Prussian Blue Nanoparticle Supported MoS2 Nanocomposites as a Peroxidase-Like Nanozyme for Colorimetric Sensing of Dopamine

Biomaterials for reliable wearable health monitoring: Applications in skin and eye integration

Recent advancements in biomaterials have significantly impacted wearable health monitoring, creating opportunities for personalized and non-invasive health assessments. These developments address the growing demand for customized healthcare solutions. Durability is a critical factor for biomaterials in wearable applications, as they must withstand diverse wearing conditions effectively. Therefore, there is a heightened focus on developing biomaterials that maintain robust and stable functionalities, essential for advancing wearable sensing technologies. This review examines the biomaterials used in wearable sensors, specifically those interfaced with human skin and eyes, highlighting essential strategies for achieving long-lasting and stable performance. We specifically discuss three main categories of biomaterials-hydrogels, fibers, and hybrid materials-each offering distinct properties ideal for use in durable wearable health monitoring systems. Moreover, we delve into the latest advancements in biomaterial-based sensors, which hold the potential to facilitate early disease detection, preventative interventions, and tailored healthcare approaches. We also address ongoing challenges and suggest future directions for research on material-based wearable sensors to encourage continuous innovation in this dynamic field.

A novel "mix-response" biosensor for colorimetric and photothermal dual-mode detection of sulfide ions in food based on silver-doping Prussian blue nanoparticle

Effective identification of sulfur ions (S2-) in foodstuff is crucial for food safety and human health, but it remains challenging. Traditional single-mode colorimetric sensing methods are simple and sensitive, but are prone to interference from colored substances which can lead to false positives or negatives results. Herein, we develop a novel "mix-response" biosensor for colorimetric and photothermal dual-mode detection of S2- with good simplicity, sensitivity and portability. In this biosensor, silver-doping Prussian blue nanoparticle (SPB NPs) was used as signal output component, which not only exhibits blue color characteristics, but also has photothermal conversion properties activated by near-infrared (NIR) laser. Upon increasing the S2- concentration, the prepared SPB NPs undergo etching, leading to the formation of new silver sulfide precipitation (Ag2S), along with different colorimetric and photothermal response signals. For the portable visualization of S2-, the color information was recorded by a smartphone in combination with RGB (red channel) analysis and the evolution of the photothermal signal was documented by a thermal imager. The introduction of smartphone and handheld thermal imager in this "mix-response" biosensor makes it suitable for on-site quantitative detection of S2- without sophisticated instrument. Moreover, the development of this "mix-response" biosensor does not need the use of recognition probes (e.g. aptamers and reaction intermediates), thereby simplifying the construct procedures of sensing strategies and improving the economic efficiency of detection. More importantly, the photothermal response signals can overcome the interference of colored substances in foods, thereby reducing the false positives or negatives of the detection results.

Nanozymes: Classification and Analytical Applications - A Review

The recent discovery of a new class of nanomaterials called nanozymes, which have the action of enzymes and are thus of tremendous significance, has altered our understanding of these previously believed to be biologically inert nanomaterials. As a significant and exciting class of synthetic enzymes, nanozymes have distinct advantages over natural enzymes. They are less expensive, more stable, and easier to work with and store, making them a viable substitute. This practical advantage of nanozymes over natural enzymes reassures us about the potential of this new technology. Peroxidase-like nanozymes have been investigated for the purpose of creating adaptable biosensors via the use of molecularly imprinted polymers (MIPs) or particular bio recognition ligands, including enzymes, antibodies, and aptamers. This review delves into the distinctions between synthetic and natural enzymes, explaining their structures and analytical applications. It primarily focuses on carbon-based nanozymes, particularly those that contain both carbon and hydrogen, as well as metal-based nanozymes like Fe, Cu, and Au, along with their metal oxide (FeO, CuO), which have applications in many fields today. Analytical chemistry finds great use for nanozymes for sensing and other applications, particularly in comparison with other classical methods in terms of selectivity and sensitivity. Nanozymes, with their unique catalytic capabilities, have emerged as a crucial tool in the early diagnosis of COVID-19. Their application in nanozyme-based sensing and detection, particularly through colorimetric and fluorometric methods, has significantly advanced our ability to detect the virus at an early stage.

