In Situ Nanoplasmonic Probing of Enzymatic Activity of Monolayer-Confined Glucose Oxidase on Colloidal Nanoparticles

The Modification and Applications of Nanopipettes in Electrochemical Analysis

Nanopipette, which is fabricated by glasses and possesses a nanoscale pore in the tip, has been proven to be immensely useful in electrochemical analysis. Numerous nanopipette-based sensors have emerged with improved sensitivity, selectivity, ease of use, and miniaturization. In this minireview, we provide an overview of the recent developments of nanopipette-based electrochemical sensors based on different types of nanopipettes, including single-nanopipettes, self-referenced nanopipettes, dual-nanopipettes, and double-barrel nanopipettes. Several important modification materials for nanopipette functionalization are highlighted, such as conductive materials, macromolecular materials, and functional molecules. These materials can improve the sensing performance and targeting specificities of nanopipettes. We also discuss examples of related applications and the future development of nanopipette-based strategies.

Recent advances of Au@Ag core-shell SERS-based biosensors

The methodological advancements in surface-enhanced Raman scattering (SERS) technique with nanoscale materials based on noble metals, Au, Ag, and their bimetallic alloy Au-Ag, has enabled the highly efficient sensing of chemical and biological molecules at very low concentration values. By employing the innovative various type of Au, Ag nanoparticles and especially, high efficiency Au@Ag alloy nanomaterials as substrate in SERS based biosensors have revolutionized the detection of biological components including; proteins, antigens antibodies complex, circulating tumor cells, DNA, and RNA (miRNA), etc. This review is about SERS-based Au/Ag bimetallic biosensors and their Raman enhanced activity by focusing on different factors related to them. The emphasis of this research is to describe the recent developments in this field and conceptual advancements behind them. Furthermore, in this article we apex the understanding of impact by variation in basic features like effects of size, shape varying lengths, thickness of core-shell and their influence of large-scale magnitude and morphology. Moreover, the detailed information about recent biological applications based on these core-shell noble metals, importantly detection of receptor binding domain (RBD) protein of COVID-19 is provided.

Nanoconfined Electrochemical Collision and Catalysis of Single Enzyme inside Carbon Nanopipettes

Revealing the electrocatalytic features of single redox enzyme is significant to both fundamental biological processes and practical catalysis and sensing applications. Herein, we directly reveal the electrocatalytic current from a single enzyme inside the carbon nanopipettes via electrochemical collision strategies, based on the increased activity at nanoscale confinement. Besides the staircase current steps from surface blockage, discrete H₂O₂ oxidation and reduction current transients catalyzed by a single enzyme are also displayed and analyzed. The carbon nanopipette would increase the catalytic activities of enzymes and lead to a detectable current response, thus opening a new way to investigate the fundamental enzymatic mechanisms at the single enzyme level.

Nanopipettes for the Electrochemical Study of Enhanced Enzymatic Activity in a Femtoliter Space

The chemical reaction in a confined space is known to be accelerated due to a high collision probability; however, the study of this confinement effect in a supersmall space down to femtoliter (fL) is seldom reported. Here, an adjustable volume [from picoliter (pL) to fL] of the aqueous phase is retrained at the tip of a nanopipette by an organic solvent so that the confinement effect on the specific activity of glucose oxidase is investigated. The activity is determined by the amount of hydrogen peroxide generated from the reaction between the oxidase and glucose using a nanoelectrode inside the nanopipette. As compared with the activity in bulk solution (82 U/mg), the activity increases up to 7500 U/mg in a 105 fL space. The 2 orders of magnitude increase in the enzymatic activity is the highest amplification in the volume-confined enzyme reaction as reported. A near-exponential drop in the activity is observed with the increase in the space volume, revealing the dominant enhancement in the confined space at the fL level for the first time. The established electrochemical nanopipettes should not only provide a strategy for the study of the enzymatic activity in supersmall confined space but also help understand the confinement effect of enzyme-catalyzed reactions.

