Antimony-doped tin oxide nanoparticles as peroxidase mimics for paper-based colorimetric detection of glucose using smartphone read-out

A robust single compartment peroxide fuel cell using mesoporous antimony doped tin oxide as the cathode material

To date, metal oxide catalysts have not been explored as cathode materials for robust and high-performance single-compartment H2O2 fuel cells due to significant non-electrochemical disproportionation losses of H2O2 on many metal oxide surfaces. Here, for the first time, we demonstrate an acidic peroxide fuel cell with antimony doped tin oxide as the cathode and widely used Ni foam as the anode material. Our constructed peroxide fuel cell records a superior open circuit potential of nearly 0.82 V and a maximum power density of 0.32 mW cm-2 with high operational stability. The fuel cell performance is further improved by increasing the ionic strength of the electrolyte with the addition of 1 M NaCl, resulting in an increased maximum power density value of 1.1 mW cm-2.

Facile green synthesis of wasted hop-based zinc oxide nanozymes as peroxidase-like catalysts for colorimetric analysis

Hops are a common ingredient in beer production, and a considerable quantity of hops is usually discarded as a waste material once the brewing process is completed. Transforming this waste material into valuable nanomaterials offers a sustainable approach that has the potential to significantly mitigate environmental impact. Herein, a facile and green protocol for the production of zinc oxide nanozymes (ZnO NZs) using wasted hop extract (WHE) as a natural precursor was demonstrated. The process involved a hydrothermal synthesis method followed by a calcination step to form the final ZnO NZs. The results revealed that lupulon, the main β-acid in hops, particularly the phenolic hydroxy group, is primarily responsible for the biosynthesis of ZnO NZs. The WHE-ZnO NZs exhibited exceptional peroxidase-like (POD-like) activity and served as effective catalysts for the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). Analysis of the catalytic mechanism revealed that the POD-like activity of these WHE-ZnO NZs originated from their ability to expedite the transfer of electrons between TMB and H2O2, resulting in the enzymatic kinetics following the standard Michaelis-Menten mechanism. Furthermore, we developed a straightforward and user-friendly colorimetric technique for detecting both H2O2 and glucose. By utilizing the WHE-ZnO NZs as POD-like catalysts, we achieved a linear detection range of 1-1000 μM and a limit of detection of 0.24 μM (S/N = 3) for H2O2 detection and a linear range of 0-100 mM and a detection limit of 16.73 μM (S/N = 3) for glucose detection. These results highlighted the potential applications of our waste-to-resource approach for nanozyme synthesis in the field of analytical chemistry.

Acute Aquatic Toxicity to Zebrafish and Bioaccumulation in Marine Mussels of Antimony Tin Oxide Nanoparticles

Antimony tin oxide (Sb₂O₅/SnO₂) is effective in the absorption of infrared radiation for applications, such as skylights. As a nanoparticle (NP), it can be incorporated into films or sheets providing infrared radiation attenuation while allowing for a transparent final product. The acute toxicity exerted by commercial Sb₂O₅/SnO₂ (ATO) NPs was studied in adults and embryos of zebrafish (Danio rerio). Our results suggest that these NPs do not induce an acute toxicity in zebrafish, either adults or embryos. However, some sub-lethal parameters were altered: heart rate and spontaneous movements. Finally, the possible bioaccumulation of these NPs in the aquacultured marine mussel Mytilus sp. was studied. A quantitative analysis was performed using single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The results indicated that, despite being scarce (2.31 × 10⁶ ± 9.05 × 10⁵ NPs/g), there is some accumulation of the ATO NPs in the mussel. In conclusion, commercial ATO NPs seem to be quite innocuous to aquatic organisms; however, the fact that some of the developmental parameters in zebrafish embryos are altered should be considered for further investigation. More in-depth analysis of these NPs transformations in the digestive tract of humans is needed to assess whether their accumulation in mussels presents an actual risk to humans.

