NFC-enabled photothermal-based microfluidic paper analytical device for glucose detection

This study introduces the development of a photothermal-based microfluidic paper analytical device (PT-µPAD) integrated with near-field communication (NFC) technology and smartphone readout for enzyme-free glucose quantification in human samples. With the properties of gold nanoparticles (AuNPs) both as a nanozyme and as a photothermal substrate, there is no need for costly reagents like enzymes or a readout instrumentation for the selective and sensitive detection of glucose. In PT-µPADs, AuNPs are etched by hydrogen peroxide (H2O2) generated from glucose catalysis. Photothermal detection from the plasmonic heating of these AuNPs when illuminated by a 533nm LED light source is achieved by inserting the PT-µPAD sensor into a portable NFC platform suitable for smartphone readout. Temperature variation is directly proportional to the glucose concentration. After optimization, we acquired a linear range between 5.0 and 20.0 µmol L-1 (R2 = 0.9967) and a limit of detection (LOD) of 25.0 nmol L-1 for glucose. Additionally, while our sensor does not utilize any enzyme, it is remarkably selective to glucose with no effects from interferences. Recovery studies in various human control samples indicated a range of 99.73-102.66% with the highest RSD of 3.53%, making it highly accurate and precise. Moreover, our method is more sensitive than other methods relying on conventional µPADs for glucose sensing. By integrating the potential benefits of microfluidics, nanomaterials as nanozymes, and NFC technology for wireless readout, our sensor demonstrates great promise as an accessible, affordable, and shelf-stable device for glucose quantification. Moreover, this concept can be extended to detect other molecules of interest as a point-of-care (POC) diagnostics device.

Photothermal biosensing integrated with microfluidic paper-based analytical device for sensitive quantification of sarcosine

This article presents the development of a photothermal biosensing integrated with microfluidic paper-based analytical device (PT-μPAD) as a quantitative biosensor method for monitoring sarcosine in human control urine, plasma, and serum samples. The device utilizes gold nanoparticles (AuNPs) as both a peroxidase-like nanozyme and a photothermal substrate to enable sarcosine detection. In our PT-μPAD, hydrogen peroxide (H2O2) is generated through the oxidation of sarcosine by a sarcosine oxidase (SOx) enzyme. Subsequently, the H2O2 flows through the paper microchannels to the detection zone, where it etches the pre-deposited AuNPs, inducing a temperature change upon exposure by a 532 nm laser. The temperature variation is then measured using a portable and inexpensive infrared thermometer. Under optimized conditions, we obtained a linear range between 10.0 and 40.0 nmol L-1 (R2 = 0.9954) and a detection limit (LOD) of 32.0 pmol L-1. These values fall within the clinical range for sarcosine monitoring in prostate cancer diagnostics in humans. Moreover, our approach exhibits high selectivity without interfering effects. Recovery studies in various human control samples demonstrated a range of 99.05-102.11 % with the highest RSD of 2.25 %. The PT-μPAD was further validated for sarcosine determination in human control urine and compared with a commercial ELISA assay, revealing no significant difference between these two methods at a 95 % confidence level. Overall, our proposed sarcosine biosensor is well-suited for prostate cancer monitoring, given its affordability, sensitivity, and user-friendliness, even for unskilled individuals. Moreover, this strategy has promising prospects for broader applications, potentially detecting various biomarkers as a point-of-care (POC) diagnostic tool.

GAA/(Au-Au/IrO2)@Cu(PABA) reactor with cascade catalytic activity for α-glucosidase inhibitor screening

BACKGROUND

In vitro screening strategies based on the inhibition of α-glucosidase (GAA) activity have been widely used for the discovery of potential antidiabetic drugs, but they still face some challenges, such as poor enzyme stability, non-reusability and narrow range of applicability. To overcome these limitations, an in vitro screening method based on GAA@GOx@Cu-MOF reactor was developed in our previous study. However, the method was still not satisfactory enough in terms of construction cost, pH stability, organic solvent resistance and reusability. Thence, there is still a great need for the development of in vitro screening methods with lower cost and wider applicability.

RESULTS

A colorimetric sensing strategy based on GAA/(Au-Au/IrO2)@Cu(PABA) cascade catalytic reactor, which constructed through simultaneous encapsulating Au-Au/IrO2 nanozyme with glucose oxidase-mimicking and peroxidase-mimicking activities and GAA in Cu(PABA) carrier with peroxidase-mimicking activity, was innovatively developed for in vitro screening of GAA inhibitors in this work. It was found that the reactor not only exhibited excellent thermal stability, pH stability, organic solvent resistance, room temperature storage stability, and reusability, but also possessed cascade catalytic performance, with approximately 12.36-fold increased catalytic activity compared to the free system (GAA + Au-Au/IrO2). Moreover, the in vitro GAA inhibitors screening method based on this reactor demonstrated considerable anti-interference performance and detection sensitivity, with a detection limit of 4.79 nM for acarbose. Meanwhile, the method owned good reliability and accuracy, and has been successfully applied to the in vitro screening of oleanolic acid derivatives as potential GAA inhibitors.

SIGNIFICANCE

This method not only more effectively solved the shortcomings of poor stability, narrow scope of application, and non-reusability of natural enzymes in the classical method compared with our previous work, but also broaden the application scope of Au-Au/IrO2 nanozyme with glucose oxidase and peroxidase mimicking activities, and Cu(PABA) carrier with peroxidase mimicking activity, which was expected to be a new generation candidate method for GAA inhibitor screening.