LSPR-based colorimetric biosensing for food quality and safety

Ensuring consistently high quality and safety is paramount to food producers and consumers alike. Wet chemistry and microbiological methods provide accurate results, but those methods are not conducive to rapid, onsite testing needs. Hence, many efforts have focused on rapid testing for food quality and safety, including the development of various biosensors. Herein, we focus on a group of biosensors, which provide visually recognizable colorimetric signals within minutes and can be used onsite. Although there are different ways to achieve visual color-change signals, we restrict our focus on sensors that exploit the localized surface plasmon resonance (LSPR) phenomenon of metal nanoparticles, primarily gold and silver nanoparticles. The typical approach in the design of LSPR biosensors is to conjugate biorecognition ligands on the surface of metal nanoparticles and allow the ligands to specifically recognize and bind the target analyte. This ligand-target binding reaction leads to a change in color of the test sample and a concomitant shift in the ultraviolet-visual absorption peak. Various designs applying this and other signal generation schemes are reviewed with an emphasis on those applied for evaluating factors that compromise the quality and safety of food and agricultural products. The LSPR-based colorimetric biosensing platform is a promising technology for enhancing food quality and safety. Aided by the advances in nanotechnology, this sensing technique lends itself easily for further development on field-deployable platforms such as smartphones for onsite and end-user applications.

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

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

Manipulating Bimetallic Nanostructures With Tunable Localized Surface Plasmon Resonance and Their Applications for Sensing

Metal nanocrystals with well-controlled shape and unique localized surface plasmon resonance (LSPR) properties have attracted tremendous attention in both fundamental studies and applications. Compared with monometallic counterparts, bimetallic nanocrystals endow scientists with more opportunities to precisely tailor their LSPR and thus achieve excellent performances for various purposes. The aim of this mini review is to present the recent process in manipulating bimetallic nanostructures with tunable LSPR and their applications for sensing. We first highlight several significant strategies in controlling the elemental ratio and spatial arrangement of bimetallic nanocrystals, followed by discussing on the relationship between their composition/morphology and LSPR properties. We then focus on the plasmonic sensors based on the LSPR peak shift, which can be well-controlled by seed-mediated growth and selective etching. This review provides insights of understanding the “rules” involving in the formation of bimetallic nanocrystals with different structures and desired LSPR properties, and also forecasts the development directions of plasmonic sensors in the future.

Nitrogen-containing three-dimensional biomass porous carbon materials as an efficient enzymatic biosensing platform for glucose sensing

Schematic illustration of the fabrication and structure of the 3D-CVS/GOD electrode.

Nucleus and Mitochondria Targeting Theranostic Plasmonic Surface-Enhanced Raman Spectroscopy Nanoprobes as a Means for Revealing Molecular Stress Response Differences in Hyperthermia Cell Death between Cancerous and Normal Cells

Metallic plasmonic nanoparticles have been intensively exploited as theranostic nanoprobes for plasmonic photothermal therapy (PPT) and surface-enhanced Raman spectroscopy (SERS) applications. But the underlying molecular mechanisms associated with PPT-induced apoptosis between cancerous and normal cells have remained largely unknown or disputed. In this study, we designed an organelle-targeting theranostic plasmonic SERS nanoprobe (CDs-Ag/Au NS) composed of porous Ag/Au nanoshell (p-Ag/Au NSs) and carbon dots (CDs) for nucleus and mitochondria targeted PPT of cells. The differences in molecular stress response in the PPT-induced hyperthermia cell death between cancerous HeLa and normal L929 and H8 cells have been revealed by site-specific single-cell SERS detection. The contents of tryptophan (Trp), phenylalanine (Phe), and tyrosine (Tyr) in HeLa cells were found more evidently increased than L929 and H8 cells during the PPT-induced cell-death process. And from the mitochondria point of view, we found that the PPT-induced cell apoptosis for HeLa cells mainly stems from (or is regulated through) cellular thermal stress-responsive proteins, while for L929 and H8 cells it seems more related to DNA. Understanding molecular stress response difference of the PPT-induced cell apoptosis between cancerous and normal cells is helpful for diagnosis and treatment of cancer, and the method will open an avenue for single-cell studies.

