Multifunctional light-controllable nanozyme enabled bimodal fluorometric/colorimetric sensing of mercury ions at ambient pH

Detection of arsenate in colored grains using an interference-free dual-signal ratiometric HEC sensor

The design of novel homogeneous electrochemical (HEC) sensors with dual-signal ratiometric response holds great potential for highly sensitive and reliable detection of arsenic in food matrices. Herein, COF-based hybrids were prepared by integrating methylene blue (MB) signals and MnO2 nanozyme coatings, possessing the advantages of high signal loading, oxidase-mimicking activity, and ascorbic acid (AA)-specific recognition to realize ratiometric HEC detection of arsenate. The hydrolysate AA, produced from ALP-catalyzed AAP hydrolysis, could decompose MnO2 coatings into Mn2+, and regulate MB release and o-phenylenediamine oxidation to 2,3-diaminophenazine (DAP). Furthermore, arsenate specifically inhibited ALP, subsequently restraining AA formation and MnO2 decomposition. Consequently, a decreased MB current and an increased DAP current with opposite responses were regulated by arsenate compared with those without arsenate. Thus, this dual-signal ratiometric HEC sensor achieved sensitive detection of arsenate, with a LOD of 0.509 ppb. It was successfully applied to reliable detection of arsenate in complex food matrices.

Lysine enhances the photoresponsive oxidase-like activity of twin Cd0.7Zn0.3S for direct colorimetric detection of lysine

BACKGROUND

Lysine (Lys) is one of the eight essential amino acids for the human body, which can't be synthesized by the body and must be obtained from external sources. And the detection of Lys is of significance for disease monitoring. The construction of photoresponsive nanozymes based analytical methods have received increasing attention and have been successfully achieved for the detection of metal ions, small molecules and natural enzymes. However, the exploration of photoresponsive nanozyme in amino acids detection has not been tapped.

RESULTS

This study presents an innovative method based on surface passivation by Lys to stimulate the photoresponsive nanozyme activity of twin Cd0.7Zn0.3S nanomaterials. Specifically, Lys can bind with twin Cd0.7Zn0.3S, which filled the dangling bonds on the surface of Cd0.7Zn0.3S and caused passivation of the surface state, resulting in the promotion of the separation efficiency of electrons and holes, along with the facilitation of the production of active intermediates. Therefore, the Cd0.7Zn0.3S in the presence of Lys showed a high catalytic oxidation ability for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to oxidized TMB (oxTMB). This new kind of photoresponsive oxidase-like activity could be regulated by switching visible light sources and showed the specificity of being only affected by Lys without influenced by other amino acids, thus achieved direct colorimetric detection of Lys. The linear range for Lys detection was 1-100 μM, with a detection limit of 0.18 μM (S/N = 3).

SIGNIFICANCE

This study developed a new nanozyme of twin Cd0.7Zn0.3S, whose activity leverages on Lys as a stimulator. Moreover, the Lys detection method proposed by us had the characteristics of high sensitivity, good selectivity, fast detection speed, and low cost. Therefore, it holds significant potential application value, making it a promising candidate in the field of Lys detection and related research areas.

Dual-mode sensing platform for the detection of multiple metal ions based on amine-functionalized MIL-101 (Fe) Y-shaped DNAzyme-assisted fluorescence and colorimetric analysis

Our environment is being polluted by numerous sources of heavy metals, which are discharged by various industries, and hence, monitoring of heavy metals in environment and other fields is very essential. Herein, an amine-functionalized metal organic framework (NH2-MIL-101(Fe)) was prepared via a hydrothermal method. DNA sequences with enzyme and substrate strands were annealed to form a Y-shaped DNAzyme and used as the recognition element. Subsequently, we developed a fluorescence/colorimetric dual channel for the sensitive detection of Pb2+, Hg2+ and Cu2+ using NH2-MIL-101(Fe) and Y-shaped DNAzyme with the ability to be magnetically separated. A good linear response and detection limit were observed by fluorescence method like 0.21 nM for Pb2+, 0.23 nM for Hg2+ and 0.37 nM for Cu2+ and by colorimetric method such as 0.43 nM for Pb2+, 0.57 nM for Hg2+ and 0.99 nM for Cu2+. Therefore, we employed the conventional method for the dual-mode detection of Pb2+, Hg2+ and Cu2+ ions and obtained high specificity, high accuracy and satisfactory results in real sample analyses.

