Boosting the peroxidase-like activity of gold nanoclusters for the colorimetric detection of oxytetracycline in rat serum

Colorimetric detection of neomycin sulfate in serum based on ultra-small gold nanoparticles with peroxidase-like activity

Neomycin sulfate (NEO) is a kind of aminoglycoside antibiotics. Because of its strong ototoxicity, nephrotoxicity and other side effects, its content in the body should be strictly monitored during use. In this paper, a rapid colorimetric detection method for NEO based on ultrasmall polyvinylpyrrolidone modified gold nanoparticles (PVP/Au NPs) with peroxidase-like activity was developed. Firstly, ultra small PVP/Au NPs with weak peroxidase-like activity were synthetized. When they were mixed with NEO, strong hydrogen bonds were formed between NEO and PVP, resulting in the aggregation of PVP/Au NPs, and the aggregated PVP/Au NPs showed stronger peroxidase-like activity. Therefore, rapid colorimetric detection of NEO was achieved by utilizing the enhanced peroxidase-like activity mechanism caused by the aggregation of ultra small PVP/Au NPs. The naked eye detection limit of this method is 50 nM. Within the range of 1 nM-300 nM, there was a good linear relationship between NEO concentration and the change in absorbance intensity of PVP/Au NPs-H2O2-TMB solution at 652 nm, with the regression curve of y = 0.0045x + 0.0525 (R2 = 0.998), and the detection limit is 1 nM. In addition, this method was successfully applied to the detection of NEO in mouse serum. The recoveries were 104.4 % -107.6 % compared with HPLC assay results, indicating that this method for NEO detection based on PVP/Au NPs has great potential in actual detection of NEO in serum.

Photoactive nanocatalysts as DTT-assisted BSA-AuNCs with enhanced oxidase-mimicking ability for sensitive fluorometric detection of antioxidants

Redox imbalance and oxidative stress are increasingly recognized as significant factors in health disorders such as neurodegenerative disorders, premature aging and cancer. However, detecting antioxidant levels that is crucial for managing oxidative stress, can be challenging due to existing assays' limitations, such as insensitivity to thiol-containing antioxidants. This study presents a simple fluorescence-based assay for antioxidant detection employing the enhanced photocatalytic oxidase-like activity of dithiothreitol (DTT)-assisted bovine serum albumin (BSA)-stabilized gold nanoclusters (DTT@BSA-AuNCs). The reported nanozyme exhibits remarkable stability, versatility, and catalytic activity. Under LED irradiation, DTT@BSA-AuNCs generate singlet oxygen, which converts non-fluorescent thiamine to fluorescent thiochrome, utilizing dissolved oxygen for catalysis. Antioxidants inhibit thiochrome formation, leading to fluorescence quenching. This method enables sensitive detection of antioxidants such as ascorbic acid and glutathione with limits of detection of 0.08 µM and 0.32 µM, respectively, under neutral pH, outperforming previous studies. The assay successfully detects antioxidants in human saliva and cancer cell models. The DTT@BSA-AuNCs-based assay offers a cost-effective, sensitive, and straightforward approach for detecting antioxidants in biological samples, facilitating improved monitoring of oxidative stress in various diseases.

A Lanthanide-Incorporated Phospho(III)tungstate Aggregate Constructed from [HPIIIW8O31]10- and [W11O39]12- Building Blocks and Its Nanocomposite with CdS for Ultrasensitive Photoelectrochemical Detection of Oxytetracycline

