Fabrication of a Wearable Flexible Sweat pH Sensor Based on SERS-Active Au/TPU Electrospun Nanofibers

Abstract

Development of wearable sensing platforms is essential for the advancement of continuous health monitoring and point-of-care testing. Eccrine sweat pH is an analyte that can be noninvasively measured and used to diagnose and aid in monitoring a wide range of physiological conditions. Surface-enhanced Raman scattering (SERS) offers a rapid, optical technique for fingerprinting of biomarkers present in sweat. In this paper, a mechanically flexible, nanofibrous, SERS-active substrate was fabricated by a combination of electrospinning of thermoplastic polyurethane (TPU) and Au sputter coating. This substrate was then investigated for suitability toward wearable sweat pH sensing after functionalization with two commonly used pH-responsive molecules, 4-mercaptobenzoic acid (4-MBA), and 4-mercaptopyridine (4-MPy). The developed SERS pH sensor was found to have good resolution (0.14 pH units for 4-MBA; 0.51 pH units for 4-MPy), with only 1 μL of sweat required for a measurement, and displayed no statistically significant difference in performance after 35 days (p = 0.361). Additionally, the Au/TPU nanofibrous SERS pH sensors showed fast sweat-absorbing ability as well as good repeatability and reversibility. The proposed methodology offers a facile route for the fabrication of SERS substrates which could also be used to measure a wide range of health biomarkers beyond sweat pH.

Flexible microfluidic nanoplasmonic sensors for refreshable and portable recognition of sweat biochemical fingerprint

“…Such a microfluidic device ensures continuous freshly-secreted sweat sampling. In this way, the risk of mixed effect between new and old sweat can be minimized 10 , which is a key improvement compared to non-microfluidic sweat SERS system 35,38,39 . Surprisingly, only 0.5 μL of sample solution was sufficient to produce Raman signal for pH measurement.…”

“…Flexible plasmonic devices by integration of SERS with wearable techniques have attracted tremendous attention for diverse wearable biomedical applications [32][33][34][35][36][37] . At the present, only few wearable SERS sweat sensors have been demonstrated 35,38,39 . However, these non-microfluidic sweat systems rely on sweat-permeable (porous) SERS substrates that allow sweat to wick and occupy the hotspots.…”

Fast Synthesis of Au Nanoparticles on Metal–Phenolic Network for Sweat SERS Analysis

“…The electrolyte content determines the pH value of sweat. 4-MBA is a well-defined pH-responsive molecule that has been widely used for pH sensing [ 14 , 45 , 46 ]. We also fabricated a pH SERS nanoprobe by covalently grafting 4-MBA onto Au-MPN.…”

“…The use of real-time portable photoelectric sensors helps to provide athletes with scientific sports data, formulate better training programs, and avoid training risk [ 13 ]. However, the accurate detection of a tiny volume of sweat is still a challenge [ 14 ].…”

Disposable pH Sensor on Paper Using Screen-Printed Graphene-Carbon Ink Modified Zinc Oxide Nanoparticles

“…A wide range of pH sensing techniques ranging from optical to electrochemical to physicochemical methods has been developed using materials such as metal oxides, polymer, and carbon-based composites. However, not all are suitable for in situ soil condition monitoring in agricultural applications, where disposable sensors capable of providing single and/or multiple reliable measurements over a short duration are preferred [7]. As an example, traditional glass-based pH sensors are bulky, and it is difficult to have them in a portable and biocompatible form to enable a large number of sensor deployments in smart agriculture settings [8].…”