A small-molecule-linked DNA–graphene oxide-based fluorescence-sensing system for detection of biotin

Target-Induced Enzymatic Cascade Reaction Method: Integrating Strand Displacement Amplification and CRISPR/Cas12a for Homogeneous Assays of Biotin

The important biological role of biotin emphasizes the need for a sensitive method to detect it in foodstuffs. This article introduces a homogeneous and sensitive biotin analysis method that leverages a target-induced enzymatic cascade reaction, incorporating strand-displacement amplification (SDA) and the CRISPR/Cas12a system. Without target biotin, streptavidin (SA) specifically binds to the biotinylated probe DNA, hindering Klenow polymerase from extending the primer single-stranded DNA (ssDNA) due to the steric hindrance created by the SA-biotin complex, resulting in low fluorescence. Conversely, competition between the target biotin and the biotin label for binding to SA reduces the amount of SA captured on the primer ssDNA. The SDA process, which involves Klenow polymerase and the Nb.BbvCI enzyme, proceeds smoothly, thereby activating the CRISPR/Cas12a system and producing an intense fluorescence signal. Utilizing this principle, precise and sensitive biotin detection in food matrices was achieved, with a limit of detection of 0.01 nM.

Highly sensitive and label-free detection of biotin using a liquid crystal-based optofluidic biosensor

A liquid crystal (LC)-based optofluidic whispering gallery mode (WGM) resonator has been applied as a biosensor to detect biotin. Immobilized streptavidin (SA) act as protein molecules and specifically bind to biotin through strong non-covalent interaction, which can interfere with the orientation of LCs by decreasing the vertical anchoring force of the alignment layer in which the WGM spectral wavelength shift is monitored as a sensing parameter. Due to the double magnification of the LC molecular orientation transition and the resonance of the WGM, the detection limit for SA can reach 1.25 fM (4.7 × 10^-13 g/ml). The measurable concentration of biotin and the wavelength shift of the WGM spectrum have an excellent linearity in the range of 0 to 0.1 pg/ml, which can achieve ultra-low detection limit (0.4 fM), i.e., seven orders of magnitude improvement over conventional polarized optical microscope (POM) method. The proposed optofluidic biosensor is highly reproducible and can be used as an ultrasensitive real-time monitoring biosensor, which will open the door for applications to other receptor and ligand models.

On the interface between biomaterials and two-dimensional materials for biomedical applications

Two-dimensional (2D) materials have garnered significant attention due to their ultrathin 2D structures with a high degree of anisotropy and functionality. Reliable manipulation of interfaces between 2D materials and biomaterials is a new frontier for biomedical nanoscience and combining biomaterials with 2D materials offers a promising way to fabricate innovative 2D biomaterials composites with distinct functionality for biomedical applications. Here, we focus exclusively on a summary of the current work in the interface investigation of 2D biomaterials. Specifically, we highlight extraordinary features that make 2D materials so desirable, as well as the molecular level interactions between 2D materials and biomaterials that have been studied thus far. Furthermore, the approaches for investigating the interface characteristics of 2D biomaterials are presented and described in depth. To capture the emerging trend in mass manufacturing of 2D materials, we review the research progress on biomaterial-assisted exfoliation. Finally, we present a critical assessment of newly developed 2D biomaterials in biomedical applications.

Application of HRP-streptavidin bionanoparticles for potentiometric biotin determination

Biotin is widely used in infant formula to prevent biotin deficiency of newborn babies and in beauty products as nutritional supplements for coenzymatic functions and having strong nails, shiny hair, and skin over the last few years. There is a need for the development of a fast, simple and reusable assay method to perform biotin determination at very low concentrations. Biotin determination has achieved with a prepared potentiometric biotin sensor that has a very wide concentration range (10-15M-10-7M) and a lower detection limit (0.3 10-15M) with a very good regression coefficient (0.9925). A quick response (7 min), good accuracy (recovery 100.4-103.7%), reproducible, reusable (10 times), and long-term stability (3 months) have been obtained using the prepared potentiometric sensor. The obtained results have proved that the prepared potentiometric sensor can be used for biotin determination in real samples.

