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A novel strategy based on gradient porous hollow fiber membrane (GPF) is proposed for the modular assembly of enzyme-nanozyme cascade systems. The porous structure of GPF provided sufficient specific surface area, while the gradient structure effectively minimized the leaching of enzymes and nanozymes. To enhance stability, we prepared and immobilized metal–organic framework (MOF) nanozymes, resulting in the fabrication of GPF-MOF with excellent stability and reusability for colorimetric H2O2 detection. To improve specificity and expand the detection range, micro-crosslinked natural enzymes were modularly assembled, using glucose oxidase as the model enzyme. The assembled system, GPF-mGOx@MOF, achieved a low detection limit of 0.009 mM and a linear range of 0.2 to 11 mM. The sensor retained 87.2% and 80.7% of initial activity after being stored for 49 days and 9 recycles, respectively. Additionally, the reliability of the biosensor was validated through glucose determination of human blood and urine samples, yielding comparable results to a commercial glucose meter. [ABSTRACT FROM AUTHOR]

The ability of shape-controlled octahedral Pt nanoparticles to act as nanozyme mimicking glucose oxidase enzyme is reported. Extended {111} particle surface facets coupled with a size comparable to natural enzymes and easy-to-remove citrate coating give high affinity for glucose, comparable to the enzyme as proven by the steady-state kinetics of glucose electrooxidation. The easy and thorough removal of the citrate coating, demonstrated by X-ray photoelectron spectroscopy analysis, allows a highly stable deposition of the nanozymes on the electrode. The glucose electrochemical detection (at −0.2 V vs SCE) shows a linear response between 0.36 and 17 mM with a limit of detection of 110 μM. A good reproducibility has been achieved, with an average relative standard deviation (RSD) value of 9.1% (n = 3). Similarly, a low intra-sensor variability has been observed, with a RSD of 6.6% (n = 3). Moreover, the sensor shows a long-term stability with reproducible performances for at least 2 months (RSD: 7.8%). Tests in saliva samples show the applicability of Pt nanozymes to commercial systems for non-invasive monitoring of hyperglycemia in saliva, with recoveries ranging from 92 to 98%. [ABSTRACT FROM AUTHOR]

A novel magnetic nanozyme Fe3O4@MXene-Au nanocomposite, which possessed higher peroxidase-like activity than that of Fe3O4 nanoparticles and Fe3O4@MXene nanocomposites, was developed. The outstanding magnetic properties of the nanozyme endowed it with the ability of simple and rapid separation, achieving great recyclability. Based on Fe3O4@MXene-Au nanocomposites and glucose oxidase (Glu Ox), a highly selective colorimetric biosensor for glucose detection was developed. Fe3O4@MXene-Au nanocomposites can catalyze H2O2 produced from glucose catalyzed by glucose oxidase to ·OH and oxidize colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) with a significant absorbance at 652 nm. The linear range of glucose was 0–1.4 mM under optimal conditions, with a limit of detection (LOD) of 0.11 mM. Glucose in human whole blood was successfully detected with satisfactory recoveries. Furthermore, a facile agarose hydrogel detection platform was designed. With smartphone software, glucose detection can be realized by the agarose hydrogel platform, demonstrating the potential in on-site and visual detection of glucose. [ABSTRACT FROM AUTHOR]

Fe–N-doped carbon nanomaterials (Fe–N/CMs) were designed as a novel biomimetic enzyme with excellent peroxidase-like activity to achieve high-efficient enzyme cascade catalytic amplification with the aid of glucose oxidase (GOx), which was further combined with target-induced DNA walker amplification to develop a sensitive electrochemical biosensor for thrombin detection. Impressively, massive output DNA was transformed from small amounts of target thrombin by highly effective DNA walker amplification as protein-converting strategy, which could then induce the immobilization of functionalized nanozyme on the electrode surface to achieve the high-efficient electrochemical biomimetic enzyme cascade amplification. As a result, an amplified enzyme cascade catalytic signal was measured for thrombin detection ranging from 0.01 pM to 1 nM with a low detection limit of 3 fM. Importantly, the new biomimetic enzyme cascade reaction coupled the advantages of natural enzyme and nanozyme, which paved an avenue to construct varied artificial multienzymes amplification systems for biosensing, bioanalysis, and disease diagnosis applications. [ABSTRACT FROM AUTHOR]

A flexible photoelectrochemical (PEC) biosensor is proposed for the sensitive detection of ochratoxin A (OTA) based on glucose oxidase (GOx)-encapsulated target-responsive hydrogel, using Fenton reaction-mediated in situ formation of polyaniline (PANI) as signal amplified strategy. The target-responsive DNA hydrogels with high loading capacity can carry a large amount of GOx, which not only avoids laborious labeling process but also enhances the analytical performance. Upon introduction of target molecules, the hydrogel can be opened, and multiple GOx was released, thus producing lots of H2O2 via catalytic reduction of glucose. As a component of the Fenton reagent, H2O2 can react with the Fe2+ on the graphene oxidase-PAMAM-Fe2+ (GO-PAMAM-Fe2+) to generate Fe3+ and ·OH. This in turn can oxidize aniline and generate polyaniline (PANI), resulting in the enhancement of the photocurrent signal of GO-MoS2-CdS photoelectrode. The GO-PAMAM-Fe2+ as the neighborhood component of GO-MoS2-CdS-based photoactive material not only can increase the loading amount of Fe2+, but also can inhibit the decrease of photocurrent of GO-MoS2-CdS by direct modification of Fe2+ on the photoactive material. Moreover, the high loading capacity of DNA hydrogel can efficiently promote the performance of the PEC biosensor. The PEC biosensor exhibited satisfactory analytical performance for OTA with a linear range of 0.0001–0.1 ng/mL and a low detection limit of 0.05 pg/mL. It presents recommendable specificity, stability, and practical applications. Importantly, the PEC biosensor provides a new concept for construction of PEC biosensing platform. [ABSTRACT FROM AUTHOR]

An aminated Fe–Ni bimetallic metal–organic framework (Fe3Ni-MOF-NH2) with both peroxidase-like activity and fluorescence properties was developed. Fe3Ni-MOF-NH2 possessed the enhanced peroxidase-like activity through the enhanced electron transfer process and hydroxyl radical (·OH) generation. It was found that the amino group endowed the material with fluorescent property and the metal site Ni in Fe3Ni-MOF-NH2 could also enhance the fluorescence emission intensity (Ex = 345 nm, Em = 452 nm). Based on the dual excellent performance of Fe3Ni-MOF-NH2, a novel sensitive fluorescence detection strategy for H2O2 and glucose was designed and achieved. First, Fe3Ni-MOF-NH2 converted H2O2 to ·OH by exerting peroxidase-like activity, and ·OH converts catechol to o-benzoquinone. Then, the amino group in Fe3Ni-MOF-NH2 connected to o-benzoquinone, which resulted in its fluorescence quenching. The detection limit of H2O2 was as low as 5 nM. Combined with glucose oxidase which can oxidize glucose and produce H2O2 the glucose could be indirectly determined with a detection limit of 40 nM. The method was applied to the detection of low-level glucose in human urine samples with good recoveries and reproducibilities. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Monitoring exocellular adenosine-5′-triphosphate (ATP) is a demanding task but the biosensor development is limited by the low concentration and rapid degradation of ATP. Herein, we developed a simple yet effective biosensor based on ZIF-67 loaded with bi-enzymes of glucose (GOx) and hexokinase (HEX) for effective detection of ATP. In the confined space of the porous matrix, the bi-enzymes competed for the glucose substrate in the presence of ATP, facilitating the biosensor to detect low ATP concentrations down to the micromole level (3.75 μM) at working potential of 0.55 V (vs. Ag/AgCl). Furthermore, ZIF-67 with cobalt served as a porous matrix to specifically adsorb ATP molecules, allowing it to differentiate isomers with sensitivity of 0.53 nA/μM, RSD of 5.4%, and recovery rate of 93.3%. We successfully applied the fabricated biosensor to measure ATP secreted from rat PC12 cells in the pericellular space thus realizing time-resolving measurement. This work paved the path for real-time monitoring of ATP released by cells, which will aid in understanding tumor cell glycolysis and immune responses. [ABSTRACT FROM AUTHOR]

