An ultrasensitive fluorescent aptasensor for detection of cancer marker proteins based on graphene oxide–ssDNA

A novel biosensing platform was developed by integrating a new ssDNA aptamer and graphene oxide (GO) for highly sensitive and selective detection of liver cancer biomarkers (alpha-fetoprotein, AFP). The key concept of this biosensing platform is that the fluorescence of dye-modified ssDNA can be effectively quenched by GO after forming the hybrid structure of graphene oxide–ssDNA (GO–ssDNA). The AFP can selectively react with GO–ssDNA and lead to the decomposition of GO–ssDNA, which results in the recovery of fluorescence, and an increase in fluorescence intensity with the increasing concentration of AFP in the range of 0 to 300 pg mL⁻¹. The linear range was obtained from 1 to 150 pg mL⁻¹ and the detection limit was 0.909 pg mL⁻¹. Moreover, this biosensing platform can be applied to serum and cell imaging for the detection of AFP. The results show that the proposed biosensor has great potential application in AFP-related clinical diagnosis and research.

A novel biosensing platform was developed by integrating a new ssDNA aptamer and graphene oxide (GO) for highly sensitive and selective detection of liver cancer biomarkers (AFP).     

A novel,highly sensitive electrochemical 1,4-dioxane sensor based on reduced graphene oxide–curcumin nanocomposite

1,4-Dioxane is a carcinogenic, non-biodegradable, organic water pollutant which is used as a solvent in various industries. It is also formed as an undesired by-product in the cosmetic and pharmaceutical industry. Given its carcinogenicity and ability to pollute, it is desirable to develop a sensitive and selective sensor to detect it in drinking water and other water bodies. Current works on this sensor are very few and involve complex metal oxide composite systems. A sensitive electrochemical sensor for 1,4-dioxane was developed by modifying a glassy carbon electrode (GCE) with a reduced graphene oxide–curcumin (rGO–CM) nanocomposite synthesized by a simple solution approach. The prepared rGO–CM was characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and Scanning Electron Microscopy (SEM). The rGO–CM/GCE sensor was employed for the detection of 1,4-dioxane in the range of 0.1–100 μM. Although, the detection range is narrower compared to reported literature, the sensitivity obtained for the proposed sensor is far superior. Moreover, the limit of detection (0.13 μM) is lower than the dioxane detection target defined by the World Health Organization (0.56 μM). The proposed rGO–CM/GCE also showed excellent stability and good recovery values in real sample (tap water and drinking water) analysis.

Reduced graphene oxide–curcumin (rGO–CM) nanocomposite was prepared from graphite oxide using curcumin. The rGO–CM/GCE was used for highly sensitive 1,4-dioxane detection. The LOD obtained (0.13 μM) was lower than the WHO guideline value.     

Enhanced electron transfer mediated detection of hydrogen peroxide using a silver nanoparticle–reduced graphene oxide–polyaniline fabricated electrochemical sensor

The current study aims at the development of an electrochemical sensor based on a silver nanoparticle–reduced graphene oxide–polyaniline (AgNPs–rGO–PANI) nanocomposite for the sensitive and selective detection of hydrogen peroxide (H₂O₂). The nanocomposite was fabricated by simple in situ synthesis of PANI at the surface of rGO sheet which was followed by stirring with AEC biosynthesized AgNPs to form a nanocomposite. The AgNPs, GO, rGO, PANI, rGO–PANI, and AgNPs–rGO–PANI nanocomposite and their interaction were studied by UV-vis, FTIR, XRD, SEM, EDX and XPS analysis. AgNPs–rGO–PANI nanocomposite was loaded (0.5 mg cm⁻²) on a glassy carbon electrode (GCE) where the active surface area was maintained at 0.2 cm² for investigation of the electrochemical properties. It was found that AgNPs–rGO–PANI–GCE had high sensitivity towards the reduction of H₂O₂ than AgNPs–rGO which occurred at −0.4 V vs. SCE due to the presence of PANI (AgNPs have direct electronic interaction with N atom of the PANI backbone) which enhanced the rate of transfer of electron during the electrochemical reduction of H₂O₂. The calibration plots of H₂O₂ electrochemical detection was established in the range of 0.01 μM to 1000 μM (R² = 0.99) with a detection limit of 50 nM, the response time of about 5 s at a signal-to-noise ratio (S/N = 3). The sensitivity was calculated as 14.7 μA mM⁻¹ cm⁻² which indicated a significant potential as a non-enzymatic H₂O₂ sensor.

