Yolk-shell nanostructured Fe3O4@C magnetic nanoparticles with enhanced peroxidase-like activity for label-free colorimetric detection of H2O2 and glucose

Synthesis of histidine, serine and folic acid-functionalized and boron and iron-doped graphene quantum dot with excellent optical behavior and peroxidase-like activity for colorimetric and fluorescence detection of H2O2 in food

Low fluorescence under visible light excitation and catalytic activity limit many applications of graphene quantum dots in optical detection, biosensing, catalysis and biomedical. The paper reports design and synthesis of histidine, serine and folic acid-functionalized and boron and iron-doped graphene quantum dot (Fe/B-GQD-HSF). The Fe/B-GQD-HSF shows excellent fluorescence behavior and peroxidase-like activity. Excitation of 330 nm ultraviolet light produces the strongest blue fluorescence and excitation of 480 nm visible light produces the strongest yellow fluorescence. The specific activity reaches 92.67 U g-1, which is higher than that of other graphene quantum dots. The Fe/B-GQD-HSF can catalyze oxidation of 3,3',5,5'-tetramethylbenzidine with H2O2 to form blue compound. Based on this, it was used for colorimetric and fluorescence detection of H2O2. The absorbance at 652 nm linearly increases with the increase of H2O2 concentration between 0.5 and 100 μM with detection limit of 0.43 μM. The fluorescence signal linearly decreases with the increase of H2O2 concentration between 0.05 and 100 μM with detection limit of 0.035 μM. The analytical method has been satisfactorily applied in detection of H2O2 in food. The study also paves one way for design and synthesis of functional graphene quantum dots with ideal fluorescence behavior and catalytic activity.

Preparation of hollow double-layer Pt@CeO2 nanospheres as oxidase mimetics for the colorimetric-fluorescent-SERS triple-mode detection of glutathione in serum

Glutathione (GSH) is an essential antioxidant in the human body, but its detection is difficult due to the interference of complex components in serum. Herein, hollow double-layer Pt@CeO2 nanospheres were developed as oxidase mimetics, and the light-assisted oxidase mimetics effects were found. The oxidase activity was enhanced significantly by utilizing the synergistic effect of Schottky junction and the localized surface plasmon resonance (LSPR) of Pt under UV light. A novel GSH colorimetric-fluorescent-SERS sensing platform was established, with the sensing performance notably boosted by using the light-assisted oxidase mimetics effects. This platform boasts an exceptionally low detection limit (LOD) of 0.084 μM, while the detection time was shortened from 10 min to just 2 min. The anti-interference detection with high recovery rate (96.84%-107.4 %) in real serum made it be promising for practical application.

A Colorimetric RT-LAMP Assay for Rapid Detection of Soybean mosaic Virus SC15

Soybean mosaic virus (SMV) represents one of the most devastating viral diseases affecting soybeans worldwide. Among its strains, SMV-SC15 is notable for its virulence, predominance, and widespread occurrence. Rapid and on-site diagnosis is important for controlling the spread of SMV-SC15. In this study, we proposed a colorimetric reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay for the detection of SMV-SC15 using three color indicators for visual interpretation: Neutral Red (N-Red), Bromothymol Blue (BTB), and SYBR Green I. The SMV-SC15 in the soybean tissue was detected with remarkable sensitivity and specificity within 30 min, achieving a detection limit as low as 10-4 ng/μL. 200 soybean leaf samples from the field were analyzed by the colorimetric RT-LAMP assays, holding significant potential for rapid screening of SMV-SC15-resistant cultivars, thereby contributing to effective SMV control.

Detection of tetanus toxoid with iron magnetic nanobioprobe

Diagnosis of diseases with low facilities, speed, accuracy and sensitivity is an important matter in treatment. Bioprobes based on iron oxide nanoparticles are a good candidate for early detection of deadly and infectious diseases such as tetanus due to their high reactivity, biocompatibility, low production cost and sample separation under a magnetic field. In this study, silane groups were coated on surface of iron oxide nanoparticles using tetraethoxysilane (TEOS) hydrolysis. Also, NH2groups were generated on the surface of silanized nanoparticles using 3-aminopropyl triethoxy silane (APTES). Antibody was immobilized on the surface of silanized nanoparticles using TCT trichlorothriazine as activator. Silanization and stabilized antibody were investigated by using of FT-IR, EDX, VSM, SRB technique. UV/vis spectroscopy, fluorescence, agglutination test and ELISA were used for biosensor performance and specificity. The results of FT-IR spectroscopy showed that Si-O-Si and Si-O-Fe bonds and TCT chlorine and amine groups of tetanus anti-toxoid antibodies were formed on the surface of iron oxide nanoparticles. The presence of Si, N and C elements in EDX analysis confirms the silanization of iron oxide nanoparticles. VSM results showed that the amount of magnetic nanoparticles after conjugation is sufficient for biological applications. Antibody stabilization on nanoparticles increased the adsorption intensity in the uv/vis spectrometer. The fluorescence intensity of nano bioprobe increased in the presence of 10 ng ml-1. Nanobio probes were observed as agglomerates in the presence of tetanus toxoid antigen. The presence of tetanus antigen caused the formation of antigen-nanobioprobe antigen complex. Identification of this complex by HRP-bound antibody confirmed the specificity of nanobioprobe. Tetanus magnetic nanobioprobe with a diagnostic limit of 10 ng ml-1of tetanus antigen in a short time can be a good tool in LOC devices and microfluidic chips.

Fe3O4 nanoparticles entrapped in the inner surfaces of N-doped carbon microtubes with enhanced biomimetic activity

Tubular structured composites have attracted great interest in catalysis research owing to their void-confinement effects. In this work, we synthesized a pair of hollow N-doped carbon microtubes (NCMTs) with Fe3O4 nanoparticles (NPs) encapsulated inside NCMTs (Fe3O4@NCMTs) and supported outside NCMTs (NCMTs@Fe3O4) while keeping other structural features the same. The impact of structural effects on the catalytic activities was investigated by comparing a pair of hollow-structured nanocomposites. It was found that the Fe3O4@NCMTs possessed a higher peroxidase-like activity when compared with NCMTs@Fe3O4, demonstrating structural superiority of Fe3O4@NCMTs. Based on the excellent peroxidase-like catalytic activity and stability of Fe3O4@NCMTs, an ultra-sensitive colorimetric method was developed for the detection of H2O2 and GSH with detection limits of 0.15 μM and 0.49 μM, respectively, which has potential application value in biological sciences and biotechnology.

