Transforming the fabrication and biofunctionalization of gold nanoelectrode arrays into versatile electrochemical glucose biosensors

Non-Invasive Blood Glucose Monitoring Technology: A Review

In recent years, with the rise of global diabetes, a growing number of subjects are suffering from pain and infections caused by the invasive nature of mainstream commercial glucose meters. Non-invasive blood glucose monitoring technology has become an international research topic and a new method which could bring relief to a vast number of patients. This paper reviews the research progress and major challenges of non-invasive blood glucose detection technology in recent years, and divides it into three categories: optics, microwave and electrochemistry, based on the detection principle. The technology covers medical, materials, optics, electromagnetic wave, chemistry, biology, computational science and other related fields. The advantages and limitations of non-invasive and invasive technologies as well as electrochemistry and optics in non-invasives are compared horizontally in this paper. In addition, the current research achievements and limitations of non-invasive electrochemical glucose sensing systems in continuous monitoring, point-of-care and clinical settings are highlighted, so as to discuss the development tendency in future research. With the rapid development of wearable technology and transdermal biosensors, non-invasive blood glucose monitoring will become more efficient, affordable, robust, and more competitive on the market.

Current Trends of Nanobiosensors for Point-of-Care Diagnostics

In order to provide better-quality health care, it is very important that high standards of health care management are achieved by making timely decisions based on rapid diagnostics, smart data analysis, and informatics analysis. Point-of-care testing ensures fast detection of analytes near to the patients facilitating a better disease diagnosis, monitoring, and management. It also enables quick medical decisions since the diseases can be diagnosed at an early stage which leads to improved health outcomes for the patients enabling them to start early treatment. In the recent past, various potential point-of-care devices have been developed and they are paving the way to next-generation point-of-care testing. Biosensors are very critical components of point-of-care devices since they are directly responsible for the bioanalytical performance of an essay. As such, they have been explored for their prospective point-of-care applications necessary for personalized health care management since they usually estimate the levels of biological markers or any chemical reaction by producing signals mainly associated with the concentration of an analyte and hence can detect disease causing markers such as body fluids. Their high selectivity and sensitivity have allowed for early diagnosis and management of targeted diseases; hence, facilitating timely therapy decisions and combination with nanotechnology can improve assessment of the disease onset and its progression and help to plan for treatment of many diseases. In this review, we explore how nanotechnology has been utilized in the development of nanosensors and the current trends of these nanosensors for point-of-care diagnosis of various diseases.

Rapid and Label-Free Detection of Interferon Gamma via an Electrochemical Aptasensor Comprising a Ternary Surface Monolayer on a Gold Interdigitated Electrode Array

A label-free electrochemical impedance spectroscopy (EIS) aptasensor for rapid detection (<35 min) of interferon-gamma (IFN-γ) was fabricated by immobilizing a RNA aptamer capture probe (ACP), selective to IFN-γ, on a gold interdigitated electrode array (Au IDE). The ACP was modified with a thiol group at the 5' terminal end and subsequently co-immobilized with 1,6-hexanedithiol (HDT) and 6-mercapto-1-hexanolphosphate (MCH) to the gold surface through thiol-gold interactions. This ACP/HDT-MCH ternary surface monolayer facilitates efficient hybridization with IFN-γ and displays high resistance to nonspecific adsorption of nontarget proteins [i.e., fetal bovine serum (FBS) and bovine serum albumin (BSA)]. The Au IDE functionalized with ACP/HDT-MCH was able to measure IFN-γ in actual FBS solution with a linear sensing range from 22.22 pM to 0.11 nM (1-5 ng/mL) and a detection limit of 11.56 pM. The ability to rapidly sense IFN-γ within this sensing range makes the developed electrochemical platform conducive toward in-field disease detection of a variety of diseases including paratuberculosis (i.e., Johne's Disease). Furthermore, experimental results were numerically validated with an equivalent circuit model that elucidated the effects of the sensing process and the influence of the immobilized ternary monolayer on signal output. This is the first time that ternary surface monolayers have been used to selectively capture/detect IFN-γ on Au IDEs.