The current study aims at the development of an electrochemical sensor based on a silver nanoparticle–reduced graphene oxide–polyaniline (AgNPs–rGO–PANI) nanocomposite for the sensitive and selective detection of hydrogen peroxide (H₂O₂).     

An electrochemical platform based on a hemin–rGO–cMWCNTs modified aptasensor for sensitive detection of kanamycin

Kanamycin (KANA) residue in meat is particularly harmful to public health and there is an urgent need to establish a fast, accurate and low-cost method to determinate KANA in food quality control. In this paper, hemin–reduced graphene oxide-carboxylated multiwalled carbon nanotubes (hemin–rGO–cMWCNTs) were designed and prepared, and the characteristics of hemin–rGO–cMWCNTs are presented. After that, an aptamer/hemin–rGO–cMWCNTs sensor for determination of KANA was developed. The electrochemical characteristics were studied by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under optimal conditions, the sensitive response of the aptasensor towards KANA presented a wide concentration range of 10⁻⁹ to 10⁻⁶ M and a low detection limit of 0.36 nM (S/N = 3). Meanwhile, the aptasensor showed prominent selectivity, high stability and acceptable reproducibility in the application of KANA detection. In addition, the aptasensor detection in real samples correlated well with that obtained by liquid chromatograph mass spectrometer (LCMS).

An electrochemical aptasensor based on hemin–rGO–cMWCNTs was established. The aptasensor exhibited a low detection limit and a wide linear range. Excellent stability, reproducibility and applicability were presented for KANA.     

A dopamine electrochemical sensor based on a platinum–silver graphene nanocomposite modified electrode

A platinum–silver graphene (Pt–Ag/Gr) nanocomposite modified electrode was fabricated for the electrochemical detection of dopamine (DA). Electrochemical studies of the Pt–Ag/Gr nanocomposite towards DA detection were performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The CV analysis showed that Pt–Ag/Gr/GCE had enhanced electrocatalytic activity towards DA oxidation due to the synergistic effects between the platinum–silver nanoparticles and graphene. The DPV results showed that the modified sensor demonstrated a linear concentration range between 0.1 and 60 μM with a limit of detection of 0.012 μM. The Pt–Ag/Gr/GCE presented satisfactory results for reproducibility, stability and selectivity. The prepared sensor also showed acceptable recoveries for a real sample study.

A platinum–silver graphene nanocomposite was synthesized and characterized. A nanocomposite modified electrode was fabricated in order to investigate the electrochemical detection of dopamine.     

Construction of myoglobin–amphiphilic alginate caprylamide–graphene composite modified electrode for the direct electron transfer between redox proteins and electrode and electrocatalysis of myoglobin

To achieve the dispersion of the hydrophobic graphene (GR), the amphiphilic alginate caprylamide (ACA) was synthesized to fabricate electroactive Nafion/Mb–ACA–GR/CILE for the accurate determination of trichloroacetic acid (TCA). SEM observation, FT-IR and UV-Vis spectroscopic analysis indicated that ACA could tightly immobilize Mb and GR on the electrode surface by constructing biointerfaces, which not only provided Mb a suitable microenvironment to maintain its biological activity, but also shortened the distances between the active centers of Mb with carbon ionic liquid electrode (CILE), thus promoting the electron transfer rate. The electrochemical characterization of Nafion/Mb–ACA–GR/CILE showed that the direct electron transfer of Mb was realized on the modified electrode, which was attributed to the high electrical conductivity and excellent electrocatalytic activity of GR and good biocompatibility of ACA. Moreover, Nafion/Mb–ACA–GR/CILE exhibited good electrocatalytic activity towards TCA with the linear range from 2.5 to 47.3 mmol L⁻¹ and lower K_M^app value of 8.3 mmol L⁻¹. Moreover, the modified electrode also revealed good stability, reproducibility and accurate detection of tap-water, exhibiting great potential for the applications as the third-generation electrochemical biosensors.