Nanozymes: Potential Therapies for Reactive Oxygen Species Overproduction and Inflammation in Ischemic Stroke and Traumatic Brain Injury

Nanozymes, which can selectively scavenge reactive oxygen species (ROS), have recently emerged as promising candidates for treating ischemic stroke and traumatic brain injury (TBI) in preclinical models. ROS overproduction during the early phase of these diseases leads to oxidative brain damage, which has been a major cause of mortality worldwide. However, the clinical application of ROS-scavenging enzymes is limited by their short in vivo half-life and inability to cross the blood-brain barrier. Nanozymes, which mimic the catalytic function of natural enzymes, have several advantages, including cost-effectiveness, high stability, and easy storage. These advantages render them superior to natural enzymes for disease diagnosis and therapeutic interventions. This review highlights recent advancements in nanozyme applications for ischemic stroke and TBI, emphasizing their potential to mitigate the detrimental effect of ROS overproduction, oxidative brain damage, inflammation, and blood-brain barrier compromise. Therefore, nanozymes represent a promising treatment modality for ROS overproduction conditions in future medical practices.

Nanostructured transition metal dichalcogenides-based colorimetric sensors: Synthesis, characterization, and emerging applications

Nanostructured transition metal dichalcogenides (TMDCs) have garnered significant attention as prospective materials for the development of highly sensitive and versatile colorimetric sensors. This work explores the synthesis, characterization, and emerging applications of TMDC-based sensors, focusing on their unique structural aspects and inherent properties. The synthesis methods involve tailored fabrication techniques, such as chemical vapor deposition and hydrothermal processes, aimed at producing well-defined nanostructures that enhance sensor performance. Characterization techniques, including microscopy, spectroscopy, and surface analysis, are employed to elucidate the structural and chemical features of the nanostructured TMDCs. These analyses provide insights into the correlation between the material's morphology and its sensing capabilities. The colorimetric sensing mechanism relies on the modulation of optical properties in response to specific analytes, enabling rapid and visual detection. The emerging applications of TMDC-based colorimetric sensors span diverse fields, including environmental monitoring, healthcare, and industrial processes. The sensors exhibit high sensitivity, selectivity, and real-time response, making them ideal candidates for detecting various target analytes. Furthermore, their integration with complementary technologies such as microfluidics, can facilitate the development of on-site and point-of-care applications. This work highlights the interdisciplinary significance of nanostructured TMDC-based colorimetric sensors and underscores their potential contributions to addressing contemporary challenges in sensing technology.

Colorimetric and Electrochemical Dual-Mode Detection of Thioredoxin 1 Based on the Efficient Peroxidase-Mimicking and Electrocatalytic Property of Prussian Blue Nanoparticles

As a potent detection method for cancer biomarkers in physiological fluid, a colorimetric and electrochemical dual-mode sensing platform for breast cancer biomarker thioredoxin 1 (TRX1) was developed based on the excellent peroxidase-mimicking and electrocatalytic property of Prussian blue nanoparticles (PBNPs). PBNPs were hydrothermally synthesized using K3[Fe(CN)6] as a precursor and polyvinylpyrrolidone (PVP) as a capping agent. The synthesized spherical PBNPs showed a significant peroxidase-like activity, having approximately 20 and 60% lower Km values for 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2, respectively, compared to those of horseradish peroxidase (HRP). The PBNPs also enhanced the electron transfer on the electrode surface. Based on the beneficial features, PBNPs were used to detect target TRX1 via sandwich-type immunoassay procedures. Using the strategies, TRX1 was selectively and sensitively detected, yielding limit of detection (LOD) values as low as 9.0 and 6.5 ng mL-1 via colorimetric and electrochemical approaches, respectively, with a linear range of 10-50 ng mL-1 in both strategies. The PBNP-based TRX1 immunoassays also exhibited a high degree of precision when applied to real human serum samples, demonstrating significant potentials to replace conventional HRP-based immunoassay systems into rapid, robust, reliable, and convenient dual-mode assay systems which can be widely utilized for the identification of important target molecules including cancer biomarkers.

