Transducing Platform Research Articles

Self-assembled prussian blue nanoparticles on MXene quantum dots modified AuNPs for sensitive and reproducible biosensing of ovarian specific antigen (CA-125)

In this study, a practical approach has been developed to detect ovarian specific antigen (CA-125) with high sensitivity and specificity. The method utilizes enhanced differential pulse voltammogram signals of a self-assembled prussian blue nanoparticles (PB) decorated on MXene Quantum dots (QDs) supported by electrodeposited Au nanoparticles modified glassy carbon electrode (AuNP/PB/MXene QD/GCE). The fabrication procedure was completed by casting an optimized value of streptavidin and CA-125 antibody on the transducing platform. The improved electrochemical characteristics of the MXene QD/PB/AuNPs modification were ascribed to the combined impacts of MXene QD, PB, and AuNPs. The integration of MXene QD-PB composite within the modified layer contributed to enhanced mechanical strength. Additionally, the inclusion of gold nanoparticles (AuNPs) notably enhanced conductivity and promoted the attachment of anti-CA-125 onto the modified glassy carbon electrode (GCE), consequently improving sensitivity. Several analytical methods, such as energy-dispersive X-ray spectroscopy (EDS) and field emission scanning electron microscopy (FE-SEM) were utilized to investigate the structural, elemental composition and morphological characteristics. The functionality of the newly created immunosensor was evaluated using electrochemical impedance spectroscopy, differential pulse voltammetry and cyclic voltammetry to evaluate the synergistic effects. By employing this highly efficient analysis strategy, the measurement of CA-125 with differential pulse voltammetry (DPV) results a remarkable sensitivity with a detection limit of 0.57 pU.mL−1 and a wide linear range of 1 pU.mL−1 to 0.12 nU.mL−1 (R2 = 0.9824). Comparable results were obtained by analyzing serum samples from ovarian cancer patients at various stages. This study offers a significant insight into the advancement of immunosensor techniques for fabricating electrochemical transducers for the clinical detection of CA-125.

Palladium/Graphene Oxide Nanocomposite for Hydrogen Gas Sensing Applications Based on Tapered Optical Fiber.

Gaseous pollutants such as hydrogen gas (H2) are emitted in daily human activities. They have been massively studied owing to their high explosivity and widespread usage in many domains. The current research is designed to analyse optical fiber-based H2 gas sensors by incorporating palladium/graphene oxide (Pd/GO) nanocomposite coating as sensing layers. The fabricated multimode silica fiber (MMF) sensors were used as a transducing platform. The tapering process is essential to improve the sensitivity to the environment through the interaction of the evanescent field over the area of the tapered surface area. Several characterization methods including FESEM, EDX, AFM, and XRD were adopted to examine the structure properties of the materials and achieve more understandable facts about their functional performance of the optical sensor. Characterisation results demonstrated structures with a higher surface for analyte gas reaction to the optical sensor performance. Results indicated an observed increment in the Pd/GO nanocomposite-based sensor responses subjected to the H2 concentrations increased from 0.125% to 2.00%. The achieved sensitivities were 33.22/vol% with a response time of 48 s and recovery time of 7 min. The developed optical fiber sensors achieved excellent selectivity and stability toward H2 gas upon exposure to other gases such as ammonia and methane.

On-Chip Self-Referenced Micro-Resonators Enhanced by Digital Optical Frequency Comb for Ultra-Sensitive C-Reactive Protein Detection

An on-chip self-referenced transducer assisted by digital optical frequency comb (DOFC) technology is presented for the biomolecules detection in the lower detecting limit. This self-referenced stricture eliminates temperature cross sensitivity between the detecting and reference micro-resonators fabricated on the chalcogenide glass platform. The high-resolution DOFC technology has the ultra-fine-comb spacers offering for visualized spectral analysis of micro-resonators and capturing the subtle changes of ultra-low concentrations. Combining the self-referenced and DOFC technology, the detection of C-reactive protein in the concentration from 0.1 ng/mL to 500 ng/mL with the theoretically limit of detection of 0.0146 ng/mL is achieved. Given its small footprint, compactness and high analytical performances, the proposed transducing platform has the potential for applications on integration and minimization sensing on a single integrated chip.

