A Ternary Composite Based on Graphene, Hemin, and Gold Nanorods with High Catalytic Activity for the Detection of Cell-Surface Glycan Expression

Microperoxidase-11 functionalized nanozyme with enhanced peroxidase-mimicking activities for visual detection of cysteine

Various nanomaterials with peroxidase activity (nanozyme) have been designed for bio catalysis and biosensing, however, most of them need further design and modification of probe molecules for the specific binding reaction with targets. This results in a decrease in catalysis activity and hinders them to be perfect alternatives to natural enzyme in biosensing. In this work, an enhanced nanozyme was synthesized by functionalizing natural microperoxidase-11 (MP-11) on a hybrid graphene oxide-gold (GO-Au) material. The designed nanozyme showed an enhanced catalysis activity and realized a robust and efficient colorimetric detection of cysteine based on specific binding reaction between active iron center from MP-11 and thiol in cysteine. The enhanced properties show promising applications of complex nanozyme and provides a great opportunity for developing efficient sensing systems.

Selective and Sensitive Fluorometric Determination of Piroxicam Based on Nitrogen-doped Graphene Quantum Dots and Gold Nanoparticles Coated with Phenylalanine

In this study, a sensitive fluorimetric method is proposed for the determination of piroxicam using nitrogen graphene quantum dots (N-GQDs) and gold nanoparticles coated with phenylalanine. The fluorescence emission of N-GQDs at 440 nm decreases with the increase of gold nanoparticles coated with phenylalanine. However, the addition of piroxicam causes the release of gold nanoparticles from the surface of quantum dots followed by the retrieval of the fluorescence emission of N-GQDs. Under the optimum conditions, the calibration graph was linear in the concentration range of 2.0-35.0 nmol L^-1 for piroxicam with a limit of detection of 0.11 nmol L^-1. The developed method was successfully applied for the determination of piroxicam in urine and serum samples.

Recent Advance in Biological Responsive Nanomaterials for Biosensing and Molecular Imaging Application

In recent decades, as a subclass of biomaterials, biologically sensitive nanoparticles have attracted increased scientific interest. Many of the demands for physiologically responsive nanomaterials in applications involving the human body cannot be met by conventional technologies. Due to the field's importance, considerable effort has been expended, and biologically responsive nanomaterials have achieved remarkable success thus far. This review summarizes the recent advancements in biologically responsive nanomaterials and their applications in biosensing and molecular imaging. The nanomaterials change their structure or increase the chemical reaction ratio in response to specific bio-relevant stimuli (such as pH, redox potentials, enzyme kinds, and concentrations) in order to improve the signal for biologically responsive diagnosis. We use various case studies to illustrate the existing issues and provide a clear sense of direction in this area. Furthermore, the limitations and prospects of these nanomaterials for diagnosis are also discussed.

Advanced bioactive nanomaterials for biomedical applications

Bioactive materials are a kind of materials with unique bioactivities, which can change the cellular behaviors and elicit biological responses from living tissues. Bioactive materials came into the spotlight in the late 1960s when the researchers found that the materials such as bioglass could react with surrounding bone tissue for bone regeneration. In the following decades, advances in nanotechnology brought the new development opportunities to bioactive nanomaterials. Bioactive nanomaterials are not a simple miniaturization of macroscopic materials. They exhibit unique bioactivities due to their nanoscale size effect, high specific surface area, and precise nanostructure, which can significantly influence the interactions with biological systems. Nowadays, bioactive nanomaterials have represented an important and exciting area of research. Current and future applications ensure that bioactive nanomaterials have a high academic and clinical importance. This review summaries the recent advances in the field of bioactive nanomaterials, and evaluate the influence factors of bioactivities. Then, a range of bioactive nanomaterials and their potential biomedical applications are discussed. Furthermore, the limitations, challenges, and future opportunities of bioactive nanomaterials are also discussed.

Functionalization of GroEL nanocages with hemin for label-free colorimetric assays

The design of functionalized protein nanocages as enzyme mimics is a relatively new and promising field as these biogenic nanocapsules are inherently monodisperse with precise architectures, unattainable by purely synthetic processes. This work explored the catalytic properties of the bacterial GroEL-nanocaged hemin and its performance in label-free colorimetric assays. It is demonstrated that the hemin-GroEL biohybrid has peroxidase-like activity and follows the typical Michaelis-Menten kinetics and ping-pong mechanism in the model sensing processes. The open nature and nanoreactor effect of the GroEL cage and the addition of ATP are shown to significantly influence the catalytic activity. For glucose detection with the hemin-GroEL complex, the linearity between the analyte concentration and UV-vis absorption was determined to range from 0 to 200 μM with a limit of detection (LOD) of ~ 12 μM under the defined conditions. In addition, the colorimetric detection of catechol led to a linear dynamic range of 0-120 μM with a LOD of ~ 17 μM. This indicates that the same assay could be used as a sensing platform for the detection or even oxidative removal of phenolic contaminants in the presence of H₂O₂. Thus, GroEL cage is a valuable tool for the development of nanozymes and practical applications such as clinical analysis and environmental monitoring.

