Cu2O and Au/Cu2O particles: surface properties and applications in glucose sensing

Sunlight-Driven Photocatalytic Degradation of Methylene Blue with Facile One-Step Synthesized Cu-Cu2O-Cu3N Nanoparticle Mixtures

Sunlight-driven photocatalytic degradation is an effective and eco-friendly technology for the removal of organic pollutants from contaminated water. Herein, we describe the one-step synthesis of Cu-Cu₂O-Cu₃N nanoparticle mixtures using a novel non-aqueous, sol-gel route and their application in the solar-driven photocatalytic degradation of methylene blue. The crystalline structure and morphology were investigated with XRD, SEM and TEM. The optical properties of the as-prepared photocatalysts were investigated with Raman, FTIR, UV-Vis and photoluminescence spectroscopies. The influence of the phase proportions of Cu, Cu₂O and Cu₃N in the nanoparticle mixtures on the photocatalytic activity was also investigated. Overall, the sample containing the highest quantity of Cu₃N exhibits the highest photocatalytic degradation efficiency (95%). This enhancement is attributed to factors such as absorption range broadening, increased specific surface of the photocatalysts and the downward band bending in the p-type semiconductors, i.e., Cu₃N and Cu₂O. Two different catalytic dosages were studied, i.e., 5 mg and 10 mg. The higher catalytic dosage exhibited lower photocatalytic degradation efficiency owing to the increase in the turbidity of the solution.

Dancing in local space: rolling hoop orbital amplification combined with local cascade nanozyme catalytic system to achieve ultra-sensitive detection of exosomal miRNA

The exosomal miRNA (exo-miRNA) derived from tumor cells contains rich biological information that can effectively aid in the early diagnosis of disease. However, the extremely low abundance imposes stringent requirements for accurate detection techniques. In this study, a novel, protease-free DNA amplification strategy, known as “Rolling Hoop Orbital Amplification” (RHOA), was initially developed based on the design concept of local reaction and inspired by the childhood game of rolling iron ring. Benefiting from the local space constructed by the DNA orbital, the circular DNA enzyme rolls directionally and interacts efficiently with the amplification element, making it nearly 3-fold more productive than conventional free-diffusion amplification. Similarly, the localized cascade nanozyme catalytic system formed by bridging DNA probes also exhibits outperformed than free ones. Therefore, a localized energized high-performance electrochemiluminescence (ECL) biosensor was constructed by bridging cascading nanozymes on the electrode surface through DNA probes generated by RHOA, with an impressive limit of detection (LOD) of 1.5 aM for the detection of exosomal miRNA15a-5p and a stable linearity over a wide concentration range from 10^− 2 to 10⁸ fM. Thus, this work is a focused attempt at the localized reaction, which is expected to provide a reliable method for accurately detecting of exo-miRNAs.

Tuning the Redox Chemistry of Copper Oxide Nanoarchitectures Integrated with rGOP via Facet Engineering: Sensing H2S toward SRB Detection

The ultrasensitive determination of sulfate reducing bacteria (SRB) is of great significance for their crucial roles in environmental and industrial harms together with the early detection of microbial corrosion. In this work, we report the development of highly efficient electrocatalysts, i.e., Cu₂O-CuO extended hexapods (EHPs), which are wrapped on homemade freestanding graphene paper to construct a flexible paper electrode in the electrochemical sensing of the biomarker sulfide for SRB detection. Herein Cu₂O-CuO EHPs have been synthesized via a highly controllable and facile approach at room temperature, where the redox centers of copper oxide nanoarchitectures are tuned via facet engineering, and then they are deposited on the graphene paper surface through an electrostatic adsorption to enable homogeneous and highly dense distribution. Owing to the synergistic contribution of high electrocatalytic activity from the Cu mixed oxidation states and abundant catalytically active facets of Cu₂O-CuO EHPs and high electrical conductivity of the graphene paper electrode substrate, the resultant nanohybrid paper electrode has exhibited superb electrochemical sensing properties for H₂S with a wide linear range up to 352 μM and an extremely low detection limit (LOD) of 0.1 nM with a signal-to-noise ratio of 3 (S/N = 3), as well as high sensitivity, stability, and selectivity. Furthermore, taking advantage of the good biocompatibility and mechanical flexibility, the electrochemical sensing platform based on the proposed electrode has been applied in the sensitive detection of SRB in environmental samples through the sensing of sulfide from SRB, which holds great promise for on-site and online corrosion and environmental monitoring.

