ZnO nanorods array based field-effect transistor biosensor for phosphate detection

Nanomaterials-based biosensor and their applications: A review

A sensor can be called ideal or perfect if it is enriched with certain characteristics viz., superior detections range, high sensitivity, selectivity, resolution, reproducibility, repeatability, and response time with good flow. Recently, biosensors made of nanoparticles (NPs) have gained very high popularity due to their excellent applications in nearly all the fields of science and technology. The use of NPs in the biosensor is usually done to fill the gap between the converter and the bioreceptor, which is at the nanoscale. Simultaneously the uses of NPs and electrochemical techniques have led to the emergence of biosensors with high sensitivity and decomposition power. This review summarizes the development of biosensors made of NPssuch as noble metal NPs and metal oxide NPs, nanowires (NWs), nanorods (NRs), carbon nanotubes (CNTs), quantum dots (QDs), and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

Nanotechnology-Enabled Biosensors: A Review of Fundamentals, Design Principles, Materials, and Applications

Biosensors are modern engineering tools that can be widely used for various technological applications. In the recent past, biosensors have been widely used in a broad application spectrum including industrial process control, the military, environmental monitoring, health care, microbiology, and food quality control. Biosensors are also used specifically for monitoring environmental pollution, detecting toxic elements' presence, the presence of bio-hazardous viruses or bacteria in organic matter, and biomolecule detection in clinical diagnostics. Moreover, deep medical applications such as well-being monitoring, chronic disease treatment, and in vitro medical examination studies such as the screening of infectious diseases for early detection. The scope for expanding the use of biosensors is very high owing to their inherent advantages such as ease of use, scalability, and simple manufacturing process. Biosensor technology is more prevalent as a large-scale, low cost, and enhanced technology in the modern medical field. Integration of nanotechnology with biosensors has shown the development path for the novel sensing mechanisms and biosensors as they enhance the performance and sensing ability of the currently used biosensors. Nanoscale dimensional integration promotes the formulation of biosensors with simple and rapid detection of molecules along with the detection of single biomolecules where they can also be evaluated and analyzed critically. Nanomaterials are used for the manufacturing of nano-biosensors and the nanomaterials commonly used include nanoparticles, nanowires, carbon nanotubes (CNTs), nanorods, and quantum dots (QDs). Nanomaterials possess various advantages such as color tunability, high detection sensitivity, a large surface area, high carrier capacity, high stability, and high thermal and electrical conductivity. The current review focuses on nanotechnology-enabled biosensors, their fundamentals, and architectural design. The review also expands the view on the materials used for fabricating biosensors and the probable applications of nanotechnology-enabled biosensors.

A facile COF loaded-molybdate resonance Rayleigh scattering and fluorescence dimode probe for determination of trace PO43

A new covalent organic framework loaded-molybdate (COF_Mo) nanomaterial was prepared simply by solvothermal procedure and characterized by electron microscopy and molecular spectral techniques. The COF_Mo had a strong resonance Rayleigh scattering (RRS) signal at 465 nm and a fluorescence peak at 345 nm. When the PO₄^3- was added in the system, it reacted with the molybdate, which loaded on the surface of COF particles, to form stable phosphomolybdic acid occurring RRS/fluorescence-energy transfer, the RRS and fluorescence signals were decreased. The decreased RRS/fluorescence intensities were linear to the PO₄^3- concentration in the range of 0.053-3.2 nmol/L and 0.10-3.2 nmol/L, with a detection limit of 0.050 nmol/L and 0.090 nmol/L respectively. Accordingly, a new and facile RRS/fluorescence dimode method for detection of trace PO₄^3- was established, only one fluorometer was used.

A smartphone-integrated light-up lanthanide fluorescent probe for the visual and ratiometric detection of total phosphorus in human urine and environmental water samples

Phosphate (Pi) plays an essential role in aquatic ecosystems as well as in physiological processes. Here, a dual-emission probe for the sensitive, specific and visual analysis of Pi is fabricated by coordinating Eu³⁺ with luminol and 2,6-pyridinedicarboxylic acid (DPA). Pi can significantly enhance the characteristic fluorescence of Eu³⁺ at 615 nm by promoting energy transfer from DPA to Eu³⁺ and reducing the quenching effect of water molecule, luminol with inherent emission at 423 nm further enhances the Eu³⁺ fluorescence. Accordingly, ratiometric detection of Pi can be achieved with the fluorescence ratio F₆₁₅/F₄₂₃ as a function of Pi concentration. Linearity between F₆₁₅/F₄₂₃ and Pi concentration in the range of 0.1-25 μM is shown, and the limit of detection (LOD, 3σ/K) for Pi is 0.027 µM. In addition, a continuous change in the fluorescence color of the probe from blue to red is observed with increasing Pi concentration under a UV lamp, and a smartphone-based visual method is used for the convenient and effective semi-quantitative determination of Pi. The dual-emission probe has been successfully applied to ratiometric and visual analysis of Pi in human urine and environmental water samples, and adequate results are obtained.

