Electrochemical sensors and biosensors

Electrochemical flow injection analysis platforms for biomedical applications - Progress and prospects

Flow injection analysis coupled with electrochemical detection (FIA-ECD) techniques has to be a key technological development for wide variety of applications in various domains such as synthetic analytical chemistry, materials science, biomedical and point-of-care devices. FIA-ECD techniques have to be unique due to decreasing the time of analysis, sample pre-treatment, reactions and separation-free detection for multi-analytes. In biomedical domain, various electrochemical sensors were decorated with bioactive molecules, i.e., DNA, antibodies, enzymes along with biocompatible polymers for the detection of biologically important chemicals and analytes. The flexibility and practical applicability of these sensors may serve as a new pattern for clinical and biomedical analytical instrumentations. This review covers the highlights and overview of the most successful and promising electrochemical sensors, biosensors and immunosensors integrated with the flow injection analysis platforms, fabrication and analytical parameters, pros and cons of these sensor technologies, challenges and future opportunities in point-of-care clinical analysis.

Comprehensive insights into electrochemical nicotine sensing technologies

Nicotine is a significant alkaloid that is abundant in tobacco products. Given the addictive nature of tobacco products and the health risks associated with their consumption, accurate real-time monitoring of nicotine levels is necessary. Electrochemical sensors are low-cost and noninvasive devices for detecting various target molecules, even at trace levels, with advantages such as high sensitivity, portability, and fast response time. Nevertheless, reliable electrochemical detection of nicotine is particularly difficult because of the active interferents present in complex sample matrices. Recent advances in electrochemical sensing have focused on the development of chemically modified electrodes that mimic the oxidase activity of cytochrome P450, thereby improving the selectivity and sensitivity of nicotine detection. This paper discusses several innovative materials and strategies for the practical detection and quantification of nicotine in complex real-world samples. This study focuses on evaluating the factors influencing the sensing performance of the various electrode materials and electrochemical techniques used. The comprehensive information presented in this study will inform future research on the practical real-time monitoring of nicotine in tobacco products, emphasizing the simplicity, efficiency, and cost-effectiveness of the sensor design.

A novel ratiometric electrochemical assay for detection of formaldehyde in real food samples

This study developed a novel ratiometric electrochemical sensor for detecting formaldehyde content in food. For the first time, we innovatively utilized 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT), a traditional colorimetric probe that specifically reacts with formaldehyde, as an electrochemical probe to construct the electrochemical assay. The reaction product of AHMT with formaldehyde exhibits different redox potentials from AHMT, thereby enabling ratiometric detection of formaldehyde. We systematically investigated the electrochemical behavior of AHMT and its reaction product with formaldehyde. Under optimized conditions, this novel ratiometric electrochemical assay demonstrated high sensitivity and selectivity for formaldehyde, with a response linear range of 0.1-20 μM and a detection limit of 21 nM. Additionally, the sensor was successfully applied to detect formaldehyde in various mushrooms and fish, with measured concentrations of 1.34 μg g-1 in shimeji mushrooms, 0.80 μg g-1 in oyster mushrooms, 1.41 μg g-1 in enoki mushrooms, and 1.12 μg g-1 in king oyster mushrooms. For seafood, concentrations of 2.45 μg g-1 in cuttlefish and 0.83 μg∙g-1 in cutlassfish fish were detected. These results were validated against the standard method, underscoring the sensor's potential and reliability for practical applications. This study is anticipated to offer valuable insights for the development of innovative electrochemical sensors for food analysis.

Synergistic Effect of Nickel Hydroxide/Hexagonal Boron Nitride Hybrid: An Efficient Electrocatalyst for Detecting 5-Fluorouracil in Human Blood Serum

5-Fluorouracil (5-Fu) is the third-most often used chemotherapeutic medication and has been scientifically demonstrated to be effective in treating solid tumors, including colorectal, stomach, cutaneous, and breast cancers. When used in excess, it accumulates toxic metabolites, which can have deadly and very harmful effects on people, including neurotoxicity and the induction of morbidity. Therefore, sensitive and rapid analytical techniques for detecting 5-Fu in human blood serum are needed to enhance chemotherapy and forecast the possible adverse effects of 5-Fu residues in the human body. In this report, we developed a simple preparation of three-dimensional/two-dimensional (3D/2D) Nickel hydroxide/hexagonal boron nitride modified with a glassy carbon electrode [Ni(OH)2/h-BN/GCE] for effective electrochemical detection of the 5-fluorouracil with high selectivity. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution scanning electron microscopy (HR-SEM), and HR-Transmission electron microscopy (HR-TEM) were used to characterize the crystalline, structural, and chemical properties of the as-synthesized materials. Moreover, the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), square wave voltammetry (SWV), and i-t curves examined the electrode's electrochemical properties and sensor applications. Therefore, under ideal circumstances, Ni(OH)2/h-BN/GCE demonstrated outstanding 5-Fu selectivity, durability, a low LOD (0.001 μM), and a good linear range (0.02-12 μM). Finally, excellent results were obtained while testing this sensor for 5-Fu sensing in human blood serum.

Electrochemical Biosensors 3D Printed by Fused Deposition Modeling: Actualities, Trends, and Challenges

The technology of 3D printing, particularly fused deposition modeling (FDM) 3D printing, has revolutionized the development of electrochemical biosensors, offering a versatile and cost-effective approach for clinical applications. This review explores the integration of FDM in fabricating biosensing platforms tailored for clinical diagnostics, emphasizing its role in detecting various biomarkers and viral pathogens. Advances in 3D printing materials, especially the emergence of bespoke conductive filaments, have allowed the production of highly customizable and efficient biosensors. A detailed discussion focuses on the design and application of these biosensors for viral detection, highlighting their potential to improve diagnostic accuracy. Furthermore, the review addresses current trends, including the push towards miniaturization and multianalyte detection, alongside challenges such as material optimization and regulatory hurdles. By providing a comprehensive overview, this work underscores the transformative impact of 3D-printed electrochemical biosensors in clinical diagnostics while also identifying critical areas for future research and development.

Selective apigenin assay in plant extracts and herbal supplement with molecularly imprinted polymer-based electrochemical sensor

This study is the first successful application of a nanomaterial-supported molecularly imprinted polymer (MIP)-based electrochemical sensor for the sensitive and selective determination of apigenin (API), which is a naturally occurring product of the flavone class that is an aglycone of several glycosides. Secondary metabolites are biologically active substances produced by plants in response to various environmental factors. The levels of these compounds can vary depending on factors such as climate, soil conditions and the season in which the plants are grown. Therefore, the analysis of these compounds is essential to properly understand the biological effects of plant extracts and to ensure their safe use. To increase the glassy carbon electrode (GCE) surface's active surface area and porosity, zinc oxide nanoparticles (ZnO NPs) were integrated into the MIP-based electrochemical sensor design. Tryptophan methacrylate (TrpMA) was selected as the functional monomer along with other MIP components such as 2-hydroxyethyl methacrylate (HEMA, basic monomer), 2-hydroxy-2-methylpropiophenone (initiator), and ethylene glycol dimethacrylate (EGDMA, crosslinking agent). The morphological and electrochemical characterizations of the developed API/ZnO NPs/TrpMA@MIP-GCE sensor were performed with scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The indirect measurement approach via 5.0 mM [Fe(CN)6]3-/4- solution was utilized to determine API in the linear range of 1.0x10-13 M - 1.0x10-12 M. The limit of detection (LOD) and limit of quantification (LOQ) for standard solutions were found to be 2.47x10-14 and 8.23x10-14 M, respectively. In addition, the extraction processes were carried out using ultrasound-assisted extraction (UAE) and maceration (MCR) procedures. For Apium graveolens L., Petroselinum crispum (Mill.) Fuss and herbal supplement, the API recoveries varied from 98.79 % to 102.71 %, with average relative standard deviations (RSD) less than 2.25 % in all three cases. The sensor's successful performance in the presence of components with chemical structures similar to the API was also demonstrated, revealing its unique selectivity.

