Ultra-selective fiber optic SPR platform for the sensing of dopamine in synthetic cerebrospinal fluid incorporating permselective nafion membrane and surface imprinted MWCNTs-PPy matrix

Dopamine-Regulated Plasticity in MoO3 Synaptic Transistors

Field-effect transistor-based biosensors have gained increasing interest due to their reactive surface to external stimuli and the adaptive feedback required for advanced sensing platforms in biohybrid neural interfaces. However, complex probing methods for surface functionalization remain a challenge that limits the industrial implementation of such devices. Herein, a simple, label-free biosensor based on molybdenum oxide (MoO3) with dopamine-regulated plasticity is demonstrated. Dopamine oxidation facilitated locally at the channel surface initiates a charge transfer mechanism between the molecule and the oxide, altering the channel conductance and successfully emulating the tunable synaptic weight by neurotransmitter activity. The oxygen level of the channel is shown to heavily affect the device's electrochemical properties, shifting from a nonreactive metallic characteristic to highly responsive semiconducting behavior. Controllable responsivity is achieved by optimizing the channel's dimension, which allows the devices to operate in wide ranges of dopamine concentration, from 100 nM to sub-mM levels, with excellent selectivity compared with K+, Na+, and Ca2+.

Enzymatic Electrochemical/Fluorescent Nanobiosensor for Detection of Small Chemicals

The detection of small molecules has attracted enormous interest in various fields, including the chemical, biological, and healthcare fields. In order to achieve such detection with high accuracy, up to now, various types of biosensors have been developed. Among those biosensors, enzymatic biosensors have shown excellent sensing performances via their highly specific enzymatic reactions with small chemical molecules. As techniques used to implement the sensing function of such enzymatic biosensors, electrochemical and fluorescence techniques have been mostly used for the detection of small molecules because of their advantages. In addition, through the incorporation of nanotechnologies, the detection property of each technique-based enzymatic nanobiosensors can be improved to measure harmful or important small molecules accurately. This review provides interdisciplinary information related to developing enzymatic nanobiosensors for small molecule detection, such as widely used enzymes, target small molecules, and electrochemical/fluorescence techniques. We expect that this review will provide a broad perspective and well-organized roadmap to develop novel electrochemical and fluorescent enzymatic nanobiosensors.

Advanced Nanomaterials-Based Electrochemical Biosensors for Catecholamines Detection: Challenges and Trends

Catecholamines, including dopamine, epinephrine, and norepinephrine, are considered one of the most crucial subgroups of neurotransmitters in the central nervous system (CNS), in which they act at the brain's highest levels of mental function and play key roles in neurological disorders. Accordingly, the analysis of such catecholamines in biological samples has shown a great interest in clinical and pharmaceutical importance toward the early diagnosis of neurological diseases such as Epilepsy, Parkinson, and Alzheimer diseases. As promising routes for the real-time monitoring of catecholamine neurotransmitters, optical and electrochemical biosensors have been widely adopted and perceived as a dramatically accelerating development in the last decade. Therefore, this review aims to provide a comprehensive overview on the recent advances and main challenges in catecholamines biosensors. Particular emphasis is given to electrochemical biosensors, reviewing their sensing mechanism and the unique characteristics brought by the emergence of nanotechnology. Based on specific biosensors' performance metrics, multiple perspectives on the therapeutic use of nanomaterial for catecholamines analysis and future development trends are also summarized.

Impact of Initial Cyclic Loading on Mechanical Properties and Performance of Nafion

Nafion possesses many interesting properties such as a high ion-conductivity, hydrophilicity, and thermal and chemical stability that make this material highly suitable for many applications including fuel cells and various (bio-)chemical and physical sensors. However, the mechanical properties of a Nafion membrane that are known to be affected by the viscoplastic characteristics of the material itself have a strong impact on the performance of Nafion-based sensors. In this study, the mechanical properties of Nafion under the cyclic loading have been investigated in detail. After cyclic tensile loading (i.e., maximum elongation about 25% at a room temperature and relative humidity about 40%) a time-dependent recovery comes into play. This recovery process is also shown being strain-rate dependent. Our results reveal that the recovery behavior weakens after performing several stress-strain cycles. Present findings can be of a great importance in future design of various chemical and biological microsensors and nanosensors such as hydrogen or glucose ones.

