Insertion of Hemin into Metal–Organic Frameworks: Mimicking Natural Peroxidase Microenvironment for the Rapid Ultrasensitive Detection of Uranium

Abstract

Constructing enzyme-like active sites in mimic enzyme systems is critical for achieving catalytic performances comparable to natural enzymes and can shed light on the natural development of enzymes. In this study, we described a specific hemin-based mimetic enzyme, which was facilely synthesized by the assembly of zeolitic imidazolate framework-L (ZIF-L) and hemin. The obtained hemin-based mimetic enzyme (denoted as ZIF-L-hemin) displayed enhanced peroxidase activity compared to free hemin in solution. Such excellent activity originated from the ZIF-L framework mimicking the active site cavity microenvironment of horseradish peroxidase in terms of axially coordinated histidine and distal histidine. Additionally, the constructed peroxidase mimetic was extremely resistant to a variety of severe circumstances that would normally denature natural enzymes. These characteristics made ZIF-L-hemin a potential platform for the colorimetric sensor of uranium (UO 2 2+ ) with wide linear ranges (0.25−40 μM) and low limits of detection (0.079 μM). Moreover, the detection mechanism demonstrated that the coordination of uranyl ion with imidazole of ZIF-L-hemin reduced the catalytic efficiency of ZIF-L-hemin. The current work not only proposed a novel approach for fabricating artificial peroxidase but also offered facile colorimetric methods for selective radionuclide detection.

Al3+ Cofactor Evoking Iron Porphyrin-AuNP Hybrids as Oxidase-Mimicking Nanozymes with Prominent Catalytic Efficiency in a Broad pH Range

“…The controlled results in Figure A have indicated that individual AuNPs or FeTCPP does not possess oxidase-mimicking activity, which is consistent with earlier studies. − ,− In CYP, the metallo-porphyrin has the ability to activate molecular oxygen. , Unlike heme-containing oxygenases, iron porphyrin nanozymes cannot activate oxygen due to the inappropriate coordination and the ferric state of ions since the delicate local microenvironment around iron porphyrin is absent. Thus, iron porphyrin nanozymes have exhibited only peroxidase-mimicking activity but no oxidase-like activity up to now. − Loading FeTCPP on AuNP supports in the presence of Al 3+ can significantly alter the microenvironment around FeTCPP, which contributes to substrate binding and activation (Scheme ).…”

“…Iron porphyrins are widely present as active sites in many natural enzymes, and oxygen reduction catalyzed by porphyrins has been of great interest in biological systems. − Iron porphyrin-based nanozymes have received great interest because of their potential applications in environmental and biological fields. − Unfortunately, hemin-based nanozymes only have been demonstrated to display peroxidase-mimicking properties, but no oxidase-mimicking properties capable of reversibly binding dioxygen at ambient temperature and neutral pH. Free heme is fast-oxidized into ferric hemin in air, so earlier studies about heme-containing nanozymes did not address a direct correlation between the ferrous heme and oxygen activation. − Furthermore, different from natural oxygenases (e.g., cytochrome P450s (CYP)), heme nanozymes have no proper microenvironment around active sites for substrate activation because of the absence of a precise structure.…”

Threonine Phosphorylation of an Electrochemical Peptide-Based Sensor to Achieve Improved Uranyl Ion Binding Affinity

“…Table 1 shows the key analytical properties of the U-pT-12 sensor and several previously reported U(VI) sensors and detection methods [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. The LOD of the current sensor compares well with several other U(VI) sensors, including colorimetric, SERS, and electrochemical sensors [ 11 , 13 , 14 , 15 ].…”

“…Table 1 shows the key analytical properties of the U-pT-12 sensor and several previously reported U(VI) sensors and detection methods [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. The LOD of the current sensor compares well with several other U(VI) sensors, including colorimetric, SERS, and electrochemical sensors [ 11 , 13 , 14 , 15 ]. Although there are sensors with significantly lower LODs [ 10 , 12 ], these sensors require custom designed and synthesized U(VI)-specific ligand and/or nanomaterials.…”

“…To meet this demand, several analytical techniques have been developed for detecting and monitoring uranium, specifically UO 2 2+ (U(VI)). These techniques include inductively coupled plasma mass spectrometry [ 7 , 8 ], UV spectrophotometry [ 9 , 10 , 11 ], fluorescence spectroscopy [ 12 ], and surface enhanced Raman spectroscopy (SERS) [ 13 , 14 ]. Various electrochemical U(VI) detection approaches have also been reported recently [ 15 , 16 , 17 , 18 ].…”