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While over half a century has passed since the introduction of enzyme glucose biosensors by Clark and Lyons, this important field has continued to be the focus of immense research activity. Extensive efforts during the past decade have led to major scientific and technological innovations towards tight monitoring of diabetes. Such continued progress toward advanced continuous glucose monitoring platforms, either minimal- or non-invasive, holds considerable promise for addressing the limitations of finger-prick blood testing toward tracking glucose trends over time, optimal therapeutic interventions, and improving the life of diabetes patients. However, despite these major developments, the field of glucose biosensors is still facing major challenges. The scope of this review is to present the key scientific and technological advances in electrochemical glucose biosensing over the past decade (2010–present), along with current obstacles and prospects towards the ultimate goal of highly stable and reliable real-time minimally-invasive or non-invasive glucose monitoring. After an introduction to electrochemical glucose biosensors, we highlight recent progress based on using advanced nanomaterials at the electrode–enzyme interface of three generations of glucose sensors. Subsequently, we cover recent activity and challenges towards next-generation wearable non-invasive glucose monitoring devices based on innovative sensing principles, alternative body fluids, advanced flexible materials, and novel platforms. This is followed by highlighting the latest progress in the field of minimally-invasive continuous glucose monitoring (CGM) which offers real-time information about interstitial glucose levels, by focusing on the challenges toward developing biocompatible membrane coatings to protect electrochemical glucose sensors against surface biofouling. Subsequent sections cover new analytical concepts of self-powered glucose sensors, paper-based glucose sensing and multiplexed detection of diabetes-related biomarkers. Finally, we will cover the latest advances in commercially available devices along with the upcoming future technologies. [ABSTRACT FROM AUTHOR]

A new wearable potentiometric tattoo biosensor for real-time on-body monitoring of G-type nerve agents simulant is described. The skin-worn flexible biosensor responds rapidly and selectively to the fluorine-containing organophosphates (OP) nerve agent simulant diisopropyl fluorophosphate (DFP, a model OP analyte) in both liquid and vapor phases. The epidermal potentiometric OP biosensor relies on the pH-sensitive polyaniline (PANi) coating on a flexible printed transducer for monitoring the proton release during the enzymatic hydrolysis of DFP by enzyme organophosphate hydrolase (OPH). The sensing electrodes are screen printed on a temporary tattoo paper and are interfaced to a conformal electronic interface that provides wireless data transmission. The skin-worn OP potentiometric sensor can withstand severe mechanical strains without compromising its analytical performance. The biosensor displays a wide dynamic range, fast response and high selectivity towards DFP (including efficient discrimination against organophosphate pesticides), and good reproducibility. The attractive performance of the new wearable biosensor indicates considerable promise for on-body threat detection towards rapid warning regarding potential exposure to G-series nerve agents. [ABSTRACT FROM AUTHOR]

Electrodes modified with organic layers and nanoparticles are promising tools for analytical devices. A major challenge however is how to make electrodes that resist the nonspecific protein adsorption from biological media? Herein, we report gold electrode–organic layer-gold nanoparticle constructs as a platform for electrochemical biosensing. This study focuses on the fabrication of antifouling electrodes with the organic layers formed by two different approaches; self-assembled monolayer (SAM) procedure and electrochemical reduction of aryl diazonium salts, followed by the attachment of gold nanoparticle (AuNP) to allow the electrochemistry to proceed. The results show that the electrodes modified with ethylene oxide-based SAM enable a better antifouling behaviour with less adsorption of human serum albumin (HSA) as compared to the electrodes modified with ethylene oxide-based aryl diazonium-derived layer. Furthermore, findings suggest such distinction could be due to the surface packing and/or conformation of organic film on Au electrodes. [ABSTRACT FROM AUTHOR]

Biofouling on surfaces can deleteriously affect the function of electrochemical sensor used in a biological fluid. The demand is thus to develop a sensor operatable in complex matrices. Herein, we concisely review the technologies developed to date to minimize fouling of electrochemical interfaces by blood-based fluids with an emphasis on affinity biosensing. The methods toward this sensor fabrication that are discussed here include approaches where; chemically modified surfaces with antifouling layers such as ethylene oxides, zwitterionics and some alternative antifouling agents; physical forces such as fluidic systems; electrode surface topography, prevent biofouling, as well as recent approaches where biofouling does not interfere with the response (aptasensors). Furthermore, the important emerging field of implantable biosensors, originated from such fabrication procedures is discussed. [ABSTRACT FROM AUTHOR]

