Detection of Inosine Monophosphate (IMP) in Meat Using Double-Enzyme Sensor

Molecular characterization of adenosine monophosphate deaminase 1 and the correlation analysis between its mRNA expression levels and inosine monophosphate content in large yellow croaker (Larimichthys crocea)

Declining flesh quality has drawn considerable attention in the farmed large yellow croaker (LYC; Larimichthys crocea) industry. Inosine monophosphate (IMP) is the primary flavor substance in aquatic animals. Adenosine monophosphate deaminase 1 (AMPD1) plays a critical role in IMP formation by catalyzing the deamination of AMP to IMP in the purine nucleotide cycle. To further evaluate the correlation between ampd1 mRNA expression levels and IMP content in the LYC muscle tissue, the relevant open reading frame (ORF) of L. crocea (Lcampd1) was cloned, and the IMP content and Lcampd1 mRNA expression in the muscles of LYCs of different sizes were examined. The ORF cDNA of Lcampd1 was 2211 bp in length and encoded a polypeptide of 736 amino acids (AAs). The deduced protein, LcAMPD1, possesses conserved AMPD active regions (SLSTDDP) and shows high homology with AMPD proteins of other teleost fishes. The genomic DNA sequence of Lcampd1 exhibits a high degree of evolutionary conservation in terms of structural organization among species. Phylogenetic analysis of the deduced AA sequence revealed that teleost fish and mammalian AMPD1 were separate from each other and formed a cluster with AMPD3, suggesting that AMPD1 and AMPD3 arose by duplication of a common primordial gene. In healthy LYC, Lcampd1 mRNA was expressed only in the muscle tissue. The IMP content in the muscle of LYCs with different average body weights was measured by high-performance liquid chromatography; the results showed that the IMP content in the muscle of LYCs with greater body weight was significantly higher than that in LYC with lower body weight. Moreover, a similar trend in Lcampd1 expression was observed in these muscle tissues. The Pearson correlation analysis further showed that the Lcampd1 mRNA expression was positively correlated with IMP content in the muscles of different-sized LYCs. These results suggest the potential function of Lcampd1 in determining the IMP content in LYC and provide a theoretical basis for flesh quality improvement, as well as a scientific basis for the development of the molecular breeding of LYC.

Novel competitive electrochemical impedance biosensor for the ultrasensitive detection of umami substances based on Pd/Cu-TCPP(Fe)

The development of biosensors capable of assessing umami intensity has elicited significant attention. However, the detection range of these biosensors is constrained by the sensing components and strategies used. In this study, we introduce a novel competitive, ultra-high-sensitivity impedance biosensor by utilizing composite nanomaterials and T1R1 as a composite signal probe. Pd/Cu-TCPP(Fe) had a substantial surface area, effectively enhancing the loading capacity of the T1R1 and thus augmenting the biosensor's recognition precision. Furthermore, the Pd/Cu-TCPP(Fe) elevated peroxidase-like activity catalyzed the formation of insoluble precipitates of 4-chloro-1-naphthol (4-CN), resulting in cascaded amplification of the impedance signal. The remarkable catalytic activity of the composite signal probe endowed the biosensor with exceptional analytical performance, featuring a limit of detection (LOD) of 0.86 pg/mL and a linear detection range spanning from 10 to 10,000 pg/mL. Successful application of the biosensor for umami detection in fish was demonstrated, signifying its substantial potential in food-flavor evaluation.