Rapid electrochemical detection of COVID-19 genomic sequence with dual-function graphene nanocolloids based biosensor

Discovered in December 2019, the Severe Acute Respiratory Syndrome Coronavirus 2 (aka SARS-CoV-2 or 2019-nCoV) has attracted worldwide attention and concerns due to its high transmissibility and the severe health consequences experienced upon its infection, particularly by elderly people. Over 329 million people have been infected till date and over 5.5 million people could not survive the respiratory illness known as COVID-19 syndrome. Rapid and low-cost detection methods are of utmost importance to monitor the diffusion of the virus and to aid in the global fight against the pandemic.We propose here the use of graphene oxide nanocolloids (GONC) as an electroactive nanocarbon material that can act simultaneously as a transducing platform as well as the electroactive label for the detection of 2019-nCoV genomic sequences. The ability of GONC to provide an intrinsic electrochemical signal arising from the reduction of the electrochemically reducible oxygen functionalities present on its surface, allows GONC to be used as a simple and sensitive biosensing platform. Different intrinsic electroactivity of the material was obtained at each step of the genosensing process, starting from the immobilization of a short-stranded DNA probe and followed by the incubation with different concentrations of the target 2019-nCoV DNA strand. Monitoring such variations enabled the quantification of the target analyte over a wide dynamic range between 10−10 and 10−5 M.All in all, this proof-of-concept system serves as a stepping stone for the development of a rapid, sensitive and selective analytical tool for the detection of 2019-nCoV as well as other similar viral vectors. The use of cost-effective electrochemical detection methods coupled with the vast availability and suitability of carbon-based nanomaterials make this sensing system a valid candidate for low-cost and point-of-care analysis.

Angstrom-scale-porous plasmonic molybdenum oxide for ultrasensitive optical chemical sensing

Nanoporous plasmonic nanostructures based on noble metals have received extensive attention on the high-performance detection of chemical analytes. However, the size of such pores is rarely at the angstrom scale given the limitation of current fabrication methods. This leads to a relatively poor performance in the detection of ions. Here, we demonstrate the formation of angstrom-scale pores in ultra-thin plasmonic ammonium doped molybdenum oxide through crystal nucleation. The molybdenum oxide octahedra assemble into hexagonal rings, in which dopants fill in parts of the rings to stabilize the crystal structure and simultaneously generate a broad plasmon resonance across the visible to near-infrared regions. As a result, the unfilled centers of the rings effectively become angstrom-scale pores. Na+ ion sensing capability is investigated by integrating plasmonic ammonium doped molybdenum oxide onto D-shaped optical fibers. The ions are facilely accommodated within the pores and induce a charge re-distribution in the host. This alters the plasmon resonance behavior and modulates the optical output of the fiber transducing platform, through a strong light-matter interaction. The structure is sensitive to a wide concentration range of Na+ ions from subnanomolar (sub-nM) to submolar (sub-M) with the limit of detection (LOD) of ~5 fM, and high selectivity in both the aqueous solution and simulated serum conditions, which is a superior sensitivity over other reported optical ion sensors. This work demonstrates the strong potential of angstrom-scale porous plasmonic materials for chemical detection, and the possibility of being integrated with popular optical transducing platforms for practical high-performance sensing.

Doping and Decorating 2D Materials for Biosensing: Benefits and Drawbacks

AbstractThe rapid advancements in the field of materials science, especially nanoscience, have played a critical role in the advancement of sensors, in particular the development of novel transducer platforms. Sensors are devices that respond to specific phenomena with recordable and analytically useful output signals and have found their way into a myriad of applications in daily life. Some of these applications include the measurement of glucose and cholesterol levels and detection of emerging infectious diseases for biomedical purposes, environmental monitoring, and food analysis. 2D materials proffer numerous advantageous physical, chemical, electronic, and optical attributes such as large specific surface areas, excellent electrical and thermal conductivity, an abundance of catalytic sites, ease of functionalization, and tuneable electronic structures, allowing them to hold promising potential for the development of sensors with high sensitivity. Although layered materials demonstrate many beneficial attributes for the development of sensors, the properties and electronic structure of layered materials can be fine‐tuned via doping or decorating to enhance the sensing performance. This review highlights the current progress of electrical and optical sensors based upon metal‐decorated and metal‐doped 2D materials and examines the effects of decorating and doping 2D materials for sensor developments.