A highly sensitive electrochemical sensor is reported for glucose detection using carbon nanotubes grown in situ at low temperatures on photolithographically defined gold microelectrode arrays printed on a glass substrate (CNTs/Au MEA). One of the main advantages of the present design is its potential to monitor 64 samples individually for the detection of glucose. The selectivity of the fabricated MEA towards glucose detection is achieved via modification of CNTs/Au MEA by immobilizing glucose oxidase (GOx) enzyme in the matrix of poly (paraphenylenediamine) (GOx/poly (p-PDA)/CNTs/Au MEA). The electrocatalytic and electrochemical responses of the proposed sensing platform towards glucose determination were examined via cyclic voltammetry and electrochemical impedance spectroscopy. The developed impedimetric biosensor exhibits a good linear response towards glucose detection, i.e., 0.2–27.5 µM concentration range with sensitivity and detection limits of 168.03 kΩ−1 M−1 and 0.2 ± 0.0014 μM, respectively. The proposed glucose biosensor shows excellent reproducibility, good anti-interference property, and was successfully tested in blood serum samples. Further, the applicability of the proposed sensor was successfully validated through HPLC. These results supported the viability of using such devices for the simultaneous detection of multiple electroactive biomolecules of physiological relevance. [ABSTRACT FROM AUTHOR]

A dual-signal readout has been designed detecting platform based on a cascade reaction for Escherichia coli (E. coli) detection by using colorimetric approach and a handheld pH meter. The immunoreaction was conducted using polydopamine@copper ferrite-Ag nanoparticles (PDA@CuFe2O4-Ag NP) and a glucose oxidase (GOD)–conjugated graphene oxide-gold nanosheet composite (GOD-GO/Au NS) to synthesize a sandwich complex mode between targets. Together with the formation of immune complexes, the GOD-GO/Au NS can catalyze glucose to produce gluconic acid and hydrogen peroxide (H2O2). The gluconic acid produced altered the pH of the detection solution. Since the PDA@CuFe2O4-Ag NP have good peroxidase-like activity, they can catalyze the oxidation of TMB to the blue product oxTMB once H2O2 is produced in the reaction system, and the absorbance change of oxTMB at 652 nm can be recorded using ultraviolet–visible (UV–Vis) spectroscopy. Interestingly, the PDA@CuFe2O4-Ag NP composites can consume the generated H2O2, and can create a reaction cycle that promotes glucose oxidation. Under optimal conditions, the proposed dual-channel signal platform is proportional to the logarithm of the E. coli concentration within a range of 102–107 cfu mL−1. Additionally, the devised approach was successfully used to detect E. coli at the required levels in real samples. This dual-mode detection method notably enhances the accuracy and diversity of detection, and curbs the false negative and positive rates. [ABSTRACT FROM AUTHOR]

Copper-based metal–organic frameworks (MOF) and multi-walled carbon nanotubes (HKUST-1-MWCNTs) composite were synthesized by one-step hydrothermal method, and PDA-enzyme-HKUST-1-MWCNTs composite was prepared by one-pot method for the construction of glucose biosensors, which realized the sensitive amperometric detection of glucose at 0.7 V (vs. SCE). The sensitivity of the sensor for glucose detection was 178 μA mM−1cm−2 in the wide linear range of 0.005 ~ 7.05 mM, the detection limit was 0.12 μM and the corresponding RSD was 3.8%. Its high performance is mainly benefitted from the high porosity and large specific surface area of HKUST-1, the good conductivity of MWCNTs, and the excellent adhesion and dispersion of PDA. The strategy of combining PDA and MWCNTs to improve the dispersion and conductivity of MOF is expected to achieve a wider application of MOF-based materials in the electrochemical biosensing field. [ABSTRACT FROM AUTHOR]

By employing NH2-MIL-88 as a template, we synthesized the intermediate Fe@CN under high-temperature calcination and further fabricated the FeS2@CN nanocomposites in the presence of sulfur powder. Under varying temperatures (300–600 °C) and Fe@CN-to-S ratios (1:3–6), FeS2@CN500-5 nanocomposites had the highest peroxidase-mimetic activity. Under optimized conditions (incubation temperature 40 °C; solution pH 4.0 and nanocomposite concentration 10 μg/mL; 652-nm absorption), the Michaelis-Menten constant (Km) of FeS2@CN was much lower than that of horseradish peroxidase (HRP), therefore demonstrating that it had a higher affinity for both chromogenic substrates than conventional HRP. The limits of detection for H2O2 and glucose were 0.15 and 0.30 μmol/L, respectively, and the recoveries for glucose were 91.8–103% with RSDs <5.2%. The novelty of this study lies in (1) the FeS2@CN was confirmed to possess stronger enzyme-mimetic activity than its precursors (NH2-MIL-88 and Fe@CN); (2) the enhanced activity resulted from the unsaturated sites of N and S doping and the plentiful defects on the porous carbon surface; and (3) free radical trapping experiments evidenced that •OH played a major role in the catalytic reaction, while h+ and •O2− simultaneously participated in the catalytic process. These convincing performance metrics lead us to postulate that the FeS2@CN-based colorimetric biosensor provides a promising approach for several real-world applications, such as point-of-care diagnosis and workplace health evaluations. [ABSTRACT FROM AUTHOR]

An efficient electrochemiluminescence resonance energy transfer (ECL-RET) method is proposed which combines the luminescent materials of tris(4,4′-dicarboxylicacid-2,2′-bipyridyl) ruthenium(II) (energy donor) and tin dioxide and tin disulfide quantum dots (SnO2/SnS2QDs) (energy acceptor) into the isoreticular metal − organic framework-3 (IRMOF-3) material to form a composite. In this mode, the distance between the energy donor and the acceptor was greatly shortened, reducing the energy loss, and thereby effectively improving RET efficiency and further significantly improving the ECL signal. The obtained composite (SnO2/SnS2QDs-Ru@IRMOF-3) was combined with sandwich immunoreaction to construct an ECL immunosensor for the sensitive detection of procalcitonin (PCT). Under the optimized experimental conditions with a working potential of − 1.48 V (vs Ag/AgCl), the proposed PCT biosensor exhibited a linear concentration range of 1 × 10−4–200 ng mL−1, with a detection limit of 0.029 pg mL−1 (S/N = 3). The biosensor was used to detect PCT in actual samples. The biosensor has broad application prospects in biological analysis and clinical diagnosis due to its high sensitivity, good selectivity, and good stability. [ABSTRACT FROM AUTHOR]