The phenomenon of nanoparticles attached to an electrode passivated by an organic layer allowing efficient electron transfer between redox species in solution and the underlying electrode to be restored has resulted in Chazalviel and Ailongue proposing a theory [Chazalviel, J.-N.; Allongue, p. j. Am. Chem. Soc. 2011, 133, 762-764] to explain this phenomenon The theory suggests that with electrode.organic layer-nanoparticle constructs, high exchange current densities, compared with when the nanopartides are absent, results in the rate of electron transfer being independent of the thickness of the organic layer until a threshold thickness is exceeded. Thereafter, the thicker the organic layer, the slower the rate of electron transfer. Herein we provide the first experimental data to support this theory using a single experimental system that can show the transition from thickness independent electron transfer kinetics to distant dependent kinetics. This was achieved using ethylenediamine electrodeposited on a glassy carbon electrode. Different numbers of deposition cycles were applied in order to fabricate different thicknesses of the organic film. The deposited films showed progressively greater blocking abilities toward ruthenium hexamine, as a redox active probe in solution, as the films got thicker. Electron transfer kinetics of nanoparticle-decorated surfaces showed a change from thickness independent to thickness dependent as the organic layer exceeded an average thickness of 2.0 A. Electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, ellipsometry, and atomic force microscopy were used to characterize the fabricated surfaces. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the electrochemical behavior of thianthrene (TH) and its application toward the electrocatalytic oxidation of guanosine (Gs) and DNA in a non-aqueous solution are investigated using different voltammetric techniques. Guanosine and DNA are adsorbed on the glassy carbon electrode (GCE) by applying a positive potential to the GCE. The rate constant of catalytic reaction between DNA and TH and also between Gs and TH were evaluated using chronoamperometry which gave rate constants of 2.41×106 cm3 mol−1 s−1 and 2.68 (±0.19)×106 cm3 mol−1 s−1, respectively. Also the diffusion coefficient of TH was obtained using hydrodynamic voltammetry (3.17×10−5 cm2 s−1). Furthermore, using hydrodynamic voltammetry, a one-electron mechanism for oxidation of Gs is suggested. [Copyright &y& Elsevier]

• Field screening of opioids with a wearable glove-based electrochemical sensor. • Rapid "swipe, scan, and detect" operating procedure. • Progress towards a complete forensic "Lab-on-Glove". Rapid, on-site detection of fentanyl is of critical importance, as it is an extremely potent synthetic opioid that is prone to abuse. Here we describe a wearable glove-based sensor that can detect fentanyl electrochemically on the fingertips towards decentralized testing for opioids. The glove-based sensor consists of flexible screen-printed carbon electrodes modified with a mixture of multiwalled carbon nanotubes and a room temperature ionic liquid, 4-(3-butyl-1-imidazolio)-1-butanesulfonate. The sensor shows direct oxidation of fentanyl in both liquid and powder forms with a detection limit of 10 μM using square-wave voltammetry. The "Lab-on-a-Glove" sensors, combined with a portable electrochemical analyzer, provide wireless transmission of the measured data to a smartphone or tablet for further analysis. The integrated sampling and sensing methodology on the thumb and index fingers, respectively, enables rapid screening of fentanyl in the presence of a mixture of cutting agents and offers considerable promise for timely point-of-need screening for first responders. Such a glove-based "swipe, scan, sense, and alert" strategy brings chemical analytics directly to the user's fingertips and opens new possibilities for detecting substances of abuse in emergency situations. [ABSTRACT FROM AUTHOR]

By providing a more comfortable and convenient glucose testing experience, non-invasive, wearable biosensors could bolster patients' engagement with their diabetes mellitus (DM). We investigated the accuracy and acceptability of a novel, needle-free continuous glucose sensor. At 2 g and 5 x 4 mm, this sensor is ultra-light, thin, flexible, and self-adherent to the skin. A mild electrical current applied to the epidermis causes sodium ions, then interstitial fluid (ISF) glucose molecules, to migrate toward an electrode. The sensor gauges glucose by detecting its electrical charge strength. Four individuals with DM participated (age 42-61 years, mean 51.5 years; 1 patient with type 1 DM). Over 4 hours, we obtained 3 sensor and 3 glucometer readings concurrently at each of the following time points: following an 8-hour fast, and every 60 minutes after a standard 500-kcal, 75-g high-carbohydrate meal. The correlation coefficient of sensor and glucometer readings was 0.80 (p = 0.00023). Participants rated on a 1-5 scale, with 5 being the highest: 4.25 for comfort, and 4.0 for being receptive to long-term use of such a sensor. Two individuals denied discomfort; 1 felt tingling; and 1 noted a needle-like sensation. The function and patient-friendly design of a wearable glucose sensor may help substantially advance glucose testing, and in turn, improve clinical outcomes and quality of life. Disclosure: E. Chao: None. E. De La Paz Andres: None. A. Barfidokht: None. J. Wang: None. Funding: University of California, San Diego; National Institutes of Health (UL1TR001442) [ABSTRACT FROM AUTHOR]

A flexible skin‐mounted microfluidic potentiometric device for simultaneous electrochemical monitoring of sodium and potassium in sweat is presented. The wearable device allows efficient natural sweat pumping to the potentiometric detection chamber, containing solid‐contact ion‐selective Na+ and K+ electrodes, during exercise activity. The fabricated microchip electrolyte‐sensing device displays good analytical performance and addresses sweat mixing and carry‐over issues of early epidermal potentiometric sensors. Such soft skin‐worn microchip platform integrates potentiometric measurement, microfluidic technologies with flexible electronics for real‐time wireless data transmission to mobile devices. The new fully integrated microfluidic electrolyte‐detection device paves the way for practical fitness and health monitoring applications. [ABSTRACT FROM AUTHOR]