Vertically Aligned Nanostructured Topographies for Human Neural Stem Cell Differentiation and Neuronal Cell Interrogation

AbstractNeurodegenerative disorders are a widespread global health concern caused by aging, disease, and trauma, for which there are limited treatment options. Stem cell therapies, tissue engineering, and nanobiotechnologies offer hope for improved therapeutic delivery approaches, as well as tissue repair and regenerative medicine interventions. The complexity of the human brain, coupled with its limited availability for research, makes human neural lineage cells and their precursor stem cells integral to the further understanding of brain functions in health, development, and disease.Engineered nanomaterials provide highly specialized microenvironments, enabling precise interrogation of the impact of external and spatial stimuli on human neural cells in vitro, greatly advancing the knowledge of human neural function. Interacting with neural cells at the nanoscale, vertically aligned nanostructured (VA‐NS) arrays can influence cell fate and aid in more efficient cell reprogramming, and lend themselves to the development of highly targeted, sensitive signal transducer platforms suitable for in vivo monitoring of neural cell health and activity.This perspective highlights the current state of stem cell nanoneurobiology, specifically focusing on interdisciplinary advances made by VA‐NS arrays to manipulate human neural stem cells in translatable research applications. Current challenges and identify are discussed underexplored and emerging future research areas.

Multiresponsive 2D Ti3C2Tx MXene via Implanting Molecular Properties.

The design and fabrication of active nanomaterials exhibiting multifunctional properties is a must in the so-called global "Fourth Industrial Revolution". In this sense, molecular engineering is a powerful tool to implant original capabilities on a macroscopic scale. Herein, different bioinspired 2D-MXenes have been developed via a versatile and straightforward synthetic approach. As a proof of concept, Ti3C2Tx MXene has been exploited as a highly sensitive transducing platform for the covalent assembly of active biomolecular architectures (i.e., amino acids). All pivotal properties originated from the anchored targets were proved to be successfully transferred to the resulting bioinspired 2D-MXenes. Appealing applications have been devised for these 2D-MXene prototypes showing (i) chiroptical activity, (ii) fluorescence capabilities, (iii) supramolecular π-π interactions, and (iv) stimuli-responsive molecular switchability. Overall, this work demonstrates the fabrication of programmable 2D-MXenes, taking advantage of the inherent characteristics of the implanted (bio)molecular components. Thus, the current bottleneck in the field of 2D-MXenes can be overcome after the significant findings reported here.

Dual Transduction of H2O2 Detection Using ZnO/Laser-Induced Graphene Composites

Zinc oxide (ZnO)/laser-induced graphene (LIG) composites were prepared by mixing ZnO, grown by laser-assisted flow deposition, with LIG produced by laser irradiation of a polyimide, both in ambient conditions. Different ZnO:LIG ratios were used to infer the effect of this combination on the overall composite behavior. The optical properties, assessed by photoluminescence (PL), showed an intensity increase of the excitonic-related recombination with increasing LIG amounts, along with a reduction in the visible emission band. Charge-transfer processes between the two materials are proposed to justify these variations. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy evidenced increased electron transfer kinetics and an electrochemically active area with the amount of LIG incorporated in the composites. As the composites were designed to be used as transducer platforms in biosensing devices, their ability to detect and quantify hydrogen peroxide (H2O2) was assessed by both PL and CV analysis. The results demonstrated that both methods can be employed for sensing, displaying slightly distinct operation ranges that allow extending the detection range by combining both transduction approaches. Moreover, limits of detection as low as 0.11 mM were calculated in a tested concentration range from 0.8 to 32.7 mM, in line with the values required for their potential application in biosensors.