To achieve the dispersion of the hydrophobic graphene (GR), the amphiphilic alginate caprylamide (ACA) was synthesized to fabricate electroactive Nafion/Mb–ACA–GR/CILE for the accurate determination of trichloroacetic acid (TCA).     

Developing a screen-printed graphite–polyurethane composite electrode modified with gold nanoparticles for the voltammetric determination of dopamine

A screen-printed electrode (SPGPUE) was prepared with graphite–polyurethane composite ink containing gold nanoparticles (AuNPs), resulting in a screen-printed graphite–polyurethane composite electrode modified with gold nanoparticles (SPGPUE–AuNPs). Gold nanoparticles were prepared by the citrate method and extracted from the water medium since polyurethane is not compatible with humidity. After extraction to chloroform, they were characterized via transmission electron microscopy (TEM). The presence of gold on the SPGPUE–AuNP surface was confirmed via SEM and EDX analyses, while thermogravimetry revealed the presence of approximately 3.0% (m/m) gold in the composite. An electrochemical pretreatment in 0.10 mol L⁻¹ phosphate buffer (pH 7.0) with successive cycling between −1.0 V and 1.0 V (vs. pseudo-Ag/AgCl) under a scan rate of 200 mV s⁻¹ and 150 cycles was required in order to provide a suitable electrochemical response for the voltammetric determination of dopamine. After the optimization of the parameters of differential pulse voltammetry (DPV), an analytical curve was obtained within a linear dynamic range of 0.40–60.0 μmol L⁻¹ and detection limit (LOD) of 1.55 ×10⁻⁸ mol L⁻¹ for dopamine at the SPGPUE–AuNP. A non-modified SPGPUE was used for comparison and a linear range was obtained between 2.0 and 10 μmol L⁻¹ with an LOD of 2.94 × 10⁻⁷ mol L⁻¹. During the dopamine determination in cerebrospinal synthetic fluid (CSF), recoveries between 89.3 and 103% were achieved. There were no significant interferences from ascorbic acid and uric acid, but some from epinephrine due to the structural similarity.

A screen-printed modified composite electrode (SPGPUE) was prepared with graphite–polyurethane ink containing gold nanoparticles (AuNPs), resulting in a sensor with improved sensitivity regarding the unmodified device in dopamine determination.     

Simultaneous determination of hydroquinone and catechol by a reduced graphene oxide–polydopamine–carboxylated multi-walled carbon nanotube nanocomposite

A reduced graphene oxide–polydopamine–carboxylated multi-walled carbon nanotube (RGO–PDA–cMWCNT) nanocomposite was fabricated via a facile, one-pot procedure and was characterized by a variety of techniques. A novel electrochemical sensor based on RGO–PDA–cMWCNT was constructed to determine hydroquinone (HQ) and catechol (CT) simultaneously. This newly prepared nanocomposite shows excellent electrocatalytic efficacy in the electrode reaction of the two isomers. Specifically, the peak-to-peak potential difference between the two dihydroxybenzenes is 115 mV for oxidation, which is obviously larger than similar electrochemical sensors. The established method displays a wide linear range from 0.5 to 5000 μM with a detection limit (S/N = 3) of 0.066 μM for HQ and 0.073 μM for CT. In addition, this electrochemical approach has been tested to measure the two dihydroxybenzenes in real samples and satisfactory results were recorded.

A novel reduced graphene oxide–polydopamine–carboxylated multi-walled carbon nanotube nanocomposite (RGO–PDA–cMWCNT) was fabricated for the sensitive and simultaneous determination of hydroquinone (HQ) and catechol (CT).     

Superficial fabrication of gold nanoparticles modified CuO nanowires electrode for non-enzymatic glucose detection

