An enzyme-free quartz crystal microbalance biosensor for sensitive glucose detection in biological fluids based on glucose/dextran displacement approach

A sensitive and facile quartz crystal microbalance (QCM) biosensor for glucose detection in biological fluids was developed by means of a displacement-type assay mode between glucose and its analogy dextran for concanavalin A (ConA) binding sites on a graphene-based sensing platform. To construct such a displacement-based sensor, phenoxy-derived dextran (DexP) molecules were initially assembled onto the surface of graphene-coated QCM probe via π-π stacking interaction, and ConA molecules were then immobilized on the dextran through the dextran-ConA interaction. Upon addition of glucose, the analyte competed with the dextran for the ConA, and displaced it from the QCM probe, leading to a change in the frequency. Under optimal conditions, the frequency change relative to the basic resonant frequency was proportional to glucose concentration, and exhibited a dynamic range from 0.01 to 7.5 mM with a low detection limit (LOD) of 5.0 μM glucose (at 3σ). The relative standard deviations (RSDs) were below 6.2% and 9.0% for the reproducibility and selectivity of the QCM glucose sensors, respectively. In addition, the assay system was evaluated with glucose spiking samples into the distilled water and blank cattle serum, receiving in excellent correlation with the referenced values.     

A novel microfluidic flow-injection analysis device with fluorescence detection for cation sensing. Application to potassium

A microfabricated device has been developed for fluorimetric detection of potassium ions without previous separation. It is based on use of a fluorescent molecular sensor, calix–bodipy, specially designed to be sensitive to and selective for the target ion. The device is essentially made of a Y-shape microchannel moulded in PDMS fixed on a glass substrate. A passive mixer is used for mixing the reactant and the analyte. The optical detection arrangement uses two optical fibres, one for excitation by a light-emitting diode, the other for collection of the fluorescence. This system enabled the flow-injection analysis of the concentration of potassium ions in aqueous solutions with a detection limit of 0.5 mmol L⁻¹ and without interference with sodium ions. A calibration plot was constructed using potassium standard solutions in the range 0–16 mmol L⁻¹, and was used for the determination of the potassium content of a pharmaceutical pill. Figure Photography of the microfluidic channel showing the ridges in the PDMS substrate at the top of the channel     

A novel strategy to prepare LDH networks loaded carbon structure by C-MEMS techniques for glucose detection

NiAl-layered double hydroxide (NiAl-LDH) networks loaded carbon microcylinder (CMC) hybrid was synthesized for the first time using typical carbon based microelectromechanical systems (C-MEMS) techniques combined with in situ growth progress. The incorporation of NiAl-LDH on C-MEMS structures via a simple pyrolysis of modified photoresist was investigated. With proper control of parameters in lithography and hydrothermal processes, the NiAl-LDH/CMC composites with suitable morphology were fabricated. When the composites applied as new catalytic material for glucose detection, this simple sensor showed satisfying electrocatalytic properties towards glucose oxidation owing to its unique structure and excellent electric conductivity. It is also worth pointing out that this novel fabrication process can equip carbon microfeatures with various nanostructures, and have wide potential applications in scaling up carbon based nanocomposites.     

Advances in enzyme-free electrochemical sensors for hydrogen peroxide,glucose, and uric acid

Enzyme-free (also called non-enzymatic or direct) electrochemical sensors have been widely used for the determination of hydrogen peroxide, glucose, and uric acid. This review covers the recent progress made in this field. We also discuss the respective sensor materials which have strong effect on the electro-catalytic properties of the electrodes and govern the performance of these sensors. In addition, perspectives and current challenges of enzyme-free electrochemical sensors are outlined. Contains 142 references.