Plasmon-Based Colorimetric Nanosensors for Ultrasensitive Molecular Diagnostics

Colorimetric detection of target analytes with high specificity and sensitivity is of fundamental importance to clinical and personalized point-of-care diagnostics. Because of their extraordinary optical properties, plasmonic nanomaterials have been introduced into colorimetric sensing systems, which provide significantly improved sensitivity in various biosensing applications. Here we review the recent progress on these plasmonic nanoparticles-based colorimetric nanosensors for ultrasensitive molecular diagnostics. According to their different colorimetric signal generation mechanisms, these plasmonic nanosensors are classified into two categories: (1) interparticle distance-dependent colorimetric assay based on target-induced forming cross-linking assembly/aggregate of plasmonic nanoparticles; and (2) size/morphology-dependent colorimetric assay by target-controlled growth/etching of the plasmonic nanoparticles. The sensing fundamentals and cutting-edge applications will be provided for each of them, particularly focusing on signal generation and/or amplification mechanisms that realize ultrasensitive molecular detection. Finally, we also discuss the challenge and give our future perspective in this emerging field.

Scaffolding of Enzymes on Virus Nanoarrays: Effects of Confinement and Virus Organization on Biocatalysis

Organizing active enzyme molecules on nanometer-sized scaffolds is a promising strategy for designing highly efficient supported catalytic systems for biosynthetic and sensing applications. This is achieved by designing model nanoscale enzymatic platforms followed by thorough analysis of the catalytic activity. Herein, the virus fd bacteriophage is considered as an enzyme nanocarrier to study the scaffolding effects on enzymatic activity. Nanoarrays of randomly oriented, or directionally patterned, fd bacteriophage virus are functionalized with the enzyme glucose oxidase (GOx), using an immunological assembly strategy, directly on a gold electrode support. The scaffolding process on the virus capsid is monitored in situ by AFM (atomic force microscopy) imaging, while cyclic voltammetry is used to interrogate the catalytic activity of the resulting functional GOx-fd nanoarrays. Kinetic analysis reveals the ability to modulate the activity of GOx via nanocarrier patterning. The results evidence, for the first time, enhancement of the enzymatic activity due to scaffolding on a filamentous viral particle.

Gold–platinum bimetallic nanoclusters with enhanced peroxidase-like activity and their integrated agarose hydrogel-based sensing platform for the colorimetric analysis of glucose levels in serum

Bimetallic Au–PtNCs with enhanced peroxidase-like activity were integrated into agarose hydrogels for direct visualization of glucose in human serum.

Nano-Engineered Biomimetic Optical Sensors for Glucose Monitoring in Diabetes

Diabetes is a rapidly growing disease that can be monitored at an individual level by controlling the blood glucose level, hence minimizing the negative impact of the disease. Significant research efforts have been focused on the design of novel and improved technologies to overcome the limitations of existing glucose analysis methods. In this context, nanotechnology has enabled the diagnosis at the single cell and molecular level with the possibility of incorporation in advanced molecular diagnostic biochips. Recent years have witnessed the exploration and synthesis of various types of nanomaterials with enzyme-like properties, with their subsequent integration into the design of biomimetic optical sensors for glucose monitoring. This review paper will provide insights on the type, nature and synthesis of different biomimetic nanomaterials. Moreover, recent developments in the integration of these nanomaterials for optical glucose biosensing will be highlighted, with a final discussion on the challenges that must be addressed for successful implementation of these nano-devices in the clinical applications is presented.

An enhanced chemiluminescence bioplatform by confining glucose oxidase in hollow calcium carbonate particles

A chemiluminescence (CL) amplification platform based on HCC/Lucigenin&GOx (HLG) film was developed. Hollow structural calcium carbonate (HCC) particles were used as alternative materials for carrying both enzyme and CL reagent. The model enzyme (GOx), immobilized in confined space of HCC particles, exhibited an improved biocatalysis. The Michaelis constant (Km) and the enzymatic rate constant (kcat) were determined to be 0.209 μM and 2.21 s(-1), respectively, which are much better than those of either free GOx in aqueous solution or the GOx immobilized on common nanomaterials. Based on the HLG platform, CL signal was effectively amplified and visualized after adding trace glucose, which could be attributed to the HCC particles' high biocompatibility, large specific surface area, attractive interfacial properties and efficient interaction with analyses. The visual CL bioplatform showed an excellent performance with high selectivity, wide linear range and low detection limit for sensing trace glucose. Because it eliminates the need of complicated assembly procedure and enables visualization by the naked eye, the sensitive and selective CL bioplatform would provide wide potential applications in disease diagnosis and food safety.