The Nanozyme Revolution: Enhancing the Performance of Medical Biosensing Platforms

Nanozymes represent a class of nanosized materials that exhibit innate catalytic properties similar to biological enzymes. The unique features of these materials have positioned them as promising candidates for applications in clinical sensing devices, specifically those employed at the point-of-care. They notably have found use as a means to amplify signals in nanosensor-based platforms and thereby improve sensor detection limits. Recent developments in the understanding of the fundamental chemistries underpinning these materials have enabled the development of highly effective nanozymes capable of sensing clinically relevant biomarkers at detection limits that compete with "gold-standard" techniques. However, there remain considerable hurdles that need to be overcome before these nanozyme-based sensors can be utilized in a platform ready for clinical use. An overview of the current understandings of nanozymes for disease diagnostics and biosensing applications and the unmet challenges that must be considered prior to their translation in clinical diagnostic tests is provided.

Orientation-Controllable Enzyme Cascade on Electrode for Bioelectrocatalytic Chain Reaction

The accomplishment of concurrent interenzyme chain reaction and direct electric communication in a multienzyme-electrode is challenging since the required condition of multienzymatic binding conformation is quite complex. In this study, an enzyme cascade-induced bioelectrocatalytic system has been constructed using solid binding peptide (SBP) as a molecular binder that coimmobilizes the invertase (INV) and flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase gamma-alpha complex (GDHγα) cascade system on a single electrode surface. The SBP-fused enzyme cascade was strategically designed to induce diverse relative orientations of coupling enzymes while enabling efficient direct electron transfer (DET) at the FAD cofactor of GDHγα and the electrode interface. The interenzyme relative orientation was found to determine the intermediate delivery route and affect overall chain reaction efficiency. Moreover, interfacial DET between the fusion GDHγα and the electrode was altered by the binding conformation of the coimmobilized enzyme and fusion INVs. Collectively, this work emphasizes the importance of interenzyme orientation when incorporating enzymatic cascade in an electrocatalytic system and demonstrates the efficacy of SBP fusion technology as a generic tool for developing cascade-induced direct bioelectrocatalytic systems. The proposed approach is applicable to enzyme cascade-based bioelectronics such as biofuel cells, biosensors, and bioeletrosynthetic systems utilizing or producing complex biomolecules.

Nanomaterials with Glucose Oxidase-Mimicking Activity for Biomedical Applications

Glucose oxidase (GOD) is an oxidoreductase that catalyzes the aerobic oxidation of glucose into hydrogen peroxide (H₂O₂) and gluconic acid, which has been widely used in industrial raw materials production, biosensors and cancer treatment. However, natural GOD bears intrinsic disadvantages, such as poor stability and a complex purification process, which undoubtedly restricts its biomedical applications. Fortunately, several artificial nanomaterials have been recently discovered with a GOD-like activity and their catalytic efficiency toward glucose oxidation can be finely optimized for diverse biomedical applications in biosensing and disease treatments. In view of the notable progress of GOD-mimicking nanozymes, this review systematically summarizes the representative GOD-mimicking nanomaterials for the first time and depicts their proposed catalytic mechanisms. We then introduce the efficient modulation strategy to improve the catalytic activity of existing GOD-mimicking nanomaterials. Finally, the potential biomedical applications in glucose detection, DNA bioanalysis and cancer treatment are highlighted. We believe that the development of nanomaterials with a GOD-like activity will expand the application range of GOD-based systems and lead to new opportunities of GOD-mimicking nanomaterials for various biomedical applications.

Nanomaterials integrated with microfluidic paper-based analytical devices for enzyme-free glucose quantification

In this study, nanomaterials capable of enzyme-free glucose quantification and colorimetric readout are integrated into a microfluidic paper-based analytical devices (μPADs). Gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) were utilized as a peroxidase-like nanozyme and a colorimetric probe to achieve glucose monitoring. In this developed device, glucose is oxidized by AuNPs to generate hydrogen peroxide (H₂O₂), which flows in the paper microchannels toward detection zones. H₂O₂ then etches the immobilized AgNPs to induce a color change. The intensity of color change is easily monitored using a smartphone application. Following method optimization, we obtained a linear range from 0.50 to 10.0 mmol L^-1 (R² = 0.9921) and a detection limit (LOD) of 340.0 μmol L^-1. This falls in the clinically relevant range for glucose monitoring and diabetes diagnosis in humans. In addition, the total analysis time is just 20 min, which is significantly less than the same experiment performed in the solution phase. Also, our method is markedly selective; other substrates do not interfere. The recovery test in human control samples was in the range of 98.47-102.34% and the highest relative standard deviation (RSD) was 3.58%. The enzyme-free approach for glucose sensing is highly desirable for diabetes diagnosis as it replaces the more expensive enzyme with cheaper nanomaterials. Furthermore, since nanomaterials are more environmentally stable compared to enzymes, it has the potential for widespread deployment as point-of-care diagnostics (POC) in resource-limited settings.

Machine Learning-Assisted Nanoenzyme/Bioenzyme Dual-Coupled Array for Rapid Detection of Amyloids

Array-based sensing methods offer significant advantages in the simultaneous detection of multiple amyloid biomarkers and thus have great potential for diagnosing early-stage Alzheimer's disease. Yet, detecting low concentrations of amyloids remains exceptionally challenging. Here, we have developed a fluorescent sensor array based on the dual coupling of a nanoenzyme (AuNPs) and bioenzyme (horseradish peroxidase) to detect amyloids. Various ss-DNAs were bound to the nanoenzyme for regulating enzymatic activity and recognizing amyloids. A simplified sensor array was generated from a screening model via machine learning algorithms and achieved signal amplification through a two-step enzymatic reaction. As a result, our sensing system could discriminate the aggregation species and aggregation kinetics at 200 nM with 100% accuracy. Moreover, AD model mice and healthy mice were distinguished with 100% accuracy through the sensor array, providing a powerful sensing platform for diagnosing AD.