Flexible epidermal tattoo and textile-based electrochemical biosensors have been developed for vapor-phase detection of organophosphorus (OP) nerve agents. These new wearable sensors, based on stretchable organophosphorus hydrolase (OPH) enzyme electrodes, are coupled with a fully integrated conformal flexible electronic interface that offers rapid and selective square-wave voltammetric detection of OP vapor threats and wireless data transmission to a mobile device. The epidermal tattoo and textile sensors display a good reproducibility (with RSD of 2.5% and 4.2%, respectively), along with good discrimination against potential interferences and linearity over the 90–300 mg/L range, with a sensitivity of 10.7 µA∙cm 3 ∙mg −1 (R 2 = 0.983) and detection limit of 12 mg/L in terms of OP air density. Stress-enduring inks, used for printing the electrode transducers, ensure resilience against mechanical deformations associated with textile and skin-based on-body sensing operations. Theoretical simulations are used to estimate the OP air density over the sensor surface. These fully integrated wearable wireless tattoo and textile-based nerve-agent vapor biosensor systems offer considerable promise for rapid warning regarding personal exposure to OP nerve-agent vapors in variety of decentralized security applications. [ABSTRACT FROM AUTHOR]

Semiconducting electrodes that are in depletion, can support appreciable electron transfer only when illuminated. This phenomenon has been implemented on silicon electrodes passivated by a protective organic self-assembled monolayer (SAM) to confine electrochemistry to microscale regions on an unstructured electrode surface by shining light only on those regions. This method, referred to as light-activated electrochemistry (LAE), has so far only been studied using electrodes with surface-bound redox mediators that are either covalently or electrostatically attached to a SAM-modified silicon electrode. In the current report, we extend LAE to redox species in solution using gold nanoparticles (AuNPs) attached to the SAM-modified silicon electrodes. Cyclic voltammetry showed that faradaic electron transfer to redox species in solution can be switched on/off using light. Furthermore, the modified silicon electrodes were stable to more than 650 redox cycles, even when scanning to anodic potentials, with negligible oxide growth and no noticeable change in the voltammograms. Using a variety of redox species in solution, it was shown that with n − -Si-SAM-AuNP electrodes negligible current was observed in the dark but appreciable faradaic electrochemistry was observed upon illumination. It was also shown that to ensure electron transfer proceeded via the AuNPs only, nonspecific adsorption of the redox species to the monolayer surface needed to be avoided. [ABSTRACT FROM AUTHOR]

Herein we combined the use of self-assembled monolayer (SAM) modified electrodes and gold coated magnetic nanoparticles (Au@MNPs) to modulate faradaic electrochemistry when nanoparticles are absorbed on and removed from, a passivated electrode using an external magnetic field. Substantial faradaic electrochemistry of potassium ferricyanide in solution is first prevented by modifying gold electrodes with 11-mercaptoundecanoic acid to form a passivating SAM. Restoration of the faradaic electrochemistry is then achieved by introducing Au@MNPs which are brought to the surface using an external magnetic field. The faradaic electrochemistry can again be suppressed by removing Au@MNPs from the SAM using another external magnetic field. [ABSTRACT FROM AUTHOR]

The development of wearable biosensors for continuous noninvasive monitoring of target biomarkers is limited to assays of a single sampled biofluid. An example of simultaneous noninvasive sampling and analysis of two different biofluids using a single wearable epidermal platform is demonstrated here. The concept is successfully realized through sweat stimulation (via transdermal pilocarpine delivery) at an anode, alongside extraction of interstitial fluid (ISF) at a cathode. The system thus allows on‐demand, controlled sampling of the two epidermal biofluids at the same time, at two physically separate locations (on the same flexible platform) containing different electrochemical biosensors for monitoring the corresponding biomarkers. Such a dual biofluid sampling and analysis concept is implemented using a cost‐effective screen‐printing technique with body‐compliant temporary tattoo materials and conformal wireless readout circuits to enable real‐time measurement of biomarkers in the sampled epidermal biofluids. The performance of the developed wearable device is demonstrated by measuring sweat‐alcohol and ISF‐glucose in human subjects consuming food and alcoholic drinks. The different compositions of sweat and ISF with good correlations of their chemical constituents to their blood levels make the developed platform extremely attractive for enhancing the power and scope of next‐generation noninvasive epidermal biosensing systems. A wearable dual iontophoresis tattoo for simultaneous detection of glucose in interstitial fluid‐ISF and alcohol in sweat is reported. A temporary tattoo electrode is used to perform reverse iontophoresis and pilocarpine iontophoretic delivery, simultaneously, to extract ISF‐glucose and sweat‐alcohol after eating and drinking. Variations in the glucose‐ISF and sweat‐alcohol concentrations correlate with the blood glucose and alcohol levels. [ABSTRACT FROM AUTHOR]