Wearable Microneedle-Based Array Patches for Continuous Electrochemical Monitoring and Drug Delivery: Toward a Closed-Loop System for Methotrexate Treatment.

Wearable devices based on microneedle (MN) technology have recently emerged as tools for in situ transdermal sensing or delivery in interstitial fluid (ISF). Particularly, MN-based electrochemical sensors allow the continuous monitoring of analytes in a minimally invasive manner through ISF. Exogenous small molecules found in ISF such as therapeutic drugs are ideal candidates for MN sensors due to their correlation with blood levels and their relevance for the optimal management of personalized therapies. Herein, a hollow MN array patch is modified with conductive pastes and functionalized with cross-linked chitosan to develop an MN-based voltammetric sensor for continuous monitoring of methotrexate (MTX). Interestingly, the chitosan coating avoids biofouling while enabling the adsorption of MTX at the electrode's surface for sensitive analysis. The MN sensor exhibits excellent analytical performance in vitro with protein-enriched artificial ISF and ex vivo under a Franz diffusion cell configuration. The MN sensor shows a linear range from 25 to 400 µM, which fits within the therapeutic range of high-dose MTX treatment for cancer patients and an excellent continuous operation for more than two days. Moreover, an iontophoretic hollow MN array patch is developed with the integration of both the anode and cathode in the single MN array patch. The ex vivo characterization demonstrates the transdermal on-demand drug delivery of MTX. Overall, the combination of both MN patches represents impactful progress in closed-loop systems for therapeutic drug management in disorders such as cancer, rheumatoid arthritis, or psoriasis.

Highly stable silver-platinum core-shell nanowires for H2O2 detection.

Silver nanowire (Ag NW) networks have great potential to replace commercial transparent conducting oxides due to their superior properties in conjunction with their competitive cost, availability and mechanical flexibility. However, there are still challenges to overcome for the large scale utilization of Ag NWs in devices due to oxidation/sulfidation of NWs, which leads to performance loss. Here, we develop a solution-based strategy to deposit a thin platinum (Pt) shell layer (15 nm) onto Ag NWs to improve their chemical, environmental and electrochemical stabilities. Environmental and thermal stabilities of the core-shell NW networks were monitored under different relative humidity conditions (RH of 43, 75 and 85%) and temperature settings (75 °C for 120 hours and 150 °C for 40 hours) and compared to those of bare Ag NWs. Afterwards, stability of core-shell NW networks in hydrogen peroxide was investigated and compared to that of bare Ag NW networks. The potential window for electrochemical stability of the Ag NW networks was broadened to 0-1 V (vs. Ag/AgCl) upon Pt deposition, while bare Ag NWs were stable only in the 0-0.6 V range. Moreover, Ag-Pt core-shell NWs were used for the detection of hydrogen peroxide, where a high sensitivity of 0.04 µA µM-1 over a wide linear range of concentrations (16.6-990.1 µM) with a low detection limit (10.95 µM) was obtained for the fabricated sensors. All in all, this highly effective and simple strategy to improve the stability of Ag NWs will certainly open new avenues for their large-scale utilization in various electrochemical and sensing devices.

All-Solution-Processed, Oxidation-Resistant Copper Nanowire Networks for Optoelectronic Applications with Year-Long Stability.

Copper nanowires (Cu NWs) hold promise as they possess equivalent intrinsic electrical conductivity and optical transparency to silver nanowires (Ag NWs) and cost substantially less. However, poor resistance to oxidation is the historical challenge that has prevented the large-scale industrial utilization of Cu NWs. Here, we use benzotriazole (BTA), an organic corrosion inhibitor, to passivate Cu NW networks. The stability of BTA-passivated networks under various environmental conditions was monitored and compared to that of bare Cu NW control samples. BTA passivation greatly enhanced the stability of networks without deteriorating their optoelectronic performance. Moreover, to demonstrate their potential, BTA-passivated networks were successfully utilized in the fabrication of a flexible capacitive tactile sensor. This passivation strategy has a strong potential to pave the way for large-scale utilization of Cu NW networks in optoelectronic devices.