Sequence-Independent DNA Adsorption on Few-Layered Oxygen-Functionalized Graphene Electrodes: An Electrochemical Study for Biosensing Application

DNA is strongly adsorbed on oxidized graphene surfaces in the presence of divalent cations. Here, we studied the effect of DNA adsorption on electrochemical charge transfer at few-layered, oxygen-functionalized graphene (GO_x) electrodes. DNA adsorption on the inkjet-printed GO_x electrodes caused amplified current response from ferro/ferricyanide redox probe at concentration range 1 aM–10 nM in differential pulse voltammetry. We studied a number of variables that may affect the current response of the interface: sequence type, conformation, concentration, length, and ionic strength. Later, we showed a proof-of-concept DNA biosensing application, which is free from chemical immobilization of the probe and sensitive at attomolar concentration regime. We propose that GO_x electrodes promise a low-cost solution to fabricate a highly sensitive platform for label-free and chemisorption-free DNA biosensing.

Disordered protein-graphene oxide co-assembly and supramolecular biofabrication of functional fluidic devices

Supramolecular chemistry offers an exciting opportunity to assemble materials with molecular precision. However, there remains an unmet need to turn molecular self-assembly into functional materials and devices. Harnessing the inherent properties of both disordered proteins and graphene oxide (GO), we report a disordered protein-GO co-assembling system that through a diffusion-reaction process and disorder-to-order transitions generates hierarchically organized materials that exhibit high stability and access to non-equilibrium on demand. We use experimental approaches and molecular dynamics simulations to describe the underlying molecular mechanism of formation and establish key rules for its design and regulation. Through rapid prototyping techniques, we demonstrate the system's capacity to be controlled with spatio-temporal precision into well-defined capillary-like fluidic microstructures with a high level of biocompatibility and, importantly, the capacity to withstand flow. Our study presents an innovative approach to transform rational supramolecular design into functional engineering with potential widespread use in microfluidic systems and organ-on-a-chip platforms.

A G-quadruplex/hemin DNAzyme-based microchip electrophoresis chemiluminescence assay for highly sensitive detection of biotin in flour

Quantitative analysis of biotin in biological fluids, foods, and pharmaceutical is important for diagnosis and treatment of biotin-related diseases and health maintenance. In this work, a novel G-quadruplex/hemin DNAzyme-based microchip electrophoresis chemiluminescence (CL) assay method was established for rapid and highly sensitive detection of biotin. This method is based on the specific binding between biotin and streptavidin, the catalytic CL characteristics of G-quadruplex/hemin DNAzyme to the oxidation-reduction reaction of hydrogen peroxide with luminol, and the on-line separation function of microchip electrophoresis. Under the optimal experimental conditions, on-chip biotin analysis was achieved within 1 min. The CL intensity is linearly proportional to the concentration of biotin in the range of 13-630 nM with a detection limit of 6.4 nM. The proposed method has been applied for the detection of biotin in flour, biotin contents in three flour samples are found in the range of 199-223 ng/g with a mean value of 214 ng/g. The recoveries were in the range of 94-103%. With excellent sensitivity and good selectivity, the proposed method could be applied in a wide range of biological fluids, foods, and pharmaceutical analysis.

Removing Metal Ions from Water with Graphene⁻Bovine Serum Albumin Hybrid Membrane

Here we report the fabrication of graphene oxide (GO)-based membranes covalently combined with bovine serum albumin (BSA) for metal ions detection. In this system, BSA acts as a transporter protein in the membrane and endows the membrane with selective recognition of Co2+, Cu2+, AuCl₄-, and Fe2+. Combining the metal-binding ability of BSA and the large surface area of GO, the hybrid membrane can be used as a water purification strategy to selectively absorb a large amount of AuCl₄- from HAuCl₄ solution. Moreover, BSA could reduce the membrane-immobilized AuCl₄- by adding sodium borohydride (NaBH₄). Interestingly, adsorption experiments on three kinds of metal ions showed that the GO⁻BSA membrane had good selective adsorption of Co2+ compared with Cu2+ and Fe2+. The morphology and composition changes of the membrane were observed with atomic force microscopy (AFM) and Raman spectroscopy, respectively. It is expected that this facile strategy for fabricating large-scale graphene-biomolecule membranes will spark inspirations in the development of functional nanomaterials and wastewater purification.

Small molecule-protein interactions in branch migration thermodynamics: modelling and application in the homogeneous detection of proteins and small molecules

We have disclosed the unique inhibition effect of small molecule-protein interactions toward the DNA branch migration process and constructed a complete thermodynamic model for it. The disclosed effect was further coupled with the steric hindrance effect to establish a homogeneous assay for proteins and small molecules with ultra-high inhibition factors and sensitivity.