Enhanced "Electronic Tongue" for Dental Bacterial Discrimination and Elimination Based on a DNA-Encoded Nanozyme Sensor Array

Bacterial infections are the second leading cause of death around the world, especially those caused by delayed treatment and misdiagnosis. Therefore, rapid discrimination and effective elimination of multiple bacteria are of great importance for improving the survival rate in clinic. Herein, a novel colorimetric sensor array for bacterial discrimination and elimination is constructed using programmable DNA-encoded iron oxide nanoparticles (IONPs) as sensing elements. Utilizing differential interactions of bacteria on DNA-encoded IONPs, 11 kinds of dental bacteria and 6 kinds of proteins have been successfully identified by linear discriminant analysis (LDA). Moreover, the developed sensing system also performs well in the quantitative determination of individual bacteria and identification of bacterial mixtures. More importantly, the practicability of this sensing strategy is further verified by precise differentiation of blind and artificial saliva samples. Furthermore, the sensor array is used for efficiently killing multiple bacteria, demonstrating great potential in clinical prophylaxis and therapy.

Multifunctional molecularly imprinted nanozymes with improved enrichment and specificity for organic and inorganic trace compounds

Although nanozymes exhibit properties superior to those of natural enzymes and conventional engineered enzymes, the development of highly specific nanozymes remains a challenge. New yolk-shell Fe3O4 molecularly imprinted (MIP@void@Fe3O4) nanozymes with peroxidase-like activity were developed by modelling the substrate channels of natural enzymes through molecular imprinting techniques and interfacial affinity modifications in this study. To establish a platform technology for the adsorption and determination of inorganic and organic contaminants, lead ion (Pb2+) and diazinon (DIZ), respectively, were selected as imprinting templates, and a hollow mesoporous shell was synthesized. The as-prepared MIP@void@Fe3O4 nanozymes, characterized using TEM, HRTEM, SEM, FT-IR, TGA, VSM and XPS, not only affirmed the successful fabrication of a magnetic nanoparticle with a unique hollow core-shell structure but also facilitated an exploration of the interfacial bonding mechanisms between Fe3O4 and other shell layers. The enrichment of the MIP@void@Fe3O4 nanozymes due to imprinting was approximately 5 times higher than the local substrate concentration and contributed to the increased activity. Based on selective and competitive recognition experiments, the synthesized nanozymes could selectively recognize organic and inorganic targets with the lowest detection limits (LOD) of 6.6 × 10-9 ppm for Pb2+ and 5.13 × 10-11 M for DIZ. Therefore, the proposed biosensor is expected to be a potent tool for trace pollutant detection, which provides a rational design for more advanced and subtle methods to bridge the activity gap between natural enzymes and nanozymes.

Quantification of Neuronal Cell-Released Hydrogen Peroxide Using 3D Mesoporous Copper-Enriched Prussian Blue Microcubes Nanozymes: A Colorimetric Approach in Real Time and Anticancer Effect

Despite the effectiveness and selectivity of natural enzymes, their instability has paved the way for developing nanozymes with high peroxidase activity using a straightforward technique, thereby expanding their potential for multifunctional applications. Herein, meso-copper-Prussian blue microcubes (Meso-Cu-PBMCs) nanozymes were successfully prepared via a cost-effective hydrothermal route. It was found that the Cu-PBMCs nanozymes, with three-dimensional (3D) mesoporous cubic morphologies, exhibited an excellent peroxidase-like property. Based on the high affinity of Meso-Cu-PBMCs toward H2O2 (Km = 0.226 μM) and TMB (Km = 0.407 mM), a colorimetric sensor for in situ H2O2 detection was constructed. On account of the high catalytic activity, affinity, and cascade strategy, the Meso-Cu-PBMCs nanozyme generated rapid multicolor displays at varying H2O2 concentrations. Under optimized conditions, the proposed sensor exhibits a preferable sensitivity of 18.14 μA μM-1, a linear range of 10 nM-25 mM, and a detection limit of 6.36 nM (S/N = 10). The reliability of the sensor was verified by detecting H2O2 in spiked human blood serum and milk samples, as well as by detecting in situ H2O2 generated from the neuron cell SH-SY5Y. Besides, the Meso-Cu-PBMCs nanozyme facilitated the catalysis of H2O2 in cancer cells, generating •OH radicals that induce the death of cancer cells (HCT-116 colon cancer cells), which holds substantial potential for application in chemodynamic therapy (CDT). This proposed strategy holds promise for simple, rapid, inexpensive, and effective intracellular biosensing and offers a novel approach to improve CDT efficacy.

Glucose sandwich assay based on surface-enhanced Raman spectroscopy

A facile and sensitive glucose sandwich assay using surface-enhanced Raman scattering (SERS) has been developed. Glucose was captured by 3-aminopheyonyl boronic acid (APBA) modified Ag nanoparticles decorated onto a polyamide surface. Then, Ag nanoparticles modified with 3-amino-6-ethynylpicolinonitrile (AEPO) and APBA were used as SERS tags. APBA forms specific cis-diol compounds with glucose molecules avoiding interference by other saccharides and biomolecules in urine enabling its selective detection. As the actual Raman reporter, AEPO exhibited a distinctive SERS peak in the Raman silent region, thus increasing the sensitivity of the glucose detection to 10-11 M. Additionally, the developed SERS assay was reusable, and its applicability in artificial urine samples demonstrated future clinical utility confirming the potential of this innovative technology as a diagnostic tool for glucose sensing.