A novel tartronic acid decorated hexa-CeIII-incorporated phospho(III)tungstate aggregate (C4H12NO)6Na18H2[(HPW8O31)2[W11O39]2(H2TAD)4(H2O)4W4Ce6H2P2O14]·84H2O (1, H3TAD = tartronic acid) was synthesized by a one-step assembly strategy. Its main skeleton is constructed from two [W11O39]12- fragments, two [HPIIIW8O31]10- segments and one H2TAD--ornamented dodecanuclear heterometallic [W4Ce6H2PIII2O14(H2TAD)4(H2O)4]18+ cluster. In the structure, the [HPIIIO3]2- groups not only work as the heteroatom template to induce the formation of lacunary [HPIIIW8O31]10- segments but also function as the connector to bridge Ce3+ cations. With the help of a reaction strategy of combining ultrasonication treatment with the continuous ion layer adsorption method, the 1/CdS composite was constructed and exhibits prominent photoelectrochemical activity. The 1/CdS composite was used as a photoelectrochemical sensor for oxytetracycline detection at 0 V (vs Ag/AgCl), which displays excellent properties with quick response and low limit of detection (0.042 nM). This work can provide some helpful references in the construction of novel PIII-induced polyoxometalates consisting of different building blocks and can extend the applications of polyoxometalate-based nanocomposites into photoelectrochemical detection for antibiotics as well as biomolecules.

Construction of colorimetric sensor arrays using steel slag-based composites for highly sensitive detection of tetracycline antibiotics

Sensor array methods have received much attention in recent years. In this study, a colorimetric sensor array consisting of three kinds of steel slag-based composites (including porphyrin-functionalized non-magnetic steel slag (NMSS-Por), alkali-excited steel slag (A-SS), and platinum modified steel slag (ALANH-Pt)) was developed for the detection and recognition of tetracycline antibiotics (TCs) such as tetracycline (TC), oxytetracycline (OTC) and doxycycline (DOX). Linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA) showed that the colorimetric sensor array has excellent recognition ability for TCs. The detection limits of this sensor array for TC, OTC, and DOX were 0.059 μM, 0.111 μM and 0.118 μM, respectively, which provided higher sensitivity compared to the colorimetric sensors composed of a single steel slag-based composite material. At the same time, the array sensor has anti-interference ability, and this study provides a new application route for steel slag.

From synthesis to applications of biomolecule-protected luminescent gold nanoclusters

Gold nanoclusters (AuNCs) are a class of novel luminescent nanomaterials that exhibit unique properties of ultra-small size, featuring strong anti-photo-bleaching ability, substantial Stokes shift, good biocompatibility, and low toxicity. Various biomolecules have been developed as templates or ligands to protect AuNCs with enhanced stability and luminescent properties for biomedical applications. In this review, the synthesis of AuNCs based on biomolecules including amino acids, peptides, proteins and DNA are summarized. Owing to the advantages of biomolecule-protected AuNCs, they have been employed extensively for diverse applications. The biological applications, particularly in bioimaging, biosensing, disease therapy and biocatalysis have been described in detail herein. Finally, current challenges and future potential prospects of bio-templated AuNCs in biological research are briefly discussed.

The roles of templates consisting of amino acids in the synthesis and application of gold nanoclusters

Gold nanoclusters (AuNCs) with low toxicity, high photostability, and facile synthesis have attracted great attention. The ligand is of great significance in stabilizing AuNCs and regulating their properties. Ligands consisting of amino acids (proteins and peptides) are an ideal template for synthesizing applicative AuNCs due to their inherent bioactivity, biocompatibility, and accessibility. In this review, we summarize the correlation of the template consisting of amino acids with the properties of AuNCs by analyzing different peptide sequences. The selection of amino acids can regulate the fluorescence excitation/emission and intensity, size, cell uptake, and light absorption. By analyzing the role played by AuNCs stabilized by proteins and peptides in the application, universal rules and detailed performances of sensors, antibacterial agents, therapeutic reagents, and light absorbers are reviewed. This review can guide the template design and application of AuNCs when selecting proteins and peptides as ligands.