3D nanostructured inkjet printed graphene via UV-pulsed laser irradiation enables paper-based electronics and electrochemical devices

Emerging research on printed and flexible graphene-based electronics is beginning to show tremendous promise for a wide variety of fields including wearable sensors and thin film transistors. However, post-print annealing/reduction processes that are necessary to increase the electrical conductivity of the printed graphene degrade sensitive substrates (e.g., paper) and are whole substrate processes that are unable to selectively anneal/reduce only the printed graphene-leaving sensitive device components exposed to damaging heat or chemicals. Herein a pulsed laser process is introduced that can selectively irradiate inkjet printed reduced graphene oxide (RGO) and subsequently improve the electrical conductivity (Rsheet∼0.7 kΩ□(-1)) of printed graphene above previously published reports. Furthermore, the laser process is capable of developing 3D petal-like graphene nanostructures from 2D planar printed graphene. These visible morphological changes display favorable electrochemical sensing characteristics-ferricyanide cyclic voltammetry with a redox peak separation (ΔEp) ≈ 0.7 V as well as hydrogen peroxide (H2O2) amperometry with a sensitivity of 3.32 μA mM(-1) and a response time of <5 s. Thus this work paves the way for not only paper-based electronics with graphene circuits, it enables the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells, and theranostic devices.

pulSED: pulsed sonoelectrodeposition of fractal nanoplatinum for enhancing amperometric biosensor performance

A technique for deposition of fractal nanometal as a transducer in electrochemical sensing is described. The effect(s) of duty cycle and deposition time were explored, and two sensors are demonstrated.

Boronic Acid Functionalized Aza-Bodipy (azaBDPBA) based Fluorescence Optodes for the Analysis of Glucose in Whole Blood

A near-infrared fluorescent dye (aza-bodipy or azaBDPBA) functionalized with boronic acid groups was synthesized for the preparation of optodes to measure glucose in 40-fold diluted whole blood. Boronic acid groups as an electron deficient group on aza-bodipy was reacted with hydrogen peroxide into an electron-rich phenolic group leading to the red-shift of emission wavelength from 682 to 724 nm. The emission in near-infrared region offered a low level of background interference from whole blood. Also, the dual-wavelength emission guaranteed our probe to measure glucose in whole blood accurately after the conversion of glucose into hydrogen peroxide using glucose oxidase. The measuring range of glucose from 0.2 to 200 mM in the buffer was achieved with high selectivity. To facilitate the blood test, the probe was immobilized into thin hydrophobic polymer films to prepare the disposal glucose optode, which could detect glucose in the solution from 60 μM to 100 mM. The concentration of glucose in 40-fold diluted whole blood was determined using our optode and the reference method, respectively. The consistence in the concentration obtained from these two assays revealed that our azaBDPBA-based optodes were promising for the clinic assay of glucose in the whole blood.

Increasing the activity of immobilized enzymes with nanoparticle conjugation

The efficiency and selectivity of enzymatic catalysis is useful to a plethora of industrial and manufacturing processes. Many of these processes require the immobilization of enzymes onto surfaces, which has traditionally reduced enzyme activity. However, recent research has shown that the integration of nanoparticles into enzyme carrier schemes has maintained or even enhanced immobilized enzyme performance. The nanoparticle size and surface chemistry as well as the orientation and density of immobilized enzymes all contribute to the enhanced performance of enzyme-nanoparticle conjugates. These improvements are noted in specific nanoparticles including those comprising carbon (e.g., graphene and carbon nanotubes), metal/metal oxides and polymeric nanomaterials, as well as semiconductor nanocrystals or quantum dots.

A microfluidic-based controllable synthesis of rolled or rigid ultrathin gold nanoplates

A microfluidic-based controllable seeded synthesis of rolled or rigid ultrathin gold nanoplates.

