Sensitive colorimetric assay for the determination of alkaline phosphatase activity utilizing nanozyme based on copper nanoparticle-modified Prussian blue

Colorimetric-SERS dual-mode sensing of Pb(II) ions in traditional Chinese medicine samples based on carbon dots-capped gold nanoparticles as nanozyme

Peroxidase (POD)-mimicking nanozymes have got great progress in the sensing field, but most nanozyme assaying systems are built with a single-signal output mode, which is vulnerable to the effect of different factors. Thus, establishment of a dual-signal output mode is necessary for acquiring dependable and durable performance. This work described an Fe doped noradrenaline-based carbon dots and Prussian blue (Fe,NA-CDs/PB) nanocomposite as a POD-like nanozyme and modified gold nanoparticles (AuNPs) for the colorimetric and surface-enhanced Raman scattering (SERS) dual-mode sensor of Pb(II) in traditional Chinese medicine samples. With 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and 3,3',5,5'-tetramethylbenzidine (TMB) as the substrates, it was found that the addition of Pb(II) inhibited the POD-like activity of Fe,NA-CDs/PB and AuNPs, so it was used for colorimetric and SERS dual-mode assays. The POD-like activity was shown to be a "ping-pong" catalytic mechanism, whereas the addition of Pb(II) produced noncompetitive inhibition with modulatory effects on Fe,NA-CDs/PB. The linear response range for colorimetric and SERS sensor detection of Pb(II) was 0.01-1.00 mg/L with the detection limit of 5 μg/L and 8 μg/L, respectively. This dual-mode detection system shows excellent selectivity. More importantly, the Pb(II) in traditional Chinese medicine samples have successfully assayed with good recovery from 90.4 to 108.9 %.

Turn-off enzyme activity of histidine-rich peptides for the detection of lysozyme

An assay that integrates histidine-rich peptides (HisRPs) with high-affinity aptamers was developed enabling the specific and sensitive determination of the target lysozyme. The enzyme-like activity of HisRP is inhibited by its interaction with a target recognized by an aptamer. In the presence of the target, lysozyme molecules progressively assemble on the surface of HisRP in a concentration-dependent manner, resulting in the gradual suppression of enzyme-like activity. This inhibition of HisRP's enzyme-like activity can be visually observed through color changes in the reaction product or quantified using UV-visible absorption spectroscopy. Under optimal conditions, the proposed colorimetric assay for lysozyme had a detection limit as low as 1 nM and exhibited excellent selectivity against other nonspecific interferents. Furthermore, subsequent research validated the practical applicability of the developed colorimetric approach to saliva samples, indicating that the assay holds significant potential for the detection of lysozymes in samples derived from humans.

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

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

Specializing Carbon Nanozyme Active Sites for Sensitive Alkaline Phosphatase Activity Metal-Free Detection

As biological enzymes regulate metabolic processes, alkaline phosphatase (ALP) is a critical diagnostic indicator associated with many diseases. To accurately measure the enzyme activity, nanozymactic materials can offer sensitive strategies for ALP detection. However, nanozymes often lack specific target binding sites, and the presence of common co-components, e. g., metal ions, may cause false-positive or false-negative results in enzyme activity determination. Herein, we developed a colorimetric assay for ALP detection using metal-free nanozymatic carbon dots (CDs). The ALP hydrolysis of pyrophosphate ions (PPi) to phosphate ions (Pi) induces a "turn-on" response based on the nanozyme activity. This PPi-induced inhibition mechanism is extensively studied via the Michaelis-Menten model, revealing that PPi acts as a noncompetitive inhibitor for CDs at a binding site distinct from the common nanozyme active site. With superior responses to ALP substrates, a highly sensitive and selective method is established for sensing ALP activity with a linear range of 0.010-0.200 U/L and a detection limit of 0.009 U/L. This finding explores the recognition and binding behavior of nanozymes, allowing for precise and reliable measurements even in complex samples, and represents a significant breakthrough for nanozyme-based assays in biological analysis.

