Microbiosensors based on DNA modified single-walled carbon nanotube and Pt black nanocomposites

Acoustofluidic multimodal diagnostic system for Alzheimer's disease

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative brain disorder that affects tens of millions of older adults worldwide and has significant economic and societal impacts. Despite its prevalence and severity, early diagnosis of AD remains a considerable challenge. Here we report an integrated acoustofluidics-based diagnostic system (ADx), which combines triple functions of acoustics, microfluidics, and orthogonal biosensors for clinically accurate, sensitive, and rapid detection of AD biomarkers from human plasma. We design and fabricate a surface acoustic wave-based acoustofluidic separation device to isolate and purify AD biomarkers to increase the signal-to-noise ratio. Multimodal biosensors within the integrated ADx are fabricated by in-situ patterning of the ZnO nanorod array and deposition of Ag nanoparticles onto the ZnO nanorods for surface-enhanced Raman scattering (SERS) and electrochemical immunosensors. We obtain the label-free detections of SERS and electrochemical immunoassay of clinical plasma samples from AD patients and healthy controls with high sensitivity and specificity. We believe that this efficient integration provides promising solutions for the early diagnosis of AD.

The effect of anions on the electrochemical properties of polyaniline for supercapacitors

To investigate the effect of anions on the electrochemical properties of polyaniline (PANI) for supercapacitors, electrochemical performance tests of PANI with different dopant anions were carried out in the corresponding acid solutions by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) methods. In particular, ionic fluxes and solvent molecules involved in redox processes can be analyzed by the electrochemical quartz crystal microbalance (EQCM) technique and discriminated by simultaneously recording cyclic voltammograms and mass changes during redox switching. The emeraldine base (EB) form of PANI prepared in a protonic acid with bigger anions can be easily doped by a protonic acid with smaller anions, and conversely, PANI-EB is hard to be doped. The anodic reversal potential of potentiodynamic cycling heavily influences the electrochemical stability of PANI. High anodic potentials result in PANI degradation. Its supercapacitive properties including specific capacitance, power density and cycling stability are strongly dependent upon the type of dopant anion. PANI with the dopant anions of oxalic acid has the highest specific capacitance and the best cycling stability among the used acids. The diffusion coefficient of anions plays a key role in determining power density. PANI films with organic dopant anions exhibit better cycling stability than their inorganic counterparts. It is believed that the hydrolysis of PANI facilitated by the additional water molecules accompanied by dopant anions into and out of the PANI matrix is a key factor responsible for the cycling instability.

DNA-wrapped multi-walled carbon nanotube modified electrochemical biosensor for the detection of Escherichia coli from real samples

This paper introduces DNA-wrapped multi-walled carbon nanotube (MWCNT)-modified genosensor for the detection of Escherichia coli (E. coli) from polymerase chain reaction (PCR)-amplified real samples while Staphylococcus aureus (S. aureus) was used to investigate the selectivity of the biosensor. The capture probe specifically recognizing E. coli DNA and it was firstly interacted with MWCNTs for wrapping of single-stranded DNA (ssDNA) onto the nanomaterial. DNA-wrapped MWCNTs were then immobilised on the surface of disposable pencil graphite electrode (PGE) for the detection of DNA hybridization. Electrochemical behaviors of the modified PGEs were investigated using Raman spectroscopy and differential pulse voltammetry (DPV). The sequence selective DNA hybridization was determined and evaluated by changes in the intrinsic guanine oxidation signal at about 1.0V by DPV. Numerous factors affecting the hybridization were optimized such as target concentration, hybridization time, etc. The designed DNA sensor can well detect E. coli DNA in 20min detection time with 0.5pmole of detection limit in 30µL of sample volume.

pulSED: pulsed sonoelectrodeposition of fractal nanoplatinum for enhancing amperometric biosensor performance

A technique for deposition of fractal nanometal as a transducer in electrochemical sensing is described. The effect(s) of duty cycle and deposition time were explored, and two sensors are demonstrated.

Hybrids of Nucleic Acids and Carbon Nanotubes for Nanobiotechnology

Recent progress in the combination of nucleic acids and carbon nanotubes (CNTs) has been briefly reviewed here. Since discovering the hybridization phenomenon of DNA molecules and CNTs in 2003, a large amount of fundamental and applied research has been carried out. Among thousands of papers published since 2003, approximately 240 papers focused on biological applications were selected and categorized based on the types of nucleic acids used, but not the types of CNTs. This survey revealed that the hybridization phenomenon is strongly affected by various factors, such as DNA sequences, and for this reason, fundamental studies on the hybridization phenomenon are important. Additionally, many research groups have proposed numerous practical applications, such as nanobiosensors. The goal of this review is to provide perspective on biological applications using hybrids of nucleic acids and CNTs.

