Electrochemical Biosensing Platforms Using Platinum Nanoparticles and Carbon Nanotubes

Direct electrochemical deposition of polyaniline nanowire array on reduced graphene oxide modified graphite electrode for direct electron transfer biocatalysis

Direct electron transfer biocatalysis was achieved via electrochemically produced ordered PANI nanowire array on reduced graphene oxide modified graphite electrodes.

A sensitive dopamine biosensor based on ultra-thin polypyrrole nanosheets decorated with Pt nanoparticles

A Pt/UltraPPy modified glassy carbon electrode is a highly sensitive new sensor for the detection of dopamine.

Monitoring of the velocity of high-affinity glutamate uptake by isolated brain nerve terminals using amperometric glutamate biosensor

Glutamate is the major excitatory neurotransmitter in the central nervous system, which is involved in the main aspects of normal brain functioning. High-affinity Na(+)-dependent glutamate transporters is key proteins, which transport extracellular glutamate to the cytoplasm of nerve cells, thereby preventing continuous activation of glutamate receptors, and thus the development of neurotoxicity. Disturbance in glutamate uptake is involved in the pathogenesis of major neurological disorders. Amperometric biosensors are the most promising and successful among electrochemical biosensors. In this study, we developed (1) amperometric glutamate biosensor, (2) methodological approach for the analysis of glutamate uptake in liquid samples of isolated rat brain nerve terminals (synaptosomes). The basal level of glutamate, the initial velocity of glutamate uptake and time-dependent accumulation of glutamate by synaptosomes were determined using developed glutamate biosensor. Comparative analysis of the data with those obtained by radioactive analysis, spectrofluorimetry and ion exchange chromatography was performed. Therefore, the methodological approach for monitoring of the velocity of glutamate uptake, which takes into consideration the definite level of endogenous glutamate in nerve terminals, was developed using glutamate biosensor.

In situ generation of a high-performance Pd-polypyrrole composite with multi-functional catalytic properties

We report on a bottom up approach for the synthesis of a Pd-polypyrrole nanocomposite material. The composite material was characterized by means of different techniques, such as UV-vis, IR, and Raman spectroscopy, which offered information about the chemical structure of the polymer, whereas electron microscopy images provided information regarding the morphology of the composite material and the distribution of the metal particles in the polymer matrix. During the synthesis of the nanocomposite, the Pd nanoparticles act as a catalyst for a model proton-coupled electron transfer reaction. The Pd-polypyrrole nanocomposite material was also used as a catalyst for the electro-catalytic detection of tryptophan, a precursor for some neurotransmitters.

Synthesis of Pt nanoparticles and their burrowing into Si due to synergistic effects of ion beam energy losses

We report the synthesis of Pt nanoparticles and their burrowing into silicon upon irradiation of a Pt-Si thin film with medium-energy neon ions at constant fluence (1.0 × 10(17) ions/cm(2)). Several values of medium-energy neon ions were chosen in order to vary the ratio of the electronic energy loss to the nuclear energy loss (S e/S n) from 1 to 10. The irradiated films were characterized using Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). A TEM image of a cross section of the film irradiated with S e/S n = 1 shows ≈5 nm Pt NPs were buried up to ≈240 nm into the silicon. No silicide phase was detected in the XRD pattern of the film irradiated at the highest value of S e/S n. The synergistic effect of the energy losses of the ion beam (molten zones are produced by S e, and sputtering and local defects are produced by S n) leading to the synthesis and burrowing of Pt NPs is evidenced. The Pt NP synthesis mechanism and their burrowing into the silicon is discussed in detail.

Platinum-paper micromotors: an urchin-like nanohybrid catalyst for green monopropellant bubble-thrusters

Platinum nanourchins supported on microfibrilated cellulose films (MFC) were fabricated and evaluated as hydrogen peroxide catalysts for small-scale, autonomous underwater vehicle (AUV) propulsion systems. The catalytic substrate was synthesized through the reduction of chloroplatinic acid to create a thick film of Pt coral-like microstructures coated with Pt urchin-like nanowires that are arrayed in three dimensions on a two-dimensional MFC film. This organic/inorganic nanohybrid displays high catalytic ability (reduced activation energy of 50-63% over conventional materials and 13-19% for similar Pt nanoparticle-based structures) during hydrogen peroxide (H2O2) decomposition as well as sufficient propulsive thrust (>0.5 N) from reagent grade H2O2 (30% w/w) fuel within a small underwater reaction vessel. The results demonstrate that these layered nanohybrid sheets are robust and catalytically effective for green, H2O2-based micro-AUV propulsion where the storage and handling of highly explosive, toxic fuels are prohibitive due to size-requirements, cost limitations, and close person-to-machine contact.

