Dual-Functional Peroxidase-Copper Phosphate Hybrid Nanoflowers for Sensitive Detection of Biological Thiols

Ficin-copper hybrid nanoflowers with enhanced peroxidase-like activity for colorimetric detection of biothiols

The proteolytic enzyme ficin exhibits peroxidase-like activity but it is low and insufficient for real applications. Herein, we developed ficin-copper hybrid nanoflowers and demonstrated that they have significantly enhanced peroxidase-like activity of over 6-fold higher than that of free ficin, with one of the lowest Km and highest kcat values among all reported ficin-based peroxidase-like nanozymes. This was most likely caused by the synergistic catalysis of co-existing ficin and crystalline copper phosphate within nanoflower matrices having a large surface area. The nanoflowers were easily prepared by incubating ficin and copper sulfate at ambient temperature, causing coordination interactions between ficin's amine/amide moieties and copper ions, followed by concomitant anisotropic growth of petals composed of copper phosphate crystals with ficin. When compared to free ficin and natural horseradish peroxidase, the resulting nanoflowers' affinity toward H2O2 was greatly increased, yielding Km values of half and one-tenth, respectively, as well as noticeably improved stability. The nanoflowers were then applied to colorimetric determination of biological thiols (biothiols), such as cysteine (Cys), glutathione (GSH), and homocysteine (Hcy), based on their inhibition of nanoflowers' peroxidase-like activity, producing reduced color intensities as the concentration of biothiols increased. This strategy achieved highly sensitive colorimetric determinations of Cys, GSH, and Hcy after only 25-min incubation. Additionally, using this technique, biothiols in human serum were successfully determined with excellent precision, suggesting the potential application of this technology in clinical settings, particularly in point-of-care testing environments.

Bovine Serum Albumin - Hydroxyapatite Nanoflowers as Potential Local Drug Delivery System of Ciprofloxacin

Introduction

Hybrid nanoflowers are structures consisting of organic (enzymes, proteins, nucleic acids) and inorganic components (mostly metal phosphates) with a flower-like hierarchical structure. Novel hybrid nanoflowers based on bovine serum albumin (BSA) and hydroxyapatite (HA) were obtained and characterized. Study on BSA-HA nanoflowers as potential drug delivery system is reported for the first time.

Methods

Embedding ciprofloxacin in the structure of hybrid nanoflowers was confirmed by ATR-FTIR and thermogravimetric analysis. The inorganic phase of the nanoflowers was determined by X-ray diffraction. UV‒Vis spectroscopy was used to evaluate the release profiles of ciprofloxacin from nanoflowers in buffer solutions at pH 7.4 and 5. The agar disk diffusion method was used to study the antibacterial activity of the synthesized nanoflowers against Staphylococcus aureus and Pseudomonas aeruginosa.

Results

Bovine serum albumin - hydroxyapatite nanoflowers were obtained with diameters of ca. 1-2 µm. The kinetics of ciprofloxacin release from nanoflowers were described by the Korsmeyer-Peppas model. The antibacterial activity of the synthesized nanoflowers was demonstrated against S. aureus and P. aeruginosa, two main pathogens found in osteomyelitis.

Conclusion

The formulated nanoflowers may act as an efficient local antibiotic delivery system. Due to the use of nonhazardous, biodegradable components and benign synthesis, hybrid nanoflowers are very promising drug delivery systems that could be applied in the treatment of skeletal system infections.

Acetylcholinesterase-Cu3(PO4)2 hybrid nanoflowers for electrochemical detection of dichlorvos using square-wave voltammetry

Immobilization of enzymes is one of the key steps in the development of high-performance enzymatic electrochemical biosensors, and various nanostructured materials have been designed and developed to achieve this goal. Herein, hybrid nanoflowers (HNFs) were synthesized using acetylcholinesterase (AChE) as an organic component and copper phosphate (Cu₃(PO₄)₂) as an inorganic component. These AChE-Cu₃(PO₄)₂ HNFs exhibit a three-dimensional hierarchical flower-like structure, which not only has a large specific surface area but also promotes the affinity between AChE and its substrate with better catalytic activity. Not only that, the surface modification of the glassy carbon electrode (GCE) by the joint use of gold nanoparticles (AuNPs) and graphene oxide (GO) extended the electroactive area. Using square-wave voltammetry (SWV), the as-prepared biosensor (i.e., AChE-Cu₃(PO₄)₂ HNF/AuNP/GO/GCE) demonstrated superior sensing performance in the detection of dichlorvos. The detection limit is as low as 0.07 pM, and the linear detection range can range from 0.5 pM to 10 μM. In addition, the biosensor was feasible in real agricultural samples with satisfactory recoveries (98.65% to 103.43%). The reported biosensor provides an alternative tool for the direct measurements of AChE activity and its inhibition. Besides organophosphorus pesticides represented by dichlorvos, this biosensor has the potential to detect other AChE inhibitors, such as carbamate pesticides, drugs for Alzheimer's disease, etc., thus having broader applications in food safety and drug screening.