Light-Addressable Electrochemical Sensors toward Spatially Resolved Biosensing and Imaging Applications

The light-addressable electrochemical sensor (LAES) is a recently emerged bioanalysis technique combining electrochemistry with the photoelectric effect in a semiconductor. In an LAES, a semiconductor substrate is illuminated locally to generate charge carriers in a well-defined area, thereby confining the electrochemical process to a target site. Benefiting from the unique light addressability, an LAES can not only detect multiple analytes in parallel within a single sensor plate but also act as a bio(chemical) imaging sensor to visualize the two-dimensional distribution of specific analytes. An LAES usually has three working modes: a potentiometric mode using light-addressable potentiometric sensors (LAPS) and an impedance mode using scanning photoinduced impedance microscopy (SPIM), while an amperometric mode refers to light-addressable electrochemistry (LAE) and photoelectrochemical (PEC) sensing. In this review, we describe the detection principles of each mode of LAESs and the concept of light addressability. In addition, we highlight the recent progress and advance of LAESs in spatial resolution, sensor system design, multiplexed detection, and bio(chemical) imaging applications. An outlook on current research challenges and future prospects is also presented.

A Comprehensive Review on Water Quality Monitoring Devices: Materials Advances, Current Status, and Future Perspective

Water quality monitoring has become more critical in recent years to ensure the availability of clean and safe water from natural aquifers and to understand the evolution of water contaminants across time and space. The conventional water monitoring techniques comprise of sample collection, preservation, preparation, tailed by laboratory testing and analysis with cumbersome wet chemical routes and expensive instrumentation. Despite the high accuracy of these methods, the high testing costs, laborious procedures, and maintenance associated with them don't make them lucrative for end end-users and field testing. As the participation of ultimate stakeholders, that is, common man for water quality and quantity can play a pivotal role in ensuring the sustainability of our aquifers, thus it is essential to develop and deploy portable and user-friendly technical systems for monitoring water sources in real-time or on-site. The present review emphasizes here on possible approaches including optical (absorbance, fluorescence, colorimetric, X-ray fluorescence, chemiluminescence), electrochemical (ASV, CSV, CV, EIS, and chronoamperometry), electrical, biological, and surface-sensing (SPR and SERS), as candidates for developing such platforms. The existing developments, their success, and bottlenecks are discussed in terms of various attributes of water to escalate the essentiality of water quality devices development meeting ASSURED criterion for societal usage. These platforms are also analyzed in terms of their market potential, advancements required from material science aspects, and possible integration with IoT solutions in alignment with Industry 4.0 for environmental application.

Wide-Linear Range Cholesterol Detection Using Fe2O3 Nanoparticles Decorated ZnO Nanorods Based Electrolyte-Gated Transistor

Electrolyte-gated transistor (EGT)-based biosensors are created with nanomaterials to harness the advantages of miniaturization and excellent sensing performance. A cholesterol EGT biosensor based on iron oxide (Fe2O3) nanoparticles decorated ZnO nanorods is proposed here. ZnO nanorods are directly grown on the seeded channel using a hydrothermal method, keeping in mind the stability of nanorods on the channel during biosensor measurements in an electrolyte. Most importantly, ZnO nanorods can be effectively grown and modified with Fe2O3 nanoparticles to enhance stability, surface roughness, and performance. The cholesterol oxidase (ChOx) enzyme is immobilized over Fe2O3 nanoparticles decorated ZnO nanorods for cholesterol detection. With cholesterol addition in buffer solution, the electro-oxidation of cholesterol on enzyme immobilized surface led to increased the biosensor’s current response. The cholesterol EGT biosensor detected cholesterol in wide-linear range (i.e., 0.1 to 60.0 mM) with high sensitivity (37.34 µA/mMcm2) compared to conventional electrochemical sensors. Furthermore, we obtained excellent selectivity, fabrication reproducibility, long-term storage stability, and practical applicability in real serum samples. The demonstrated EGT biosensor can be extended with changing enzymes or nanomaterials or hybrid nanomaterials for specific analyte detection.