A colorimetric sensor array based on peroxidase activity nanozyme for the highly efficient differential sensing of tea polyphenols and Tieguanyin adulteration

Tieguanyin (TGY) is one of top ten famous teas in China, but in the process of brand building there is the phenomenon of falsehood, thus harming the interests of consumers. To solve theadulterate problem of TGY, a colorimetric sensor array (CSA) based onperoxidase activity of nanozyme was constructed. Nanozymes can catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to 3,3',5,5'-tetramethyl -[1,1'-bis(cyclohexyl)]-2,2',5,5'-tetraene-4,4'-diimine (oxTMB), while the tea polyphenols (TPs) can inhibit this process, and the degree of inhibition varies significantly with the reaction time. We selected two nanozymesand three reaction time points to construct CSA. It can successfully distinguish TPsin TGY. The discriminative analysiscan achieve: (1)distinction between TGY and adulterated tea, (2)discrimination of TGY in various seasons and seasonal adulteration in different degrees. The method constructed in this work is promising for both the class and quality differentiation of TGY and other teas with TPs as the main activity.

Inosine 5'- monophosphate derived umami taste intensity of beef determination by electrochemistry and chromatography

The umami sensation contributes to beef taste and acceptability. Inosine 5'- monophosphate (IMP), the most abundant 5'-ribonucleotide in meat, is known to impart an umami taste without the undesired side effects commonly associated with glutamate. Nevertheless, the investigation of IMP's role in beef flavor has thus far been overlooked. Traditional methods for detecting IMP have relied on liquid chromatography coupled with ultraviolet spectroscopy or mass spectrometry techniques. However, these methods are not practical for production settings due to the complexity and resource demands of sophisticated laboratory techniques. Alternative methods like cyclic voltammetry might offer more practical solutions for rapidly detecting IMP. The objectives of this study were to evaluate the efficiency of using electrochemistry and chromatography on differentiating beef strips spiked with different IMP contents. The IMP threshold was 0.30 mM determined by a trained panel using the Best Estimates Threshold method. Beef strip steaks of USDA Prime, Choice, and Select were spiked at 0.30 and 0.60 mM of IMP, based on green weight and an estimated moisture content of 65%. In this study, differences in the IMP content of steaks were not detected by liquid chromatography-mass spectrometry. However, the cyclic voltammetry approach differentiated IMP concentrations at 0.50 mM or above in aqueous solutions and subsequentially meat extracts from the buffered blank solutions. In conclusion, cyclic voltammetry holds potential as a rapid and effective approach for detecting IMP in beef and other meat products, offering promising applications for future research.

Degradation mechanism and development of detection technologies of ATP-related compounds in aquatic products: recent advances and remaining challenges

The degradation of ATP-related compounds is an important biochemical process that reflects the freshness of aquatic products after death. There has been considerable interest in investigating the factors affecting the degradation of ATP-related compounds in aquatic products and in developing techniques to detect them. This review provides the latest knowledge on the degradation mechanisms of ATP-related compounds during the storage of aquatic products and discusses the latest advances in ATP-related compound detection techniques. The degradation mechanisms discussed include mainly degradation pathways, endogenous enzymes, and microbial mechanisms of action. Microbial activity is the main reason for the degradation of IMP and related products during the mid to late storage of aquatic products, mainly through the related enzymes produced by microorganisms. Further elucidation of the degradation mechanisms of ATP-related compounds provides new ideas for quality control techniques in raw aquatic products during storage. The development of new technologies for the detection of ATP-related compounds has become a significant area of research. And, biosensors further improve the efficiency and accuracy of detection and have potential application prospects. The development of biosensor back-end modalities (test strips, fluorescent probes, and artificial intelligence) has accelerated the practical application of biosensors for the detection of ATP-related compounds.

Titanium Carbide (Ti3C2Tx) MXene as Efficient Electron/Hole Transport Material for Perovskite Solar Cells and Electrode Material for Electrochemical Biosensors/Non-Biosensors Applications

