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Miniaturization and wireless continuous glucose monitoring are key factors for the successful management of diabetes. Electrochemical sensors are very versatile and can be easily miniaturized for wireless glucose monitoring. The authors report a microneedle-based enzyme-free electrochemical wireless sensor for painless and continuous glucose monitoring. The microneedles (MNs) fabricated consist of a 3 × 5 sharp and stainless-steel electrode array configuration. Each MN in the 3 × 5 array has 575 µm × 150 µm in height and width, respectively. A glucose-catalyzing layer, porous platinum black, was electrochemically deposited on the tips of the MNs by applying a fixed cathodic current of 2.5 mA cm -2 for a period of 200 s. For the non-interference glucose sensing, the platinum (Pt)-black-coated MN was carefully packaged into a biocompatible ionomer, nafion. The surface morphologies of the bare and modified MNs were studied using field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray analysis (EDX). The wireless glucose sensor displayed a broad linear range of glucose (1→30 mM), a good sensitivity and higher detection limit of 145.33 μA mM -1 cm -2 and 480 μM, respectively, with bare AuMN as a counter electrode. However, the wireless device showed an improved sensitivity and enhanced detection limit of 445.75, 165.83 μA mM -1 cm -2 and 268 μM, respectively, with the Pt-black-modified MN as a counter electrode. The sensor also exhibited a very good response time (2 s) and a limited interference effect on the detection of glucose in the presence of other electroactive oxidizing species, indicating a very fast and interference-free chronoamperometric response.

• A proof-of-concept for CGM based on a non-enzymatic MNEAs. • Electrodeposition of catalytic Pt-black on Au MNs for CGM in-vitro and in-vivo. • MNs showed a good dynamic range (1-20 mM) and detection limit (10 µM) in PBS. • The fabricated device showed a good stability as CGMS for 7 days in-vivo. Individuals with diabetes can considerably benefit from continuous glucose monitoring (CGM). Addressing this challenge, a proof-of-concept for a pain-free CGM was presented based on a highly porous platinum black (Pt-black)-modified non-enzymatic microneedle electrode arrays (MNEAs). Porous Pt-black was electrodeposited on microneedle substrates using potentiometry by employing a charge density of -2.5 mA cm˗2. The surface of the porous Pt-black-modified microneedles (MNs) was optimally packed using Nafion (Nf) biocompatible ionomer. The dimensions of the fabricated microneedles were 650 µm × 110 µm × 150 µm in height, width, and thickness, respectively. The surface morphology of the modified MNs was studied using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The microneedle sensor showed a wide glucose dynamic range (1 − 20 mM) in phosphate buffer saline (PBS) and artificial interstitial fluid (ISF) in-vitro with good sensitivities (PBS: 5.786 µA mM−1 cm−2, ISF: 4.380 µA mM−1 cm−2), detection limits (PBS: 10 µM, ISF: 22.5 µM), stability (2% lost at the end of 7 h), selectivity, reproducibility (2.32% RSD), and a response time of 2 s with good glucose recoveries in ISF (98%-102.5%). The device exhibited good stability (7 days) as a sensor in-vivo and lost its functional activity after 7 days due to electrode biofouling. [ABSTRACT FROM AUTHOR]

Individuals with diabetes can benefit considerably from continuous blood glucose monitoring. To address this challenge, a proof-of-concept was performed for continuous glucose monitoring (CGM) based on an enzymeless porous nanomaterial (pNM)-modified microneedle electrode array (MNEA). The pNM sensing layer was electrochemically deposited on MNs by applying a fixed negative current of −2.5 mA cm˗2 for 400 s. The pNM-modified MNEA was packed using a biocompatible Nafion ionomer. The fabricated MNEAs were 600 × 100 × 150 µm in height, width, and thickness, respectively. The surfaces of the modified MNs were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The fabricated MNEAs showed a wide dynamic range (1–30 mM) in phosphate-buffered saline (PBS) and in artificial interstitial fluid (ISF), with good sensitivities (PBS: 1.792 ± 0.25 µA mM−1 cm−2, ISF: 0.957 ± 0.14 µA mM−1 cm−2) and low detection limits (PBS: 7.2 µM, ISF: 22 µM). The sensor also showed high stability (loss of 3.5% at the end of 16 days), selectivity, and reproducibility (Relative standard deviations (RSD) of 1.64% and 0.70% for intra- and inter-assay, respectively) and a good response time (2 s) with great glucose recovery rates in ISF (98.7–102%). [ABSTRACT FROM AUTHOR]

The authors report on a microneedle-based amperometric nonenzymatic glucose sensor for painless and continuous monitoring of glucose. It consists of 3 × 5 sharp stainless steel microneedles micromachined from a stainless steel substrate. The microneedles are 600 and 100 μm in height and width, respectively. Nafion and platinum black were sequentially coated onto the tip of gold-coated microneedles and used for nonenzymatic (direct) sensing of glucose. Attractive features of the modified microneedle electrode include (a) a low working potential (+0.12 V vs. Ag/AgCl), (b) a linear response in the physiologically relevant range (1-40 mM), (c) a sensitivity as high as 175 μA mM−1 cm−2, (d) a 23 μM detection limit, and (e) a response time of 2 s. The sensor also exhibits good reproducibility and stability. The sensor is selective for glucose even in the presence of 10-fold higher concentrations of ascorbic acid, lactic acid, dopamine, uric acid, and acetaminophen.Schematic representation of the fabrication sequence for a nonenzymatic electrochemical glucose sensor using Nafion and platinum black coated microneedle electrode array. The sensor is based on measuring the faradaic current at +0.12 V vs. Ag/AgCl by the direct electrochemical oxidation of glucose to gluconic acid on the surface of a Pt black sensing layer. [ABSTRACT FROM AUTHOR]