Visual Detection of Cucumber Green Mottle Mosaic Virus Based on Terminal Deoxynucleotidyl Transferase Coupled with DNAzymes Amplification

A simple, rapid, and sensitive visual detection method for observing cucumber green mottle mosaic virus was reported based on the template-independent polymerization activity of terminal deoxynucleotidyl transferase (TdT), coupled with the cascade amplification of Mg²⁺-dependent DNAzyme and hemin/G-quadruplex DNAzyme. Briefly, the hybridized dsDNA of T1/P1 was cut into two parts at its position of 5′-AA↓CG↑TT-3′ by the restricted enzyme AcII. The longer, newborn fragment originating from P1 was tailed at its 3’-end by oligo dG, and an intact enzymatic sequence of Mg²⁺-dependent DNAzyme was generated. The substrate sequence in the loop segment of the hairpin probe (HP) hybridized with the newborn enzymatic sequence and was cleaved into two parts in the presence of Mg²⁺. The locked G-quadruplex sequence in the stem segment of the HP was released, which catalyzed the oxidation of ABTS^2- in the presence of H₂O₂, and the resulting solution turned green. A correlation between the absorbance and concentration of T1 was obtained in a range from 0.1 pM to 2 nM, with a detection limit of 0.1 pM. In addition to promoting a lower detection limit and shorter monitoring time, this method also demonstrated an excellent selectivity to single or double nucleotide changes. Therefore, the designed strategy provided a rapid and efficient platform for viral inspection and plant protection.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Nanotechnology in Glycomics: Applications in Diagnostics, Therapy, Imaging, and Separation Processes

This review comprehensively covers the most recent achievements (from 2013) in the successful integration of nanomaterials in the field of glycomics. The first part of the paper addresses the beneficial properties of nanomaterials for the construction of biosensors, bioanalytical devices, and protocols for the detection of various analytes, including viruses and whole cells, together with their key characteristics. The second part of the review focuses on the application of nanomaterials integrated with glycans for various biomedical applications, that is, vaccines against viral and bacterial infections and cancer cells, as therapeutic agents, for in vivo imaging and nuclear magnetic resonance imaging, and for selective drug delivery. The final part of the review describes various ways in which glycan enrichment can be effectively done using nanomaterials, molecularly imprinted polymers with polymer thickness controlled at the nanoscale, with a subsequent analysis of glycans by mass spectrometry. A short section describing an active glycoprofiling by microengines (microrockets) is covered as well.

Versatile aptasensor for electrochemical quantification of cell surface glycan and naked-eye tracking glycolytic inhibition in living cells

Quantifying the glycan expression status on cell surfaces is of vital importance for insight into the glycan function in biological processes and related diseases. Here we developed a versatile aptasensor for electrochemical quantification of cell surface glycan by taking advantage of the cell-specific aptamer, and the lectin-functionalized gold nanoparticles acting as both a glycan recognition unit and a signal amplification probe. To construct the aptasensor, amine-functionalized mucin 1 protein (MUC1) aptamer was first covalently conjugated to carboxylated-magnetic beads (MBs) using the succinimide coupling (EDC-NHS) method. On the basis of the specific recognition between aptamer and MUC1 protein that overexpressed on the surface of MCF-7 cells, the aptamer conjugated MBs showed a predominant capability for cell capture with high selectivity. Moreover, a lectin-based nanoprobe was designed by noncovalent assembly of concanavalin A (ConA) on gold nanoparticles (AuNPs). This nanoprobe incorporated the abilities of both the specific carbohydrate recognition and the signal amplification based on the gold-promoted reduction of silver ions. By coupling with electrochemical stripping analysis, the proposed sandwich-type cytosensor showed an excellent analytical performance for the ultrasensitive detection of MCF-7 cells and quantification of cell surface glycan. More importantly, taking advantage of Con A-gold nanoprobe catalyzed silver enhancement, the proposed method was further used for naked-eye tracking glycolytic inhibition in living cells. This aptasensor holds great promise as a new point-of-care diagnostic tool for analyzing glycan expression on living cells and further helps cancer diagnosis and treatment.