Synthetic Protocell as Efficient Bioreactor: Enzymatic Superactivity and Ultrasensitive Glucose Sensing in Urine

It is believed that membraneless cellular condensates play a critical role in accelerating various slow and thermodynamically unfavorable biochemical processes. However, the exact mechanisms behind the enhanced activity within biocondensates remain poorly understood. Here, we report the fabrication of a high-performance integrated cascade bioplatform based on synthetic droplets for ultrasensitive glucose sensing. Using a horseradish peroxidase (HRP) and glucose oxidase (GOx) cascade pair, we report an unprecedented enhancement in the catalytic activity of HRP inside the synthetic membraneless droplet. Liquidlike membraneless droplets have been prepared via multivalent electrostatic interactions between adenosine triphosphate (ATP) and poly(diallyldimethylammonium chloride) (PDADMAC) in an aqueous medium. Compartmentalized enzymes (GOx/HRP@Droplet) exhibit high encapsulation efficiency, low leakage, prolong retention of activity, and exceptional stability toward protease digestion. Using an HRP@Droplet composite, we have shown that the enzymatic reaction within the droplet follows the classical Michaelis-Menten model. Our findings reveal remarkable enhancement in the catalytic activity of up to 100- and 51-fold for HRP@Droplet and GOx/HRP@Droplet, respectively. These enhanced activities have been explained on the basis of increased local concentrations of enzymes and substrates, along with altered conformations of sequestered enzymes. Furthermore, we have utilized highly efficient and recyclable GOx/HRP@Droplet composite to demonstrate ultrasensitive glucose sensing with a limit of detection of 228 nM. Finally, the composite platform has been exploited to detect glucose in spiked urine samples in solution and filter paper. Our present study illustrates the unprecedented activity of the compartmentalized enzymes and paves the way for next-generation composite bioreactors for a wide range of applications.

Au-Fe3O4 heterodimer multifunctional nanoparticles-based platform for ultrasensitive naked-eye detection of Salmonella typhimurium

In this work, we developed an ultrasensitive colorimetry for Salmonella typhimurium detection with multifunctional Au-Fe₃O₄ dumbbell-like nanoparticles (DBNPs) which possessed easy bio-modifiability, excellent LSPR characteristics, superparamagnetic properties and super peroxidase-like activity. In the detection, the anti-S. typhimurium antibody modified DBNPs (IDBNPs) bound with S. typhimurium and aggregated on their surfaces in a large number, which showed much quicker magnetic response than free IDBNPs. By controlling appropriate separation conditions, IDBNPs@S. typhimurium composites were captured, while free IDBNPs were remained in the supernatant. Therefore, by detecting the absorbance of the supernatant, quantitative detection was achieved from 10 to 1000 CFU/mL. Moreover, utilizing the peroxidase-like activity of IDBNPs, we further realized semi-quantitative naked-eye detection. By adding ABTS into the above supernatant, which was oxidized to green chelate (OxABTS), colorimetric signal was amplified significantly, and meanwhile, the green chelates and the wine-red IDBNPs engendered mixed color, enhancing the range of color gradation and greatly improving the visual resolution. Finally, a detection limit (10 CFU/mL) comparable with that of above spectrum measurement was achieved. Besides, our method exhibited efficient capture capability (nearly 100% even for rare S. typhimurium), and had good stability and specificity, and acceptable anti-interference ability in fetal bovine serum and milk samples.

Targeting Acne Bacteria and Wound Healing In Vitro Using Plectranthus aliciae, Rosmarinic Acid, and Tetracycline Gold Nanoparticles

Gold nanoparticles from plant extracts and their bioactive compounds to treat various maladies have become an area of interest to many researchers. Acne vulgaris is an inflammatory disease of the pilosebaceous unit caused by the opportunistic bacteria Cutibacterium acnes and Staphylococcus epidermis. These bacteria are not only associated with inflammatory acne but also with prosthetic-implant-associated infections and wounds. Studies have hypothesised that these bacteria have a mutualistic relationship and act as a multispecies system. It is believed that these bacteria form a multispecies biofilm under various conditions and that these biofilms contribute to increased antibiotic resistance compared to single-species biofilms. This study aimed to investigate the antibacterial and wound healing potential of synthesised gold nanoparticles (AuNP_s) from an endemic South African plant, Plectranthus aliciae (AuNP_PAE), its major compound rosmarinic acid (AuNP_RA) and a widely used antibiotic, tetracycline (AuNP_TET). Synthesised gold nanoparticles were successfully formed and characterised using ultraviolet–visible spectroscopy (UV–vis), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), zeta potential (ζ-potential), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED), and they were investigated for stability under various biological conditions. Stable nanoparticles were formed with ζ-potentials of −18.07 ± 0.95 mV (AuNP_PAE), −21.5 ± 2.66 mV (AuNP_RA), and −39.83 ± 1.6 mV (AuNP_TET). The average diameter of the AuNP_s was 71.26 ± 0.44 nm, 29.88 ± 3.30 nm, and 132.6 ± 99.5 nm for AuNP_PAE, AuNP_RA, and AuNP_TET, respectively. In vitro, biological studies confirmed that although no antibacterial activity or biofilm inhibition was observed for the nanoparticles tested on the multispecies C. acnes and S. epidermis systems, these samples had potential wound closure activity. Gold nanoparticles formed with rosmarinic acid significantly increased wound closure by 21.4% at 25% v/v (≈29.2 µg/mL) compared to the negative cell control and the rosmarinic acid compound at the highest concentration tested of 500 µg/mL. This study concluded that green synthesised gold nanoparticles of rosmarinic acid could potentially be used for treating wounds.