Thermo- and sulfate-controllable bioelectrocatalysis of glucose based on horseradish peroxidase and glucose oxidase embedded in poly(N,N-diethylacrylamide) hydrogel films

Dual-responsive poly(N,N-diethylacrylamide) (PDEA) hydrogel films with entrapped horseradish peroxidase (HRP) and glucose oxidase (GOD) were successfully prepared on electrode surface with a simple one-step polymerization procedure under mild conditions, designated as PDEA-HRP-GOD. Cyclic voltammetric (CV) response of electroactive probe K3Fe(CN)6 at the film electrodes displayed reversible thermo- and sulfate-responsive switching behavior. For example, at 25 °C, the K3Fe(CN)6 demonstrated a well-defined CV peak pair with large peak currents for the films, showing the on state, while at 40 °C, the CV response was greatly suppressed and the system was at the off state. The influence of temperature and Na2SO4 concentration on the switching behavior of the film system was not independent or separated, but was synergetic. The responsive mechanism of the system was ascribed to the structure change of PDEA component in the films with temperature and sulfate concentration. This switching property of the PDEA-HRP-GOD films could be further used to realize dual-responsive catalytic oxidation of glucose sequentially by HRP and GOD entrapped in the films with Fe(CN)6 (3-) as the mediator through changing the surrounding temperature and Na2SO4 concentration. This system may establish a foundation for fabricating a new type of multi-switchable electrochemical biosensors based on bienzyme electrocatalysis.

Functionalized graphene oxide for the fabrication of paraoxon biosensors

There is an increasing need to develop biosensors for the detection of harmful pesticide residues in food and water. Here, we report on a versatile strategy to synthesize functionalized graphene oxide nanomaterials with abundant affinity groups that can capture histidine (His)-tagged acetylcholinesterase (AChE) for the fabrication of paraoxon biosensors. Initially, exfoliated graphene oxide (GO) was functionalized by a diazonium reaction to introduce abundant carboxyl groups. Then, Nα,Nα-bis(carboxymethyl)-l-lysine hydrate (NTA-NH2) and Ni(2+) were anchored onto the GO based materials step by step. AChE was immobilized on the functionalized graphene oxide (FGO) through the specific binding between Ni-NTA and His-tag. A low anodic oxidation potential was observed due to an enhanced electrocatalytic activity and a large surface area brought about by the use of FGO. Furthermore, a sensitivity of 2.23 μA mM(-1) to the acetylthiocholine chloride (ATChCl) substrate was found for our composite covered electrodes. The electrodes also showed a wide linear response range from 10 μM to 1mM (R(2)=0.996), with an estimated detection limit of 3 μM based on an S/N=3. The stable chelation between Ni-NTA and His-tagged AChE endowed our electrodes with great short-term and long-term stability. In addition, a linear correlation was found between paraoxon concentration and the inhibition response of the electrodes to paraoxon, with a detection limit of 6.5×10(-10) M. This versatile strategy provides a platform to fabricate graphene oxide based nanomaterials for biosensor applications.

Single-stranded DNA functionalized single-walled carbon nanotubes for microbiosensors via layer-by-layer electrostatic self-assembly

In this letter, the facial noncovalent adsorption of single-stranded DNA (ssDNA) provided single-walled carbon nanotubes (SWNTs) with biofunctionality while their superior properties were retained. In this case, we innovatively demonstrated the feasibility of employing the negative surface charge of ssDNA-SWNTs to realize layer-by-layer electrostatic self-assembly. On the basis of such a sandwichlike structure, an applicable glucose microbiosensor with direct electrochemistry and high performance was fabricated. The proposed protocol provided an ideal platform for various sensing applications, and might have profound influence on related nanotechnology.

Highly selective detection of Epinephrine at oxidized Single-Wall Carbon Nanohorns modified Screen Printed Electrodes (SPEs)

Oxidized Single-Wall Carbon Nanohorns (o-SWCNHs) were used, for the first time, to assemble chemically modified Screen Printed Electrodes (SPEs) selective towards the electrochemical detection of Epinephrine (Ep), in the presence of Serotonine-5-HT (S-5HT), Dopamine (DA), Nor-Epineprhine (Nor-Ep), Ascorbic Acid (AA), Acetaminophen (Ac) and Uric Acid (UA). The Ep neurotransmitter was detected by using Differential Pulse Voltammetry (DPV), in a wide linear range of concentration (2-2500 μM) with high sensitivity (55.77 A M(-1) cm(-2)), very good reproducibility (RSD% ranging from 2 to 10 for different SPEs), short response time for each measurement (only 2s) and low detection of limit (LOD=0.1 μM). o-SWCNHs resulted in higher analytical performances when compared with other nanomaterials used in literature for electrochemical sensors assembly.