Imparting insoluble-soluble property to Cyt c by immobilizing Cyt c in UCST-pH dual responsive polymer for highly sensitive detection of phenol

Immobilization of enzymes in porous organic framework (POF) materials is popular strategy to stabilize enzymes. For such solid enzyme catalysis system, improving the catalytic efficiency is challenging due to the diffusion resistance from solid-liquid interface and inner pores. Here, UCST-pH dual responsive polymeric carrier (PEG-b-PAAm-b-P(GMA-co-AAc)) was synthesized to immobilize cytochrome c (Cyt c), which impart the reversibly insoluble-soluble property to the immobilized Cyt c. The PEG-b-PAAm-b-P(GMA-co-AAc) could serve as an insoluble-soluble matrix to fast and efficiently immobilize Cyt c via covalent attachment, achieving a remarkable 92 % loading efficiency within just 120 min. The obtained insoluble PEG-b-PAAm-b-P(GMA-co-AAc)-Cyt c micelles exhibited an improvement in thermal, pH stability and reusability. The completely soluble PEG-b-PAAm-b-P(GMA-co-AAc)-Cyt c conjugates accelerated substrate diffusion and then enhanced the catalytic efficiency. These excellent advantages led to low detection limit (1.99 μM), lower than the presently reported biosensors based on enzyme mimics in the colorimetric detection of phenol. This UCST-pH dual responsive window presents a new platform to efficiently control the immobilization and release of enzymes, which will achieve excellent stability and catalytic efficiency.

Dual-modal biosensor for mercuric ion detection based on Cu2O@Cu2S/D-TA COF heterojunction with excellent catalase-like, electrochemical and photoelectrochemical properties

In this study, a dual-mode biosensor based on the heterojunction of Cu2O@Cu2S/D-TA COF was constructed for ultra-sensitive detection of Hg2+ using both photoelectrochemical and electrochemical approaches. Briefly, a 2D ultra-thin covalent organic framework film (D-TA COF film) with excellent photoelectrochemical signals was prepared on ITO surfaces through an in situ growth method. Subsequently, the probe H1 was immobilized onto the biosensor via Au-S bonds. In the presence of Hg2+, the formation of T-Hg2+-T complexes triggered hybridization chain reactions (HCR), leading to the attachment of abundant Cu2O@Cu2S probes onto the biosensor. As a p-type semiconductor, Cu2O@Cu2S could form a heterojunction with the underlying D-TA COF films. Meanwhile, it exhibited catalase-like activity, and the O2 produced by its catalytic decomposition of H2O2 can interact with the D-TA COF films, thus achieving double amplification of the photocurrent signal. Benefiting from the excellent and inherent Cu2+/Cu+ redox pairs of Cu2O@Cu2S, satisfactory differential pulse voltammetry (DPV) signals were obtained. As expected, the dual-mode biosensor was realized with wider linear ranges and low detection limits. Additionally, the analytical performance for Hg2+ in real water samples was excellent. Briefly, this suggested approach offers a facile and highly efficient modality for monitoring heavy metal ions in aquatic environments.

