Fabrication and Optimization of Fiber-Based Lithium Sensor: A Step toward Wearable Sensors for Lithium Drug Monitoring in Interstitial Fluid

Abstract

A miniaturized, flexible fiber-based lithium sensor was fabricated from low-cost cotton using a simple, repeatable dip-coating technique. This lithium sensor is highly suited for ready-to-use wearable applications and can be used directly without the preconditioning steps normally required with traditional ion-selective electrodes. The sensor has a stable, rapid, and accurate response over a wide Li concentration range that spans over the clinically effective and the toxic concentration limits for lithium in human serum. The sensor is selective to Li in human plasma even in the presence of a high concentration of Na ions. This novel sensor concept represents a significant advance in wearable sensor technology which will target lithium drug monitoring from under the skin.

Thread-Based Sensors

“…A cotton fiber-based lithium sensor was fabricated by dip-coating cotton thread (5 mm) in SWCNT ink until a resistance of 500 Ω had been reached. The resulting dry conductive cotton fiber was further dip-coated 9 times with lithium membrane solution [5]. The lithium membrane solution was composed of 28 wt% PVC, 68.5 wt% NPOE, 1.5 wt% Li ionophore VI, 0.5 wt % lithium tetrakis(pentafluorophenyl)borate ethyl etherate (LiTPFPB) and 1.5% TOPO.…”

“…CNT-coated cotton was applied to pH, K + and NH4 + sensing [3]. This paper describes recent research at Surrey developing pH and lithium drug sensors, based on cotton threads [4,5]. Epidermal pH gives an indication of the skin physiology and the state of wound healing.…”

Towards wearable and implantable continuous drug monitoring: A review

“…In addition, Sweilam et al [ 38 ] developed a miniaturised, flexible fibre-based sensor for constant detection of lithium, the main antipsychotic drug for treating mood disorders. Functionalised with single-walled carbon nanotubes (SWCNT) and an ion-selective membrane cocktail, the lithium sensor detected lithium in aqueous LiCl solutions without the preconditioning steps required for traditional ion-selective electrodes.…”

“… Type Sensing platforms Surface modification Drug Testing medium LOD (Linear range) Assay time (Duration) Comments Ref. In vitro E-NB Sensor: Graphite SPE MWCNTs + Cytochrome P450 Naproxen Mouse serum Buffer: 16 μM, serum: 33 μM (50–300 μM) N/A (16 h) High sensitivity, extreme simplicity, and low cost [ 35 ] E-NB Sensor: PGE 58% graphite + 36% clay + 5% wax Propofol Buffer 7.79 μM (1–60 μM) N/A (4 h) High sensitivity and prevents of fouling [ 36 ] E-NB Sensor: PGE-based IoT system 58% graphite + 36% clay + 5% wax Propofol Paracetamol Full human serum N/A for both (APAP: 10–80μM, Para: 50–250μM) 30 s (24 min) Includes a PCB, a PDMS fluidic device, and an IoT network [ 37 ] E-NB Sensor: Conductive cotton fibre SWCNT + ion-selective membrane Lithium Solution; human plasma N/A (0.40–8.00 μM) Solution: <20 s (26 min) High potential for use as a wearable sensor [ 38 ] Ex-vivo Ex vivo E-AB Sensor MB-modified aptamer Doxorubicin Humans; Rats Buffer: 0.01μM (nonlinear: 0.01–10.00 μM) 45 s (4.5 h) Antif...…”

Solid-Contact Ion-Selective Electrodes: Response Mechanisms, Transducer Materials and Wearable Sensors

“…The composition of interstitial fluid and human plasma have great in common, except for a higher protein content in the latter. Considering the difficulty of commercial acquisition of interstitial fluid, human plasma was used in this work to Considering the difference of ion concentrations measurements inside and outside of the skin, Crean et al fabricated a conductive cotton fiber-based SC-ISEs for realizing extraction and analysis simultaneously combined with reverse iontophoresis [89] (Figure 11D,E). This can also be viewed as another kind of in-situ monitoring with simplified approach.…”