Recent Advances in Chemical Sensors for Soil Analysis: A Review

The continuously rising interest in chemical sensors’ applications in environmental monitoring, for soil analysis in particular, is owed to the sufficient sensitivity and selectivity of these analytical devices, their low costs, their simple measurement setups, and the possibility to perform online and in-field analyses with them. In this review the recent advances in chemical sensors for soil analysis are summarized. The working principles of chemical sensors involved in soil analysis; their benefits and drawbacks; and select applications of both the single selective sensors and multisensor systems for assessments of main plant nutrition components, pollutants, and other important soil parameters (pH, moisture content, salinity, exhaled gases, etc.) of the past two decades with a focus on the last 5 years (from 2017 to 2021) are overviewed.

Zinc(ii) Schiff base complexes as dual probes for the detection of NH4+ and HPO42− ions

Three novel Zn(ii) Schiff base complexes were obtained by solvent evaporation technique. 1 and 2 show selectively recognition of NH4+ and HPO42− accompanied with an efficient fluorescence “turn off” phenomenon.

Organic Bioelectronic Devices for Metabolite Sensing

Electrochemical detection of metabolites is essential for early diagnosis and continuous monitoring of a variety of health conditions. This review focuses on organic electronic material-based metabolite sensors and highlights their potential to tackle critical challenges associated with metabolite detection. We provide an overview of the distinct classes of organic electronic materials and biorecognition units used in metabolite sensors, explain the different detection strategies developed to date, and identify the advantages and drawbacks of each technology. We then benchmark state-of-the-art organic electronic metabolite sensors by categorizing them based on their application area (in vitro, body-interfaced, in vivo, and cell-interfaced). Finally, we share our perspective on using organic bioelectronic materials for metabolite sensing and address the current challenges for the devices and progress to come.

Selective, Ultra-sensitive and Rapid Detection of Serotonin by Optimized ZnO Nanorod FET Biosensor

BACKGROUND

Fluctuation in serotonin (5-HT) level is an essential manifestation of several neurological disorders. In view of such importance, it is necessary to monitor the levels of 5-HT with good sensitivity, selectivity, affordability and low response time. Zinc oxide (ZnO) based field effect transistors (FET) with attributes like minimized noise levels and large on-off ratio are regarded as emerging high performance biosensor platforms. However, their response is significantly non-linear and there has been no appreciable endeavor for improving the non-linearity.

METHOD

In this paper, we have introduced embedded gate electrode encompassing the channel of the FET which improves the uniformity in electric field line distribution through the electrolyte and proportionately enhances the capture of target biomolecule at ultra low concentrations, thereby increasing the linearity. Further, we have incorporated the optimized parameters of ZnO nanorods reported previously, for rapid and selective detection of 5-HT.

RESULTS

It has been observed that the fabricated ZnO FET biosensor lowers the detection limit down to 0.1fM which is at least one order of magnitude lower than the existing reports. The sensor also has wide linear range from 0.1fM to 1nM with a detection time of about 20 minutes.

CONCLUSION

The proposed zinc oxide nanorod-based sensor can be used as an excellent tool for future diagnosis of neurological disorders.

A Review of Nanocomposite-Modified Electrochemical Sensors for Water Quality Monitoring

Electrochemical sensors play a significant role in detecting chemical ions, molecules, and pathogens in water and other applications. These sensors are sensitive, portable, fast, inexpensive, and suitable for online and in-situ measurements compared to other methods. They can provide the detection for any compound that can undergo certain transformations within a potential window. It enables applications in multiple ion detection, mainly since these sensors are primarily non-specific. In this paper, we provide a survey of electrochemical sensors for the detection of water contaminants, i.e., pesticides, nitrate, nitrite, phosphorus, water hardeners, disinfectant, and other emergent contaminants (phenol, estrogen, gallic acid etc.). We focus on the influence of surface modification of the working electrodes by carbon nanomaterials, metallic nanostructures, imprinted polymers and evaluate the corresponding sensing performance. Especially for pesticides, which are challenging and need special care, we highlight biosensors, such as enzymatic sensors, immunobiosensor, aptasensors, and biomimetic sensors. We discuss the sensors' overall performance, especially concerning real-sample performance and the capability for actual field application.