The unexpected activity of Pd nanoparticles prepared using a non-ionic surfactant template

Pd deposits on vitreous carbon substrates were prepared by electrodeposition from liquid crystal phases (both micellar and hexagonal phases) consisting of self-assembled non-ionic surfactant molecules. The morphology of the deposits varied significantly with the concentration of the surfactant but all are made up of aggregated nanoparticles circa 9 nm in diameter. The deposits from the micellar phase of the surfactant offer the largest electroactive area and specific activity for the hydrogen evolution, oxygen evolution and reduction reactions and formic acid and ethanol oxidations. Unexpectedly the deposits lead to an increase in catalytic activity far in excess of that expected from an enhancement in electroactive area.

Platinum nanocatalysts loaded on graphene oxide-dispersed carbon nanotubes with greatly enhanced peroxidase-like catalysis and electrocatalysis activities

A powerful enzymatic mimetic has been fabricated by employing graphene oxide (GO) nanocolloids to disperse conductive carbon supports of hydrophobic carbon nanotubes (CNTs) before and after the loading of Pt nanocatalysts. The resulting GOCNT-Pt nanocomposites could present improved aqueous dispersion stability and Pt spatial distribution. Unexpectedly, they could show greatly enhanced peroxidase-like catalysis and electrocatalysis activities in water, as evidenced in the colorimetric and electrochemical investigations in comparison to some inorganic nanocatalysts commonly used. Moreover, it is found that the new enzyme mimetics could exhibit peroxidase-like catalysis activity comparable to natural enzymes; yet, they might circumvent some of their inherent problems in terms of catalysis efficiency, electron transfer, environmental stability, and cost effectiveness. Also, sandwiched electrochemical immunoassays have been successfully conducted using GOCNT-Pt as enzymatic tags. Such a fabrication avenue of noble metal nanocatalysts loaded on well-dispersed conductive carbon supports should be tailored for the design of different enzyme mimics promising the extensive catalysis applications in environmental, medical, industrial, and particularly aqueous biosensing fields.

Electrocatalysis and photoelectrochemistry based on functional nanomaterials

Catalysis plays a key role in chemical production, energy processing, air purification, water treatment, food processing, and the life sciences. Nanostructured materials with high surface areas and some unique properties have received widespread interest in electrocatalysis and photocatalysis. Recently, the author’s research team has designed and studied a variety of novel functional nanomaterials. This review article is derived from the author’s 2013 Canadian Catalysis Lectureship Award Lecture and focuses primarily on the electrocatalytic activities of platinum- and palladium-based nanomaterials and the development of TiO2-based nanostructured photocatalysts. Palladium possesses several exceptional properties that may enable promising applications in hydrogen detection, purification, and storage. The significant roles of palladium-based nanomaterials in facilitating the growth of a hydrogen economy are addressed. As platinum-based catalysts are vital to the development of fuel cells and sensors, the design of high-performance platinum-based electrocatalysts is highlighted. Additionally, TiO2 is considered to be one of the most promising photocatalysts due to its nontoxicity, high stability, and cost effectiveness. The modification of TiO2 nanomaterials to achieve visible light response is discussed as well. It is anticipated that the development of advanced functional nanostructured catalysts will further improve the efficiency and reduce the cost of electrochemical and photochemical processes, making them more attractive in addressing the pressing global energy and environmental issues.

Nanomaterial-Based Electrochemical Immunosensors for Clinically Significant Biomarkers

Nanotechnology has played a crucial role in the development of biosensors over the past decade. The development, testing, optimization, and validation of new biosensors has become a highly interdisciplinary effort involving experts in chemistry, biology, physics, engineering, and medicine. The sensitivity, the specificity and the reproducibility of biosensors have improved tremendously as a result of incorporating nanomaterials in their design. In general, nanomaterials-based electrochemical immunosensors amplify the sensitivity by facilitating greater loading of the larger sensing surface with biorecognition molecules as well as improving the electrochemical properties of the transducer. The most common types of nanomaterials and their properties will be described. In addition, the utilization of nanomaterials in immunosensors for biomarker detection will be discussed since these biosensors have enormous potential for a myriad of clinical uses. Electrochemical immunosensors provide a specific and simple analytical alternative as evidenced by their brief analysis times, inexpensive instrumentation, lower assay cost as well as good portability and amenability to miniaturization. The role nanomaterials play in biosensors, their ability to improve detection capabilities in low concentration analytes yielding clinically useful data and their impact on other biosensor performance properties will be discussed. Finally, the most common types of electroanalytical detection methods will be briefly touched upon.