二氧化铈纳米微粒过氧化物酶活性及其在葡萄糖检测中的应用

合成了一种稳定和水溶性的聚丙烯酸修饰CeO2 NPs,利用动态光散射(DLS)、傅里叶变换红外光谱(FT-IR)和X射线光电子能谱(XPS)进行表征.结果表明,CeO2 NPs能够催化H2O2氧化3,3′,5,5′-四甲基联苯胺(TMB)发生显色反应,表现出过氧化物模拟酶催化活性.利用Raman和顺磁共振(EPR)光谱技术研究了其催化机理.基于CeO2 NPs催化TMB变色反应对H2O2浓度的依赖性和葡萄糖氧化酶能够催化溶解氧氧化葡萄糖产生H2O2的原理,构建了一种简单、灵敏、选择性高的测定血清中葡萄糖的检测方法.在优化条件下,测定葡萄糖的线性范围为0.5~10 mmol/L,检出限(3σ)为0.1 mmol/L.对1.0 mmol/L葡萄糖进行11次平行测定,其相对标准偏差为2.4%.该方法已成功用于血清样品中葡萄糖的测定.     

A fully integrated graphene-polymer field-effect transistor biosensing device for on-site detection of glucose in human urine

Convenient and rapid self-measurement of the glucose level in the body is of great significance for diabetics to know their health conditions in time. In view of this, a polymer functionalized graphene field-effect transistor (P-GFET) portable biosensing device is demonstrated for glucose monitoring. The polymer is synthesized by acrylamide/3-acrylamidophenylboronic acid (AAPBA)/N, N-dimethylaminopropyl acrylamide. In the presence of glucose, the P-GFET shows Dirac point shifts and current changes as a result of the covalent bond between glucose and AAPBA in the synthesized polymer on graphene. The sensitivity of this P-GFET sensor can increase while the density of AAPBA in polymer increases. The used sensor could regain the detection capability after hydrochloric acid treatment due to the reversible reaction between polymer and glucose. In addition, the chemisorption interaction between polymer and glucose, which is stronger than physisorption interaction with other objects in urine, has been supported by the density functional theory study. The P-GFET shows high sensitivity of 822 μA1cm^?21mM^?1 with a limit of detection of 1.9 μM during human urine glucose monitoring. The sensor holds a detection range of 0.04–10 mM and good reusability over 20 times. With the customized portable real-time measurement capability in urine, our P-GFET sensor can offer advantages over current glucose detection methods.     

Sensitive and enzyme-free detection for single nucleotide polymorphism using microbead-assisted toehold-mediated strand displacement reaction

This report described a free-enzyme, convenient and inexpensive genotyping biosensor capable of detecting single nucleotide polymorphism at normal temperature based on the combination of toeholdmediated strand displacement reaction(toehold-SDR) and microbead-capture technique. The biosensor consists of a pre-hybridized strand formed by a reporter probe and a capture probe. In the presence of a mutant sequence, there is no toehold-mediated strand displacement and the reporter probe cannot be released from the pre-hybridized strand. Microbeads capture the fluorescent pre-hybridized strand through biotin–streptavidin interaction, so microbeads give out significant fluorescence signal, while there is no fluorescence in the solution. However, in the presence of a matched target, the strand displacement is effectively initiated and the reporter probe is released from pre-hybridized strand. After adding microbeads, the solution produces bright fluorescence, while microbeads have no obvious signal.Genotypes are identified conveniently according to the fluorescence intensity of the solution. The method provides a simple and inexpensive strategy to detect point mutation. Moreover, this biosensor shows the linear relationship in the range of 1–40 nmol/L and reaches a detection limit of 0.3 nmol/L.     

Fabrication of a liquid-gated enzyme field effect device for sensitive glucose detection

This study presents fabrication of a liquid-gated enzyme field effect device and its implementation as a glucose biosensor. The device consisted of four electrodes on a glass substrate with a channel functionalized by carboxylated multi-walled carbon nanotubes-polyaniline nanocomposite (MWCNTCOOH/PAn) and glucose oxidase. The resistance of functionalized channel increased with increasing the concentration of glucose when an electric field was applied to the liquid gate. The most effective and stable performance was obtained at the applied electric field of 100 mV. The device resistance, R, exhibited a linear relationship with the logarithm of glucose concentration in the range between 0.005 and 500 mM glucose. The detection limit (S/N = 3) for glucose was about 0.5 μM. Large effective area and good conductivity properties of MWCNTCOOH/PAn nanocomposite were the key features of the fabricated sensitive and stable glucose biosensor.     

