Biointerface by cell growth on layered graphene-artificial peroxidase-protein nanostructure for in situ quantitative molecular detection

A chemically modified DNAzyme-based electrochemical sensor for binary and highly sensitive detection of reactive oxygen species

Reactive oxygen species (ROS) play a critical role in regulating various physiological processes. To gain a comprehensive understanding of their distinct functions in different physiological events, it is imperative to detect binary ROS simultaneously. However, the development of the sensing method capable of binary ROS detection remains a significant challenge. In this study, we address this challenge by integrating chemically modified DNAzyme probes with a functionalized metal-organic framework (MOF) to create an efficient electrochemical sensing platform for the binary detection of ROS. ROS targets would activate the DNAzyme cleavage activity by removing the phenylboronate (BO) and phosphorothioate (PS) modifications, leading to the controlled release of doxorubicin (DOX) and methylene blue (MB) enclosed within MOF nanocomposites. This process generates two distinct voltammetric current peaks, with their potentials and intensities reflecting the identity and concentration of the ROS targets. The sensor demonstrates simultaneous detection of multiple ROS (H2O2 and HClO) produced by cancer cells with high sensitivity across a broad linear range of 1 to 200 nM and a low detection limit in the sub-nanomolar range. The design strategies behind the developed ROS sensing system could also be exploited to create other biosensors with highly sensitive and binary detection to promote clinical research and revolutionize disease diagnostics.

Quantum Dot/TiO2 Nanocomposite-Based Photoelectrochemical Sensor for Enhanced H2O2 Detection Applied for Cell Monitoring and Visualization

This work exploits the possibility of using CdSe/ZnS quantum dot (QD)-electrodes to monitor the metabolism of living cells based on photoelectrochemical (PEC) measurements. To realize that, the PEC setup is improved with respect to an enhanced photocurrent signal, better stability, and an increased signal-to-noise ratio, but also for a better biocompatibility of the sensor surface on which cells have been grown. To achieve this, a QD-TiO2 heterojunction is introduced with the help of atomic layer deposition (ALD). The heterojunction reduces the charge carrier recombination inside the semiconductor nanoparticles and improves the drift behavior. The PEC performance is carefully analyzed by adjusting the TiO2 thickness and combining this strategy with multilayer immobilizations of QDs. The optimal thickness of this coating is ≈5 nm; here, photocurrent generation can be enhanced significantly (e.g., for a single QD layer electrode by more than one order of magnitude at 0 V vs Ag/AgCl). The resulting optimized electrode is used for hydrogen peroxide (H2O2) sensing with a good sensitivity down to µmolar concentrations, reusability, stability, response rate, and repeatability. Finally, the sensing system is applied to monitor the activity of cells directly grown on top of the electrode surface.

PBA-Derived Heteroatom-Doped Mesoporous Graphitic Spheroids as Peroxidase Nanozyme for In Vitro Tumor Cells Detection

Inspired by the two kinds of naturally occurring peroxidases (POD) with vanadium or heme (iron)-based active catalytic centers, we have developed a dual metal-based nanozyme with dual V and Fe-based active catalytic centers. Co-doping of graphene with heteroatoms has a synergistic effect on the catalytic properties of the nanomaterial as the distances of migration of the substrates drastically reduce. However, a few studies have reported the codoping of heterometallic elements in the graphene structure due to the complexity of the synthesis procedures. Herein, we report the synthesis of in situ doped bimetallic VNFe@C mesoporous graphitic spheroids nanozyme via pyrolysis without the assistance of any template assisted method. The Prussian-blue analog-based precursor material was synthesized by a facile one-step low-temperature synthesis procedure. The bimetallic spheroids showed an excellent affinity toward H2O2, with a Km value of 0.26 mM when compared to 0.436 for the natural POD, which is much better than the natural POD, which was utilized to detect tumor cells in vitro through the intracellular H2O2 produced by these cells under high oxidative stress. The VNFe@C mesoporous spheroids generate dual reactive oxygen species, including the •OH and •O2H- radicals, in the presence of H2O2, which are responsible for the POD-like activity of these nanozymes, while the bimetallic V/Fe doping plays a synergistic role in the enhancement of the activity of codoped graphitic spheroids.