Real-Time Monitoring of Neurotransmitters in the Brain of Living Animals

Neurotransmitters, as important chemical small molecules, perform the function of neural signal transmission from cell to cell. Excess concentrations of neurotransmitters are often closely associated with brain diseases, such as Alzheimer's disease, depression, schizophrenia, and Parkinson's disease. On the other hand, the release of neurotransmitters under the induced stimulation indicates the occurrence of reward-related behaviors, including food and drug addiction. Therefore, to understand the physiological and pathological functions of neurotransmitters, especially in complex environments of the living brain, it is urgent to develop effective tools to monitor their dynamics with high sensitivity and specificity. Over the past 30 years, significant advances in electrochemical sensors and optical probes have brought new possibilities for studying neurons and neural circuits by monitoring the changes in neurotransmitters. This Review focuses on the progress in the construction of sensors for in vivo analysis of neurotransmitters in the brain and summarizes current attempts to address key issues in the development of sensors with high selectivity, sensitivity, and stability. Combined with the latest advances in technologies and methods, several strategies for sensor construction are provided for recording chemical signal changes in the complex environment of the brain.

Optically Active Nanomaterials and Its Biosensing Applications-A Review

This article discusses optically active nanomaterials and their optical biosensing applications. In addition to enhancing their sensitivity, these nanomaterials also increase their biocompatibility. For this reason, nanomaterials, particularly those based on their chemical compositions, such as carbon-based nanomaterials, inorganic-based nanomaterials, organic-based nanomaterials, and composite-based nanomaterials for biosensing applications are investigated thoroughly. These nanomaterials are used extensively in the field of fiber optic biosensing to improve response time, detection limit, and nature of specificity. Consequently, this article describes contemporary and application-based research that will be of great use to researchers in the nanomaterial-based optical sensing field. The difficulties encountered during the synthesis, characterization, and application of nanomaterials are also enumerated, and their future prospects are outlined for the reader's benefit.

Advances in Novel Nanomaterial-Based Optical Fiber Biosensors-A Review

This article presents a concise summary of current advancements in novel nanomaterial-based optical fiber biosensors. The beneficial optical and biological properties of nanomaterials, such as nanoparticle size-dependent signal amplification, plasmon resonance, and charge-transfer capabilities, are widely used in biosensing applications. Due to the biocompatibility and bioreceptor combination, the nanomaterials enhance the sensitivity, limit of detection, specificity, and response time of sensing probes, as well as the signal-to-noise ratio of fiber optic biosensing platforms. This has established a practical method for improving the performance of fiber optic biosensors. With the aforementioned outstanding nanomaterial properties, the development of fiber optic biosensors has been efficiently promoted. This paper reviews the application of numerous novel nanomaterials in the field of optical fiber biosensing and provides a brief explanation of the fiber sensing mechanism.

Carbon Nanotubes-Based Fuel Cell for Cr(VI) Removal and Electricity Generation

A fuel cell, an energy transducer, can convert chemical energy into electrical energy. In this work, graphite felt (GF) loaded with polypyrrole (PPy) and carboxylic carbon nanotubes (CNTs-COOH) was used as a cathode (GF/PPy/CNTs-COOH) in a double-chamber nonbiofuel cell (D-nBFC) to remove Cr(VI) efficiently. Therein, Na₂S₂O₃ in an alkaline solution and Cr(VI) in a strongly acidic solution were employed as anode and cathode solutions, respectively. An agar salt bridge, consisting of saturated KCl solution, was used to transport ions between the anode and cathode. This system suggested that the removal efficiency of Cr(VI) could reach 99.6%. The maximum current, power, and power density could achieve 136.8 μA, 18.7 μW, and 20.8 mW/m² at 90 min, respectively. Additionally, GF/PPy/CNTs-COOH also had good electrocatalytic stability and reusability after four cycles, which played an important role in the development of the D-nBFC system. Therefore, this study provides an environmentally friendly and efficient method to remove Cr(VI) and generate electricity simultaneously.

A Ratiometric Fiber Optic Sensor Based on CdTe QDs Functionalized with Glutathione and Mercaptopropionic Acid for On-Site Monitoring of Antibiotic Ciprofloxacin in Aquaculture Water

A ratiometric fluorescence fiber-optical sensor system (RFFS) merging a Y-type optical fiber spectrometer and CdTe QDs composite functionalized with glutathione and mercaptopropionic acid (GMPA@CdTe-QDs) for highly selective and on-site detection of ciprofloxacin (CIP) in environmental water samples was designed. Our preliminary results suggested that the red fluorescence of the synthesized GMPA@CdTe-QDs was effectively quenched by CIP. Based on this, the RFFS/GMPA@CdTe-QDs system was successfully fabricated and used for highly selective and rapid detection of CIP on site in the concentration range from 0 to 45 μM with the detection limit of 0.90 μM. The established method exhibited good interference resistance to the analogues of CIP and provided a great potential platform for real-time detection of CIP residues in environmental water. In addition, the fluorescence quenching mechanism of GMPA@CdTe-QDs by CIP was also investigated by means of temperature effect, fluorescence lifetime, ultraviolet (UV) visible absorption, and fluorescent spectra. Our results suggested clearly that the red fluorescence of GMPA@CdTe-QDs was quenched by CIP via the photoinduced electron-transfer (PET) mode.