Biogenic-Mediated Synthesis of Mesoporous Cu2O/CuO Nano-Architectures of Superior Catalytic Reductive towards Nitroaromatics

Cu₂O/CuO nano-architectures were prepared by biogenic-mediated synthesis using pomegranate seeds extract as the reducing/stabilizing mediator during an aqueous solution combustion process of the Cu²⁺ precursor. The fabricated Cu₂O/CuO nanocomposite were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and nitrogen sorption. Nitrobenzene (NB) was applied a probe to test the catalytic activities of the fabricated Cu₂O/CuO nanocomposite. The results indicated that pomegranate seeds extract (PSE) manifest Cu₂O/CuO NPs of tiny particle size, larger pore volume and greater surface area compared to the bulky CuO synthesized in the absence of PSE. The surface area and total pore volume of Cu₂O/CuO NPs were 20.1 m² g⁻¹ and 0.0362 cm³ g⁻¹, respectively. The FESEM image shows the formation of broccoli-like architecture. The fabricated Cu₂O/CuO nanocomposite possesses surprising activity towards the reduction of nitro compounds in the presence of NaBH₄ into amino compounds with high conversion (94%). The reduction process was performed in water as a green solvent. Over four consecutive cycles the resulting nanocomposite also exhibits outstanding stability. In addition, the resulting Cu₂O/CuO nanocomposite suggested herein may encourage scientists to start preparing more cost-effective catalysts for marketing instead of complicated catalysts.

Towards one-step design of tailored enzymatic nanobiosensors

NP-based enzymatic biosensors were prepared by the simultaneous encapsulation of glucose and alcohol oxidases, Nafion and noble metal NPs via co-deposition from a phosphate multiple electrolyte on top of the sensor surface.

An amperometric biosensor based on Cu2O@Au nanocomposites for the detection of galectin-1 via lactose-galectin interactions

In this work, a novel label-free electrochemical biosensor is developed for the detection of galectin-1 (Gal-1) based on gold nanoparticle (AuNP) loaded octahedral Cu₂O (Cu₂O@Au) nanocomposites. The AuNPs on the surface of the Cu₂O nanocrystals not only enhance the electrochemical performance, but also serve as the binding sites for the lactose ligand which can specifically bind with Gal-1. The Cu₂O@Au nanocomposites provide the synergic effect of electrochemical signal amplification and lactose-galectin reaction as the recognition strategy. Under optimal conditions, the proposed biosensor exhibits a variation of electrochemical responses to different concentrations of Gal-1 ranging from 0.1 pg ml^-1 to 10 ng ml^-1. This work presents an alternative electrochemical biosensor for the detection of tumor biomarkers based on a simple and economical lactose ligand incorporated Cu₂O@Au biosensor platform.

pH-Control as a way to fine-tune the Cu/Cu2O ratio in radiation induced synthesis of Cu2O particles

In this work we have optimized the γ-radiation induced synthesis of Cu-Cu2O particles from aqueous CuSO4 solution by investigating the effect of pH. The obtained precipitate was analyzed by XRD and SEM techniques. The results indicated that at solution pH lower than 3.75, quasi-spherical Cu agglomerates can be formed while at pH higher than 4.40 only octahedron-shaped Cu2O particles are produced. At solution pH in the range from 3.75 to 4.40, a Cu-Cu2O mixture is produced. It was found that the relative amount of Cu2O in the Cu-Cu2O precipitate increases with pH in the studied range. The influence of solution pH on the Cu/Cu2O ratios in the product can be explained on the basis of pH-dependent competition kinetics between the reactions leading to either Cu or Cu2O formation. As a consequence, the composition and morphology of the Cu-Cu2O precipitate can be tuned by controlling pH of the aqueous CuSO4 solution during the γ-radiation induced synthesis.