Sb-doped FeOCl nanozyme-based biosensor for highly sensitive colorimetric detection of glutathione

Nanozymes have been emerging as substitutes for natural enzymes to construct biosensors towards biomolecular detection. However, the detection of glutathione (GSH) by nanozyme-based biosensors still remains a great challenge for research on catalytic activity enhancement and the detection mechanism. In this work, Sb-doped iron oxychloride (Sb-FeOCl) with a well-defined nanorod-like structure is prepared by high-temperature calcination. Sb-FeOCl nanorods have high peroxidase-like activity, which can catalyze the decomposition of H₂O₂ into ·OH and then oxidize 3,3',5,5'-tetramethylbenzidine (TMB). In view of these intriguing observations, a reliable colorimetric method with a simple mixing and detection strategy is developed for the detection of GSH. The linear range of GSH detection is 1-36 μM. The detection limit of GSH reaches a low level of 0.495 μM (3σ/slope). The GSH sensing system also exhibits excellent specificity and anti-interference. Taking advantage of the advantages of the Sb-FeOCl nanorod-based biosensor, it can be used to quantitatively detect GSH levels in human serum. It can be anticipated that the Sb-FeOCl nanorods have broad prospects in the field of enzymatic biochemical reactions.

Light-enhanced transparent hydrogel for uric acid and glucose detection by four different analytical platforms

The lack of solid-phase media limits the portability of colorimetric sensing platforms. In this study, a series of transparent polyvinyl alcohol (PVA) hydrogels encapsulated antimony tin oxide nanoparticles (ATO NPs) and 3,3',5,5'-tetramethylbenzidine (TMB) were developed as the solid-phase sensing media for glucose and uric acid. Under the conditions of H₂O₂ and UV light, the hydrogel presented a multicatalytic ability (photo Fenton-like and peroxidase-like activities), which accelerated the oxidation of TMB, turning the hydrogel from colorless to blue and finally enhancing the detection signal. The plasticity of the hydrogel allowed it to be designed into various shapes (membrane, microsphere etc.) to adapt multiple detection platforms (a liquid/solid-phase UV spectrophotometer, a NanoPhotometer, and smartphone spectroscopy). The hydrogel sensing media exhibited excellent tunability and enhanced the photocatalytic ability. The proposed material was successfully applied to detect glucose and uric acids in real samples by four detection platforms to evaluate its practicability.

Chitosan-Based Hydrogels for Bioelectronic Sensing: Recent Advances and Applications in Biomedicine and Food Safety

Due to the lack of efficient bioelectronic interfaces, the communication between biology and electronics has become a great challenge, especially in constructing bioelectronic sensing. As natural polysaccharide biomaterials, chitosan-based hydrogels exhibit the advantages of flexibility, biocompatibility, mechanical tunability, and stimuli sensitivity, and could serve as an excellent interface for bioelectronic sensors. Based on the fabrication approaches, interaction mechanisms, and bioelectronic communication modalities, this review divided chitosan-based hydrogels into four types, including electrode-based hydrogels, conductive materials conjugated hydrogels, ionically conductive hydrogels, and redox-based hydrogels. To introduce the enhanced performance of bioelectronic sensors, as a complementary alternative, the incorporation of nanoparticles and redox species in chitosan-based hydrogels was discussed. In addition, the multifunctional properties of chitosan-based composite hydrogels enable their applications in biomedicine (e.g., smart skin patches, wood healing, disease diagnosis) and food safety (e.g., electrochemical sensing, smart sensing, artificial bioelectronic tongue, fluorescence sensors, surface-enhanced Raman scattering). We believe that this review will shed light on the future development of chitosan-based biosensing hydrogels for micro-implantable devices and human-machine interactions, as well as potential applications in medicine, food, agriculture, and other fields.

Nanozyme-based colorimetric biosensor with a systemic quantification algorithm for noninvasive glucose monitoring

Diabetes mellitus accompanies an abnormally high glucose level in the bloodstream. Early diagnosis and proper glycemic management of blood glucose are essential to prevent further progression and complications. Biosensor-based colorimetric detection has progressed and shown potential in portable and inexpensive daily assessment of glucose levels because of its simplicity, low-cost, and convenient operation without sophisticated instrumentation. Colorimetric glucose biosensors commonly use natural enzymes that recognize glucose and chromophores that detect enzymatic reaction products. However, many natural enzymes have inherent defects, limiting their extensive application. Recently, nanozyme-based colorimetric detection has drawn attention due to its merits including high sensitivity, stability under strict reaction conditions, flexible structural design with low-cost materials, and adjustable catalytic activities. This review discusses various nanozyme materials, colorimetric analytic methods and mechanisms, recent machine learning based analytic methods, quantification systems, applications and future directions for monitoring and managing diabetes.