The valine-based N-doped carbon dots with high peroxidase-like activity

Developing artificial nanoparticles with peroxidase-like activity are being attracted great interests because their catalytic activity are not easy to lose under harsh conditions compared with natural enzymes. In this work, the N-doped carbon dots (CDs) were prepared, and it was found that the N-doped CDs showed high peroxidase-like catalytic activity towards the reaction system of hydrogen peroxide - 3, 3', 5, 5'-tetramethylbenzidine (TMB). The catalytic mechanism of the N-doped CDs was explored by usingelectron spin resonance (ESR) spectra, cyclic voltammetry (CV) method and simulation of density functional theory calculation. This work can offer a new feasible method for synthesizing N-doped CQDs used as artificial peroxidases in biological and environment applications.

Surface Functionalization of Enzyme-Coronated Gold Nanoparticles with an Erythrocyte Membrane for Highly Selective Glucose Assays

Colorimetric glucose sensors using enzyme-coronated gold nanoparticles have been developed for high-throughput assays to monitor the blood glucose levels of diabetic patients. Although those sensors have shown sensitivity and wide linear detection ranges, they suffer from poor selectivity and stability in detecting blood glucose, which has limited their practical use. To address this limitation, herein, we functionalized glucose-oxidase-coronated gold nanoparticles with an erythrocyte membrane (EM-GOx-GNPs). Because the erythrocyte membrane (EM) selectively facilitates the permeation of glucose via glucose transporter-1 (GLUT1), the functionalization of GOx-GNPs with EM improved the stability, selectivity (3.3- to 15.8-fold higher), and limit of detection (LOD). Both membrane proteins, GLUT1 and aquaporin-1 (AQP1), on EM were shown to be key components for selective glucose detection by treatment with their inhibitors. Moreover, we demonstrated the stability of EM-GOx-GNPs in high-antioxidant-concentration conditions, under long-term storage (∼4 weeks) and a freeze-thaw cycle. Selectivity of the EM-GOx-GNPs against other saccharides was increased, which improved the LOD in phosphate-buffered saline and human serum. Our results indicated that the functionalization of colorimetric glucose sensors with EM is beneficial for improving selectivity and stability, which may make them candidates for use in a practical glucose sensor.

Application of Au or Ag nanomaterials for colorimetric detection of glucose

In recent years, Au and Ag nanomaterials have been widely used in the determination of glucose owing to their specific properties such as large specific surface area, high extinction coefficient, strong localized surface plasmon resonance effect and enzyme-mimicking activity. Compared with other methods, colorimetric determination of glucose with Au or Ag nanomaterials features the advantages of simple operation, low cost and easy observation. In this review, several typical synthesis methods of Au and Ag nanomaterials are introduced. Strategies for the colorimetric determination of glucose by Au or Ag nanomaterials are elaborated. The challenges and prospects of the application of Au or Ag nanomaterials for colorimetric detection of glucose are also discussed.

Au-Au/IrO2@Cu(PABA) Reactor with Tandem Enzyme-Mimicking Catalytic Activity for Organic Dye Degradation and Antibacterial Application

Herein, a Au-Au/IrO₂ nanocomposite with tandem enzyme-mimicking activity was innovatively synthesized, which can show outstanding glucose oxidase (GOx)-like activity and peroxidase-like activity simultaneously under neutral conditions. Moreover, a Au-Au/IrO₂@Cu(PABA) reactor was prepared via encapsulation of the Au-Au/IrO₂ nanocomposite in a Cu(PABA) metal organic framework. The reactor not only exhibits excellent organic solvent stability, acid resistance, and reusability but also displays better cascade reaction catalytic efficiency (k_cat/K_m = 148.86 min^-1 mM^-1) than the natural free enzyme system (GOx/HRP) (k_cat/K_m = 98.20 min^-1 mM^-1) and Au-Au/IrO₂ nanocomposite (k_cat/K_m = 135.24 min^-1 mM^-1). In addition, it is found that the reactor can catalyze glucose or dissolved oxygen to produce active oxygen species (ROS) including HO, ₁O², and O₂^-· through its enzyme-mimicking activity. Finally, the novel reactor was successfully used in organic dye degradation and antibacterial application. The results show that it can effectively degrade methyl orange, methylene blue, and rhodamine B, which all can reach a degradation rate of nearly 100% after interacting with Au-Au/IrO₂@Cu (PABA) for 3.5 h. Furthermore, the reactor also exhibits excellent antibacterial activity, so as to achieve a complete bactericidal effect to Staphylococcus aureus and Escherichia coli at a concentration of 12.5 μg mL^-1.

Tailoring cysteine detection in colorimetric techniques using Co/Fe-functionalized mesoporous silica nanoparticles

Over the past decade, there has been a dramatic increase in the number of studies focused on sensors for cysteine (Cys) as a crucial factor in physiological function and disease diagnosis. Among those sensors, nanomaterial-based peroxidase mimetics have received particular attention from researchers. This study introduces a new series of mesoporous silica nanoparticles (MSNs) incorporated with iron and cobalt (Co/Fe-MSN) with a molar ratio of Si/Fe = 10 and cobalt species at 1, 3, and 5 wt% that have great potential in the sensing application. These nanomaterial characterization was investigated by FTIR spectroscopy, SEM, TEM, XRD, and nitrogen adsorption-desorption. The peroxidase activity of these nanomaterials was studied through kinetic analysis. The findings revealed that Co/Fe-MSN (1%) showed higher peroxidatic activity than the others towards the common chromogenic substrate 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) diammonium salt. Based on the enzymatic activity of Co/Fe-MSN (1%), a colorimetric sensing platform was designed to detect H2O2 and Cys. The limit of detection (LOD) for H2O2 and Cys was determined to be 1.1 μM and 0.89 nM, respectively. The results indicated that the proposed enzyme mimic exhibited excellent potential as a sensor in medical diagnostics and biological systems.

