Featured Application: Nanosensors for extracellular oxygen-sensing.Abstract: Three four-arm amphiphilic block copolymers with different chain lengths, consisting of a hydrophilic chain of polyethylene glycol (PEG) and hydrophobic segment of polycaprolactam (PCL), were synthesized and used to encapsulate the high-efficient and hydrophobic oxygen probe of platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP) to form polymer micelles. This approach enabled the use of PtTFPP in aqueous solution for biosensing. Experimental results demonstrated that the particle sizes of these nano-oxygen sensors between 40.0 and 203.8 nm depend on the structures of block copolymers. PtTFPP in these micelles showed an effective quantum yield under nitrogen environment, ranging from 0.06 to 0.159. The new sensors are suitable for analyzing dissolved oxygen concentrations in the range of 0.04-39.3 mg/L by using the linear Stern-Volmer equation at room temperature. In addition, it has been shown that these sensors are capable of in situ monitoring the dissolved oxygens in the culture medium of E. coli and Romas cells during the respiration process, and distinguishing the drug activity of antibiotic ampicillin from that of antimycin A. This study showed that the use of these nanostructured multi-arm block copolymer micelles can achieve efficient biological applications without specific structural modification of the hydrophobic PtTFPP probe, which is expected to have broad prospects.
New amphiphilic star or multi-arm block copolymers with different structures were synthesized for enabling the use of hydrophobic oxygen probe of platinum (II)-tetrakis (pentafluorophenyl) porphyrin (PtTFPP) for bioanalysis. The amphiphilic star polymers were prepared through the Atom Transfer Radical Polymerization (ATRP) method by using hydrophilic 4-arm polyethylene glycol (4-arm-PEG) as an initiator. Among the five block copolymers, P1 series (P1a, P1b, and P1c) and P3 possess fluorine-containing moieties to improve the oxygen sensitivity with its excellent capacity to dissolve and carry oxygen. A polymer P2 without fluorine units was also synthesized for comparison. The structure-property relationship was investigated. Under nitrogen atmosphere, high quantum efficiency of PtTFPP in fluorine-containing micelles could reach to 22% and long lifetime could reach to 76 μs. One kind of representative PtTFPP-containing micelles was used to detect the respiration of Escherichia coli (E. coli) JM109 and macrophage cell J774A.1 by a high throughput plate reader. In vivo hypoxic imaging of tumor-bearing mice was also achieved successfully. This study demonstrated that using well-designed fluoropolymers to load PtTFPP could achieve high oxygen sensing properties, and long lifetime, showing the great capability for further in vivo sensing and imaging.
The theoretical finding of a large group of intrinsic off‐stoichiometry quaternary Heusler‐like semiconductors with mixing and tunable occupation of 4c‐4d atomic sites, such as FexCoyTiSb with non‐integer x + y > 1 are reported. Those semiconductors are never reported before, and they radically break the well‐recognized 18‐ (or 24‐) valence electron counting (VEC) rule and the exact 4c‐ (or both 4c‐ and 4d‐) atomic sites stoichiometry for the traditional quaternary half‐Heusler (or full‐Heusler) semiconductors. Physically, the novel semiconductors can be designed by following a d‐orbital‐determined compensation rule. The extra atoms fill in the tetrahedral vacancies of the half‐Heusler structure, introduce symmetry‐constrained d orbitals near the Fermi level, large crystal field splitting, and then form a bandgap at appropriate fractional compositions, which leads to an exact compensated electronic structure. The newly established compensation rule reveals an abundant phase space of the quaternary Heusler‐like Xx8Xy9YZ${\rm{X}}_x^8{\rm{X}}_y^9YZ$ (2x + 3y = 3 for VECY+Z = 9, 2x + 3y = 4 for VECY+Z = 8, and 2x + 3y = 5 for VECY+Z = 7) compounds. High‐throughput screenings reveal many new FexCoyYZ semiconductors, all of which possess strong disorder, weak magnetism, spin compensation, and wide composition‐range tunability. The intertwined orders may either find functionalities surpassing the existing materials or give rise to new potential applications.
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