Photoplasmonic platforms are being
demonstrated as excellent means
for bridging nanochemistry and biosensing approaches at advanced interfaces,
thereby augmenting the sensitivity and quantification of the desired
analytes. Although resonantly coupled electromagnetic waves at the
surface plasmon-coupled emission (SPCE) interface are investigated
with myriad nanomaterials in order to boost the detection limits,
rhodamine moieties are ubiquitously used as SPCE reporter molecules
in spite of their well-known limitations. In order to overcome this
constraint, in this work, a benzoxazolium-based fluorescent molecule,
(E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]oxazol-3-ium iodide (DSBO), was synthesized
to selectively detect the cyanide (CN–) ions in
water samples. To this end, the sensitivity of the fabricated SPCE
substrates is tested in spacer, cavity, and extended cavity nanointerfaces
to rationalize the configurational robustness. The performance of
the sensor is further improved with the careful engineering of gold
(Au)-graphene oxide (GO) cryosoret nanoassemblies fabricated via an
adiabatic cooling technology. The unique dequenching (turn-on) of
the quenched (turn-off) fluorescent signal is demonstrated with the
hybridized metal-π plasmon synergistic coupling in the nanovoids
and nanocavities assisting delocalized Bragg and localized Mie plasmons.
The spectro-plasmonic analysis yielded highly directional, polarized
(>95%), and enhanced emission attributes with an attomolar limit
of
detection of 10 aM of CN– ions with high linearity
(R
2 = 0.996) and excellent reliability,
in addition to an exceptional correlation with the theoretically obtained
TFclac simulations. The CN– ion sensing is experimentally
validated with the smartphone-based cost-effective SPCE detection
technology to render the device amenable to resource-limited settings.
We believe that the unique fluorophore–cryosoret nanoassemblage
presented here encourages development of frugal, unconventional, and
highly desirable strategies for the selective quantitation of environmentally
and physiologically relevant analytes at trace concentrations for
use in point-of-care diagnostics.
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