In a new approach, we considered the special affinity between Ni and poly-histidine tags of recombinant urate oxidase to utilize Ni-MOF for immobilizing the enzyme. In this study, a carbon paste electrode (CPE) was modified by histidine-tailed urate oxidase (H-UOX) and nickel-metal–organic framework (Ni-MOF) to construct H-UOX/Ni-MOF/CPE, which is a rapid, sensitive, and simple electrochemical biosensor for UA detection. The use of carboxy-terminal histidine-tailed urate oxidase in the construction of the electrode allows the urate oxidase enzyme to be positioned correctly in the electrode. This, in turn, enhances the efficiency of the biosensor. Characterization was carried out by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), and field emission scanning electron microscopy (FE-SEM). At optimum conditions, the biosensor provided a short response time, linear response within 0.3–10 µM and 10–140 µM for UA with a detection limit of 0.084 µM, repeatability of 3.06%, and reproducibility of 4.9%. Furthermore, the biosensor revealed acceptable stability and selectivity of UA detection in the presence of the commonly coexisted ascorbic acid, dopamine, L-cysteine, urea, and glucose. The detection potential was at 0.4 V vs. Ag/AgCl. [ABSTRACT FROM AUTHOR]

The increasing demand for food and the need for a sustainability vision in the agri-food sector have boosted novel approaches for food management, enhancing the valorization of wastes and by-products belonging to the food industry. Herein, we present a novel paper-based origami device to assess the amount of both glucosinolate and glucose in a food waste product belonging to Brassicaceae plants, to evaluate the quality value and the correct management of waste samples. The device has been designed as an origami paper-based platform constituted of two paper-based biosensors to work synergistically in a multiplexed detection. In detail, a monoenzymatic biosensor and a bienzymatic biosensor were configured for the detection of glucose and glucosinolates, respectively, using filter paper pads preloaded with glucose oxidase and/or myrosinase. To complete the paper-based platform, the enzyme-preloaded pads were combined with office paper-based electrodes modified with Carbon black/Prussian Blue nanoparticles for the measurement of enzymatic by-product at a low applied potential (i.e., 0 V versus Ag/AgCl). Overall, this paper-based platform measured glucose and glucosinolate (i.e., sinigrin) with a linear range up to 2.5 and 1.5 mM, and detection limits of 0.05 and 0.07 mM, respectively. The repeatability corresponded to an RSD% equal to 5% by testing 10 mM of glucose, and 10% by testing 1 mM of sinigrin. The accuracy of the developed multiplex device was evaluated by recovery studies at two different levels of sinigrin, i.e., 0.25 and 0.5 mM, obtaining recoveries values equal to (111 ± 3) % and (86 ± 1) %, respectively. The multiplex detection of both glucose and glucosinolate in Brassicaceae samples evaluates the quality values of the waste sample, ensuring the quality of the re-used food product waste by using an eco-designed analytical tool. The combination of paper-based devices for quality control of food waste with the re-use of these food products represents a sustainable approach that perfectly matches sustainable agrifood practices as well as the overall approach of the circular economy. [ABSTRACT FROM AUTHOR]

The use of colloidal nanoparticles suffers from the drawbacks of potential color interference and substrate-induced aggregation. To overcome the limitations, a catalyst was developed by crosslinking Cu-doped carbon dots (Cu-CDs) with chitosan. Cu-CDs with high peroxidase activity were prepared by using a rapid microwave-assisted method. The Cu-CDs containing 6.88% of Cu had an average particle size of 2.25 nm and exhibited 9% of fluorescence quantum yield. The nanozyme/film composite was prepared by crosslinking between the amino groups of Cu-CDs and those of chitosan via a glutaraldehyde linker. A H2O2-mediated tetramethylbenzidine (TMB) oxidation reaction was use to evaluate the peroxidase activity of the film. Based on the TMB color changes, colorimetric assays were developed for the detection of H2O2 and glucose at an absorption wavelength 652 nm. Under the optimal conditions, the linear ranges for H2O2 and glucose were 0.625–40 µM and 1.9–125 µM, respectively, and the detection limits were 0.12 µM and 0.69 µM, respectively. The colorimetric assay was also applied to analyze diluted human serum samples spiked with glucose. Furthermore, this biodegradable, non-toxic, and easy-to-handle nanozyme composite could be stored for over 4 weeks without a significant decrease in activity. [ABSTRACT FROM AUTHOR]

The successful synthesis of ruthenium oxide/reduced graphene oxide (RuO2/rGO) heterostructures by one-pot hydrothermal method using graphene oxides and RuCl3 as precursors is reported. The heterostructures had high peroxidase-like (POD-like) activities, which catalyzes the oxidation of classical peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to create a blue colored reaction product. The catalytic activity was significantly enhanced by the synergistic effect between RuO2 nanoparticles and rGO. RuO2/rGO had a low Km of 0.068 mM and a high vmax of 1.228 × 10−7 M·s−1 towards TMB in the TMB-H2O2 catalytic oxidation system. In addition, the POD-like activity originating from the electron transfer mechanism was confirmed by cytochrome C (Cyt C) oxidation experiment. A colorimetric method based on RuO2/rGO heterostructures was developed with good sensitivity and selectivity for glucose detection with a limit of detection of 3.34 μM and a linear range of 0–1500 μM. The RuO2/rGO heterostructures have potential applications in the biomedical areas, such as biosensor and diagnostics. [ABSTRACT FROM AUTHOR]

In 2006, Prof. Malcolm Smyth at Dublin City University and I published a widely cited mini-review (https://doi.org/10.1002/elan.200503415) about the application of nanoparticles in electrochemical sensors and biosensors, and we summarized the functions of nanoparticles in the electrochemical sensing systems. Electrochemical sensors and biosensors, owing to their unique advantages such as high sensitivity, low cost, and ease for miniaturization and automatization, have attracted increasing attention in the past years. Zhou et al. developed an ultrasensitive luminol electrochemiluminescence biosensor for the detection of prostate specific antigen (PSA) based on glucose oxidase-decorated hemin-graphene oxide-gold nanoflowers (https://doi.org/10.1007/s00604-022-05387-2). [Extracted from the article]

Three-dimensional (3D) cobalt molybdate (CoMoO4) hierarchical nanoflake arrays on pencil graphite electrode (PGE) (CoMoO4/PGE) are actualized via one-pot hydrothermal technique. The morphological features comprehend that the CoMoO4 nanoflake arrays expose the 3D, open, porous, and interconnected network architectures on PGE. The formation and growth mechanisms of CoMoO4 nanostructures on PGE are supported with different structural and morphological characterizations. The constructed CoMoO4/PGE is operated as an electrocatalytic probe in enzyme-less electrochemical glucose sensor (ELEGS), confronting the impairments of cost- and time-obsessed conventional electrode polishing and catalyst amendment progressions and obliged the employment of a non-conducting binder. The wide-opened interior and exterior architectures of CoMoO4 nanoflake arrays escalate the glucose utilization efficacy, whilst the intertwined nanoflakes and graphitic carbon layers, respectively, of CoMoO4 and PGE articulate the continual electron mobility and catalytically active channels of CoMoO4/PGE. It jointly escalates the ELEGS concerts of CoMoO4/PGE including high sensitivity (1613 μA mM−1 cm−2), wide linear glucose range (0.0003–10 mM), and low detection limit (0.12 µM) at a working potential of 0.65 V (vs. Ag/AgCl) together with the good recovery in human serum. Thus, the fabricated CoMoO4/PGE extends exclusive virtues of modest electrode production, virtuous affinity, swift response, and excellent sensitivity and selectivity, exposing innovative prospects to reconnoitring the economically viable ELEGSs with binder-free, affordable cost, and expansible 3D electrocatalytic probes. [ABSTRACT FROM AUTHOR]