Oligonucleotide-stabilized fluorescent silver nanoclusters for the specific and sensitive detection of biotin

A novel biotin fluorescent probe based on oligonucleotide-stabilized silver nanoclusters (DNA-AgNCs) was synthesized by employing a biotinylated cytosine-rich sequence as a synthesized template. The fluorescence properties of the DNA-AgNCs are related to the modified position of the DNA. When biotin is linked to the middle thymine base of the DNA sequence, the DNA-AgNCs emit the strongest fluorescence. Moreover, the stability of the DNA-AgNCs was affected by avidin through biotin-avidin binding, quenching the fluorescence of the DNA-AgNCs. In contrast, if free biotin is further introduced into this system, the quenching is apparently weakened by competition, leading to the restoration of fluorescence. This phenomenon can be utilized for the detection of biotin. Under the optimal conditions, the fluorescence recovery is linearly proportional to the concentration of biotin in the range of 10 nM-1.0 μM with a detection limit of 6.0 nM. This DNA-AgNCs probe with excellent fluorescent properties is sensitive and selective for the detection of biotin and has been applied for the determination of biotin in wheat flour.

Fabrication of graphene–biomacromolecule hybrid materials for tissue engineering application

In this review, we demonstrated the recent advances in the fabrication strategies of graphene–biomacromolecule hybrid materials and their applications in the field of tissue engineering, such as implant materials, cell culture scaffolds, and regenerative medicine.

The analysis of proteins and small molecules based on sterically tunable nucleic acid hyperbranched rolling circle amplification

In this work, we succeeded in establishing a new method for proteins and small molecules analysis based on the small molecule-linked DNA and nucleic acid hyperbranched rolling circle amplification (HRCA). Small molecule linked DNA by chemical modification was used as a flexible tool to study protein-small molecule interactions. The HRCA reaction which would produce signal amplification was regulated by the steric effect depending on whether the target proteins were present. In the implement of the proposed strategy, streptavidin (SA)-biotin and anti-digoxin antibody (anti-Dig)-digoxin were chosen as two model partners. Experimental results showed that the quantitative detection of SA and anti-Dig was realized both with nanomolar detection limits. The small molecules biotin and digoxin were also detected at nanomolar levels in a wide range of 1nM~100µM and 1nM~10µM, respectively. Meanwhile, the results indicated that the method had a favorable specificity in analyzing proteins or small molecules. Thus, it may be expected to quantitatively analyze some protein markers and small molecular drugs in complex biological samples.

When biomolecules meet graphene: from molecular level interactions to material design and applications

Graphene-based materials have attracted increasing attention due to their atomically-thick two-dimensional structures, high conductivity, excellent mechanical properties, and large specific surface areas. The combination of biomolecules with graphene-based materials offers a promising method to fabricate novel graphene-biomolecule hybrid nanomaterials with unique functions in biology, medicine, nanotechnology, and materials science. In this review, we focus on a summarization of the recent studies in functionalizing graphene-based materials using different biomolecules, such as DNA, peptides, proteins, enzymes, carbohydrates, and viruses. The different interactions between graphene and biomolecules at the molecular level are demonstrated and discussed in detail. In addition, the potential applications of the created graphene-biomolecule nanohybrids in drug delivery, cancer treatment, tissue engineering, biosensors, bioimaging, energy materials, and other nanotechnological applications are presented. This review will be helpful to know the modification of graphene with biomolecules, understand the interactions between graphene and biomolecules at the molecular level, and design functional graphene-based nanomaterials with unique properties for various applications.

A dual-signal strategy for the solid detection of both small molecules and proteins based on magnetic separation and highly fluorescent copper nanoclusters

Recently, a variety of analytical methods for the detection of small molecules or proteins based on small molecule-protein interaction have been developed. However, these methods often focus on either small molecules or proteins. Few efforts are made to detect both of them in the same system. In this work, a dual-signal strategy for the solid detection of both small molecules and proteins based on small molecule-protein interaction is proposed by using the streptavidin-biotin couple as a model. In our strategy, magnetic nanoparticles (MNPs) are adopted for target separation, and highly fluorescent copper nanoclusters (CuNCs) are synthesized in situ to give signals. In the absence of the targets, CuNCs are associated with the MNPs and present in the precipitate under magnetic field; whereas in the presence of either streptavidin or biotin, the CuNCs will present in the supernate. By monitoring the fluorescent intensity of each, dual-signal can be obtained for the solid detection of either the protein or the small molecule. Results show that sensitive and specific detection of both streptavidin (detection limit: 0.47nM) and biotin (detection limit: 3.1nM) can be achieved. This method can be extended for the detection of other small molecule-protein couples, and thereby has the potential for biomedical and clinical applications.

