Real-time
transdermal biosensing provides a direct route to quantify biomarkers
or physiological signals of local tissues. Although microneedles (MNs)
present a mini-invasive transdermal technique, integration of MNs
with advanced nanostructures to enhance sensing functionalities has
rarely been achieved. This is largely due to the fact that nanostructures
present on MNs surface could be easily destructed due to friction
during skin insertion. In this work, we reported a dissolvable polymer-coating
technique to protect nanostructures-integrated MNs from mechanical
destruction during MNs insertion. After penetration into the skin,
the polymer could readily dissolve by interstitial fluids so that
the superficial nanostructures on MNs could be re-exposed for sensing
purpose. To demonstrate this technique, metallic and resin MNs decorated
with vertical ZnO nanowires (vNWs) were employed as an example. Dissolvable
poly(vinyl pyrrolidone) was spray-coated on the vNW-MNs surface as
a protective layer, which effectively protected the superficial ZnO
NWs when MNs penetrated the skin. Transdermal biosensing of H2O2 biomarker in skin tissue using the polymer-protecting
MNs sensor was demonstrated both ex vivo and in vivo. The results
indicated that polymer coating successfully preserved the sensing
functionalities of the MNs sensor after inserting into the skin, whereas
the sensitivity of the MN sensor without a coating protection was
significantly compromised by 3-folds. This work provided unique opportunities
of protecting functional nanomodulus on MNs surface for minimally
invasive transdermal biosensing.
The temperature and pressure of seawater are of great importance to investigate the environmental evolution for the research of ocean science. With this regard, we proposed and experimentally demonstrated a seawater temperature and pressure sensor realized by a polyimide (PI) tube-based Fabry-Perot interferometer (FPI) together with a fiber Bragg grating (FBG). Benefiting from the higher thermo-optical coefficient and larger elasticity of polymer than the fused silica fiber, the sensitivity of the sensor is largely improved. The FBG is used to compensate the cross effect of the temperature. The measured temperature and pressure sensitivities of the sensor are 18.910 nm/°C and −35.605 nm/MPa, respectively. Furthermore, the temperature and pressure information measured by the sensor can be achieved simultaneously using the sensitivity matrix method. In addition, the proposed sensor has advantages of easy fabrication, compact size, as well as capability of multiplexing and long-distance measurement, making it competitive and promising during the marine monitoring.
A Sagnac loop interferometer based on concatenated polarization-maintaining fiber (PMF) tapers is proposed for simultaneous measurement of seawater salinity and temperature. The influences of the distance between the PMF tapers as well as fiber taper diameter on sensor performance have been investigated. Experimental results indicate that the fabricated sensor with a distance of 3 cm between adjacent fiber tapers possesses the salinity and temperature sensitivities of 0.367 nm/% and
−
0.728
n
m
/
∘
C
, respectively, and the taper waist diameter of 20 µm would help to improve salinity sensitivity in comparison with a sensor of 30 µm in diameter. The proposed Sagnac loop interferometer based on concatenated PMF tapers is expected to find potential applications in the measurement of seawater salinity.
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