Colorimetric and electrochemical dual-mode uric acid determination utilizing peroxidase-mimicking activity of CoCu bimetallic nanoclusters

We present the preparation of CoCu bimetallic nanoclusters (Co@Cu-BNCs) by a hydrothermal and one-step pyrolysis method to build a colorimetric and electrochemical dual-mode sensing platform for uric acid (UA) detection. In the presence of H2O2, Co@Cu-BNCs with peroxidase-mimicking activity may convert colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue-colored oxidized TMB (oxTMB). However, due to the inhibitory effect of uric acid (UA) on the oxidation process of TMB, the characteristic absorption peak intensity of oxTMB decreased when UA was added into a mixed solution. In this approach, a colorimetric assay platform for the detection of UA was demonstrated, with a linear range of 0.1-195 μM and a low limit of detection of 0.06 μM (S/N ratio of 3). In addition, an even wider detection range is achieved in the electrochemical method, due to the pronounced electrocatalytic activity of Co@Cu-BNCs. The surface of the glassy carbon electrode was modified with Co@Cu-BNCs to build an electrochemical sensor for detecting UA. The sensor achieves a wider linear range from 2 to 1000 μM and a limit of detection of 0.61 μM (S/N ratio of 3). Moreover, the detection of UA in a human serum sample showed satisfactory results. The results proved that the colorimetric and electrochemical dual-mode detection platform was sensitive, convenient and accurate.

Multiscale Bioresponses of Metal Nanoclusters

Metal nanoclusters (NCs) are well-recognized novel nano-agents that hold great promise for applications in nanomedicine because of their ultrafine size, low toxicity, and high renal clearance. As foreign substances, however, an in-depth understanding of the bioresponses to metal NCs is necessary but is still far from being realized. Herein, this review is deployed to summarize the biofates of metal NCs at various biological levels, emphasizing their multiscale bioresponses at the molecular, cellular, and organismal levels. In the parts-to-whole schema, the interactions between biomolecules and metal NCs are discussed, presenting typical protein-dictated nano-bio interfaces, hierarchical structures, and in vivo trajectories. Then, the accumulation, internalization, and metabolic evolution of metal NCs in the cellular environment and as-imparted theranostic functionalization are demonstrated. The organismal metabolism and transportation processes of the metal NCs are subsequently distilled. Finally, this review ends with the conclusions and perspectives on the outstanding issues of metal NC-mediated bioresponses in the near future. This review is expected to provide inspiration for tailoring the customization of metal NC-based nano-agents to meet practical requirements in different sectors of nanomedicine.

In situ green synthesis of the nanocomposites of MnO2/graphene as an oxidase mimic for sensitive colorimetric and electrochemical dual-mode biosensing

Herein we report the colorimetry and an electrochemical for the determination of dopamine (DA) by using MnO2 nanoparticles and graphene nanosheets composite (MnO2@G) that display oxidase mimicking property. MnO2@G could directly oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue product (oxTMB) without extra oxidants such as H2O2. Nevertheless, the presence of DA will inhibit the TMB oxidation due to the presence of the competitive reaction of MnO2@G and DA, giving a product color change from blue to colorless. A colorimetric assay for detect the concentration of DA was worked out according to this finding. Response is linear in the 0.1 to 15 μM DA concentration range, and the detection limit is 0.14 μM. Wider detection range is achieved in an electrochemical method which is due to the pronounced electrocatalytic activity of MnO2@G. The MnO2@G was modified on the surface of the glassy carbon electrode in order to fabricate one type electrochemical sensor. The sensor achieves a wide detection two linear ranges from 0.4 to 70 μM, with the detection limit of 1.16 μM. The detection of DA in real serum sample proved that the nanozyme based on MnO2@G could be developed into a colorimetry and electrochemical dual-readout sensing platform.

Fabrication of 2D/1D Bi2WO6/halloysite nanotubes photocatalyst towards water purification: a support effect onin situconstruction and electron-hole separation

In this research work, a reusable and efficient 2D/1D heterogeneous structured photocatalyst based on amine-functionalized halloysite nanotubes (MHNTs) and Bi2WO6nanosheet (BWO) was prepared using a facile hydrothermal method for decomposing PPCPs under simulated sunlight. On the degradation of tetracycline hydrochloride (TCH), the effects of composite catalysts prepared under various conditions were discussed. The results showed that over BWO/MHNTs with a mass ratio was 3:1, the synthesizing temperature was 120 °C and the precursor pH value was 1, the TCH (10 mg l-1) degradation efficiency reached 100% after 1 h irradiation of simulated sunlight. Moreover, BWO/MHNTs composites kept good recovery and stable photocatalytic activity after 5 cycles. The excellent dispersion of Bi2WO6on the surface of clay minerals and the oxygen vacancy enhanced electron-hole separation may be responsible for the its high activity and stability. Futhermore, the radical capture test demonstrated that ·O-2was primarily responsible for the photodegradation of TCH. Thus, BWO/MHNTs composites exhibit a good application prospect in the field of sunlight-driven photocatalytic degradation towards PPCPs pollutants in water.