A chemiluminescence excited photoelectrochemistry aptamer-device equipped with a tin dioxide quantum dot/reduced graphene oxide nanocomposite modified porous Au-paper electrode

A paper-based chemiluminescence excited photoelectrochemical aptamer device integrated with an all-solid-state paper supercapacitor was demonstrated.

Ultrathin gold nanowire-functionalized carbon nanotubes for hybrid molecular sensing

Carbon nanotubes (CNTs) have shown great potential as sensing component in the electrochemical field effect transistor and optical sensors, because of their extraordinary one-dimensional electronic structure, thermal conductivity, and tunable and stable near-infrared emission. However, the insolubility of CNTs due to strong van der Waals interactions limits their use in the field of nanotechnology. In this study, we demonstrate that noncovalent ultrathin gold nanowires functionalized multiwalled carbon nanotube (GNW-CNT) hybrid sensing agents show highly efficient and selective immune molecular sensing in electrochemical and near-infrared photoacoustic imaging methods. A detection limit of 0.01 ng/mL for the alpha-fetoprotein (AFP) antigen with high selectivity is shown. The extraordinary optical absorption, thermal, and electric conductivity of hybrid GNW-CNTs presented in this study could be an effective tactic to integrate imaging, sensing, and treatment functionalities.

Preparation and characterization of three dimensional graphene foam supported platinum-ruthenium bimetallic nanocatalysts for hydrogen peroxide based electrochemical biosensors

The large surface, the excellent dispersion and the high degrees of sensitivity of bimetallic nanocatalysts were the attractive features of this investigation. Graphene foam (GF) was a three dimensional (3D) porous architecture consisting of extremely large surface and high conductive pathways. In this study, 3D GF was used incorporating platinum-ruthenium (PtRu) bimetallic nanoparticles as an electrochemical nanocatalyst for the detection of hydrogen peroxide (H2O2). PtRu/3D GF nanocatalyst exhibited a remarkable performance toward electrochemical oxidation of H2O2 without any additional mediator showing a high sensitivity (1023.1 µA mM(-1)cm(-2)) and a low detection limit (0.04 µM) for H2O2. Amperometric results demonstrated that GF provided a promising platform for the development of electrochemical sensors in biosensing and PtRu/3D GF nanocatalyst possessed the excellent catalytic activity toward the H2O2 detection. A small particle size and a high degree of the dispersion in obtaining of large active surface area were important for the nanocatalyst for the best H2O2 detection in biosensing. Moreover, potential interference by ascorbic acid and uric acid appeared to be negligible.

Facile preparation of high-quality Pt/reduced graphene oxide nanoscrolls for methanol oxidation

A simple and novel approach for the preparation of a Pt/reduced graphene oxide nanoscroll (Pt/RGOS) nanocatalyst is reported for the first time. The Pt/reduced graphene oxide (Pt/RGO) was fabricated by the co-reduction of GO and Pt salt using ethylene glycol under microwave irradiation, then the Pt/RGOSs were obtained by oxygen implosion in situ rolling up of the Pt/RGO using catalytic decomposition of Pt towards H2O2 under ultrasonication. Transmission electron microscopy shows that the Pt nanoparticles are uniformly dispersed on the reduced graphene oxide nanoscrolls with tubular structure, open edges and ends, and tubular diameter ranging from 10 to 100 nm. X-ray diffraction indicates that the crystal structure and diffraction intensity of the platinum practically remains unchanged, and the RGO has not been oxidized before or after rolling. Raman spectroscopy reveals that the Pt/RGOSs have a higher D/G ratio (1.2) than Pt/RGO (1.1). BET (Brunauer, Emmett and Teller) results exhibit that the Pt/RGOSs possess higher specific surface area and broader pore size range (188 m(2) g(-1), 25-45 nm) than Pt/RGO (122 m(2) g(-1), 30-38 nm). Additionally, the electrocatalytic performance of the Pt/RGOSs for methanol oxidation was evaluated, and the results show that the Pt/RGOSs possess significantly higher electrocatalytic activity and stability than Pt/RGO.