G-/C-rich ssDNA-based Fe and Cu/Fe nanoclusters with peroxidase-like activity for intracellular ROS production and cytotoxicity applications

Five G-/C-rich single-stranded DNA (ssDNA) with different sequences and lengths were templated to prepare the DNA-Cu, DNA-Fe, and bimetallic DNA-Cu/M nanoclusters (NCs). The peroxidase-like activities of these nanomaterials were studied using H₂O₂ and 3,3',5,5''-tetramethylbenzidine (TMB) as the reaction substrates in HAc-NaAc buffer. It was found that T30-G2-Fe NCs and T30-G2-Cu/Fe NCs, with a size of about 2 nm, exhibit similar and the strongest enzyme-like activity under optimal conditions. Both NCs possess a similarly high affinity to substrates, and the Michaelis-Menten constant (K_m) values to TMB and H₂O₂ are about 11 and 2-3 times lower than those of natural horseradish peroxidase (HRP), respectively. The activity of both nanozymes decreases to about 70% after being kept for one week in pH 4.0 buffer at 4 °C, which is comparable with HRP. Hydroxyl radicals (•OH) are the main reactive oxygen species (ROS) produced in the catalytic reaction. Moreover, both NCs can facilitate in situ generation of ROS in HeLa cells using endogenous H₂O₂. MTT assays indicate that the T30-G2-Cu/Fe NCs exhibit the strong selective cytotoxicity to HeLa cells over HL-7702 cells. The cellular viability is about 70% and 50% after incubating with 0.6 M NCs for 24 h without or with 2 mM H₂O₂, respectively. The current study shows that the T30-G2-Cu/Fe NCs have the potential for chemical dynamic treatment (CDT).

DNA-Programmed Tuning of the Growth and Enzyme-Like Activity of a Bimetallic Nanozyme and Its Biosensing Applications

Nanozymes, which combine the merits of both nanomaterials and natural enzymes, have aroused tremendous attention as new representatives of artificial enzyme mimics. However, it still remains to be a great challenge to rationally engineer the morphologies and surface properties of nanostructures that lead to the desired enzyme-like activities. Here, we report a DNA-programming seed-growth strategy to mediate the growth of platinum nanoparticles (PtNPs) on gold bipyramids (AuBPs) for the synthesis of a bimetallic nanozyme. We find that the preparation of a bimetallic nanozyme is in a sequence-dependent manner, and the encoding of a polyT sequence allows the successful formation of bimetallic nanohybrids with greatly enhanced peroxidase-like activity. We further observe that the morphologies and optical properties of T15-mediated Au/Pt nanostructures (Au/T15/Pt) change over the reaction time, and the nanozymatic activity can be tuned by controlling the experimental conditions. As a concept application, Au/T15/Pt nanozymes are used to establish a simple, sensitive, and selective colorimetric assay for the determination of ascorbic acid (AA), alkaline phosphatase (ALP), and the inhibitor sodium vanadate (Na₃VO₄), demonstrating excellent analytical performance. This work provides a new avenue for the rational design of bimetallic nanozymes for biosensing applications.

Single-Atom Fe Nanozyme with Enhanced Oxidase-like Activity for the Colorimetric Detection of Ascorbic Acid and Glutathione

Single-atom nanozymes (SAzymes) have drawn ever-increasing attention due to their maximum atom utilization efficiency and enhanced enzyme-like activity. Herein, a facile pyrolysis strategy is reported for the synthesis of the iron-nitrogen-carbon (Fe-N-C) SAzyme using ferrocene trapped within porous zeolitic imidazolate framework-8 (ZIF-8@Fc) as a precursor. The as-prepared Fe-N-C SAzyme exhibited exceptional oxidase-mimicking activity, catalytically oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) with high affinity (K_m) and fast reaction rate (V_max). Taking advantage of this property, we designed two colorimetric sensing assays based on different interaction modes between small molecules and Fe active sites. Firstly, utilizing the reduction activity of ascorbic acid (AA) toward oxidized TMB (TMBox), a colorimetric bioassay for AA detection was established, which exhibited a good linear range of detection from 0.1 to 2 μM and a detection limit as low as 0.1 μM. Additionally, based on the inhibition of nanozyme activity by the thiols of glutathione (GSH), a colorimetric biosensor for GSH detection was constructed, showing a linear response over a concentration range of 1-10 μM, with a detection limit of 1.3 μM. This work provides a promising strategy for rationally designing oxidase-like SAzymes and broadening their application in biosensing.

A copper foam-based surface-enhanced Raman scattering substrate for glucose detection

Raman spectroscopy can quickly achieve non-destructive, qualitative and quantitative detection, and analysis the molecular structure of substances. Herein, a facile and low-cost method for preparation of highly sensitivity SERS substrates was implemented through the displacement reaction of copper foam immersed in AgNO₃ ethanol solution. Due to the 3D structure of copper film and homogenous displacement, the Ag-Cu substrate showed high performance SERS enhancement (1.25 × 10⁷), and the lowest detection concentration for R6G reached 10^-10 Mol/L. For glucose detection, mixed decanethiol (DT)/mercaptohexanol (MH) interlayer was used to enable glucose attach to the substrate surface, and the limit of detection reached to 1 uM/L. SERS substrate makes the Ag-Cu SERS substrate promising for biological applications.

The adsorption of single Au atom and nucleation on γ-Al2O3 surfaces

Single-atom catalysts (SACs) in heterogeneous catalysts have attracted increasing attention and the adsorption and nucleation of single atom on the surface are closely related to the performance of the catalyst. The present work employed density functional theory calculations to examine the adsorption of single Au atom and nucleation on γ-Al₂O₃ surfaces at the atomic level. The effect of surface hydroxyls group on the adsorption and nucleation of single Au atom on γ-Al₂O₃ surfaces is explored. It was found that the spillover reactions of surface hydroxyls H atoms with the deposited Au_- are not available on the hydroxylated surface. The interaction of Au to the clean surface is the stronger than to the hydroxylated surface. The even-odd alternations of Au_x and weak binding of single Au atoms to γ-Al₂O₃ leads to large even-numbered Au cluster on the surface. Density of states and electron density difference analysis show that the electronic structure of Au/γ-Al₂O₃ is quite different from the reported Cu and Pd on Al₂O₃.

Sensitive bioanalytical methods for telomerase activity detection: a cancer biomarker

Telomerase is an enzyme that protects the length of telomeres by adding guanine-rich repetitive sequences. In tumors, gametes, and stem cells, telomerase activity is exerted. Telomerase activity can be a cancer biomarker for therapeutic and diagnosis approaches. So, a number of studies concentrating on the discovery of telomerase activity were reported. Bioanalytical devices, in comparison with other tests, have numerous advantages including low expense, simplicity, and excellent sensitivity and specificity. In this article we reviewed recent studies on the subject of various bioanalytical methods based on different nanomaterials. Optical, electrochemical, and quartz crystal microbalance (QCM) are prominent analytical techniques that are mentioned in this paper.

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.