Portable, stable, and sensitive assay to detect phosphate in water with gold nanoparticles (AuNPs) and dextran tablet

A novel and highly sensitive tablet-based colorimetric sensor is developed for the detection of phosphate (Pi) in drinking and surface water using mercaptoacetic acid-capped gold nanoparticles (MA-AuNPs). Characterization of AuNPs and MA-AuNPs was achieved by ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and Dynamic light scattering (DLS). The principle of this sensor is based on the aggregation and disaggregation mechanisms of AuNPs that result in a color change from blue to red due to the surface plasmon resonance effect, where europium ions (Eu³⁺) act as the aggregating agent. Herein, dextran is used to encapsulate the Eu³⁺ ions into a tablet format to make the detection system user friendly. Hence, the sensor only requires dissolving a Eu³⁺-dextran tablet into the water sample and subsequently adding MA-AuNPs for the colorimetric quantification of phosphate. This assay is very sensitive with a calculated detection limit of 0.3 μg L^-1 and an upper detection limit of 26 μg L^-1, while 10 μg L^-1 is the allowable limit of Pi in drinking water. A comparative study with a conventional Hach kit confirmed the accuracy of our sensor. Also, real water samples from river, lake, and tap sources were tested to examine the sensor's applicability towards commercialization. The assay did not interfere with common ions in water, thus being Pi-specific, and the performance of the assay was stable for up to at least three weeks. Overall, our new approach provides a simple, stable, rapid, low-cost and promising device for Pi detection in water.

Lanthanum-Zinc Binary Oxide Nanocomposite with Promising Heterogeneous Catalysis Performance for the Active Conversion of 4-Nitrophenol into 4-Aminophenol

This work intended to enhance the unique and outstanding properties of lanthanum by synthesizing its nanocomposite. A lanthanum-based nanocomposite was prepared by a simple and cost-effective “co-precipitation” method. Lanthanum nitrate (La (NO3)3) and zinc nitrate (Zn (NO3)2) were used as precursors. The lanthanum/zinc oxide nano composite formed was then calcined at 450 °C for 4 h in order to obtain a fine powder with size in the nano range of 1–100 nm. Characterization of the prepared catalyst was done by ultraviolet/visible spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence. Crystallinity and morphology were found by X-ray diffraction and scanning electron microscopy. The synthesized nanocomposite material was also tested for heterogeneous catalytic applications of 4-nitrophenol (4-NP) reduction into 4-aminophenol (4-AP). It was found to be successful in complete reduction of 4-NP with enhanced catalytic performance.

Recent Advances of Field-Effect Transistor Technology for Infectious Diseases

Field-effect transistor (FET) biosensors have been intensively researched toward label-free biomolecule sensing for different disease screening applications. High sensitivity, incredible miniaturization capability, promising extremely low minimum limit of detection (LoD) at the molecular level, integration with complementary metal oxide semiconductor (CMOS) technology and last but not least label-free operation were amongst the predominant motives for highlighting these sensors in the biosensor community. Although there are various diseases targeted by FET sensors for detection, infectious diseases are still the most demanding sector that needs higher precision in detection and integration for the realization of the diagnosis at the point of care (PoC). The COVID-19 pandemic, nevertheless, was an example of the escalated situation in terms of worldwide desperate need for fast, specific and reliable home test PoC devices for the timely screening of huge numbers of people to restrict the disease from further spread. This need spawned a wave of innovative approaches for early detection of COVID-19 antibodies in human swab or blood amongst which the FET biosensing gained much more attention due to their extraordinary LoD down to femtomolar (fM) with the comparatively faster response time. As the FET sensors are promising novel PoC devices with application in early diagnosis of various diseases and especially infectious diseases, in this research, we have reviewed the recent progress on developing FET sensors for infectious diseases diagnosis accompanied with a thorough discussion on the structure of Chem/BioFET sensors and the readout circuitry for output signal processing. This approach would help engineers and biologists to gain enough knowledge to initiate their design for accelerated innovations in response to the need for more efficient management of infectious diseases like COVID-19.

A Review on Biosensors and Recent Development of Nanostructured Materials-Enabled Biosensors