Efficient double-quenching of electrochemiluminescence from CdS:Eu QDs by hemin-graphene-Au nanorods ternary composite for ultrasensitive immunoassay

A novel ternary composite of hemin-graphene-Au nanorods (H-RGO-Au NRs) with high electrocatalytic activity was synthesized by a simple method. And this ternary composite was firstly used in construction of electrochemiluminescence (ECL) immunosensor due to its double-quenching effect of quantum dots (QDs). Based on the high electrocatalytic activity of ternary complexes for the reduction of H₂O₂ which acted as the coreactant of QDs-based ECL, as a result, the ECL intensity of QDs decreased. Besides, due to the ECL resonance energy transfer (ECL-RET) strategy between the large amount of Au nanorods (Au NRs) on the ternary composite surface and the CdS:Eu QDs, the ECL intensity of QDs was further quenched. Based on the double-quenching effect, a novel ultrasensitive ECL immunoassay method for detection of carcinoembryonic antigen (CEA) which is used as a model biomarker analyte was proposed. The designed immunoassay method showed a linear range from 0.01 pg mL⁻¹ to 1.0 ng mL⁻¹ with a detection limit of 0.01 pg mL⁻¹. The method showing low detection limit, good stability and acceptable fabrication reproducibility, provided a new approach for ECL immunoassay sensing and significant prospect for practical application.

Graphene oxide-based electrochemical label-free detection of glycoproteins down to aM level using a lectin biosensor

A label-free ultrasensitive impedimetric biosensor with lectin immobilised on graphene oxide (GO) for the detection of glycoproteins from 1 aM is shown here. This is the first time a functional lectin biosensor with lectin directly immobilised on a graphene-based interface without any polymer modifier has been described. The study also shows that hydrophilic oxidative debris present on GO has a beneficial effect on the sensitivity of (8.46 ± 0.20)% per decade for the lectin biosensor compared to the sensitivity of (4.52 ± 0.23)% per decade for the lectin biosensor built up from GO with the oxidative debris washed out.

Immobilization of bilirubin oxidase on graphene oxide flakes with different negative charge density for oxygen reduction. The effect of GO charge density on enzyme coverage, electron transfer rate and current density

Previously we showed that an effective bilirubin oxidase (BOD)-based biocathode using graphene oxide (GO) could be prepared in 2 steps: 1. electrostatic adsorption of BOD on GO; 2. electrochemical reduction of the BOD-GO composite to form a BOD-ErGO (electrochemically reduced GO) film on the electrode. In order to identify an optimal charge density of GO for BOD-ErGO composite preparation, several GO fractions differing in an average flake size and ζ-potential were prepared using centrifugation and consequently employed for BOD-ErGO biocathode preparation. A simple way to express surface charge density of these particular GO nanosheets was developed. The values obtained were then correlated with biocatalytic and electrochemical parameters of the prepared biocathodes, i.e. electrocatalytically active BOD surface coverage (Γ), heterogeneous electron transfer rate (k_S) and a maximum biocatalytic current density. The highest bioelectrocatalytic current density of (597±25)μAcm^-2 and the highest Γ of (23.6±0.9)pmolcm^-2 were obtained on BOD-GO composite having the same moderate negative charge density, but the highest k_S of (79.4±4.6)s^-1 was observed on BOD-GO composite having different negative charge density. This study is a solid foundation for others to consider the influence of a charge density of GO on direct bioelectrochemistry/bioelectrocatalysis of other redox enzymes applicable for construction of biosensors, bioanodes, biocathodes or biofuel cells.

Electrocatalytic reduction of a coreactant using a hemin–graphene–Au nanoparticle ternary composite for sensitive electrochemiluminescence cytosensing

A sensitive electrochemiluminescence cytosensor was designed using a hemin–RGO–Au ternary composite with high electrocatalytic activity for H₂O₂ reduction.

Reduced graphene oxide-Hemin-Au nanohybrids: Facile one-pot synthesis and enhanced electrocatalytic activity towards the reduction of hydrogen peroxide

A facile and effective strategy is demonstrated for the synthesis of ternary reduced graphene oxide-Hemin-Au (rGO-H-Au) nanohybrids. The nanohybrids were synthesized through a one-pot in situ reduction of GO and HAuCl4 under alkaline conditions using GO, Hemin and HAuCl4 as the starting materials. The synthesis process can be finished within 1h in a solution phase, without adding any additional surfactant, stabilizing agent and toxic or harsh chemical reducing agents. The resulting nanohybrids were characterized by UV-vis spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and so on. Electrochemical measurements showed that the rGO-H-Au nanohybrids exhibited good electrocatalytic activity for the reduction of hydrogen peroxide (H2O2). Based on this property, a simple and highly sensitive amperometric biosensor for H2O2 had been developed. The linear relationships were obtained from 0.1 µM to 40 µM and the detection limit was estimated to be 30 nM. The simple and sensitive sensing platform showed great promising applications in the pharmaceutical, clinical and industrial detection of H2O2.