A novel non-enzymatic glucose sensor based on poly(caffeic acid)@multi-walled carbon nanotubes decorated with CuO nanoparticles (PCA@MWCNT-CuO) was developed. The described approach involves the complexation/accumulation of Cu(II) on PCA@MWCNT followed by electrochemical CuO deposition in an alkaline electrolyte. The morphology and surface characteristics of the nanomaterial were determined by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), Raman spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS). A hybrid-support sensor device was then developed to assess the glucose concentration in different solutions. The sensitivity of the electrode is 2412 μA mM−1 cm−2. The electrode exhibited a broad linear range of 2 µM to 9 mM and a low limit of detection (LOD) of 0.43 µM (relative standard deviation, RSD = 2.3%) at + 0.45 V vs Ag/AgCl. The excellent properties obtained for glucose detection were most likely due to the synergistic effect of the combination of individual components: poly(caffeic acid), MWCNTs, and CuO. Good accuracy and high precision were demonstrated for quantifying glucose concentrations in human serum and blood samples (the recovery ranged from 95.0 to 99.5%). The GC/PCA@MWCNT-CuO sensor represents a novel, simple, and low-cost approach to the fabrication of devices for amperometric sensing of glucose. [ABSTRACT FROM AUTHOR]

A novel molecularly imprinted electrochemical biosensor for glucose detection is reported based on a hierarchical N-rich carbon conductive-coated TNO structure (TNO@NC). Firstly, TNO@NC was fabricated by a novel polypyrrole-chemical vapor deposition (PPy-CVD) method with minimal waste generation. Afterward, the electrode modification with TNO@NC was performed by dropping TNO@NC particles on glassy carbon electrode surfaces by infrared heat lamp. Finally, the glucose-imprinted electrochemical biosensor was developed in presence of 75.0 mM pyrrole and 25.0 mM glucose in a potential range from + 0.20 to + 1.20 V versus Ag/AgCl via cyclic voltammetry (CV). The physicochemical and electrochemical characterizations of the fabricated molecularly imprinted biosensor was conducted by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) method, X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and CV techniques. The findings demonstrated that selective, sensitive, and stable electrochemical signals were proportional to different glucose concentrations, and the sensitivity of molecularly imprinted electrochemical biosensor for glucose detection was estimated to be 18.93 μA μM−1 cm−2 (R2 = 0.99) at + 0.30 V with the limit of detection (LOD) of 1.0 × 10−6 M. Hence, it can be speculated that the fabricated glucose-imprinted biosensor may be used in a multitude of areas, including public health and food quality. [ABSTRACT FROM AUTHOR]

A chemiluminescence (CL) sensor was constructed for the one-step determination of glucose. Glucose oxidase (GOx) was successfully encapsulated into Zn-doped zeolitic imidazolate framework-67 (Zn–ZIF–67) via a simple one-pot strategy. The as-prepared GOx@Zn–ZIF–67 nanocomposite can trigger cascade reactions of glucose oxidation to generate H2O2 and H2O2-mediated luminol reaction to give an intense CL emission. The sensor responds linearly to glucose in the 20.0–400.0 μmol·L–1 range with a limit of detection (LOD) of 4.7 μmol·L–1. Eleven replicated measurements of 200.0 μmol·L–1 glucose solution gives a relative standard deviation (RSD) of 1.7%. The sensor exhibits good selectivity and stability and was successfully applied to the determination of glucose in real human serum samples. Schematic representation of one-step determination of serum glucose with GOx@Zn–ZIF–67 nanocomposite triggering cascade reactions between luminol and glucose. [ABSTRACT FROM AUTHOR]

Polyaniline (PANI) was functionalized by thiol-ene click chemistry to obtain carboxylic acid–tethered polyaniline (PCOOH). The versatility of PCOOH as an immobilization matrix was demonstrated by constructing four different biosensors for detection of metabolites and cancer biomarker. Immobilization efficiency of PCOOH was investigated by surface plasmon resonance and fluorescence microscopic analysis which revealed dense immobilization of biomolecules on PCOOH as compared to conventional PANI. A sandwich electrochemical biosensor was constructed using PCOOH for detection of liver cancer biomarker, α-fetoprotein (AFP). The sensor displayed sensitivity of 15.24 µA (ng mL−1)−1 cm−2, with good specificity, reproducibility (RSD 3.4%), wide linear range (0.25–40 ng mL−1) at − 0.1 V (vs. Ag/AgCl), and a low detection limit of 2 pg mL−1. The sensor was validated by estimating AFP in human blood serum samples where the AFP concentrations obtained are consistent with the values estimated using ELISA. Furthermore, utilization of PCOOH for construction of enzymatic biosensor was demonstrated by covalent immobilization of glucose oxidase, uricase, and horseradish peroxidase (HRP) for detection of glucose, uric acid, and H2O2, respectively. The biosensors displayed reasonable sensitivity (50, 148, 127 µA mM−1 cm−2), and linear ranges (0.1–5, 0.1–6, 0.1–7 mM) with a detection limit of 10, 1, and 8 µM for glucose, uric acid, and H2O2, respectively. The present study demonstrates the capability of PCOOH to support and enable oxidation of H2O2 generated by oxidase enzymes as well as HRP enzyme catalyzed reduction of H2O2. Thus, PCOOH offers a great promise as an immobilization matrix for development of high-performance biosensors to quantify a variety of other disease biomarkers. Carboxylic acid–tethered polyaniline synthesized by thiol-ene click chemistry was used as matrix to construct four different electrochemical biosensors for detection of cancer biomarker α-fetoprotein, glucose, uric acid, and H2O2. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) printing has showed great potential for the construction of electrochemical sensor devices. However, reported 3D-printed biosensors are usually constructed by physical adsorption and needed immobilizing reagents on the surface of functional materials. To construct the 3D-printed biosensors, the simple modification of the 3D-printed device by non-expert is mandatory to take advantage of the remote, distributed 3D printing manufacturing. Here, a 3D-printed electrode was prepared by fused deposition modeling (FDM) 3D printing technique and activated by chemical and electrochemical methods. A glucose oxidase-based 3D-printed nanocarbon electrode was prepared by covalent linkage method to an enzyme on the surface of the 3D-printed electrode to enable biosensing. X-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the glucose oxidase-based biosensor. Direct electrochemistry glucose oxidase-based biosensor with higher stability was then chosen to detect the two biomarkers, hydrogen peroxide and glucose by chronoamperometry. The prepared glucose oxidase-based biosensor was further used for the detection of glucose in samples of apple cider. The covalently linked glucose oxidase 3D-printed nanocarbon electrode as a biosensor showed excellent stability. This work can open new doors for the covalent modification of 3D-printed electrodes in other electrochemistry fields such as biosensors, energy, and biocatalysis. [ABSTRACT FROM AUTHOR]

