
(TNT) in aqueous solution [26], particularly interesting for the
security field. The SPR sensor was prepared as mentioned before
[16]. The planar gold layer was employed for depositing
an MIP layer used as the specific receptor. A very low volume
of 100 μl of the prepolymeric mixture containing TNT as the
template molecule was dropped directly on the D-shaped gold
surface of the POF and spun at 1000 rpm for 35 s. The polymerization
was then carried out at 70 °C for about 16 h. Then,
TNT was extracted by an appropriate washing procedure. The
experimental setup, arranged to measure the transmitted light
spectrum, was characterized by a halogen lamp, illuminating
the optical sensor system and a spectrum analyzer. The sensor
was characterized by dropping aqueous solutions of TNT directly
on the D-shaped chemically modified sensing region.
The realized sensor demonstrated the ability to detect TNT
even at low concentration, down to about 50 μM [26].
In 2015, the same authors realized a different sensor configuration
for TNT detection, this time based on LSPR with
improved performances. LSPR was excited in five-branched
gold nanostars (GNS) suspended in the MIP (GNS-MIP) specific
for TNT [27]. To better investigate the sensitivity, the
sensing layer was deposited directly on two different POF
platforms: tapered and not-tapered. Both sensors showed better
performances than the previously proposed, in which the
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,
the sensor with a GNS-MIP sensing layer on the not-tapered
POF exhibited a sensitivity of 8.5 × 104
nm/ M, three times
higher than in the gold layer sensor. The sensor with GNS-MIP
sensing layer on the tapered POF demonstrated a further sensitivity
up to 8.3 × 105
nm/M, thirty times higher than in the
gold layer sensor [27].
Recently an interesting application of SPR-POF-MIP sensors
has been developed for the detection of a particular class
of emerging pollutants, perfluoroalkyl substances (PFAs).
These pollutants are widely distributed in the environment,
and it is possible to detect them in various kinds of
micro-polluted water, such as river water, lake water and seawater.
Due to their chemical stability, they are particularly
inert and refractory to different chemical and microbiological
treatments. Consequently, they are persistent, bio-accumulative
and toxic to mammalian species. In fact, the immune-toxic
effects of PFAs are largely demonstrated. Thus, great efforts
must be done to identify possible novel approaches for
water treatment and/or detection of the PFAs in the environment.
The detection of such substances is performed by using
Fig. 1. (a) Resonance spectra obtained at different concentrations of PFBS in water solution (0 - 20.7 ppb) by a plasmonic POF-MIP sensor. Inset: zoom of the
resonance wavelengths. Adapted from Cennamo et al. [28]. (b) Dose-response curve (resonance wavelength versus PFBS concentration) along with Hill Fitting of
data [28]. (Figures used with permission, ©IEEE, 2019).
52
IEEE Instrumentation & Measurement Magazine
August 2021

Instrumentation & Measurement Magazine 24-5

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