Nanoporous anodic alumina rugate filters for sensing of ionic mercury: toward environmental point-of-analysis systems

Herein, we present an ultrasensitive, cost-competitive, and portable optical sensing system for detecting ionic mercury in environmental water. This analytical system combines structurally engineered and chemically modified nanoporous anodic alumina rugate filters (NAA-RFs) with reflection spectroscopy (RfS). The sensing performance of the proposed system is assessed through several tests, establishing its sensing performance (i.e., linear working range from 1 to 100 μM of Hg(2+), low limit of detection 1 μM of Hg(2+) ions (i.e., 200 ppb), and sensitivity of 0.072 nm μM(-1)), chemical selectivity (i.e., exposure to different metal ions Co(2+), Mg(2+), Ni(2+), Cu(2+), Pb(2+), Fe(3+), Ca(2+), Cr(6+), and Ag(+)) and metal ions binding mechanism (i.e., fitting to Langmuir and Freundlich isotherm models). Furthermore, the detection of Hg(2+) ions in tap and environmental water (River Torrens) is successfully carried out, demonstrating the suitability of this system for developing environmental point-of-analysis systems.

Enzyme-labeled Pt@BSA nanocomposite as a facile electrochemical biosensing interface for sensitive glucose determination

Electrocatalytic reactions of glucose oxidation based on enzyme-labeled electrochemical biosensors demand a high enzymatic activity and fast electron transfer property to produce the amplified signal response. Through a "green" synthesis method, Pt@BSA nanocomposite was prepared as a biosensing interface for the first time. Herein we presented a convenient and effective glucose sensing matrix based on Pt@BSA nanocomposite along with the covalent adsorption of glucose oxidase (GOD). The electrocatalytic activity toward oxygen reduction was significantly enhanced due to the excellent bioactivity of anchored GOD and superior catalytic performance of interior platinum nanoparticles, which was gradually restrained with the addition of glucose. A sensitive glucose biosensor was then successfully developed upon the restrained oxygen reduction peak current. Differential pulse voltammetry (DPV) was employed to investigate the determination performance of the enzyme biosensor, resulting in a linear response range from 0.05 to 12.05 mM with an optimal detection limit of 0.015 mM. The as-proposed sensing technique revealed high selectivity against endogenous interfering species, satisfactory storage stability, acceptable durability, and favorable fabrication reproducibility with the RSD of 3.8%. During the practical application in human blood serum samples, this glucose biosensor obtained a good detection accuracy of analytical recoveries within 97.5 to 104.0%, providing an alternative scheme for glucose level assay in clinical application.

Nanomaterial-mediated Biosensors for Monitoring Glucose

Real-time monitoring of physiological glucose transport is crucial for gaining new understanding of diabetes. Many techniques and equipment currently exist for measuring glucose, but these techniques are limited by complexity of the measurement, requirement of bulky equipment, and low temporal/spatial resolution. The development of various types of biosensors (eg, electrochemical, optical sensors) for laboratory and/or clinical applications will provide new insights into the cause(s) and possible treatments of diabetes. State-of-the-art biosensors are improved by incorporating catalytic nanomaterials such as carbon nanotubes, graphene, electrospun nanofibers, and quantum dots. These nanomaterials greatly enhance biosensor performance, namely sensitivity, response time, and limit of detection. A wide range of new biosensors that incorporate nanomaterials such as lab-on-chip and nanosensor devices are currently being developed for in vivo and in vitro glucose sensing. These real-time monitoring tools represent a powerful diagnostic and monitoring tool for measuring glucose in diabetes research and point of care diagnostics. However, concerns over the possible toxicity of some nanomaterials limit the application of these devices for in vivo sensing. This review provides a general overview of the state of the art in nanomaterial-mediated biosensors for in vivo and in vitro glucose sensing, and discusses some of the challenges associated with nanomaterial toxicity.

α-Oxo aldehyde or glyoxylyl group chemistry in peptide bioconjugation

Since the 1990s, α-oxo aldehyde or glyoxylic acid chemistry has inspired a vast array of synthetic tools for tailoring peptide or protein structures, for developing peptides endowed with novel physicochemical properties or biological functions, for assembling a large diversity of bioconjugates or hybrid materials, or for designing peptide-based micro or nanosystems. This past decade, important developments have enriched the α-oxo aldehyde synthetic tool box in peptide bioconjugation chemistry and explored novel applications. The aim of this review is to give a large overview of this creative field.