Facile Synthesis of Iron Oxide Nanozymes for Synergistically Colorimetric and Magnetic Resonance Detection Strategy

Iron oxide nanomaterials with mimic enzymes activity have been paid more attention in the clinical diagnosis field. The modified surface molecules would influence the catalytic activity of nanozyme, which is worth studying. Furthermore, the traditional detection strategy is based on colorimetric change of substrates, however, the optical signal is easy to be interfered in complex biological applications. In our research, an efficient and facile preparation strategy was developed to obtain functional artificial nanozymes. Herein, three kinds of surfactants, including citrate acid, poly(ethylene glycol) bis (carboxymethyl) ether and tannic acid have been applied to modify these nanomaterials that showed uniform size, high soluble dispersity and stability. Furthermore, these nanozymes exhibited different peroxidase-like activity to catalyze the hydrogen peroxide and 3,3′,5,5′-tetramethylbenzidine. More importantly, magnetic relaxation effect of iron oxide nanozymes was found to be changed during the catalytic reaction. In addition, the relationship between the magnetic signal of nanozymes and the substrate concentration showed a good linear dependence. Combined with the natural enzymes, the magnetic detection of iron oxide nanozymes also exhibited excellent substrate specificity. On these bases, a dual-function specific assay was constructed and further used for glucose detection. In conclusion, this study demonstrated an efficient iron oxide nanozymes preparation method and constructed a new synergistically colorimetric-magnetic diagnosis strategy.

Tungsten disulfide nanosheets-based colorimetric assay for glucose sensing

We have developed a glucose oxidase (GOx)-mediated strategy for glucose detection, which is based on the intrinsic peroxidase-like activity of WS₂ as a catalyst for the 3,3',5,5'-tetramethylbenzidine‑hydrogen peroxide (TMB-H₂O₂) reaction. The colorimetric assay involves two parts: generation of H₂O₂ from the oxidation of glucose catalyzed by GOx, and WS₂ nanosheets that catalyze the reaction between TMB and H₂O₂. In this colorimetric assay, the enhancement of colorimetric signals depends directly on the increased H₂O₂ concentration, which, in turn, relies on the glucose concentration. The results show that the concentrations of the glucose were directly proportional to absorbance of the TMB solutions over a range of 1 nM-500 μM with a limit of detection of 0.1445 nM. In addition, this new colorimetric assay has been utilized for glucose detection in human serum with a satisfactory result.

Gold Nanoclusters, Gold Nanoparticles, and Analytical Techniques for Their Characterization

Many reliable and reproducible methods exist for manufacturing gold nanoparticles with the desired and specific compositions, structures, arrangements, and physicochemical properties. In this report, we review the key principles guiding the formation and growth of nanoclusters, their evolution into nanoparticles, and the role and contribution of coatings. We describe a range of imaging methods for characterization of nanoparticles at atomic resolution and a range of spectroscopy methods for structural and physicochemical characterization of such nanoparticles. This chapter concludes with a short review of the emergent applications of nanoparticles in biosciences.

DNA-scaffold copper nanoclusters integrated into a cerium(III)-triggered Fenton-like reaction for the fluorometric and colorimetric enzymatic determination of glucose

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. Graphical abstractSchematic representation of a fluorometric and colorimetric dual-readout strategy for the sensitive determination of hydrogen peroxide and glucose. The assay has been designed by integrating copper nanoclusters into a Ce(III)-triggered Fenton-like reaction.

Nanozymes: From New Concepts, Mechanisms, and Standards to Applications

Nanozymes are nanomaterials with intrinsic enzyme-like characteristics that have been booming over the past decade because of their capability to address the limitations of natural enzymes such as low stability, high cost, and difficult storage. Along with the rapid development and ever-deepening understanding of nanoscience and nanotechnology, nanozymes hold promise to serve as direct surrogates of traditional enzymes by mimicking and further engineering the active centers of natural enzymes. In 2007, we reported the first evidence that Fe₃O₄ nanoparticles (NPs) have intrinsic peroxidase-mimicking activity, and since that time, hundreds of nanomaterials have been found to mimic the catalytic activity of peroxidase, oxidase, catalase, haloperoxidase, glutathione peroxidase, uricase, methane monooxygenase, hydrolase, and superoxide dismutase. Uniquely, a broad variety of nanomaterials have been reported to simultaneously exhibit dual- or multienzyme mimetic activity. For example, Fe₃O₄ NPs show pH-dependent peroxidase-like and catalase-like activities; Prussian blue NPs simultaneously possess peroxidase-, catalase-, and superoxide dismutase-like activity; and Mn₃O₄ NPs mimic all three cellular antioxidant enzymes including superoxide dismutase, catalase, and glutathione peroxidase. Taking advantage of the physiochemical properties of nanomaterials, nanozymes have shown a broad range of applications from in vitro detection to replacing specific enzymes in living systems. With the emergence of the new concept of "nanozymology", nanozymes have now become an emerging new field connecting nanotechnology and biology. Since the landmark paper on nanozymes was published in 2007, we have extensively explored their catalytic mechanism, established the corresponding standards to quantitatively determine their catalytic activities, and opened up a broad range of applications from biological detection and environmental monitoring to disease diagnosis and biomedicine development. Here we mainly focus on our progress in the systematic design and construction of functionally specific nanozymes, the standardization of nanozyme research, and the exploration of their applications for replacing natural enzymes in living systems. We also show that, by combining the unique physicochemical properties and enzyme-like catalytic activities, nanozymes can offer a variety of multifunctional platforms with a broad of applications from in vitro detection to in vivo monitoring and therapy. For instance, targeting antibody-conjugated ferromagnetic nanozymes simultaneously provide three functions: target capture, magnetic separation, and nanozyme color development for target detection. We finally will address the prospect of nanozyme research to become "nanozymology". We expect that nanozymes with unique physicochemical properties and intrinsic enzyme-mimicking catalytic properties will attract broad interest in both fundamental research and practical applications and offer new opportunities for traditional enzymology.