Recently, two-dimensional (2D) MXenes materials have received enormous attention because of their excellent physiochemical properties such as high carrier mobility, metallic electrical conductivity, mechanical properties, transparency, and tunable work function. MXenes play a significant role as additives, charge transfer layers, and conductive electrodes for optoelectronic applications. Particularly, titanium carbide (Ti3C2Tx) MXene demonstrates excellent optoelectronic features, tunable work function, good electron affinity, and high conductivity. The Ti3C2Tx has been widely used as electron transport (ETL) or hole transport layers (HTL) in the development of perovskite solar cells (PSCs). Additionally, Ti3C2Tx has excellent electrochemical properties and has been widely explored as sensing material for the development of electrochemical biosensors. In this review article, we have summarized the recent advances in the development of the PSCs using Ti3C2Tx MXene as ETL and HTL. We have also compiled the recent progress in the fabrication of biosensors using Ti3C2Tx-based electrode materials. We believed that the present mini review article would be useful to provide a deep understanding, and comprehensive insight into the research status.

Recent Progress in Emerging Novel MXenes Based Materials and their Fascinating Sensing Applications

Early transition metals based 2D carbides, nitrides and carbonitrides nanomaterials are known as MXenes, a novel and extensive new class of 2D materials family. Since the first accidently synthesis based discovery of Ti₃ C₂ in 2011, more than 50 additional compositions have been experimentally reported, including at least eight distinct synthesis methods and also more than 100 stoichiometries are theoretically studied. Due to its distinctive surface chemistry, graphene like shape, metallic conductivity, high hydrophilicity, outstanding mechanical and thermal properties, redox capacity and affordable with mass-produced nature, this diverse MXenes are of tremendous scientific and technological significance. In this review, first we'll come across the MXene based nanomaterials possible synthesis methods, their advantages, limitations and future suggestions, new chemistry related to their selected properties and potential sensing applications, which will help us to explain why this family is growing very fast as compared to other 2D families. Secondly, problems that help to further improve commercialization of the MXene nanomaterials based sensors are examined, and many advances in the commercializing of the MXene nanomaterials based sensors are proposed. At the end, we'll go through the current challenges, limitations and future suggestions.

Bimetallic bionic taste sensor for perception of the synergistic effect of umami substances

Synergistic effect is one of the main properties of umami substances, elucidating the synergistic effect of umami is of great significance in the food industry. In this study, a bimetallic bionic taste sensor was developed to evaluate the synergistic effect of umami substances based on the perceptual mechanism of the human taste system. The Venus flytrap domain of T1R1 which is in charge of recognizing umami ligands was employed as the sensing element and self-assembled on the bimetallic nanomaterial (MoS₂-PtPd) by Au-S bonding, the binding of receptors and ligands is characterized by changes of electrical signals. The sensor had good linearity (R² > 0.99) and wide detection range in the detection of different kinds of umami substances (amino acids, nucleotides, organic acids, umami peptides) with detection limits as low as 0.03 pM. Comparing with electronic tongues, the sensor owned multiple characteristics of human taste system and could recognize the presence of synergistic effect of umami substances in a variety of real samples. Moreover, the differences in synergistic effect at different concentrations and ratios were also explored, the findings showed that the synergistic effect was more obvious at lower concentrations and balanced ratios of multiple umami substances added. The strategy would afford a promising platform for in-depth research on the mechanism of synergistic effect and multifunctional industrial applications.