This paper describes a low-cost facile method to construct gold (Au) nanoparticles (NPs) modified copper oxide (CuO) nanowires (NWs) electrode on copper foil for the detection of glucose. Copper foil has been converted to aligned CuO NWs arrays by sequential formation of Cu(OH)₂ followed by heat treatment induced phase transformation to CuO. Au NPs are deposited on CuO NWs via simple reductive solution chemistry to impart high surface to volume ratio and enhanced catalytic activity of the resulting electrode. Structure, microstructure and morphology of Cu, Cu(OH)₂ NWs, CuO NWs, and Au NPs modified CuO NWs are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The homogeneous distribution of Au NPs (average diameter ∼12 nm) on CuO NWs (average diameter 100 nm and aspect ratio ∼20) is confirmed by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) and elemental mapping. This CuO based glucose detection method gives the highest sensitivity along with the maximum linearity range. This non-enzymatic glucose sensor based on Au modified CuO NWs electrode gives broad linearity range from 0.5 μM to 5.9 mM. The sensor exhibits sensitivity of 4398.8 μA mM⁻¹ cm⁻², lower detection limit of 0.5 μM, and very fast response time of ∼5 s. Properties of the proposed glucose sensor are also investigated in human blood and it is found that the sensor is highly accurate and reliable. In addition, higher sensitivity and lower detection limit confirm that this device is suitable for invasive detection in saliva and urine.

This paper describes a low-cost facile method to construct gold (Au) nanoparticles (NPs) modified copper oxide (CuO) nanowires (NWs) electrode on copper foil for the detection of glucose.     

Fabrication of an antimony doped tin oxide–graphene nanocomposite for highly effective capacitive deionization of saline water

In this study, antimony doped tin oxide loaded reduced graphene oxide (ATO–RGO) nanocomposites were synthesized via a facile hydrothermal approach. As a typical N-type semiconductor, the ATO in the composite can enhance the conductivity between graphene sheets, thus improving the specific capacitance and electrosorption performance. Under the optimal conditions, the largest surface area was 445.2 m² g⁻¹ when the mass content of ATO in the nanocomposite was 20 wt%. The synthesized optimal ATO–RGO electrode displayed excellent specific capacity (158.2 F g⁻¹) and outstanding electrosorptive capacity (8.63 mg g⁻¹) in sodium chloride solution, which were much higher than the corresponding results of pristine graphene (74.3 F g⁻¹ and 3.98 mg g⁻¹). At the same applied voltage, electrosorption capacity and charge efficiency of the ATO–RGO (20 wt%) material were better than those of reported carbon materials in recent years.

Antimony doped tin oxide–graphene nanocomposites synthesized via a facile hydrothermal approach displayed good specific capacity and electrosorptive capacity.     

l-Cysteine modified metal–organic framework as a chiral stationary phase for enantioseparation by capillary electrochromatography

A new kind of chiral zirconium based metal–organic framework, l-Cys-PCN-222, was synthesized using l-cysteine (l-Cys) as a chiral modifier by a solvent-assisted ligand incorporation approach and utilized as the chiral stationary phase in the capillary electrochromatography system. l-Cys-PCN-222 was characterized by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier-transform infrared spectra, nitrogen adsorption/desorption, circular dichroism spectrum, zeta-potential and so on. The results revealed that l-Cys-PCN-222 had the advantages of good crystallinity, high specific surface area (1818 m² g⁻¹), thermal stability and chiral recognition performance. Meanwhile, the l-Cys-PCN-222-bonded open-tubular column was prepared using l-Cys-PCN-222 particles as the solid phase by ‘thiol–ene’ click chemistry reaction and characterized by scanning electron microscopy, which proved the successful bonding of l-Cys-PCN-222 to the column inner wall. Finally, the stability, reproducibility and chiral separation performance of the l-Cys-PCN-222-bonded OT column were measured. Relative standard deviations (RSD) of the column efficiencies for run-to-run, day-to-day, column-to-column and runs were 1.39–6.62%, and did not obviously change after 200 runs. The enantiomeric separation of 17 kinds of chiral compounds including acidic, neutral and basic amino acids, imidazolinone and aryloxyphenoxypropionic pesticides, and fluoroquinolones were achieved in the l-Cys-PCN-222-bonded OT column. These results demonstrated that the chiral separation system of the chiral metal–organic frameworks (CMOFs) coupled with capillary electrochromatography has good application prospects.

A new kind of chiral zirconium-based metal–organic framework, l-Cys-PCN-222, was synthesized by the SALI method and utilized as the chiral stationary phase in a capillary electrochromatography system for enantioseparation.     

Simple strategy for sensitive detection of dopamine using CdTe QDs modified glassy carbon electrode

Background

Cellular and brain metabolism of dopamine can be correlated with a number of neurodegenerative disorders, our study was to explore a simple and efficient method to detect dopamine in real samples.