Enzymes have demonstrated great potential in the development of advanced electroanalysis devices due to their unique recognition and catalytic properties. However, unsatisfactory stability and limited electron communication of traditional enzyme sensors seriously hinder their large-scale application. In this work, a simple and effective method is proposed to improve the stability of enzyme sensors by using sodium hyaluronate (SH) as a protective film, MXene-Ti3C2/Glucose oxidase (GOD) as the reaction layer, and chitosan (CS) /reduced graphene oxide (rGO) as the adhesion layer. Results demonstrate that the repeatability of the designed sensor increased by 73.3% after improving the adhesion between the reaction layer and the current collector and that its response ability was greatly enhanced. Moreover, the long-term stability of the electrode surface with SH protective film proved to be superior than that without protective film, which suggests that this design can effectively improve the overall performance of the enzyme biosensor. This work proposed a multi-tier synergistic approach for improving the reliability of enzyme sensors. [ABSTRACT FROM AUTHOR]

An ultrathin micro-patterned MXene/PEDOT:PSS-based organic electrochemical transistor biosensor was constructed, which can significantly amplify the amperometric signal and transistor's performance. A novel interdigitated OECTs biosensor has been developed for reliable determination of survivin for the following considerations: (1) The synergistic effect of intercalated MXene and ionic PEDOT:PSS enhanced the mobility and volumetric capacitance of OECTs biosensor. (2) Compared with the best previous literatures, our assay demonstrated enhanced detection limit of survivin down to 10 pg mL−1, as well as satisfactory selectivity, reproducibility, and reliability. (3) Comparison of OECTs against commercial ELISA kit yielded favorable linearity (Y = 1.0015*X + 0.0039) and correlation coefficient (R2 = 0.9717). Those advantages are expected to pave the way to design of an OECTs biosensor with robustness, non-invasiveness, and miniaturization for the point-of-care applications. [ABSTRACT FROM AUTHOR]

The design and development of a 3D hierarchical CdS/NiO heterojunction and its application in a self-powered cathodic photoelectrochemical (PEC) bioanalysis is introduced. Specifically, NiO nanoflakes (NFs) were in situ formed on carbon fibers via a facile liquid-phase deposition method followed by an annealing step and subsequent integration with CdS quantum dots (QDs). The glucose oxidase (GOx) was then coated on the photocathode to allow the determination of glucose. Under 5 W 410 nm LED light and at a working voltage of 0.0 V (vs. Ag/AgCl), this method can assay glucose concentrations down to 1.77×10−9 M. The linear range was 5×10−7 M to 1×10−3 M, and the relative standard deviation (RSD) was below 5%. The photocathodic biosensor achieved target detection with high sensitivity and selectivity. This work is expected to stimulate more passion in the development of innovative hierarchical heterostructures for advanced self-powered photocathodic bioanalysis. [ABSTRACT FROM AUTHOR]

Using an ultrasonication-assisted liquid exfoliation method, we have synthesized PtS2 nanosheets with good reproducibility. Herein, intrinsic peroxidase-like activity was for the first time demonstrated for PtS2 nanosheets, which can catalyze H2O2 oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate a colored solution. The catalytic mechanism of PtS2 nanosheets was investigated, which indicated that acceleration of the electron transfer between TMB and H2O2 was the main reason for the peroxidase-like activity of PtS2 nanosheets. Based on these observations, we exploited PtS2 nanosheets integrated into dopamine-functionalized hyaluronic acid (HA-DA) hydrogel microspheres by droplet microfluidics to construct PtS2 nanosheet– and PtS2@HA-DA microsphere–based sensors for highly sensitive determination of H2O2. When coupled with glucose oxidase, we further developed two glucose sensors based on the above two methods. Among them, the linearity of the PtS2 nanosheet–based spectrophotometry was in the range of 0.5 to 150 μM and the limit of detection as low as 0.20 μM. The linearity of the microsphere-based colorimetry was in the range 200 to 12,000 μM with a detection limit of 29.95 μM. Both of the glucose sensors can be applied to the determination of glucose in human serum with reliable results and reproducibility. [ABSTRACT FROM AUTHOR]

Rosette-shaped graphitic carbon nitride (rosette-GCN) is described as a promising alternative to natural peroxidase for its application to fluorescence-based glucose assays. Rosette-GCN was synthesized via a rapid reaction between melamine and cyanuric acid for 10 min at 35 °C, followed by thermal calcination for 4 h. Importantly, rosette-GCN possesses a peroxidase-like activity, producing intense fluorescence from the oxidation of Amplex UltraRed in the presence of H2O2 over a broad pH-range of, including neutral pH; the peroxidase activity of rosette-GCN was ~ 10-fold higher than that of conventional bulk-GCN. This enhancement of peroxidase activity is presumed to occur because rosette-GCN has a significantly larger surface area and higher porosity while preserving its unique graphitic structure. Based on the high peroxidase activity of rosette-GCN along with the catalytic action of glucose oxidase (GOx), glucose was reliably determined down to 1.2 μM with a dynamic linear concentration range of 5.0 to 275.0 μM under neutral pH conditions. Practical utility of this strategy was also successfully demonstrated by determining the glucose levels in serum samples. This work highlights the advantages of GCNs synthesized via rapid methods but with unique structures for the preparation of enzyme-mimicking catalysts, thus extending their applications to the diagnostics field and other biotechnological fields. [ABSTRACT FROM AUTHOR]

An interferometric reflectance spectroscopy-based biosensor for the determination of cathepsin B (Cat B) as a cancer-related enzyme has been fabricated. For this purpose, the nanoporous anodic alumina (NAA) was fabricated electrochemically. The NAA was then modified with the amino-silane coupling agent. After that, human serum albumin (HSA) was immobilized into the NAA pores by using glutaraldehyde as a cross-linking agent. Subsequently, the carboxylic group of HSA was activated with N-ethyl-N′-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to attach to thionine (TH) as a photoprobe to fabricate the labeled HSA (HSA-TH). HSA-TH plays a significant role in this sensor to determine cathepsin B as a model analyte for the development of the interferometric reflectance spectroscopy-based biosensor for the measurement of protease. The attached TH adsorbed the illuminated white light on NAA modified with HSA-TH. Therefore, the intensity of the reflected light to the charge-coupled device (CCD) detector decreased in the wavelength range 450–1050 nm. In the presence of Cat B, HAS-TH cleaved into short peptide fragments and washed away by flow cell system. Since TH was removed from NAA, the intensity of the reflected light increased. The peak area has a logarithmic relationship with the concentration of Cat B in the range 0.5 to 64.0 nM. The limit of detection of the biosensor sensor was 0.08 nM. The optical sensor was used for the determination of Cat B in a human serum sample. [ABSTRACT FROM AUTHOR]