Integrated Sandwich-Paper 3D Cell Sensing Device to In Situ Wirelessly Monitor H2O2 Released from Living Cells

Point-of-care testing (POCT) has attracted great interest because of its prominent advantages of rapidness, precision, portability, and real-time monitoring, thus becoming a powerful biomedical device in early clinical diagnosis and convenient medical treatments. However, its complicated manufacturing process and high expense severely impede mass production and broad applications. Herein, an innovative but inexpensive integrated sandwich-paper three-dimensional (3D) cell sensing device is fabricated to in situ wirelessly detect H2O2 released from living cells. The paper-based electrochemical sensing device was constructed by a sealed sandwiched bottom plastic film/fiber paper/top hole-centered plastic film that was printed with patterned electrodes. A new (Fe, Mn)3(PO4)2/N-doped carbon nanorod was developed and immobilized on the sensing carbon electrode while cell culture solution filled the exposed fiber paper, allowing living cells to grow on the fiber paper surrounding the electrode. Due to the significantly shortening diffusion distance to access the sensing sites by such a unique device and a rationally tuned ratio of Fe2+/Mn2+, the device exhibits a fast response time (0.2 s), a low detection limit (0.4 μM), and a wide detection range (2-3200 μM). This work offers great promise for a low-cost and highly sensitive POCT device for practical clinic diagnosis and broad POCT biomedical applications.

Fluorescent sensor based on PtS2-PEG nanosheets with peroxidase-like activity for intracellular hydrogen peroxide detection and imaging

Hydrogen peroxide (H₂O₂) is produced in living organisms and is involved in a variety of redox-regulated processes. Therefore, the detection of H₂O₂ is important for tracing the molecular mechanisms of some biological events. Here, we demonstrated for the first time the peroxidase activity of PtS₂-PEG NSs under the physiological conditions. PtS₂ NSs were synthesized by mechanical exfoliation followed by functionalization with polyethylene glycol amines (PEG-NH₂) to improve their biocompatibility and physiological stability. Fluorescence was generated by catalyzing the oxidation of o-phenylenediamine (OPD) by H₂O₂ in the presence of the PtS₂ NSs. The proposed sensor had a limit of detection (LOD) of 248 nM and a detection range of 0.5-50 μM in the solution state, which was better than or comparable to previous reports in the literature. The developed sensor was further applied for the detection of H₂O₂ released from cells as well as for imaging studies. The results show that the sensor is promising for future applications in clinical analysis and pathophysiology.

Potassium cobalt hexacyanoferrate as a peroxidase mimic for electrochemical immunosensing of Lactobacillus rhamnosus GG

In this paper, the potassium cobalt hexacyanoferrate (II), K₂CoFe(CN)₆, with peroxidase-like activity was used for the fabrication of a novel label-free Lactobacillus rhamnosus GG (LGG) electrochemical immunosensor. The K₂CoFe(CN)₆ nanocubes were made by a simple hydrothermal method and followed by low-temperature calcination. In addition to structural characterization, the peroxidase-mimicking catalytic property of the material was confirmed by a chromogenic reaction. It is known that H₂O₂ can oxidize electroactive thionine molecules under the catalysis of horseradish peroxidase (HRP). In this nanozyme-based electrochemical immunoassay, due to the steric hindrance, the formation of immune-complex of LGG and LGG antibody on the modified GCE inhibits the catalytic activity of the peroxidase mimics of K₂CoFe(CN)₆ and thus reduced the current signal. Therefore, the developed electrochemical immunosensor achieved quantitative detection of LGG. Under optimal conditions, the linear range of the sensor was obtained from 10¹ to 10⁶ CFU mL^-1 with a minimum detection limit (LOD) of 12 CFU mL^-1. Furthermore, the immunosensor was successfully applied in the quantitative detection of LGG in dairy product samples with recoveries ranging from 93.2% to 106.8%. This protocol presents a novel immunoassay method, which provides an alternative implementation pathway for the quantitative detection of microorganisms.

Three-dimensional flexible and stretchable gold foam scaffold for real-time electrochemical sensing in cells and in vivo

Compared with typical two-dimensional electrodes, the three-dimensional (3D) cell culture platform can simulate the real cell survival environment for cell growth to accurately reproduce cell functions. Moreover, considering that living cells are exposed to various of mechanical force in the microenvironment, the construction of 3D electrodes with excellent flexible, stretchable, and biocompatibility is of great significance to real-time monitor mechanically evoked biomolecule release from cells. Herein, we demonstrated a straightforward and effective three-step approach to fabricate three-dimensional flexible and stretchable gold foam scaffold (3D Au foam scaffold) for construction of 3D cell culture integrated electrochemical sensing platform. The excellent biological and electrical properties of Au nanostructures and porous networks of the 3D scaffold endow the platform with desirable biocompatibility and sensitive electrochemical sensing performance. As a proof of concept, the 3D Au foam scaffold functionalized with cobalt based nanocubes (Co NCs/Au foam scaffold) was validated to provide 3D culture for human umbilical vein endothelial cells (HUVECs), and synchronously real-time monitor superoxide anion (O₂^•-) released by HUVECs under mechanical stretching. Furthermore, 3-mercaptopropionic acid (3-MPA) modified 3D Au foam (3-MPA/Au foam scaffold) was successfully used for real-time monitoring of catecholamines in rat brain. The results demonstrate the great potential of this 3D Au foam scaffold for real-time electrochemical monitoring biomolecules in vitro and in vivo, providing convenience for future research on mechanotransduction relevant processes.