Evaluation of Meat Quality of Local Pigeon Varieties in China

To evaluate the germplasm characteristics and nutritional value of Chinese native pigeon varieties, this study analyzed the nutrient composition of the meat of four Chinese native pigeon varieties and then compared them with those of the White King pigeon, which is the most commonly used in China. A total of 150 pigeons aged 28 d (squabs) of 5 breeds including Taihu pigeon, Shiqi pigeon, Ta-rim pigeon, Boot pigeon, and White King pigeon were selected for slaughter. The basic meat quality parameters and contents of conventional nutritional compositions, inosine acid, amino acids, and fatty acids were measured. The results showed that there were significant differences in flesh color (L*, b*), pH, and water loss rate of different breeds of suckling pigeons (p < 0.05). Compared with White King pigeons, four local breeds had dark breast meat and a low water loss rate. The protein contents of Taihu, Tarim, and Shiqi suckling pigeons were significantly higher than those of White King pigeons (p < 0.05). Taihu pigeons had the highest protein content, reaching 22.72%. The inosinic acid content of Tarim pigeons was the highest (1.31 mg/g) and was significantly higher than that of Shiqi pigeons, Boot pigeons, and White King pigeons (p < 0.05). There was no significant difference in the content of amino acids, the ratio of essential amino acids, and the ratio of umami amino acids in the meat of different breeds of pigeons (p > 0.05). The percentage of saturated fatty acids (SFAs) in the breast muscle of local breeding pigeons was significantly lower than that of White King pigeons (p < 0.05), and the percentages of lauric acid, palmitic acid, eicosanoic acid, and behenic acid in SFAs reached significant levels (p < 0.05). The content of eicosapentaenoic acid (EPA) in the meat of Taihu pigeons was significantly higher than that in other breeds. In conclusion, compared with the White King pigeon, the meat of local breed pigeons (Taihu pigeon, Shiqi pigeon, Tarim pigeon, and Boot pigeon) had dark flesh, good water retention, high protein and inosine contents, a high proportion of essential amino acids, and a low saturated fatty acid ratio. In addition, Taihu pigeons had the highest protein content (22.72%), monounsaturated fatty acids (44.58%), and EPA (0.47%) compared to other breeds.

Toward Smart Sensing by MXene

The Internet of Things era has promoted enormous research on sensors, communications, data fusion, and actuators. Among them, sensors are a prerequisite for acquiring the environmental information for delivering to an artificial data center to make decisions. The MXene-based sensors have aroused tremendous interest because of their extraordinary performances. In this review, the electrical, electronic, and optical properties of MXenes are first introduced. Next, the MXene-based sensors are discussed according to the sensing mechanisms such as electronic, electrochemical, and optical methods. Initially, biosensors are introduced based on chemiresistors and field-effect transistors. Besides, the wearable pressure sensor is demonstrated with piezoresistive devices. Third, the electrochemical methods include amperometry and electrochemiluminescence as examples. In addition, the optical approaches refer to surface plasmonic resonance and fluorescence resonance energy transfer. Moreover, the prospects are delivered of multimodal data fusion toward complicated human-like senses. Eventually, future opportunities for MXene research are conveyed in the new material discovery, structure design, and proof-of-concept devices.

Advanced growth of 2D MXene for electrochemical sensors

Over the last few years, electroanalysis has made significant advancements, particularly in developing electrochemical sensors. Electrochemical sensors generally include emerging Photoelectrochemical and Electrochemiluminescence sensors, which combine optical techniques and traditional electrochemical bio/non-biosensors. Numerous EC-detecting methods have also been designed for commercial applications to detect biological and non-biological markers for various diseases. Analytical applications have recently focused significantly on one of the novel nanomaterials, the MXene. This material is being extensively investigated for applications in electrochemical sensors due to its unique mechanical, electronic, optical, active functional groups and thermal characteristics. This study extensively discusses the salient features of MXene-based electrochemical sensors, photoelectrochemical sensors, enzyme-based biosensors, immunosensors, aptasensors, electrochemiluminescence sensors, and electrochemical non-biosensors. In addition, their performance in detecting various substances and contaminants is thoroughly discussed. Furthermore, the challenges and prospects the MXene-based electrochemical sensors are elaborated.

Design fabrication of electrochemical sensor based on Ru(bpy)22+/SMWCNTs/Au/GCE electrode for the selective determination of 5′-guanosine monophosphate

5'-Guanosine monophosphate (5'-GMP) is one main source of freshness in broths. Herein, an electrochemical platform based on a novel ternary nanocomposite glassy carbon electrode modified with advantageously-united gold nanoparticles, 2,2'-bipyridine hydrated ruthenium (Ru(bpy)₂Cl₂) and sulfonated multi-walled carbon nanotubes (SMWCNTs)was prepared and used to detect 5'-GMP. After conditions optimization, the best performance of the electrochemical sensor was found in acidic media, including high specificity, sensitivity and selectivity. The electrochemical sensor exhibited a wide linear range under the optimal conditions. The enhanced sensitivity of this sensor was attributed to the Ru(bpy)₂Cl₂ and functionalized SMWCNTs that provided high electrical conductivity and electrocatalytic properties during electrochemical reaction. Precise analysis of 5'-GMP in actual broth samples showed satisfactory recovery. Thus, the sensor can be used in the market and food enterprises.