Bimetallic FeMn@C derived from Prussian blue analogue as efficient nanozyme for glucose detection

In recent decades, nanomaterial-based artificial enzymes called nanozymes have received more and more attention and have been applied in biological, chemical, medical, and other fields. In this work, bimetallic FeMn@C was synthesized by calcination from the Prussian blue analogue. The synthesized bimetallic FeMn@C exhibits efficient peroxidase-like activity. The effect of Mn doping amount, catalytic kinetics, and mechanism of FeMn@C nanozyme was further studied in detail. The results show that the peroxidase-like activity of bimetallic FeMn@C is nearly 16 times higher than that of single-metal Fe@C. The peroxidase-like activity of FeMn@C originates from its production of radicals. Compared with natural enzymes, FeMn@C nanozyme has a better affinity for the substrates. Besides, FeMn@C nanozyme has better stability than natural enzymes. Because of its strong magnetism, FeMn@C nanozyme can be recycled easily and exhibits excellent recycling performance. Based on the good affinity of FeMn@C for H₂O₂, a rapid and selective colorimetric assay for glucose detection is constructed, with a wide linear range of 0.01-0.75 mM and low detection limit of 4.28 µM. This sensor has been successfully applied to the determination of glucose in fruit juice, showing good selectivity and accuracy. The synthesis of bimetallic FeMn@C provides a feasible way to design nanozymes with excellent catalytic activity, high stability, and easy separation.

Colorimetric assay based on NiCo2S4@N,S-rGO nanozyme for sensitive detection of H2O2 and glucose in serum and urine samples

Traditional bimetallic sulfide-based nanomaterials often have a small specific surface area (SSA), low dispersion, and poor conductivity, thereby limiting their wide applications in the nanozyme-catalytic field. To address the above issues, we herein integrated NiCo2S4 with N,S-rGO to fabricate a nanocomposite (NiCo2S4@N,S-rGO), which showed a stronger peroxidase-mimetic activity than its pristine components. The SSA (155.8 m2 g-1) of NiCo2S4@N,S-rGO increased by ∼2-fold compared to NiCo2S4 with a pore size of 7-9 nm, thus providing more active sites and charge transfer channels. Based on the Michaelis-Menten equation, the affinity of this nanocomposite increased 40% and 1.1∼10.6-fold compared with NiCo2S4 with N,S-rGO, respectively, highlighting the significant enhancement of the peroxidase-like activity. The enhanced activity of this nanocomposite is derived from the joint participation of ˙OH, ˙O2 -, and photogenerated holes (h+), and was dominated by h+. To sum up, N,S-codoping, rich S-vacancies, and multi-valence states for this nanocomposite facilitate electron transfer and accelerate reaction processes. The nanocomposite-based colorimetric sensor gave low detection limits for H2O2 (12 μM) and glucose (0.3 μM). In comparison with the results detected by a common glucose meter, this sensor provided the relative recoveries across the range of 97.4-101.8%, demonstrating its high accuracy. Moreover, it exhibited excellent selectivity for glucose assay with little interference from common co-existing macromolecules/ions, as well as high reusability (>6 times). Collectively, the newly developed colorimetric sensor yields a promising methodology for practical applications in H2O2 and glucose detection with advantages of highly visual resolution, simple operation, convenient use, and satisfactory sensitivity.

Modulating the Biomimetic and Fluorescence Quenching Activities of Metal-Organic Framework/Platinum Nanoparticle Composites and Their Applications in Molecular Biosensing

Nanoscale metal-organic frameworks (nMOFs) have gained considerable attention with significant potential applications. Although great efforts have been devoted to designing and fabricating nanoscaffold structures, approaches of deliberately regulating the intrinsic functionality of nMOFs have been poorly explored. Herein, we report a simple and novel strategy to regulate the catalytic and fluorescence quenching behaviors of nMOFs through coordination-driven self-assembly. As a proof-of-concept, we synthesized a synergistic and stable MOF-metal nanocomposite by loading platinum nanoparticles (PtNPs) on a commonly used Fe-MOF, i.e., MIL-88B-NH₂/Pt, as a MOF composite model for exploration. On one hand, the complexation with ATP effectively broke the pH limitation of the peroxidase-mimicking MIL-88B-NH₂/Pt nanozyme, bringing a 10-fold increased catalytic activity under alkaline condition. Based on the distinct catalytic enhancement between ATP and other nucleotides, real-time monitoring of apyrase activity as well as colorimetric detection of alkaline phosphatase (ALP) was performed. On the other hand, interactions of MIL-88B-NH₂/Pt with fluorescent DNA were tolerant of different nucleic acids and, more importantly, were further manipulated by inorganic molecules. As a result, H₂O₂ could only trigger the release of a G-rich sequence, while phosphates could readily induce desorption of various DNA molecules with varying lengths, sequences, and fluorescent dyes. Accordingly, fluorescent DNA and MIL-88B-NH₂/Pt as functional probe-quencher pairs were proposed, allowing the establishment of a fluorescence bioassay for ALP and PPase detection and Boolean logic calculations. This work offers a means to tune the intrinsic activities of nMOFs by surface engineering, benefiting design of functional nanomaterials and development of advanced biosensing systems.

Glucose detection through surface-enhanced Raman spectroscopy: A review

Glucose detection is of vital importance to diabetes diagnosis and treatment. Optical approaches in glucose sensing have received much attention in recent years due to the relatively low cost, portable, and mini-invasive or non-invasive potentials. Surface enhanced Raman spectroscopy (SERS) endows the benefits of extremely high sensitivity because of enhanced signals and specificity due to the fingerprint of molecules of interest. However, the direct detection of glucose through SERS was challenging because of poor adsorption of glucose on bare metals and low cross section of glucose. In order to address these challenges, several approaches were proposed and utilized for glucose detection through SERS. This review article mainly focuses on the development of surface enhanced Raman scattering based glucose sensors in recent 10 years. The sensing mechanisms, rational design and sensing properties to glucose are reviewed. Two strategies are summarized as intrinsic sensing and extrinsic sensing. Four general categories for glucose sensing through SERS are discussed including SERS active platform, partition layer functionalized surface, boronic acid based sensors, and enzymatic reaction based biosensors. Finally, the challenges and outlook for SERS based glucose sensors are also presented.