A differential photoelectrochemical (PEC) method for glucose determination is reported using a nanocomposite with double mimic enzymes of glucose oxidase (GOx) and peroxidase. The nanocomposite was prepared by soaking zeolite imidazole framework-67 (ZIF-67) in 0.1 M NaOH solution at room temperature for 30 min, abbreviated as CoxOyHz@ZIF-67. The Michaelis–Menten constant of CoxOyHz@ZIF-67 to H2O2 and glucose is 121 μM and 3.95 mM, respectively. Using the photoelectrode of CoxOyHz@ZIF-67/TiO2 nanotubes (NTs), glucose was oxidized firstly by dissolved oxygen to generate H2O2 under the catalysis of CoxOyHz film as the mimics of GOx. The product of H2O2 enhanced the photocurrent of TiO2 NTs under the catalysis of ZIF-67 as the mimics of peroxidase. The molecular sieve effect of ZIF-67 frameworks reduces the interferences from molecules with size larger than the apertures in ZIF-67. Under the excitation of a 150 W xenon lamp with full spectrum, the photocurrent was measured in a two-electrode system without external additional potential. By using the photocurrent difference between two photocells, i.e CoxOyHz@ZIF-67/TiO2 NTs and Pt electrode, ZIF-67/TiO2 NTs and Pt electrode, as the signal, the selectivity for glucose determination is improved further. The differential PEC method was applied to the determination of glucose with a linear range 0.1 μM~1 mM and a detection limit of 0.03 μM. [ABSTRACT FROM AUTHOR]

A carbon silver nano-assembly was prepared from silver nanoparticles and carbon dots (AgNP@CD). It was used to quantify hydrogen peroxide and glucose by UV-visible spectroscopy. Banana peels were used to prepare the CDs by a microwave-assisted method. The CDs can be prepared within 5 min at 700 W. They act as (a) substrate, (b) stabilizer, and (c) reductant to convert silver ions to AgNPs. The nano-assembly was characterized by UV-visible spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy, and transmission electron microscopy. The CDs have a particle size of 1.4 nm. Photoexcitation of the CDs with a UV lamp of 365 nm results in blue fluorescence. The absorption spectra of the CDs show a peak at 205 nm along the wide shoulder absorption band. On incorporation of the Ag nanoparticles into the CDs matrix, the color of the CDs turns into yellow and an additional absorbance peak at 408 nm appears. FTIR spectroscopy shows that different functional groups are present on the CDs. They are responsible for the stabilization of the AgNPs. On exposure to H2O2, the color of the nano-assembly disappears gradually. Hence, the assembly can be used as a colorimetric indicator probe for H2O2 with a linear response in the 0.1-100 μM concentration range. It can also be applied to the determination of glucose by using glucose oxidase which causes the formation of H2O2 from glucose. The linear response ranges from 1- 600 μM. The detection limits for H2O2 and glucose are 9 nM and 10 nM, respectively. In our perception, this is the lowest detection limit reported so far. The AgNP@CD nano-assembly does not respond to saccharides, maltose, fructose, and lactose. It can be used to quantify glucose in diluted blood plasma. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotubes coated with cobalt(II) sulfide nanoparticles were prepared and used for immobilization of glucose oxidase (GOx) to obtain an electrochemical glucose biosensor. The nanocomposite was synthesized through an in-situ hydrothermal method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electrochemical impedance spectroscopy. The results show that the nanocomposite possesses a large specific surface area and apparently enhances the direct electron transfer between GOx and the surface of the electrode, best at a potential near −0.43 V (vs. SCE). The immobilized GOx retains its good bioactivity even at a high surface coverage of 30 pmol cm−2. Under the optimum conditions. The biosensor exhibits a wide linear range (from 8 μM to 1.5 mM), a high sensitivity (15 mA M −1 cm−2), and a 5 μM detection limit (at S/N = 3). The sensor is selective, acceptably repeatable, specific and stable. [ABSTRACT FROM AUTHOR]

A method is described for modulating the anodic photoelectrochemistry of netlike CdS quantum dots through the deposition and dissolution of the electron acceptor manganese dioxide (MnO2) on the surface of the photoelectrode. Specifically, the photocurrent of a CdS-modified indium tin oxide (ITO/CdS) electrode is inhibited by chemical deposition of MnO2. However, the photocurrent becomes recovered by oxidative removal of MnO2 with H2O2. This deposition-dissolution reaction modulates the photoelectrochemistry of CdS effectively. A bioassay for Escherichia coli (E. coli) O157:H7 is designed that uses the antimicrobial peptide magainin I as the recognition element. Glucose oxidase (GOx) acts as a catalytic label tracer to produce the signaling molecule H2O2 in the microwell plates. The enzymatically generated H2O2 etches the deposited MnO2 on the photoelectrode and thus enhances the photocurrent. This detection scheme does not cause any damage to biomolecules. It also avoids the adverse effects of immobilized biomolecules for retarding signal production and leads to improved detection when compared to conventional PEC configurations. E. coli can be detected in the 10 to 5.0 × 106 CFU·mL−1 concentration range, and the limit of detection is 3 CFU·mL−1. [ABSTRACT FROM AUTHOR]

A fluorometric and colorimetric method are described for the determination of hydrogen peroxide and glucose by integrating copper nanoclusters (CuNCs) into a Fenton-like reaction. The mechanism mainly depends on the fast formation of long-strand DNA-templated CuNCs with strong red fluorescence (with excitation/emission maxima at 340/640 nm) in the absence of H2O2. The DNA can be cleaved into short-oligonucleotide fragments by hydroxy radicals as formed in the Ce(III)-triggered Fenton-like reaction in the presence of H2O2. As a result, short-strand DNA loses the ability as a template for the formation of CuNCs. This leads to a decrease of fluorescence. The colorimetric assay, in turn, is based on the oxidation of colorless Ce(III) ions to the distinctly yellow Ce(IV) ions (with an absorption maximum at 400 nm) by H2O2. Compared with those assays based on the use of enzyme mimics, this method does not require any chromogenic substrates such as ABTS and TMB. Based on the dual-signal readout platform, we successfully achieved the detection of H2O2 and glucose. LODs are as low as 0.266 μM and 2.92 μM. The methods were applied to the sensitive determination of glucose by using glucose oxidase (GOx) which catalyzes the oxidization of glucose to produce H2O2. The practical application was demonstrated by determination of glucose in human serum, with apparent recoveries of 98.4–101.9% and 99.1–105.6%, respectively. The concentration of glucose ranges from 1 to 500 μM and 50 to 600 μM based on the dual-signal readout platform, respectively. This fluorometric and colorimetric dual-mode strategy will pave a new avenue for constructing effective assays for H2O2-related analytes in biochemical and clinical applications. [ABSTRACT FROM AUTHOR]

Gold-silver core-shell nanoparticles (Au@Ag NPs) were prepared by two successive reductions in a seed-growth method. The Au@Ag NPs are used as both a colorimetric and Raman spectroscopic probe for ultrasensitive determination of H2O2 and glucose. It is found that H2O2 (as produced from glucose by the action of glucose oxidase) can directly oxidize and gradually corrode the silver shell of the Au@Ag NPs. This results in a drop in the surface plasmon resonance absorbance at 400 nm, and the color of the solution changes from brownish yellow to purple. Without adding any additional chromogenic agents, the color change can be visually observed and detected photometrically. Silver NPs also are an excellent surface-enhanced Raman scattering (SERS) substrate. Due to corrosion of the silver shell, the SERS intensity (measured at 1083 cm−1) gradually decreases with increasing glucose concentration. The detection limits are 300 nM of glucose for the colorimetric assays, and 20 nM for the SERS assay. [ABSTRACT FROM AUTHOR]