Methods

A new quantum dots (CdTe QDs) could be prepared using the hydrothermal method, the electrochemical biosensor was established by dropping CdTe QDs on the surface of glassy carbon electrode (GCE).

Results

The CdTe QDs/GCE exhibited the excellent electrochemical catalytic activity toward dopamine (DA) with good stability and high sensitivity in presence of interfering substances. The detection limit of DA was calculated by differential pulse voltammetry (DPV) as low as 0.3 μmol L⁻¹ with a linear dynamic range of 1 μmol L⁻¹ to 400 μmol L⁻¹.

Conclusion

In this paper, the proposed electrochemical biosensor could be effectively used for the direct and rapid detection of DA in human serum and urine samples.

     

Enhanced catalytic performance of reduced graphene oxide–TiO2 hybrids for efficient water treatment using microwave irradiation

Towards achieving efficient waste water treatment, the degradation of a common water pollutant, Orange G azo dye, was studied using a new hybrid catalyst and microwave irradiation. The fabrication of a hybrid catalyst based on reduced graphene oxide–titania (rGO–TiO₂), was first achieved in a single mode microwave cavity by reducing the precursor consisting of graphene oxide (GO) and titania. Catalytic performance was then assessed in both microwave assisted and conventional heat treatment conditions. The hybrid catalyst showed significant improvement under microwave irradiation, with more than 88% dye degradation after 20 minutes of treatment at 120 °C. The microwave effect was found to be more dominant in the early stages of the catalysis – the hybrid catalyst decomposed ∼65% of the dye in just 5 minutes of microwave treatment compared to only 18% degradation obtained during conventional heating. The improved performance with microwaves is mainly attributed to the formation of the hot spots at the surface of the hybrid catalyst which ultimately results in higher degradation rates. The morphological and catalytic properties of the hybrid catalyst are investigated using High Resolution Transmission Electron Microscopy (HRTEM) and UV-Vis Spectroscopy, respectively. Successful reduction of GO to rGO was confirmed using Raman spectroscopy and X-ray diffraction. The outstanding performance of microwave irradiated hybrids offers a viable low energy, low carbon footprint process with a new catalyst for wastewater treatment and for highly polluted wastewater conditions where photocatalysis is deemed not feasible.

Microwave irradiated graphene-based hybrid catalysts for short reaction time, low carbon footprint treatment processes for highly polluted wastewater.     

Organic–inorganic hybrid perovskite quantum dot light-emitting diodes using a graphene electrode and modified PEDOT:PSS

Perovskite quantum dot (PQD) light-emitting diodes (LEDs) have rapidly developed in the past several years due to the excellent optoelectronic properties of lead halide perovskites. However, PQD LEDs using graphene electrodes have not been reported despite their huge potential for applications in flexible displays and lighting sources. Herein, graphene was first used as the electrode of PQD LEDs. To overcome graphene''s limitations such as hydrophobicity and graphene-induced film nonuniformity, the modification of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with Triton X-100 and dimethyl sulfoxide (DMSO) codoping was reported, which not only improved the wettability of the graphene surface and the sequent film quality, but also reduced the dissolution of the PQD solvent to the bottom poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine] and PEDOT:PSS. More importantly, the synergistic effect of Triton X-100 and DMSO altered the PEDOT:PSS morphology from a coiled structure to a nanofibril conductive network, sufficiently enhancing the electrical conductivity of PEDOT:PSS. With this modification strategy, green PQD LEDs with CH₃NH₃PbBr₃ emission layers were successfully fabricated on graphene anodes, with 3.7- and 4.4-fold enhancements in luminance and current efficiency, respectively, compared to those of their counterparts without PEDOT:PSS modification. The film modification strategy and graphene-based PQD LEDs in this work are expected to shed light on the further design and manufacture of flexible highly efficient PQD display and lighting devices.

A graphene electrode together with modified PEDOT:PSS was first applied into perovskite quantum dot light-emitting diodes to improve the device performance.     