Colorimetric sensing strategy for detection of cysteine, phenol cysteine, and phenol based on synergistic doping of multiple heteroatoms into sponge-like Fe/NPC nanozymes

Nanozymes have both the high catalytic activity of natural enzymes and the stability and economy of mimetic enzymes. Research on nanozymes is rapidly emerging, and the continuous development of highly catalytic active nanozymes is of far-reaching significance. This work reports heteroatomic nitrogen (N) and phosphorus (P) double-doped mesoporous carbon structures and metallic Fe coordination generated sponge-like nanozymes (Fe/NPCs) with good peroxidase activity. On this basis, we constructed a highly sensitive colorimetric sensor with cysteine and phenol as simulated analytes using Fe/NPCs nanozymes, and the response limits reached 53.6 nM and 5.4 nM, respectively. Besides, the method has high accuracy in the detection of cysteine and phenol at low concentrations in serum and tap water, which lays a foundation for application in the fields of environmental protection and biosensors.

Metal-Nanoparticle-Supported Nanozyme-Based Colorimetric Sensor Array for Precise Identification of Proteins and Oral Bacteria

Convenient, precise, and high-throughput discrimination of multiple bioanalytes is of great significance for an early diagnosis of diseases. Array-based pattern recognition has proven to be a powerful tool to detect diverse analytes, but developing sensing elements featuring favorable surface diversity still remains a challenge. In this work, we presented a simple and facile method to prepare programmable metal-nanoparticle (NP)-supported nanozymes (MNNs) as artificial receptors for the accurate identification of multiple proteins and oral bacteria. The in situ reduction of metal NPs on hierarchical MoS₂ on polypyrrole (PPy), which generated differential nonspecific interactions with bioanalytes, was envisaged as the encoder to break through the limited supply of the receptor's quantity. As a proof of concept, three metal NPs, i.e., Au, Ag, and Pd NPs, were taken as examples to deposit on PPy@MoS₂ as colorimetric probes to construct a cross-reactive sensor array. Based on the principal component analysis (PCA), the proposed MNN sensor array could well discriminate 11 proteins with unique fingerprint-like patterns at a concentration of 250 nM and was sufficiently sensitive to determine individual proteins with a detection limit down to the nanomolar level. Remarkably, two highly similar hemoglobins from different species (hemoglobin and bovine hemoglobin) have been precisely identified. Additionally, five oral bacteria were also well separated from each other without cross-classification at the level of 10⁷ CFU mL^-1. Furthermore, the sensor array allowed effective discrimination of complex protein mixtures either at different molar ratios or with minor varying components. Most importantly, the blind samples, proteins in human serums, proteins in simulated body fluid environment, the heat-denatured proteins, and even clinical cancer samples all could be well distinguished by the sensor array, demonstrating the real-world applications in clinical diagnosis.

A Label-Free Colorimetric Assay Based on Gold Nanoparticles for the Detection of H2O2 and Glucose

The significance of sensing hydrogen peroxide (H2O2) is due to its ubiquity, being a potential biomarker as well as an end-product of several oxidation reactions. Herein, based on gold nanoparticles (AuNPs) and coupled with single-stranded DNA (ssDNA) and ceria nanoparticles (CeO2), we developed a novel colorimetric method to detect H2O2 and glucose in NaCl solutions. In the presence of H2O2, ssDNA adsorbed on the surface of CeO2 could be released and subsequently decorated AuNPs, resulting in a distinct color change of the aqueous solution from purple to red, which could be observed by the naked eye. Since H2O2 can be produced in the process of glucose oxidation by glucose oxidase (GOx), this approach can also be employed to detect glucose. By employing this sensing system, the detection limits for H2O2 and glucose are about 0.21 μM and 3.01 µM, respectively. Additionally, monitoring the content of glucose in blood serum samples was successfully achieved by the proposed strategy. This work opens a potential avenue for the quantitative detection of H2O2 and glucose in clinical diagnostics.

Synergistic function of Au NPs/GeO2 nanozymes with enhanced peroxidase-like activity and SERS effect to detect choline iodide

A novel Au NPs/GeO₂ nanozymes are developed as Surface-Enhanced Raman Scattering (SERS) substrates with the promising prospect for detection ChI. Herein, it is discovered that both Au NPs and GeO₂ nanozymes have peroxidase-like activity, catalyzing colorless 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue TMB_ox. Interestingly, compared with single Au NPs or GeO₂ nanozymes, the Au NPs/GeO₂ nanozymes show stronger peroxidase-like activity, and significantly ameliorated SERS signal of TMB_ox. The mentioned two enhancements are ascribed to a positive synergistic function of Au NPs/GeO₂ nanozymes. Surprisingly, choline iodide (ChI) can inhibit the positive synergy in Au NPs/GeO₂ nanozymes, and slow down the reaction of TMB-H₂O₂-Au NPs/GeO₂ system. On this foundation, a new Au NPs/GeO₂ SERS technique with high sensitivity, label-free detection method of choline iodide (ChI) is established, suggesting that Au NPs/GeO₂ nanozymes have the potential application of water environment.

Simultaneous detection of dual biomarkers using hierarchical MoS2 nanostructuring and nano-signal amplification-based electrochemical aptasensor toward accurate diagnosis of prostate cancer

Accurate and reliable quantification of tumor biomarkers in clinical samples is of vital importance for early stage diagnosis and treatment of cancer. However, a poor specificity of prostate specific antigen (PSA) testing alone fostering overdetection and overtreatment, remains a great controversy in prostate cancer (PCa) screening. Here we report an electrochemical aptasensor using hierarchical MoS₂ nanostructuring and SiO₂ nano-signal amplification for simultaneous detection of dual PCa biomarkers, PSA and sarcosine, to enhance the diagnostic performance of PCa. In this strategy, hierarchical flower-like MoS₂ nanostructures as functional interface accelerated intermolecular accessibility and improved DNA hybridization efficiency. Moreover, the spherical SiO₂ nanoprobe that conjugated with both electroactive tags and DNA probes, allowed effective electrochemical signal amplification. By deliberately designing different hybridization modes, we individually implemented the optimization of PSA and sarcosine sensing system. Based on this, simultaneous determination of PSA and sarcosine was achieved, with limit of detection (LOD) down to 2.5 fg/mL and 14.4 fg/mL, respectively, as well as excellent selectivity. More importantly, using this approach, we could directly differentiate cancer patients with healthy ones for clinical serum samples. The ultrasensitive biosensor provides single-step analysis with simple operation and a small sample volume (∼12 μL), shedding new light on accurate diagnosis and early-detection of cancer in clinical applications.