Optical Biomedical Diagnostics Using Lab-on-Fiber Technology: A Review

Point-of-care and in-vivo bio-diagnostic tools are the current need for the present critical scenarios in the healthcare industry. The past few decades have seen a surge in research activities related to solving the challenges associated with precise on-site bio-sensing. Cutting-edge fiber optic technology enables the interaction of light with functionalized fiber surfaces at remote locations to develop a novel, miniaturized and cost-effective lab on fiber technology for bio-sensing applications. The recent remarkable developments in the field of nanotechnology provide innumerable functionalization methodologies to develop selective bio-recognition elements for label free biosensors. These exceptional methods may be easily integrated with fiber surfaces to provide highly selective light-matter interaction depending on various transduction mechanisms. In the present review, an overview of optical fiber-based biosensors has been provided with focus on physical principles used, along with the functionalization protocols for the detection of various biological analytes to diagnose the disease. The design and performance of these biosensors in terms of operating range, selectivity, response time and limit of detection have been discussed. In the concluding remarks, the challenges associated with these biosensors and the improvement required to develop handheld devices to enable direct target detection have been highlighted.

Portable fiber-optic SPR platform for the detection of NS1-antigen for dengue diagnosis

Here, we present a portable, selective and cost-effective fiber-optic surface plasmon resonance (SPR) based platform for early detection of Dengue virus. NS1 protein was targeted as the biomarker of dengue. Antibody-antigen specific binding was exploited for NS1 antigen detection. The binding of antibody was assisted by a self-assembled monolayer of alkanethiols on the surface of silver-coated unclad fiber. A wavelength interrogation mode of SPR was utilized to detect NS1 antigen in the dynamic range of 0.2-2.0 μg/ml. The 40 nm thick silver coated optical fiber exhibited resonance wavelength around 500 nm and change in resonance wavelength was monitored for each attachment step on the fiber. The sensitivity at the lowest concentration of NS1 antigen was found to be 54.7 nm/(μg/ml). The limit of detection of the sensor was found to be 0.06 μg/ml, which lies in the physiological range of NS1 protein present in the infected blood, hence the present technique may provide a very early detection advantage. Real blood serum samples were also successfully tested on the set-up, confirming compatibility with the conventional methods. The presented field-deployable platform has wide applications in mass monitoring of dengue, such as during outbreaks and epidemics.

A digital SERS sensing platform using 3D nanolaminate plasmonic crystals coupled with Au nanoparticles for accurate quantitative detection of dopamine

We report a digital surface-enhanced Raman spectroscopy (SERS) sensing platform using the arrays of 3D nanolaminate plasmonic crystals (NLPC) coupled with Au nanoparticles and digital (on/off) SERS signal analysis for the accurate quantitative detection of dopamine (DA) at ultralow concentrations. 3D NLPC SERS substrates were fabricated to support the optically dense arrays of vertically-stacked multi-nanogap hotspots and combined with Raman tag-conjugated Au nanoparticles for NLPC-based dual-recognition structures. We demonstrate that the 3D NLPC-based dual-recognition structures including Au nanoparticle-induced additional hotspots can enable more effective SERS enhancement through the molecular recognition of DA. For the accurate quantification of DA at ultralow concentrations, we conducted digital SERS analysis to reduce stochastic signal variation due to various microscopic effects, including molecular orientation/position variation and the spatial distribution of nanoparticle-coupled hotspots. The digital SERS analysis allowed the SERS mapping results from the DA-specific dual-recognition structures to be converted into binary "On/Off" states; the number of "On" events was directly correlated with low-abundance DA molecules down to 1 pM. Therefore, the digital SERS platform using the 3D NLPC-based dual-recognition structures coupled with Au nanoparticles and digital SERS signal analysis can be used not only for the ultrasensitive, accurate, and quantitative determination of DA, but also for the practical and rapid analysis of various molecules on nanostructured surfaces.