Functionalized gold nanoparticles for sample preparation: A review

Sample preparation is a crucial step for the reliable and accurate analysis of both small molecule and biopolymers which often involves processes such as isolation, pre-concentration, removal of interferences (purification), and pre-processing (e.g., enzymatic digestion) of targets from a complex matrix. Gold nanoparticle (GNP)-assisted sample preparation and pre-concentration has been extensively applied in many analytical procedures in recent years due to the favorable and unique properties of GNPs such as size-controlled synthesis, large surface-to-volume ratio, surface inertness, straightforward surface modification, easy separation requiring minimal manipulation of samples. This review article primarily focuses on applications of GNPs in sample preparation, in particular for bioaffinity capture and biocatalysis. In addition, their most common synthesis, surface modification and characterization methods are briefly summarized. Proper surface modification for GNPs designed in accordance to their target application directly influence their functionalities, e.g., extraction efficiencies, and catalytic efficiencies. Characterization of GNPs after synthesis and modification is worthwhile for monitoring and controlling the fabrication process to ensure proper quality and functionality. Parameters such as morphology, colloidal stability, and physical/chemical properties can be assessed by methods such as surface plasmon resonance, dynamic light scattering, ζ-potential determinations, transmission electron microscopy, Taylor dispersion analysis, and resonant mass measurement, among others. The accurate determination of the surface coverage appears to be also mandatory for the quality control of functionality of the nanoparticles. Some promising applications of (functionalized) GNPs for bioanalysis and sample preparation are described herein.

Peroxidase-Like Activity of Smart Nanomaterials and Their Advanced Application in Colorimetric Glucose Biosensors

Diabetes is a dominating health issue with 425 million people suffering from the disease worldwide and 4 million deaths each year. To avoid further complications, the diabetic patient blood glucose level should be strictly monitored despite there being no cure for diabetes. Colorimetric biosensing has attracted significant attention because of its low cost, simplicity, and practicality. Recently, some nanomaterials have been found that possess unexpected peroxidase-like activity, and great advances have been made in fabricating colorimetric glucose biosensors based on the peroxidase-like activity of these nanomaterials using glucose oxidase. Compared with natural horseradish peroxidase, the nanomaterials exhibit flexibility in structure design and composition, and have easy separation and storage, high stability, simple preparation, and tunable catalytic activity. To highlight the significant progress in the field of nanomaterial-based peroxidase-like activity, this work discusses the various smart nanomaterials that mimic horseradish peroxidase and its mechanism and development history, and the applications in colorimetric glucose biosensors. Different approaches for tunable peroxidase-like activity of nanomaterials are summarized, such as size, morphology, and shape; surface modification and coating; and metal doping and alloy. Finally, the conclusion and challenges facing peroxidase-like activity of nanomaterials and future directions are discussed.

Glucose Oxidase-Instructed Fluorescence Amplification Strategy for Intracellular Glucose Detection

The accurate detection of glucose at cellular level remains a big challenge. In this study, a signal amplification strategy mediated by silver nanocube (AgNC), glucose oxidase (GOx), and silver ion fluorescence probe (denoted as AgNC-GOx/Ag⁺-FP) is proposed for amplified intracellular glucose detection. The AgNC is oxidized into Ag⁺ by H₂O₂ generated from GOx-catalyzed glucose oxidation reaction, and Ag⁺ remarkably enhances the red fluorescence of Ag⁺-FP. Our results show that AgNC-GOx/Ag⁺-FP is highly sensitive and specific to glucose and H₂O₂. Afterward, the feasibility of using AgNC-GOx/Ag⁺-FP to detect intracellular glucose is verified in five different cell lines. In summary, a sensitive and specific fluorescence amplification strategy has been developed for intracellular glucose detection.

Enzyme-triggeredin situformation of Ag nanoparticles with oxidase-mimicking activity for amplified detection of alkaline phosphatase activity

ALP-triggeredin situformation of Ag NPs with high oxidase-mimicking activity for colorimetric detection of alkaline phosphatase activity.

A photoelectrochemical glucose sensor based on gold nanoparticles as a mimic enzyme of glucose oxidase

This work reports the first construction of the ternary layers of ITO/PbS/SiO₂/AuNPs nanostructure for development of photoelectrochemical (PEC) glucose sensor. Herein, the thioglycolic acid-capped PbS quantum dots was employed as a PEC active probe, which is very sensitive to oxygen. The small gold nanoparticles (AuNPs) were act as nanozyme (mimic enzyme of glucose oxidase) to catalytically oxidize glucose in the presence of oxygen, meanwhile consumed oxygen and then resulted in the decrease of cathodic photocurrent. The insertion layer of SiO₂ nanoparticles between PbS and AuNPs could reduce efficiently the base current due to its low electroconductivity, which improved the detection limit. The proposed PEC sensor exhibited high sensitivity and gold selectivity towards glucose. The linear response of glucose concentrations ranged from 1.0 μM to 1.0 mM with detection limit of 0.46 μM (S/N = 3). The results suggest the potential of design and development of numerous nanozyme-based PEC biosensors with the advantage of the simplicity, stability, and efficiency.

This work reports the first construction of the ternary layers of ITO/PbS/SiO₂/AuNPs nanostructure for development of photoelectrochemical (PEC) glucose sensor.