In situ generation of exfoliated graphene layers on recycled graphite rods for enhanced capacitive performance of Ni–Co binary hydroxide

A functionalized exfoliated graphite rod (FEGR), with a high surface area, is produced for use as a promising substrate for supercapacitors, via controlled oxidative treatment of a recycled graphite rod of exhausted zinc–carbon batteries. SEM, EDX, XPS, FT-IR, Raman, and contact angle measurements are carried out to disclose the surface characteristics of the FEGR. The surface of the FEGR is characterized by in situ generated grooves, together with graphene layers which are directly attached to the underlying graphite base. The FEGR electrodes enhance the capacitive performance of Ni(OH)₂ and binary Ni–Co(OH)₂. The Ni–Co(OH)₂/FEGR electrode displays a superb specific capacity value (2552.6 C g⁻¹) at a current density of 5 A g⁻¹ and this value is retained to 70.8% at a high current density of 50 A g⁻¹ indicating the outstanding rate performance of this electrode material. This enhanced behavior is attributed to the facile interaction of electrolyte species, even at high current density, with the active sites of the redox catalyst layer (distributed over a larger fraction of the underlying substrate with enhanced hydrophilicity). Moreover, the excellent electrical conductivity of the in situ surface generated graphene layers is another promoting factor.

A functionalized exfoliated graphite rod (FEGR), with a high surface area, is produced for use as a promising substrate for supercapacitors, via controlled oxidative treatment of a recycled graphite rod of exhausted zinc–carbon batteries.     

In vitro cytotoxicity and antibiotic application of green route surface modified ferromagnetic TiO2 nanoparticles

The enormous numbers of applications of TiO₂ nanoparticles (NPs) cause concern about their risk to the environment and human health. Consequently, motivated by the necessity of searching for new sources of TiO₂ NPs of low cytotoxicity with antibacterial activity, we synthesized TiO₂ NPs by a green route using a solution of titanium(iv) isopropoxide as a precursor and an aqueous extract of Artocarpus heterophyllus leaf as a reducing and surface modifying agent. We investigated their structure, shape, size, and magnetic properties, and evaluated their antibiotic application and cytotoxicity. The synthesized TiO₂ NPs were applied against two Gram-negative bacteria (E. coli and S. typhimurium) and two Gram-positive bacteria (S. aureus and B. subtilis) to observe their antibacterial activity; and eventually clear zones of inhibition formed by the TiO₂ NPs were obtained. Moreover, after exposing the synthesized TiO₂ NPs to HeLa cells (carcinoma cells) and Vero cells (normal cells), no toxic effect was found up to a dose of 1000 mg L⁻¹, indicating the safe use of the samples up to at least 1000 mg L⁻¹. However, toxic effects on HeLa cells and Vero cells were observed at doses of 2000 mg L⁻¹ and 3000 mg L⁻¹, respectively. These results indicate the safe use of Artocarpus heterophyllus leaf extract mediated synthesized TiO₂ NPs in their potential applications.

Artocarpus heterophyllus leaf extract mediated green synthesized TiO₂ nanoparticles exhibit less toxicity with high antibacterial activity.     

In situ synthesis of monolayer graphene on silicon for near-infrared photodetectors

Direct integration of monolayer graphene on a silicon (Si) substrate is realized by a simple thermal annealing process, involving a top copper (Cu) layer as the catalyst and an inserted polymethylmethacrylate (PMMA) as the carbon source. After spin-coating the PMMA carbon source on the Si substrate, the Cu catalyst was deposited on PMMA/Si by electron beam evaporation. After that, graphene was directly synthesized on Si by decomposition and dehydrogenation of PMMA and the catalyzation effect of Cu under a simple thermal annealing process. Furthermore, under an optimized growth condition, monolayer graphene directly formed on the Si substrate was demonstrated. Utilizing the as-grown graphene/Si heterojunction, near-infrared photodetectors with high detectivity (∼1.1 × 10¹⁰ cm Hz^1/2 W⁻¹) and high responsivity (50 mA W⁻¹) at 1550 nm were directly fabricated without any post-transfer process. The proposed approach for directly growing graphene on silicon is highly scalable and compatible with present nano/micro-fabrication systems, thus promoting the application of graphene in microelectronic fields.

Direct integration of monolayer graphene on a silicon (Si) substrate is realized by a simple thermal annealing process, involving a top copper (Cu) layer as the catalyst and an inserted polymethylmethacrylate (PMMA) as the carbon source.     