Engineering Nickel(II) Porphyrin-Conjugated Polymers with Different Aryl meso-Substituents for n-Type and p-Type Ammonia Sensors

Conjugated polymers have revolutionized the field of conductometric gas sensors for sensing toxic gases arising from the fast urbanization and industrialization. In this work, we report the synthesis of a series of 5,15-diaryl Ni(II) porphyrin-conjugated polymers (pNiD(Aryl)P) and their integration as the top layer on an octafluorinated copper phthalocyanine (CuF8Pc) sublayer to construct bilayer heterojunction (BLH) devices for ammonia sensing. For the first time, we report the pioneering demonstration of polarity engineering within a BLH device by manipulating the meso-substituent of the 5,15-diaryl Ni(II) porphyrin-conjugated polymer constituting the top layer of the CuF8Pc/pNiD(Aryl)P BLH device. The BLH devices prepared from the 5,15-diaryl Ni(II) porphyrin-conjugated polymer bearing electron-donating meso-substituents as the top layer exhibit a p-type behavior, whereas an n-type behavior is observed for the BLH devices prepared from the 5,15-diaryl Ni(II) porphyrin-conjugated polymer bearing electron-withdrawing meso-substituents. Laser desorption ionization high-resolution mass spectrometry, UV/vis/NIR, and X-ray photoelectron spectroscopy studies provide evidence of a decrease in intramolecular dehydrogenative coupling in pNiD(Aryl)P bearing electron-withdrawing meso-substituents, resulting in low electrical conductivity of the thin films. Density functional theory calculations reveal noninvolvement of electron-withdrawing meso-substituents toward π-delocalization in the fused Ni(II) porphyrin tapes. Interestingly, all the CuF8Pc/pNiD(Aryl)P BLH devices exhibit remarkable sensing response toward NH3. Among all the devices, CuF8Pc/pNiDPP displays the highest sensitivity of -1.17% ppm-1 for NH3, whereas CuF8Pc/pNiDNapP and CuF8Pc/pNiDCNPP exhibit the best limit of detection for NH3, below 200 ppb. In addition, CuF8Pc/pNiDCNPP shows short response and recovery times of 13 and 255 s, respectively, making this device highly suitable for deployment in emergency services.

Scientific Insights into the Quantum Dots (QDs)-Based Electrochemical Sensors for State-of-the-Art Applications

Size-dependent optical and electronic properties are unique characteristics of quantum dots (QDs). A significant advantage is the quantum confinement effect that allows their precise tuning to achieve required characteristics and behavior for the targeted applications. Regarding the aforementioned factors, QDs-based sensors have exhibited dramatic potential for the diverse and advanced applications. For example, QDs-based devices have been potentially utilized for bioimaging, drug delivery, cancer therapy, and environmental remediation. In recent years, use of QDs-based electrochemical sensors have been further extended in other areas like gas sensing, metal ion detection, monitoring of organic pollutants, and detection of radioactive isotopes. Objective of this study is to rationalize the QDs-based electrochemical sensors for state-of-the-art applications. This review article comprehensively illustrates the importance of aforementioned devices along with sources from which QDs devices have been formulated and fabricated. Other distinct features of QDs devices are associated with their extremely high active surfaces, inherent ability of reproducibility, sensitivity, and selectivity for the targeted analyte detection. In this review, major categories of QD materials along with justification of their key roles in electrochemical devices have been demonstrated and discussed. All categories have been evaluated with special emphasis on the advantages and drawbacks/challenges associated with QD materials. However, in the interests of readers and researchers, recent improvements also have been included and discussed. On the evaluation, it has been concluded that despite significant challenges, QDs-based electrochemical sensors exhibit excellent performances for state-of-the-art and targeted applications.

Chirality identification of Ibuprofen enantiomers by a terahertz polarization-sensitive metasurface sensor

Chirality plays an important role in medicine, biology, and chemistry. Molecules of different chirality could display dramatically different medical effects, pharmacological activities, and physiological impacts. Ibuprofen is an important anti-inflammatory drug in clinics. The anti-inflammatory effect is almost solely attributed to the (S)-(+)-Ibuprofen, while its enantiomer (R)-(-)-Ibuprofen plays a negative effect on increasing the metabolic burden. In this work, a terahertz (THz) polarization-sensitive metasurface sensor is proposed for qualitative and quantitative identification of the chiral Ibuprofen. The chirality parameters of Ibuprofen are extracted from the circular-polarized transmission coefficients. The parameters are further used to simulate the coupling mechanism between the Ibuprofen and the sensor to explain the principle of recognition. The sensitivities of (R)-(-)-Ibuprofen and (S)-(+)-Ibuprofen are found to be 1.5 THz/(mg/L) and 1.8 THz/(mg/L) for the TM polarization, respectively, and 1.7 THz/(mg/L) and 2.1 THz/(mg/L) for the TE polarization, respectively. The difference enables the chirality identification according to the different frequency shift at the same concentration. The exceptional specificity and sensitivity provide a new avenue for chiral molecular recognition.

Eco-friendly bupropion detection sensor with co-formulated dextromethorphan in AUVELITY tablet and spiked plasma

Molecularly Imprinted Polymers (MIPs) are synthetic materials designed to selectively recognize and bind to specific target molecules. The process of determining Bupropion (BUP) using MIPs involves preparing the MIP, extracting the target molecule, and conducting subsequent analysis. A bio-inspired MIP-based electrochemical sensor was developed to detect BUP, utilizing the specific binding of MIPs to Bupropion molecules, enabling precise and sensitive detection. The combination of molecular imprinting and electrochemistry in this approach allows for the development of a highly reliable and effective sensor specifically designed for BUP detection. In this method, copolymerization conditions were carefully optimized to ensure selectivity and sensitivity in detecting BUP. Different monomers, including o-phenylenediamine, 4-aminophenol, L-dopa, and 1,4-phenylenediamine, were explored, with the best interaction observed for L-dopa and 1,4-phenylenediamine. Consequently, their copolymer was implemented to create selective MIPs through a straightforward electropolymerization process on a disposable pencil graphite electrode (PGE) substrate for BUP detection. The functionality of the copolymer of L-dopa and 1,4-phenylenediamine as an electroactive copolymer in preparing electro-polymerized MIP films was investigated for the first time. This was demonstrated by constructing a novel electrochemical sensor for the selective recognition of BUP in different matrices. The interactions between L-dopa and 1,4-phenylenediamine, used as functional monomers, and the template were studied experimentally using UV spectroscopy. BUP was used as the template, and the copolymer was electrografted onto PGE. The constructed sensor was characterized using cyclic voltammetry (CV), and BUP binding to the MIP cavities was measured indirectly with differential pulse voltammetry (DPV) using a ferrocyanide/ferricyanide redox probe. A linear and repeatable response was displayed by the sensor across a range of 1.0 × 10⁻13 M to 1.0 × 10⁻11 M of BUP, with a limit of detection of 3.18 × 10⁻14 M. The sensor demonstrated robust selectivity for BUP over interfering drugs, such as dextromethorphan, in pharmaceutical dosage forms and spiked human plasma. The environmental impact of the proposed approach was evaluated using green analytical chemistry principles, including the Green Analytical Procedure Index (GAPI) and the Analytical GREEnness (AGREE) metric.