Antioxidant colloids via heteroaggregation of cerium oxide nanoparticles and latex beads

Antioxidant colloids were developed via controlled heteroaggregation of cerium oxide nanoparticles (CeO₂ NPs) and sulfate-functionalized polystyrene latex (SL) beads. Positively charged CeO₂ NPs were directly immobilized onto SL particles of opposite surface charge via electrostatic attraction (SL/Ce composite), while negatively charged CeO₂ NPs were initially functionalized with poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte and then, aggregated with the SL particles (SPCe composite). The PDADMAC served to induce a charge reversal on CeO₂ NPs, while the SL support prevented nanoparticle aggregation under conditions, where the dispersions of bare CeO₂ NPs were unstable. Both SL/Ce and SPCe showed enhanced radical scavenging activity compared to bare CeO₂ NPs and were found to mimic peroxidase enzymes. The results demonstrate that SL beads are suitable supports to formulate CeO₂ particles and to achieve remarkable dispersion storage stability. The PDADMAC functionalization and immobilization of CeO₂ NPs neither compromised the peroxidase-like activity nor the radical scavenging potential. The obtained SL/Ce and SPCe artificial enzymes are foreseen to be excellent antioxidant agents in various applications in the biomedical, food, and cosmetic industries.

Smartphone-based colorimetric detection systems for glucose monitoring in the diagnosis and management of diabetes

Diabetes is a group of metabolic conditions resulting in high blood sugar levels over prolonged periods that affects hundreds of millions of patients worldwide. Measuring glucose concentration enables patient-specific insulin therapy, and is essential to reduce the severity of the disease, potential complications, and related mortalities. Recent advances and developments in smartphone-based colorimetric glucose detection systems are discussed in this review. The importance of glucose monitoring, data collection, transfer, and analysis, via non-invasive/invasive methods is highlighted. The review also presents various approaches using 3D-printed materials, screen-printed electrodes, polymer templates, designs allowing multiple glucose analysis, bioanalytes and/or nanostructures for glucose detection. The positive effects of advances in improving the performance of smartphone-based platforms are introduced along with future directions and trends in the application of emerging technologies in smartphone-based diagnostics.

Three-in-one via syringe needle-based device: sampling, microextraction and peroxidase-like catalysis for colorimetric detection of the change of biogenic amines levels with time in meat

In this work, a syringe needle-based integrated method was designed for the detection of biogenic amines (BAs) in raw meat samples. Based on a sequential process, the needle-based sampling, micro liquid-phase extraction and peroxidase-like catalysis were adopted for the sample collection, target analytes extraction and colorimetric analysis, respectively. The proposed method exhibited high selectivity towards BAs (the total amount of histamine, putrescine and cadaverine was utilized to present the level of BAs), where the linear range is 5-50 μM and 50-1000 μM, and the limit of detection is 1.52 μM. Specifically, the whole process could be completed in a single syringe needle. In addition, due to the minimized sampling, the change of BAs levels with time in different area of real samples (fish) can be conveniently investigated. This method has the advantages of simplicity, low cost, high sensitivity and selectivity, endowing it a promising candidate for food analysis.

A long-term stable paper-based glucose sensor using a glucose oxidase-loaded, Mn2BPMP-conjugated nanocarrier with a smartphone readout

A simple paper-based analytical device (PAD) for the one-pot detection of glucose was developed herein using an artificial peroxidase-functionalized and glucose oxidase (GOx)-loaded pluronic-based nanocarrier (PNC). Mn₂BPMP (BPMP; 2,6-bis[(bis(2-pyridylmethyl)amino)-methyl]-4-methylphenolate), an artificial peroxidase, was conjugated to PNC, allowing GOx to be loaded with a very high encapsulation efficiency. In solution, Mn₂BPMP-PNC showed higher peroxidase-like catalytic efficiency than did Mn₂BPMP at physiological pH. In addition, glucose detection via enzyme cascade reaction between GOx and Mn₂BPMP in the GOx loaded-Mn₂BPMP-PNC was more sensitive than the simple combination of Mn₂BPMP and GOx with excellent selectivity. Subsequently, a PAD was fabricated using a laser printer with an assay substance containing GOx loaded-Mn₂BPMP-PNC and peroxidase chromogenic substrate. The prepared Mn₂BPMP-PNC-based PAD quantitatively measured glucose in human serum ranging from normal levels to those typical for diabetics as well as in buffer by obtaining RGB (red, green, and blue) color values through smartphone readout or the naked eye. Importantly, the present PNC-based PAD maintained the detection efficiency during storage at room temperature for 6 weeks in contrast to the rapid decrease in detection efficiency obtained for PAD containing Mn₂BPMP and GOx without PNC.