A label-free colorimetric sensor for Pb2+ detection based on the acceleration of gold leaching by graphene oxide

In this work, we developed a novel, label-free, colorimetric sensor for Pb(2+) detection based on the acceleration of gold leaching by graphene oxide (GO) at room temperature. Gold nanoparticles (AuNPs) can be dissolved in a thiosulfate (S2O3(2-)) aqueous environment in the presence of oxygen; however, the leaching rate is very slow due to the high activation energy (27.99 kJ mol(-1)). In order to enhance the reaction rate, some accelerators should be added. In comparison with the traditional accelerators (metal ions or middle ligands), we found that GO could efficiently accelerate the gold leaching reaction. Kinetic data demonstrate that the dissolution rate of gold in the Pb(2+)-S2O3(2-)-GO system is 5 times faster than that without GO at room temperature. In addition, the effects of surface modification and the nanoparticle size on the etching of AuNPs were investigated. Based on the GO-accelerated concentration-dependent colour changes of AuNPs, a colorimetric sensor for Pb(2+) detection was developed with a linear range from 0.1 to 20 μM and the limit of detection (LOD) was evaluated to be 0.05 μM. This colorimetric assay is simple, low-cost, label-free, and has numerous potential applications in the field of environmental chemistry.

Modulation of the optical transmittance in monolayer graphene oxide by using external electric field

Graphene oxide (GO) emerges as a functional material in optoelectronic devices due to its broad spectrum response and abundant optical properties. In this article, it is demonstrated that the change of optical transmittance amplitude for monolayer GO (mGO) could be up to 24.8% by an external electric field. The frequency harmonics for transmittance spectra are analyzed by use of Fast Fourier Transforms to give an insight into the modulation mechanism. Two physical models, the electrical permittivity and the sheet conductivity which linearly vary as the electric field, are proposed to response for the transmittance modulation. The model-based simulations agree reasonable well with the experimental results.

The graphene/nucleic acid nanobiointerface

In this critical review, we present the recent advances in the design and fabrication of graphene/nucleic acid nanobiointerfaces, as well as the fundamental understanding of their interfacial properties and various nanobiotechnological applications.

Organic liquids-responsive β-cyclodextrin-functionalized graphene-based fluorescence probe: label-free selective detection of tetrahydrofuran

In this study, a label-free graphene-based fluorescence probe used for detection of volatile organic liquids was fabricated by a simple, efficient and low-cost method. To fabricate the probe, a bio-based β-cyclodextrin (β-CD) was firstly grafted on reduced graphene surfaces effectively and uniformly, as evidenced by various characterization techniques such as Ultraviolet/Visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The subsequent inclusion of Rhodamine B (RhB) into the inner cavities of the β-CD grafted on the graphene surfaces was achieved easily by a solution mixing method, which yielded the graphene-based fluorescent switch-on probe. In addition, the gradual and controllable quenching of RhB by Fluorescence Resonance Energy Transfer from RhB to graphene during the process of stepwise accommodation of the RhB molecules into the β-CD-functionalized graphene was investigated in depth. A wide range of organic solvents was examined using the as-fabricated fluorescence probe, which revealed the highest sensitivity to tetrahydrofuran with the detection limit of about 1.7 μg/mL. Some insight into the mechanism of the different responsive behaviors of the fluorescence sensor to the examined targets was also described.

Terminal protection of small molecule-linked DNA for small molecule-protein interaction assays

Methods for the detection of specific interactions between diverse proteins and various small-molecule ligands are of significant importance in understanding the mechanisms of many critical physiological processes of organisms. The techniques also represent a major avenue to drug screening, molecular diagnostics, and public safety monitoring. Terminal protection assay of small molecule-linked DNA is a demonstrated novel methodology which has exhibited great potential for the development of simple, sensitive, specific and high-throughput methods for the detection of small molecule–protein interactions. Herein, we review the basic principle of terminal protection assay, the development of associated methods, and the signal amplification strategies adopted for performance improving in small molecule–protein interaction assay.