“Three-in-One” Nanocomposite as Multifunctional Nanozyme for Ultrasensitive Ratiometric Fluorescence Detection of Alkaline Phosphatase

Nanozymes, as a unique class of nanomaterials with enzyme-like properties, have attracted significant interests due to their potential applications in many significant fields. Great endeavours have been devoted to improving...

Recent development for biomedical applications of magnetic nanoparticles

In recent decades, the use of engineered nanoparticles has been increasing in various sectors, including biomedicine, diagnosis, water treatment, and environmental remediation leading to significant public concerns. Among these nanoparticles, magnetic nanoparticles (MNPs) have gained many attentions in medicine, pharmacology, drug delivery system, molecular imaging, and bio-sensing due to their various properties. In addition, various studies have reviewed MNPs main applications in the biomedical engineering area with intense progress and recent achievements. Nanoparticles, especially the magnetic nanoparticles, have recently been confirmed with excellent antiviral activity against different viruses, including SARS-CoV-2(Covid-19) and their recent development against Covid-19 also has also been discussed. This review aims to highlight the recent development of the magnetic nanoparticles and their biomedical applications such as diagnosis of diseases, molecular imaging, hyperthermia, bio-sensing, gene therapy, drug delivery and the diagnosis of Covid-19.

Peroxidase-mimetic activity of a nanozyme with uniformly dispersed Fe3O4 NPs supported by mesoporous graphitized carbon for determination of glucose

A Fe₃O₄/mesoporous graphitized carbon (Fe₃O₄/m-GC) composite was prepared through a facile calcination method with iron-based metal-organic frameworks (Fe-MOFs) as a sacrificial template. After carbonization, the Fe₃O₄ nanoparticles were uniformly dispersed in the mesoporous carbon support, resulting in spatial structural stability. The mesoporous carbon support obtained was highly graphitized and exhibited eminent electrical conductivity, which accelerated the electron transfer between the Fe₃O₄ nanoparticles by Fe(II)/Fe(III) redox cycles and m-GC by C = C_sp2/C-C_sp3 redox cycles, leading to the excellent peroxidase-mimetic activity of Fe₃O₄/m-GC. K_m values for tetramethylbenzidine (TMB) and H₂O₂ were 26.8 and 15.8 times lower than that of natural horseradish peroxidase, respectively. Taking advantage of the peroxidase-mimetic activity of Fe₃O₄/m-GC, a colorimetric assay was fabricated for detecting glucose in the range 0.5 ~ 200 μM, with a limit of detection of 0.24 μM. Fig 1 A Schematic illustration of the preparation process of Fe₃O₄/m-GC, B schematic illustration of a proposed synergistic catalytic mechanism of TMB oxidation by Fe₃O₄/m-GC.

Fe doped MoS2/polypyrrole microtubes towards efficient peroxidase mimicking and colorimetric sensing application

Molybdenum disulfide (MoS2) nanosheets have been found to exhibit intrinsic peroxidase-like activity that could be applied in colorimetric sensing platforms. However, their poor conductivity and few exposed edge sites often lead to poor catalytic activity, impeding the application of MoS2 nanosheets in enzyme-like catalysis. Here, a novel strategy was developed to selectively deposit Fe-doped MoS2 nanosheets on polypyrrole microtubes to obtain Fe-MoS2@PPy microtubes to address these issues. In the synthesized Fe-MoS2@PPy microtubes, PPy microtubes can not only be used as a conductive support to promote the electron transfer, but also greatly alleviate the aggregations of MoS2 nanosheets, and thus improve the enzyme-like activity. Meanwhile, additional active sites, formed by Fe doping, also endow the catalyst with excellent activity in enzyme-like catalysis. Notably, in the process of sulfidation, the dissolution, redistribution and diffusion result in the disappearance of MoO3@FeOOH cores and the formation of Fe doped MoS2 nanosheets, which significantly facilitate the deposition of Fe-doped MoS2 nanosheets on PPy microtubes. On the basis of the high peroxidase-like catalytic efficiency of the Fe-MoS2@PPy microtubes, a simple and convenient colorimetric strategy for the rapid and sensitive detection of L-cysteine has been developed. This strategy introduces both the PPy layer and Fe doping to increase the conductivity and the density of active sites of MoS2 nanosheets, thus enhancing the catalytic activity and stability. More importantly, Fe-MoS2@PPy microtubes could be used as a good support for loading other materials such as Au and Ag nanoparticles (NPs), forming ternary Fe-MoS2/Ag, Au@PPy nanotubes. This work offers an opportunity to develop low-cost and highly active MoS2-based nanocomposites for promising potential applications in electrochemical energy conversion and medical diagnostics.

Keratin-inorganic hybrid nanoflowers decorated with Fe3O4 nanoparticles as enzyme mimics for colorimetric detection of glucose

Fe3O4 magnetic nanoparticles (MNPs) are highly active enzyme-like catalysts. However, low stability is still a big challenge for Fe3O4-based enzyme mimics because the Fe3O4 MNPs can be easily dissolved when exposed to acidic conditions. Inspired by the numerous catalytic sites of a flower-like structure and the biological functions of amino acids in structural proteins, herein, by employing keratin as a protein component, stable Fe3O4-based MNP embedded keratin-Cu3(PO4)2 nanoflowers were constructed, from which hierarchical nanostructures with a three-dimensional petal-like morphology were selected for subsequent studies owing to their excellent enzymic catalytic activity. The keratin-nanoflower@Fe3O4 exhibited significantly enhanced catalytic activity compared with that of keratin-Cu3(PO4)2 nanoflowers and individual Fe3O4 MNPs. Remarkably, keratin-nanoflower@Fe3O4 exhibited superior long-term stability to Fe3O4 MNPs under more acidic conditions and favorable reusability. This method has been successfully exploited for the colorimetric determination of glucose in human serum with satisfactory sensitivity and specificity, offering a novel approach for glucose detection.