Dumbbell probe-mediated cascade isothermal amplification: A novel strategy for label-free detection of microRNAs and its application to real sample assay

Considering the great significance of microRNAs (miRNAs) in cancer detection and typing, the development of sensitive, specific, quantitative, and low-cost methods for the assay of expression levels of miRNAs is desirable. We describe a highly efficient amplification platform for ultrasensitive analysis of miRNA (taking let-7a miRNA as a model analyte) based on a dumbbell probe-mediated cascade isothermal amplification (DP-CIA) strategy. The method relies on the circularization of dumbbell probe by binding target miRNA, followed by rolling circle amplification (RCA) reaction and an autonomous DNA machine performed by nicking/polymerization/displacement cycles that continuously produces single-stranded G-quadruplex to assemble with hemin to generate a color signal. In terms of the high sensitivity (as low as 1 zmol), wide dynamic range (covering 9 orders of magnitude), good specificity (even single-base difference) and easy operation (one probe and three enzymes), the proposed label-free assay is successfully applied to direct detection of let-7a miRNA in real sample (total RNA extracted from human lung tissue), demonstrating an attractive alternative for miRNA analysis for gene expression profiling and molecular diagnostics, particularly for early cancer diagnosis.     

A novel paper-based device coupled with a silver nanoparticle-modified boron-doped diamond electrode for cholesterol detection

A novel paper-based analytical device (PAD) coupled with a silver nanoparticle-modified boron-doped diamond (AgNP/BDD) electrode was first developed as a cholesterol sensor. The AgNP/BDD electrode was used as working electrode after modification by AgNPs using an electrodeposition method. Wax printing was used to define the hydrophilic and hydrophobic areas on filter paper, and then counter and reference electrodes were fabricated on the hydrophilic area by screen-printing in house. For the amperometric detection, cholesterol and cholesterol oxidase (ChOx) were directly drop-cast onto the hydrophilic area, and H₂O₂ produced from the enzymatic reaction was monitored. The fabricated device demonstrated a good linearity (0.39 mg dL⁻¹ to 270.69 mg dL⁻¹), low detection limit (0.25 mg dL⁻¹), and high sensitivity (49.61 μA mM⁻¹ cm⁻²). The precision value for ten replicates was 3.76% RSD for 1 mM H₂O₂. In addition, this biosensor exhibited very high selectivity for cholesterol detection and excellent recoveries for bovine serum analysis (in the range of 99.6–100.8%). The results showed that this new sensing platform will be an alternative tool for cholesterol detection in routine diagnosis and offers the advantages of low sample/reagent consumption, low cost, portability, and short analysis time.     

A novel sensitive non-enzymatic glucose sensor

Cu nanoclusters were electrochemically deposited on the film of a Nafion-solubilized multi-wall carbon nanotubes (CNTs) modified glassy carbon electrode (CNTs-GCE), which fabricated a Cu-CNTs composite sensor (Cu-CNTs-GCE) to detect glucose with non-enzyme. The linear range is 7.0×10-7 to 3.5×10-3 mol/L with a high sensitivity of 17.76μA/(mmol L), with a low detection limit 2.1×10-7 mol/L, fast response time (within 5 s), good reproducibility and stability.     

Paper-based enzyme-free immunoassay for rapid detection and subtyping of influenza A H1N1 and H3N2 viruses

Development of rapid screening in the ambulatory environment is the most pressing needs for the control of spread of infectious disease. Despite there are many methods to detect the immunoassay results, quantitative measurement in rapid disease screening is still a great challenge for point-of-care applications. In this work, based on the internal structural protein, i.e., nucleoprotein (NP), and outer surface glycoproteins, i.e., H1 and H3, of the influenza viruses, specific and sensitive immunoassay on paper-based platform was evaluated and confirmed. Detection and subtyping of influenza A H1N1 and H3N2 viruses found in people were demonstrated by colorimetric paper-based sandwich immunoassay. Concentration-dependent response to influenza viruses was shown and the detection limits could achieve 2.7 × 10³ pfu/assay for H1 detection and 2.7 × 10⁴ pfu/assay for H3 detection, which are within the clinical relevant level. Moreover, detection of influenza virus from infected cell lysate and clinical samples was demonstrated to further confirm the reliability of the paper-based immunoassay. The use of paper for the development of diagnostic devices has the advantages of lightweight, ease-of-use, and low cost and paper-based immunoassay is appropriate to apply for rapid screening in point-of-care applications.     