Exploring the potential of electroless and electroplated noble metal-semiconductor hybrids within bio- and environmental sensing

Over the last two decades, the rapid development and widespread application of nanomaterials has significantly influenced research in various fields, including analytical chemistry and biosensing technologies. In particular, the simple functionalization and tuning of noble metal nanoparticle (NP) surface chemistry resulted in the development of a series of novel biosensing platforms with quick read-out and enhanced capabilities towards specific analyte detection. Moreover, noble metal NPs possess a number of unique properties, viz. high surface-to-volume ratio and excellent spectral, optical, thermal, electrical and catalytic characteristics. This manuscript provides an elaborate review on galvanic noble metal NPs deposited onto semiconductor surfaces, from the preparation stage towards their application in biosensors and gas sensing. Two types of deposition approaches, viz. galvanic displacement/electroless and conventional electroplating, are introduced and compared. Furthermore, the analytical merit of hybrid nanomaterials towards the improvement of sensing abilities is highlighted. Finally, some limitations and challenges related to progress in the development and application of analytical devices based on electroless and electroplated noble metal NPs-semiconductor hybrids (NMNPsHs) in biochemical and environmental sensing are discussed.

Facet-Inspired Core-Shell Gold Nanoislands on Metal Oxide Octadecahedral Heterostructures: High Sensing Performance toward Sulfide in Biotic Fluids

The development of structurally modified metal oxide heteroarchitectures with higher energy facets exposed has been of extensive research interests because of their unique construction and synergy effect of multifunctioning characteristics. In this study, we reported for the first time the development of a distinct type of gold nanoislands (AuNIs) on metal oxides (i.e., Cu₂O-CuO) octadecahedral (ODH) heterostructures through the galvanic exchange reaction, where Cu₂O not only acts as a stabilizer but also functions as a reductant. The electrocatalytic performance of the resultant core-shell Cu₂O-CuO@AuNI ODH-based electrochemical sensing platform has been evaluated in ultrasensitive detection of sulfide as early disease diagnostics and bacterial marker. Owing to the synergistic collaboration of enhanced surface active sites, exposed {110} crystallographic facets, mixed valances of copper that encourage redox reactions at electrode material/analyte interface, and the polarization effect provide by AuNIs decorated onto the Cu₂O surface, Cu₂O-CuO@AuNI ODH-modified electrode has demonstrated striking electrochemical sensing performance toward sulfide oxidation in terms of broad linear range, real detection limit down to 1 nM (S/N = 3), and incredible durability and reproducibility. In virtue of marvelous efficiency, the proposed electrochemical sensor based on Cu₂O-CuO@AuNI ODH has been employed in in situ sensitive detection of a ubiquitous amount of sulfide engendered by sulfate-reducing bacteria and real-time tracking of sulfide efflux from live cells as early diagnostic strategies.

Ni-introduced CuAu nanocages: facile co-reduction synthesis of a novel magnetic multi-metallic nanostructure with high peroxidase mimetic activity

We design a simple route for the synthesis of novel octahedral Ni-introduced CuAu nanocages via a mild co-reduction process. Experiments showed that the as-prepared magnetic multi-metallic nanocages could be used as an efficient recyclable peroxidase-like catalyst.

Size Controlled Copper (I) Oxide Nanoparticles Influence Sensitivity of Glucose Biosensor

Copper (I) oxide (Cu₂O) is an appealing semiconducting oxide with potential applications in various fields ranging from photovoltaics to biosensing. The precise control of size and shape of Cu₂O nanostructures has been an area of intense research. Here, the electrodeposition of Cu₂O nanoparticles is presented with precise size variations by utilizing ethylenediamine (EDA) as a size controlling agent. The size of the Cu₂O nanoparticles was successfully varied between 54.09 nm to 966.97 nm by changing the concentration of EDA in the electrolytic bath during electrodeposition. The large surface area of the Cu₂O nanoparticles present an attractive platform for immobilizing glucose oxidase for glucose biosensing. The fabricated enzymatic biosensor exhibited a rapid response time of <2 s. The limit of detection was 0.1 μM and the sensitivity of the glucose biosensor was 1.54 mA/cm². mM. The Cu₂O nanoparticles were characterized by UV-Visible spectroscopy, scanning electron microscopy and X-ray diffraction.

Electrochemical aptasensor for thrombin using co-catalysis of hemin/G-quadruplex DNAzyme and octahedral Cu2O-Au nanocomposites for signal amplification