A polyoxometalate/chitosan-Ti3C2Tx MXene nanocomposite constructed by electrostatically mediated strategy for electrochemical detecting L-tryptophan in milk

L-tryptophan (L-Trp) is crucial for human metabolism, and its imbalance or deficiency can lead to certain diseases, such as insomnia, depression, and heart disease. Since the body cannot synthesize L-Trp and must obtain it from external sources, accurately monitoring L-Trp levels in food is essential. Herein, a nanocomposite film based on polyoxometalate (P2Mo17V), Ti3C2Tx MXene, and chitosan (Cs) was developed through a green electrostatically mediated layer-by-layer self-assembly strategy for electrochemical detection of L-Trp. The composite film exhibits fast electron transfer and remarkable electrocatalytic performance for L-Trp with a wide linear range (0.1-103 μM), low limit of detection (0.08 μM, S/N = 3), good selectivity, reproducibility, and repeatability. In milk sample, the recoveries of L-Trp were from 95.78% and 104.31%. The P2Mo17V/Cs-Ti3C2Tx electrochemical sensor not only provides exceptional recognition and detection capabilities for L-Trp but also shows significant potential for practical applications, particularly in food safety and quality control.

Progress and Challenges of Monometallic Titanium Coordination Polymers

The realm of titanium coordination polymer research is still in its nascent stages and presents a formidable challenge in the field of coordination chemistry. In recent decades, the focus has predominantly been on manipulating titanium reactions in solution, resulting in the synthesis of ≈60 targeted compounds. Despite the limited number of documented instances, these materials showcase a diverse array of structures, encompassing 1D chains, 2D layers, and 3D frameworks. This suggests potential for fine-tuning coordination modes and structural features in future investigations. Moreover, titanium coordination polymers not only exhibit photo-active and photo-responsive properties but also hold promise for various other significant applications. This article offers an exhaustive review tracing the evolution of titanium coordination polymer development while providing an update on recent advancements. The review encompasses a synopsis of reported synthetic strategies, methodologies, structural diversity, and associated applications. Additionally, it delves into critical issues that necessitate attention for future progressions and proposes potential avenues to effectively propel this research field forward at an accelerated pace.

Stainless Steel Mesh in Electrochemistry: Comprehensive Applications and Future Prospects

Stainless steel mesh (SSM) has emerged as a cornerstone in electrochemical applications owing to its exemplary versatility, electrical conductivity, mechanical robustness, and corrosion resistance. This state-of-the-art review delves into the diverse roles of SSM across a spectrum of electrochemical domains, including energy conversion and storage devices, water treatment technologies, electrochemical sensors, and catalysis. We meticulously explore its deployment in supercapacitors, batteries, and fuel cells, highlighting its utility as a current collector, electrode, and separator. The review further discusses the critical significance of SSM in water treatment processes, emphasizing its efficacy in supporting membranes and facilitating electrocoagulation, as well as its novel uses in electrochemical sensing and catalysis, which include electrosynthesis and bioelectrochemistry. Each section delineates the recent advancements, identifies the inherent challenges, and suggests future directions for leveraging SSM in electrochemical technologies. This comprehensive review showcases the current state of knowledge and articulates the novel integration of SSM with emerging materials and technologies, thereby establishing a new paradigm for sustainable and efficient electrochemical applications. Through critical analysis and insightful recommendations, this review positions itself as a seminal contribution, paving the way for researchers and practitioners to harness the full potential of SSM in advancing the electrochemistry frontiers.

Metal Organic Frameworks Based Wearable and Point-of-Care Electrochemical Sensors for Healthcare Monitoring

The modern healthcare system strives to provide patients with more comfortable and less invasive experiences, focusing on noninvasive and painless diagnostic and treatment methods. A key priority is the early diagnosis of life-threatening diseases, which can significantly improve patient outcomes by enabling treatment at earlier stages. While most patients must undergo diagnostic procedures before beginning treatment, many existing methods are invasive, time-consuming, and inconvenient. To address these challenges, electrochemical-based wearable and point-of-care (PoC) sensing devices have emerged, playing a crucial role in the noninvasive, continuous, periodic, and remote monitoring of key biomarkers. Due to their numerous advantages, several wearable and PoC devices have been developed. In this focused review, we explore the advancements in metal-organic frameworks (MOFs)-based wearable and PoC devices. MOFs are porous crystalline materials that are cost-effective, biocompatible, and can be synthesized sustainably on a large scale, making them promising candidates for sensor development. However, research on MOF-based wearable and PoC sensors remains limited, and no comprehensive review has yet to synthesize the existing knowledge in this area. This review aims to fill that gap by emphasizing the design of materials, fabrication methodologies, sensing mechanisms, device construction, and real-world applicability of these sensors. Additionally, we underscore the importance and potential of MOF-based wearable and PoC sensors for advancing healthcare technologies. In conclusion, this review sheds light on the current state of the art, the challenges faced, and the opportunities ahead in MOF-based wearable and PoC sensing technologies.

Recent advances in ctDNA detection using electrochemical biosensor for cancer

In the quest for early cancer diagnosis, early identification and treatment are paramount. Recently, ctDNA detection has emerged as a viable avenue for early screening of cancer. The examination of ctDNA in fluid biopsies has gained substantial attention in tumor diagnosis and therapy. Both the scientific community and industry are actively exploring this field. However, developing cost-effective, portable, and real-time ctDNA measurement methods using conventional gene detection equipment poses a significant challenge. This challenge has led to the exploration of alternative approaches. Electrochemical biosensors, distinguished by their heightened sensitivity, remarkable specificity, affordability, and excellent portability, have emerged as a promising avenue for ctDNA detection. This review is dedicated to the specific focus on ctDNA detection, highlighting recent advancements in this evolving detection technology. We aimed to reference previous studies related to ctDNA-targeted cancer detection using electrochemical biosensors to advocate the utilization of electrochemical biosensors in healthcare diagnostics. Further research is imperative for the effective integration of ctDNA analysis into point-of-care cancer testing. Innovative approaches utilizing multiple markers need to be explored to advance this technology and make substantial contributions to societal well-being.

Synthesis, Modulation, and Application of Two-Dimensional TMD Heterostructures

Two-dimensional (2D) transition metal dichalcogenide (TMD) heterostructures have attracted a lot of attention due to their rich material diversity and stack geometry, precise controllability of structure and properties, and potential practical applications. These heterostructures not only overcome the inherent limitations of individual materials but also enable the realization of new properties through appropriate combinations, establishing a platform to explore new physical and chemical properties at micro-nano-pico scales. In this review, we systematically summarize the latest research progress in the synthesis, modulation, and application of 2D TMD heterostructures. We first introduce the latest techniques for fabricating 2D TMD heterostructures, examining the rationale, mechanisms, advantages, and disadvantages of each strategy. Furthermore, we emphasize the importance of characteristic modulation in 2D TMD heterostructures and discuss some approaches to achieve novel functionalities. Then, we summarize the representative applications of 2D TMD heterostructures. Finally, we highlight the challenges and future perspectives in the synthesis and device fabrication of 2D TMD heterostructures and provide some feasible solutions.