Fabrication of superior laccase-mimicking enzyme with catalytic oxidative and photothermal properties for anti-bacterial and dual-mode glutathione S-transferase monitoring

A novel laccase mimic enzyme Cu-Mn with excellent photothermal properties was firstly prepared via a combination of hydrothermal and in situ synthesis. Cu-Mn nanozymes could catalyze the typical laccase substrate 2,4-dichlorophenol (2,4-DP) to generate the red quinone imine. Further, loading the MnO2 nanosheets with photothermal properties, Cu-Mn nanozymes possessed not only excellent laccase catalytic activity, but also high photothermal conversion efficiency. The presence of glutathione S-transferase (GST) recovered the glutathione (GSH)-induced weakness of the laccase activity and photothermal properties of Cu-Mn. Hence, a GST enzyme-regulated dual-mode sensing strategy was established based on Cu-Mn nanozymes. The detection limits of GST monitoring based on colorimetric and photothermal methods were 0.092 and 0.087 U/L with response times of 20 min and 8 min, respectively. Furthermore, the proposed method enabled the measuring of GST levels in human serum and was successfully employed in the primary evaluation of hepatitis patients. Another attraction, the impressive photothermal behavior also endowed the Cu-Mn nanozymes with promising antimicrobial properties, which exhibited significant antimicrobial effects against Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus). Unsurprisingly, multifunctional Cu-Mn nanozymes certainly explore new paths in biochemical analysis and antimicrobial applications.

Characterisation of a SapYZU11@ZnFe2O4 biosensor reveals its mechanism for the rapid and sensitive colourimetric detection of viable Staphylococcus aureus in food matrices

Although bacteriophage-based biosensors hold promise for detecting Staphylococcus aureus in food products in a timely, simple, and sensitive manner, the associated targeting mechanism of the biosensors remains unclear. Herein, a colourimetric biosensor SapYZU11@ZnFe2O4, based on a broad-spectrum S. aureus lytic phage SapYZU11 and a ZnFe2O4 nanozyme, was constructed, and its capacity to detect viable S. aureus in food was evaluated. Characterisation of SapYZU11@ZnFe2O4 revealed its effective immobilisation, outstanding biological activity, and peroxidase-like capability. The peroxidase activity of SapYZU11@ZnFe2O4 significantly decreased after the addition of S. aureus, potentially due to blockage of the nanozyme active sites. Moreover, SapYZU11@ZnFe2O4 can detect S. aureus from various sources and S. aureus isolates that phage SapYZU11 could not lyse. This may be facilitated by the adsorption of the special receptor-binding proteins on the phage tail fibre and wall teichoic acid receptors of S. aureus. Besides, SapYZU11@ZnFe2O4 exhibited remarkable sensitivity and specificity when employing colourimetric techniques to rapidly determine viable S. aureus counts in food samples, with a detection limit of 0.87 × 102 CFU/mL. Thus, SapYZU11@ZnFe2O4 has broad application prospects for the detection of viable S. aureus cells on food substrates.

Folic acid capping Bi3+-doped Ag quantum dots for enzyme-like dual-mode recognition of toxic S2- and visual sensing of NO2. Anal Chim Acta 2024;1319:342963. [PMID: 39122276 DOI: 10.1016/j.aca.2024.342963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

BACKGROUND

NO2- and S2- are two kinds of common toxic anions widely distributed in environmental water, soil and food products. Human beings have suffered a lot of diseases from intake of excessive NO2- or S2-, i.e., infantile methemoglobin, cancer and even to death. Although tremendous efforts have been afforded to monitor NO2- and S2-, most were high instrument-depended with complex processing procedures. To keep food safety and to protect human health, it will be a huge challenge to develop a convenient and efficient way to monitor S2- and NO2- in practice.

RESULTS

A kind of folic acid capping Bi3+-doped Ag quantum dots (FA@Bi3+-Ag QDs) was developed for the first time by one-pot homogeneous reduced self-assembly. Not only did FA@Bi3+-Ag QDs possess intrinsic fluorescent property, it expressed synergistic peroxidase-like activity to catalyze the redox of 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 with Km/vmax of 0.087 mM/6.61 × 10-8 M s-1 and 6.42 mM/6.25 × 10-7 M s-1 respectively. Interestingly, trace S2- could exclusively alter its fluorescent property and peroxidase-like activity, exhibiting significant hypochromic and "turn-on" fluorescent effects. While trace NO2- could make FA@Bi3+-Ag QDs-TMB-H2O2 system hyperchromic. Under the optimized conditions, FA@Bi3+-Ag QDs were applied for dual-mode recognition of S2- and visual sensing of NO2- in real food samples with satisfactory recoveries, i.e., 100.7-107.9 %/95.8-104.7 % and 97.2-104.8 % respectively. The synergistic enzyme-mimic mechanism of FA@Bi3+-Ag QDs and its selective response mechanisms to S2- and NO2- were also proposed.