2D Co3O4 modified by IrO2 nanozyme for convenient detection of aqueous Fe2+ and intercellular H2O2

A portable sensor for visual monitoring of Fe²⁺ and H₂O₂, two-dimensional Co₃O₄ modified by nano-IrO₂ (IrO₂@2D Co₃O₄) was prepared in this work, for the first time, with the help of microwave radiation at 140 °C, which was further stabilized onto common test strips. The present IrO₂@2D Co₃O₄ possessed superior dual-function enzyme-like activity with low toxicity and excellent biocompatibility. Especially, trace Fe²⁺ and H₂O₂ could exclusively alter their enzyme-like catalytic activity with discriminating hyperchromic or hypochromic effect, i.e., from blue to colorless or to dark blue for both IrO₂@2D Co₃O₄ dispersion and its functionalized test strips. The linear regression equations were A₆₅₂ = 0.5940 - 0.00041 c_Fe²⁺ (10^-8 M, R² = 0.9927) for Fe²⁺ and ∆A₆₅₂ = 0.0023 c_H2O2 + 0.00025 (10^-7 M, R² = 0.9982) for H₂O₂, respectively. When applied to visual monitoring of aqueous Fe²⁺ and intercellular H₂O₂, the recoveries were 101.2 ~ 102.5% and 95.8 ~ 103.7% with detection limits of 1.25 × 10^-8 mol/L and 1.02 × 10^-7 mol/L, respectively, far below the permitted values in drinking water set by the World Health Organization. The mechanisms for the enhancing enzyme-mimetic activity of IrO₂@2D Co₃O₄ and its selective responses to Fe²⁺ and H₂O₂ were investigated in detail.

Preparation of a pH-responsive controlled-release electrochemical immunosensor based on polydopamine encapsulation for ultrasensitive detection of alpha-fetoprotein

To accomplish ultra-sensitive detection of alpha-fetoprotein(AFP), a novel electrochemical immunosensor using polydopamine-coated Fe₃O₄ nanoparticles (PDA@Fe₃O₄ NPs) as a smart label and polyaniline (PANI) and Au NPs as substrate materials has been created. The sensor has the following advantages over typical immunoassay technology: (1) The pH reaction causes PDA@Fe₃O₄ NPs to release Prussian blue (PB) prosoma while also destroying the secondary antibody label and immunological platform and lowering electrode impedance; (2) PB has a highly efficient catalytic effect on H₂O₂, allowing for the obvious amplification of electrical impulses; (3) PANI was electrodeposited on the electrode surface to avoid PB loss and signal leakage, which effectively absorbed and fixed PB while considerably increasing electron transmission efficiency. The sensor's detection limit was 0.254 pg·mL^-1 (S/N = 3), with a detection range of 1 pg·mL^-1 to 100 ng·mL^-1. The sensor has a high level of selectivity, repeatability, and stability, and it is predicted to be utilized to detect AFP in real-world samples.

Guided Synthesis of a Mo/Zn Dual Single-Atom Nanozyme with Synergistic Effect and Peroxidase-like Activity

We present a facile route towards a dual single-atom nanozyme composed of Zn and Mo, which utilizes the non-covalent nano-assembly of polyoxometalates, supramolecular coordination complexes as the metal-atom precursor, and a macroscopic amphiphilic aerogel as the supporting substrate. The dual single-atoms of Zn and Mo have a high content (1.5 and 7.3 wt%, respectively) and exhibit a synergistic effect and a peroxidase-like activity. The Zn/Mo site was identified as the main active center by X-ray absorption fine structure spectroscopy and density functional theory calculation. The detection of versatile analytes, including intracellular H₂ O₂ , glucose in serum, cholesterol, and ascorbic acid in commercial beverages was achieved. The nanozyme has an outstanding stability and maintained its performance after one year's storage. This study develops a new peroxidase-like nanozyme and provides a robust synthetic strategy for single-atom catalysts by utilizing an aerogel as a facile substrate that is capable of stabilizing various metal atoms.