Surface Plasmon Resonance-Based Immunosensor for Igm Detection with Gold Nanoparticles

In this work, a surface plasmon resonance (SPR) based immunosensor was prepared by the immobilization of the amine-functionalized gold nanoparticles (N-AuNPs) on the sensing surface to sense immunoglobulin M (IgM) antibodies in the aqueous solution and artificial plasma. The characterization studies of SPR based immunosensor for IgM detection were performed with scanning electron microscope (SEM), contact angle measurements, and ellipsometry. Kinetic studies for the IgM immunosensor were carried out in the range of 1.0 to 200 ng/mL IgM concentrations in an aqueous solution. The total IgM analysis time including adsorption, desorption, and regeneration cycles was nearly 10 min for the prepared immunosensor. The limit of detection (LOD) and limit of quantification (LOQ) were found as 0.08 and 0.26 ng/mL, respectively. The reusability of the proposed immunosensor was tested with 6 consecutive adsorption-desorption, and regeneration cycles. Also, enzyme-linked immunosorbent assay (ELISA) method was utilized in the validation of the immunosensor.

The chemical tools for imaging dopamine release

Dopamine is a modulatory neurotransmitter involved in learning, motor functions, and reward. Many neuropsychiatric disorders, including Parkinson's disease, autism, and schizophrenia, are associated with imbalances or dysfunction in the dopaminergic system. Yet, our understanding of these pervasive public health issues is limited by our ability to effectively image dopamine in humans, which has long been a goal for chemists and neuroscientists. The last two decades have witnessed the development of many molecules used to trace dopamine. We review the small molecules, nanoparticles, and protein sensors used with fluorescent microscopy/photometry, MRI, and PET that shape dopamine research today. None of these tools observe dopamine itself, but instead harness the biology of the dopamine system-its synthetic and metabolic pathways, synaptic vesicle cycle, and receptors-in elegant ways. Their advantages and weaknesses are covered here, along with recent examples and the chemistry and biology that allow them to function.

Brain neurochemical monitoring

Brain neurochemical monitoring aims to provide continuous and accurate measurements of brain biomarkers. It has enabled significant advances in neuroscience for application in clinical diagnostics, treatment, and prevention of brain diseases. Microfabricated electrochemical and optical spectroscopy sensing technologies have been developed for precise monitoring of brain neurochemicals. Here, a comprehensive review on the progress of sensing technologies developed for brain neurochemical monitoring is presented. The review provides a summary of the widely measured clinically relevant neurochemicals and commonly adopted recognition technologies. Recent advances in sampling, electrochemistry, and optical spectroscopy for brain neurochemical monitoring are highlighted and their application are discussed. Existing gaps in current technologies and future directions to design industry standard brain neurochemical sensing devices for clinical applications are addressed.

Selective dopamine detection by SPR sensor signal amplification using gold nanoparticles

In this study, selective and sensitive detection of neurotransmitter dopamine from both aqueous solution and biological samples was performed by surface plasmon resonance sensor based on molecular imprinting technique.

Dopamine Sensing Based on Ultrathin Fluorescent Metal-Organic Nanosheets

The importance of dopamine (DA) detection as a biomarker for several diseases, especially Parkinson''s disease, has persuaded scientists to develop new nanomaterials for efficient sensing of DA in clinical samples. Ultrathin metal-organic nanosheets due to their exceptional thickness, large surface area, and flexibility are endowed with many accessible active sites and optimal surface interaction with the target analyte molecules. In this regard, a novel layered fluorescent metal-organic nanomaterial with a honeycomb topology based on europium, [Eu(pzdc)(Hpzdc)(H₂O)]_n (ECP) (H₂pzdc = 2,3-pyrazine dicarboxylic acid), was synthesized. X-ray crystallography revealed that the 3D supramolecular architecture of ECP is constructed from noncovalent interactions of coordinated water molecules between the 2D layers along the b axis. These layers that are only ∼4 nm thick were conveniently separated through ultrasound-induced liquid phase exfoliation. Optical studies show that the reduction of ECP thickness enhances the fluorescence intensity and serves as an efficient optical marker for DA detection. ECP nanoflakes exhibited fast response and high selectivity for DA detection in clinical samples. Good linearity for DA detection in the range of 0.1-10 μM with a detection limit of 21 nM proves the potential of ECP nanoflakes in DA sensing applications.