SIGNIFICANCE

This represents the first nanozyme-based FA@Bi3+-Ag QDs system for dual-mode recognition of S2- and visual sensing of NO2-, well meeting the basic requirement in drinking water set by WHO. It will offer a promising way for multi-mode monitoring of different pollution using the same nanozyme-based sensor.

Hydroxyl radical-mediated synthesis of carbonyl functionalized graphene quantum dots-like as enzyme mimics with tunable fluorescence emission

The synthesis of graphene quantum dots-like enriched with specific oxygenated groups (o-GQDs) exhibiting great catalytic performance offers a promising tool for diagnosis and biomedicine, but introducing specific oxygen groups remains a challenge. Here, we propose a mild synthetic protocol for producing regulated fluorescence emission (from blue to yellow) carbonyl functionalized GQDs with double catalytic function through Fe3O4-catalyzed hydroxyl radical (·OH) oxidation the precursors like graphene oxide, polyaniline (PANI) and polydopamine (PDA). The method can be carried out at room temperature than the traditional high-temperature oxidation in concentrated acid. Interestingly, o-GQDs exhibit excellent peroxidase (POD)- and ascorbate oxidase-like activity. XPS characterization showed a significant increase in carbonyl content in o-GQDs compared to the precursor, even a 14-fold increase in blue-emitting iron-doped GQDs (b-Fe-GQDs). The introduction of Fe3O4 during the synthesis process results in a minor degree of Fe doping, which enhances the catalytic activity of b-Fe-GQDs through coordination with N. Based on this feature, highly sensitive single-signal and ultra-selective dual-signal methods for alkaline phosphatase detection were developed. This low cost and safe synthesis strategy paves the way for practical usage of o-GQDs.

A nanozyme multifunctional platform based on iron doped carbon dots derived from Tibetan Ganoderma lucidum waste for glucose sensing, anti-counterfeiting applications, and anticancer cell effect

Implementing the concept of turning waste into treasure, the conversion of biomass waste into high-value carbon materials, especially carbon dots (CDs), has pointed out a new direction for disease diagnosis, tumor treatment, and other aspects. In this work, we have reported the GL-CDs(Fe) via a simple synthesis route exploiting Ganoderma lucidum waste as the precursor. Thanks to their excellent optical property and peroxidase mimetic activity, a novel GL-CDs(Fe)-based ratio fluorescence/colorimetric/smartphone triple mode sensing platform is cleverly fabricated for glucose determination with the LOD of 0.28, 0.37, and 0.52 μΜ separately. Especially, this triple mode biosensor is successfully utilized for glucose detection in serum samples with the relative error of less than ±8 % compared with clinical reports. Surprisingly, the GL-CDs(Fe) also presents immense application prospects in high-level anti-counterfeiting aspects due to their excellent luminescent properties, high water-solubility, and easy availability. Furthermore, GL-CDs(Fe) can catalyze excessive H2O2 inside tumor cells to produce massive hydroxyl radicals (·OH) which break down the redox levels of cancer cells and thereby eliminate tumor cells. Thus, this integrated "Three-in-One" multifunctional platform based on GL-CDs(Fe) unveils enormous research and application prospects for bio-sensing, anti-counterfeiting, cancer treatment.

