Xing Xuan

A Fully Integrated and Miniaturized Heavy-metal-detection Sensor Based on Micro-patterned Reduced Graphene Oxide

For this paper, a fully integrated and highly miniaturized electrochemical sensor was designed and fabricated on a silicon substrate. A solvothermal-assisted reduced graphene oxide named “TRGO” was then successfully micro-patterned using a lithography technique, followed by the electrodeposition of bismuth (Bi) on the surface of the micro-patterned TRGO for the electrochemical detection of heavy metal ions. The fully integrated electrochemical micro-sensor was then measured and evaluated for the detection of cadmium and lead-heavy metal ions in an acetic-acid buffered solution using the square wave anodic stripping voltammetry (SWASV) technique. The fabricated micro-sensor exhibited a linear detection range of 1.0 μg L−1 to 120.0 μg L−1 for both of the metal ions, and detection limits of 0.4 μg L−1 and 1.0 μg L−1 were recorded for the lead and cadmium (S/N = 3), respectively. Drinking-water samples were used for the practical assessment of the fabricated micro-sensor, and it showed an acceptable detection performance regarding the metal ions.

A wearable electrochemical glucose sensor based on simple and low-cost fabrication supported micro-patterned reduced graphene oxide nanocomposite electrode on flexible substrate

In this study, a reduced graphene oxide (rGO)-based nanostructured composite working electrode of high quality was successfully microfabricated and micro-patterned on a flexible polyimide substrate using simple low-cost fabrication processes. Gold and platinum alloy nanoparticles were electrochemically deposited onto the microfabricated rGO surface and chitosan-glucose oxidase composites were integrated onto the modified surface of the working electrode to develop a human sweat-based wearable glucose sensor application. The fabricated biosensor exhibited excellent amperometric response to glucose at a detection range of 0-2.4 mM (covers the glucose range in sweat), with a sensitivity of 48 μA/mMcm2, a short response time (20 s), and high linearity (0.99). The detection limit for glucose was calculated as 5 µm. The human sweat/mixing glucose samples initially used for testing indicated acceptable detection performance and stability for low glucose concentrations. These results confirm that the proposed nanostructured composite flexible working electrode and fabrication process are highly promising for application as human sweat-based electrochemical glucose sensors.

Semi-implantable glucose sensor based on dual-stacked polymeric film for wireless continuous monitoring

In this paper, we have newly developed semi-implantable non-enzymatic glucose sensor based on dual-stacked biocompatible polymeric film for wireless continuous monitoring. The dual-stacked polymeric film is comprised of polyimide (PI) and hard cured SU-8 in order to improve the adhesion and durability of substrate. Nanoporous Pt (nPt) was successfully deposited on the dual-stacked polymeric film as working and counter electrodes for glucose sensor fabrication. The fabricated sensor was interconnected and tested with wireless monitoring system. The sensitivity of glucose sensor was 5.7 μA/mM·cm2 and R square between output signal and real glucose value was 0.912.

Implantable enzyme free glucose sensor based on flexible stainless steel for continuous monitoring and mass production

In this study, implantable and flexible enzyme free glucose sensor was developed by using thin medical grade stainless steel for continuous glucose monitoring and mass production. Unlike conventional polymer substrate, a thin stainless steel based sensing electrode has large effective surface area and small difference in the coefficient of thermal expansion between the substrate and electrode. Furthermore, electroplating technique was useful for the mass production of sensor due to simple fabrication steps. The fabricated glucose sensor exhibited the sensitivity of 1 μA/mM and response time of 15 s. In addition, it also showed a good current response to glucose in human plasma with the sensitivity of 0.45 μA/mM and correlation coefficient of 0.94071.

A highly stretchable and conductive 3D porous graphene metal nanocomposite based electrochemical-physiological hybrid biosensor

Recently, highly stretchable and flexible electrodes essential for wearable electronic devices has been reported. However, their electrical resistances are high, the fabrication processes are complicated and involve a high cost, and deformations such as stretching can lead to the degradation on electrical performance. To address these issues, a novel fabrication process (both inexpensive and simple) for the highly stretchable and conductive electrodes using well patterned 3D porous laser-induced graphene silver nanocomposite was developed. The fabricated electrode exhibited a high, uniform electrical conductivity even under mechanical deformations. Addition of platinum and gold nanoparticles (PtAuNP) on the 3D porous LIG greatly improved the electrochemical performance for wearable glucose sensor applications. The fabricated glucose sensor exhibited low detection limit (5 µM), and acceptable detection range from 0 to 1.1 mM (covers the glucose range in sweat), and high linearity (0.99). In addition, the fabricated pH sensor also exhibited a linear response (66 mV/pH) at the range from 4 to 7. This work successfully demonstrates the potential of this novel fabrication technique and stretchable LIG metal nanocomposite for wearable electrochemical-physiological hybrid biosensors.

Wearable, robust, non-enzymatic continuous glucose monitoring system and its in vivo investigation

Electroplating of nanoporous Pt (nPt) induces an extremely strong tensile stress, which results in the exfoliation of nPt on flexible polymer substrate despite plasma treatment to improve adhesion. Here, we overcame this challenge by modifying flexible stainless-steel, and developed wearable, robust, flexible, and non-enzymatic continuous glucose monitoring system. The flexible stainless-steel was highly effective in improving the adhesion between the metal layer and substrate. The developed wireless system included electrochemical analysis circuits, a microcontroller unit, and a wireless communication module. Finally, we evaluated the continuous glucose monitoring system through two animal testing, by implanting into subcutaneous tissue and measuring interstitial fluid (ISF) glucose values at 5-15-min intervals. Comparison of the measured ISF glucose with blood glucose determined by the Clarke error grid analysis showed that 82.76% of the measured glucose was within zone A. Furthermore, the wearable glucose sensor exhibited bio-compatible to implant through various bio-compatibility tests.

Semi-implantable polyimide/PTFE needle-shaped biosensor for continuous glucose monitoring

In this paper, semi-implantable and highly miniaturized needle-shaped biosensor was newly developed for painless and continuous glucose monitoring. Three electrochemical electrodes (nanoporous Pt and Ag/AgCl for working, counter, and reference electrodes, respectively) were micro-fabricated on a flexible polyimide film using electroplating technique, diced, and firmly wrapped onto a medical PTFE catheter by using silicone adhesive. The fabricated bio-sensor was much improved in stability and reliability because the PTFE catheter was used as the supporting structure of flexible sensor. The fabricated sensor could also be easily delivered to subcutaneous tissue by using stainless steel guide needle through minimally invasive tool without surgery. In addition, the catheter can also simultaneously be sued as a tool for drug delivery. Diameter and total length of the polyimide/PTFE needle is 900 μm and 500 mm, respectively. The fabricated bio-sensor indicated 415 nA/mM of sensitivity and 0.996 of R-square for glucose and good selectivity for interfering reagents. In addition, in-vivo measurement was successfully demonstrated in the dynamic glucose variation during 2 hours.