Sensitive colorimetric detection of glucose and cholesterol by using Au@Ag core–shell nanoparticles

Sensitive colorimetric detection of glucose and cholesterol by using Au@Ag core–shell nanoparticles.

A glucose biosensor based on glucose oxidase immobilized on three-dimensional porous carbon electrodes

A schematic illustration of a 3D-KSC/GOD glucose biosensor is presented.

Ionic strength-modulated catalytic efficiency of a multienzyme cascade nanoconfined on charged hierarchical scaffolds

Understanding the effect of ionic strength on the efficiency of this enzyme cascade within charged hierarchical nanospace is not only fundamentally interesting, but also important for translating biochemical pathways to noncellular environments.

Highly precise plasmonic and colorimetric sensor based on enzymatic etching of nanospheres for the detection of blood and urinary glucose

A highly precise glucose sensor was developed based on plasmon peak shift induced by the glucose oxidase mediated etching of Au–Ag nanoparticles. The platform enabled quantitative glucose detection in human blood and urine samples.

An enzyme–inorganic hybrid nanoflower based immobilized enzyme reactor with enhanced enzymatic activity

Ca₃(PO₄)₂–ChT hybrid nanoflowers were synthesized by a facile approach. The nanoflowers exhibited an enhanced enzymatic activity and can be used as an immobilized enzyme reactor (IMER) for highly efficient protein digestion.

A green approach to the synthesis of novel "Desert rose stone"-like nanobiocatalytic system with excellent enzyme activity and stability

3D hierarchical layer double hydroxides (LDHs) have attracted extensive interest due to their unique electronic and catalytic properties. Unfortunately, the existing preparation methods require high temperature or toxic organic compounds, which limits the applications of the 3D hierarchical LDHs in biocatalysis and biomedicine. Herein, we present a green strategy to synthesize “Desert Rose Stone”-like Mg-Al-CO₃ LDH nanoflowers in situ deposited on aluminum substrates via a coprecipitation method using atmospheric carbon dioxide. Using this method, we construct a novel “Desert Rose Stone”-like nanobiocatalytic system by using HRP as the model enzyme. Compared with the free HRP, the HRP/Mg-Al-LDH nanobiocatalytic system exhibits higher catalytic activity and stability. A smaller apparent Michaelis-Menten constant (0.16 mM) of this system suggests that the encapsulated HRP shows higher affinity towards H₂O₂.

Small-angle neutron scattering study of differences in phase behavior of silica nanoparticles in the presence of lysozyme and bovine serum albumin proteins

The differences in phase behavior of anionic silica nanoparticles (88 Å) in the presence of two globular proteins [cationic lysozyme (molecular weight (MW) 14.7 kD) and anionic bovine serum albumin (BSA) (MW 66.4 kD)] have been studied by small-angle neutron scattering. The measurements were carried out on a fixed concentration (1 wt %) of Ludox silica nanoparticles with varying concentrations of proteins (0-5 wt %) at pH = 7. It is found that, despite having different natures (opposite charges), both proteins can render to the same kind of aggregation of silica nanoparticles. However, the concentration regions over which the aggregation is observed are widely different for the two proteins. Lysozyme with very small amounts (e.g., 0.01 wt %) leads to the aggregation of silica nanoparticles. On the other hand, silica nanoparticles coexist with BSA as independent entities at low protein concentrations and turn to aggregates at high protein concentrations (>1 wt %). In the case of lysozyme, the charge neutralization by the protein on the nanoparticles gives rise to the protein-mediated aggregation of the nanoparticles. The nanoparticle aggregates coexist with unaggregated nanoparticles at low protein concentrations, whereas, they coexist with a free protein at higher protein concentrations. For BSA, the nonadsorbing nature of the protein produces the depletion force that causes the aggregation of the nanoparticles at higher protein concentrations. The evolution of the interaction is modeled by the two Yukawa potential, taking account of both attractive and repulsive terms of the interaction in these systems. The nanoparticle aggregation is found to be governed by the short-range attraction for lysozyme and the long-range attraction for BSA. The aggregates are characterized by the diffusion limited aggregate type of mass fractal morphology.