Nanomaterial based self-referencing microbiosensors for cell and tissue physiology research

Physiological studies require sensitive tools to directly quantify transport kinetics in the cell/tissue spatial domain under physiological conditions. Although biosensors are capable of measuring concentration, their applications in physiological studies are limited due to the relatively low sensitivity, excessive drift/noise, and inability to quantify analyte transport. Nanomaterials significantly improve the electrochemical transduction of microelectrodes, and make the construction of highly sensitive microbiosensors possible. Furthermore, a novel biosensor modality, self-referencing (SR), enables direct measurement of real-time flux and drift/noise subtraction. SR microbiosensors based on nanomaterials have been used to measure the real-time analyte transport in several cell/tissue studies coupled with various stimulators/inhibitors. These studies include: glucose uptake in pancreatic β cells, cancer cells, muscle tissues, intestinal tissues and P. Aeruginosa biofilms; glutamate flux near neuronal cells; and endogenous indole-3-acetic acid flux near the surface of Zea mays roots. Results from the SR studies provide important insights into cancer, diabetes, nutrition, neurophysiology, environmental and plant physiology studies under dynamic physiological conditions, demonstrating that the SR microbiosensors are an extremely valuable tool for physiology research.

Synthesis of a hydrophilic poly-l-lysine/graphene hybrid through multiple non-covalent interactions for biosensors

Surface modification has been proved to be one of the effective strategies for enhancing the properties of graphene sheets. When a non-covalent modification method is appropriately designed, novel opportunities for better performance of graphene nanosheets can be expected since this strategy can tailor the properties of graphene while its natural structure is retained. This paper introduces a simple route to prepare a highly biocompatible, stable and conductive graphene hybrid modified by poly-l-lysine (PLL) for biosensors using the non-covalent strategy. Results show that PLL adopts a random conformation with the nonpolar parts exposed to outside since its side chains are positively charged under neutral conditions. This conformation allows the strong adhesion of PLL to graphene surface via the hydrophobic interaction between butyl chains of PLL and graphene surface, cation-π interaction of protonated amine groups on PLL with the π electrons in graphene, and electrostatic interaction between the protonated amine groups on PLL and the negatively charged carboxyl groups remaining on graphene. All these interactions make the resultant PLL-G hybrid stable and dispersible in aqueous solutions. The resultant hybrid is then used to construct high performance biosensors. As demonstration, hemoglobin (Hb) carrying negative charges can be easily immobilized on the hybrid via electrostatic interactions with the positively charged lysine side chains of PLL modified on graphene surface, forming the Hb@PLL-G bionanocomposite. The immobilized protein retains its native structure and exhibits reversible direct electrochemistry. The Hb@PLL-G based enzymatic electrochemical biosensor shows excellent catalytic activity toward its substrate hydrogen peroxide. Its electrochemical response shows the linear dependence of hydrogen peroxide concentration in a range between 10 μM and 80 μM with a detection limit of 0.1 μM. The apparent Michaelis-Menten constant is calculated as 0.0753 mM, demonstrating the significant catalytic ability of the protein. The present strategy can be extended to modify other carbon materials and the resultant nanocomposites are promising for construction of biosensors, bioelectronics and biofuel cells.

An aqueous media based approach for the preparation of a biosensor platform composed of graphene oxide and Pt-black

The combination of Pt nanoparticles and graphene was more effective in enhancing biosensing than either nanomaterial alone according to previous reports. Based on the structural similarities between water soluble graphene oxide (GrO(x)) and graphene, we report the fabrication of an aqueous media based GrO(x)/Pt-black nanocomposite for biosensing enhancement. In this approach GrO(x) acted as a nanoscale molecular template for the electrodeposition of Pt-black, an amorphously nanopatterned isoform of platinum metal. Scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy (EDS) showed that Pt-black was growing along GrO(x). The effective surface area and electrocatalytic activity towards H(2)O(2) oxidation of GrO(x)/Pt-black microelectrodes were significantly higher than for Pt-black microelectrodes. When used to prepare a bio-nanocomposite based on protein functionalization with the enzyme glucose oxidase (GOx), the GrO(x)/Pt-black microbiosensors exhibited improved sensitivity over the Pt-black microbiosensors. This suggested that the GrO(x)/Pt-black nanocomposite facilitated an increase in electron transfer, and/or minimized mass transport limitations as compared to Pt-black used alone. Glucose microbiosensors based on GrO(x)/Pt-black exhibited high sensitivity (465.9 ± 48.0 nA/mM), a low detection limit of 1 μM, a linear response range of 1 μM-2mM, and response time of ≈ 4s. Additionally the sensor was stable and highly selective over potential interferents.