Dual-mode colorimetric and photothermal aptasensor for detection of kanamycin using flocculent platinum nanoparticles

Chitosan (CS)-stabilized platinum nanoparticles (CS/PtNPs) were employed to develop a novel aptamer-based dual-mode colorimetric and photothermal biosensor for selective detection of kanamycin (KAN). As a peroxidase-like catalyst, the CS/PtNPs showed outstanding catalytic activity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). As a stabilizing agent, CS excelled at fixing the KAN binding aptamer on the surface of the CS/PtNPs, amplifying their catalytic activity and enhancing colloidal dispersion and stability. The oxidized TMB (TMBox) functioned as a signal for the colorimetric, photothermal aptasensor because of its observable absorbance of light in the visible and near-infrared (NIR) regions. When light from a NIR laser was absorbed by the TMBox in the reaction solution, heat was generated in inverse proportion to the KAN concentration. The developed colorimetric and photothermal modes of the aptasensor showed a linear detection range of 0.1-50 and 0.5-50 μM, with a limit of detection (LOD) of 0.04 and 0.41 μM, respectively. Moreover, the aptasensor successfully determined KAN concentrations in spiked milk samples, verifying the reliability and reproducibility in practical applications. The dual-mode aptasensor based on CS/PtNPs for KAN detection, utilizing both color change and heat generation signals through a single probe (TMBox), demonstrates rapid response, simplicity in operation, cost-effectiveness, and high sensitivity. In addition, unlike typical immunoassays, this aptamer-based peroxidase-like nanozyme activation and inhibition strategy required no washing process, which was very effective in terms of reducing the time required for an assay and sustaining a high sensitivity.

A Homogeneous Colorimetric Strategy Based on Rose-like CuS@Prussian Blue/Pt for Detection of Dopamine

The development of effective methods for dopamine detection is critical. In this study, a homogeneous colorimetric strategy for the detection of dopamine based on a copper sulfide and Prussian blue/platinum (CuS@PB/Pt) composite was developed. A rose-like CuS@PB/Pt composite was synthesized for the first time, and it was discovered that when hydrogen peroxide was present, the 3,3',5,5'-tetramethylbenzidine (TMB) changed from colorless into blue-oxidized TMB. The CuS@PB/Pt composite was characterized with a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and an X-ray photoelectron spectrometer (XPS). Moreover, the catalytic activity of the CuS@PB/Pt composite was inhibited by the binding of dopamine to the composite. The color change of TMB can be evaluated by the UV spectrum and a portable smartphone detection device. The developed colorimetric sensor can be used to quantitatively analyze dopamine between 1 and 60 µM with a detection limit of 0.28 μM. Furthermore, the sensor showed good long-term stability and good performance in human serum samples. Compared with other reported methods, this strategy can be performed rapidly (16 min) and has the advantage of smartphone visual detection. The portable smartphone detection device is portable and user-friendly, providing convenient colorimetric analysis for serum. This colorimetric strategy also has considerable potential for the development of in vitro diagnosis methods in combination with other test strips.

Nitrocellulose membranes in situ grown with Prussian blue nanoparticles as stable nanozyme pads for colorimetric detection of dopamine

Prussian blue (PB) is a typical peroxidase mimic with simple preparation, low cost and high eco-friendliness, but it still has drawbacks of poor stability (e.g., decomposition in aqueous dispersions) and intrinsic optical interference (e.g., high extinction coefficient over a wide wavelength range) in colorimetric assays. Herein, we used nitrocellulose (NC) membranes as synthesis hosts of PB nanoparticles (NPs) to develop a new type of three-dimensional (3D) porous nanozyme pad. By means of an in situ synthesis route, PB NPs were uniformly grown on the surfaces of the fiber scaffolds with desirable stability, which also avoided signal interference from PB NPs owing to the easy handling of the pads in a quantitative solid state. The pads showed significant peroxidase-mimicking activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with the output of colorimetric signals. Based on the reduction of oxidized TMB (oxTMB) by dopamine (DA), the pads were exploited for simple and quantitative colorimetric detection of DA with a limit of detection (LOD) of 0.59 μM and a satisfactory accuracy for analysis of real human urine samples. This is the first attempt at exploiting NC membranes as the synthesis hosts to develop nanozyme pads, which solves the above drawbacks of traditional PB-based peroxidase mimics and has promise for various colorimetric bioanalyses, given the structural benefits of NC membranes and their broad applications in biosensors.