Cortisol: Biosensing and detection strategies

Cortisol, a crucial steroid hormone synthesized by the adrenal glands, has diverse impacts on multiple physiological processes, such as metabolism, immune function, and stress management. Disruption in cortisol levels can result in conditions like Cushing's syndrome and Addison's disease. This review provides an in-depth exploration of cortisol, covering its structure, various forms in the body, detection methodologies, and emerging trends in cancer treatment and detection. Various techniques for cortisol detection, including electrochemical, chromatographic, and immunoassay methods were discussed and highlighted for their merits and applications. Electrochemical immunosensing emerges as a promising approach, which offered high sensitivity and low detection limits. Moreover, the review delves into the intricate relationship between cortisol and cancer, emphasizing cortisol's role in cancer progression and treatment outcomes. Lastly, the utilization of biomarkers, in-silico modeling, and machine learning for electrochemical cortisol detection were explored, which showcased innovative strategies for stress monitoring and healthcare advancement.

Curcumin-derivatives as fluorescence-electrochemical dual probe for ultrasensitive detections of picric acid in aqueous media

We are reporting the two curcumin derivatives, ferrocenyl curcumin (Fc-cur) and 4-nitro-benzylidene curcumin (NBC), as a probe through dual modalities, i.e., fluorescence and electrochemical methods, for the detection of nitro-analytes, such as picric acid (PA). The probes exhibited aggregation-induced enhanced emission (AIEE), and the addition of picric acid (PA) demonstrated good and specific fluorimetric identification of PA in the aggregated state. By using density functional theory (DFT), the mechanism of picric acid's (PA) interactions with the probes was further investigated. DFT studies shows evidence of charge transfer from curcumin derivatives probe to picric acid resulting into the formation of an adduct. The reduction of trinitrophenol (PA) to 2, 4, 6-trinitrosophenol was investigated utilizing a probe-modified glassy carbon electrode (GCE) with a good detection limit of 9.63 ± 0.001 pM and 41.01 ± 0.002 pM, respectively, for Fc-cur@GCE and NBC@GCE, taking into account the redox behavior of the probe. The applicability of the designed sensor has been utilized for real-time application in the estimation of picric acid in several water samples collected from the different source.

Ferritin Single-Electron Transistor

We report on the fabrication of a single-electron transistor based on ferritin using wide self-aligned nanogap devices. A local gate below the gap area enables three-terminal electrical measurements, showing the Coulomb blockade in good agreement with the single-electron tunneling theory. Comparison with this theory allows extraction of the tunnel resistances, capacitances, and gate coupling. Additionally, the data suggest the presence of two separate islands coupled in series or in parallel: information that was not possible to distinguish by using only two-terminal measurements. To interpret the charge transport features, we propose a scenario based on the established configuration structures of ferritin involving either iron sites in the organic shell or two dissimilar clusters within the core.

Surface-Enhanced Raman Spectroscopy and Electrochemistry: The Ultimate Chemical Sensing and Manipulation Combination

One of the lessons we learned from the COVID-19 pandemic is that the need for ultrasensitive detection systems is now more critical than ever. While sensors' sensitivity, portability, selectivity, and low cost are crucial, new ways to couple synergistic methods enable the highest performance levels. This review article critically discusses the synergetic combinations of optical and electrochemical methods. We also discuss three key application fields-energy, biomedicine, and environment. Finally, we selected the most promising approaches and examples, the open challenges in sensing, and ways to overcome them. We expect this work to set a clear reference for developing and understanding strategies, pros and cons of different combinations of electrochemical and optical sensors integrated into a single device.

Portable sensing methods based on carbon dots for food analysis

Food analysis is significantly important in monitoring food quality and safety for human health. Traditional methods for food detection mainly rely on benchtop instruments and require a certain amount of analysis time, which promotes the development of portable sensors. Portable sensing methods own many advantages over traditional techniques such as flexibility and accessibility in diverse environments, real-time monitoring, cost-effectiveness, and rapid deployment. This review focuses on the portable approaches based on carbon dots (CDs) for food analysis. CDs are zero-dimensional carbon-based material with a size of less than 10 nm. In the manner of sensing, CDs exhibit rich functional groups, low biotoxicity, good biocompatibility, and excellent optical properties. Furthermore, there are many methods for the synthesis of CDs using various precursor materials. The incorporation of CDs into food science and engineering for enhancing food safety control and risk assessment shows promising prospects.

The Biomedical Applications of Biomolecule Integrated Biosensors for Cell Monitoring

Cell monitoring is essential for understanding the physiological conditions and cell abnormalities induced by various stimuli, such as stress factors, microbial invasion, and diseases. Currently, various techniques for detecting cell abnormalities and metabolites originating from specific cells are employed to obtain information on cells in terms of human health. Although the states of cells have traditionally been accessed using instrument-based analysis, this has been replaced by various sensor systems equipped with new materials and technologies. Various sensor systems have been developed for monitoring cells by recognizing biological markers such as proteins on cell surfaces, components on plasma membranes, secreted metabolites, and DNA sequences. Sensor systems are classified into subclasses, such as chemical sensors and biosensors, based on the components used to recognize the targets. In this review, we aim to outline the fundamental principles of sensor systems used for monitoring cells, encompassing both biosensors and chemical sensors. Specifically, we focus on biosensing systems in terms of the types of sensing and signal-transducing elements and introduce recent advancements and applications of biosensors. Finally, we address the present challenges in biosensor systems and the prospects that should be considered to enhance biosensor performance. Although this review covers the application of biosensors for monitoring cells, we believe that it can provide valuable insights for researchers and general readers interested in the advancements of biosensing and its further applications in biomedical fields.

A highly sensitive ion-selective chemiresistive sensor for online monitoring of lead ions in water

Dissolved lead is a serious but common health hazard in drinking water, yet there is still no practical way to monitor its levels continuously in the distribution system or at the point of use. Here we propose using a lead-selective membrane on top of a chemiresistive device to continuously measure Pb2+ ion concentrations in real time. The detection limit was lowered by stabilizing the surface of the resistive film with sodium hydroxide and 15-crown-5 ether and optimizing the sensor geometry to maximize the effective surface area. The detection mechanism is based on the complexation of the Pb2+ ions by the lead ionophores within the membrane, thus modulating the interactions between the ionophores and the chemiresistive film. The limit of detection of the fabricated devices was reliably below 2 μg L-1, with concentrations up to 3 mg L-1 routinely quantifiable over several measurement cycles. The chemiresistive sensors can thus achieve lower detection limits than potentiometric devices while being more robust and simpler to fabricate by omitting the reference electrode. Ion-selective membrane-covered chemiresistors can therefore be deployed to continuously monitor drinking water sources and detect harmful levels of lead in real time.

Adaptive Fabrication of Electrochemical Chips with a Paste-Dispensing 3D Printer

Electrochemical (EC) detection is a powerful tool supporting simple, low-cost, and rapid analysis. Although screen printing is commonly used to mass fabricate disposable EC chips, its mask is relatively expensive. In this research, we demonstrated a method for fabricating three-electrode EC chips using 3D printing of relatively high-viscosity paste. The electrodes consisted of two layers, with carbon paste printed over silver/silver chloride paste, and the printed EC chips were baked at 70 °C for 1 h. Engineering challenges such as bulging of the tubing, clogging of the nozzle, dripping, and local accumulation of paste were solved by material selection for the tube and nozzle, and process optimization in 3D printing. The EC chips demonstrated good reversibility in redox reactions through cyclic voltammetry tests, and reliably detected heavy metal ions Pb(II) and Cd(II) in solutions using differential pulse anodic stripping voltammetry measurements. The results indicate that by optimizing the 3D printing of paste, EC chips can be obtained by maskless and flexible 3D printing techniques in lieu of screen printing.