A highly sensitive NADH sensor based on a mycelium-like nanocomposite using graphene oxide and multi-walled carbon nanotubes to co-immobilize poly(luminol) and poly(neutral red) hybrid films

Hybridization of poly(luminol) (PLM) and poly(neutral red) (PNR) has been successfully performed and further enhanced by a conductive and steric hybrid nanotemplate using graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs). The morphology of the PLM-PNR-MWCNT-GO mycelium-like nanocomposite is studied by SEM and AFM and it is found to be electroactive, pH-dependent, and stable in the electrochemical system. It shows electrocatalytic activity towards NADH with a high current response and low overpotential. Using amperometry, it has been shown to have a high sensitivity of 288.9 μA mM(-1) cm(-2) to NADH (Eapp. = +0.1 V). Linearity is estimated in a concentration range of 1.33 × 10(-8) to 1.95 × 10(-4) M with a detection limit of 1.33 × 10(-8) M (S/N = 3). Particularly, it also shows another linear range of 2.08 × 10(-4) to 5.81 × 10(-4) M with a sensitivity of 151.3 μA mM(-1) cm(-2). The hybridization and activity of PLM and PNR can be effectively enhanced by MWCNTs and GO, resulting in an active hybrid nanocomposite for determination of NADH.

Development of spiropyran-based electrochemical sensor via simultaneous photochemical and target-activatable electron transfer

In traditional electrochemical sensors, the electrochemical signal transduction of the redox-active material is usually controlled by the analytical target. Due to non-specific interaction between the redox mediator and the target, false signal by single stimulus may not be avoided. To address this issue, we have developed a new electrochemical sensor that uses a functional spiropyran, an important class of photo and thermochromic compounds, as both recognition receptor and latent redox mediator, to realize simultaneous photochemical and target-modulated electron transfer. As a proof of principle, β-galactosidase was chosen as a model target. The new synthesized spiropyran probe, SP-β-gal, undergoes reversibly structural isomerization to form merocyanine under UV light irradiation. After the glycosidic bond being cleaved by β-galactosidase, the opened merocyanine of SP-β-gal forms redox-active 2-(2.5-dihydroxystyryl)-1.3.3-trimethyl-3H-indolium, and thus produces a pair of reversible redox current peaks under the electrochemical scanning. To amplify the detection signal, SP-β-gal was self-assembled with single-walled carbon nanotubes (SWCNTs) on the surface of glass carbon electrode. Kinetics experiments confirm that the probe is an ideal candidate for the determination of different concentrations of β-galactosidase digestion kinetics. Further, the SP-β-gal/SWCNTs-modified electrode is chemically stable in complex biological fluids. It was successfully applied to monitor β-galactosidase activity in the 10% calf thymus. This work represents not only a significant step forward in the further development of low-dimensional carbon nanomaterials/small organic molecular probes-based electrochemical biosensors, but also a new platform which may be extended to the assay of other enzyme such as β-D-glycosidase and so on by translating the biorecognition into electrochemical signal responses.

Processing and bioactivity of 45S5 Bioglass(®)-graphene nanoplatelets composites

Well dispersed 45S5 Bioglass(®) (BG)-graphene nanoplatelets (GNP) composites were prepared after optimising the processing conditions. Fully dense BG nanocomposites with GNP loading of 1, 3 and 5 vol% were consolidated using Spark plasma sintering (SPS). SPS avoided any structural damage of GNP as confirmed using Raman spectroscopy. GNP increased the viscosity of BG-GNP composites resulting in an increase in the sintering temperature by ~50 °C compared to pure BG. Electrical conductivity of BG-GNP composites increased with increasing concentration of GNP. The highest conductivity of 13 S/m was observed for BG-GNP (5 vol%) composite which is ~9 orders of magnitude higher compared to pure BG. For both BG and BG-GNP composites, in vitro bioactivity testing was done using simulated body fluid for 1 and 3 days. XRD confirmed the formation of hydroxyapatite for BG and BG-GNP composites with cauliflower structures forming on top of the nano-composites surface. GNP increased the electrical conductivity of BG-GNP composites without affecting the bioactivity thus opening the possibility to fabricate bioactive and electrically conductive scaffolds for bone tissue engineering.

