# Nanodroplets versus Nanofibers Ion-Selective Optodes toward Biocompatible Sensors

## TL;DR

This paper compares nanodroplets and nanofibers as biocompatible ion-selective sensors, showing both can detect calcium ions effectively in unbuffered samples.

## Contribution

The study introduces a novel comparison of nanodroplet and nanofiber formats for ion-selective optodes using biocompatible materials.

## Key findings

- Both nanodroplets and nanofibers showed increased Nile red emission intensity with higher calcium ion concentration.
- Nile blue emission changes were specific to the format, with nanofibers showing consistent results within experimental error.
- Nanofiber mats allow for optical signal detection in and out of solution, offering reusability and flexibility in sensor application.

## Abstract

This work compared the performance of ion-selective optodes
in
different nanostructural formats: nanodroplets and nanofibers prepared
from biocompatible materials using classical ionophores and ion exchangers.
Nanodroplets tested contained minute amounts of plasticizer acetyl
tributyl citrate stabilized with poly­(vinyl alcohol) and were suspended
in the aqueous phase. It was shown that this system was not directly
transferable to the nanofiber format; thus, nanofibers obtained from
polycaprolactone were used as the support material. Both nanodroplets
and nanofibers were used in Nile blue/Nile red-based systems operating
as novel ion-selective sensor optical transducers, allowing sensors
to be applied in unbuffered samples. As a model system, calcium sensors
were prepared and tested. It was shown that, regardless of format,
optodes were characterized by increased emission intensity at the
Nile red characteristic wavelength (605 nm) for increasing calcium
ion concentration in the sample. Nile blue emission changes for varying
analyte concentrations were specific for the format (they changed
for nanodroplets, whereas for nanofibers, they were similar within
the range of experimental error). For both systems, a linear dependence
of the ratio of emission intensity was recorded for Nile red and Nile
blue characteristic wavelength on the changes in analyte concentration
in the sample within the range from 10–5 to 10–1 M. The unique advantages of using nanofiber mats
include the determination of optical signals for both sensors present
in solution and probes removed from solution; moreover, the same sensor
can be transferred between different solutions. This is a clear advantage
of the application of nanofiber mats as sensors, especially when used
on a dedicated, 3D-made holder.