Assessing Meat Freshness via Nanotechnology Biosensors: Is the World Prepared for Lightning-Fast Pace Methods?

In the rapidly evolving field of food science, nanotechnology-based biosensors are one of the most intriguing techniques for tracking meat freshness. Purine derivatives, especially hypoxanthine and xanthine, are important signs of food going bad, especially in meat and meat products. This article compares the analytical performance parameters of traditional biosensor techniques and nanotechnology-based biosensor techniques that can be used to find purine derivatives in meat samples. In the introduction, we discussed the significance of purine metabolisms as analytes in the field of food science. Traditional methods of analysis and biosensors based on nanotechnology were also briefly explained. A comprehensive section of conventional and nanotechnology-based biosensing techniques is covered in detail, along with their analytical performance parameters (selectivity, sensitivity, linearity, and detection limit) in meat samples. Furthermore, the comparison of the methods above was thoroughly explained. In the last part, the pros and cons of the methods and the future of the nanotechnology-based biosensors that have been created are discussed.

Dietary ribose supplementation improves flesh quality through purine metabolism in gibel carp (Carassius auratus gibelio)

Since the aquaculture industry is currently observing a deterioration in the flesh quality of farmed fish, the use of nutrients as additives to improve the flesh quality of farmed fish species is a viable strategy. The aim of this study was to investigate the effect of dietary D-ribose (RI) on the nutritional value, texture and flavour of gibel carp (Carassius auratus gibelio). Four diets were formulated containing exogenous RI at 4 gradient levels: 0 (Control), 0.15% (0.15RI), 0.30% (0.30RI) and 0.45% (0.45RI). A total of 240 fish (150 ± 0.31 g) were randomly distributed into 12 fibreglass tanks (150 L per tank). Triplicate tanks were randomly assigned to each diet. The feeding trial was carried out in an indoor recirculating aquaculture system for 60 d. After the feeding trial, the muscle and liver of gibel carp were analysed. The results showed that RI supplementation did not result in any negative impact on the growth performance and 0.30RI supplementation significantly increased the whole-body protein content compared to the control group. The contents of collagen and glycogen in muscle were enhanced by RI supplementation. The alterations in the flesh indicated that RI supplementation improved the texture of the flesh in terms of its water-holding capacity and hardness, therefore improving the taste. Dietary RI facilitated the deposition of amino acids and fatty acids in the muscle that contributed to the meaty taste and nutritional value. Furthermore, a combination of metabolomics and expression of key genes in liver and muscle revealed that 0.30RI activated the purine metabolism pathways by supplementing the substrate for nucleotide synthesis and thereby promoting the deposition of flavour substance in flesh. This study offers a new approach for providing healthy, nutritious and flavourful aquatic products.

Advances of MXenes; Perspectives on Biomedical Research

The last decade witnessed the emergence of a new family of 2D transition metal carbides and nitrides named MXenes, which quickly gained momentum due to their exceptional electrical, mechanical, optical, and tunable functionalities. These outstanding properties also rendered them attractive materials for biomedical and biosensing applications, including drug delivery systems, antimicrobial applications, tissue engineering, sensor probes, auxiliary agents for photothermal therapy and hyperthermia applications, etc. The hydrophilic nature of MXenes with rich surface functional groups is advantageous for biomedical applications over hydrophobic nanoparticles that may require complicated surface modifications. As an emerging 2D material with numerous phases and endless possible combinations with other 2D materials, 1D materials, nanoparticles, macromolecules, polymers, etc., MXenes opened a vast terra incognita for diverse biomedical applications. Recently, MXene research picked up the pace and resulted in a flood of literature reports with significant advancements in the biomedical field. In this context, this review will discuss the recent advancements, design principles, and working mechanisms of some interesting MXene-based biomedical applications. It also includes major progress, as well as key challenges of various types of MXenes and functional MXenes in conjugation with drug molecules, metallic nanoparticles, polymeric substrates, and other macromolecules. Finally, the future possibilities and challenges of this magnificent material are discussed in detail.