Electrospun doping of carbon nanotubes and platinum nanoparticles into the β-phase polyvinylidene difluoride nanofibrous membrane for biosensor and catalysis applications

A novel β-phase polyvinylidene difluoride (PVDF) nanofibrous membrane decorated with multiwalled carbon nanotubes (MWCNTs) and platinum nanoparticles (PtNPs) was fabricated by an improved electrospinning technique. The morphology of the fabricated PVDF-MWCNT-PtNP nanofibrous membrane was observed by scanning electron microscopy, and the formation of high β-phase in the hybrid nanofibrous membrane was investigated by Fourier transform infrared spectroscopy and differential scanning calorimetry. The uniform dispersion of MWCNTs and PtNPs in the PVDF hybrid nanofibrous membrane and their interaction were explored by transmission electron microscopy and X-ray diffraction. For the first time, we utilized this created PVDF-MWCNT-PtNP nanofibrous membrane for biosensor and catalysis applications. The nonenzymatic amperometric biosensor with highly stable and sensitive, and selective detection of both H2O2 and glucose was successfully fabricated based on the electrospun PVDF-MWCNT-PtNP nanofibrous membrane. In addition, the catalysis of the hybrid nanofibrous membrane for oxygen reduction reaction was tested, and a good catalysis performance was found. We anticipate that the strategies utilized in this work will not only guide the further design of functional nanofiber-based biomaterials and biodevices but also extend the potential applications in energy storage, cytology, and tissue engineering.

Trends in Nanomaterial-Based Non-Invasive Diabetes Sensing Technologies

Blood glucose monitoring is considered the gold standard for diabetes diagnostics and self-monitoring. However, the underlying process is invasive and highly uncomfortable for patients. Furthermore, the process must be completed several times a day to successfully manage the disease, which greatly contributes to the massive need for non-invasive monitoring options. Human serums, such as saliva, sweat, breath, urine and tears, contain traces of glucose and are easily accessible. Therefore, they allow minimal to non-invasive glucose monitoring, making them attractive alternatives to blood measurements. Numerous developments regarding noninvasive glucose detection techniques have taken place over the years, but recently, they have gained recognition as viable alternatives, due to the advent of nanotechnology-based sensors. Such sensors are optimal for testing the amount of glucose in serums other than blood thanks to their enhanced sensitivity and selectivity ranges, in addition to their size and compatibility with electronic circuitry. These nanotechnology approaches are rapidly evolving, and new techniques are constantly emerging. Hence, this manuscript aims to review current and future nanomaterial-based technologies utilizing saliva, sweat, breath and tears as a diagnostic medium for diabetes monitoring.

Enzyme-labeled Pt@BSA nanocomposite as a facile electrochemical biosensing interface for sensitive glucose determination

Electrocatalytic reactions of glucose oxidation based on enzyme-labeled electrochemical biosensors demand a high enzymatic activity and fast electron transfer property to produce the amplified signal response. Through a "green" synthesis method, Pt@BSA nanocomposite was prepared as a biosensing interface for the first time. Herein we presented a convenient and effective glucose sensing matrix based on Pt@BSA nanocomposite along with the covalent adsorption of glucose oxidase (GOD). The electrocatalytic activity toward oxygen reduction was significantly enhanced due to the excellent bioactivity of anchored GOD and superior catalytic performance of interior platinum nanoparticles, which was gradually restrained with the addition of glucose. A sensitive glucose biosensor was then successfully developed upon the restrained oxygen reduction peak current. Differential pulse voltammetry (DPV) was employed to investigate the determination performance of the enzyme biosensor, resulting in a linear response range from 0.05 to 12.05 mM with an optimal detection limit of 0.015 mM. The as-proposed sensing technique revealed high selectivity against endogenous interfering species, satisfactory storage stability, acceptable durability, and favorable fabrication reproducibility with the RSD of 3.8%. During the practical application in human blood serum samples, this glucose biosensor obtained a good detection accuracy of analytical recoveries within 97.5 to 104.0%, providing an alternative scheme for glucose level assay in clinical application.

Ultra-wide-range electrochemical sensing using continuous electrospun carbon nanofibers with high densities of states

Carbon-based sensors for wide-range electrochemical detection of redox-active chemical and biological molecules were fabricated by the electrospinning of polyacrylonitrile fibers directly onto a polyacrylonitrile-coated substrate followed by carbonization at 1200 °C. The resulting electrospun carbon nanofibers (ECNFs) were firmly attached to the substrate with good mesh integrity and had high densities of electronic states (DOS), which was achieved without need for further modifications or the use of any additives. The mass of ECNFs deposited, and thus the electroactive surface area (ESA) of the sensor, was adjusted by varying the electrospinning deposition time, thereby enabling the systematic manipulation of the dynamic range of the sensor. A standard redox probe (Fe(CN)6(3-/4-)) was used to demonstrate that the ECNF sensor exhibits strong electrocatalytic activity without current saturation at high analyte concentrations. Dopamine was used as a model analyte to evaluate the sensor performance; we find that the ECNF device exhibits a dynamic range ∼10(5) greater than that of many existing carbon-based sensors. The ECNF sensors exhibited excellent sensitivity, selectivity, stability, and reproducibility for dopamine detection.