Dual-Modal Immunosensor with Functionalized Gold Nanoparticles for Ultrasensitive Detection of Chloroacetamide Herbicides

Convenient and ultrasensitive detection of pesticides is demanded for healthcare and environmental monitoring, which can be realized with a dual-modal strategy. In this paper, based on a biotin-labeled IgG-modified gold nanoparticle (AuNP@IgG-bio) probe, a dual-modal immunosensor was proposed for detecting chloroacetamide herbicides. This platform is relied on the dephosphorylation of ascorbic acid 2-phosphate (AA2P) by alkaline phosphatase (ALP). In addition to this process, ascorbic acid (AA)-triggered deposition of silver on gold nanostars (AuNSs) and the fluorogenic reaction of dehydrogenated AA and o-phenylenediamine (OPD) occur sequentially. Thus, the dual readout of the color change of red-green-blue (RGB) and fluorescence generation in situ induced by crystal growth can be used. The limits of detection (LODs) were as low as 1.20 ng/mL of acetochlor (ATC), 0.89 ng/mL of metolachlor, 1.22 ng/mL of propisochlor, and 0.99 ng/mL of their mixture by a smartphone and 0.44 ng/mL of ATC, 1.59 ng/mL of metolachlor, 2.80 ng/mL of propisochlor, and 0.72 ng/mL of their mixture by a spectrofluorometer. The recoveries from corn were 91.4-105.1% of the colorimetric mode and 92.4-106.2% of the fluorescent mode. Due to its simple observation mode and good performance, this dual-modal immunosensor possesses considerable application prospects.

A colorimetric paper-based ATONP-ALP nanobiosensor for selective detection of Cd2+ ions in clams and mussels

A colorimetric paper-based enzyme-coupled antimony tin oxide nanoparticle (ATONP) nanobiosensor for selective detection of Cd²⁺ ions in clams and mussels is presented. Alkaline phosphatase (ALP) was immobilized on ATONPs via 16-phosphonohexadecanoic acid (16-PHA) to develop ATONP-ALP nanobiosensor. The biosensor was characterized using XPS, Raman spectroscopy, SEM, and EDX. ATONP-ALP nanobiosensor exhibited high selectivity towards detection of Cd²⁺ ion with a LOD 0.006 μg L^-1 and linear range of detection 0.005-1 μg L^-1. The developed biosensor was further integrated into a low-cost paper-based format. A visual color change was obtained for Cd²⁺ ion in the range 0.1-10 μg L^-1. The developed biosensor was successfully demonstrated for the analysis of Cd²⁺ ions in clams with recoveries 101-104%. The ATONP-ALP nanobiosensor was validated using mussel tissue (BCR-668) and the conventional ICP-OES and ICP-MS techniques.

Novel hierarchical CuNiAl LDH nanotubes with excellent peroxidase-like activity for wide-range detection of glucose

Novel hierarchical CuNiAl layered double hydroxide (CuNiAl LDH) nanotubes were prepared with in situ transformation of Al₂O₃ produced using the atomic layer deposition (ALD) method. Based on the characterizations using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), CuNiAl LDH displays a typical nanotube-like structure consisting of uniform ultrathin nanoflakes. It is also confirmed that nitrate precursors play a crucial role in the formation of the LDH hierarchical structure. The unique hierarchical tube-like structure for CuNiAl LDH can supply more active sites and higher surface areas, leading to outstanding peroxidase mimicking property. The kinetic analyses indicate that the catalytic behavior of CuNiAl LDH follows classic Michaelis-Menten models and the affinity of CuNiAl LDH to the substrate is significantly higher than horseradish peroxidase. A simple and label-free method was developed for the colorimetric detection of glucose. As low as 2.9 μM of glucose can be detected with a broad linear range from 10 to 200 μM. The established method is also proved to be suitable for glucose detection in juice samples.