The Challenges and Opportunities for TiO2 Nanostructures in Gas Sensing

Chemiresistive gas sensors based on metal oxides have been widely applied in industrial monitoring, medical diagnosis, environmental pollutant detection, and food safety. To further enhance the gas sensing performance, researchers have worked to modify the structure and function of the material so that it can adapt to different gas types and environmental conditions. Among the numerous gas-sensitive materials, n-type TiO2 semiconductors are a focus of attention for their high stability, excellent biosafety, controllable carrier concentration, and low manufacturing cost. This Perspective first introduces the sensing mechanism of TiO2 nanostructures and composite TiO2-based nanomaterials and then analyzes the relationship between their gas-sensitive properties and their structure and composition, focusing also on technical issues such as doping, heterojunctions, and functional applications. The applications and challenges of TiO2-based nanostructured gas sensors in food safety, medical diagnosis, environmental detection, and other fields are also summarized in detail. Finally, in the context of their practical application challenges, future development technologies and new sensing concepts are explored, providing new ideas and directions for the development of multifunctional intelligent gas sensors in various application fields.

A MOF-Templated Double-Shelled Co3O4/NiCo2O4 Nanocomposite for Electrochemical Detection of Alfuzosin

We developed a novel electrochemical sensor for the detection of alfuzosin (AFZ), a drug used to treat benign prostatic hyperplasia, using a double-shelled Co3O4/NiCo2O4 nanocomposite-modified electrode. The nanocomposites were synthesized using a template-assisted approach, with zeolitic imidazole framework-67 (ZIF-67) as the sacrificial template, involving the formation of uniform ZIF-67/Ni-Co layered double hydroxide (LDH) hollow structures followed by calcination to achieve the final nanocomposite. The nanocomposite was characterized by various techniques and showed high porosity, large surface area, and good conductivity. The nanocomposite-modified electrode exhibited excellent electrocatalytic activity towards AFZ oxidation, with a wide linear range of 5-180 µM and a low limit of detection of 1.37 µM. The sensor also demonstrated good repeatability, reproducibility, and stability selectivity in the presence of common interfering substances. The sensor was successfully applied to determine the AFZ in pharmaceutical tablets and human serum samples, with satisfactory recoveries. Our results suggest that the double-shelled Co3O4/NiCo2O4 nanocomposite is a promising material for the fabrication of electrochemical sensors for AFZ detection.

Singlet oxygen-based photoelectrochemical detection of single-point mutations in the KRAS oncogene

Single nucleotide point mutations in the KRAS oncogene occur frequently in human cancers, rendering them intriguing targets for diagnosis, early detection and personalized treatment. Current detection methods are based on polymerase chain reaction, sometimes combined with next-generation sequencing, which can be expensive, complex and have limited availability. Here, we propose a novel singlet oxygen (1O2)-based photoelectrochemical detection methodology for single-point mutations, using KRAS mutations as a case study. This detection method combines the use of a sandwich assay, magnetic beads and robust chemical photosensitizers, that need only air and light to produce 1O2, to ensure high specificity and sensitivity. We demonstrate that hybridization of the sandwich hybrid at high temperatures enables discrimination between mutated and wild-type sequences with a detection rate of up to 93.9%. Additionally, the presence of background DNA sequences derived from human cell-line DNA, not containing the mutation of interest, did not result in a signal, highlighting the specificity of the methodology. A limit of detection as low as 112 pM (1.25 ng/mL) was achieved without employing any amplification techniques. The developed 1O2-based photoelectrochemical methodology exhibits unique features, including rapidity, ease of use, and affordability, highlighting its immense potential in the field of nucleic acid-based diagnostics.

Recent Advances in Low-Dimensional Metal Oxides via Sol-Gel Method for Gas Detection

Low-dimensional metal oxides have drawn significant attention across various scientific domains due to their multifaceted applications, particularly in the field of environment monitoring. Their popularity is attributed to a constellation of unique properties, including their high surface area, robust chemical stability, and remarkable electrical conductivity, among others, which allow them to be a good candidate for detecting CO, CO2, H2, NH3, NO2, CH4, H2S, and volatile organic compound gases. In recent years, the Sol-Gel method has emerged as a powerful and versatile technique for the controlled synthesis of low-dimensional metal oxide materials with diverse morphologies tailored for gas sensing applications. This review delves into the manifold facets of the Sol-Gel processing of metal oxides and reports their derived morphologies and remarkable gas-sensing properties. We comprehensively examine the synthesis conditions and critical parameters governing the formation of distinct morphologies, including nanoparticles, nanowires, nanorods, and hierarchical nanostructures. Furthermore, we provide insights into the fundamental principles underpinning the gas-sensing mechanisms of these materials. Notably, we assess the influence of morphology on gas-sensing performance, highlighting the pivotal role it plays in achieving exceptional sensitivity, selectivity, and response kinetics. Additionally, we highlight the impact of doping and composite formation on improving the sensitivity of pure metal oxides and reducing their operation temperature. A discussion of recent advances and emerging trends in the field is also presented, shedding light on the potential of Sol-Gel-derived nanostructures to revolutionize the landscape of gas sensing technologies.

CA19-9 and CEA biosensors in pancreatic cancer

Cancer is a complex pathophysiological condition causing millions of deaths each year. Early diagnosis is essential especially for pancreatic cancer. Existing diagnostic tools rely on circulating biomarkers such as Carbohydrate Antigen 19-9 (CA19-9) and Carcinoembryonic Antigen (CEA). Unfortunately, these markers are nonspecific and may be increased in a variety of disorders. Accordingly, diagnosis of pancreatic cancer generally involves more invasive approaches such as biopsy as well as imaging studies. Recent advances in biosensor technology have allowed the development of precise diagnostic tools having enhanced analytical sensitivity and specificity. Herein we examine these advances in the detection of cancer in general and in pancreatic cancer specifically. Furthermore, we highlight novel technologies in the measurement of CA19-9 and CEA and explore their future application in the early detection of pancreatic cancer.

Nanomaterials based sensors for analysis of food safety

The freshnessof the food is a major issue because spoiled food lacks critical nutrients for growth and could be harmful to human health if consumed directly. Nanomaterials are captivating due to their unique properties like large surface area, high selectivity, small dimension, great biocompatibility and conductivity, real-time onsite analysis, etc. which give them an advantage over conventional evaluation techniques. Despite these advantages of nanomaterials used in food safety and their preservation, food products can still get affected by various environmental factors (like pH, temperature, etc.), making the use of time-temperature indicators more condescending. This review is a comprehensive study on food safety, its causes, the responsible analytes, their remedies by various nanomaterials, the development of various nanosensors, and the various challenges faced in maintaining food safety standards to reduce the risk of contaminants.