Sensitive Oxidation of Sorbitol-Mediated Fe2+ by H2O2: A Reliable TD-NMR Method for Clinical Blood Glucose Detection

The clinical challenge of high-accuracy blood glucose detection schemes is to overcome the detection error caused by the background interferences in different individuals. H₂O₂ as the specific product of glucose oxidation can be involved in the Fe²⁺/Fe³⁺ conversion and detected by the time-domain nuclear magnetic resonance (TD-NMR) method sensitively. But, in clinical applications, the oxidation of Fe²⁺ is susceptible to the complex sample substrates. In this work, we sorted out two kinds of possible interference mechanisms of Fe²⁺ oxidation in the NMR blood glucose detection method and proposed a feasible scheme that uses sorbitol to weaken the adverse effects of interference. We found that sorbitol-mediated Fe²⁺ can greatly enhance the sensitivity of the T₂ value to H₂O₂. The chain reaction caused by sorbitol can significantly amplify the efficiency of Fe²⁺ oxidation at the same concentration of H₂O₂. Thereby, we can achieve the higher dilution multiple of serum samples to reduce the amount of interfering substances involved in the Fe²⁺/Fe³⁺ conversion. We justified the accuracy and availability of our method by successfully detecting and confirming the correlation between the T₂ decrease and glucose concentration of the serum samples collected from 16 subjects. The sorbitol-Fe²⁺ glucose detection method with high sensitivity can be further combined with miniature NMR analyzers to satisfy the calibration requirements of glucose monitoring in diabetic patients instead of frequent medical visits.

A facile SERS strategy to detect glucose utilizing tandem enzyme activities of Au@Ag nanoparticles

Surface-Enhanced Raman Scattering (SERS) is a powerful analysis technology, attracting more and more attention due to its high sensitivity and selectivity. Herein, we report a simple seed-mediated method to synthesize Au@Ag nanoparticles (NPs) as a multifunctional biosensor for the label-free detection of hydrogen peroxide (H₂O₂) and glucose by SERS. Au@Ag NPs, as an ultrasensitive SERS substrate, show the dual activities (peroxidase-like and GOx-like activities). Under the condition of pH 4.0 NaAc buffer solution, the glucose and H₂O can be catalyzed by Au@Ag NPs to produce glucose acid and H₂O₂, and then H₂O₂ can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to form a blue oxidation product oxidic TMB (oxTMB) which exhibits strong SERS signals at 1188, 1330, 1605 cm^-1. Thus, we have developed a new SERS strategy for analysis of glucose with a detection limit of 5 × 10^-10molL^-1, suggesting that Au@Ag NPs have the potential for biosensor, immunoassay and medical treatment.

Renal Clearable Ultrasmall Single-Crystal Fe Nanoparticles for Highly Selective and Effective Ferroptosis Therapy and Immunotherapy

Iron-based nanoparticles have attracted much attention because of their ability to induce ferroptosis via a catalyzing Fenton reaction and to further potentiate immunotherapy. However, current iron-based nanoparticles need to be used in cooperation with other treatments or be applied in a high dose for effective therapy because of their low reactive oxygen species production efficacy. Here, we synthesized ultrasmall single-crystal Fe nanoparticles (bcc-USINPs) that stayed stable in a normal physiological environment but were highly active in a tumor microenvironment because of the selective acidic etching of an Fe₃O₄ shell and the exposure of the Fe(0) core. The bcc-USINPs could efficiently induce tumor cell ferroptosis and immunogenetic cell death at a very low concentration. Intravenous injection of iRGD-bcc-USINPs at three doses of 1 mg/kg could effectively suppress the tumor growth, promote the maturation of dendritic cells, and trigger the adaptive T cell response. Combined with programmed death-ligand 1 (PD-L1) immune checkpoint blockade immunotherapy, the iRGD-bcc-USINP-mediated ferroptosis therapy greatly potentiated the immune response and developed strong immune memory. In addition, these USINPs were quickly renal excreted with no side effects in normal tissues. These iRGD-bcc-USINPs provide a simple, safe, effective, and selectively tumor-responsive Fe(0) delivery system for ferroptosis-based immunotherapy.

Nanozymes in Point-of-Care Diagnosis: An Emerging Futuristic Approach for Biosensing

Nanomaterial-based artificial enzymes (or nanozymes) have attracted great attention in the past few years owing to their capability not only to mimic functionality but also to overcome the inherent drawbacks of the natural enzymes. Numerous advantages of nanozymes such as diverse enzyme-mimicking activities, low cost, high stability, robustness, unique surface chemistry, and ease of surface tunability and biocompatibility have allowed their integration in a wide range of biosensing applications. Several metal, metal oxide, metal-organic framework-based nanozymes have been exploited for the development of biosensing systems, which present the potential for point-of-care analysis. To highlight recent progress in the field, in this review, more than 260 research articles are discussed systematically with suitable recent examples, elucidating the role of nanozymes to reinforce, miniaturize, and improve the performance of point-of-care diagnostics addressing the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to the end user) criteria formulated by World Health Organization. The review reveals that many biosensing strategies such as electrochemical, colorimetric, fluorescent, and immunological sensors required to achieve the ASSURED standards can be implemented by using enzyme-mimicking activities of nanomaterials as signal producing components. However, basic system functionality is still lacking. Since the enzyme-mimicking properties of the nanomaterials are dictated by their size, shape, composition, surface charge, surface chemistry as well as external parameters such as pH or temperature, these factors play a crucial role in the design and function of nanozyme-based point-of-care diagnostics. Therefore, it requires a deliberate exertion to integrate various parameters for truly ASSURED solutions to be realized. This review also discusses possible limitations and research gaps to provide readers a brief scenario of the emerging role of nanozymes in state-of-the-art POC diagnosis system development for futuristic biosensing applications.

Magnetic Molecularly Imprinted Polymers: Synthesis and Applications in the Selective Extraction of Antibiotics

Recently, magnetic molecularly imprinted polymers (MMIPs) have integrated molecular imprinting technology (MIT) and magnetic separation technology and become a novel material with specific recognition and effective separation of target molecules. Based on their special function, they can be widely used to detect contaminants such as antibiotics. The antibiotic residues in the environment not only cause harm to the balance of the ecosystem but also induce bacterial resistance to specific antibiotics. Given the above consideration, it is especially important to develop sensitive and selective methods for measuring antibiotics in the complex matrix. The combination of MMIPs and conventional analytical methods provides a rapid approach to separate and determine antibiotics residues. This article gives a systematic overview of synthetic approaches of the novel MMIPs materials, briefly introduces their use in sample pretreatment prior to antibiotic detection, and provides a perspective for future research.