Tungsten disulfide nanosheets-based colorimetric assay for glucose sensing

We have developed a glucose oxidase (GOx)-mediated strategy for glucose detection, which is based on the intrinsic peroxidase-like activity of WS₂ as a catalyst for the 3,3',5,5'-tetramethylbenzidine‑hydrogen peroxide (TMB-H₂O₂) reaction. The colorimetric assay involves two parts: generation of H₂O₂ from the oxidation of glucose catalyzed by GOx, and WS₂ nanosheets that catalyze the reaction between TMB and H₂O₂. In this colorimetric assay, the enhancement of colorimetric signals depends directly on the increased H₂O₂ concentration, which, in turn, relies on the glucose concentration. The results show that the concentrations of the glucose were directly proportional to absorbance of the TMB solutions over a range of 1 nM-500 μM with a limit of detection of 0.1445 nM. In addition, this new colorimetric assay has been utilized for glucose detection in human serum with a satisfactory result.

Application of smartphone-based spectroscopy to biosample analysis: A review

The emergence of the smartphones has brought extensive changes to our lifestyles, from communicating with one another, to shopping and enjoyment of entertainment, and from studying to functioning at the workplace (and in the field). At the same time, this portable device has also provided new possibilities in scientific research and applications. Based on the growing awareness of good health management, researchers have coupled health monitoring to smartphone sensing technologies. Along the way, there have been developed a variety of smartphone-based optical detection platforms for analyzing biological samples, including standalone smartphone units and integrated smartphone sensing systems. In this review, we outline the applications of smartphone-based optical sensors for biosamples. These applications focus mainly on three aspects: Microscopic imaging sensing, colorimetric sensing and luminescence sensing. We also discuss briefly some limitations of the current state of smartphone-based spectroscopy and present prospects of the future applicability of smartphone sensors.

Hydrothermal method-based synthesized tin oxide nanoparticles: Albumin binding and antiproliferative activity against K562 cells

The interaction of nanoparticles with protein and cells may provide important information regarding their biomedical implementations. Herein, after synthesis of tin oxide (SnO₂) nanoparticles by hydrothermal method, their interaction with human serum albumin (HSA) was evaluated by multispectroscopic and molecular docking (MD) approaches. Furthermore, the selective antiproliferative impact of SnO₂ nanoparticles against leukemia K562 cells was assessed by different cellular assays, whereas lymphocytes were used as control cells. TEM, DLS, zeta potential and XRD techniques showed that crystalline SnO₂ nanoparticles have a size of less than 50 nm with a good colloidal stability. Fluorescence and CD spectroscopy analysis indicated that the HSA undergoes some slight conformational changes after interaction with SnO₂ nanoparticles, whereas the secondary structure of HSA remains intact. Moreover, MD outcomes revealed that the charged residues of HSA preferentially bind to SnO₂ nanoclusters in the binding pocket. Antiproliferative examinations displayed that SnO₂ nanoparticles can selectively cause the mortality of K562 cells through induction of cell membrane leakage, activation of caspase-9, -8, -3, down regulation of Bcl-2 mRNA, the elevation of ROS level, S phase arrest, and apoptosis. In conclusion, this data may indicate that SnO₂ nanoparticles can be used as promising particles to be integrated into therapeutic platforms.

Recent advances in the application of layered double hydroxides in analytical chemistry: A review

In recent years, layered double hydroxides (LDHs) have garnered a lot of attention in analytical chemistry, due to their advantages such as relatively simple synthesis, low cost, possession of large specific surface area and high catalytic activity, and biocompatibility. The most common applications of LDH in analytical chemistry such as sorbents in sample extraction, electrode materials in electrochemical sensing and color indicators in colorimetric detection have been well reported. Generally, the LDHs are prepared as composites with nanomaterials, or constructed with specific three-dimensional structures, befitting the applications desired for them. However, the applications of LDHs (as extraction sorbents, color indicators and in electrochemical sensing) are usually limited in these scenarios. To help address these challenges, future trends and developmental prospects of LDHs materials in analytical chemistry are discussed in this article. Besides, the strategies associated with the design of LDHs, including the structural aspects, for potential analytical applications are presented and reviewed.