Platinum nanoparticles (Pt NPs) covered with a bovine serum albumin scaffold and a particle size of 1.5 nm (BSA-PtS NPs) are shown to display enhanced multiple enzyme-mimicking activities including peroxidase, oxidase, and catalase-like activities. The peroxidase-like activity is characterized by robustness and low signal background. BSA-PtS NPs were used to design colorimetric assays for H2O2 and glucose. H2O2 latter reacts with 3,3′,5,5′-tetramethylbenzidine in the presence of BSA-PtS NPs to form a blue product with an absorption maximum at 652 nm. The assay works in the 5–250 μM H2O2 concentration range. The glucose assay is based on its glucose oxidase-catalyzed oxidation to produce gluconic acid and H2O2 which then is colorimetrically quantified. Response is linear in the 10–120 μM glucose concentration range, and the detection limit is 2 μM (at S/N = 3). The method correlates well with the glucose standard method (R2 = 0.997 in the 95% confidence interval) which confirms that glucose in human serum has been successfully detected. [ABSTRACT FROM AUTHOR]

A porous carbon nitride (PCN) modified with cobalt phosphides (CoP) was synthesized. In this nanocomposite, the CoP (in different weight fractions) serves (a) as the electron acceptor to accelerate the photoinduced charge separation, and (b) as the photosensitizer to increase the photoelectrochemical (PEC) response to visible light. Dissolved oxygen acts as the electron acceptor to generate PEC current. If glucose oxidase (GOx) catalyzes the oxidation of glucose, dissolved oxygen is consumed. This leads to the suppression of photocurrent. The photocathode biosensor has a linear response in the 0.05 to 0.7 mM glucose concentration range and a 1.1 μM limit of detection. [ABSTRACT FROM AUTHOR]

An optical method is described for the quantitation of glucose by using oxygen-deficient α-MoO3-x nanoflakes. It is based on the use of glucose oxidase (GOx) which produces hydrogen peroxide on oxidation of glucose. Hydrogen peroxide then oxidizes the α-MoO3-x nanoflakes, and this results in a visible color change from blue to colorless. The color change can be measured photometrically at 740 nm. The method has a 68 nM detection limit. [ABSTRACT FROM AUTHOR]

The intrinsic peroxidase-like activity of rhodium nanoparticles (RhNPs) and their use as catalytic labels for sensitive colorimetric assays is presented. RhNPs catalyze the oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue reaction product with a maximum absorbance at 652 nm. Kinetic studies show catalysis to follow Michaelis-Menten kinetics and a "ping-pong" mechanism. The calculated kinetic parameters indicate high affinity of RhNPs for both the substrate TMB and H2O2. In fact, they are better than other peroxidase mimicking nanomaterials and even the natural enzyme horseradish peroxidase. On the other hand, RhNPs exhibit no reactivity towards saccharides, thiols, amino acids and ascorbic acid. Based on these findings, a sensitive and selective colorimetric method was worked out for the determination of H2O2 in real samples with a linear response in the 1-100 µM concentration range. By employing glucose oxidase, the glucose assay has a linear range that covers the 5 to 125 µM glucose concentration range. The detection limits are <0.75 µM for both species. The methods were applied to the determination of H2O2 in spiked pharmaceutical formulations, and of glucose in soft drinks and blood plasma. Figures of merit include (a) good accuracy (with errors of <6%), (b) high recoveries (96.5-103.7%), and (c) satisfactory reproducibility (<6.3%). [ABSTRACT FROM AUTHOR]

The authors describe an analytical detection scheme based on the use of multiwalled carbon nanotubes (MWCNTs) that accept and store electrons upon contact with photo-irradiated TiO2 nanoparticles (TiO2-NPs). The Fermi level equilibration with photoirradiated TiO2-NPs has a storage value of 0.35 mM of electrons per 120 mg⋅L-1 of MWCNTs. The stored electrons can be discharged on demand upon addition of electron acceptors to the TiO2-NP/MWCNT composite. These findings are applied to detect the quencher hydrogen peroxide. H2O2 also is produced on enzymatic action of glucose oxidase on glucose, and this enables glucose also to be quantified by using the TiO2-NP/MWCNT fluorescent nanoprobe. The wide scope of the method also is demonstrated by an assay for aflatoxin B1 that is making use of an FAM-labeled aptamer where the FAM fluorophore on the aptamer quenches the emission of the nanoprobe. The following analytical linear ranges and limits of detection are found: H2O2: 0.1-100 µM and 15 nM; glucose: 5-200 µM and 0.5 µM; aflatoxin: 0.1-40 ng⋅mL-1 and 0.02 ng⋅mL-1. The method was applied to the determination of glucose in human serum. [ABSTRACT FROM AUTHOR]

This research describes a nanowire network-based method for detecting the activity of myeloperoxidase (MPO), a biomarker of acute coronary syndromes (ACS). Trimetallic CuPdPt nanowire networks (CuPdPt NWNWs) were prepared by a one-step chemical reduction method. The metallic precursors quickly form nanowire network structures without the need for additional capping agents or surfactants. This process creates a product with a clean surface. The NWNWs were dropped onto a glassy carbon electrode (GCE) to obtain a sensor with good catalytic activity towards the reduction of hydrogen peroxide (H2O2), which was used as an electrochemical probe working at -0.4 V (vs. SCE). It also provided a large surface for further modification. Next, an antibody against MPO was immobilized on the modified GCE via the stable conjunction between Cu, Pt, Pd and amino groups. Upon binding of MPO to the antibody on the GCE, the current response to H2O2 was reduced by 35 μA•cm-2. The immunosensor had a linear response within the 100 fg⋅mL-1 to 50 ng⋅mL-1 MPO concentration range and a 33 fg⋅mL-1 detection limit (at an S/N ratio of 3). The recovery of spiked serum samples ranged from 99.8 to 103.6%. This result suggests that the method can be applied to the quantitation of MPO in human serum samples. [ABSTRACT FROM AUTHOR]

The effect of graphene nanosheets on the glucose sensing performance of CuO powders was investigated. CuO and graphene-modified CuO nanoparticles (NPs) were fabricated by microwave-assisted synthesis and characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The material was placed on a glassy carbon electrode (GCE) which then was characterized by cyclic voltammetry and chronoamperometry with respect to the capability of sensing glucose both at pH 13 and pH 7.4. The results revealed that the modified GCE has a fast and selective linear response to glucose at pH 13 that covers the 0.21 µM to 12 mM concentration range, with a 0.21 µM low detection limit. The presence of graphene nanosheets results in an improved sensitivity which is to 700 µA mM-1 cm-2. In solution of pH 7.4, the respective data are a linear analytical range from 5 to 14mM; a 5 µMLOD and a sensitivity of 37.63 µAmM-1 cm-2 at working potential of -0.05 V (vs. Ag/AgCl) and scan rate of 50 mV s-1. Ascorbic acid, dopamine, uric acid, sucrose, maltose and fructose do not interfere. [ABSTRACT FROM AUTHOR]