A turn-off fluorimetric -aptasensor for early detection of apoptosis inside the cells

To detect cytochrome c (Cyt c) as an important biomarker of apoptosis inside the cells, a simple, label-free, fluorometric detection method has been presented. For this purpose, an aptamer/gold nanocluster probe (Aptamer@AuNCs) was produced which could specifically bind to Cyt c leading to fluorescence quenching of AuNCs. The developed aptasensor showed two linear ranges of 1-80 μM and 100-1000 μM and a detection limit of 0.77 μM and 297.5 μM, respectively. This platform was successfully used to assay Cyt c release inside the apoptotic cells and their cell lysate. Aptamer@AuNC due to its enzyme-like properties could replace antibodies in Cyt c detection by conventional blotting techniques.

Structural Analysis and Intrinsic Enzyme Mimicking Activities of Ligand-Free PtAg Nanoalloys

Nanozymes are nanomaterials with biocatalytic properties under physiological conditions and are one class of artificial enzymes to overcome the high cost and low stability of natural enzymes. However, surface ligands on nanomaterials will decrease the catalytic activity of the nanozymes by blocking the active sites. To address this limitation, ligand-free PtAg nanoclusters (NCs) are synthesized and applied as nanozymes for various enzyme-mimicking reactions. By taking advantage of the mutual interaction of zeolitic imidazolate frameworks (ZIF-8) and Pt precursors, a good dispersion of PtAg bimetal NCs with a diameter of 1.78 ± 0.1 nm is achieved with ZIF-8 as a template. The incorporation of PtAgNCs in the voids of ZIF-8 is confirmed with structural analysis using the atomic pair-distribution function and powder X-ray diffraction. Importantly, the PtAgNCs present good catalytic activity for various enzyme-mimicking reactions, including peroxidase-/catalase- and oxidase-like reactions. Further, this work compares the catalytic activity between PtAg NCs and PtAg nanoparticles with different compositions and finds that these two nanozymes present a converse dependency of Ag-loading on their activity. This study contributes to the field of nanozymes and presents a potential option to prepare ligand-free bimetal biocatalysts with sizes in the nanocluster regime.

Fluorescence Imaging-Incorporated Transcriptome Study of Glutathione Depletion-Enhanced Ferroptosis Therapy via Targeting Gold Nanoclusters

Ferroptosis plays an important role in tumor inhibition and is a new type of programmed cell death. Recent studies have shown that glutathione (GSH) depletion is an effective method to enhance the therapeutic efficacy of ferroptosis; however, a systematic investigation of the phenomenon is limited. Herein, we provide a facile fluorescence imaging-incorporated transcriptome strategy to visualize the process and explore the mechanism of GSH depletion-enhanced ferroptosis. The proposed multifunctional nanoplatform is achieved using simple transferrin receptor aptamer-functionalized fluorescent gold nanoclusters (termed TfRA-AuNCs), which exhibit efficient hydroxyl radical generation and GSH-depleting capabilities. Live cell fluorescence imaging results revealed that TfRA-AuNCs were endocytosed into 4T1 cells and were mostly distributed in lysosomes. In vitro results indicated that TfRA-AuNCs enhanced the ferroptosis effect in 4T1 cells. Importantly, transcriptome analysis indicated that 4T1 cells treated with TfRA-AuNCs regulated the expression change of ferroptosis-related genes, and the Kyoto Encyclopedia of Genes and Genomes pathway identified the GSH metabolism pathway involved in ferroptosis, thus revealing the exact molecular mechanism of ferroptosis induced by TfRA-AuNCs at the RNA level. Furthermore, in vivo results confirmed the tumor inhibition effect, tumor-targeted fluorescence imaging, and long-term biocompatibility after TfRA-AuNC treatment. This study introduces a new possibility for the mechanistic study of nanoagent-induced ferroptosis in tumor treatment.