Exceptional peroxidase-like activity of an iron and copper based organic framework nanosheet for consecutive colorimetric biosensing of glucose and kanamycin in real food samples

Two-dimensional metal-organic framework nanosheets are attractive as peroxidase mimicking nanocatalysts due to their rich chemical functional groups, large surface area, high porosity, and accessible active sites. In this study, we synthesized FeCu bifunctional 2D MOF nanosheets using a solvothermal method. Fe and Cu ions were added as metal precursors, while organic amine and acid served as the organic ligands to construct the FeCu-MOF nanosheets. These nanosheets demonstrated robust peroxidase-like catalytic activities and were employed to develop a visual detection system for multiple targets, such as glucose and kanamycin. In the detection mechanism, glucose was oxidized into gluconic acid by glucose oxidase (GOx), leading to the generation of H2O2. When H2O2 is present, the FeCu-MOF NSs demonstrate high intrinsic peroxidase-like activity, which might catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) into a blue-coloured oxTMB product with a strong UV absorption at 654 nm. Subsequently, kanamycin was added to the above sensing system. The kanamycin strongly interacted with the FeCu-MOF NSs through H-bonding and blocked electron transfer, resulting in a colour change of the solution from blue to colourless with a weak UV absorption at 654 nm. Under the optimal conditions, the proposed colorimetric sensor exhibits an excellent linear response to glucose and kanamycin over the 0.25-5 μM and 0.02-0.1 μM ranges, respectively. The proposed colorimetric assay detection limits for glucose and kanamycin were found to be as low as 0.1 μM and 8 nM, respectively, and such a sensor shows excellent selectivity and sensitivity against different potential interferents. Thus, our proposed colorimetric assay was satisfactory when applied to glucose and kanamycin detection in agricultural and livestock husbandry samples.

Apta-sensor for selective determination of dopamine using chitosan-stabilized Prussian blue nanoparticles

Chitosan-stabilized Prussian blue nanoparticles (CS/PBNPs) were fabricated by a simple synthetic method and used to develop a novel aptamer-based colorimetric assay for selective determination of dopamine (DA). Scanning electron microscopy (SEM) images exhibited a uniform shape of the CS/PBNPs with an average diameter of 37.0 ± 3.2 nm. The CS/PBNPs exhibited strong peroxidase-like activity that catalyzed the reaction between 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide (H₂O₂). Chitosan was used for stabilization of the PBNPs and fixation of the DA aptamer on the surface of the CS/PBNPs. The catalytic mechanism of the CS/PBNPs was confirmed to involve first the decomposition of H₂O₂ into a hydroxyl radical (˙OH) and then oxidation of TMB by the ˙OH to produce a blue color. An aptamer-based colorimetric assay was made with the CS/PBNPs to detect DA at concentrations of 0.25-100 μM with a limit of detection (LOD) of 0.16 μM. For comparison, a gold nanoparticle (AuNP)-based apta-sensor detected DA in concentrations of 1-25 μM with a LOD of 0.55 μM. The recovery results of DA concentrations (0.25, 0.5, and 1 μM) from spiked human serum were 92.6%, 102.1%, and 103.9%, verifying the reliability and reproducibility of the CS/PBNP-based apta-sensor for determination of DA level in clinical applications. Moreover, compared to traditional immunoassay, this aptamer-based nanozyme activation/inhibition system needs no washing step, which is very useful to shorten the assay time and maintain high sensitivity.

Recent advances in colorimetric sensors based on nanozymes with peroxidase-like activity

Nanozymes have been widely used to construct colorimetric sensors due to their advantages of cost-effectiveness, high stability, good biocompatibility, and ease of modification. The emergence of nanozymes greatly enhanced the detection sensitivity and stability of the colorimetric sensing platform. Recent significant research has focused on designing various sensors based on nanozymes with peroxidase-like activity for colorimetric analysis. However, with the deepening of research, nanozymes with peroxidase-like activity has also exposed some problems, such as weak affinity and low catalytic activity. In view of the above issues, existing investigations have shown that the catalytic properties of nanozymes can be improved by adding surface modification and changing the structure of nanomaterials. In this review, we summarize the recent trends and advances of colorimetric sensors based on several typical nanozymes with peroxidase-like activities, including noble metals, metal oxides, metal sulfides/metal selenides, and carbon and metal-organic frameworks (MOF). Finally, the current challenges and prospects of colorimetric sensors based on nanozymes with peroxidase-like activity are summarized and discussed to provide a reference for researchers in related fields.

