Optical sensors capable of colorimetric visualization and/or fluorescence detection have shown tremendous potential for field technicians and emergency responders, owing to the portability and low cost of such devices. Polydiacetylene (PDA)-enhanced nanofibers are particularly promising due to high surface area, facile functionalization, simple construction, and the versatility to empower either colorimetric or fluorescence signaling. We demonstrate here a dual-mode optical sensing with electrospun nanofibers embedded with various PDAs. The solvent-dependent fluorescent transition of nanofibers generated a pattern that successfully distinguished four common organic solvents. The colorimetric and fluorescent sensing of biotin-avidin interactions by embedding biotinylated-PCDA monomers into silica-reinforced nanofiber mats were realized for detection of biomolecules. Finally, a PDA-based nanofiber sensor array consisting of three monomers has been fabricated for the determination and identification of organic amine vapors using colorimetry and principal component analysis (PCA). The combination of PCA and the strategy of probing analytes in two different concentration ranges (ppm and ppth) led to successful analysis of all eight amines.
A hybrid computational and experimental approach was employed toward the rational design of a silver nanoparticle (AgNP)/polydiacetylene (PDA) metal-enhanced fluorophore (MEF) ensemble system contained within a poly(ethylene oxide) (PEO) electrospun nanofiber matrix for creation of high-performance sensors. Simulations based on Mie theory and finite-difference time domain (FDTD) algorithms were performed to understand and optimize spectral overlap between the AgNP localized surface plasmon resonance and the absorbance and emission spectra of PDA, a supramolecular polymer fluorophore. A series of AgNPs of varied sizes were investigated for fluorescence enhancement capability, and an optimal size of 134 nm in diameter was chosen for synthesis and incorporation into the electrospun nanofibers of a PDA/PEO composite for experimental characterization and confirmation. Results on individual nanofibers indicated a clear metal-enhanced fluorescence effect, and a 4.6-fold enhancement over neat PDA/PEO fluorescent nanofibers was observed. The nanofiber/nanoparticle/MEF ensemble system offers new avenues for generating effective sensing devices with polymeric fluorophores using a straightforward incorporation approach.
Electrospun nanofibers of a polyaniline (PANi)/ (?)-camphor-10-sulfonic acid (HCSA)/poly(ethylene oxide) (PEO) composite doped with different variants of graphene oxide (GO) were fabricated and evaluated as chemiresistor gas sensors operating at room temperature. A new strategy for enhancing PANi/PEO gas sensor performance is demonstrated using GO dopants reduced via thermal (trGO) or chemical (crGO) routes. By varying the chemical reduction duration (6 h, crGO-6 or 24 h, crGO-24), tunable enhancement of sensor response was achieved. Upon exposure to short-chain aliphatic alcohol vapors, the partially reduced crGO-6 dopant exhibited higher response than GO and crGO-24, suggesting that the dopant enhances sensor performance via increased electrical conductivity over neat GO, and enhanced hydrogen bonding capability over the further-reduced crGO-24 variant. Sensor arrays consisting of PANi/PEO doped with trGO, crGO-6 or crGO-24 moieties successfully identified methanol, ethanol, and 1-propanol vapors using principal component analysis (PCA). Graphical abstract
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