Molecular imprinting technology for sensing foodborne pathogenic bacteria.

Foodborne diseases caused by bacterial pathogens pose a widespread and growing threat to public health in the world. Rapid detection of pathogenic bacteria is of great importance to prevent foodborne diseases and ensure food safety. However, traditional detection methods are time-consuming, labour intensive and expensive. In recent years, many attempts have been made to develop alternative methods for bacterial detection. Biosensors integrated with molecular imprinted polymers (MIPs) and various transducer platforms are among the most promising candidates for the detection of pathogenic bacteria in a highly sensitive, selective and ultra-rapid manner. In this review, we summarize the most recent advances in molecular imprinting for bacterial detection, introduce the underlying recognition mechanisms and highlight the applications of MIP-based biosensors. In addition, the challenges and future perspectives are discussed with the aim of accelerating the development of MIP-based biosensors and extending their applications.

A novel electrochemical sensor based on double-walled carbon nanotubes and graphene hybrid thin film for arsenic(V) detection

In this work, we demonstrate the preparation of hybrid thin films based on double-walled carbon nanotubes and graphene for electrochemical sensing applications. The hybrid films were synthesized on polycrystalline copper foil by thermal chemical vapor deposition under low pressure. This carbonaceous hybrid film has exhibited high transparency with a transmittance of 94.3 %. The occurrence of this hybrid material on the electrode surface of screen-printed electrodes was found to increase electroactive surface area by 1.4 times, whereas electrochemical current was enhanced by 2.4 times. Such a highly transparent and conductive hybrid film was utilized as a transducing platform of enzymatic electrochemical arsenic(V) sensor. The as-prepared sensor shows the linear detection of arsenic(V) in the range from 1 to 10 ppb, with a limit of detection as low as 0.287 ppb. These findings provide a promising approach to develop new multifunctional electrochemical sensing systems for environmental monitoring and biomedical diagnostics.

Aqueous electrodeposition of (AuNPs/MWCNT–PEDOT) composite for high-affinity acetylcholinesterase electrochemical sensors

In this work, an electrochemical transducing platform constructed from carbonaceous tubes modified with thiophene polymer and gold nanoparticles was described. The negatively charged carbon tubes attracted monomers on their surface, then migrated toward the electrode upon electrical driving force, and finally deposited on the electrode surface. Consequently, these carbon tubes were coiled and wrapped with prolonged conjugated polymer chains. Gold nanoparticles were found to be mainly nucleated and grown at highly conductive sites on carbon tubes. The combination of 2-D polymer segments, 1-D carbon tubes, and 0-D metal particles has resulted in a highly porous 3-D architecture which is crucial to increasing the electrochemical responses. Meanwhile, the charge propagation was promoted due to synergistic effect between these biocompatible and conductive materials and evidenced by a significant increase in charge transfer rate (3.5 times) and dramatic reduction in charge transfer resistance (disappearance of semicircle in Nyquist plot). The acetylcholinesterase sensor based on as-prepared hybrid film shows good attraction to acetylthiocholine (Kappm = 0.182 mM). Thus, the developed sensor will provide a promising tool to analyze neurotransmitters and enzyme inhibitors.

Exciton-Driven Chemical Sensors Based on Excitation-Dependent Photoluminescent Two-Dimensional SnS.

Excitation wavelength-dependent photoluminescence (PL) in two-dimensional (2D) transition-metal chalcogenides enables a strong excitonic interaction for high-performance chemical and biological sensing applications. In this work, we explore the possible candidates in the domain of post-transition-metal chalcogenides. Few-layered 2D p-type tin monosulfide (SnS) nanoflakes with submicrometer lateral dimensions are synthesized from the liquid phase exfoliation of bulk crystals. Excitation wavelength-dependent PL is found, and the excitonic radiative lifetime is more than one order enhanced compared to that of the bulk counterpart because of the quantum confinement effect. Paramagnetic NO2 gas is selected as a representative to investigate the exciton-driven chemical-sensing properties of 2D SnS. Physisorption of NO2 results in the formation of dipoles on the surface of 2D SnS, causing the redistribution of photoexcited charges in the body and therefore modifying PL properties. For practical sensing applications, 2D SnS is integrated into a resistive transducing platform. Under light irradiation, the sensor exhibits excellent sensitivity and selectivity to NO2 at a relatively low operating temperature of 60 °C. The limit of detection is 17 parts per billion (ppb), which is significantly improved over other previously reported 2D p-type semiconductor-based NO2 sensors.