A cage-like PbS nanostructure was functionalized with platinum nanoparticles, and the resulting material (PtNP@PbS) was deposited on a glassy carbon electrode in order to study the direct electron transfer to FADH in glucose oxidase (GOx) and further to construct a glucose biosensor. The PtNP@PbS nanostructure and the biosensor were characterized using scanning electron microscopy, UV-vis and electrochemical impedance spectroscopy, and by cyclic voltammetry. Compared to the use of cage-like PbS alone, the PtNP@PbS nanostructure shows much higher electrochemical activity and an enhanced direct electron transfer rate. The GOx loaded onto the nanostructure displays good enzymatic activity and an apparent electron transfer rate constant of 3.0 s. The glucose biosensor is operated best at −0.4 V (vs. SCE) and then exhibits a linear range that extends from 4 μM to 1.1 mM, with a detection limit as low as 1 μM (at an S/N ratio of 3). The biosensor is selective, acceptably repeatable and stable. It was applied to the determination of glucose in human serum samples. [ABSTRACT FROM AUTHOR]

The authors describe a new kind of enzymatic glucose assay. The strategy involves three processes: (a) Generation of HO via glucose oxidase catalyzed oxidation of glucose; (b) production of 2,3-diaminophenazine (DAP) from HO and o-phenylenediamine (OPD) via peroxidase-catalyzed oxidation; and (c) a reduction of the blue fluorescence of SiNPs with emission maxima at 445 nm via an inner filter effect that is caused by DAP which is yellow and has an absorption peak at 450 nm. Fluorescence drops with increasing glucose concentrations in the 0.01 to 7 mM concentration range, and the detection limit is 3.5 μM. The assay was successfully applied to the analysis of glucose in human serum. [ABSTRACT FROM AUTHOR]

The paper describes a colorimetric sandwich enzyme-linked immunosorbent assay (ELISA) for the determination of human IgG. It is based on the use of an Fe(II) coordination complex as a signal amplifier and of mesoporous silica nanoparticles modified with glucose oxidase (GOx) and secondary antibodies (Ab). After formation of the immuno sandwich complex, the quantity of GOx is proportional to the quantity of IgG. On addition of Fe(II) and glucose, GOx catalyzes the oxidation of glucose to produce hydrogen peroxide which oxidizes Fe(II) to Fe(III). After adding a stop solution containing the complexing ligand 1,10-phenanthroline (Phen), un-reacted Fe(II) forms an orange-red complex with Phen which can be detected by plate reader and even seen with bare eyes. This sandwich ELISA has a linear response in the 1 pg.mL to 100 ng.mL human IgG concentration range and a 860 fg.mL detection limit. This is 20 times lower than the commercial ELISA for human IgG. The assay also is selective, stable, highly sensitive and cost-effective. [ABSTRACT FROM AUTHOR]

A composite material consisting of multiwalled carbon nanotubes and palladium containing particles was synthesized and applied to the preparation of bulk-modified screen-printed carbon electrodes (Pd-MWCNT-SPCE) and surface-modified screen-printed carbon electrodes (Pd-MWCNT/SPCE). They were characterized by cyclic voltammetry and hydrodynamic chronoamperometry in solution of pH 7.5. Both electrodes were then modified with glucose oxidase (GOx) by drop-coating a solution of GOx and Nafion® on their surface. Glucose can be determined via enzymatically formed HO. In an alternative approach, gold nanoparticles (5 nm) were incorporated into the biolayer of the electrodes. The resulting electrodes of type GOx/Pd-MWCNT-SPCE and GOx-Au/Pd-MWCNT-SPCE showed acceptable analytical performance at working potentials between −0.20 V and −0.50 V in case of hydrodynamic chronoamperometry. Both electrodes can be operated best at a working potential of −0.40 V vs SCE, with acceptable linearity of the methods in sub mM concentration ranges and with LOQs of 0.14 mM and 0.07 mM for glucose for the GOx/Pd-MWCNT-SPCE and GOx-Au/Pd-MWCNT-SPCE, respectively. Incorporation of gold nanoparticles prolongs the operational lifetime of the electrodes by two weeks. The GOx/Pd-MWCNT-SPCE based method was applied to the determination of glucose in multifloral honey, and the GOx-Au/Pd-MWCNT-SPCE method to the determination of glucose in blood serum. In both cases there was a good agreement with the results obtained by commercially available equipment for determination of glucose. [ABSTRACT FROM AUTHOR]

The authors describe a fluorescence immunoassay for galectin-4, a candidate biomarker for various cancers. Glucose oxidase was encapsulated into a zeolitic imidazolate framework to give a composite (GOx/ZIF-8 composite) that acts as a signal-transduction tag via a biomimetic mineralization process. After modification of the composite with streptavidin, it binds biotinylated antibody against galectin-4. In the immunoassay, the response to galectin-4 results from the enzymatic oxidation of glucose. This reaction produces hydrogen peroxide (HO) that reacts with iron(II) ions to generate hydroxy radical (•OH), which leads to the quenching of the fluorescence of gold nanoclusters (AuNCs). Accordingly, the fluorescence quenching of AuNCs depends on the concentration of target galectin-4. The GOx/ZIF-8 composite has a high loading capacity for GOx at uncompromised enzymatic activity. The fluorescence of AuNCs is sensitively quenched by •OH radicals. Galectin-4 can be detected by this method in concentrations as low as 10 pg·mL. It is expected that this kind of enzyme/MOF composite-based immunoassay has a wide scope in that it may be adapted to other low-abundance proteins and biomarkers. [ABSTRACT FROM AUTHOR]

The authors have prepared a platinum nanoparticle-assembled nanoflake-like SnS nanocomposite of the type PtNP@SnS as a support for immobilization of glucose oxidase (GOx) to obtain an electrochemical glucose biosensor based on direct electron transfer of GOx. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, static water contact angle measurements, and cyclic voltammetry were used to characterize the nanocomposite and the glucose biosensor. The nanocomposite has a large surface-to-volume ratio, excellent hydrophiliciy, and high electrochemical activity. This promotes the direct electron transfer between GOx and the surface of a glassy carbon electrode (GCE). The GOx immobilized on the nanocomposite displays good bioactivity, and the surface coverage of the modified electrode is 4.15 × 10 mol·cm. Under optimum conditions and at a working voltage of −0.4 V vs. SCE, the glucose biosensor exhibits a linear response in the 0.1 to 1.0 mM and 1.0 to 12 mM glucose concentration ranges, with a lower detection limit of 2.5 μM (at an S/N ratio of 3). The biosensor shows excellent selectivity and was successfully applied to the determination of glucose in human serum samples. [ABSTRACT FROM AUTHOR]

The authors describe enzyme based nanobiosensors for continuous monitoring of glucose, with the long term goal of using them as smart diagnostic tattoos. The method is founded on two main features: (1) The fluorescence intensity and decay times of glucose oxidase (GOx) and of GOx labeled with fluorescein (FS) or a ruthenium chelate (Ru) reversibly change during interaction with glucose; (2) The (labeled) enzyme is linked to magnetite magnetic nanoparticles (MNPs) which permits the MNPs to be physically manipulated. It is found that a stable link between MNPs and GOx is only accomplished if the number of amino groups on the GOX is artificially enlarged (to form GOx). Fluorescence decay data are best acquired with 8-nm MNPs where scattering is marginal; The activity of GOx is found not to be affected by immobilization on the MNPs. The various immobilized enzymes (GOx, GOx-FS and GOx-Ru; all on MNPs) differ only slightly in terms of linear response to glucose which ranged from 0.5 mM to at least 3.5 mM. The RSDs are about 5% (for n = 5), the detection limits are at ∼50 μM, and the sensor lifetimes are >1 week. [ABSTRACT FROM AUTHOR]