Tetrabutylammonium-chloride-glycerol of deep eutectic solvent functionalized MnO2: a novel mimic enzyme for the quantitative and qualitative colorimetric detection of L-cysteine

L-Cysteine is a common amino acid that plays an important role in human livelihood and production. Therefore, a novel method for the simultaneous quantitative and qualitative determination of L-cysteine by a colorimetric detection system is proposed. As a viable oxidase mimic, [N₄₄₄₄]Cl-G/MnO₂, which consisted of MnO₂ nanosheets functionalized by a tetrabutylammonium chloride-glycerol ([N₄₄₄₄]Cl-G) based deep eutectic solvent (DES) was fabricated. Owing to the oxidation of MnO₂ nanosheets, [N₄₄₄₄]Cl-G/MnO₂ could oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue product (oxTMB) with the characteristic UV-vis spectrum absorbance at 652 nm. The oxidation of TMB by DES/MnO₂ was inhibited when L-cysteine was introduced, and the absorbance decreased proportionally with the increase in L-cysteine concentration. Due to this inhibition effect, a colorimetric detection system ([N₄₄₄₄]Cl-G/MnO₂-TMB) was developed for the quantitative determination of L-cysteine. Under optimal conditions, the assay showed good linearity over the concentration range of 0.125-2.00 μg mL^-1 with a low detection limit of 5.96 ng mL^-1. A study of the inhibition mechanism demonstrated that the sulfhydryl group of L-cysteine could decompose [N₄₄₄₄]Cl-G/MnO₂ into Mn²⁺, thus limiting the conversion of TMB to oxTMB. In addition, the [N₄₄₄₄]Cl-G/MnO₂-TMB system was used in test strips for the visual qualitative detection of L-cysteine. The selectivity and test strip results demonstrated the high selectivity, simple operation, and rapid response of the [N₄₄₄₄]Cl-G/MnO₂-TMB system for the qualitative detection of L-cysteine. Given the satisfying performance of the detection strategy, colorimetric sensing based on the [N₄₄₄₄]Cl-G/MnO₂-TMB system is considered to have prospective application value in the quantitative and qualitative detection of L-cysteine.

One-Pot Preparation of Imidazole-Ring-Modified Graphitic Carbon Nitride Nanozymes for Colorimetric Glucose Detection

Nanozymes are highly desired to overcome the shortcomings of natural enzymes, such as low stability, high cost and difficult storage during biosensing applications. Herein, by imitating the structure of natural enzymes, we propose a one-pot annealing process to synthesis imidazole-ring-modified graphitic carbon nitride (g-C₃N₄-Im) with enhanced peroxidase-like activity. g-C₃N₄-Im shows enhanced peroxidase-like activity by 46.5 times compared to unmodified g-C₃N₄. Furthermore, imidazole rings of g-C₃N₄-Im make it possible to anchor Cu(II) active sites on it to produce g-C₃N₄-Im-Cu, which shows a further increase in peroxidase-like activity by three times. It should be noted that the as-prepared g-C₃N₄-Im-Cu could show obvious peroxidase-like activity over a broad range of pH values and at a low temperature (5 °C). The ultrahigh peroxidase-like activity is attributed to the electronic effect of imidazole rings and the active sites of Cu(II) for ·OH production. Based on the enhanced peroxidase-like activity, a H₂O₂ and glucose biosensor was developed with a high sensitivity (limit of detection, 10 nM) and selectivity. Therefore, the biosensor shows potential for applications in diabetic diagnoses in clinical practice.

Hierarchical microtubes constructed using Fe-doped MoS2 nanosheets for biosensing applications

The structural design of multiple functional components could enhance the synergistic catalytic performance of MoS₂-based composites in enzyme-like catalysis. Herein, one-dimensional (1D) Fe-MoS₂ microtubes were designed to prepare tubular Fe-doped MoS₂ composites with MoO₃ microrods as self-sacrificing precursors. Remarkably, the results indicated that the generated ammonia released from the sulfidation process led to the dissolution of MoO₃ cores and the generation of a tubular structure. The Fe-MoS₂ composites integrated the synergistic effects of Fe-doped MoS₂ nanosheets (NSs) and the 1D tubular structure. Thus, a higher catalytic activity was observed in peroxidase-like catalysis than in other components, such as MoO₃@FeOOH, FeOOH and MoS₂ NSs. The peroxidase-like mechanism originated from the generation of the ˙OH radical. The Fe-MoS₂ microtube-based colorimetric assay was used to detect H₂O₂ with a detection limit (LOD) of 0.51 μM in a linear range from 1.25 to 50 μM. The colorimetric method was simple, selective, and sensitive for glutathione (GSH) detection in the range of 0.25-125 μM with a detection limit (LOD) of 0.12 μM. Thus, we provide a facile synthetic strategy for simultaneously integrating electronic modulation and structural design to develop an efficient MoS₂-based functional catalyst.