Template-Regulated Bimetallic Sulfide Nanozymes with High Specificity and Activity for Visual Colorimetric Detection of Cellular H2O2

For the past several decades, most of the research studies on nanozymes have been aimed at improving their catalytic activity and diversity; however, developing nanozymes with strong catalytic activity and great specificity remains a challenge. Herein, a simple and efficient template synthesis method was used to synthesize bimetallic sulfide nanoparticles, NiCo₂S₄ NPs, and prove that they have excellent peroxidase-like activity with good specificity. By regulating polyvinyl pyrrolidone (PVP) and hexadecyl trimethyl ammonium bromide as the templating agent, we have obtained the NiCo₂S₄ (PVP) NPs with a high Ni/Co ratio, thus exhibiting superior peroxidase activity. In addition, the NiCo₂S₄ NPs selectively catalyzed and oxidized colorless 3,3,5,5-tetramethylbenzidine (TMB). On being treated with H₂O₂, TMB turns blue while other substrates did not undergo the oxidation reaction under the same conditions, such as 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium (ABTS) and dopamine. The high specificity of NiCo₂S₄ NPs is due to the strong electrostatic driving coordination between negatively charged NiCo₂S₄ NPs and positively charged TMB. Due to the peroxidase activity of the developed NiCo₂S₄ NPs, a simple, low-cost, and reliable colorimetric method was established. Simultaneously, this method for in situ quantitative monitoring of H₂O₂ produced by MDA-MB-231 cells was also achieved. This study has provided a theoretical basis for the improvement of the activity and specificity of bimetallic sulfide nanozymes and may offer guidance for the further reasonable design of related materials.

Amplified electrochemical biosensing based on bienzymatic cascade catalysis confined in a functional DNA structure

Herein, an amplified and renewable electrochemical biosensor was developed via bienzymatic cascade catalysis of glucose oxidase (GOx) and horseradish peroxidase (HRP), which were confined in a functional Y-shaped DNA nanostructure oriented by a dual-thiol-ended hairpin probe (dSH-HP) with a paired stem as a rigid scaffold and unpaired loop as enclosed binding platform. For proof-of-concept assay of sequence-specific biomarker DNA related to Alzheimer's disease (aDNA), GOx and redox ferrocene-modified HRP (Fc@HRP) were chemically conjugated in two enzyme strands (GOx-ES1 and Fc@HRP-ES2), respectively. The repeated recycling of aDNA was powered by the displacement of GOx-ES1 by aDNA and exonuclease III (ExoIII)-assisted cleavage reaction for amplified output of numerous GOx-ES1 as dependent transducers, together with Fc@HRP-ES2 which was simultaneously hybridized with dSH-HP to assemble this DNA structure. Rationally, the bienzymatic cascade catalysis was motivated through GOx-catalyzed glucose oxidization to in situ generate hydrogen peroxide (H₂O₂) and overlapped HRP-catalyzed H₂O₂ decomposition to promote the electron transfer, producing significantly enhanced electrochemical signal of Fc with an ultrahigh sensitivity down to 0.22 fM of aDNA. Benefited from the unique design of dSH-HP-oriented bienzymatic cascades, this one-step strategy without non-specific blockers passivation was simple and renewable, and would pave a promising avenue for sensitive electrochemical assay of biomolecules.

Fe-MOGs-based enzyme mimetic and its mediated electrochemiluminescence for in situ detection of H2O2 released from Hela cells

Enzyme mimetics have attracted wide interest due to their inherent enzyme-like activity and unique physicochemical properties, as well as promising applications in disease diagnosis, treatment and monitoring. Inspired by the attributes of nonheme iron enzymes, synthetic models were designed to mimic their capability and investigate the catalytic mechanisms. Herein, metal-organic gels (Fe-MOGs) with horseradish peroxidase (HRP) like Fe-N_X structure were successfully synthesized though the coordination between iron and 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) and exhibited excellent peroxidase-like activity. Its structure-activity relationship and the in-situ electrochemiluminescence (ECL) detection of H₂O₂ secreted by Hela cells were further investigated. The highly dispersed Fe-N_X active sites inside Fe-MOGs were able to catalyze the decomposition of H₂O₂ into large amounts of reactive oxygen species (ROS) via a Fenton-like reaction under a low overpotential. Due to the accumulation of ROS free radicals, the luminol ECL emission was significantly amplified. A proof-of-concept biosensor was constructed with a detection limit as low as 2.2 nM and a wide linear range from 0.01 to 40 μM. As a novel metal organic gels based enzyme mimetic, Fe-MOGs show great promises in early cancer detection and pathological process monitoring.