"Non-Naked" Gold with Glucose Oxidase-Like Activity: A Nanozyme for Tandem Catalysis

It has been widely reported that "naked" gold nanoparticles (Au NPs) without protectors have glucose oxidase (GOx)-like activity, and the use of protectors can inhibit the GOx-like activity. Here, "non-naked" Au NPs with GOx-like activity are synthesized by using protein as protector. Although "naked" Au NPs have peroxidase-like activity and GOx-like activity, the optimal pH ranges of the both activities are obviously different. Fortunately, as-synthesized "non-naked" Au NPs show the dual enzyme-like activities at the same pH. So, "non-naked" Au NPs can be described as "tandem nanozyme." As another bonus, the participation of protein protector can stabilize the GOx-like activity and make Au NPs modifiable. Even though Au NPs are connected with graphene oxide (GO), the GOx-like activity is still not changed. Further, Au NPs-GO nanocomposites are applied on the one-pot nonenzymatic glucose colorimetric detection. The "non-naked" gold not only broadens the species of tandem nanozymes, but also facilitates the functionalization of nanozymes, which is promising for immunoassay, biosensor, and medical treatment.

A novel inhibition based biosensor using urease nanoconjugate entrapped biocomposite membrane for potentiometric glyphosate detection

A potentiometric biosensor based on agarose-guar gum (A-G) entrapped bio-nanoconjugate of urease with gold nanoparticles (AUNps), has been reported for the first time for glyphosate detection. The biosensor is based on inhibition of urease activity by glyphosate, which was measured by direct potentiometry using ammonium ion selective electrode covered with A-G-urease nanoconjugate membrane. TEM and FTIR analysis revealed nanoconjugate formation and its immobilization in A-G matrix respectively. The composite biopolymer employed for immobilization yields thin, transparent, flexible membrane having superior mechanical strength and stability. It retains the maximum activity (92%) of urease with negligible leaching. The conjugation of urease with AUNps allows improvement in response characteristics for potentiometric measurement. The biosensor shows a linear response in the glyphosate concentration range from 0.5ppm-50ppm, with limit of detection at 0.5ppm, which covers maximum residual limit set by WHO for drinking water. The inhibition of catalytic activity of urease nanoconjugate by gyphosate was confirmed by FTIR analysis. The response of fabricated biosensor is selective towards glyphosate as against various other pesticides. The biosensor exhibits good performance in terms of reproducibility and prolonged storage stability of 180days. Thus, the present biosensor provides an alternative method for simple, selective and cost effective detection of glyphosate based on urease inhibition.

MoS2–Au@Pt nanohybrids as a sensing platform for electrochemical nonenzymatic glucose detection

A MoS₂–Au@Pt nanohybrid was used as a sensing platform for electrochemical nonenzymatic glucose detection with high sensitivity, selectivity and stability.

Outer membrane vesicles extracted from Neisseria meningitidis serogroup X for prevention of meningococcal disease in Africa

Meningococcal disease is caused mainly by serogroups A, B, C, Y, W of N. meningitidis. However, numerous cases of meningitis caused by serogroup X N. meningitidis (MenX) have recently been reported in several African countries. Currently, there are no licensed vaccines against this pathogen and most of the MenX cases have been caused by meningococci from clonal complex (c.c) 181. Detergent extracted meningococcal outer membrane vesicle (dOMV) vaccines have previously shown to be safe and effective against epidemics of serogroup B meningococcal disease in all age groups. The aim of this work is therefore to obtain, characterize and evaluate the vaccine potential of dOMVs derived from a MenX strain (OMVx). Three experimental lots of OMVx were prepared by deoxycholate extraction from the MenX strain BF 2/97. Size and morphology of the vesicles was determined by Dynamic Light Scattering and electron microscopy, whereas the antigenic composition was characterized by gel electrophoresis and immunoblotting. OMVx were thereafter adsorbed to aluminium hydroxide (OMVx/AL) and two doses of OMVx were administered s.c. to groups of Balb/c mice three weeks apart. The immunogenicity and functional antibody activities in sera were evaluated by ELISA (anti-OMVx specific IgG responses) and serum bactericidal activity (SBA) assay. The size range of OMVx was shown to be between 90 and 120nm, whereas some of the antigens detected were the outer membrane proteins PorA, OpcA and RmpM. The OMVx/AL elicited high anti-OMVx antibody responses with bactericidal activity and no bactericidal activity was observed in the control group of no immunised mice. The results demonstrate that OMVx are immunogenic and could form part of a future vaccine to prevent the majority of meningococcal disease in the African meningitis belt.

Colorimetric detection of glucose based on gold nanoparticles coupled with silver nanoparticles

We have coupled gold nanoparticles (AuNPs) with silver nanoparticles (AgNPs) to assemble a plasmonic sensing platform for colorimetric detection of glucose. In this system, small AuNPs (~4nm) can act as glucose oxidase (GOD) mimic enzyme to catalytically oxidize glucose in the presence of oxygen, producing hydrogen peroxide, which dissolves AgNPs to lead the color changes. Glucose can be detected not only by naked eyes (from yellow to red) but also by spectrophotometer in the concentration range of 5-70μM, with detection limit of 3μM. More importantly, we found that l-cysteine added in the system can markedly improve the selectivity for the detection of glucose. The proposed method was used to application for the detection of glucose in human serum with satisfactory results. This system is simple and low cost without using any enzymes and organic chromogenic agents.

Visual detection of glucose using triangular silver nanoplates and gold nanoparticles

A sensitive spectrophotometric detection of glucose based on triangular silver nanoplates (Ag TNPs) coupled with gold nanoparticles (Au NPs) was carried out.

Ag@Au nanoprism-metal organic framework-based paper for extending the glucose sensing range in human serum and urine

Ag@Au nanoprism-MOFs-based paper for enhancing the glucose sensing range in human serum and in urine.