A biosensor is an integrated receptor-transducer device, which can convert a biological response into an electrical signal. The design and development of biosensors have taken a center stage for researchers or scientists in the recent decade owing to the wide range of biosensor applications, such as health care and disease diagnosis, environmental monitoring, water and food quality monitoring, and drug delivery. The main challenges involved in the biosensor progress are (i) the efficient capturing of biorecognition signals and the transformation of these signals into electrochemical, electrical, optical, gravimetric, or acoustic signals (transduction process), (ii) enhancing transducer performance i.e., increasing sensitivity, shorter response time, reproducibility, and low detection limits even to detect individual molecules, and (iii) miniaturization of the biosensing devices using micro-and nano-fabrication technologies. Those challenges can be met through the integration of sensing technology with nanomaterials, which range from zero- to three-dimensional, possessing a high surface-to-volume ratio, good conductivities, shock-bearing abilities, and color tunability. Nanomaterials (NMs) employed in the fabrication and nanobiosensors include nanoparticles (NPs) (high stability and high carrier capacity), nanowires (NWs) and nanorods (NRs) (capable of high detection sensitivity), carbon nanotubes (CNTs) (large surface area, high electrical and thermal conductivity), and quantum dots (QDs) (color tunability). Furthermore, these nanomaterials can themselves act as transduction elements. This review summarizes the evolution of biosensors, the types of biosensors based on their receptors, transducers, and modern approaches employed in biosensors using nanomaterials such as NPs (e.g., noble metal NPs and metal oxide NPs), NWs, NRs, CNTs, QDs, and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

Graphene/MoS2 Nanohybrid for Biosensors

Graphene has been studied a lot in different scientific fields because of its unique properties, including its superior conductivity, plasmonic property, and biocompatibility. More recently, transition metal dicharcogenide (TMD) nanomaterials, beyond graphene, have been widely researched due to their exceptional properties. Among the various TMD nanomaterials, molybdenum disulfide (MoS2) has attracted attention in biological fields due to its excellent biocompatibility and simple steps for synthesis. Accordingly, graphene and MoS2 have been widely studied to be applied in the development of biosensors. Moreover, nanohybrid materials developed by hybridization of graphene and MoS2 have a huge potential for developing various types of outstanding biosensors, like electrochemical-, optical-, or surface-enhanced Raman spectroscopy (SERS)-based biosensors. In this review, we will focus on materials such as graphene and MoS2. Next, their application will be discussed with regard to the development of highly sensitive biosensors based on graphene, MoS2, and nanohybrid materials composed of graphene and MoS2. In conclusion, this review will provide interdisciplinary knowledge about graphene/MoS2 nanohybrids to be applied to the biomedical field, particularly biosensors.

Biosensing based on field-effect transistors (FET): Recent progress and challenges

The use of field-Effect-Transistor (FET) type biosensing arrangements has been highlighted by researchers in the field of early biomarker detection and drug screening. Their non-metalized gate dielectrics that are exposed to an electrolyte solution cover the semiconductor material and actively transduce the biological changes on the surface. The efficiency of these novel devices in detecting different biomolecular analytes in a real-time, highly precise, specific, and label-free manner has been validated by numerous research studies. Considerable progress has been attained in designing FET devices, especially for biomedical diagnosis and cell-based assays in the past few decades. The exceptional electronic properties, compactness, and scalability of these novel tools are very desirable for designing rapid, label-free, and mass detection of biomolecules. With the incorporation of nanotechnology, the performance of biosensors based on FET boosts significantly, particularly, employment of nanomaterials such as graphene, metal nanoparticles, single and multi-walled carbon nanotubes, nanorods, and nanowires. Besides, their commercial availability, and high-quality production on a large-scale, turn them to be one of the most preferred sensing and screening platforms. This review presents the basic structural setup and working principle of different types of FET devices. We also focused on the latest progression regarding the use of FET biosensors for the recognition of viruses such as, recently emerged COVID-19, Influenza, Hepatitis B Virus, protein biomarkers, nucleic acids, bacteria, cells, and various ions. Additionally, an outline of the development of FET sensors for investigations related to drug development and the cellular investigation is also presented. Some technical strategies for enhancing the sensitivity and selectivity of detection in these devices are addressed as well. However, there are still certain challenges which are remained unaddressed concerning the performance and clinical use of transistor-based point-of-care (POC) instruments; accordingly, expectations about their future improvement for biosensing and cellular studies are argued at the end of this review.

Tri-functional Fe-Zr bi-metal-organic frameworks enable high-performance phosphate ion ratiometric fluorescent detection