Advances in nanobiosensors during the COVID-19 pandemic and future perspectives for the post-COVID era

The unprecedented threat of the highly contagious virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes exponentially increased infections of coronavirus disease 2019 (COVID-19), highlights the weak spots of the current diagnostic toolbox. In the midst of catastrophe, nanobiosensors offer a new opportunity as an alternative tool to fill a gap among molecular tests, rapid antigen tests, and serological tests. Nanobiosensors surpass the potential of antigen tests because of their enhanced sensitivity, thus enabling us to see antigens as stable and easy-to-access targets. During the first three years of the COVID-19 pandemic, a substantial number of studies have reported nanobiosensors for the detection of SARS-CoV-2 antigens. The number of articles on nanobiosensors and SARS-CoV-2 exceeds the amount of nanobiosensor research on detecting previous infectious diseases, from influenza to SARS-CoV and MERS-CoV. This unprecedented publishing pace also implies the significance of SARS-CoV-2 and the present pandemic. In this review, 158 studies reporting nanobiosensors for detecting SARS-CoV-2 antigens are collected to discuss the current challenges of nanobiosensors using the criteria of point-of-care (POC) diagnostics along with COVID-specific issues. These advances and lessons during the pandemic pave the way for preparing for the post-COVID era and potential upcoming infectious diseases.

A molecularly imprinted sensor for single-molecule detection of pesticide metabolite at the amol/L level sensitized by water-soluble luminol derivative encapsulated liposome via click reaction

A novel luminol derivative, 4-[(1,4-dioxo-1,2,3,4-tetrahydrophthalazin-5-yl)amino]-4-oxobut-2-enoic acid (ALD) with electrochemiluminescence intensity and stability characteristics similar to luminol, but higher solubility in near neutral solution, was designed and synthesized in this study. Using this derivative, a molecular imprinted electrochemiluminescence sensor (MIECLS) was prepared for the sensitive and selective determination of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT), a metabolite of bismerthiazol, thiediazole copper, thiazole zinc, and other pesticides. The ALD probes encapsulated in liposomes are immobilized on the molecularly imprinted film by light-triggered click reaction, and the concurrent release of multiple probes allows for highly sensitive detection. In the AMT concentration range of 1.00 × 10-18 - 5.00 × 10-13 mol/L, the relation between ECL response and log AMT concentration is linear. With a detection limit of 5.25 × 10-19 mol/L (about 4 - 6 molecules in 10 μL of the sample), the sensor allows for high sensitivity analysis of ultra-trace amounts of small organic compounds. In general, the ECL-based single-molecule detection technique proposed herein might be a promising alternative to fluorescence single-molecule detection.

MoO2 Pump-Enhanced Flexible TiO2 Nanojungle-Based Chemiresistors for Rapid Room-Temperature Detection of H2S at Parts-per-Billion Levels

In this study, we developed a gas sensing platform that can sensitively and specifically detect trace H2S in a high-humidity atmosphere at RT. Upon integrating a carbon nitride (C3N4) nanofilm and molybdenum dioxide (MoO2) nanosheets onto nanojungle-like TiO2 nanotube arrays (TiNTs), the fabricated chemiresistor showed rapid response (38 s)/recovery (58 s) abilities and remarkable detection sensitivity for H2S at concentrations down to 2 ppb, with an estimated detection limit of 1.13 ppb at RT and room-environmental light (REL). Importantly, the gas sensor exhibited satisfactory H2S sensing performance even in dark conditions with a response of 1.9 at 200 ppb. In this design, apart from the architectural advantages of the nanojungle-like TiNTs for accelerating the gas flow efficiency and the abundant sensing sites provided by the C3N4 film, the MoO2 nanosheets act as the essential electron pump not only for the H2S response but also for the subsequent recovery process in air. After employing the MoO2 pump onto C3N4/TiNTs, the response time and recovery time of the system are shortened to ∼35 and ∼11%, respectively. Moreover, we demonstrated the good performance of the flexible gas sensor in detecting trace H2S in human exhaled breath with good humidity resistance. These results highlight the possibility of designing chemiresistors operating in RT and REL conditions and to use these environmentally friendly TiO2-based sensors in real applications.

Quantifying arsenic and mercury in aqueous media via bio-inspired gold nanoparticles modified by mango leaf extract

The present study conveys a new method for detecting arsenic(iii) and mercury(ii) in aqueous solution via bio-inspired gold nanoparticles. The process of synthesizing gold nanoparticles involves the utilization of the chemical reduction method. The functionalization of gold nanoparticles' surface is achieved via mango leaf extract. The as-synthesized nanoparticles are characterized by UV-Vis and DLS which reveal a plasmonic peak around ∼520 nm with an average size distribution of ∼44 nm. The modified gold nanoparticles have demonstrated selective detection capabilities towards arsenic(iii) as well as mercury(ii), as evidenced by color changes observed in the presence of ions of arsenic as well as mercury. The addition of mercury and arsenic lead to the overall aggregation-thereby bringing a colorimetric response. The limit of detection was determined to be 1 ppb and 1.5 ppb for arsenic(iii) and mercury(ii) ions, respectively along with exceptional linearity.

Green synthesis of Ag nanoparticle supported on graphene oxide for efficient nitrite sensing in a water sample

Water is essential for conserving biodiversity, ecology, and human health, but because of population growth and declining clean water supplies, wastewater must be treated to meet demand. Nitrite is one of the contaminants in wastewater that is well-known. It is crucial to identify nitrite since it can be fatal to humans in excessive doses. Utilizing a straightforward and effective electrochemical sensor, nitrite in actual water samples may be determined electrochemically. The sensor is created by coating the surface of a GC electrode with a thin layer of graphene oxide (GO), followed by a coating of silver nanoparticles. The modified electrode reached a linear detection range of 1-400 µM. thus, the activity of the electrode was investigated at different pH values ranging from 4 to 10 to cover acidic to highly basic environments. However, the electrode recorded limit of detection (LOD) is equal to 0.084, 0.090, and 0.055 µM for pH 4, 7, and 10, respectively. Additionally, the electrode activity was utilized in tap water and wastewater that the LOD reported as 0.16 and 0.157 µM for tape water and wastewater, respectively.

An ion-selective chemiresistive platform as demonstrated for the detection of nitrogen species in water

The use of ion-selective electrodes (ISE) is a well-established technique for the detection of ions in aqueous solutions but requires the use of a reference electrode. Here, we introduce a platform of ion-selective chemiresistors for the detection of nitrogen species in water as an alternative method without the need for reference electrodes. Chemiresistors have a sensitive surface that is prone to damage during operation in aqueous solutions. By applying a layer of ion-selective membrane to the surface of the chemiresistive device, the surface becomes protected and highly selective. We demonstrate both anion-selective (NO3-, NO2-) and cation-selective (NH4+) membranes. The nitrate sensors are able to measure nitrate ions in a range of 2.2-220 ppm with a detection limit of 0.3 ppm. The nitrite sensors respond between 67 ppb and 67 ppm of nitrite ions (64 ppb detection limit). The ammonium sensors can measure ammonium concentrations in a wide range from 10 ppb to 100 ppm (0.5 ppb detection limit). The fast responses to nitrate and nitrite are due to a mechanism involving electrostatic gating repulsion between negative charge carriers of the film and anions while ammonium detection arises from two mechanisms based on electrostatic gating repulsion and adsorption of ammonium ions at the surface of the p-doped chemiresistive film. The adsorption phenomenon slows down the recovery time of the ammonium sensor. This sensor design is a new platform to continuously monitor ions in industrial, domestic, and environmental water resources by robust chemiresistive devices.