Determination of lysophosphatidylcholine using peroxidase-mimic PVP/PtRu nanozyme

Lysophosphatidylcholine (LPC) can be used as a biomarker for diseases such as cancer, diabetes, atherosclerosis, and sepsis. In this study, we demonstrated the ability of nanozymes to displace the natural derived enzyme in enzyme-based assays for the measurement of LPC. Synthesized polyvinylpyrrolidone-stabilized platinum-ruthenium nanozymes (PVP/PtRu NZs) had a uniform size of 2.48 ± 0.24 nm and superb peroxidase-mimicking activity. We demonstrated that the nanozymes had high activity over a wide pH and temperature range and high stability after long-term storage. The LPC concentration could be accurately analyzed through the absorbance and fluorescence signals generated by the peroxidation reaction using the synthesized nanozyme with substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) and 10-acetyl-3,7-dihydroxyphenoxazine (Ampliflu™ Red). LPC at a concentration of 0-400 µM was used for the analysis, and the coefficient of determination (R²) was 0.977, and the limit of detection (LOD) was 23.1 µM by colorimetric assay. In the fluorometric assay, the R² was 0.999, and the LOD was 8.97 µM. The spiked recovery values for the determination of LPC concentration in human serum samples were 102-115%. Based on these results, we declared that PVP/PtRu NZs had an ability comparable to that of the native enzyme horseradish peroxidase (HRP) in the enzyme-based LPC detection method.

Smart Biomimetic Nanozymes for Precise Molecular Imaging: Application and Challenges

New nanotechnologies for imaging molecules are widely being applied to visualize the expression of specific molecules (e.g., ions, biomarkers) for disease diagnosis. Among various nanoplatforms, nanozymes, which exhibit enzyme-like catalytic activities in vivo, have gained tremendously increasing attention in molecular imaging due to their unique properties such as diverse enzyme-mimicking activities, excellent biocompatibility, ease of surface tenability, and low cost. In addition, by integrating different nanoparticles with superparamagnetic, photoacoustic, fluorescence, and photothermal properties, the nanoenzymes are able to increase the imaging sensitivity and accuracy for better understanding the complexity and the biological process of disease. Moreover, these functions encourage the utilization of nanozymes as therapeutic agents to assist in treatment. In this review, we focus on the applications of nanozymes in molecular imaging and discuss the use of peroxidase (POD), oxidase (OXD), catalase (CAT), and superoxide dismutase (SOD) with different imaging modalities. Further, the applications of nanozymes for cancer treatment, bacterial infection, and inflammation image-guided therapy are discussed. Overall, this review aims to provide a complete reference for research in the interdisciplinary fields of nanotechnology and molecular imaging to promote the advancement and clinical translation of novel biomimetic nanozymes.

Manganese-Based Nanozymes: Preparation, Catalytic Mechanisms, and Biomedical Applications

Manganese (Mn) has attracted widespread attention due to its low-cost, nontoxicity, and valence-rich transition. Various Mn-based nanomaterials have sprung up and are employed in diverse fields, particularly Mn-based nanozymes, which combine the physicochemical properties of Mn-based nanomaterials with the catalytic activity of natural enzymes, and are attracting a surge of research, especially in the field of biomedical research. In this review, the typical preparation strategies, catalytic mechanisms, advances and perspectives of Mn-based nanozymes for biomedical applications are systematically summarized. The application of Mn-based nanozymes in tumor therapy and sensing detection, together with an overview of their mechanism of action is highlighted. Finally, the prospective directions of Mn-based nanozymes from five perspectives: innovation, activity enhancement, selectivity, biocompatibility, and application broadening are discussed.

Core-Shell Polydopamine/Cu Nanometer Rods Efficiently Deactivate Microbes by Mimicking Chloride-Activated Peroxidases

Cu-modified nanoparticles have been designed to mimic peroxidase, and their potent antibacterial and anti-biofilm abilities have been widely investigated. In this study, novel core-shell polydopamine (PDA)/Cu₄(OH)₆SO₄ crystal (PDA/Cu) nanometer rods were prepared. The PDA/Cu nanometer rods show similar kinetic behaviors to chloride-activated peroxidases, exhibit excellent photothermal properties, and are sensitive to the concentrations of pH values and the substrate (i.e., H₂O₂). PDA/Cu nanometer rods could adhere to the bacteria and catalyze hydrogen peroxide (H₂O₂) to generate more reactive hydroxy radicals (^•OH) against Staphylococcus aureus and Escherichia coli, Furthermore, PDA/Cu nanometer rods show enhanced catalytic and photothermal synergistic antibacterial activity. This work provides a simple, inexpensive, and effective strategy for antibacterial applications.