Nanozymes with Multiple Activities: Prospects in Analytical Sensing

Given the superiorities in catalytic stability, production cost and performance tunability over natural bio-enzymes, artificial nanomaterials featuring enzyme-like characteristics (nanozymes) have drawn extensive attention from the academic community in the past decade. With these merits, they are intensively tested for sensing, biomedicine and environmental engineering. Especially in the analytical sensing field, enzyme mimics have found wide use for biochemical detection, environmental monitoring and food analysis. More fascinatingly, rational design enables one fabrication of enzyme-like materials with versatile activities, which show great promise for further advancement of the nanozyme-involved biochemical sensing field. To understand the progress in such an exciting field, here we offer a review of nanozymes with multiple catalytic activities and their analytical application prospects. The main types of enzyme-mimetic activities are first introduced, followed by a summary of current strategies that can be employed to design multi-activity nanozymes. In particular, typical materials with at least two enzyme-like activities are reviewed. Finally, opportunities for multi-activity nanozymes applied in the sensing field are discussed, and potential challenges are also presented, to better guide the development of analytical methods and sensors using nanozymes with different catalytic features.

An entropy-driven signal-off DNA circuit for label-free, visual detection of small molecules with enhanced accuracy

An entropy-driven DNA circuit offers an efficient means of sensitive analyte detection with signal amplification. In this article, we rationally engineered an aptamer-based entropy-driven signal-off DNA circuit for colorimetric detection of small molecules. The proposed signal-off DNA circuit is activated by target small molecule binding to drive the collapse of G-quadruplex DNAzyme, accompanied by the colour change of the detection solution from dark blue to light blue. Entropy-driven recycling hybridization significantly magnified the input signal of the target small molecule. Such an assay enables naked-eye detection of adenosine triphosphate and oxytetracycline at concentrations as low as 0.5 μM and 1 μM respectively. Moreover, when compared with the signal-on DNA circuit, the entropy-driven signal-off DNA circuit for colorimetric detection has two advantages. Firstly, unlike in the signal-on DNA circuit, the unavoidable formation of waste complexes in the absence of a target in the signal-off DNA circuit has no influence on target detection performance as its background signal is only determined by the substrate complex. Secondly, the signal-on DNA circuit cannot distinguish false-positive signals generated by invasive catalysts (e.g., HRP, serum, Fe₃O₄), while the signal-off DNA circuit can distinguish those signals as undesired signals. Overall, the signal-off DNA circuit affords a novel strategy for sensitive and accurate detection of small molecules.

Fluorescent PEI@Pd nanoclusters: facile synthesis and application

Metal nanoclusters (NCs) have recently emerged as a novel class of luminescent nanomaterials and held significant potential in analytical chemistry. In this work, novel polyethyleneimine stabilized palladium nanoclusters (PEI-Pd NCs) were synthesized by chemical reduction at 60 °C for 6 h, and used as a fluorescent nanosensor for the detection of oxytetracycline (OTC). The spectral characteristics, surface structure and morphology of the Pd NCs were studied. The selectivity and stability of the nanosensor were also investigated. The experimental results showed that the Pd NCs had good biocompatibility, stability and photobleaching resistance in aqueous solution. The fluorescence quenching effect showed a good linear relationship with the degree of fluorescence quenching of Pd NCs and OTC in the range of 25-440 nM, with a correlation coefficient of 0.99. The limit of detection (LOD) of the proposed nanosensor for OTC was calculated to be 22 nM. The mechanism of determination was thought to be an inner filter effect (IFE) between OTC and Pd NCs. Based on this, we have established a new nanosensing analysis method for detecting OTC.