Smart Contact Lenses as Wearable Ophthalmic Devices for Disease Monitoring and Health Management

The eye contains a complex network of physiological information and biomarkers for monitoring disease and managing health, and ocular devices can be used to effectively perform point-of-care diagnosis and disease management. This comprehensive review describes the target biomarkers and various diseases, including ophthalmic diseases, metabolic diseases, and neurological diseases, based on the physiological and anatomical background of the eye. This review also includes the recent technologies utilized in eye-wearable medical devices and the latest trends in wearable ophthalmic devices, specifically smart contact lenses for the purpose of disease management. After introducing other ocular devices such as the retinal prosthesis, we further discuss the current challenges and potential possibilities of smart contact lenses.

Recent Advances in Electrochemical Biosensors for the Detection of Foodborne Pathogens: Current Perspective and Challenges

Foodborne pathogens cause many diseases and significantly impact human health and the economy. Foodborne pathogens mainly include Salmonella spp., Escherichia coli, Staphylococcus aureus, Shigella spp., Campylobacter spp. and Listeria monocytogenes, which are present in agricultural products, dairy products, animal-derived foods and the environment. Various pathogens in many different types of food and water can cause potentially life-threatening diseases and develop resistance to various types of antibiotics. The harm of foodborne pathogens is increasing, necessitating effective and efficient methods for early monitoring and detection. Traditional methods, such as real-time polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and culture plate, are time-consuming, labour-intensive and expensive and cannot satisfy the demands of rapid food testing. Therefore, new fast detection methods are urgently needed. Electrochemical biosensors provide consumer-friendly methods to quickly detect foodborne pathogens in food and the environment and achieve extensive accuracy and reproducible results. In this paper, by focusing on various mechanisms of electrochemical transducers, we present a comprehensive overview of electrochemical biosensors for the detection of foodborne pathogens. Furthermore, the review introduces the hazards of foodborne pathogens, risk analysis methods and measures of control. Finally, the review also emphasizes the recent research progress and solutions regarding the use of electrochemical biosensors to detect foodborne pathogens in food and the environment, evaluates limitations and challenges experienced during the development of biosensors to detect foodborne pathogens and discusses future possibilities.

Acetylcholinesterase biosensors for electrochemical detection of neurotoxic pesticides and acetylcholine neurotransmitter: A literature review

Neurotoxic pesticides are a group of chemicals that pose a severe threat to both human health and the environment. These molecules are also known to accumulate in the food chain and persist in the environment, which can lead to long-term exposure and adverse effects on non-target organisms. The detrimental effects of these pesticides on neurotransmitter levels and function can lead to a range of neurological and behavioral symptoms, which are closely associated with neurodegenerative diseases. Hence, the accurate and reliable detection of these neurotoxic pesticides and associated neurotransmitters is essential for clinical applications, such as diagnosis and treatment. Over the past few decades, acetylcholinesterase (AchE) biosensors have emerged as a sensitive and reliable tool for the electrochemical detection of neurotoxic pesticides and acetylcholine. These biosensors can be tailored to utilize the high specificity and sensitivity of AchE, enabling the detection of these chemicals. Additionally, enzyme immobilization and the incorporation of nanoparticles have further improved the detection capabilities of these biosensors. AchE biosensors have shown tremendous potential in various fields, including environmental monitoring, clinical diagnosis, and pesticide residue analysis. This review summarizes the advancements in AchE biosensors for electrochemical detection of neurotoxic pesticides and acetylcholine over the past two decades.

Electrospun Nanofiber-Based Bioinspired Artificial Skins for Healthcare Monitoring and Human-Machine Interaction

Artificial skin, also known as bioinspired electronic skin (e-skin), refers to intelligent wearable electronics that imitate the tactile sensory function of human skin and identify the detected changes in external information through different electrical signals. Flexible e-skin can achieve a wide range of functions such as accurate detection and identification of pressure, strain, and temperature, which has greatly extended their application potential in the field of healthcare monitoring and human-machine interaction (HMI). During recent years, the exploration and development of the design, construction, and performance of artificial skin has received extensive attention from researchers. With the advantages of high permeability, great ratio surface of area, and easy functional modification, electrospun nanofibers are suitable for the construction of electronic skin and further demonstrate broad application prospects in the fields of medical monitoring and HMI. Therefore, the critical review is provided to comprehensively summarize the recent advances in substrate materials, optimized fabrication techniques, response mechanisms, and related applications of the flexible electrospun nanofiber-based bio-inspired artificial skin. Finally, some current challenges and future prospects are outlined and discussed, and we hope that this review will help researchers to better understand the whole field and take it to the next level.

Advances in point-of-care genetic testing for personalized medicine applications

Breakthroughs within the fields of genomics and bioinformatics have enabled the identification of numerous genetic biomarkers that reflect an individual's disease susceptibility, disease progression, and therapy responsiveness. The personalized medicine paradigm capitalizes on these breakthroughs by utilizing an individual's genetic profile to guide treatment selection, dosing, and preventative care. However, integration of personalized medicine into routine clinical practice has been limited-in part-by a dearth of widely deployable, timely, and cost-effective genetic analysis tools. Fortunately, the last several decades have been characterized by tremendous progress with respect to the development of molecular point-of-care tests (POCTs). Advances in microfluidic technologies, accompanied by improvements and innovations in amplification methods, have opened new doors to health monitoring at the point-of-care. While many of these technologies were developed with rapid infectious disease diagnostics in mind, they are well-suited for deployment as genetic testing platforms for personalized medicine applications. In the coming years, we expect that these innovations in molecular POCT technology will play a critical role in enabling widespread adoption of personalized medicine methods. In this work, we review the current and emerging generations of point-of-care molecular testing platforms and assess their applicability toward accelerating the personalized medicine paradigm.

An enzyme-responsive electrochemical DNA biosensor achieving various dynamic range by using only-one immobilization probe

Developing a simple and easy-to-operate biosensor with tunable dynamic range would provide enormous opportunities to promote the diagnostic applications. Herein, an enzyme-responsive electrochemical DNA biosensor is developed by using only-one immobilization probe. The immobilization probe was designed with a two-loop hairpin-like structure that contained the mutually independent target recognition and enzyme (EcoRI restriction endonuclease) responsive domains. The target recognition was based on a toehold-mediated strand displacement reaction strategy. The toehold region was initially caged in the loop of the immobilization probe and showed a relatively low binding affinity with target, which was improved via EcoRI cleavage of immobilization probe to liberate the toehold region. The EcoRI cleavage operation for immobilization probe demonstrated the well regulation ability in detection performance. It showed a largely extended dynamic range, a significantly lowered detection limit and better discrimination ability toward the mismatched sequences whether in two buffers (with high or low salt concentrations) or in the serum system. The advantages also includes simplicity in probe design, and facile biosensor fabrication and operation. It thus opens a new avenue for the development of the modulated DNA biosensor and hold a great potential for the diagnostic applications and drug monitoring.

Glucose micro-biosensor for scanning electrochemical microscopy characterization of cellular metabolism in hypoxic microenvironments

Mapping of the metabolic activity of tumor tissues represents a fundamental approach to better identify the tumor type, elucidate metastatic mechanisms and support the development of targeted cancer therapies. The spatially resolved quantification of Warburg effect key metabolites, such as glucose and lactate, is essential. Miniaturized electrochemical biosensors scanned over cancer cells and tumor tissue to visualize the metabolic characteristics of a tumor is attractive but very challenging due to the limited oxygen availability in the hypoxic environments of tumors that impedes the reliable applicability of glucose oxidase-based glucose micro-biosensors. Herein, the development and application of a new glucose micro-biosensor is presented that can be reliably operated under hypoxic conditions. The micro-biosensor is fabricated in a one-step synthesis by entrapping during the electrochemically driven growth of a polymeric matrix on a platinum microelectrode glucose oxidase and a catalytically active Prussian blue type aggregate and mediator. The as-obtained functionalization improves significantly the sensitivity of the developed micro-biosensor for glucose detection under hypoxic conditions compared to normoxic conditions. By using the micro-biosensor as non-invasive sensing probe in Scanning Electrochemical Microscopy (SECM), the glucose uptake by a breast metastatic adenocarcinoma cell line, with an epithelial morphology, is measured.