The mechanisms of HSA@PDA/Fe nanocomposites with enhanced nanozyme activity and their application in intracellular H2O2 detection

Nanozymes have drawn increasing attention with their broad applications but most nanozymes lack enzyme-like molecular structures, resulting in weak selectivity and low activity. Bioinspired molecular assembly provides an extremely promising strategy to mimic natural enzyme processes and develop function enhanced architectures. Herein, a new bioinspired molecular assembly strategy based on human serum albumin@polydopamine/Fe nanocomposites (HSA@PDA/Fe NCs) was proposed, in which Fe(iii)/Fe(ii) were anchored on HSA supported on PDA. HSA@PDA/Fe NCs with iron as the active center and HSA@PDA as the skeleton showed excellent peroxidase-like activity, which was nearly 1000 times higher than that of free Fe(iii). This may be attributed to the phenomenon that the cycle of quinones and the hydroxyl group on the nanocomposite surface greatly accelerate the conversion of Fe(iii)/Fe(ii) in acidic microenvironments. Systematic experimental studies illustrated that its activity was mainly affected by the metal active center, followed by the polymeric ligand, while the protein framework has little effect on its activity. Meanwhile, even after freeze-thaw and thermal cycle tests, it also showed excellent catalytic stability. Besides, a colorimetric assay based on HSA@PDA/Fe NCs was developed for detection of H₂O₂in vitro and in situ detection of H₂O₂ generated from live cells. This work will facilitate the developments on theoretical analysis, rational design and practical applications of nanozymes based on bioinspired molecular assemblies.

Stretchable Electrode Based on Au@Pt Nanotube Networks for Real-Time Monitoring of ROS Signaling in Endothelial Mechanotransduction

Vascular endothelial cells (ECs) are natively exposed to dynamic cyclic stretch and respond to it by the production of vasoactive molecules. Among them, reactive oxygen species (ROS) are closely implicated to the endothelial function and vascular homeostasis. However, the dynamic monitoring of ROS release during endothelial mechanotransduction remains a steep challenge. Herein, we developed a stretchable electrochemical sensor by decoration of uniform and ultrasmall platinum nanoparticles (Pt NPs) on gold nanotube (Au NT) networks (denoted as Au@Pt NTs). The orchestrated structure exhibited prominent electrocatalytic property toward the oxidation of hydrogen peroxide (H₂O₂) (as the most stable ROS) while maintaining excellent mechanical compliance of Au NT networks. Moreover, the favorable biocompatibility of Au NTs and Pt NPs promoted the adhesion and proliferation of ECs cultured thereon. These allowed in situ inducing ECs mechanotransduction and synchronously real-time monitoring of H₂O₂ release. Further investigation revealed that the production of H₂O₂ was positively correlated with the applied mechanical strains and could be boosted by other coexisting pathogenic factors. This indicates the great prospect of our proposed sensor in exploring ROS-related signaling for the deep understanding of cell mechanotransduction and vascular disorder.

A controllable synthesis of hollow pumpkin-like CuO/Cu2O composites for ultrasensitive non-enzymatic glucose and hydrogen peroxide biosensors

Different ratios of hollow pumpkin-like CuO/Cu₂O composites are investigated and their remarkable catalytic capability for glucose and H₂O₂ detection are demonstrated.

2D Materials in Development of Electrochemical Point-of-Care Cancer Screening Devices

Effective cancer treatment requires early detection and monitoring the development progress in a simple and affordable manner. Point-of care (POC) screening can provide a portable and inexpensive tool for the end-users to conveniently operate test and screen their health conditions without the necessity of special skills. Electrochemical methods hold great potential for clinical analysis of variety of chemicals and substances as well as cancer biomarkers due to their low cost, high sensitivity, multiplex detection ability, and miniaturization aptitude. Advances in two-dimensional (2D) material-based electrochemical biosensors/sensors are accelerating the performance of conventional devices toward more practical approaches. Here, recent trends in the development of 2D material-based electrochemical biosensors/sensors, as the next generation of POC cancer screening tools, are summarized. Three cancer biomarker categories, including proteins, nucleic acids, and some small molecules, will be considered. Various 2D materials will be introduced and their biomedical applications and electrochemical properties will be given. The role of 2D materials in improving the performance of electrochemical sensing mechanisms as well as the pros and cons of current sensors as the prospective devices for POC screening will be emphasized. Finally, the future scopes of implementing 2D materials in electrochemical POC cancer diagnostics for the clinical translation will be discussed.

Fe-N-C Single-Atom Nanozymes for the Intracellular Hydrogen Peroxide Detection

Recently, in situ detection of hydrogen peroxide (H₂O₂) generated from live cells have caused tremendous attention, because it is of great significance in the control of multiple biological processes. Herein, Fe-N-C single-atom nanozymes (Fe-N-C SAzymes) with intrinsic peroxidase-like activity were successfully prepared via high-temperature calcination using FeCl₂, glucose, and dicyandiamide as precursors. The Fe-N-C SAzymes with FeN_x as active sites were similar to natural metalloproteases, which can specifically enhance the peroxidase-like activity rather than oxidase-like activity. Accordingly, owing to the excellent catalytic efficiency of the Fe-N-C SAzymes, colorimetric biosensing of H₂O₂ in vitro was performed via a typical 3,3',5,5'-tetramethylbenzidine induced an allochroic reaction, demonstrating the satisfactory specificity and sensitivity. With regard to the practical application, in situ detection of H₂O₂ generated from the Hela cells by the Fe-N-C SAzymes was also performed, which can expand the applications of the newborn SAzymes.