A novel metal–organic framework of Ba–hemin with enhanced cascade activity for sensitive glucose detection

Early glucose detection is important in both healthy people and diabetic patients. Glucose biosensing based on glucose oxidase (GOX) is a common method. However, native proteins are mostly membrane impermeable and are prone to degradation in complex sample environments. Herein, we report a facile one-step biomineralization method by simply mixing aqueous solutions of hemin and barium nitrate with glucose oxidase (GOX) to form Ba–hemin@GOX composites. Glucose (Glu) is introduced through self-driven sampling to trigger the GOX-catalysed production of hydrogen peroxide, which could help the subsequent 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation reaction catalysed by Ba–hemin to yield the blue-coloured product. The sensor exhibited a detection limit as low as 3.08 μM. The operability and accuracy of the Ba–hemin@GOX biosensor were confirmed by the quantitative determination of glucose in real samples, such as tap water, serum and drinks. Moreover, the Ba–hemin@GOX-based colorimetric biosensor showed good selectivity, storage stability and recoverability. The experimental results reveal that a GOX activity of more than 90% was still maintained even after being incubated at 60 °C for 30 minutes, and Ba–hemin@GOX could be reused for glucose detection at least six times. Even after 30 days of storage, the relative activity was still more than 90%. Overall, the developed Ba–hemin@GOX biosensor provides a valuable and general platform for applications in colorimetric biosensing and medical diagnostics.

The Ba–hemin@GOX composite is used for sensitive glucose detection.     

In situ synthesis of MoS2/graphene nanosheets as free-standing and flexible electrode paper for high-efficiency hydrogen evolution reaction

In this article, an exquisite flexible hybrid MoS₂/graphene free-standing electrocatalyst paper was fabricated by a one-step in situ solvothermal process. The assembled MoS₂/graphene catalysts exhibit significantly enhanced electrocatalytic activity and cycling stability towards the splitting of water in acidic solution. Furthermore, a strategic balance of abundant active sites at the edge of the S–Mo–S layers with efficient electron transfer in the MoS₂/graphene hybrid catalyst plays a key role in controlling the electrochemical performance of the MoS₂ nanosheets. Most importantly, the hybrid MoS₂/graphene nanosheet paper shows excellent flexibility and high electrocatalytic performance under the various bending states. This work demonstrates an opportunity for the development of flexible electrocatalysts, which have potential applications in renewable energy conversion and energy storage systems.

An improved flexible hybrid MoS₂/graphene free-standing electrocatalyst paper was fabricated by a one-step in situ solvothermal process for hydrogen evolution reaction applications.     

Highly sensitive detection of cytochrome c in the NSCLC serum using a hydrophobic paper based–gold nanourchin substrate

Cytochrome c (Cyt c) is a biomarker of early apoptosis that plays a critical role in the diagnosis and therapy of non-small cell lung cancer (NSCLC). In this work, we proposed a novel surface-enhanced Raman scattering (SERS)-based biosensor to implement the ultrasensitive detection of Cyt c in the serum of NSCLC patients. The SERS-supporting substrates based on hydrophobic filter paper were composed of gold nanourchins (GNUs) surface-functionalized with the Cyt c aptamer and the cyanine 5-labeled complementary DNA. In the existence of Cyt c, it could specifically bind to its aptamer, which leads to the detachment of complementary strands modified with Cy5 and the great weakness of SERS signal. The finite-difference time domain (FDTD) simulation showed that the excellent SERS performance of GNUs aggregation was strongly dependent on a large number of “hot spots” at the tips and between the nanogaps of aggregated GNUs. Alkyl ketene dimer (AKD) was used to make the filter paper modify its property from hydrophilic to hydrophobic, which consequently increased the density of GNUs and extended the retention time of the analyte. SERS biosensors based on hydrophobic paper exhibited prominent reproducibility and selectivity. The detection limit of Cyt c in PBS was 1.148 pg/mL, while the detection limit in human serum was 1.79 pg/mL. Moreover, the analysis of the serum samples of healthy subjects and NSCLC patients confirmed the feasibility of its clinical application. The results were consistent with enzyme-linked immunosorbent assay results. This method can be a powerful strategy for quantitative detection of extracellular Cyt c, and it is expected that the SERS-based biosensors could be applied in the practical clinical diagnoses of NSCLC.