Approach To Deliver Two Antioxidant Enzymes with Mesoporous Silica Nanoparticles into Cells

Reactive oxygen species (ROS) are important factors in many clinical diseases. However, direct delivery of antioxidant enzymes into cells is difficult due to poor cell uptake. A proper design of delivery of enzymes by nanoparticles is very desirable for therapeutic purposes. To overcome the cell barrier problem, a designed mesoporous silica nanoparticle (MSN) system with attached TAT-fusion denatured enzyme for enhancing cell membrane penetration has been developed. Simultaneous delivery of two up-downstream antioxidant enzymes, superoxide dismutase (SOD) and glutathione peroxidase(GPx), reveals synergistic efficiency of ROS scavenging, compared to single antioxidant enzyme delivery. TAT peptide conjugation provided a facile nonendocytosis cell uptake and escape from endosome while moving and aggregating along the cytoskeleton that would allow them to be close to each other at the same time, resulting in the cellular antioxidation cascade reaction. The two-enzyme delivery shows a significant synergistic effect for protecting cells against ROS-induced cell damage and cell cycle arrest. The nanocarrier strategy for enzyme delivery demonstrates that intracellular anti-ROS cascade reactions could be regulated by multifunctional MSNs carrying image fluorophore and relevant antioxidation enzymes.

An enzyme–copper nanoparticle hybrid catalyst prepared from disassembly of an enzyme–inorganic nanocrystal three-dimensional nanostructure

Enzyme–copper nanoparticle hybrid catalysts were prepared with highly retained enzymatic and Cu-catalytic activities, enabling the chemo-enzymatic cascade reactions.

Glucose oxidase stabilized fluorescent gold nanoparticles as an ideal sensor matrix for dual mode sensing of glucose

A simple, facile and green route for the preparation of glucose oxidase stabilized simple Au NPs and fluorescent Au NPs for the dual mode bio-sensing application of glucose using colourimetric and electrochemical methods is demonstrated.

Intrinsic peroxidase-like activity and the catalytic mechanism of gold@carbon dots nanocomposites

The mechanism of AuNPs@CDs as nano-enzyme catalysing the oxidation of TMB in the presence of H₂O₂.

Whole blood glucose analysis based on smartphone camera module

Complementary metal oxide semiconductor (CMOS) image sensors have received great attention for their high efficiency in biological applications. The present work describes a CMOS image sensor-based whole blood glucose monitoring system through a point-of-care (POC) approach. A simple poly-ethylene terephthalate (PET) chip was developed to carry out the enzyme kinetic reaction at various concentrations (110–586 mg∕dL) of mouse blood glucose. In this technique, assay reagent is immobilized onto amine functionalized silica (AFSiO2) nanoparticles as an electrostatic attraction in order to achieve glucose oxidation on the chip. The assay reagent immobilized AFSiO2 nanoparticles develop a semi-transparent reaction platform, which is technically a suitable chip to analyze by a camera module. The oxidized glucose then produces a green color according to the glucose concentration and is analyzed by the camera module as a photon detection technique; the photon number decreases when the glucose concentration increases. The combination of these components, the CMOS image sensor and enzyme immobilized PET film chip, constitute a compact, accurate, inexpensive, precise, digital, highly sensitive, specific, and optical glucose-sensing approach for POC diagnosis.

Reversible Regulation of Catalytic Activity of Gold Nanoparticles with DNA Nanomachines

Reversible catalysis regulation has gained much attention and traditional strategies utilized reversible ligand coordination for switching catalyst's conformations. However, it remains challenging to regulate the catalytic activity of metal nanoparticle-based catalysts. Herein, we report a new DNA nanomachine-driven reversible nano-shield strategy for circumventing this problem. The basic idea is based on the fact that the conformational change of surface-attached DNA nanomachines will cause the variation of the exposed surface active area on metal nanoparticles. As a proof-of-concept study, we immobilized G-rich DNA strands on gold nanoparticles (AuNPs) which have glucose oxidase (GOx) like activity. Through the reversible conformational change of the G-rich DNA between a flexible single-stranded form and a compact G-quadruplex form, the catalytic activity of AuNPs has been regulated reversibly for several cycles. This strategy is reliable and robust, which demonstrated the possibility of reversibly adjusting catalytic activity with external surface coverage switching, rather than coordination interactions.

A glucose oxidase-coupled DNAzyme sensor for glucose detection in tears and saliva

Biosensors have been widely investigated and utilized in a variety of fields ranging from environmental monitoring to clinical diagnostics. Glucose biosensors have triggered great interest and have been widely exploited since glucose determination is essential for diabetes diagnosis. In here, we designed a novel dual-enzyme biosensor composed of glucose oxidase (GOx) and pistol-like DNAzyme (PLDz) to detect glucose levels in tears and saliva. First, GOx, as a molecular recognition element, catalyzes the oxidation of glucose forming H2O2; then PLDz recognizes the produced H2O2 as a secondary signal and performs a self-cleavage reaction promoted by Mn(2+), Co(2+) and Cu(2+). Thus, detection of glucose could be realized by monitoring the cleavage rate of PLDz. The slope of the cleavage rate of PLDz versus glucose concentration curve was fitted with a Double Boltzmann equation, with a range of glucose from 100 nM to 10mM and a detection limit of 5 μM. We further applied the GOx-PLDz 1.0 biosensor for glucose detection in tears and saliva, glucose levels in which are 720±81 μM and 405±56 μM respectively. Therefore, the GOx-PLDz 1.0 biosensor is able to determine glucose levels in tears and saliva as a noninvasive glucose biosensor, which is important for diabetic patients with frequent/continuous glucose monitoring requirements. In addition, induction of DNAzyme provides a new approach in the development of glucose biosensors.