Biomedical engineering of two-dimensional MXenes

The emergence of two-dimensional (2D) transition metal carbides, carbonitrides and nitrides, referred to MXenes, with a general chemical formula of M_n+1X_nT_x have aroused considerable interest and shown remarkable potential applications in diverse fields. The unique ultrathin lamellar structure accompanied with charming electronic, optical, magnetic, mechanical and biological properties make MXenes as a kind of promising alternative biomaterials for versatile biomedical applications, as well as uncovering many new fundamental scientific discoveries. Herein, the current state-of-the-art advances of MXenes-related biomaterials are systematically summarized in this comprehensive review, especially focusing on the synthetic methodologies, design and surface engineering strategies, unique properties, biological effects, and particularly the property-activity-effect relationship of MXenes at the nano-bio interface. Furthermore, the elaborated MXenes for varied biomedical applications, such as biosensors and biodevices, antibacteria, bioimaging, therapeutics, theranostics, tissue engineering and regenerative medicine, are illustrated in detail. Finally, we discuss the current challenges and opportunities for future advancement of MXene-based biomaterials in-depth on the basis of the present situation, aiming to facilitate their early realization of practical biomedical applications.

2D metal carbides and nitrides (MXenes) for sensors and biosensors

MXenes are layered two-dimensional (2D) materials discovered in 2011 (Ti₃C₂X) and are otherwise called 2D transition metal carbides, carbonitrides, and nitrides. These 2D layered materials have been in the limelight for a decade due to their interesting properties such as large surface area, high ion transport, biocompatibility, and low diffusion barrier. Therefore, MXenes are widely preferred by researchers for applications in electronics, sensing, biosensing, electrocatalysis, super-capacitors and fuel cells. There are a number of methods available for the bulk synthesis of MXene-based nanomaterials. In addition, the possibility of structural modification as required and its outstanding surface chemistry offer a fascinating interface for the development of novel biosensors. In this review, we specifically discuss important MXene synthesis routes. Moreover, critical parameters such as surface functionalization that can dictate the mechanical, electronic, magnetic, and optical properties of MXenes are also discussed. Following this, methods available for the surface functionalization and modification strategies of MXenes are also discussed. Furthermore, the emergence of gas, electrochemical, and optical biosensors based on MXenes since its first report is discussed in detail. Finally, future directions of MXenes biosensors for critical applications are discussed.

Preparation of yolk-shell structure NH2-MIL-125 magnetic nanoparticles for the selective extraction of nucleotides

Yolk-shell structure magnetic metal-organic framework nanoparticles were prepared via post solvothermal method and employed as a magnetic solid-phase extraction adsorbent for selective pre-concentration of 5'-ribonucleotides by π stacking interaction, hydrogen bonding, and the strong interaction between titanium ions (Ti⁴⁺) and phosphate group. The properties of the materials were confirmed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, vibrating sample magnetometer, infrared spectroscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller analysis. The main parameters affecting the adsorption-desorption process, including adsorbent amount, incubation time, incubation temperature, sample pH, shaking speed, elution solution, and elution time, were systematically optimized. Finally, 1.0 mg of adsorbent mixed with 1.0 mL sample solution (10.0 mmol⋅L^-1 NaCl, pH 3.0) and shaken at 135 rpm for 5 min at 40 °C, washed with 1.0 mL Na₃PO₄-NH₃∙H₂O under vortex for 5 min were selected as optimized adsorption-desorption conditions. The binding performance of adsorbent towards five nucleotides was evaluated by static adsorption experiments. The data are well-fitted to the Langmuir isotherm model and the maximum adsorption capacity is 27.8 mg g^-1 for adenosine 5'-monophosphate. The limit of detection of the method is 19.44-38.41 ng mL^-1. Under the optimal conditions, the adsorbent was successfully applied to magnetic solid-phase extraction and high performance liquid chromatography determination of five nucleotides in octopus, chicken, fish, and pork samples.

