Point-of-Care Diabetes Diagnostics: Towards a Self-Powered Sensor

A cutting-edge biosensor has been developed to monitor blood glucose levels, which is particularly vital for people with diabetes. This advanced technology uses a miniaturized and membraneless enzymatic fuel cell (EFC) as a compact electrical reader for rapid on-site diabetes diagnosis. Using disposable screen-printed gold electrodes (Au-SPE) modified with the enzyme glucose oxidase (GOx), the biosensor enables the oxidation of glucose at both the anode (counter electrode) and cathode (working electrode) of the EFC. The cathode contains graphene oxide/Prussian blue nanocubes (GO/PBNCs), while the anode uses a biographene layer. Both electrodes were modified with GOx by electrostatic/hydrogen bonding the enzyme to the modified electrodes surface. Individual evaluations of each electrode system emphasized their effectiveness. The integration of both electrodes resulted in an EFC that can generate an output power of approximately 1.8 μW/cm2 at a glucose concentration of 5 mmol/L, which is very close to physiological conditions (3.8 to 6.9 mmol/L). This technology represents a significant advance and promises fully autonomous diagnostic devices suitable for a wide range of analytes. It paves the way for diagnostics everywhere and marks a fundamental shift in point-of-care (PoC) diagnostics.

Acid-accelerated hydrolysis of NaBH4: a gas-generation reaction for diverse gas pressure biosensing

Gas pressure biosensing is a promising portable analysis method. The gas-generation reaction is crucial to its sensitivity, speed, repeatability, and usability. However, very few gas-generation reactions are available for sensitive, safe, and diverse biosensing. Herein, acid-accelerated hydrolysis of sodium borohydride (NaBH₄) was explored for the first time to achieve portable and diverse gas pressure biosensing. The slow hydrolysis and hydrogen generation of NaBH₄ in alkaline medium is accelerated with increasing acidity, which increased the gas pressure in a small and sealed tube within 10 min. Thus, a label-free bioassay is easily and specifically achieved once analytes can in-situ generate acid to accelerate the hydrolysis rate of NaBH₄, such as glucose, acetylcholine (ACh), adenosine triphosphate (ATP) and others. More importantly, analytes without acid generation could be quantitatively and selectively detected by combining target recognition with acid-generated biochemical reactions for enzyme-linked gas pressure biosensing. Inspired by this, aflatoxin B1 (AFB1)-aptamer interaction-triggered strand displacement reaction was combined with glucose oxidation by glucose oxidase (GOD) to detect AFB1 as low as 7.1 pM. Therefore, acid-accelerated hydrolysis of NaBH₄ is powerful for developing portable, cheap, and diverse gas pressure biosensing. It opens up a new way for cheap, universal, and portable biosensing.

Nanosensors for Visual Detection of Glucose in Biofluids: Are We Ready for Instrument-Free Home-Testing?

Making frequent large-scale screenings for several diseases economically affordable would represent a real breakthrough in healthcare. One of the most promising routes to pursue such an objective is developing rapid, non-invasive, and cost-effective home-testing devices. As a first step toward a diagnostic revolution, glycemia self-monitoring represents a solid base to start exploring new diagnostic strategies. Glucose self-monitoring is improving people's life quality in recent years; however, current approaches still present vast room for improvement. In most cases, they still involve invasive sampling processes (i.e., finger-prick), quite discomforting for frequent measurements, or implantable devices which are costly and commonly dedicated to selected chronic patients, thus precluding large-scale monitoring. Thanks to their unique physicochemical properties, nanoparticles hold great promises for the development of rapid colorimetric devices. Here, we overview and analyze the main instrument-free nanosensing strategies reported so far for glucose detection, highlighting their advantages/disadvantages in view of their implementation as cost-effective rapid home-testing devices, including the potential use of alternative non-invasive biofluids as samples sources.

Visual detection of alkaline phosphatase based on ascorbic acid-triggered gel-sol transition of alginate hydrogel

Stimuli-responsive hydrogel has been emerged as a popular tool for chemical sensing due to its unique mechanical properties. In this work, we fabricated an ascorbic acid (AA)-responsive alginate hydrogel for the visual detection of alkaline phosphatase (ALP). This alginate hydrogel (RhB@Alg/Fe³⁺) was crosslinked with Fe³⁺, and rhodamine B (RhB) was encapsulated into the hydrogel as an indicating reagent to assistant visual detection. Because of the weak affinity of Fe²⁺ to alginate, the presence of reductive AA can trigger the dissolution of RhB@Alg/Fe³⁺ to give an observable red color in the sol solution. On this basis, by using ascorbic acid 2-phosphate as a substrate of ALP, which can be hydrolyzed by ALP to produce AA, the gel-sol transition process of RhB@Alg/Fe³⁺ was further modulated by ALP. This finding leads to a simple visual method for ALP detection with a low detection limit of 0.37 mU/mL and an excellent selectivity over other proteins. Compared with conventional colorimetric assays, this visual sensor shows the distinct advantages of simple fabrication, cost-effectiveness and easy to implement. We believe that this study can provide a new insight into the fabrication of responsive alginate hydrogel for promising applications in chemical sensing and biomedical fields.