Fabrication of cubic PtCu nanocages and their enhanced electrocatalytic activity towards hydrogen peroxide

Cubic PtCu nanocages (NCs) were successfully synthesized through a redox reaction using cuprous oxide (Cu2O) as a sacrificial template and reducing agent. The porous PtCu NCs were composed of amounts of PtCu nanograins with an average particle size of 2.9 nm. The electrocatalytic performance of the PtCu NC electrode towards H2O2 was studied by cyclic voltammetry (CV) and chronoamperometry. The prepared PtCu NC electrode exhibited excellent electrocatalytic activity towards H2O2, with a wide liner range from 5 μM to 22.25 mM, a relatively high sensitivity of 295.3 μA mM-1 cm-2, and a low detection limit of 5 μM (S/N = 3). The hollow porous nanostructure has potential applications in biosensors.

Nanomaterials and biomaterials in electrochemical arrays for protein detection

Nanomaterials and biomaterials are important components of new electrochemical arrays designed for sensitive detection of proteins in biological fluids. Such multiplexed protein arrays are predicted to have an important future in personalized medical diagnostics, especially for cancer and heart disease. Sandwich immunoassays for proteins benefit greatly in sensitivity from the use of nanostructured sensor surfaces and multilabeled detection strategies involving nano- or microparticles. In these assays, capture agents such as antibodies or aptamers are attached to sensor surfaces in the array. Target proteins with large binding constants for the affinity agents are captured from liquid samples with high efficiency, either on the sensors or on magnetic bioconjugate particles decorated with many copies of labels and antibodies. After target proteins are captured on the sensor surfaces, the labels are detected by electrochemical techniques. This feature article begins with an overview of the recent history of nanoparticles in electrochemical protein sensors, then moves on to specific examples from our own laboratories. We discuss fabrication of nanostructured sensors and arrays with the aim of multiplexed detection as well as reusability. Following this, we describe systems that integrate particle-based protein sensing with microfluidics for multiplexed protein detection. We end with predictions on the diagnostic future of protein detection.

Centri-voltammetric dopamine detection

Centri-voltammetry is a novel method that combines centrifuge with voltammetry. In the present work centri-voltammetric detection of DA has been mad e for the first time.

Using multi-walled carbon nanotubes to enhance coimmobilization of poly(azure A) and poly(neutral red) for determination of nicotinamide adenine dinucleotide and hydrogen peroxide

Illustration of electro-codeposition of azure A and neutral red hybrid films using high ly conductive and steric MWCNTs as a template.

In situ synthesis of ultra-small platinum nanoparticles using a water soluble polyphenolic polymer with high catalytic activity

Ultra-small platinum nanoparticles are generated by in situ polymer reduction technique which shows high catalytic activity in water and in organic solvent.

Nanomaterials based electrochemical sensors for biomedical applications

A growing variety of sensors have increasingly significant impacts on everyday life. Key issues to take into consideration toward the integration of biosensing platforms include the demand for minimal costs and the potential for real time monitoring, particularly for point-of-care applications where simplicity must also be considered. In light of these developmental factors, electrochemical approaches are the most promising candidate technologies due to their simplicity, high sensitivity and specificity. The primary focus of this review is to highlight the utility of nanomaterials, which are currently being studied for in vivo and in vitro medical applications as robust and tunable diagnostic and therapeutic platforms. Highly sensitive and precise nanomaterials based biosensors have opened up the possibility of creating novel technologies for the early-stage detection and diagnosis of disease related biomarkers. The attractive properties of nanomaterials have paved the way for the fabrication of a wide range of electrochemical sensors that exhibit improved analytical capacities. This review aims to provide insights into nanomaterials based electrochemical sensors and to illustrate their benefits in various key biomedical applications. This emerging discipline, at the interface of chemistry and the life sciences, offers a broad palette of opportunities for researchers with interests that encompass nanomaterials synthesis, supramolecular chemistry, controllable drug delivery and targeted theranostics in biology and medicine.