Low-Fouling Substrates for Plasmonic Sensing of Circulating Biomarkers in Biological Fluids

The monitoring of biomarkers in body fluids provides valuable prognostic information regarding disease onset and progression. Most biosensing approaches use noninvasive screening tools and are conducted in order to improve early clinical diagnosis. However, biofouling of the sensing surface may disturb the quantification of circulating biomarkers in complex biological fluids. Thus, there is a great need for antifouling interfaces to be designed in order to reduce nonspecific adsorption and prevent inactivation of biological receptors and loss of sensitivity. To address these limitations and enable their application in clinical practice, a variety of plasmonic platforms have been recently developed for biomarker analysis in easily accessible biological fluids. This review presents an overview of the latest advances in the design of antifouling strategies for the detection of clinically relevant biomarkers on the basis of the characteristics of biological samples. The impact of nanoplasmonic biosensors as point-of-care devices has been examined for a wide range of biomarkers associated with cancer, inflammatory, infectious and neurodegenerative diseases. Clinical applications in readily obtainable biofluids such as blood, saliva, urine, tears and cerebrospinal and synovial fluids, covering almost the whole range of plasmonic applications, from surface plasmon resonance (SPR) to surface-enhanced Raman scattering (SERS), are also discussed.

Single Plasmon-Active Optical Fiber Probe for Instantaneous Chiral Detection

The chiral recognition of organic compounds is of vital importance in the field of pharmacology and medicine. Unfortunately, the common analytical routes used in this field are significantly restricted by time spent and equipment demands. In this work, we propose an unprecedented alternative, aimed at enantiomer discrimination and estimation of their concentrations in an uncomplicated and instantaneous manner. The proposed approach is based on the creation of an optical fiber probe with two pronounced plasmonic bands attributed to gold and silver. The gold or silver surfaces were grafted with moieties, able to enunciating entrap chiral amines from solution, resulting in a wavelength shift corresponding to each plasmonic metal. As a model compound of chiral amine, we chose the DOPA, also taking in mind its high medical relevancy. For chiral detection, the optical fiber probe was simply immersed in an analytical solution of DOPA, and the selective shift of gold or silver plasmon bands was observed in the reflected light depending on DOPA chirality. The observed shifts depend on the concentration of DOPA enantiomers. In the case of a racemic mixture, the shifts of both plasmonic bands emerge, making possible the simultaneous determination of enantiomer concentrations and their ratio. The analytical cycle takes several minutes and requires very simple laboratory equipment.

Nanomaterials for Healthcare Biosensing Applications

In recent years, an increasing number of nanomaterials have been explored for their applications in biomedical diagnostics, making their applications in healthcare biosensing a rapidly evolving field. Nanomaterials introduce versatility to the sensing platforms and may even allow mobility between different detection mechanisms. The prospect of a combination of different nanomaterials allows an exploitation of their synergistic additive and novel properties for sensor development. This paper covers more than 290 research works since 2015, elaborating the diverse roles played by various nanomaterials in the biosensing field. Hence, we provide a comprehensive review of the healthcare sensing applications of nanomaterials, covering carbon allotrope-based, inorganic, and organic nanomaterials. These sensing systems are able to detect a wide variety of clinically relevant molecules, like nucleic acids, viruses, bacteria, cancer antigens, pharmaceuticals and narcotic drugs, toxins, contaminants, as well as entire cells in various sensing media, ranging from buffers to more complex environments such as urine, blood or sputum. Thus, the latest advancements reviewed in this paper hold tremendous potential for the application of nanomaterials in the early screening of diseases and point-of-care testing.

Carbon-Based Nanomaterials for Plasmonic Sensors: A Review

The surface plasmon resonance (SPR) technique is a remarkable tool, with applications in almost every area of science and technology. Sensing is the foremost and majorly explored application of SPR technique. The last few decades have seen a surge in SPR sensor research related to sensitivity enhancement and innovative target materials for specificity. Nanotechnological advances have augmented the SPR sensor research tremendously by employing nanomaterials in the design of SPR-based sensors, owing to their manifold properties. Carbon-based nanomaterials, like graphene and its derivatives (graphene oxide (GO)), (reduced graphene oxide (rGO)), carbon nanotubes (CNTs), and their nanocomposites, have revolutionized the field of sensing due to their extraordinary properties, such as large surface area, easy synthesis, tunable optical properties, and strong compatible adsorption of biomolecules. In SPR based sensors carbon-based nanomaterials have been used to act as a plasmonic layer, as the sensitivity enhancement material, and to provide the large surface area and compatibility for immobilizing various biomolecules, such as enzymes, DNA, antibodies, and antigens, in the design of the sensing layer. In this review, we report the role of carbon-based nanomaterials in SPR-based sensors, their current developments, and challenges.