Wearable
systems could offer noninvasive and real-time solutions
for monitoring of biomarkers in human sweat as an alternative to blood
testing. Recent studies have demonstrated that the concentration of
certain biomarkers in sweat can be directly correlated to their concentrations
in blood, making sweat a trusted biofluid candidate for noninvasive
diagnostics. We introduce a fully on-chip integrated wearable sweat
sensing system to track biochemical information at the surface of
the skin in real time. This system heterogeneously integrates, on
a single silicon chip, state-of-the-art ultrathin body (UTB) fully
depleted silicon-on-insulator (FD-SOI) ISFET sensors with a biocompatible
microfluidic interface, to deliver a “lab-on-skin” sensing
platform. A full process for the fabrication of this system is proposed
in this work and is demonstrated by standard semiconductor fabrication
procedures. The system is capable of collecting small volumes of sweat
from the skin of a human and posteriorly passively driving the biofluid,
by capillary action, to a set of functionalized ISFETs for analysis
of pH level and Na+ and K+ concentrations. Drop-casted
ion-sensing membranes on different sets of sensors on the same substrate
enable multiparameter analysis on the same chip, with small and controlled
cross-sensitivities, whereas a miniaturized quasireference electrodes
set a stable analyte potential, avoiding the use of a cumbersome external
reference electrode. The progress of lab-on-skin technology reported
here can lead to autonomous wearable systems enabling real-time continuous
monitoring of sweat composition, with applications ranging from medicine
to lifestyle behavioral engineering and sports.
Ion
sensitive field effect transistors (ISFETs) form a very attractive
solution for wearable sensors due to their capacity for ultra-miniaturization,
low power operation, and very high sensitivity, supported by complementary
metal oxide semiconductor (CMOS) integration. This paper reports for
the first time, a multianalyte sensing platform that incorporates
high performance, high yield, high robustness, three-dimensional-extended-metal-gate
ISFETs (3D-EMG-ISFETs) realized by the postprocessing of a conventional
0.18 μm CMOS technology node. The detection of four analytes
(pH, Na+, K+, and Ca2+) is reported
with excellent sensitivities (58 mV/pH, −57 mV/dec(Na+), −48 mV/dec(K+), and −26 mV/dec(Ca2+)) close to the Nernstian limit, and high selectivity, achieved
by the use of highly selective ion selective membranes based on postprocessing
integration steps aimed at eliminating any significant sensor hysteresis
and parasitics. We are reporting simultaneous time-dependent recording
of multiple analytes, with high selectivities. In vitro real sweat
tests are carried out to prove the validity of our sensors. The reported
sensors have the lowest reported power consumption, being capable
of operation down to 2 pW/sensor. Due to the ultralow power consumption
of our ISFETs, we achieve and report a final four-analyte passive
system demonstrator including the readout interface and the remote
powering of the ISFET sensors, all powered by an radio frequency (RF)
signal.
Cell adhesion processes take place through mechanotransduction mechanisms where stretching of proteins results in biological responses. In this work, we present the first cyto-mechanoresponsive surface that mimics such behavior by becoming cell-adhesive through exhibition of arginine-glycine-aspartic acid (RGD) adhesion peptides under stretching. This mechanoresponsive surface is based on polyelectrolyte multilayer films built on a silicone sheet and where RGD-grafted polyelectrolytes are embedded under antifouling phosphorylcholine-grafted polyelectrolytes. The stretching of this film induces an increase in fibroblast cell viability and adhesion.
GFP has been genetically modified at two specific positions of its molecular architecture. These modifications allow its covalent attachment onto PEG brushes grafted on functionalized silicone surfaces. The stretching of this material leads to a reversible decrease of the fluorescence intensity due to stretch-induced forces applying on GFP molecules.
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