Metal-organic frameworks (MOFs) featured with flexible design and versatile properties are finding increasing applications. In particular, integrating multiple functions into one framework can bring them improved detection efficiency towards various analytes. Herein, for the first time, a Fe-Zr bi-metal-organic framework (UiO-66(Fe/Zr)-NH2) with three functions (intrinsic fluorescence, peroxidase-mimicking activity, and specific recognition) is designed to establish a ratiometric fluorescent platform for high-performance phosphate ion (Pi) sensing. The use of a fluorescent organic ligand endows the MOF material with a strong intrinsic fluorescence at 435 nm. The presence of Fe3+/Fe2+ nodes offers good enzyme-like capacity to catalyze the o-phenylenediamine (OPD) substrate to fluorescent OPDox (555 nm), which then quenches the intrinsic fluorescence of UiO-66(Fe/Zr)-NH2 due to the inner filter effect. The Zr4+ nodes in the MOF material act as selective sites for Pi recognition. When Pi exists, it specifically adsorbs onto UiO-66(Fe/Zr)-NH2 and decreases the latter's peroxidase-mimetic activity, resulting in the less production of fluorescent OPDox. As a consequence, the intrinsic fluorescence of UiO-66(Fe/Zr)-NH2 at 435 nm is restored, and the signal from OPDox at 555 nm is reduced inversely. With the ratiometric strategy, efficient determination of Pi with outstanding sensitivity and selectivity was realized, giving a detection limit down to 85 nM in the concentration range of 0.2-266.7 μM. Accurate measurement of the target in practical water matrices was also validated, indicating its promising application for Pi analysis in environmental and other fields.

Smartphone-assisted off─on photometric determination of phosphate ion based on target-promoted peroxidase-mimetic activity of porous CexZr1-xO2 (x≥0.5) nanocomposites

Given the level of phosphate ion (Pi) is a significant indicator of eutrophication in environmental waters, it becomes quite important to develop efficient methods for its monitoring. In this research, we developed a smartphone-assisted off─on photometric approach for Pi analysis based on the analyte-promoted peroxidase-mimicking catalytic activity of porous Ce_xZr_1-xO₂ (x ≥ 0.5) nanocomposites. The Ce⁴⁺/Ce³⁺ redox pair in Ce_xZr_1-xO₂ endowed it with certain activity to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB) color reaction with the participation of H₂O₂, and both the existing Zr⁴⁺ and Ce⁴⁺ species enabled the nanozyme to specifically recognize Pi. It was observed that the bonded Pi could greatly promote the peroxidase-like activity of the Ce_xZr_1-xO₂ nanocomposite towards positively charged TMB. According to the new finding, high-performance sensing of Pi with wide detection range, high sensitivity and good selectivity was realized, giving a detection limit down to 0.09 μM. Further, a 3D-printed smartphone-based signal reading system was designed and coupled with the sensing method, enabling the rapid, convenient, in-field and instrument-free analysis of Pi for environmental monitoring.

Metal Oxides-Based Semiconductors for Biosensors Applications

The present mini review contains a concessive overview on the recent achievement regarding the implementation of a metal oxide semiconductor (MOS) in biosensors used in biological and environmental systems. The paper explores the pathway of enhancing the sensing characteristics of metal oxides by optimizing various parameters such as synthesis methods, morphology, composition, and structure. Four representative metal oxides (TiO₂, ZnO, SnO₂, and WO₃) are presented based on several aspects: synthesis method, morphology, functionalizing molecules, detection target, and limit of detection (LOD).

A terbium(III)-functionalized zinc(II)-organic framework for fluorometric determination of phosphate

A terbium(III)-functionalized zinc(II)-organic framework (Tb-MOF-Zn) is shown to be a viable fluorescent probe for phosphate. The organic ligands 4,4',4″-[((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(oxy)]tribenzoic acid (H₃L³) contains multiple carboxyl groups that can react with zinc(II) to yield tubular MOF-Zn. The MOF-Zn was further functionalized with Tb(III) to produce a lanthanide composite of type Tb-MOF-Zn which displays strong fluorescence with excitation/emission maxima at 285/544 nm. Fluorescence is quenched by phosphate because of the specific interaction with Tb(III) in Tb-MOF-Zn. The concentration of Tb-MOF-Zn, reaction time and pH value of the solution were optimized. Fluorescence drops linearly in the 0.01 to 200.0 μM phosphate concentration range, and the detection limit is 4.0 nM. The fluorescent probe was also used to prepare a microdot array on a glass slide for visual detection of phosphate under illumination with UV light. Graphical abstractA terbium(III) functionalized zinc(II)-organic framework was synthesized and used as fluorescent probe for determination of phosphate ions.

Field-Effect Transistor Biosensors for Biomedical Applications: Recent Advances and Future Prospects

During recent years, field-effect transistor biosensors (Bio-FET) for biomedical applications have experienced a robust development with evolutions in FET characteristics as well as modification of bio-receptor structures. This review initially provides contemplation on this progress by analyzing and summarizing remarkable studies on two aforementioned aspects. The former includes fabricating unprecedented nanostructures and employing novel materials for FET transducers whereas the latter primarily synthesizes compact molecules as bio-probes (antibody fragments and aptamers). Afterwards, a future perspective on research of FET-biosensors is also predicted depending on current situations as well as its great demand in clinical trials of disease diagnosis. From these points of view, FET-biosensors with infinite advantages are expected to continuously advance as one of the most promising tools for biomedical applications.

