5 research outputs found
Polyacrylate Microspheres for Tunable Fluorimetric Zinc Ions Sensor
A novel
concept of optical fluorimetric sensing using polymeric
microspheres is explored on example of zinc ions sensors. The novel
approach proposed uses the advantage of concomitant presence in a
microsphere of two compounds: a receptor, fluorescently silent complexing
ligand and an optical transducer, fluorescent compound. Binding of
the analyte by the ligand affects its absorption spectrum, leading
to decrease of the free ligand absorption and increase of complex
absorption band. The decrease of free ligand absorption exposes emission
of the transducer, yielding increase in fluorescence intensity on
analyte concentration increase. This approach was verified experimentally
using Zn<sup>2+</sup> as a model analyte, the fluorimetric sensor
obtained uses 1-(2-pyridylazo)-2-naphthol (PAN) as analyte sensitive
receptor and pyrene as optical transducer. In the absence of zinc
ions in the sample emission of pyrene embedded in the spheres was
significantly quenched, whereas increase of Zn<sup>2+</sup> ions concentration
in the sample resulted in dependence of fluorescence intensity on
logarithm of zinc ions concentration in extraordinary wide range,
from 10<sup>ā7</sup> to 0.1 M. The response mechanism was explained
by surface accumulation of zinc ionāPAN complex on the microsphere/sample
solution interface. It was also shown that introduction of cation-exchanging
sites to the microspheres significantly alters the responses pattern
leading to high sensitivity over relatively limited concentration
range (3ā4 orders of magnitude). In the latter case the observed
responses can be tuned to occur in chosen concentration range, simply
by adjusting sample pH
Fate of Poly(3-octylthiophene) Transducer in Solid Contact Ion-Selective Electrodes
An experimental approach
allowing visualization and quantification
of the underestimated spontaneous process of partition of conducting
polymer transducer material to the ion-selective membrane phase is
proposed. The approach proposed is based on optical properties of
the transducer material applied, using polythiophene as a model system.
It is shown that this process occurs not only during the sensor preparation
step but also during pretreatment of the sensor before use. As shown,
this uncontrolled partition of the transducer to the receptor leads
to conducting polymer contents in the membrane phase reaching 0.5%
w/w; this process is accompanied by a partial spontaneous change of
the oxidation state of polythiophene. The conducting polymer present
in the membrane participates to some extent in the overall response
of the sensor, which can be observed as a change in the polythiophene
optical emission spectra. Fluorescence microscopic images obtained
clearly show that the conducting polymer is distributed throughout
the membrane thickness, being present also at the membrane/solution
interface. The experimental results presented were obtained for K<sup>+</sup>-selective sensors using polyĀ(3-octylthiophene) as a model
transducer; however, the proposed approach is also applicable for
other systems
Nanofiber-Supported Palladium NanocubesToward Highly Active and Reusable Catalyst
Electrospun nanofibers were used to support palladium
nanocubes,
resulting in a highly active, stable, and reusable catalyst. The system
proposed herein offers significant advantages compared to catalysts
in the form of nanoparticles suspension. The porous, solvent permeable
structure of the nanofiber mat ensures uniform and stable time distribution
of palladium nanoparticles; preventing coalescence and allowing multiple
use of the catalyst. The proposed cross-linked poly(vinyl alcohol)
nanofiber mat loaded with Pd nanocubes during the nanofiber preparation
step is a macroscopic structure of intrinsically nanostructural character
of the catalyst that can be easily transferred between different solutions
without compromising its effectiveness in consecutive cycles. Thus,
obtained system was characterized with high catalytic activity as
tested on a model example of 4-nitrophenol (4-NP) reduction by NaBH4 to 4-aminophenol (4-AP). It is shown that loading nanofibers
with Pd nanocubes during electrospinning resulted in a significantly
more stable system compared to surface modification of obtained nanofibers
with nanocube suspension
Nanoparticles of Fluorescent Conjugated Polymers: Novel Ion-Selective Optodes
A novel
type of ion-selective nano-optode is proposed, in which
a conjugated polymer is used as optical transducer and nanoprobe material.
Thus, contrary to most of the proposed optodes, the response does
not require presence of pH-sensitive dye in the sensor. The conjugated
polymer nanosensor material is in partially oxidized formīøit
is bearing positive charges and its emission is quenched. The receptor
is an optically silent uncharged ionophore selective for the analyte
cation. When a binding event occurs, positive charges are formed in
the nanosphere, leading to a decrease in the oxidation state of the
polymer, in the absence of redox potential change, resulting in increased
emission. This general approach herein proposed results in a simple
sensor, benefitting from a novel optical transduction mechanism and
high lipophilicity of the polymer matrix that results in linear responses
over a broad concentration range of analyte. For the model system
studied, the linear dependence of emission intensity on the logarithm
of analyte (K<sup>+</sup>) concentration was obtained for a broad
range from 10<sup>ā5</sup> M to 0.1 M
Dithizone Modified Gold Nanoparticles Films for Potentiometric Sensing
For the first time, application of a membrane composed
of gold nanoparticles decorated with complexing ligand for potentiometric
sensing is shown. Gold nanoparticles drop cast from a solution form
a porous structure on a substrate electrode surface. Sample cations
can penetrate the gold nanoparticles layer and interact with ligand
acting as a charged ionophore, resulting in Nernstian potentiometric
responses. Anchoring of complexing ligand on the gold surface abolishes
the necessity of ionophore application. Moreover, it opens the possibility
of preparation of potentiometric sensors using chelators of significantly
different selectivity patterns further enhanced by the absence of
polymeric membrane matrix. This was clearly seen, for example, for
gold nanoparticles stabilizing the applied ligandādithizoneāthiol
conformation leading to a high potentiometric selectivity toward copper
ions, much higher than that of ionophores typically used to induce
selectivity for polymeric ion-selective membranes