Nanozyme for tumor therapy: Surface modification matters

As the next generation of artificial enzymes, nanozymes have shown unique properties compared to its natural counterparts, such as stability in harsh environment, low cost, and ease of production and modification, paving the way for its biomedical applications. Among them, tumor catalytic therapy mediated by the generation of reactive oxygen species (ROS) has made great progress mainly from the peroxidase-like activity of nanozymes. Fe3O4 nanozymes, the earliest type of nanomaterial discovered to possess peroxidase-like activity, has consequently received wide attention for tumor therapy due to its ROS generation ability and tumor cell killing ability. However, inconsistent results of cytotoxicity were observed between different reports, and some even showed the scavenging of ROS in some cases. By collectively studying these inconsistent outcomes, we raise the question whether surface modification of Fe3O4 nanozymes, either through affecting peroxidase activity or by affecting the biodistribution and intracellular fate, play an important role in its therapeutic effects. This review will go over the fundamental catalytic mechanisms of Fe3O4 nanozymes and recent advances in tumor catalytic therapy, and discuss the importance of surface modification. Employing Fe3O4 nanozymes as an example, we hope to provide an outlook on the improvement of nanozyme-based antitumor activity.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

A novel MnO-CrN nanocomposite based non-enzymatic hydrogen peroxide sensor

A MnO–CrN composite was obtained via the ammonolysis of the low-cost nitride precursors Cr(NO₃)₃·9H₂O and Mn(NO₃)₂·4H₂O at 800 °C for 8 h using a sol–gel method. The specific surface area of the synthesized powder was measured via BET analysis and it was found to be 262 m² g⁻¹. Regarding its application, the electrochemical sensing performance toward hydrogen peroxide (H₂O₂) was studied via applying cyclic voltammetry (CV) and amperometry (i–t) analysis. The linear response range was 0.33–15 000 μM with a correlation coefficient (R²) value of 0.995. Excellent performance toward H₂O₂ was observed with a limit of detection of 0.059 μM, a limit of quantification of 0.199 μM, and sensitivity of 2156.25 μA mM⁻¹ cm⁻². A short response time of within 2 s was achieved. Hence, we develop and offer an efficient approach for synthesizing a new cost-efficient material for H₂O₂ sensing.

A MnO–CrN composite was obtained via the ammonolysis of the low-cost nitride precursors Cr(NO₃)₃·9H₂O and Mn(NO₃)₂·4H₂O at 800 °C for 8 h using a sol–gel method.

Construction of Bio-Nano Interfaces on Nanozymes for Bioanalysis

Nanomaterials with enzyme-like activity (nanozymes) have been of great interest in broad applications ranging from biosensing to biomedical applications. Despite that much effort has been devoted to the development of the synthesis and applications of nanozymes, it is essential to understand the interactions between nanozymes and most commonly used biomolecules, i.e., avidin, streptavidin (SA), bovine serum albumin (BSA), immunoglobulin G (IgG), and glutathione (GSH), yet they have been rarely explored. Here, a series of bio-nano interfaces were constructed through direct immobilization of proteins on a variety of iron oxide and carbon-based nanozymes with different dimensions, including Fe₃O₄ nanoparticles (NPs, 0D), Fe₃O₄@C NPs (0D), Fe₃O₄@C nanowires (NWs, 1D), and graphene oxide nanosheets (GO NSs, 2D). Such interfaces enabled the modulation of the catalytic activities of the nanozymes with varying degrees, which allowed a good identification of multiplex proteins with high accuracy. Given the maximum inhibition on Fe₃O₄@C NP by BSA, we established molecular switches based on aptamer and toehold DNA, as well as Boolean logic gates (AND and NOR) in response to both DNA and proteins. Also importantly, we developed an on-particle reaction strategy for colorimetric detection of GSH with ultrahigh sensitivity and good specificity. The proposed sensor achieved a broad dynamic range spanning 7 orders of magnitude with a detection limit down to 200 pg mL^-1, which was better than that of an in-solution reaction-based biosensor by 2 orders of magnitude. Furthermore, we explored the mechanisms of the interactions at bio-nano interfaces by studying the interfacial factors, including surface coverage, salt concentration, and the curvature of the nanozyme. This study offered new opportunities in the elaborate design and better utilization of nanozymes for bioanalysis in clinical diagnosis and in vivo detection.

Microwave assisted polyol process for time-saving synthesis of superparamagnetic nanoparticles and application in artificial mimic enzyme

A microwave assisted polyol process accomplished within 10 min was developed for synthesis of superparamagnetic Fe3O4 nanoparticles (MNPs) with well controlled size between 2 and 6 nm. Effects of reaction time and temperature on the size of the MNPs were investigated through transmission electronic microscope, x-ray diffraction pattern, thermogravimetic and magnetic analysis. The results indicates that longer reaction time or higher temperature lead to formation of MNPs with larger size. As a proof-of-concept, the MNPs were utilized as peroxidase and their activity was also investigated. Oxidation of typical substrate, 3, 3’, 5, 5’ -tetramethylbenzidine, can be proceeded by using the MNPs as artificial mimic enzyme. The MNPs display the maximal catalyzed activity under the optimum condition as pH = 3.5, 40 °C and concentration of TMB and H2O2 with 120 and 110 mmol·l−1, respectively. This work provides a new way for fast synthesis of MNPs, which are of potential application in artificial mimic enzyme.

Exploration of intrinsic peroxidase-like activity of Acidithiobacillus ferrooxidans spent medium and its application for glutathione detection

Acidithiobacillus ferrooxidans (At. ferrooxidans) is a bacterium that has the ability to metabolize iron. It converts Fe²⁺ into Fe³⁺ during its metabolic cycle. Hence, the At. ferrooxidans spent medium is rich in Fe³⁺. The presence of Fe³⁺ contributes to a peroxidase-like activity. Therefore, in this study, an attempt has been made to explore the peroxidase-like activity of the At. ferrooxidans spent medium. It has been observed that the At. ferrooxidans spent medium oxidized 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂). The effect of various process parameters on the peroxidase-like activity has been studied. Optimum peroxidase-like activity is achieved using 5 µl of the spent medium, 0.3 mM TMB concentration, 4 mM H₂O₂ concentration, 4.2 pH, and 40 °C temperature. The peroxidase-like activity of the At. ferrooxidans spent medium has been used to develop a colorimetric assay for detection of glutathione (GSH). GSH inhibits the peroxidase-like activity of the At. ferrooxidans spent medium in a concentration range of 0-1 mM. The limit of detection (LOD) of GSH, obtained using the calibration plot is 0.69 mM. The developed assay is selective toward GSH, as the presence of amino acids, metals, and sugars have shown a negligible effect on the GSH sensing ability.