Recent advances in thermo-sensitive hydrogels for drug delivery

Thermo-sensitive hydrogels based on different polymers have been broadly used in the pharmaceutical fields. In this review, the state-of-the-art thermo-sensitive hydrogels for drug delivery are elaborated

A novel ultrasensitive and non-enzymatic "turn-on-off" fluorescence nanosensor for direct determination of glucose in the serum: As an alternative approach to the other optical and electrochemical methods

A new, simple, rapid, highly sensitive and selective and non-enzymatic fluorometric method for direct determination of glucose in real samples was developed. The method was based on the inhibition of fluorescence resonance energy transfer (FRET) process between terbium (III)-1, 10-phenanthroline (Tb-phen) complex and silver nanoparticles (AgNPs). Upon the addition of glucose, the quenched FRET-based fluorescence of Tb-phen complex was gradually recovered by glucose via its strong adsorption on the surface of AgNPs and removal of Tb-phen complex from AgNPs surface. Therefore the fluorescence of Tb-phen complex switched to "turn-on" state. Under the optimum conditions, a linear relationship was obtained between the enhanced fluorescence intensity and glucose concentration in the range of (5-900) × 10^-8 M with the detection limit of 1.94 × 10^-8 M. The proposed sensing system was successfully applied to determine glucose in the spiked normal and diabetic patient serum samples after deproteinization with acetonitrile. Analytical recoveries from treated serum samples were in the range of 99.97-104.80% and 92.14-105.43%, respectively. The common interfering species, such as ascorbic acid, fructose and galactose did not cause interior interference due to unique emission properties of Tb-phen complex probe. Also the interaction of the Tb-phen complex with AgNPs, which led to the fluorescence intensity quenching of the complex, was further examined by FTIR technique. In short, as compared to most of the existing methods, the newly proposed method, provides some advantages and makes it promising for the direct rapid screening of glucose residues of real samples in clinical diagnosis of diabetes, as an alternative approach to the other exiting optical and electrochemical methods.

Pyrophosphate ion-responsive alginate hydrogel as an effective fluorescent sensing platform for alkaline phosphatase detection

A Cu²⁺-crosslinked alginate hydrogel can encapsulate fluorescent carbon dots for visually monitoring PPi-stimulated gel–sol transition and the further detection of ALP.

Hemin-Modified SnO2/Metglas Electrodes for the Simultaneous Electrochemical and Magnetoelastic Sensing of H2O2

In this work, we present a simple and efficient method for the preparation of hemin-modified SnO2 films on Metglas ribbon substrates for the development of a sensitive magneto-electrochemical sensor for the determination of H2O2. The SnO2 films were prepared at low temperatures, using a simple hydrothermal method, compatible with the Metglas surface. The SnO2 film layer was fully characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), photoluminescence (PL) and Fourier Transform-Infrared spectroscopy (FT-IR). The properties of the films enable a high hemin loading to be achieved in a stable and functional way. The Hemin/SnO2-Metglas system was simultaneously used as a working electrode (WE) for cyclic voltammetry (CV) measurements and as a magnetoelastic sensor excited by external coils, which drive it to resonance and interrogate it. The CV scans reveal direct reduction and oxidation of the immobilized hemin, as well as good electrocatalytic response for the reduction of H2O2. In addition, the magnetoelastic resonance (MR) technique allows the detection of any mass change during the electroreduction of H2O2 by the immobilized hemin on the Metglas surface. The experimental results revealed a mass increase on the sensor during the redox reaction, which was calculated to be 767 ng/μM. This behavior was not detected during the control experiment, where only the NaH2PO4 solution was present. The following results also showed a sensitive electrochemical sensor response linearly proportional to the concentration of H2O2 in the range 1 × 10−6–72 × 10−6 M, with a correlation coefficient of 0.987 and detection limit of 1.6 × 10−7 M. Moreover, the Hemin/SnO2-Metglas displayed a rapid response (30 s) to H2O2 and exhibits good stability, reproducibility and selectivity.

Mixed-solvent liquid exfoliated MoS2 NPs as peroxidase mimetics for colorimetric detection of H2O2 and glucose

Ultra-small molybdenum disulfide nanoparticles (MoS₂ NPs) were prepared by a facile liquid exfoliation method with ethanol/water as the solvent. The produced MoS₂ NPs were of high purity due to the easily removable ethanol/water solution. The prepared MoS₂ NPs exhibited an intrinsic peroxidase-like activity in analogy to that of horseradish peroxidase (HRP). A custom-made spectrometer was employed to investigate the peroxidase-like activity of MoS₂ NPs in the presence of H₂O₂ and glucose. The change in absorption detected from MoS₂ NPs is proportional to the amount of target. The calibration curve of H₂O₂ and glucose shows a good relationship between the concentration of target and the change in the absorption of MoS₂ NPs. The limit of detection of H₂O₂ and glucose achieved by this method could approach 1.25 μM and 7 μM respectively. This method has been applied for the detection of glucose in serum from humans. Therefore, these produced MoS₂ NPs offer an alternative high-efficiency and economic way to detect diabetes.