ZnO-based nanostructured electrodes for electrochemical sensors and biosensors in biomedical applications

Fascinating properties of ZnO nanostructures have created much interest due to their importance in health care and environmental monitoring. Current worldwide production and their wide range of applications signify ZnO to be a representative of multi-functional oxide material. Recent nanotechnological developments have stimulated the production of various forms of ZnO nanostructures such as nano-layers, nanoparticles, nanowires, etc. Due to their enhanced sensing properties, improved binding ability with biomolecules as well as biological activities have enabled them as suitable candidates for the fabrication of biosensor devices in the biomedical arena. In this review, the synthesis of ZnO nanostructures, mechanism of their interaction with biomolecules and their applications as sensors in health care area are discussed considering the biosensors for molecules with small molecular weight, infectious diseases, and pharmaceutical compounds.

Nozzle-Jet-Printed Silver/Graphene Composite-Based Field-Effect Transistor Sensor for Phosphate Ion Detection

High concentration of dissolved phosphate ions is the main responsible factor for eutrophication of natural water bodies. Therefore, detection of phosphate ions is essential for evaluating water eutrophication. There is a need at large-scale production of real-time monitoring technology to detect phosphorus accurately. In this study, facile enzymeless phosphate ion detection is reported using a nozzle-jet-printed silver/reduced graphene oxide (Ag/rGO) composite-based field-effect transistor sensor on flexible and disposable polymer substrates. The sensor exhibits promising results in low concentration as well as real-time phosphate ion detection. The sensor shows excellent performance with a wide linear range of 0.005-6.00 mM, high sensitivity of 62.2 μA/cm²/mM, and low detection limit of 0.2 μM. This facile combined technology readily facilitates the phosphate ion detection with high performance, long-term stability, excellent reproducibility, and good selectivity in the presence of other interfering anions. The sensor fabrication method and phosphate detection technique yield low-cost, user-friendly sensing devices with less analyte consumption, which are easy to fabricate on polymer substrates on a large scale. Besides, the sensor has the capability to sense phosphate ions in real water samples, which makes it applicable in environmental monitoring.

Recent Advances in Protein Kinase Activity Analysis Based on Nanomaterials

Protein phosphorylation regulated by protein kinases, as well as their dephosphorylation, is one of the most common post-translational modifications, and plays important roles in physiological activities, such as intracellular signal communications, gene transcription, cell proliferation and apoptosis. Over-expression of protein kinases is closely associated with various diseases. Consequently, accurate detection of protein kinases activities and their relevant inhibitors screening is critically important, not only to the biochemical research, but also to the clinical diagnosis and therapy. Nanomaterials, taking advantage of large surface areas, as well as excellent electrical, catalytic, magnetic and optical properties, have been utilized as target concentrators, recognition components, signal transducer or amplification elements in protein kinase related assays. This review summarizes the recent representative works to highlight the applications of nanomaterials in different biosensor technologies for protein kinases activities detection and their inhibitors screening. First, different nanomaterials developed for phosphoprotein/phosphopeptide enrichment and phosphate recognition are introduced. Next, representative works are selected that mainly focus on the utilization of nanomaterials as signal transducer or amplification elements in various protein kinases sensing platforms, such as electrochemical, colorimetric, fluorescent, and mass spectroscopy-based approaches. Finally, the major challenges and perspectives of nanomaterials being applied in protein kinases related assays are discussed.

Liquid gated ZnO nanorod FET sensor for ultrasensitive detection of Hepatitis B surface antigen with vertical electrode configuration

Detection of the Hepatitis-B surface antigen at the attomolar level is demonstrated using antibody functionalized liquid gated ZnO nanorods field effect transistor (FET) biosensor with vertical electrode configuration. The sensor is operated in heterodyne mode at high frequency to overcome the problem of Debye screening effect in physiological analyte. Enhanced penetration of the electric field lines through the nanorods enables significant improvement in the limit of detection and sensitivity compared to that of the conventional lateral electrode configuration. The combined effect of the probable change in the threshold voltage and the carrier mobility for vertical electrode configuration lead to a sensitivity of around 75% at 1 fM (which is an enhancement by 200%) and a detection limit of 20 aM with a dynamic range from 20 aM to 1 pM. The detection limit which is achieved with the proposed label free sensor in physiological analyte using antibodies is lowered by more than three orders of magnitude compared to the existing reports.