Optical fiber coated Zinc Oxide (ZnO) nanorods decorated with Palladium (Pd) for hydrogen sensing

A novel hydrogen (H2) sensor was developed using acid-etched optical fiber coated with zinc oxide (ZnO) nanorods. The sensing performance was done by comparing the acid-etched fiber coated with ZnO nanorods with and without decorated Palladium (Pd). The conventional optical single-mode fiber (SMF) with a diameter of 125 μm has been modified as a transducing platform by etching it to 11 μm diameter using hydrofluoric acid (HF) to enhance the evanescent field of the light propagates in the fiber core. The etched fiber was coated with ZnO nanorods via hydrothermal process by using seeding and growth solution method. The sensing layer was characterized through Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD) to verify the properties of ZnO. Catalyst Palladium (Pd) was sputtered onto the ZnO nanorods to improve H2 detection. The developed sensor operating temperature was found to be 150 °C that produces 6.36 dBm increase in response towards the 1% concentration of H2 in synthetic air. It was then tested with different concentration of H2. The sensor decorated with Pd has better performance in sensing compared to non-decorated Pd based on the output power versus time. The sensor best response and recovery times is 6 and 5 min respectively, for acid-etched optical fiber coated with ZnO nanorods decorated with Pd for 0.75% of H2 concentrations at 150 °C. The results indicate the optical fiber sensor might improve the performance towards H2 as oppose to the conventional electrical sensor.

Suppressing Non-Specific Binding of Proteins onto Electrode Surfaces in the Development of Electrochemical Immunosensors.

Electrochemical immunosensors, EIs, are systems that combine the analytical power of electrochemical techniques and the high selectivity and specificity of antibodies in a solid phase immunoassay for target analyte. In EIs, the most used transducer platforms are screen printed electrodes, SPEs. Some characteristics of EIs are their low cost, portability for point of care testing (POCT) applications, high specificity and selectivity to the target molecule, low sample and reagent consumption and easy to use. Despite all these attractive features, still exist one to cover and it is the enhancement of the sensitivity of the EIs. In this review, an approach to understand how this can be achieved is presented. First, it is necessary to comprise thoroughly all the complex phenomena that happen simultaneously in the protein-surface interface when adsorption of the protein occurs. Physicochemical properties of the protein and the surface as well as the adsorption phenomena influence the sensitivity of the EIs. From this point, some strategies to suppress non-specific binding, NSB, of proteins onto electrode surfaces in order to improve the sensitivity of EIs are mentioned.

H2 sensor based on tapered optical fiber coated with MnO2 nanostructures

A novel hydrogen (H2) sensor was developed using optical fiber coated with manganese dioxide (MnO2) nanostructures. Optical multimode fiber (MMF) of 125μm in diameter as the transducing platform was tapered to 20μm to enhance the evanescent field of the light propagates in the fiber core. The tapered fiber was coated with MnO2 nanograins synthesised via chemical bath deposition (CBD) process. Catalytic Palladium (Pd) was sputtered onto the MnO2 layer to improve the H2 detection. The sensing layer was characterized through Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), X-ray Diffraction (XRD) and Raman Spectroscopy to verify the properties of MnO2. Two sets of sensors consist of as-prepared MnO2 and 200°C annealed MnO2 were tested towards H2 gas. The tapered optical fiber coated with Pd/MnO2 nanograins was found to be sensitive towards H2 with different concentrations in synthetic air at 240°C operating temperature. The annealed sensor showed higher response and sensitivity as compared to the as-prepared sensors when measured in the visible to near infra-red optical wavelength range. The absorbance response of the annealed Pd/MnO2 on fiber has increased to 65% as compared to 20% for the as-prepared Pd/MnO2 upon exposure to 1% H2 in synthetic air.