Polypyrrole: Synthesis and electronic device application

A Ta solid electrolytic capacitor using conducting polypyrrole as a counter electrode has been developed by means of the direct film formation of electrochemical and chemical polymerization methods. Two-step electrochemical polymerization at a rapid and gentle rate yields a polypyrrole film on the dielectric surface of the capacitor. On the other hand, the homogeneous mixture dissolving pyrrole and oxidant under −70 °C allows chemical polymerization at elevated temperature, which also produces polypyrrole film on the dielectric surface. The capacitors produced by these methods demonstrate the improved characteristics, i.e., a high capacitance, low inner resistance and small leakage current, that correspond to the high-speed electronic devices.     

A novel enzyme-mimic nanosensor based on quantum dot-Au nanoparticle@silica mesoporous microsphere for the detection of glucose

QD-Au NP@silica mesoporous microspheres have been fabricated as a novel enzyme-mimic nanosensor. CdTe quantum dots (QDs) were loaded into the core, and Au nanoparticles (NPs) were encapsulated in the outer mesoporous shell. QDs and Au NPs were separated in the different space of the nanosensor, which prevent the potential energy or electron transfer process between QDs and Au NPs. As biomimetic catalyst, Au NPs in the mesoporous silica shell can catalytically oxidize glucose as glucose oxidase (GOx)-mimicking. The resultant hydrogen peroxide can quench the photoluminescence (PL) signal of QDs in the microsphere core. Therefore the nanosensor based on the decrease of the PL intensity of QDs was established for the glucose detection. The linear range for glucose was in the range of 5–200 μM with a detection limit (3σ) of 1.32 μM.     

A novel donor–acceptor molecule containing a cyclic triphenylamine dimer: synthesis,characterization, and application in memory device

A novel highly soluble push–pull molecule containing electron-rich cyclic triphenylamine dimer (TPAD) and electron-poor N-phenyl-N′-octyl-naphthalene-1,4,5,8-tetracarboxylic acid bisimide [NI-(8,PBr)] was synthesized under Suzuki-coupling conditions. The resulting compound exhibited excellent thermal stability (T_d=354.3 °C) and good solubility in common organic solvents. Cyclic voltammogram and optical absorption spectroscopy showed that both the electroactive units preserve their nature, respectively, in the ground state, whereas photophysical investigations showed a strong fluorescence quenching. Interestingly, excellent switching behavior with extremely high ON/OFF current ratio (1.6E8 at +1 V) was observed through memory devices based on thin films of this material.     

Implementing a two-layer feed-forward catalytic DNA circuit for enzyme-free and colorimetric detection of nucleic acids

In the present study, a highly sensitive and specific bio-sensing platform for enzyme-free and colorimetric detection of nucleic acids has been developed. The biosensor is composed of two DNA nanostructures and two fuel strands that construct the foundation of a feed-forward catalytic DNA circuit. Upon binding the target strand to a specific DNA nanostructure, the circuit is run in order that at the end a hemin-binding aptamer, with the ability to convert a colorless substrate into a colored substance is released. Based on this strategy, 4 pM of the target DNA can be easily detected in serum samples by naked eyes after only a two-hour incubation with the circuit; meanwhile, if the incubation time is extended to 3 h, the biosensor can detect 1 pM of the target DNA. Besides the elevated sensitivity, the circuit can truly discriminate a spurious target containing one nucleotide mismatch with high specificity. Overall, the enzyme-free catalytic DNA circuit can be used as a sensitive alternative method to enzyme-based biosensors for the specific and cost-effective detection of nucleic acids.