A Specific Turn-On Fluorescent Sensing for Ultrasensitive and Selective Detection of Phosphate in Environmental Samples Based on Antenna Effect-Improved FRET by Surfactant

Phosphate is not only an important indicator for aquatic ecosystems, but also plays vital roles in biosystems. A new strategy for ultrasensitive and selective detection of phosphate is fabricated based on a new insight found in this paper, in which a lower concentration of surfactant sodium dodecylbenzenesulfonate (SDBS) can greatly induce fluorescence resonance energy transfer (FRET) from ciprofloxacin (CIP) to Eu³⁺ in the CIP-Eu³⁺ complex. Surfactant SDBS does not act as a sensitizer for enhancing the fluorescence intensity of the system, but acts as a sensitizer of FRET and makes the native fluorescence of CIP quenched completely (switch off). Eu³⁺ ions can coordinate with the oxygen-donor atoms of phosphate, which weakens FRET from CIP to Eu³⁺ and results in the fluorescence recovery of CIP (turn on). The multicomplex of the CIP-Eu³⁺-phosphate has more sensitive fluorescent response than that of the reported coordination nanoparticle-based fluorescent probes. The LOD (S/N = 3) of this sensing system can attain 4.3 nM. The possible interferential substances existing in environmental samples, such as 17 common metal ions, 11 anions, and fulvic acid investigated, do not interfere with the phosphate detection. This sensing system has been successfully applied for phosphate detection in environmental samples such as wastewater, surface water, and atmospheric particulates. This work not only develops a fluorescent probe for the phosphate detection, but also provides a new strategy for designing fluorescent probes based on FRET or coordination nanoparticles.

Advanced bi-functional CoPi co-catalyst-decorated g-C3N4 nanosheets coupled with ZnO nanorod arrays as integrated photoanodes

In this work, a CoPi-decorated type II heterojunction composed of one-dimensional (1D) ZnO nanorod arrays (NRAs) coated with two-dimensional (2D) carbon nitride (g-C₃N₄) was successfully prepared and used as photoanode.

Field-Effect Biosensors for On-Site Detection: Recent Advances and Promising Targets

There is an explosive interest in the immediate and cost-effective analysis of field-collected biological samples, as many advanced biodetection tools are highly sensitive, yet immobile. On-site biosensors are portable and convenient sensors that provide detection results at the point of care. They are designed to secure precision in highly ionic and heterogeneous solutions with minimal hardware. Among various methods that are capable of such analysis, field-effect biosensors are promising candidates due to their unique sensitivity, manufacturing scalability, and integrability with computational circuitry. Recent developments in nanotechnological surface modification show promising results in sensing from blood, serum, and urine. This report gives a particular emphasis on the on-site efficacy of recently published field-effect biosensors, specifically, detection limits in physiological solutions, response times, and scalability. The survey of the properties and existing detection methods of four promising biotargets, exosomes, bacteria, viruses, and metabolites, aims at providing a roadmap for future field-effect and other on-site biosensors.

Highly Efficient Non-Enzymatic Glucose Sensor Based on CuO Modified Vertically-Grown ZnO Nanorods on Electrode

There is a major challenge to attach nanostructures on to the electrode surface while retaining their engineered morphology, high surface area, physiochemical features for promising sensing applications. In this study, we have grown vertically-aligned ZnO nanorods (NRs) on fluorine doped tin oxide (FTO) electrodes and decorated with CuO to achieve high-performance non-enzymatic glucose sensor. This unique CuO-ZnO NRs hybrid provides large surface area and an easy substrate penetrable structure facilitating enhanced electrochemical features towards glucose oxidation. As a result, fabricated electrodes exhibit high sensitivity (2961.7 μA mM^-1 cm^-2), linear range up to 8.45 mM, low limit of detection (0.40 μM), and short response time (<2 s), along with excellent reproducibility, repeatability, stability, selectivity, and applicability for glucose detection in human serum samples. Circumventing, the outstanding performance originating from CuO modified ZnO NRs acts as an efficient electrocatalyst for glucose detection and as well, provides new prospects to biomolecules detecting device fabrication.

Fabrication of a robust and highly sensitive nitrate biosensor based on directly grown zinc oxide nanorods on a silver electrode

This article reports the fabrication of a robust and highly sensitive nitrate biosensor based on directly-grown ZnO NRs on an electrode surface.