Molecular Imprinting Techniques Used for the Preparation of Biosensors.

Molecular imprinting is the technology of creating artificial recognition sites in polymeric matrices which are complementary to the template in their size, shape and spatial arrangement of the functional groups. Molecularly imprinted polymers (MIPs) and their incorporation with various transducer platforms are among the most promising approaches for detection of several analytes. There are a variety of molecular imprinting techniques used for the preparation of biomimetic sensors including bulk imprinting, surface imprinting (soft lithography, template immobilization, grafting, emulsion polymerization) and epitope imprinting. This chapter presents an overview of all of these techniques with examples from particular publications.

Nanoparticles Modified ITO Based Biosensor

Incorporation of nanomaterials with controlled molecular architecture shows great promise in improving electronic communication between biomolecules and the electrode substrate. In electrochemical applications metal nanoparticles (NPs) modified electrodes have been widely used and are emerging as candidates to develop highly sensitive electrochemical sensors. There has been a growing technological interest in modified indium tin oxide (ITO) electrodes due to their prominent optoelectronic properties and their wide use as a transducing platform. The introduction of NPs into the transducing platform is commonly achieved by their adsorption onto conventional electrode surfaces in various forms, including that of a composite. The aim of this review is to discuss the role of metallic NPs for surface fabrication of ITO thin films leading to detection of specific biomolecules and applications as a biosensor platform.

Electrical Cable‐based Copper Disk Electrodes as Oxidase Biosensor Platforms with Cathodic H2O2 Readout

AbstractWe report the first utilization of copper disk electrodes as suitable cathodic transducer platforms for glucose biosensors. Simple and cheap Cu disk electrodes were fabricated from ordinary electrical cable by cementing into a glass tube with epoxy resin and subsequent polishing to expose the active area. Glucose oxidase was immobilized on the electrode tips by entrapment in dropped and dried polymeric Nafion deposits. At a H2O2 detection potential of −0.15 V vs. a reference electrode, the linear response range of fabricated cable Cu glucose biosensors was 20–1500 µM, with a sensitivity of about 700 nA µM−1 cm−2. Quantitative analysis of glucose‐supplemented buffer solutions showed a recovery of 106±4 % (n=3). The principal advantage of the glucose biosensors described in this study, compared to other options, is the simplicity of the cathodic H2O2 readout, which exploits cheap and readily available electrical cable, without any extra surface modification with catalytically active micro‐ or nanomaterials. The analytical performance of the biosensor is competitive and suggests potential applications in routine glucose testing, in particular in academic teaching and research laboratories. The work is also a starting point for transfer of the methodology from simple cable Cu electrodes to arrays of miniaturized Cu sensors, using a combination of microlithography, electroforming and molding (LIGA).

Cells-on-chip based transducer platform for probing toxicity of metal nanoparticles

In this work, we developed a cells-on-chip based transducer (CoCT) platform for probing toxicity of silver nanoparticles (Ag NPs) using non-Faradaic electrochemical impedance spectroscopy (nFEIS). This transducing platform was consists of arrays of capacitor on chip in which each capacitor was functionalized with living Escherichia coli cells. These cells were capable of responding to exposure of different size and concentration of Ag NPs. The capacitive response of CoCT was dependent on size and concentration of NPs. E. coli cells-on-chip response exhibited dramatic loss of capacitance and showed that maximum toxicity to cells-on-chip occurred with smaller 10nm sized Ag NPs compared to larger size of 100nm NPs. The cells tend to resist to the larger 100nm size of NPs that did not affect the cells-on-chip. Our results demonstrated that whole-cell biosensor chip response at a particular frequency enabled determining the severity of the stress imposed by smaller size of Ag NPs. Further, our results were validated through fourier transform infrared spectroscopy (FTIR) and growth of cell/cellular debris and also determined the NPs stress induced toxicity in cells as a proof-of-concept. The methodology developed in this study potentially be extended to other nanomaterials (NMs) for classifying toxic from non-toxic NMs.