Perspective Chapter: Novel Diagnostics Methods for SARS-CoV-2

A novel coronavirus of zoonotic origin (SARS-CoV-2) has recently been recognized in patients with acute respiratory disease. COVID-19 causative agent is structurally and genetically similar to SARS and bat SARS-like coronaviruses. The drastic increase in the number of coronavirus and its genome sequence has given us an unprecedented opportunity to perform bioinformatics and genomics analysis on this class of viruses. Clinical tests such as PCR and ELISA for rapid detection of this virus are urgently needed for early identification of infected patients. However, these techniques are expensive and not readily available for point-of-care (POC) applications. Currently, lack of any rapid, available, and reliable POC detection method gives rise to the progression of COVID-19 as a horrible global problem. To solve the negative features of clinical investigation, we provide a brief introduction of the various novel diagnostics methods including SERS, SPR, electrochemical, magnetic detection of SARS-CoV-2. All sensing and biosensing methods based on nanotechnology developed for the determination of various classes of coronaviruses are useful to recognize the newly immerged coronavirus, i.e., SARS-CoV-2. Also, the introduction of sensing and biosensing methods sheds light on the way of designing a proper screening system.

Dual-monomer molecularly imprinted electrochemical sensor based on amino-functionalized MOFs and graphene for trace determination of taurine

A molecularly imprinted electrochemical sensor (MIECS) for trace determination of taurine was developed. The sensor was constructed by electropolymerizing dopamine and o-phenylenediamine as dual monomers on the surface of amino-functionalized iron-based MOFs and graphene composite-modified electrode. The porous structure and large specific surface area of amino-functionalized iron-based MOFs not only increase the number of imprinted sites, but also facilitate the binding of molecularly imprinted films. The presence of dual monomers can increase the binding sites during the formation of imprinted films. The linear range of this sensor for taurine detection is 1.00 × 10^-14-1.00 × 10^-8 mol L^-1 with a determination limit of 3.20 × 10^-15 mol L^-1. The proposed MIECS was successfully applied to quantify the amount of taurine in human serum sample with good recovery values from 97.3 to 113%.

Recent Advances in the Development of Portable Electrochemical Sensors for Controlled Substances

This review article summarizes recent achievements in developing portable electrochemical sensing systems for the detection and/or quantification of controlled substances with potential on-site applications at the crime scene or other venues and in wastewater-based epidemiology. Electrochemical sensors employing carbon screen-printed electrodes (SPEs), including a wearable glove-based one, and aptamer-based devices, including a miniaturized aptamer-based graphene field effect transistor platform, are some exciting examples. Quite straightforward electrochemical sensing systems and methods for controlled substances have been developed using commercially available carbon SPEs and commercially available miniaturized potentiostats. They offer simplicity, ready availability, and affordability. With further development, they might become ready for deployment in forensic field investigation, especially when fast and informed decisions are to be made. Slightly modified carbon SPEs or SPE-like devices might be able to offer higher specificity and sensitivity while they can still be used on commercially available miniaturized potentiostats or lab-fabricated portable or even wearable devices. Affinity-based portable devices employing aptamers, antibodies, and molecularly imprinted polymers have been developed for more specific and sensitive detection and quantification. With further development of both hardware and software, the future of electrochemical sensors for controlled substances is bright.

Recent progress in nucleic acid detection with CRISPR

Recent advances in CRISPR-based biotechnologies have greatly expanded our capabilities to repurpose CRISPR for the development of molecular diagnostic systems. The key attribute that allows CRISPR to be widely utilized is its programmable and highly specific nature. In this review, we first illustrate the principle of the class 2 CRISPR nucleases for molecular diagnostics which originates from their immunologic defence systems. Next, we present the CRISPR-based schemes in the application of diagnostics with amplification-assisted or amplification-free strategies. By highlighting some of the recent advances we interpret how general bioengineering methodologies can be integrated with CRISPR. Finally, we discuss the challenges and exciting prospects for future CRISPR-based biosensing development. We hope that this review will guide the reader to systematically learn the start-of-the-art development of CRISPR-mediated nucleic acid detection and understand how to apply the CRISPR nucleases with different design concepts to more general applications in diagnostics and beyond.

A Ni-MOF as Fluorescent/Electrochemical Dual Probe for Ultrasensitive Detection of Picric Acid from Aqueous Media

A water-stable, microporous, luminescent Ni(II)-based metal-organic framework (MOF) (Ni-OBA-Bpy-18) with a 4-c uninodal sql topology was solvothermally synthesized using mixed N-, O-donor-directed π-conjugated co-ligands. The extraordinary performance of this MOF toward rapid monitoring of mutagenic explosive trinitrophenol (TNP) in aqueous and vapor phases by the fluorescence "Turn-off" technique with an ultralow detection limit of 66.43 ppb (K_sv: 3.45 × 10⁵ M^-1) was governed by a synchronous occurrence of photoinduced electron transfer-resonance energy transfer-intermolecular charge transfer (PET-RET-ICT) and non-covalent π···π weak interactions, as revealed from density functional theory studies. The recyclable nature of the MOF, detection from complex environmental matrices, and fabrication of a handy MOF@cotton-swab detection kit certainly escalated the on-field viability of the probe. Interestingly, the presence of electron-withdrawing TNP decisively facilitated the redox events of the reversible Ni^III/II and Ni^IV/III couples under an applied voltage based on which electrochemical recognition of TNP was realized by the Ni-OBA-Bpy-18 MOF/glassy carbon electrode, with an excellent detection limit of ∼0.6 ppm. Such detection of a specific analyte by MOF-based probe via two divergent yet coherent techniques is unprecedented and yet to be explored in relevant literature.

Metal-Organic Framework (MOF) Derivatives as Promising Chemiresistive Gas Sensing Materials: A Review

The emission of harmful gases has seriously exceeded relative standards with the rapid development of modern industry, which has shown various negative impacts on human health and the natural environment. Recently, metal-organic frameworks (MOFs)-based materials have been widely used as chemiresistive gas sensing materials for the sensitive detection and monitoring of harmful gases such as NO_x, H₂S, and many volatile organic compounds (VOCs). In particular, the derivatives of MOFs, which are usually semiconducting metal oxides and oxide-carbon composites, hold great potential to prompt the surface reactions with analytes and thus output amplified resistance changing signals of the chemiresistors, due to their high specific surface areas, versatile structural tunability, diversified surface architectures, as well as their superior selectivity. In this review, we introduce the recent progress in applying sophisticated MOFs-derived materials for chemiresistive gas sensors, with specific emphasis placed on the synthesis and structural regulation of the MOF derivatives, and the promoted surface reaction mechanisms between MOF derivatives and gas analytes. Furthermore, the practical application of MOF derivatives for chemiresistive sensing of NO₂, H₂S, and typical VOCs (e.g., acetone and ethanol) has been discussed in detail.