A novel electrochemical platform for assay of alkaline phosphatase based on amifostine and ATRP signal amplification

Alkaline phosphatase (ALP), an important hydrolase involved in dephosphorylation, is a common clinical indicator of many diseases. In the present study, we constructed a novel electrochemical sensor using amifostine as the substrate of ALP and activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) as a signal amplification strategy for sensitive determination of ALP activity. In particular, in the presence of ALP, the phosphate group of amifostine was hydrolyzed to form a sulfhydryl group, which could attach to a gold electrode via a sulfur-gold bond. Then, the initiator α-bromophenylacetic acid (BPAA) was linked to the hydrolysis product of amifostine through an amide bond, resulting in the production of electroactive polymer chains on the gold electrode by the monomer ferrocenylmethyl methacrylate (FMMA) via ARGET ATRP. Under optimal parameters, the electrochemical sensor demonstrated a limit of detection (LOD) of 1.71 mU mL^-1 with a linear range of 5-100 mU mL^-1. In addition to satisfactory selectivity, the potential application of this approach for ALP activity detection in human serum samples was demonstrated. Due to its efficiency, simplicity of operation, and cost-effectiveness, the proposed electrochemical sensor has great promise as a universal method for ALP assays and inhibitor screening.

Optical assay using B-doped core-shell Fe@BC nanozyme for determination of alanine aminotransferase

B-doped core-shell Fe@BC nanozyme was synthesized. The peroxidase (POD) like activity of Fe@BC nanozyme was studied and utilized for detecting the activity of alanine aminotransferase (ALT). In the presence of ALT as well as ALT co-substrates L-alanine and α-ketoglutarate, L-glutamate is generated. The following catalytic oxidation of L-glutamate by glutamate oxidase leads to the generation of H₂O₂. The POD-like activity of Fe@BC can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to oxTMB in the presence of H₂O₂, generating a blue-colored compound. Through the detection of the amount of H₂O₂ generated, ALT activity can be determined through measuring the absorbance intensity variation at 450 nm. The limit of detection of the assay is 4 U/L, with a linear range from 10 to 1000 U/L. For human serum samples, the ALT levels determined by our assay are comparable to those determined by the hospital with a correlation coefficient of 0.991, demonstrating the reliability of our assay results.

A multicolor biosensor for alkaline phosphatase activity detection based on the peroxidase activity of copper nanoclusters and etching of gold nanorods

A multicolor biosensor for ALP activity has been developed based on the peroxidase activity of copper nanoclusters and etching of gold nanorods.

Electrochemical detection of alkaline phosphatase activity via atom transfer radical polymerization

Alkaline phosphatase (ALP) activity is a diagnostic indicator for a variety of clinical diseases. In this study, an electrochemical method for detecting ALP activity through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) was developed. Specifically, 3-mercaptopropionic (MPA) was firstly fixed on the electrode through sulfur-gold bonding. Subsequently, α-bromophenylacetic acid (BPAA) as initiator was attached to MPA through the recognized carboxylate-Zr⁴⁺-phosphate chemistry. Finally, in the existence of ALP, L-Ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAPS) was hydrolyzed to produce ascorbic acid (AA) which participated in the ARGET ATRP reaction, grafting polymer containing plenty of ferrocene electroactive probes on the surface of electrode. Under optimal experimental conditions, this method had a linear scope of 20-200 mU mL^-1, and a limit of detection (LOD) of 1.64 mU mL^-1. In addition, the proposed method had good selectivity as well as anti-interference capability, with satisfactory results in inhibition rate and human serum experiments. By merits of good analytical performance, easy operation, and low cost, such a method for ALP activity detection has promising applications in ALP-related disease detection and inhibitor screening.

Restoring the Oxidase-Like Activity of His@AuNCs for the Determination of Alkaline Phosphatase

In this paper, we propose a simple colorimetric method for the sensitive and selective detection of alkaline phosphatase (ALP) activity based on the turn off/turn on oxidase mimic activity of His@AuNCs. His@AuNCs/graphene oxide hybrids (His@AuNCs/GO) were easily obtained using the self-assembly method with poly (diallyldimethylammonium chloride) (PDDA)-coated GO and showed high oxidase-like activity compared with His@AuNCs. We found that the pyrophosphate ion (P₂O₇^4-, PPi) could effectively inhibit the oxidase mimic activity of His@AuNCs/GO, and the hydrolysis of PPi by ALP restored the inhibited activity of His@AuNCs/GO, enabling them to efficiently catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate the blue oxidized product oxTMB. The intensity of the color showed a linear dependency with the ALP activity. ALP was detected in the linear range of 0-40 mU/mL with a low detection limit (LOD) of 0.26 mU/mL (S/N = 3). The proposed method is fast, easy, and can be applied to monitor the ALP activity in serum samples accurately and effectively, which suggests its practicability and reliability in the detection of ALP activity in clinical practice.