Ultra-small molybdenum disulfide nanoparticles (MoS₂ NPs) prepared by a facile liquid exfoliation method is capable of detecting the presence of H₂O₂ and glucose. This novel colorimetric method offers an alternative way to detect diabetes.

Inducible Sequential Oxidation Process in Water-Soluble Copper Nanoclusters for Direct Colorimetric Assay of Hydrogen Peroxide in a Wide Dynamic and Sampling Range

Direct and fast detection methods for H₂O₂ have great demand in materials science, biology, and medicine. Colorimetric assay of H₂O₂ has been regarded as one versatile approach that can avoid tedious operation and complicated setup. In this report, we provided a cost-effective and time-saving H₂O₂ colorimetric assay strategy based on a mercaptosuccinic acid (MSA)-stabilized Cu nanocluster (NC) probe without using any chromogenic reagent. Direct and fast colorimetric detection of H₂O₂ was realized based on the color change of MSA-capped Cu NCs in aqueous medium. It was found that the Cu NCs presented eligible resistance to natural oxidation either in concentrated solution or in the powder state. However, the dissolved oxygen in a highly diluted solution of the Cu NCs could trigger the aggregation of the Cu NCs and their further fusion into small Cu nanoparticles (NPs). When this diluted solution served as a probe solution for detecting H₂O₂, a sequential oxidation process occurred in the newly formed Cu NPs, including the cleavage of MSAs on the surface and conversion of Cu into Cu₂O, leading to the probe with capacity for H₂O₂ assay in a wide dynamic and sampling range. The sensitive solution color change was attributed to the growth of the Cu NPs (fading of plasmonic absorption) upon the addition of low levels of H₂O₂ and the transition of the valence states of Cu (color reactions) upon the addition of high levels of H₂O₂. A concentration range of H₂O₂ from 1 μM to 1 M could be detected by a small dose of the probe. Moreover, the Cu NCs powder subsequent to storage for 10 months could maintain a similar sensitivity for H₂O₂ assay, which provides possibilities for a wide range of practical applications in water samples.

Fluorometric “Turn-On” glucose sensing through the in situ generation of silver nanoclusters

A fluorometric “turn-on” glucose detection is performed based on the Fenton reaction which can trigger the generation of Ag nanoclusters.

The analytical and biomedical potential of cytosine-rich oligonucleotides: A review

Polycytosine DNA strands are often found among natural sequences, including the ends of telomeres, centromeres, and introns or in the regulatory regions of genes. A characteristic feature of oligonucleotides that are rich in cytosine (C-rich) is their ability to associate under acidic conditions to form a tetraplex i-motif consisting of two parallel stranded cytosine-hemiprotonated cytosine (C·C+) base-paired duplexes that are mutually intercalated in an antiparallel orientation. Nanotechnology has been exploiting the advantages of i-motif pH-dependent formation to fabricate nanomachines, nanoswitches, electrodes and intelligent nanosurfaces or nanomaterials. Although a few reviews regarding the structure, properties and applications of i-motifs have been published, this review focuses on recently developed biosensors (e.g., to detect pH, glucose or silver ions) and drug-delivery biomaterials. Furthermore, we have included examples of sensors based on parallel C-rich triplexes and silver nanoclusters (AgNCs) fabricated on cytosine-rich DNA strands. The potential diagnostic and therapeutic applications of this type of material are discussed.

Visual fluorescence detection of H2O2 and glucose based on “molecular beacon”-hosted Hoechst dyes

In this work, a label-free molecular beacon (MB)-like biosensor is designed for the determination of H₂O₂ and glucose based on the fluorescence regulation of Hoechst dyes hosted by the designed AT-rich single-stranded DNA (ssDNA), in which Hg²⁺ and cysteine (Cys) act as activators.

Polypyrrole nanoparticles as promising enzyme mimics for sensitive hydrogen peroxide detection

Polypyrrole nanoparticles possess intrinsic peroxidase-like activity, which can be employed to quantitatively monitor the H₂O₂ generated by macrophages.

An ultrasensitive, non-enzymatic glucose assay via gold nanorod-assisted generation of silver nanoparticles

This report demonstrates a colorimetric, non-enzymatic glucose assay with a low detection limit of 0.07 μM based on negatively charged gold nanorod-enhanced redox reaction. This glucose assay could generate silver nanoparticles as the readout that can be visualized by the naked eye, and only 4 femtomoles of nanorods are needed for glucose determination in one human plasma sample.