This article reviews the principles, design and applications of visible-light and near-infrared fluorescence and surface-enhanced Raman scattering in point-of-care testing and bio-imaging.
Conventional paper lateral flow assays
have low sensitivity and
suffer from severe interference from complex human fluid sample matrices,
which prevents their practical application in the testing of whole
blood samples in the point-of-care settings. To solve this problem,
gold nanostar@Raman reporter@silica-sandwiched nanoparticles have
been developed as the surface-enhanced Raman scattering (SERS) probes
for sensing transduction; and a functionalized filter membrane assembly
has been designed and constructed in the paper-based lateral flow
strip (PLFS) as a built-in plasma separation unit. In this “on-strip”
plasma separation unit, three layers of filter membranes are stacked
and surface-modified to maximize the separation efficiency and the
plasma yield. As a result, the integrated PLFS has been successfully
used for the detection of carcinoembryonic antigen (CEA) in 30 μL
of whole blood with the assistance of a portable Raman reader, achieving
a limit of detection of 1.0 ng mL–1. In short, this
report presents an inexpensive, disposable, portable, and field-deployable
paper-based device as a general point-of-care testing tool for protein
biomarker detection in a drop of whole blood.
Currently cation doping is common for improving ionic conductivity of metal oxide-based lithium-ion conductors. In this work, anions (nitrogen ions) have been doped to perovskite Li3xLa2/3 − xTiO3 (LLTO) nanofibers by heat treatment in the ammonia-containing atmosphere, and substituted for oxygen anions partially in the perovskite structure. Density-functional theory (DFT) calculation results reveal that nitrogen doping weakens the bonding of Li ions on the A sites in perovskite ABO3 structure and allows for larger lattice distortion, reducing the activation energy for Li-ion hopping in both the forward and backward jumping directions. Experimental results have also confirmed that nitrogen doping has improved ionic conductivity of LLTO. Nitrogen-doped LLTO nanofibers have been incorporated with a poly (vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) polymer to form a solid-state composite electrolyte, which exhibits ionic conductivity of 3.8 × 10−4 S·cm−1 at room temperature and an electrochemical stability window of up to 4.9 V vs Li∣Li+. The all-solid-state Li metal∣composite electrolyte∣LiFePO4 lithium batteries, which employ nitrogen-doped LLTO nanofibers, show better rate capability and cycling stability at room temperature than the counterparts with pristine LLTO nanofibers.
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