Atomic matching catalysis to realize a highly selective and sensitive biomimetic uric acid sensor

A main challenge for biomimetic non-enzyme biosensors is to achieve high selectivity. Herein, an innovative biomimetic non-enzyme sensor for electrochemical detection of uric acid (UA) with high selectivity and sensitivity is realized by growing Prussian blue (PB) nanoparticles on nitrogen-doped carbon nanotubes (N-doped CNTs). The enhancement mechanism of the biomimetic UA sensor is proposed to be atomically matched active sites between two reaction sites (oxygen atoms of 2, 8-trione, 6.9 Å) of UA molecule and two redox centers (Fe^II on the diagonal, 7.2 Å) of PB. Such an atomically matching manner not only promotes strong adsorption of UA on PB but also selectively enhances electron transfer between reaction sites of UA and active Fe^II centers of PB. This biomimetic UA sensor can offer great selectivity to avoid interferences from other oxidative and reductive species, showing excellent selectivity. An electrochemical biomimetic sensor based on PB/N-doped CNTs was applied to in situ detect UA in human serum, delivering a wide dynamic detection range (0.001-1 mM) and a low detection limit (0.26 μM). This work provides a high-performance UA sensor while shedding a scientific light on using atomic matching catalysis to fabricate highly sensitive and selective biomimetic sensors.

Conductive Polymer Coated Scaffold to Integrate 3D Cell Culture with Electrochemical Sensing

Remarkable progresses have been made in electrochemical monitoring of living cells based on one-dimensional (1D) or two-dimensional (2D) sensors, but the cells cultured on 2D substrate under these circumstances are departed from their three-dimensional (3D) microenvironments in vivo. Significant advances have been made in developing 3D culture scaffolds to simulate the 3D microenvironment yet most of them are insulated, which greatly restricts their application in electrochemical sensing. Herein, we propose a versatile strategy to endow 3D insulated culture scaffolds with electrochemical performance while granting their biocompatibility through conductive polymer coating. More specifically, 3D polydimethylsiloxane scaffold is uniformly coated by poly(3,4-ethylenedioxythiophene) and further modified by platinum nanoparticles. The integrated 3D device demonstrates desirable biocompatibility for long-term 3D cell culture and excellent electrocatalytic ability for electrochemical sensing. This allows real-time monitoring of reactive oxygen species release from cancer cells induced by a novel potential anticancer drug and reveals its promising application in cancer treatment. This work provides a new idea to construct 3D multifunctional electrochemical sensors, which will be of great significance for physiological and pathological research.

Bio-inspired nitric-oxide-driven nanomotor

Current chemical-fuel-driven nanomotors are driven by gas (e.g. H₂, O₂, NH₃) which only provides motion ability, and can produce waste (e.g. Mg(OH)₂, Pt). Here, inspired by endogenous biochemical reactions in the human body involving conversion of amino acid L-arginine to nitric oxide (NO) by NO synthase (NOS) or reactive oxygen species (ROS), we report on a nanomotor made of hyperbranched polyamide/L-arginine (HLA). The nanomotor utilizes L-arginine as fuel for the production of NO both as driving force and to provide beneficial effects, including promoting endothelialisation and anticancer effects, along with other beneficial by-products. In addition, the HLA nanomotors are fluorescent and can be used to monitor the movement of nanomotors in vivo in the future. This work presents a zero-waste, self-destroyed and self-imaging nanomotor with potential biological application for the treatment of various diseases in different tissues including blood vessels and tumours.

Depletion of propellant in chemical-fuel-driven nanomotors is a limiting factor in device design and application. Here, the authors create a nitric-oxide-generating nanoparticle and explore cellular uptake and application of the nanomotors in nitric oxide treatments.

Comprehensive Application of Graphene: Emphasis on Biomedical Concerns

Graphene, sp² hybridized carbon framework of one atom thickness, is reputed as the strongest material to date. It has marked its impact in manifold applications including electronics, sensors, composites, and catalysis. Current state-of-the-art graphene research revolves around its biomedical applications. The two-dimensional (2D) planar structure of graphene provides a large surface area for loading drugs/biomolecules and the possibility of conjugating fluorescent dyes for bioimaging. The high near-infrared absorbance makes graphene ideal for photothermal therapy. Henceforth, graphene turns out to be a reliable multifunctional material for use in diagnosis and treatment. It exhibits antibacterial property by directly interacting with the cell membrane. Potential application of graphene as a scaffold for the attachment and proliferation of stem cells and neuronal cells is captivating in a tissue regeneration scenario. Fabrication of 2D graphene into a 3D structure is made possible with the help of 3D printing, a revolutionary technology having promising applications in tissue and organ engineering. However, apart from its advantageous application scope, use of graphene raises toxicity concerns. Several reports have confirmed the potential toxicity of graphene and its derivatives, and the inconsistency may be due to the lack of standardized consensus protocols. The present review focuses on the hidden facts of graphene and its biomedical application, with special emphasis on drug delivery, biosensing, bioimaging, antibacterial, tissue engineering, and 3D printing applications.

Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials

Electrically-transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high-performance electrically-transduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electrically-transduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical perspective, are summarized for four different groups of analytes: gases, volatile compounds, ions, and biomolecules. The sensing performance is discussed in the context of the molecular design, structure-property relationships, and device fabrication technology. The outlook of challenges and opportunities for 2D nanomaterials for the future development of electrically-transduced sensors is also presented.

Graphene-based advanced nanoplatforms and biocomposites from environmentally friendly and biomimetic approaches

Environmentally friendly and biomimetic approaches to fabricate graphene-based advanced nanoplatforms and biocomposites for biomedical applications are summarized in this review.

Nanostructured Nickel on Porous Carbon-Silica Matrix as an Efficient Electrocatalytic Material for a Non-Enzymatic Glucose Sensor

Nanostructured nickel on porous carbon-silica matrix (N-CS) has been synthesized using a sol gel process and subsequent pyrolysis treatment at a temperature of 650 °C. The morphology and microstructure of the N-CS sample has been investigated using XRD (X-ray Diffraction), SEM-EDS (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy), and BET (Brunauer-Emmett-Teller) analysis. The synthesized nanocomposite has been used for developing NCS-modified screen-printed electrodes (NCS-SPCEs) and was applied in the electrochemical monitoring of glucose. After electrochemical activation, via cycling the modified electrode in a potential window from 0 to 0.8 V in 0.1 M KOH solution, the fabricated NCS-SPCEs electrodes were evaluated for the voltammetric and amperometric determination of glucose. The developed sensors showed good sensing performance towards glucose, displaying a sensitivity of 585 µA/mM cm−1 in the linear range from 0.05 to 1.5 mM, a detection limit lower than 30 µM with excellent selectivity.

Cellular Signaling Pathways Activated by Functional Graphene Nanomaterials

The paper reviews the network of cellular signaling pathways activated by Functional Graphene Nanomaterials (FGN) designed as a platform for multi-targeted therapy or scaffold in tissue engineering. Cells communicate with each other through a molecular device called signalosome. It is a transient co-cluster of signal transducers and transmembrane receptors activated following the binding of transmembrane receptors to extracellular signals. Signalosomes are thus efficient and sensitive signal-responding devices that amplify incoming signals and convert them into robust responses that can be relayed from the plasma membrane to the nucleus or other target sites within the cell. The review describes the state-of-the-art biomedical applications of FGN focusing the attention on the cell/FGN interactions and signalosome activation.

Design of DNA-based innovative computing system of digital comparison

Despite great potential and extensive interest in developing biomolecule-based computing, the development of even basic molecular logic gates is still in its infancy. Digital comparator (DC) is the basic unit in traditional electronic computers, but it is difficult to construct a system for achieving large-scale integration. Here, we construct, for the first time, a novel logic computing system of DCs that can compare whether two or more numbers are equal. Our approach is by taking advantage of facile preparation and unique properties of graphene oxide and DNA. The DC system reported in this work is developed by the DNA hybridization and effective combination of GO and single-stranded DNA, which is regarded as the reacting platform. On the basis of this platform and reaction principle, we have developed 2-inputs, 3-inputs, and 4-inputs DCs to realize the comparison of two or more binary numbers. We predict that such a state-of-the-art logic system enables its functionality with large-scale input signals, providing a new direction toward prototypical DNA-based logic operations and promoting the development of advanced logic computing. STATEMENT OF SIGNIFICANCE: The overarching objective of this paper is to explore the construction of a novel DNA computing system of digital comparator driven by the interaction of DNA and graphene oxide (GO). GO can efficient bind the dye-labeled, single-stranded DNA probe and then quench its fluorescence. In the case of the target appearing, specific binding between the single-stranded probe and its target occurs, changing the conformation and relationship with GO, then restoring the fluorescence of the dye. We have developed the 2-inputs, 3-inputs, and 4-inputs digital comparator circuits, which are expected to realize the comparison of large-scale input signals and can avoid the problems of design complexity and manufacturing cost of integrated circuits in traditional computing.