Nanozyme colourimetry based on temperate bacteriophage for rapid and sensitive detection of Staphylococcus aureus in food matrices

Although bacteriophage-based biosensors are promising tools for rapid, convenient, and sensitive detection of Staphylococcus aureus in food products, the effect of biosensors using temperate phages as biorecognition elements to detect viable S. aureus isolates remains unclear. In this study, three temperate S. aureus phages were isolated and their biological features (one-step growth, host range, pH stability, temperature stability, and adsorption rate) were evaluated as the biological element. The selected phage SapYZUs8 was immobilized on the nanozyme Cu-MOF via electrostatic interactions to generate SapYZUs8@Cu-MOF, and its detection performance in real food (skim milk and pork) was then evaluated. Compared with phages SapYZUm7 and SapYZUs16, phage SapYZUs8 exhibited a broader host range, greater pH stability (3-12), and a better absorption rate (92 %, 8 min) suitable for S. aureus detection, which is likely the result of the DNA replication (DNA helicase) and phage tail protein genes in the SapYZUs8 genome. Therefore, phage SapYZUs8 was fixed on Cu-MOF to generate SapYZUs8@Cu-MOF, which exhibited good sensitivity and specificity for rapid colourimetric detection of viable S. aureus. The method took <0.5 h, and the detection limit was 1.09 × 102 CFU/mL. In addition, SapYZUs8@Cu-MOF was successfully employed for the colourimetric detection of S. aureus in food samples without interference from different food additives, NaCl concentrations, or pH values. With these benefits, it allows rapid visual assessment of S. aureus levels.

Fluorescent multichannel sensor array based on three carbon dots derived from Tibetan medicine waste for the quantification and discrimination of multiple heavy metal ions in water

A fluorescent multichannel sensor array has been established based on three carbon dots derived from Tibetan medicine waste for rapid quantification and discrimination of six heavy metal ions. Due to the chelation between metal ions and carbon dots (CDs), this fluorescence "turn off" mode sensing array can quantify six metal ions as low as "μM" level. Moreover, the six heavy metal ions display varying quenching effects on these three CDs owing to diverse chelating abilities between each other, producing differential fluorescent signals for three sensing channels, which can be plotted as specific fingerprints and converted into intuitive identification profiles via principal component analysis (PCA) and hierarchical cluster analysis (HCA) technologies to accurately distinguish Cu2+, Fe3+, Mn2+, Ag+, Ce4+, and Ni2+ with the minimum differentiated concentration of 5 μM. Valuably, this sensing array unveils good sensitivity, exceptional selectivity, ideal stability, and excellent anti-interference ability for both mixed standards and actual samples. Our contribution provides a novel approach for simultaneous determination of multiple heavy metal ions in environmental samples, and it will inspire the development of other advanced optical sensing array for simultaneous quantification and discrimination of multiple targets.

Cheap and portable paper chip with terrific oxidase-like activity and SERS enhancement performance for SERS-colorimetric bimodal detection of intracellular glutathione

Glutathione (GSH) acts a crucial role in the normal operation of manifold life activities and is closely bound up with many human diseases. Here, a SERS-colorimetric bimodal paper-based biosensor based on Mn-doped CDs/silver nanoparticles (Mn-CDs/AgNPs) has been fabricated for high-efficiency quantification of intracellular GSH. The Mn-CDs/AgNPs with fine oxidase-like characteristic and SERS enhancement ability has been assembled onto the Whatman filter paper (WFP) to cleverly fabricate paper chip (Mn-CDs/AgNPs@WFP) which can trigger the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue TMBox and simultaneously enhance the SERS signal of TMBox. However, the introduction of GSH inhibits the oxidation of TMB, leading to color fading of paper chip and diminishment of SERS signal. Considering this, the bimodal paper-based sensing platform can be exploited for SERS-colorimetric detection of GSH, manifesting excellent selectivity, reliable stability, and satisfactory precision. The detection limits of SERS and colorimetric detection modes are as low as 0.41 μM and 0.53 μM, respectively. Furthermore, this proposed bimodal biosensor has been successfully utilized for the determination of intracellular GSH and validated by commercial GSH assay kit, which provides a mighty and convenient tool for intracellular GSH detection and can boost future effort about exploitation of other multimode paper-based biosensors as well as promote their appliances in disease diagnosis.