In this work, novel octahedral Cu₂O-Au nanocomposites were synthesized and first applied in an electrochemical aptasensor to detect thrombin (TB) with the aid of a DNAzyme for signal amplification. The octahedral Cu₂O-Au nanocomposites have not only simultaneously served as signal amplifying molecules but have also been utilized as an ideal loading platform to immobilize a large number of electroactive substances and recognition probes. Gold nanoparticles (AuNPs) were grown directly on the surface of the octahedral Cu₂O nanocrystals, and the Cu₂O-Au nanocomposites obtained had the advantages of large surface areas and excellent biocompatibilities. The hemin/G-quadruplex, which was formed by intercalating hemin into the amino terminated thrombin binding aptamer (NH₂-TBA), and the electroactive toluidine blue (Tb) were immobilized onto the Cu₂O-Au nanocomposite surfaces through a stable Au-N bond. AuNPs, Cu₂O and hemin/G-quadruplex co-catalyse the H₂O₂ in the working buffer to promote the electron transfer of Tb as a multiple signal amplification strategy in order to improve the performance of the electrochemical aptasensor. Under optimal conditions, the designed aptasensor exhibited sensitive detection of TB from 100 fM to 20nM with a lower detection limit of 23fM. This proposed aptasensor exhibited good sensitivity, high specificity and acceptable reproducibility and could be widely applied in bioassay analysis.

Antiviral activity of cuprous oxide nanoparticles against Hepatitis C Virus in vitro

Small molecular inhibitors in combination with or without interferon have improved sustained antiviral responses against Hepatitis C Virus (HCV) infection. Nonetheless, resistance to these inhibitors is expected to emerge rapidly due to the high mutation rate of the virus. Thus, new antiviral drugs, in combination with currently available therapies, are urgently needed to treat HCV infection. In the present study, we evaluated the antiviral efficacy of cuprous oxide nanoparticles (CO-NPs) against HCV in the HCVcc/Huh7.5.1 cell culture system. CO-NPs were able to significantly inhibit the infectivity of HCVcc at a non-cytotoxic concentration. In addition, CO-NPs inhibited the entry of HCV pseudoparticle (HCVpp), including genotypes 1a, 1b, and 2a, while no effect on HCV replication was observed. Further time-of-addition experiment indicated that CO-NPs blocked HCV infection both at the attachment and entry stages. In conclusion, we report that CO-NPs can act as an anti-HCV agent by targeting the binding of infectious HCV particles to hepatic cells and the virus entry into the cells. These findings suggest that CO-NPs may have novel roles in the treatment of patients with chronic hepatitis C.

Effect of Au nanorods on potential barrier modulation in morphologically controlled Au@Cu2O core-shell nanoreactors for gas sensor applications

In this work, Au@Cu2O core-shell nanoparticles (NPs) were synthesized by simple solution route and applied for CO sensing applications. Au@Cu2O core-shell NPs were formed by the deposition of 30-60 nm Cu2O shell layer on Au nanorods (NRs) having 10-15 nm width and 40-60 nm length. The morphology of Au@Cu2O core-shell NPs was tuned from brick to spherical shape by tuning the pH of the solution. In the absence of Au NRs, cubelike Cu2O NPs having ∼200 nm diameters were formed. The sensor having Au@Cu2O core-shell layer exhibited higher CO sensitivity compared to bare Cu2O NPs layer. Tuning of morphology of Au@Cu2O core-shell NPs from brick to spherical shape significantly lowered the air resistance. Transition from p- to n-type response was observed for all devices below 150 °C. It was demonstrated that performance of sensor depends not only on the electronic sensitization of Au NRs but also on the morphology of the Au@Cu2O core-shell NPs.

Direct printing synthesis of self-organized copper oxide hollow spheres on a substrate using copper(II) complex ink: gas sensing and photoelectrochemical properties

The direct printing synthesis of metal oxide hollow spheres in the form of film on a substrate is reported for the first time. This method offers facile, scalable, high-throughput production and device fabrication processes. The printing was carried out via a doctor-blade method using Cu(II) complex ink with controllable high viscosity based on formate-amine coupling. Following only thermal heating in air, well-defined polycrystalline copper oxide hollow spheres with a submicrometer diameter (≤1 μm) were formed spontaneously while being assembled in the form of a film with good adhesion on the substrate. This spontaneous hollowing mechanism was found to result from the Kirkendall effect during oxidation at elevated temperature. The CuO films with hollow spheres, prepared via direct printing synthesis at 500 °C, led to the creation of a superior p-type gas sensor and photocathode for photoelectrochemical water splitting with completely hollow cores, a rough/porous shell structure, a single phase, high crystallinity, and no organic/polymer residue. As a result, the CuO hollow-sphere films showed high gas responses and permissible response speeds to reducing gases and high photocurrent density compared to conventional CuO powder films and the values previously reported. These results exemplify the successful realization of a high-throughput printing fabrication method for the creation of superior nanostructured devices.