Multifunctional compact hybrid Au nanoshells: a new generation of nanoplasmonic probes for biosensing, imaging, and controlled release

Gold nanoshells (AuNSs) with tunable localized surface plasmon resonance (LSPR) peaks in the near-infrared (NIR) region possess unique optical properties-particularly that soft tissues are "transparent" at these wavelengths-making them of great interest in cancer diagnosis and treatment. Since 1998 when Halas and co-workers invented the first generation of AuNS, with a silica core and Au shell, researchers have studied and designed AuNSs for theranostic-individualized, combination diagnosis and therapy-nanomedicine. As demand has increased for more powerful and practical theranostic applications, so has demand for the next generation of AuNSs-compact yet complex multifunctional AuNSs with finely integrated plasmonic and nonplasmonic inorganic components. For in vivo biomedical applications, such a hybrid AuNS offers the desirable optical properties of NIR LSPR. Size, however, has proved a more challenging parameter to control in hybrid AuNSs. The ideal size of therapeutic NPs is 10-100 nm. Larger particles have limited diffusion in the extracellular space, while particles less than 5 nm are rapidly cleared from the circulation through extravasation or renal clearance. Conventional methods of preparing AuNS have failed to obtain small-sized hybrid AuNSs with NIR LSPR responses. In this Account, we present a new class of multifunctional hybrid AuNSs with ultrathin AuNSs and varied, functional (nonplasmonic) core components ranging from "hard" semiconductor quantum dots (QDs), to superparamagnetic NPs, to "soft" liposomes made using poly-l-histidine as a template to direct Au deposition. The resultant hybrid AuNSs are uniform and compact (typically 15-60 nm) but also preserve the optical properties and shell-type NIR response necessary for biomedical use. We also demonstrate these particles' innovative plasmonic applications in biosensing, multimodal imaging and controlled release. More importantly, the magnetic-plasmonic Fe3O4/Au core-shell NP enables a new biological imaging method-magnetomotive photoacoustic (mmPA) imaging, which suppresses the nonmagnetomotive background and therefore offers remarkable contrast enhancement and improved specificity compared with photoacoustic images using conventional NP contrast agents. The advantages of our AuNSs are obvious: they are monodisperse, small (<100 nm), highly integrated, and have tunable visible-NIR plasmonic responses. All of these properties are crucial for in vitro or in vivo biological/biomedical studies and many applications, especially for studies of single cells or molecules which require particle monodispersity and tight size control. The plasmonic fluorescent QD/Au and the magnetic plasmonic Fe3O4/Au core-shell NPs may also reveal new physical phenomena that may lead to useful applications, owing to their well-defined core-shell nanoarchitectures and underlying nanoscale physical interactions.

Electrochemiluminescence immunosensor using poly(l-histidine)-protected glucose dehydrogenase on Pt/Au bimetallic nanoparticles to generate an in situ co-reactant

A new ECL immunosensor based on poly(l-histidine)-protected glucose dehydrogenase on Pt/Au bimetallic nanoparticles to generate co-reactantin situ.

Colorimetric visualization of glucose at the submicromole level in serum by a homogenous silver nanoprism-glucose oxidase system

In this study, we design a homogeneous system consisting of Ag nanoprisms and glucose oxidase (GOx) for simple, sensitive, and low-cost colorimetric sensing of glucose in serum. The unmodified Ag nanoprisms and GOx are first mixed with each other. Glucose is then added in the homogeneous mixture. Finally, the nanoplates are etched from triangle to round by H2O2 produced by the enzymatic oxidation, which leads to a more than 120 nm blue shift of the surface plasmon resonance (SPR) absorption band of the Ag nanoplates. This large wavelength shift can be used not only for visual detection (from blue to mauve) of glucose by naked eyes but for reliable and convenient glucose quantification in the range from 2.0 × 10(-7) to 1.0 × 10(-4) M. The detection limit is as low as 2.0 × 10(-7) M, because the used Ag nanoprisms possess (1) highly reactive edges/tips and (2) strongly tip sharpness and aspect ratio dependent SPR absorption. Owing to ultrahigh sensitivity, only 10-20 μL of serum is enough for a one-time determination. The proposed glucose sensor has great potential in the applications of point-of-care diagnostics, especially for third-world countries where high-tech diagnostics aids are inaccessible to the bulk of the population.