Graphene-based nanomaterials in biosystems

Graphene-based nanomaterials have emerged as a novel type of materials with exceptional physicochemical properties and numerous applications in various areas. In this review, we summarize recent advances in studying interactions between graphene and biosystems. We first provide a brief introduction on graphene and its derivatives, and then discuss on the toxicology and biocompatibility of graphene, including the extracellular interactions between graphene and biomacromolecules, cellular studies of graphene, and in vivo toxicological effects. Next, we focus on various graphene-based practical applications in antibacterial materials, wound addressing, drug delivery, and water purification. We finally present perspectives on challenges and future developments in these exciting fields.

"Green-reduced" graphene oxide induces in vitro an enhanced biomimetic mineralization of polycaprolactone electrospun meshes

A novel green method for graphene oxide (GO) reduction via ascorbic acid has been adopted to realize bio-friendly reduced graphene oxide (RGO)/polycaprolactone (PCL) nanofibrous meshes, as substrates for bone tissue engineering applications. PCL fibrous mats enriched with either RGO or GO (0.25 wt%) were fabricated to recapitulate the fibrillar structure of the bone extracellular matrix (ECM) and the effects of RGO incorporation on the structural proprieties, biomechanics and bioactivity of the nano-composites meshes were evaluated. RGO/PCL fibrous meshes displayed superior mechanical properties (i.e. Young's Modulus and ultimate tensile strength) besides supporting noticeably improved cell adhesion, spreading and proliferation of fibroblasts and osteoblast-like cell lines. Furthermore, RGO-based electrospun substrates enhanced in vitro calcium deposition in the ECM produced by osteoblast-like cells, which was paralleled, in human mesenchymal stem cells grown onto the same substrates, by an increased expression of the osteogenic markers mandatory for mineralization. In this respect, the capability of graphene-based materials to adsorb osteogenic factors cooperates synergically with the rougher surface of RGO/PCL-based materials, evidenced by AFM analysis, to ignite mineralization of the neodeposited matrix and to promote the osteogenic commitment of the cultured cell in the surrounding microenvironment.

A multi-scale porous scaffold fabricated by a combined additive manufacturing and chemical etching process for bone tissue engineering

It is critical to develop a fabrication technology for precisely controlling an interconnected porous structure of scaffolds to mimic the native bone microenvironment. In this work, a novel combined process of additive manufacturing (AM) and chemical etching was developed to fabricate graphene oxide/poly(L-lactic acid) (GO/PLLA) scaffolds with multiscale porous structure. Specially, AM was used to fabricate an interconnected porous network with pore sizes of hundreds of microns. And the chemical etching in sodium hydroxide solution constructed pores with several microns or even smaller on scaffolds surface. The degradation period of the scaffolds was adjustable via controlling the size and quantity of pores. Moreover, the scaffolds exhibited surprising bioactivity after chemical etching, which was ascribed to the formed polar groups on scaffolds surfaces. Furthermore, GO improved the mechanical strength of the scaffolds.

Specific Oxygenated Groups Enriched Graphene Quantum Dots as Highly Efficient Enzyme Mimics

Significant progress is achieved for the utilization of graphene quantum dots as enzyme mimics in various biomedical fields recently. Although promising, the biocatalytic performance is far from satisfactory. Here, the rational design and synthesis of specific oxygenated groups enriched graphene quantum dots (o-GQDs) via a facile oxidation reflux route is reported. These well-prepared o-GQDs with uniform size exhibit an ultrahigh peroxidase-like activity in a wide range of pH values, and their superior performance is verified by using glucose detection as a typical model. Compared with classical nanozymes, these o-GQDs show multiple times higher enzymatic activity. It is believed that the super facile synthesis strategy can greatly facilitate the practical use of o-GQDs as enzyme mimics in the future.

Low-Molecular-Weight Hydrogels as New Supramolecular Materials for Bioelectrochemical Interfaces

Controlling the interface between biological tissues and electrodes remains an important challenge for the development of implantable devices in terms of electroactivity, biocompatibility, and long-term stability. To engineer such a biocompatible interface a low molecular weight gel (LMWG) based on a glycosylated nucleoside fluorocarbon amphiphile (GNF) was employed for the first time to wrap gold electrodes via a noncovalent anchoring strategy, that is, self-assembly of GNF at the electrode surface. Scanning electron microscopy (SEM) studies indicate that the gold surface is coated with the GNF hydrogels. Electrochemical measurements using cyclic voltammetry (CV) clearly show that the electrode properties are not affected by the presence of the hydrogel. This coating layer of 1 to 2 μm does not significantly slow down the mass transport through the hydrogel. Voltammetry experiments with gel coated macroporous enzyme electrodes reveal that during continuous use their current is improved by 100% compared to the noncoated electrode. This demonstrates that the supramolecular hydrogel dramatically increases the stability of the bioelectrochemical interface. Therefore, such hybrid electrodes are promising candidates that will both offer the biocompatibility and stability needed for the development of more efficient biosensors and biofuel cells.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.