Sensing with MXenes: Progress and Prospects

Various fields of study consider MXene a revolutionary 2D material. Particularly in the field of sensors, the metal-like high electrical conductivity and large surface area of MXenes are desirable characteristics as an alternative sensor material that can transcend the boundaries of existing sensor technology. This critical review provides a comprehensive overview of recent advances in MXene-based sensor technology and a roadmap for commercializing MXene-based sensors. The existing sensors are systematically categorized as chemical, biological, and physical sensors. Each category is then classified into various subcategories depending on the electrical, electrochemical, structural, or optical sensing mechanism, which are the four fundamental working mechanisms of sensors. Representative structural and electrical approaches for boosting the performance of each category are presented. Finally, factors that hinder commercializing MXene-based sensors are discussed, and several breakthroughs in realizing commercially available MXene-based sensors are suggested. This review provides broad insights pertaining to previous and existing MXene-based sensor technology and perspectives on the future generation of low-cost, high-performance, and multimodal sensors for soft-electronics applications.

Highly sensitive determination of doxorubicin hydrochloride antitumor agent via a carbon nanotube/gold nanoparticle based nanocomposite biosensor

A glassy carbon electrode modified with multi-walled carbon nanotubes (MWCNTs) decorated with gold nanoparticles has been investigated for the first time as an ultrasensitive electrochemical sensor for the determination of doxorubicin hydrochloride (DOX), an efficient antitumor agent. The developed nanocomposite has been characterized by scanning electron microscopy (SEM), besides cyclic and linear sweep voltammetry electrochemical techniques. An efficient catalytic activity for the reduction of DOX has been demonstrated, leading to a significant increase in peak current density and a remarkable decrease in reduction over-potential. Under the optimal condition, a wide linear DOX concentration range from 1×10^-11 to 1×10^-6 M with a very low detection limit of 6.5 pM was achieved with the modified electrode. Meanwhile, the functionalized MWCNTs/gold nanoparticles indicated an appropriate selectivity, reproducibility, and repeatability as well as long-term stability. The promising outcomes of this research approved the applicability of the developed nanocomposite sensor towards trace amounts of DOX in pharmaceutical and clinical preparations.

MXenes-Based Bioanalytical Sensors: Design, Characterization, and Applications

MXenes are recently developed 2D layered nanomaterials that provide unique capabilities for bioanalytical applications. These include high metallic conductivity, large surface area, hydrophilicity, high ion transport properties, low diffusion barrier, biocompatibility, and ease of surface functionalization. MXenes are composed of transition metal carbides, nitrides, or carbonitrides and have a general formula Mn+1Xn, where M is an early transition metal while X is carbon and/or nitrogen. Due to their unique features, MXenes have attracted significant attention in fields such as clean energy production, electronics, fuel cells, supercapacitors, and catalysis. Their composition and layered structure make MXenes attractive for biosensing applications. The high conductivity allows these materials to be used in the design of electrochemical biosensors and the multilayered configuration makes them an efficient immobilization matrix for the retention of activity of the immobilized biomolecules. These properties are applicable to many biosensing systems and applications. This review describes the progress made on the use and application of MXenes in the development of electrochemical and optical biosensors and highlights future needs and opportunities in this field. In particular, opportunities for developing wearable sensors and systems with integrated biomolecule recognition are highlighted.